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Nanoindentation for investigation of microstructural compositions in SM490 steel weld zone
... Whereas, parallel to elastic modulus, hardness, and fracture toughness, two more basic plastic properties such as yield strength ( y ) and strain hardening work (n) of ductile materials, have been of interest of the investigators in the area of implementing nanoindentation [6][7][8][9][10]. Besides the studies on the mechanical properties including elastic modulus, hardness, and plastic properties of metals in general and of steels in particular, some recent investigations into constituent phases of steels and their properties have been successful carried out by utlizing nanoindentation [11][12][13][14][15]. In order to address the limitations of the aforementioned studies such as only elastic modulus and hardness of constituent phases were determined and used to identify the phases [11,12] or the constituent phases need to be positioned prior to nanoindentation [13,14], this study aims to extend the investigated method in the previous works [12]] to the plastic property such as yield strength of constituent microstructural phases in structural steel. ...
... Besides the studies on the mechanical properties including elastic modulus, hardness, and plastic properties of metals in general and of steels in particular, some recent investigations into constituent phases of steels and their properties have been successful carried out by utlizing nanoindentation [11][12][13][14][15]. In order to address the limitations of the aforementioned studies such as only elastic modulus and hardness of constituent phases were determined and used to identify the phases [11,12] or the constituent phases need to be positioned prior to nanoindentation [13,14], this study aims to extend the investigated method in the previous works [12]] to the plastic property such as yield strength of constituent microstructural phases in structural steel. ...
... Besides the studies on the mechanical properties including elastic modulus, hardness, and plastic properties of metals in general and of steels in particular, some recent investigations into constituent phases of steels and their properties have been successful carried out by utlizing nanoindentation [11][12][13][14][15]. In order to address the limitations of the aforementioned studies such as only elastic modulus and hardness of constituent phases were determined and used to identify the phases [11,12] or the constituent phases need to be positioned prior to nanoindentation [13,14], this study aims to extend the investigated method in the previous works [12]] to the plastic property such as yield strength of constituent microstructural phases in structural steel. ...
In this study, the extension of the statistical analysis application into yield strength of constituent phases of steel was conducted. A larger number of nanoindentation tests was carried out on a type of popular structural steel SS400. The mechanical properties, such as elastic modulus, hardness, and yield strength of the indented material were extracted from nanoindentation load-depth curves. The statistical analysis was then applied to analysis the material properties spectra. The experimental and analysis results revealed that the yield strength spectrum obtained from nanoindentation tests can be used in the accurate and reliable identification of the constituent microstructural phases and their strength in structural steel by applying statistical deconvolution analysis. For the present steel, three microstructural phases are known as low characteristic ferrite, high characteristic ferrite, and pearlite with the corresponding yield strength value of y = 296.1 ± 30.8 MPa, y = 423.6 ± 34.3 MPa, and y = 573.1 ± 38.9, respectively.
... E.g., Pham et al. [7] managed to distinguish, based on nanoindentation, between the different material phases that SS400 steel is composed of. Interestingly, they found distinctive stiffness differences between tested regions and the therein contained material phases; they report Young's moduli ranging from 206 to 358 GPa, see also [8,9]. Hence, their results somehow deviate from the Young's modulus of steel typically suggested in textbooks [2,[10][11][12][13], varying between 208 to 214 GPa, regardless of the exact steel composition. ...
... Nanoindentation was carried out on the (unetched) sample surfaces, prepared as described in Section 2.1, by means of a Hysitron Triboindenter TI900, using a Berkovich diamond tip. In order to ensure optimal comparability with respect to previously performed, similar studies [5,[7][8][9]15,16], nanoindentation was carried out according to the following protocol: The samples were indented in load-controlled fashion, at a load rate of 0.2 mN/s, until a maximum load of 6 mN was reached, leading to indentation depths ranging from 200 to 250 nm. After holding the maximum load for 3 s, unloading was performed, again at a rate of 0.2 mN/ s, see Fig. 2(a) for an exemplary load history, and Fig. 2(b) for the corresponding load-displacement diagram. ...
... These values are credible, as the reported roughness of 40 nm (( 200 nm ¼ h) complies with the fineness requirements formulated by Miller et al. [20]; and they also compare well with the orders of magnitude obtained in the present study, see Table 4. The aforementioned elastic material phases partially refer to the same chemical phase; in this sense, Pham et al. [9] distinguish between low-and high-stiffness ferrite; and they report similar results obtained from 390 nanoindentation tests on SM490 steel. These values also agree with the nanoindentation-derived stiffness data reported by Wang et al. [42] for ferrite, ranging from 195 GPa to 255 GPa, and with the ferrite-related data of Gadelrab et al. [43], comprising 168 nanoindentations ranging from 185 GPa to 215 GPa. ...
Tramway rail steel is exposed to extreme temperature conditions both during production (e.g. in terms of heat treatment) and over its decades-to-century-long service life (e.g. in terms of welding operations in the course of maintenance). The question arises whether this induces local stiffness reductions and hence stiffness inhomogeneities at the half-millimeter level; i.e. the characteristic size governing the structural behavior of the rail. In order to address this question, a series of 16800 nanoindentation tests, with indentation depths ranging from 200 to 250 nm (characterizing 66-to 125 nm-sized material volumes), were performed on samples with less than 10 nm surface roughness, extracted from different locations of typical tramway rail cross sections at different time points during their service lives, and including both heat-affected and non-heat-affected zones. Thereby, each of these locations was probed through a grid of 20 Â 20 nanoindentations, with a grid spacing of 500 lm. In very few cases, the indentation tip was probably moved into cracks of several lm width and tens-to-hundreds of lm length; as seen on light and electron micrographs. Zero-stiffness was assigned to the corresponding grid points. The probability distributions of the remaining, non-zero elastic moduli were fitted by one to four weighted Gaussians, representing all (non-zero) nanoindentation data as well as particular data subsets (namely data from each testing grid, data from each testing location across all rails, data from each rail, all data from heat-affected zones, and all data from non-heat-affected zones). The aforementioned Gaussians refer to different solid elastic material phases, with expected Young's moduli ranging approximately from 100 to around 300 GPa, potentially reflecting different dislocation densities. On the other hand, at a larger material scale (i.e., that of 220 to 440 lm, tested through 2.25 MHz ultrasonics), the stiffness is reduced to approximately 213 GPa (from a mean nanoindentation-derived value of approximately 246 GPa). This reduction can be explained by a micromechanical model, with the intact steel stiffness as well as with crack sizes and crack numbers as input quantities.
... Instrumented indentation technique has been widely used in many engineering fields as a powerful tool for characterization of material properties [4]. Since the technique allows accessing to the local properties in the indented area, it has been extensively utilized for investigating the properties of inhomogeneous materials such as cementitious materials, concrete, asphalt binder, or steel weld zone [5][6][7][8][9][10][11]. It has been indicated that in the indentation test on inhomogeneous material, the high indentation depth, roughly h=D > 6 (h is the indentation depth and D is the characterhttp://dx.doi.org/10.1016/j.conbuildmat.2017.08.033 0950-0618/Ó 2017 Elsevier Ltd. ...
... All rights reserved. istic size of the phases) of the phase provide access to homogenized material properties of the composite, while low indentation depth (h=D < 1=10) provide access to the properties of microstructural phase [11][12][13]. ...
... For indentation with low indenting depth, the tests were carried out in three regions, BM, HAZ, and WM of the weld. As indicated [10,11,26], a series of more than 300 nano-indentation tests need to be performed to identify the actual values of volume fraction and properties of the microstructural phases. Due to the limitation of testing condition, in which more than 300 indenting points cannot be indented in one testing time, three grids of 11 Â 11 nano-indentations with grid spacing of 50 lm were undertaken at each individual weld zone, leading to a total of 363 indenting points with three indenting areas of 500 Â 500 lm 2 at each region. ...
The volume fraction (f) and properties of microstructural phases, the mechanical properties in the weld zone, and their relevance of commonly used steel, SM520, were investigated by using instrumented indentation. The volume fraction and properties of microstructural phases in fusion zone (weld metal –WM), heat-affected zone (HAZ), and base metal (BM) of the weld zone were identified by applying the statistical analysis for observed frequency density of hardness (H), elastic modulus (E), and yield strength (σy) spectra from nano-indentation tests. The mechanical properties distributed across the weld zone were determined from the micro-indentation tests. Two different stiffness ferrite types can be characterized in each individual weld zone from the analysis of H and E results, while two different strength ferrite types can be identified in WM from the analysis of the σy spectrum obtained from nano-indentations. The results from micro-indentations exhibited that the E, H, σy, and n values in the HAZ decrease in the direction from WM to BM region and all the average values of E, H, σy, and n in HAZ are higher than those in BM. The relevance of f, E, H, and σy of microstructural phases and E, H, and σy in the weld zone and was also discussed.
... For example, DSI can allow the estimation of various basic material properties consisting of indentation hardness H, elastic modulus E, plastic properties (r y and n), and fracture toughness [16][17][18]. Recently, DSI was demonstrated to be a suitable method in order to determine mechanical properties in the steel welded joints [7,[19][20][21][22][23][24]. Eroglu et al. [19] have used optical microscope examination, DSI, and Charpy impact testing to investigate the effects of coarse initial grain size on mechanical properties and microstructure of HAZ and WM of an SAE low carbon steel weld zone. ...
... Bayraktar et al. [6] has also employed the micro-hardness tester and optical microscope examination to study the grain growth mechanism during the welding process of several interstitial free steels. Recently, DSI and finite element (FE) analysis were conducted to determine plastic properties as well as to investigate microstructural compositions in several types of structural steel weld zones [10,[21][22][23]. Nguyen et al. [25] has applied DSI to explore effects of strain rate indentation on both indentation hardness and yield strength of a structural steel. ...
... Nanoindentation has been used in many engineering fields including biomedical, civil, mechanical, and material engineering [10][11][12][13]. Recently, numerous analytical methods have been developed for characterization of basic mechanical properties (elastic modulus, yield stress, strain hardening exponents, etc.) from the load-penetration depth data of indentation tests [14][15][16][17]. ...
... Even though during cooling, the transformation of δ-ferrite to α-ferrite occurs, it is believed that the remaining δferrite in weld metal is still higher than that in base metal. The higher amount of δ-ferrite and its many transformed phase boundaries may be responsible for the greater strength, strain hardening exponent, and hardness in the weld metal than those in the base metal, while the slight higher elastic modulus in weld metal may be attributed to the "high stiffness ferrite" phase, which was discussed in the previous works [12,13]. ...
... For example, in 2020, Massar et al. applied dynamic Berkovich nanoindentation hardness and modulus of elasticity measurements, according to the OP method, for recycled battlefield scrap steel powders and cold spray-processed material consolidations in [38]. In addition to Massar et al., continued consideration of the use of nanoindentation to characterize steels in the 2010s unveils the work of Pham and Kim, which was published in 2015, wherein the authors identified the modulus of elasticity and nanoindentation hardness values associated with an SM490 steel weld zone via statistical data analysis [39]. Furthermore, Yang et al. also utilized statistical data analysis to quantify the transformation kinetics of bainite phase formation within an austempered steel [40]. ...
Numerable advancements have afforded many benefits to nanoindenter system operators since the late 20th century, such as automation of measurements, enhanced load and displacement resolutions, and indentation with in-situ capabilities. Accordingly, the present chapter details how the Oliver-Pharr method of nanoindentation testing and analysis was adopted and relied upon as a framework that brought about widespread advancements in instrumented indentation testing. The present chapter introduces an emergent and theoretically consistent approach to assessing true stress–strain curves at a micromechanical scale using a flat-punch nanoindenter tip geometry and reliance upon Hollomon power-law plasticity and constitutive parameter fitting. Finally, a novel flat-punch nanoindentation testing method and approach to plasticity parameter analysis for metallic materials using nanoindentation systems can be implemented, bringing about an instrumented strength microprobe – a long sought-after tool.
... Structural steel is applied in many different structural projects such as buildings, bridges, mines, the auto industry, and so on, because of its favorable physical properties, for example, high durability, toughness, and ductility [1][2][3][4][5]. The mechanical properties of structural steel are strongly dependent on both service conditions and metallurgical factors, which include temperature, environmental conditions, and especially the historical loading state [6,7]. ...
Grain boundary strengthening is a method of strengthening materials by changing their average crystalize (grain) size, exhibiting the basic relationship between yield stress and the grain size of the materials. This methodology is based on the observation of grain boundaries that are insurmountable borders for dislocationsand the number of dislocations located within a grain. Applying this methodology to the structural steel weld zone, the mechanical properties of each microstructural phase can be evaluated through the values of grain diameter. For structural steel weld zones, there are not many methods to directly determine the mechanicalproperties of microstructural phases. Thus, in this study, a methodology was created to evaluate the values of the yield stress of materials based on the grain boundary strengthening equation. This method was constructedby observing the average grain size and determining the mechanical properties of three microstructural phasesin the weld zone (i.e. based metal, heat-affected zone, and weld metal). The results from this study provide aneasy way for engineers, architects, and scientists to evaluate the values of mechanical properties of based metal, heat-affected zone, and weld metal in the SS400 structural steel weld zone.
... The results of their study were shown that nanoindentation was suitable method for determination of the elastic modulus and hardness of specimen. Pham and Kim [20] investigated the microstructure of the weld zone of SM490 steel welded joint by nanoindentation, microstructural examination and deconvolution technique. Young modulus and hardness was measured by nanoindentation tests from each indenting point. ...
Welding is the most commonly used joining process in the industry. Generally, weld zone consists of three different regions such as base metal, heat-affected zone (HAZ) and weld metal (WM). Microstructure of HAZ and WM changes due to the heat effects after the welding process. These effects cause changes in mechanical properties such as Young modulus, tensile strength and hardness in weld zone. The aim of this paper is to identify the mechanical properties of weld zone by uni-axial tensile test, nanoindentation test and hardness test. For this aim, quenched and tempered steel plates were chosen as a test material having high strength. These plates were welded together by flux-cored arc welding method. To determine the effect of weld pass number on the mechanical properties, the weld was completed in single and multi-pass (MP) butt welds separately. For experiments, tensile test specimens were cut by plasma cutting method according to related standard on welded plates. These specimens were subjected to three different post weld heat treatments (PWHT) such as 200 °C, 300 °C and 400 °C to evaluate the hardness change in HAZ. The effect of weld-pass number and PWHT on mechanical properties such as Young modulus, tensile strength and hardness were obtained from WM and HAZ by uni-axial tensile test and nanoindentation test and compared to each other. The yield and ultimate tensile strength of weld zone of welded tensile test specimens (WTTS)-2 is lower than WTTS-1 due to MP welding process. Furthermore, the strain behaviour of weld zone is not affected by PWHT significantly.
... Structural steel has been extensively employed in buildings, bridges, tunnels, automobiles, frames, oil rigs, and machinery parts due to its favorable material properties, i.e. high strength, toughness, ductility, and stiffness [1][2][3][4]. During the fabrication process, it is rolled, cut, and turned into many shapes without the change of physical properties and composition due to its excellent ductility [5]. ...
In this study, the evolution of the dislocation cell structure and variation of mechanical properties of structural steel under low-cycle fatigue were studied using the indentation experiment, optical microscope, and transmission electron microscope examinations. The results indicated that the dislocation cell structure was well-formed under cyclic loading. When the strain amplitude increased, the original grains were broken more, leading to the dislocation cell size tended to decrease, while dislocation density showed an increase with the further increase of strain amplitude from 0.4% to 1.0%, respectively. Both indentation hardness and yield stress tend to increase when the cyclic loading increases. The change in the dislocation structure was responsible for the strengthening of fatigue mechanical properties, meaning that the dislocation density tended to increase, while the dislocation cell size showed a decrease with the further increase of fatigue condition, leading to the increase of both hardness and yield strength since mechanical properties were inversely proportional to the mean cell size. The results of this study can be used for the practical designs as well as to understand the microstructure changes in structural steel subjected to cyclic loading.
... This technique has shown its efficiency in providing valuable information on the mechanical properties of the microstructure of steel (Pham and Kim, 2015). ...
Recycled Steel Fibers (RSF) derived from the tire recycling industry have been successfully used in concrete to improve its post-cracking load bearing capacity and energy absorption performance. For structural elements exposed to chloride environments, an important aspect of Recycled Steel Fiber Reinforced Concrete (RSFRC) durability is the corrosion resistance. However, research on the durability of RSFRC is almost inexistent, namely concerning the effects of chloride attack, which may limit the mobilization of the full potential of RSFRC.
The present thesis aims to assess the mechanical behavior and durability performance of RSFRC under chloride attack involving both experimental and analytical/numerical research, which knowledge may contribute for future design guidelines and design tools for RSFRC structures. The research activities carried out covered two main fields, the technology of RSFRC manufacturing and the investigation on the corrosion susceptibility of RSFRC.
In the first field, an experimental program was carried out to characterize the RSF in terms of geometry, chemical composition, mechanical properties and microstructure. The influence of rubber particles attached to RSF surface was assessed in the performance of RSF as concrete reinforcement and in its corrosion resistance. A sustainable mix composition of RSFRC was attained and their mechanical properties were evaluated by three-point notched beam bending tests and compressive tests.
The second research field involved an experimental program to characterize the RSF corrosion and to investigate the corrosion effects of RSF on the fiber reinforcement mechanisms developed during the fiber pull-out from cracked concrete previously exposed to corrosive environment. Additionally, the post-cracking behavior of RSFRC under chloride attack was characterized from double edge wedge splitting tests and round panel tests. In these tests, the influence of the crack width, chloride exposure period and fiber distribution/orientation profile was considered. The experimental results were used to perform numerical simulations by inverse analysis, aiming to derive the post-cracking constitutive laws of RSFRC. A simplified prediction of the critical chloride content corresponding to the beginning of fiber corrosion and of the long-term performance of a RSFRC structural element exposed to a specific dry-wet aggressive maritime environment was performed.
In addition, the technical, environmental and economic benefits of using the developed RSFRC for application to structural elements were assessed at material level and compared to Industrial Steel Fiber Reinforced Concrete.
... Rodriguez and Gutierrez 22 investigated the correlation between nanoindentation and tensile properties with experiments, reported that a linear relationship has be verified between the nanohardness and both the yield stress and the tensile stress of the material. Chen et al. 23 , Maier et al. 24 and Pham et al. 25,26 analyzed the microstructural composistions in the weld zone of a structural steel using nanoindentation and optical microscopy including base metal, heat-affected zone and weld metal. It was shown that nanoindentation is acceptable in the verification microstructural compositions in steel at three different locations of the weld zone. ...
Abstract Shielded metal arc butt welded joints for 9%Ni steel using nickel-based filler metal were analyzed by optical microscopy, scanning electron microscope, as well as transmission electron microscopy. The nanoindentation method was used to study the correlation between the structure and micromechanical properties of the fusion welded joint. The results show that there is a microstructural evolution from melted deposit to 9%Ni base steel. A significant coarse lath martensite-bainite mixture has been obtained in 9%Ni steel close to the fusion boundary while the retained austenite distributing in grain boundary of lath martensite has reduced to an undetectable level. In fusion boundary, an intermetallic layer has been observed which corresponds to the epitaxial growth of weld metal. The analysis of stress-strain behavior using nanoindentation shows that the heat-affected zone of coarse grains exhibits ductility loss and quantitative plastic deformation failure. The fusion boundary has the lowest value of yield stress while the coarse grained heat affected zone has the maximum value of yield stress.
... Relying on nanoindentation, Cao et al. [15] found the reduced value of SRS was caused by the remarkably enhanced dislocation density by rolling. Although strain ratecontrolled nanoindentation testing has been widely adopted to study the microscale SRS behavior of engineering steels [16][17][18], there are a limited number of reports about SRS at micro-zones of welded joints. ...
The high-temperature creep–fatigue (CF) interaction on the service damage of P92 welded joint was uncovered based on the evolution of local strain rate sensitivity of strength by nanoindentation. The individual creep, fatigue and creep–fatigue loadings were performed to reveal the CF interaction on both the structure and mechanical properties of the welded joint. And CF loadings interrupted at lifetime fractions of 10%, 20%, 30%, 60%, 100% were adopted to acquire the high-temperature service damage evolution. The structure changes of the heterogeneous welded joint during service damage were characterized by using electron backscatter diffraction method. According to structure evolution including the changes of grain size and dislocation density during high-temperature deformation, we systematically discussed the local variation mechanism of hardness and SRS at different microstructural zones.
... The standard constant loading rate experiments were also performed to verify the H results obtained from the CSM experiments, and as a result, the comparison of the H values was presented in Fig. 7 . The comparison indicates that the values of H obtained from the CSM experiment agree well with those obtained from the standard indentation experiments and the values reported in the literature [57] . The results in Fig. 7 can be used to investigate the ISE of BM, HAZ, and WM. ...
In this study, a series of experiments consisting of continuous stiffness measurement (CSM) nanoindentation experiments, optical microscope (OM), atomic force microscopy (AFM) examinations, and finite element (FE) analysis were performed to study the microstructures, the indentation size effects, and the rate-dependent behavior of mechanical properties in three phases of SM490 structural steel weld joint. The microstructures of base metal (BM), heat-affected zone (HAZ), and weld metal (WM) were observed using OM examinations. The size-dependent behaviors of mechanical properties in BM, HAZ, and WM were characterized and interpreted through the strain gradient theory. The CSM nanoindentation experiments were carried out in the strain rate range of 0.01–0.1 s⁻¹ to investigate the rate-dependent behavior of indentation hardness and continuous strain rate sensitivity. The results indicated that indentation hardness depended on not only the indentation size but also the strain rate of the indentation level. The strain rate sensitivity (SRS) of BM, HAZ, and WM showed the depth-dependent behavior. The SRS of WM is quite high, over 0.4 at the indentation depth of 200 nm, quickly drops to 0.1, and finally is around 0.0298 at large indents. Similarly, the SRS behavior in the case of HAZ is the same, however, the SRS values at larger indents are higher than those obtained in the WM region. At larger depths, the SRS values of the WM region are lower than those of BM and HAZ, while BM has the highest SRS value compared with WM and HAZ. The continuous SRSs of WM, HAZ, and BM are attributed to the change in the dislocation behaviors during the indentation process. The results of the present study can be used to access and understand the rate- and the size-dependent behaviors in structural steel weld zone.
... The excellent weldability and machinability of structural steel, which caused by it's high strength, stiffness, toughness, and ductility, have led to the common usage of this material in many construction fields including buildings, bridges, tunnels and in the manufaction of machinery parts and equipments [1][2][3]. Welding is considered as the efficient method to form the strong joints between the steel parts, where the structural steel is used. However, the welding joints are also considered as the weakest parts of structures [4]. ...
In this study, instrumented indentation testing was conducted at room temperature for the investigation of the effect of strain rate on the hardness and yield strength in the weld zone of a commonly used structural steel, SM520. A number of indentation tests were undertaken at a number of strain rate values from 0.02 s −1 to 0.2 s −1 in the weld metal (WM), heat-affected zone (HAZ), and base metal (BM) regions of the weld zone. The mechanical properties including yield strength (σ y) and hardness (H) in WM, HAZ, and BM were then computed from the applied load-penetration depth curves using a proposed method. As the result, the effects of strain rate indentation on yield strength and hardness in all regions of the weld zone were evaluated. The results displayed that hardness and yield strength in the weld zone's components are influenced on the strain rate, where both hardness and yield strength decrease with the decreasing strain rate.
... The excellent weldability and machinability of structural steel, which caused by it's high strength, stiffness, toughness, and ductility, have led to the common usage of this material in many construction fields including buildings, bridges, tunnels and in the manufaction of machinery parts and equipments [1][2][3]. Welding is considered as the efficient method to form the strong joints between the steel parts, where the structural steel is used. However, the welding joints are also considered as the weakest parts of structures [4]. ...
In this study, instrumented indentation testing was conducted at room temperature for the investigation of the effect of strain rate on the hardness and yield strength in the weld zone of a commonly used structural steel, SM520. A number of indentation tests were undertaken at a number of strain rate values from 0.02 s-1 to 0.2 s-1 in the weld metal (WM), heat-affected zone (HAZ), and base metal (BM) regions of the weld zone. The mechanical properties including yield strength (σy) and hardness (H) in WM, HAZ, and BM were then computed from the applied load-penetration depth curves using a proposed method. As the result, the effects of strain rate indentation on yield strength and hardness in all regions of the weld zone were evaluated. The results displayed that hardness and yield strength in the weld zone’s components are influenced on the strain rate, where both hardness and yield strength decrease with the decreasing strain rate. Keywords: indentation; mechanical properties; strain rate effect; structural steel; weld zone.
... The inhomogeneity of a cryogenic corrosion resistant equipment having welded joints could generate a local stress concentration, which could initiate extensive crack propagation and the microstructures formed in microscopic regions play an important role in controlling the mechanical performance of the welding joint [5]. Therefore, a comprehensive study of the welded joint, including base metal, heat affected zone, weld metal and partial melting zone, is essential for the mechanical performance and microstructure of cryogenic corrosion resistant equipment having welded joints [6]. ...
Nanoindentation test, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were introduced to investigate the mechanical properties and microstructure of microscopic regions of the nickel-based welded joint. Five indentation series were performed across the weld zone including base metal (BM), coarse grained heat affected zone (CGHAZ), partially melted zone (PMZ), weld metal near the partially melted zone and weld metal center (WM). The mechanical properties (E, H, and n) were then estimated from the load on sample-displacement into surface curves (P-h) data of nanoindentation and SEM analysis results. The results showed that the average nano-hardness value (H) was obviously increased in the CGHAZ. WM has the highest values of elastic modulus (E). BM has the highest plastic rheology stress exponent (n). At the same time, the relationship between the plastic rheology depth and the plastic rheology was also discussed.
... Structural steel has been extensively used in the construction of buildings, tunnels, bridges, oil rigs, automobiles, agricultural equipment, frames, and machinery parts, because of its favorable mechanical properties such as high toughness, strength, stiffness, and ductility [1][2][3]. It can also be easily cut, rolled, and turned into a variety of shapes without changing its composition and physical properties during the fabrication process. ...
... Even the transformation of δ-ferrite to α-ferrite occurs during welding, it is believed that the remaining δ-ferrite in weld metal is still higher than that in base metal. The higher amount of δ-ferrite and its abundant transformed phase boundaries may be responsible for the greater strength, strain hardening exponent, and hardness in the weld metal than those in the base metal, while the slight higher elastic modulus in weld metal may be attributed to the "high stiffness ferrite" phase, which was discussed in the previous works [25,26]. ...
In this paper, a procedure for determining mechanical properties in structural steel weld zone using indentation test and finite element (FE) analysis was established and applied for investigating mechanical properties in an SS400 steel weld zone. Instrumented indentation tests were performed across the weld zone and the mechanical properties (E, H, σ y, and n) were then determined from their load-depth data with the aid of FE analysis. The obtained mechanical properties in the weld zone were verified to be reliable by comparing with the results from tensile tests and their FE simulations of both steel and welded specimens. It is shown that in the investigated weld zone, base metal has lower values of mechanical properties (E, H, σ y, and n) than does the weld metal, and mechanical properties within heat affected zone (HAZ) gradually increase from the base metal to weld metal regions. Based on the optical microscopy examination results, the gradient of mechanical within HAZ is found to be associated with the change of grain sizes from base metal to weld metal regions.
This research investigates the nanoscopic features of Advanced High-Strength Steels (AHSS) through a bottom-up approach employing high-speed nanoindentation mapping (HSNM) to elucidate structure-property relationships. The influence of grain boundaries on nanomechanical properties was documented, highlighting the challenge of SEM-EBSD analysis in differentiating phases with identical crystal structures (BCC, FCC, etc.). Integrating SEM-EBSD with HSNM in the same region of interest is essential for detailed insights into phase/microstructure distribution and accurate grain boundary identification. A modular four-step analysis protocol, designed and validated on ferritic-bainitic TRIP steels (TBF), leverages machine learning-enhanced HSNM for significant advancements in AHSS design. The initial phase involves the application of the expectation-maximization algorithm for probability distribution fitting of HSNM data, deriving primary mechanical phase statistics. This exclusively facilitates the correlation of elastic modulus and hardness for each phase/microstructure using nanoindentation data. Further refinement of phase/microstructure to mechanical property correlations was achieved through a supervised machine learning approach, ensuring precise association between EBSD and nanoindentation data. This includes detailed image analysis and clustering of nanoindentation data, enhancing the precision in phase recognition. This methodology addresses the critical challenges in developing 3rd Generation AHSS, aiming to fill the gap in accurately identifying and quantifying phases such as martensite, austenite, bainite, and ferrite, thereby reducing classification and measurement uncertainties. The approach contributes to the fundamental understanding of AHSS microstructures and provides a scalable framework for the comprehensive characterization of structural materials.
In this study, we investigated the composition and mechanical properties of metallurgical phases present in the ASTM A36 steels subjected to post-fire temperatures using nanoindentation testing in conjunction with K++ clustering method. The specimens are exposed to target temperatures from 500°C to 1000°C with an increment of 100°C. We extracted two nanomechanical properties, namely hardness, and Young’s modulus from the nanoindentation tests and used it as descriptive features for the clustering analysis. Results obtained from this analysis show that average volume fractions of ferrite and pearlite were 84% and 16%, respectively. The results also revealed that the mean hardness values were in the range of 2.46 to 3.01 GPa for ferrite and 3.11 to 4.27 GPa for pearlite for the different temperature exposures. The Young’s moduli of ferrite ranged from 171.7 to 203.3 GPa, whereas the pearlite phase ranged from 181.1 to 206.8 GPa for the different temperature exposures. The obtained results also indicated the existence of a quadratic relation between the pearlite’s mean nanoindentation hardness and the yield and tensile strength of different post-fire ASTM A36 steels
In this work, nanoindentation was carried out for the extension of the statistical analysis application into plastic property of constituent phases in virgin materials and heat-affected region after welding of structural steels. The influence of the heat during welding on the microstructural phases and their mechanical properties in two types of popular structural steels was then investigated. The experimental and analysis results revealed that the yield strength spectrum obtained from nanoindentation tests can be used in the accurate and reliable identification of the constituent microstructural phases and their strength in structural steels by applying statistical deconvolution analysis. The heat during welding leads to the transformation of the microstructural phases and causes the increase of both hardness and yield strength of microstructural phases including ferrite and pearlite in structural steels. The correlations between the mechanical properties of the constituent phases in both virgin steels and heat-affected zones, including yield strength σy, representative stress σ0, strain hardening exponent n, elastic modulus E, and hardness H, were also investigated and discussed.
In this study, a series of experiments, which consist of constant strain rate indentation, and optical microscope examination, and finite element analysis were performed to investigate the strain rate-dependent behaviors of the mechanical properties of SS400 structural steel. The microstructures of SS400 steel was characterized using optical microscope examination. The influences of strain rate indentation on the characteristics of the loading/unloading curves were presented and the results showed a higher applied load, a higher loading curvature, and a higher loading work for a higher strain rate level. The strain rate-dependent behaviors of indentation hardness (H), yield strength (σy), and work hardening (n) were investigated. When the strain rate level increased, both H and σy strongly increased, while work hardening showed an almost linear increase. The strain rate-dependent behaviors of material properties were validated through the experimental and numerical verifications. The strain rate sensitivity (SRS) value of 0.056 ± 0.02 was reported for SS400 steel and was highly consistent with the general trend reported for several types of structural steel in the literature.
The effect of aging on the nanohardness, modulus and creep properties of non-quenched and tempered steel wire strengthened by cold forming to an area reduction of 37% was investigated by nanoindentation. It was found that aging at 300 °C can improve the nanohardness, modulus, wear resistance and creep resistance of the cold-drawn non-quenched and tempered steel. An aging time longer than 2 h is not necessary since the degree of improvement decreases. The creep procedure of all tested samples includes two distinct stages, the transient creep and steady-state creep. Aging treatment slows down the creep rate at the steady-state stage.
Reçu le 23 juin 2015, accepté le 2 septembre 2015 Résumé – Les propriétés mécaniques de mélanges caoutchoucs sontétudiéessontétudiées par traction et nanoinden-tation. Les valeurs des paramètres mécaniques obtenues sont du même ordre de grandeur entre les deux techniques ce qui permet de valider l'approche par nanoindentation. Appliquéè a des compositesàcomposites`compositesà ma-trice caoutchouc renforcés par des textiles, cette technique permet de déterminer le gradient de propriétés mécaniquesmécaniquesà l'interface et d'y suggérer une diffusion privilégiée des agents de réticulation au cours du moulage. Abstract – Nanoindentation contribution for the study of mechanical properties of a textile rubber interface. Mechanical properties of rubber blends are studied by tensile tests and nanoindenta-tion. Both techniques show similar scaling of mechanical response and this result allows for validating the nanoindentation procedure. When applied to composite, this technique highlights a mechanical property gradient at the textile-rubber interface that may be attributed to cross-linking agents' diffusion.
In this work, the effect of arc welding on microstructures and mechanical properties of industrial low carbon steel (0.19 wt. % C) was studied. This steel is used for making gas storage cylinders. In order to realize the objective, optical microscopy, EBSD, X-ray diffraction, and hardness tests were used. Different zones and some phases are identified. New microstructural phenomenons are observed by using EBSD technique.
This paper presents a preliminary exploration in tribological property and dynamic elastic/plastic behavior of cement composite material at micro- and nano- scale. Pastes were prepared by pure cement clinker with water-to-cement ratio of 0.3 and 0.4. For comparison, a polymer-based clinker composite was also introduced. Nano-scratch test was carried out to study the scratch process. Different constituents were identified by penetration depth value. Based on this identification, the coefficient of friction and elastic deformation status were analyzed. Substrate effect was found when refers to the coefficient of friction of hard clinker particles embedded in soft matrix. An H/E ratio dependent elastic/plastic behavior was also revealed for cement composite. The results confirm the nano-scratch test as a promising method for cement composite investigation; however, some important attributes of this type of material, including the complexity of multi-phase structure and the viscous effect, need to be taken into account in experimental analysis and practical application.
Synthetic calcium silicate hydrate (C–S–H) made with calcium to silicate (C/S) mixture ratios of 0.9, 1.2 and 1.5 respectively is characterized. C–S–H was produced by extracting calcium oxide (CaO) from calcium carbonate (CaCO 3) and then mixing it with micro-silica (SiO 2) and deionized water to make slurry. The slurry was continuously mixed for 7 days, then the excess water was removed and thermo gravimetric analysis (TGA) was conducted. The drying method was equilibrated to 11% relative humidity (RH). The stoichiometric formula of the synthetic C–S–H were approximated as C 0.7 SH 0.6 , C 1.0 SH 0.8 and C 1.2 SH 2.4 for C/S mixture ratios of 0.9, 1.2 and 1.5 respectively. The dried powders were characterized using X-ray dif-fraction analysis (XRDA), and 29 Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spec-troscopy. The powders were also compacted with 95 MPa pressure and nanoindentation of the compacted specimens were then undergone to mechanically characterize the synthetic C–S–H. The experiments provide insight on the nanoscale mechanical characteristics of C–S–H.
Microstructural composition of the hardened cement pastes are analyzed using nanoindentation and 29Si MAS NMR after curing time periods of 7 and 28 days. Two curing conditions, room condition (20°C with 0.1 MPa pressure) and an elevated condition (80°C with 10 MPa pressure) are prepared to hydrate cement pastes [water to cement (w/c) ratio of 0.45]. The degree of hydration of the cement paste quantified using nanoindentation was compared with that from 29Si MAS NMR. From nanoindentation of the hardened cement pastes, microstructural hydration products are characterized with respect to the corresponding modulus of elasticity. A hydration product, which has a relatively high modulus of elasticity over other known hydration products, was found in the hardened cement paste cured in elevated temperature and pressure. The effect of high pressure on the composition of the hydration product is discussed and it is hypothesized that the packing density of calcium-silicate-hydrate (C-S-H) might increase when a cement paste is hydrated under high temperature and pressure.
Composite homogenization is a numerical simulation method that allows the realization of the significance of microstructure constituents on the mechanical properties of the composite materials. Using this homogenization technique, the cement paste can be modeled as a composite material where micro particles are randomly dispersed in the cement paste matrix. Using microstructural homogenization, a representative volume element (RVE) can be developed and used to simulate the constitutive model of the composite cement paste by considering its constituent phases.
Here we consider a four phase cement paste model to describe cement paste incorporating nanosilica. We lump sum the cement paste microstructure into Phase I: hydrated cement paste, Phase II: unhydrated cement paste, Phase III: non-reacted nanosilica and Phase IV: capillary porosity. Cement hydration models are used to predict the volume fraction of the four phases based on the mixture proportion of the cement paste mix. Constitutive models for Phase I, III and IV are assumed based on the literature. Constitutive model for Phase II is identified using the RVE model by matching the stress-strain curves of the cement paste extracted from nanoindentation experiments. The validated RVE model is then used to examine the significance of changing the nanosilica content in the cement paste on the stress-strain of the composite cement paste. It is evident computationally, that increasing nanosilica content shall enable increasing the strength and stiffness of the cement paste and therefore will also increase the cement paste ability to absorb energy represented by the area under the stress-strain curve.
The local mechanical properties of ferritic and austenitic domains in a duplex stainless steel are locally studied by nanoindentation. The elastic and plastic properties of the two phases are determined. Without any specific surface treatment (chemical or electrochemical), the austenitic and ferritic domains present in the duplex stainless steel are distinguished using magnetic force microscopy. The magnetic scans allow nanoindentation results to be assigned to the respective phase, yielding the local mechanical properties of the duplex steel. The magnetic scans also show a sharp transition between the phases that is maintained even inside indentations. The ferrite phase is found to supersede austenite in the elastic modulus, hardness, and strain-hardening exponent, while both phases possess similar yield strength. Interface properties are a weighted average of the phase properties.
Using first-principles calculations within the generalized gradient approximation, we predicted the lattice parameters, elastic constants, vibrational properties, and electronic structure of cementite (Fe3C). Its nine single-crystal elastic constants were obtained by computing total energies or stresses as a function of applied strain. Furthermore, six of them were determined from the initial slopes of the calculated longitudinal and transverse acoustic phonon branches along the [100], [010] and [001] directions. The three methods agree well with each other, the calculated polycrystalline elastic moduli are also in good overall agreement with experiments. Our calculations indicate that Fe3C is mechanically stable. The experimentally observed high elastic anisotropy of Fe3C is also confirmed by our study. Based on electronic density of states and charge density distribution, the chemical bonding in Fe3C was analyzed and was found to exhibit a complex mixture of metallic, covalent, and ionic characters.
A glass–ceramic coating made by fusing dicalcium silicate and tricalcium silicate to the surface of glass-enameled steel has been successfully used to increase the bond between reinforcing steel and concrete and provide corrosion protection for the steel. A very strong interface that consists of hydrated cement and enameled glass over the top of a second strong interface between the enameled glass and the surface of the steel results from the outer layer of water-reactive silicates hydrating on contact with fresh concrete. Currently the mechanical characteristics (hardness, elastic modulus and strain-rate sensitivity), micromorphology, and the variation in interface chemical composition are being examined. Preliminary results indicate that the more gradual transition between the mechanical properties of the steel and the paste combined with improved integration between the coating and cement hydration products in the paste results in the increased bond strength observed in macroscale tests. Results from this study to characterize the developed coating are being used to engineer new optimized enamels for this unique application.
In this study, the effects of coarse initial grain size with varying heat inputs on microstructure and mechanical properties of weld metal and heat-affected zone (HAZ) were investigated. In the welding experiments, SAE 1020 steel specimens in hot-rolled and in grain-coarsened conditions were used. The specimens taken from the hot-rolled steel (original) plate were heat treated at 1100°C for 45 min and then cooled in a furnace in order to obtain a coarse initial grain size. The original and grain-coarsened specimens were welded using a submerged arc welding machine with heat inputs of 0.5, 1 and 2 kJ/mm. Following the welding, microstructure, hardness and toughness of weld metals and HAZs were investigated. From the results, we tried to establish a relationship between initial grain size, microstructure, hardness and toughness of weld metals and HAZs. From the results of the toughness tests, it was seen that the weld metals of coarse initial grain sized specimens and original specimens exhibited nearly the same toughness values with the same heat input, whereas different HAZ toughness values were obtained with the same heat input. Maximum toughness of HAZ of the coarse initial grain sized specimen was achieved with a high input, while maximum toughness of original specimen was obtained with a medium heat input. As a result, considering the heat input, it was observed that the coarse initial grain size had a great influence on the microstructure, hardness and toughness of HAZ of a low carbon steel. Thus, taking into consideration the plate thickness, a higher heat input should be used with respect to the maximum toughness of the HAZ in the welding of grain-coarsened low carbon steels.
An experimental program which includes the observation of microstructures and the Charpy impact test was conducted to evaluate the applicability of high strength TMCP steel (SM570-TMC) weld to cold regions. The experiments were also carried out on conventional structural steel (SM490B) weld for comparison. Standard V-notch Charpy specimens were prepared and tested under dynamic loading condition. The service temperatures of the weld metal, the HAZ (heat affected zone) and the base metal were derived and their applicability to cold regions was assessed by the absorbed energy, the impact test requirement and the microstructure. Test results revealed that the base metal of the SM570-TMC weld has much higher impact toughness at low temperatures compared to that of the SM490B weld, while the HAZ and the weld metal exhibit much lower impact toughness than the base metal and have a service temperature similar to their counterparts in the SM490B weld. These results imply that for the application of the TMCP steel weld to cold regions, adoption of appropriate welding process which guarantees the low temperature impact toughness of the HAZ and the weld metal along with suitable electrode should be made, at which the future works are aimed.
In this study, calcium silicate hydrate (C-S-H) is synthesized and characterized. C-S-H slurry was made with calcium oxide (CaO) to micro-silica (SiO2) mixture ratio of 1.5 and enough deionized water. The slurry was continuously mixed for 7 days, then the excess water was removed. Two methods of drying were implemented: one method used the standard d-dry technique and the other was equilibrated to 11% relative humidity (RH). The dried powders were characterized using thermo gravimetric analysis (TGA), X-ray diffraction analysis (XRDA), and 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The stoichiometric formulas of synthetic C-S-H powders dried to d-dry and 11% RH in this study were approximated as C1.2SH0.7 and C1.2SH2.4 respectively. The powders were then compacted to create specimens with porosities similar to C-S-H in hydrated cement. The specimens underwent nanoindentation to mechanically characterize C-S-H. The experiments provide insight on the nanoscale mechanical characteristics of C-S-H.
This investigation presents results of experimental work to illustrate the effect of post weld heat treatment (PWHT) on the microstructure and mechanical properties of low carbon steel AISI 1020 butt-welded components.In order to assess the effect of PWHTs, different type of heat treatments have been applied using different soaking temperature, heating rates, time durations and cooling rates.To assess the effect of these different heat treatment schemes on the mechanical properties, micro-hardness, tensile strength and notched impact tests have been carried out on the welded joint. Also metallurgical testing has been carried out to assess the change in the metal microstructure before and after heat treatments.
The mechanical properties of as-cast and hot-forging duplex stainless steel samples with the same compositions were characterized by nanoindentation. The effect of surface treating method and working state of the sample on the nanoindentation results of ferrite and austenite were discussed. The results show that the Young's modulus and hardness of ferrite and austenite may be affected by the treating method of sample surface. The difference of Young's modulus average of ferrite or austenite between as-cast and hot-forging duplex stainless steel samples is not great, but the hardness average of ferrite or austenite in hot-forging sample is obviously higher than those of as-cast sample. The difference of hardness between ferrite and austenite in the same sample is not great, but the young's modulus of ferrite is higher than that of austenite.
Thermomechanical controlled processing (TMCP) of low carbon cold heading steel in different austenite conditions were conducted by a laboratory hot rolling mill. Effect of various processing parameters on the mechanical properties of the steel was investigated. The results showed that the mechanical properties of the low carbon cold heading steel could be significantly improved by TMCP without heat treatment. The improvement of mechanical properties can be attributed mainly to the ferrite grain refinement due to low temperature rolling. In the experiments the better ultimate tensile strength and ductility are obtained by lowering finishing cooling temperature within the temperature range from 650 °C to 550 °C since the interlamellar space in pearlite colonies become smaller. Good mechanical properties can be obtained in a proper austenite condition and thermomechanical processing parameter. The ferrite morphology has a more pronounced effect on the mechanical behavior than refinement of the microstructure. It is possible to realize the replacement of medium-carbon by low-carbon for 490 MPa grade cold heading steel with TMCP.
The mechanical properties of dynamically and statically transformed ferrites were analyzed using a nanoindentater-EBSD (Electron BackScattered Diffraction) correlation technique, which can distinguish indenting positions according to the grains in the specimen. The dilatometry and the band slope and contrast maps by EBSD were used to evaluate the volume fractions of two kinds of ferrite and pearlite. Fine ferrites induced by a dynamic transformation had higher nano-hardness than the statically transformed coarse ferrites. Transmission electron microscopy (TEM) showed the dynamic ferrites to have a higher dislocation density than the statically transformed ferrites.
In this study, the effects of initial grain size with the varying heat inputs on the microstructure and toughness of intercritical heat-affected zone (HAZ) of a low-carbon steel were investigated. In the welding experiments, SAE 1020 steel specimens in hot-rolled (original), in grain-refined and in grain-coarsened conditions were welded by a submerged arc welding machine with the heat inputs of 0.5, 1 and 2 kJ mm−1. Following the welding, microstructure, hardness and toughness of the intercritical HAZs of the specimens were investigated. The determination of microstructure and measurement of hardness in the intercritical HAZs were performed on the samples taken from the welded specimens, while toughness values were obtained using the weld thermal simulation technique. From the results, we tried to establish a relationship between the heat input, initial grain size, microstructure, hardness and toughness of the intercritical HAZ. From the results of the toughness tests and microstructural observation, it was seen that the fine initial grain size was effective on the formation of ductile phases and on the higher toughness, whereas the coarse initial grain was effective on the formation of brittle phases and on the lower toughness at the same heat input. As a result, considering the microstructure, hardness and toughness of the intercritical HAZ, a higher heat input for both the coarse initial grain size and fine initial grain size gave good results. However, it was also seen that a lower heat input can be used in the welding of low carbon steel with fine initial grain size with respect to the toughness of the intercritical HAZ.
A comprehensive treatment of fracture mechanics suitable as a graduate
text and as a reference for engineers and researchers is presented. The
general topics addressed include: fundamental concepts of linear elastic
and elastic-plastic fracture mechanics; dynamic and time-dependent
fracture mechanics; micromechanisms of fracture in metals and alloys;
fracture mechanisms in polymers, ceramics, and composites; applications
to fracture toughness testing of metals and nonmetals, to structures,
fatigue crack propagation, and computational fracture mechanics.
Reference materials usually found in fracture mechanics handbooks is
provided.
The effect of alloying additions on the surface structure and properties of cementite bulk was investigated. Results showed that addition of Cr, Mn, V and Mo stabilized cementite. The formation of cementite was found to be suppressed and destabilized by Ti, Ni, and Si. Addition of Cr and Mn increased the hardness, Young's modulus, and thermal expansion coefficient of cementite.
a b s t r a c t Synthetic calcium silicate hydrate (C–S–H) made with calcium to silicate (C/S) mixture ratios of 0.9, 1.2 and 1.5 respectively is characterized. C–S–H was produced by extracting calcium oxide (CaO) from cal-cium carbonate (CaCO 3) and then mixing it with micro-silica (SiO 2) and deionized water to make slurry. The slurry was continuously mixed for 7 days, then the excess water was removed and thermo gravimet-ric analysis (TGA) was conducted. The drying method was equilibrated to 11% relative humidity (RH). The stoichiometric formula of the synthetic C–S–H were approximated as C 0.7 SH 0.6 , C 1.0 SH 0.8 and C 1.2 SH 2.4 for C/S mixture ratios of 0.9, 1.2 and 1.5 respectively. The dried powders were characterized using X-ray dif-fraction analysis (XRDA), and 29 Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spec-troscopy. The powders were also compacted with 95 MPa pressure and nanoindentation of the compacted specimens were then undergone to mechanically characterize the synthetic C–S–H. The experiments provide insight on the nanoscale mechanical characteristics of C–S–H.
The improvement of toughness in the heat affected zone by the production of acicular ferrite was studied. The acicular ferrite exhibited a yield strength in the range from 480 to 515 MPa, a ultimate tensile strength from 630 to 660 MPa with elongation of 35%, and Charpy energies higher than 100 J at 0 °C. At lower testing temperatures, a smooth ductile-brittle transition with an absorbed energy at -40 °C higher than 50 J was observed.
The indentation load-displacement behavior of six materials tested with a Berkovich indenter has been carefully documented to establish an improved method for determining hardness and elastic modulus from indentation load-displacement data. The materials included fused silica, soda–lime glass, and single crystals of aluminum, tungsten, quartz, and sapphire. It is shown that the load–displacement curves during unloading in these materials are not linear, even in the initial stages, thereby suggesting that the flat punch approximation used so often in the analysis of unloading data is not entirely adequate. An analysis technique is presented that accounts for the curvature in the unloading data and provides a physically justifiable procedure for determining the depth which should be used in conjunction with the indenter shape function to establish the contact area at peak load. The hardnesses and elastic moduli of the six materials are computed using the analysis procedure and compared with values determined by independent means to assess the accuracy of the method. The results show that with good technique, moduli can be measured to within 5%.
Concrete, bone and shale have one thing in common: their load-bearing mineral phase is a hydrated nanocomposite. Yet the link between material genesis, microstructure, and mechanical performance for these materials is still an enigma that has deceived many decoding attempts. In this article, we advance statistical indentation analysis techniques that make it possible to assess, in situ, the nanomechanical properties, packing density distributions, and morphology of hydrated nanocomposites. These techniques are applied to identify intrinsic and structural sources of anisotropy of hydrated nanoparticles: calcium–silicate–hydrate (C–S–H), apatite, and clay. It is shown that C–S–H and apatite, the binding phase in, respectively, cement-based materials and bone, are intrinsically isotropic; this is most probably due to a random precipitation and growth process of particles in calcium oversaturated pore solutions, which can also explain the nonnegligible internanoparticle friction. In contrast, the load-bearing clay phase in shale, the sealing formation of most hydrocarbon reservoirs, is found to be intrinsically anisotropic and frictionless. This is indicative of a ‘smooth’ deposition and compaction history, which, in contrast to mineral growth in confined spaces, minimizes nanoparticle interlocking. In all cases, the nanomechanical behavior is governed by packing density distributions of elementary particles delimitating macroscopic diversity.
The hot hardness was measured on the (010) plane of primary cementite in unidirectionally solidified iron-carbon, iron-carbon-chromium, and iron-carbon-boron alloys at temperatures up to 973 K, using a hot hardness tester equipped with an indenterheating system. The hardness of paramagnetic cementite against temperature was represented by the Ito-Shishokin relation. On the other hand, the hardness of ferromagnetic cementite deviated to low values from the Ito-Shishokin relation found for paramagnetic cementite. This deviation occurred from magnetostriction, because the thermal softening coefficient of cementite was found to relate to the thermal expansion coefficient regardless of the magnetic state similar to that found with fcc and bcc metals. Chromium and boron increased the hot hardness of cementite.
Despite its ubiquitous presence as binding phase in all cementitious materials, the mechanical behavior of calcium–silicate–hydrates (C–S–H) is still an enigma that has deceived many decoding attempts from experimental and theoretical sides. In this paper, we propose and validate a new technique and experimental protocol to rationally assess the nanomechanical behavior of C–S–H based on a statistical analysis of hundreds of nanoindentation tests. By means of this grid indentation technique we identify in situ two structurally distinct but compositionally similar C–S–H phases heretofore hypothesized to exist as low density (LD) C–S–H and high density (HD) C–S–H, or outer and inner products. The main finding of this paper is that both phases exhibit a unique nanogranular behavior which is driven by particle-to-particle contact forces rather than by mineral properties. We argue that this nanomechanical blueprint of material invariant behavior of C–S–H is a consequence of the hydration reactions during which precipitating C–S–H nanoparticles percolate generating contact surfaces. As hydration proceeds, these nanoparticles pack closer to center on-average around two characteristic limit packing densities, the random packing limit (η=64%) and the ordered face-centered cubic (fcc) or hexagonal close-packed (hcp) packing limit (η=74%), forming a characteristic LD C–S–H and HD C–S–H phase.
Analysis of nanoindentation experiments assumes that the indentation occurs on a flat surface. As a result, the accuracy of nanoindentation depends on reducing the surface roughness to a tolerable level. Within the context of statistical nanoindentation techniques suitable for heterogeneous materials, this study presents a criterion for roughness of cement paste surfaces for nanoindentation, and describes a method for obtaining the desired roughness. Through a systematic experimental study, we show the evolution of roughness and nanomechanical properties from indentation as a function of increased polishing. We conclude that the root-mean-squared (RMS) roughness of the sample, taken over a square area with edge dimensions of 200 times the average indentation depth of the dominating phase of the material, should be less than five times the average indentation depth of the dominating phase of the material.
The elastic constants and internal friction of induction hardened and unhardened SAE 1050 plain-carbon steel at ambient temperatures were determined by resonant ultrasonic spectroscopy. The hardened specimen contained only martensite and the unhardened specimen was ferrite-pearlite. Using an inverse Ritz algorithm with assumed orthorhombic symmetry, all nine independent elastic-stiffness coefficients were determined, and, from the resonance peak widths, all nine components of the internal-friction tensor were determined. Similar measurements and analysis on monocrystalline α-iron were performed. The steel has slight elastic anisotropy, and the isotropically approximated elastic moduli were lower in the martensite than in ferrite-pearlite: shear modulus by 3.6%, bulk modulus by 1.2%, Young modulus by 3.2%, and Poisson ratio by 1.5%. Isotropically approximated elastic moduli of α-iron were 0.6–1.3% higher than ferrite-pearlite. All components of the internal-friction in martensite were higher than those of ferrite-pearlite, but lower than those of α-iron.
Steels represent the most widely-used metallic alloy, possessing a wide range of microstructures and mechanical properties. By examining the mechanical properties of steels in conjunction with microstructure this book provides a valuable description of the development and behaviour of these materials - the very foundation of their widespread use. Updated throughout and including new chapters on nanostructured steels, and new alloys and technologies for the energy and automobile industries, the book is clearly written and illustrated, with extensive bibliographies and real-life examples. An essential reference, both compact and readily comprehensive, for metallurgists and engineers in both industry and academia. Outlines the principles determining the microstructure, mechanical behaviour and properties of steels, the most widely-used metallic alloy Thoroughly updated with new material on nanostructured steels, novel alloys for energy industries, and the latest technologies for the automobile industry, including TRIP-assisted steels Accompanied by extensive tutorial question bank and worked solutions on companion website.
Control of microstructures and properties in steel arc welds. British: Library of Congress Cataloging in Published Data
- Lars
Lars-eric S. Control of microstructures and properties in steel arc welds. British: Library of Congress Cataloging in Published Data; 1994.