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MaCh3D different specimen geometry configurations maximum tensile stress values. Red lines indicate standard deviation.
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The aim of this work is to describe the design process of a non-conventional miniaturized specimen geometry compliant to ASTM E8M and ISO 6892, expressively developed to work with MaCh3D, an innovative miniaturized tensile testing machine. The use additive manufacturing in a production perspective requires continuous certification of the fabricated...
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Context 1
... testing was performed using MaCh3D, with a constant strain rate of 0.04 mm/mm/min corresponding to a maximum crosshead speed of 2mm/min while testing full-size specimen; 5 specimens were tested for each geometry. In Figure 8 maximum stress is reported for each configuration: Average maximum tensile stress is í µí± í µí± " = 44.87 MPa with a standard deviation of 2.27 MPa, corresponding to a ±5% variation in respect to the average value. ...
Citations
... Determining the impact of the microstructure on the mechanical performance is crucial for comprehending the material behaviour in tension, particularly when sub-sized test specimens are used. According to Lorenzo et al. [77], the miniaturization of specimens induces a "scaling effect" altering material behaviour at the microscale in comparison to the macroscale. This effect can involve factors such as grain size and their quantity in the cross-section, anisotropy, micro-structural and chemical inhomogeneity and residual stress. ...
The study aimed to evaluate the tensile strength of additively manufactured (AMed) IN 625 using sub-sized test pieces and compare them to standard specimens. Cylindrical round coupons of varying diameters were manufactured along the Z-axis using the laser powder bed fusion technique and subjected to heat treatment. The simulation of the alloy solidification predicted the formation of several intermetallics and carbides under equilibrium conditions (slow cooling), apart from the γ phase (FCC). Sub-sized tensile specimens with different gauge diameters were machined from the coupons and tensile tested at ambient temperature. The results showed that sub-sized specimens exhibited lower tensile and yield strengths compared to standard specimens, but still higher than the minimum requirements of the relevant ASTM standard for AMed IN 625. The lower strength was attributed to the “size effect” of the test specimens. Fracture surfaces of the sub-sized test specimens exhibit a mixed character, combining cleavage and microvoid coalescence, with improved ductility compared to standard test pieces. The study highlights the importance of adapting characterization methods to the particularities of manufactured parts, including reduced thicknesses that make sampling standard-size specimens impractical. It concludes that sub-sized specimens are valuable for quality control and verifying compliance with requirements of AMed IN 625 tensile properties.
... However, it also harbors correlation issues as the gauge size is reduced wherein dominant micro-mechanics introduce high nonlinearity into the mechanical results. Therefore, the evolution of miniature test specimen is developed to accomplish constant characteristic geometric ratios to maintain component correlation as well as a reduction in potential stress intensity factors that develop with higher curvatures in shorter gauge lengths [146,147]. ...
Additive manufacturing has long enabled complex and less restrictive design capabilities in the world of modern manufacturing. However, industry applications require extensive analysis into reliability concerns over repeatability that currently prevent the technology from maturing to an adequate, widespread production method. With current research focus expanding on additive manufacturing technologies, a need has developed to ensure repeatability in already established methods. This paper reviews the current certification landscape surrounding additive components as well as similarly variable manufacturing processes as baselines for comparison. Next, concerns in the repeatability of additive manufacturing methods are outlined for both their occurrences and effects. Lastly, methods of verification and current developments in design and verification methodologies are presented with the aim of analyzing potential future developments to aid industry adoption of additive manufacturing.
... elongation after necking [19]. For the dimension of the transition section, Bergonzi et al. [20] considered the influence of the stress concentration degree and contact force distribution (different contact points between the specimen and clamp owing to different radii) on the test results and determined the optimal size of the transition arc between the head and the parallel section of the specimens. The STT is also applicable to curved surface specimens sampled from tubular components, and the characteristics of the test results are similar to those of curved surface CTT [21]. ...
... For flat specimens, the ratio of thickness to grain size should not be less than 5-10 [10], generally not less than 1 mm [19], and the minimum is 0.2 mm [24]; the gauge length less than 2 mm will lead data scattering [17]. The transition arc should not be too small compared to the gauge dimensions to avoid the wrong stress and strain states [20]. ...
Small specimen test techniques (SSTTs), developed for scarce materials, industrial products, in-service equipment, etc., could be challenging to obtain sufficient materials for routine testing. This review focuses on the research on millimeter- and micron-scale SSTTs of metallic materials in the past decade. Mainstream small specimens are divided into similarity, penetration, and semi-penetration. Representative tests of the above three categories are analyzed in detail, including the small tensile test, small punch test, and indentation test. The macro- or micro-correlation methods of deformation and failure parameters between the SSTTs and conventional tests are discussed, including Young's modulus, yield strength, ultimate tensile strength, damage evolution, fracture strain, and the stress–strain full-history relationships. Meanwhile, the extensive requirements for material testing are also considered, such as anisotropy and strain rate, temperature, and stress triaxiality sensitivities. The characteristics and modification strategies of the SSTTs are described from the aspects of size effects, inhomogeneous structures, and manufacturing defects. Finally, this paper discusses the application of SSTTs in forging, stamping, welding, and additive manufacturing and highlights the potential development directions of SSTTs.
Graphical Abstract
... The characterization activity is costly in terms of both time and resources used; in addition to the testing activities, the volume of components and cost of the specimens produced must be considered. Miniaturized specimens allow for significant reductions in printing time and raw material requirements, as reported by Lorenzo et al. (2019). The cylinders were fabricated with a minimum height and wall thickness. ...
Wire arc additive manufacturing (WAAM) is suitable for manufacturing large-scale complex parts due to many advantages, including high disposition rate and low cost and thus become a viable advanced manufacturing technique. In the present study, two different arc welding processes were used to fabricate 308 L austenitic stainless steel (SS) cylindrical components. The mechanism and impact of the processes on the microstructure and mechanical characteristics were analysed. The results indicated that the component produced by the cold metal transfer (CMT) arc welding process exhibits finer grains and higher amount of ferrite than conventional gas metal arc welding (GMAW) process. Furthermore, the percentage of anisotropy in tensile strength was reduced from 8.07% to 6.21% for cylinders built by the GMAW process to the CMT process. In addition, the average ultimate tensile strength (UTS), elongation (EL) and hardness of the CMT cylinder are 5.17-7.0%, 4.029-7.80% and 4.02-5.88% higher than the GMAW cylinder, irrespective of orientations. The tensile properties are higher than those of the 308 L welding wire and other arc-welding based additively manufactured 308 L stainless steel parts. The produced WAAM 308 L SS cylinders exhibited superior performance than the stainless steel made by industrial forging standards. Therefore, the 308 L SS cylindrical components made by WAAM technique are found to be suitable for industrial application.
... Although the L-PBF process itself is cost intensive, due to high initial investment, the reduced cost associated with minimised post-processing requirements justifies the use of high cost materials in AM. Furthermore, due to the possibility of reuse of AM powder and hence little material wastage, the high production costs associated with Ta processing are further reduced [46]. ...
Due to its high cost and demanding characteristics, Tantalum requires unique processing techniques and is restricted to small parts. In the present work, Ti65Ta was additively manufactured as a new potential material for small biomedical implants. Assessment of the effects of a remelt scanning strategy was solely accomplished by testing of small mechanical specimens. Yield strength was achieved superior to either L-PBF pure Ti or Ta and low-cycle fatigue behaviour was similar to that of L-PBF Ti-6Al-4V. The Ti65Ta alloy is a good candidate for a new gold standard alloy for small bone interfacing implants.
... To characterize the mechanical properties of thin wires and knitted meshes made from NiTi alloys, measuring equipment is required to accurately capture the superelastic behavior of the material during monotonic and cyclic tests at different tensile strain rates [9][10][11]. At the same time, the hardware must meet modern digital control requirements with the ability to display data in real-time during the test, along with saving and processing obtained data [12][13][14][15][16][17]. ...
A portable universal tensile testing machine for single and cyclic loading of superelastic biomaterials is presented. It’s an alternative to large-sized stationary universal testing machines. The machine is designed to obtain uniaxial cyclic tension stress-strain curves of materials with a low elastic modulus, including biological tissues. Its portability allows using it in various conditions: classrooms, production laboratories, and in the field. An interface has been developed to connect it to a computer. Computer output of experimental data allows recording and displaying load-displacement curves, setting the number of cycles, limits, and rate of cyclic deformation. Several examples of testing various biomaterials are presented. The functional advantage of the device is the wide tensile testing speed range of 0.01-10 mm/s and cyclic loading, which allow capturing viscoelastic and superelastic behavior of biomaterials.
... This was also confirmed by the authors of the work [16]. Additionally, three different miniaturized specimens were also partially validated by Bergonzi, Vettori, and Pirondi [17], determining that the stress levels achieved for different geometries are comparable. This means that it is possible to use miniaturized samples as long as they are validated with normative samples. ...
Abstract: This paper discusses the development of a flow stress model to simulate the AA3104-H19 alloy under the conditions of large plastic deformations characteristic of the beverage can manufac turing process. This study focuses on the first five steps of this process: cupping, redrawing, ironing #1, ironing #2, ironing #3. These are the stages that reduce the thickness of the base material to the maximum, resulting in an effective strain of more than 2.0, unattainable in conventional plastometric tests. To solve this problem, the specific calculation-experimental method for the development of the
flow stress model was proposed. Based on the FEM modeling of the technological process, data on the history of deformation and the trajectory of movement of the selected points of the material at all stages of the production were obtained. Microspecimens for the tensile tests were taken from the points of the beverage can wall that were determined in this way. The initial strain of each sample was taken from the FEM simulation. In this way, the tensile curves were obtained for the material
points at different stages of the production. The processing of these curves allowed the creation of a flow stress model for large strains, corresponding to production conditions. The tensile tests were performed on a Zwick Z250 machine at room temperature and strain rate of 0.005 s−1 . The FEM based algorithm for the determination of empirical coefficients of the analytical flow stress model is presented. The final flow stress model covers the range of effective strain from 0–2. Validation of the developed model based on the measured beverage can thicknesses showed that a flow stress model was developed that correctly and accurately describes the forming process.
... The final specimen geometry, which development through Finite Element Method (FEM) has been reported in the work of Bergonzi et al. [1], defined as "S-Size" is reported in Figure 1 (a) with main dimensions: % is the reduced section length, represent specimen width, specimen thickness. The maximum obtainable stress level on the reduced section, given the maximum applied load of 5 kN, is equal to 1587.30 ...
This work deals with the experimental validation of the proposed specimens geometries which design process through Finite Element Method was presented during AIAS 2019 and published afterwards [1]. In particular, non-conventional miniaturized specimen geometry compliant to ASTM E8 and ISO 6892, specifically developed to work with MaCh3D [2], an innovative miniaturized tensile testing machine, were considered. The size-reduction of specimens is advantageous both in terms of material and equipment: smaller specimens require lower forces to be broken, hence a compact tensile testing machine can perform the mechanical characterization activity. In this experimental validation, mechanical properties determined using the three proposed MaCh3D miniaturized specimens are compared to full-size ISO 6892 samples. Specimens were cut from AISI 304 stainless steel plates, with different thickness according to specimens requirements. Good accordance has been found between the standard and non-standard geometries.
In this study, the fatigue behavior of thin electrical steel sheets under cyclic loading is investigated. Results from strain-controlled and stress-controlled fatigue tests with different specimen geometries and different test setups are presented and compared with conventional testing methods. The results imply that conventional testing methods should be adjusted for testing thin electrical steel sheets because the fatigue life depends significantly on the test setup as well as the specimen geometry. Therefore, this study proposes an improved specimen geometry and test setup for stress- and strain-controlled fatigue tests of thin electrical steel sheets depending on the desired testing parameters.
A complete description of the experimental procedure for characterizing the intrinsic fatigue crack propagation threshold (ΔKth,eff) as well as the fatigue crack growth rate (FCGR) in the near-threshold regime using small-scale specimens is presented. A comparative study is carried out on the high strength steel S960QL considering different single edge notch bend (SENB) specimen geometries. On one hand, the reference dimensions of 6 mm thickness (B) and 19 mm width (W) are analysed and referred to as conventional specimens. On the other hand, small-scale specimens with B = 3 mm and W = 4 and 6 mm are also considered. Several loading configurations (3-, 4- and 8-point bending) are used and a load ratio R = 0.8 is applied to avoid crack closure effects. The direct current potential drop (DCPD) technique is used to monitor the crack length. The reduced dimensions of the small-scale specimens imply the necessity of implementing a modified testing procedure compared to the recommendations of current standards for the generation of FCGR data. The results show a good agreement between tests conducted on different specimen sizes, which opens new perspectives in the use of small-scale specimens for characterizing the fatigue crack growth properties in metallic materials. Recommendations and limitations of the procedure are provided and discussed.
