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In fracture, the various expressions of G the crack extension force per unit length of the crack-front (or energy release rate) show invariably a linear dependence of G with the crack half-length c. This is true whatever the shape (planar or non-planar) of the crack and the form f of the crack-front (f can be developed in Fourier forms). Hence some expressions of G (see relation (2.25), page 37 in Lawn (1993) Second Edition, for example) provided for the DCB specimens are under question. Are these concerned with crack propagation?
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We provide G values for Double-Cantilever Beam (DCB) specimens that depend linearly on the crack length c: see " DOUBLE-CANTILEVER BEAM SPECIMEN BENT BY PAIRS OF OPPOSITE TERMINAL TRANSVERSE LOADS" (2024) in our contributions in Research Gate.
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The aim of the research here is to prevent the propagation of the crack in the fabricated elastic medium with useful applications.
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1) Your answer is on a purely assumption level.
2) Assuming no pre-existing crack, le material would deform plastically only.
3) In presence of a pre-existing crack, expansion of the latter would be observed on the elastic applied stress range first until the blunting of the crack (crack arrest), clearly in a two-dimensional crack scheme.
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Can an elliptic crack (small enough to remain a single entity, with no internal pressure or shear force) inside an isotropic material (no boundary effect) be expanded in its own plane under externally applied shearing stresses only?
If yes, how did you show that? Do we have experimental evidence for the process?
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Recent works confirm that elliptical cracks cannot expand under applied shearing stresses parallel to their planes. Please see: Conoidal crack with elliptic bases, within cubic crystals, under arbitrarily applied loadings-I. Dislocation, crack-tip stress, and crack extension force; -III. Application to brittle fracture systems of CoSi2 single crystals (III). Theory and experiments completely agree.
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A simple crack system (Figure 1) can be readily studied to estimate the Hertzian conoidal crack angle and length, and also the stress intensity factor.
This is a 3-D brittle elastic half-space on the flat boundary Ox1x3 of which a rectilinear contact pressure along Ox3 is exerted by a cylinder whose axis is parallel to x3; the cylinder lies along Ox3 on the flat boundary. A planar straight-front crack inclined by an angle θ with respect to x1x3 is present under the action of the load along x2 due to the cylinder. The relevance of this modelling may be understood as follows. A slab of cylinder with thickness dx3 at spatial position O’ (0, 0, x3) exerts elastic fields (displacement and stress) proportional to those of a point load at O’ (proportionality coefficient dx3). Physically, this corresponds to the action of a spherical indenter to which is associated a conoidal fracture surface for sufficiently large load (Roesler (1956) as quoted by Frank and Lawn (1967)). The coalescence of conoidal cracks from different slabs of cylinder along Ox3 would produce planar fracture surface envelops parallel to x3 at large crack lengths. Therefore, we expect the modelling in Figure 1 to provide the experimentally observed fracture surface inclination angle θ and crack length l as a function of critical load P by both a spherical indenter and cylinder. This is the essence of the modelling depicted schematically in Figure 1.
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Progress is achieved with respect to previous description:
1) The crack extension force G, per unit length of the crack front, is now available in analytical form
2) G value now includes the contribution of gravitational forces due to the earth.
Please refer to “BRITTLE CRACKS IN A THREE-DIMENSIONAL ELASTIC HALF-SPACE UNDER THE RECTILINEAR CONTACT PRESSURE OF A CYLINDER: INTRODUCING GRAVITATIONAL FORCES”.
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Cross-slip, twinning and fracture are major deformation modes adopted by loaded materials. It appears sound that these apparently different deformation mechanisms can be analysed on the equal manner!
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Cross-slip, twinning, and fracture systems under applied loadings receive the same mathematical theory using continuous distributions of elliptical dislocations in the framework of linear elasticity. Essentially the theory provides a quantity G that is a ratio, defined as the decrease ΔE of the total energy of the system divided by the corresponding change ΔS of the surface of the dislocation distribution, after incremental infinitesimal time dt: G= -ΔE/ΔS. In fracture G is the energy release rate or crack-extension force per unit length of the crack-front. Stationary configurations under which d<G> = 0 are those observed experimentally. <G> is the value of G averaged over all the spatial positions on the defect front. Please refer to the following works for details: Conoidal crack with elliptic bases, within cubic crystals, under arbitrarily applied loadings-I. Dislocation, crack-tip stress, and crack extension force; -II, III, and IV: Application to systems of twinning in copper (II), fracture in CoSi2 (III), and cross-slip in copper (IV). Theory and experiments completely agree.
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Trying to estimate the DBTT temperature for A572 & RHA steel based on alloying composition.
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Dear Varun:
Without prior exoerimental data on this particular steel, I would maintain that it is practically impossible to accurately predict the DBTT for any low carbon steel. The DBTT will depend on its composition of course, but also on its microstructure and prior heat treatment. The DBTT, however, is extremely sensitive to any small amounts of impurities, such as S and P. The best low carbon steels, with the lowest DBTT, invariably have very low content of these impurity elements (this is termed "aircraft quality" in many higher strength steels). My advice to you is to experimentally measure the DBTT using such simple tests as Charpy impact tests; relying on any predictions or estimates would be highly questionable.
ROR
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Poisson's Ratio
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Theoretically, it doesn't matter whether the specimen is rectangular or circular, But technically a problem may arise with circular specimens if you use knife edges on your transverse extensometer. The knives may bite into the specimen by an unpredictable depth, depending on radius. On flat surfaces their clamping force is distributed. It is not a coincidence that testing standards like ASTM E132 advise to use rectangular cross-section for measuring Poisson's ratio.
Also, it is beneficial to have specimens as wide as possible to increase gauge length of transverse measurement. At the same time it is not wise to increase greatly the overal cross-section, because that may require buying a new, testing machnie with bigger force limit ). Rectangular shape allows to vary with and thickness independently.
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The motivation comes from the following common observation. Blocks of stone with large dimensions (say of the order of three meters or larger) can be easily fractured into two pieces. First, cylindrical holes are introduced at top surface using drills. Second, fracture is initiated from the holes with the help of sledgehammers and wedges. Without any additional action, the crack will move with time downward other very large distance and separate the block of stone into two parts. The fracture surface is perfectly flat. What is the reason?
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Phenomena such as the Al Naslaa Rock, Active cracks in Yosemite National Park find explanation from gravitational forces.
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Quasi-static indentation test conducted on Aluminium 5052-H32 sheet with 3 different thickness;0.5 mm,1 mm, 2 mm. 
using 12.7 mm hemispherical indenter, speed 1.25 mm/minute, both edges clamped. The test was conducted until specimen perforated.
For 1 mm and 2 mm thickness there is a flat plateau as shown in the load-displacement graph.
can anyone explain this?
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It turns out that thickening the material leads to new mechanisms of resistance/plasticity. A reasonable question arises here, but what is the minimum thickness for such a situation? It is clear that 0.5 < x < 1, but I would like to be more precise. Perhaps this is not one mechanism, but several.
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Under dominant mode I loading, planar cracks have been observed to move from zero velocity v= 0; for a certain value v= v1, these turn into non-planar crack configurations. An explanation is offered below.
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We refer to the work “NON-PLANAR CRACKS IN UNIFORM MOTION UNDER GENERAL LOADING” by ANONGBA (2020):
When the velocity v of planar cracks increases toward the terminal velocity ve = 0.52 ct (ct, the velocity of transverse sound wave), moving non-planar crack configurations have been found (0.33 ct < v < 0.55 ct, approximately) with average crack extension force < G > much larger than those of planar cracks. This indicates that non-planar cracks may be associated with larger decrease of the energy of the system on change of crack configuration. Hence, the starter planar crack transforms itself into a non-planar configuration to maintain higher speed motion during its evolution in steady motion.
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Fatigue fracture surfaces of broken high strength materials exhibit rough conoidal cracks at the vertex of which are located inclusions or heterogeneities
Experimental: The observations refer to Sakai et al. (2002), Abdesselam et al. (2018), Stinville et al. (2018) ... These cracks have been named “fish-eye marks” by two former authors and their formations have been divided into three stages: (i) formation of the characteristic area as a fine granular area (FGA); (ii) crack propagation to form the fish-eye (i.e. according to us “rough conoidal crack”); (iii) rapid crack propagation to cause the catastrophic fracture.
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With this work at hand (i.e. "ROUGH CONOIDAL CRACK GROWING UNIFORMLY UNDER GENERAL LOADING"), it becomes possible to follow the evolution (propagation) of highest complexity cracks that nucleate from defects (such as heterogeneities, inclusions ...) located inside materials. The provided G (the crack extension force per unit length of the crack front) is function of highest number of variables and parameters.
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This subject is important because evidence of conoidal rough cracks is observed experimentally on various macrographs of broken specimens, under fatigue for instance. Our recent works (see below in answers) provides associated physical quantities.
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Again with this work at hand, it becomes possible to follow the evolution (propagation) of highest complexity cracks that nucleate from defects (such as heterogeneities, inclusions ...) located inside materials. The provided G (the crack extension force per unit length of the crack front) is function of highest number of variables and parameters.
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YES! THIS HAS BEEN SHOWN IN “PLANAR CRACKS IN UNIFORM MOTION UNDER MODE I AND II LOADINGS” (ANONGBA 2020).
Earlier works have suggested that crack speeds v could not exceed Rayleigh wave velocity, in the subsonic velocity regime (v< ct transverse sound wave velocity).
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YES! THIS HAS BEEN SHOWN IN “PLANAR CRACKS IN UNIFORM MOTION UNDER MODE I AND II LOADINGS” (ANONGBA 2020).
THIS IS WITHIN THE THEORY OF LINEAR ELASTICITY!!!
In mode I loading and in the subsonic velocity regime (v < ct, the velocity of transverse sound wave), G (I) increases continuously with v from the value in the static case G(I)0 (v = 0) to a maximum G(I)max = 1.32 G(I)0 at v = v (e) =0.52ct; then, G (I) decreases rapidly to zero when v tends to ct. In agreement with experiments, the value v (e) corresponding to the maximum of the crack extension force is identified to the terminal tensile crack velocity, observed in the fracture of brittle materials. No reference is made to the Rayleigh wave velocity cR. In the transonic speed regime (ct < v < cl), the crack characteristic functions are identical in form with those of the subsonic regime. However, for v < ct√2, we show that the faces of the crack, separated under load before the extension of the crack, close under motion; this indicates that the crack movement is hindered. for v > ct√2, the motion of the crack is possible. In mode II loading and in the subsonic regime (v < ct), G (II) increases continuously with v (when v < cR) from the value in the static case G(II)0(v = 0); when v approaches cR, G (II) increases very rapidly. Above cR (cR < v < ct), the relative displacement of the faces of the crack, formed under load before crack motion, closes in motion; this indicates that crack motion is impeded. The velocity of uniformly moving cracks is limited by the Rayleigh wave velocity. In the intermediate speed regime (ct < v < cl), the crack characteristic functions are similar in form to those below cR. The mouvement of the crack is possible.
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This question deserves to be posed and clarified. It is at this price that we will be able to consider an improvement involving analyses including new concepts. The answer to this question is given below.
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YES, FRACTURE MECHANICS IS BEAUTIFULLY COMPLETED. It has been suggested and demonstrated that a crack in an elastic loaded solid in the framework of linear elasticity may be viewed as a continuous distribution of infinitesimal dislocations (For a review, see Bilby and Eshelby, 1968). These authors provide an expression for G, the crack extension force per unit length of the crack front (or energy release rate), for steady motion. G is sum of terms that are products of stresses and values of the relative displacement of the faces of the crack at the tip of the crack. We find in recent works (Anongba, 2021 and 2022) that for a dislocation in the form of an arbitrary closed loop, there exists only one singularity in the dislocation stress fields. This singularity is of the Cauchy type: i.e., 1 / │r - r0│; r the position in the medium and r0 the position on the dislocation where G is evaluated. These are terms involving that singularity which contribute a non-zero value to G. All the other additional terms in the dislocation stress fields are bounded and contribute nothing. In this sense, we may say that Fracture Mechanics is completed.
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e.g. if f'c = 35MPa (AS3600) what would fcu =  ? MPA (BS8110)
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Cylinder Strength = Cube Strength * 0.8
The conversion factor of 0.8 is commonly used to convert between cube and cylinder strengths in the Australian construction industry. This factor takes into account the differences in the shape and size of cubes and cylinders used for testing concrete strength.
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Method that used in most of automotive industries to detect cracks or damage
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There are several methods used in the automotive industry to detect damage or cracks, depending on the type of material and the location of the potential damage. Here are a few examples:
  1. Visual inspection
  2. Liquid penetrant testing
  3. Ultrasonic testing
  4. X-ray inspection
  5. Magnetic particle testing
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This subject is very important because evidence of circular cracks is observed experimentally on various macrographs of broken specimens, under fatigue for instance. Our recent work (see below in answers) provides associated physical quantities.
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A corresponding work (Anongba, 2021) is intitled ʺ Elliptical crack under general loading: dislocation, crack-tip stress, and crack extension forceʺ. The various physical quantities displayed there depend implicitly on time t through the dependence on time of the circular crack radius R ≡ vt (v= constant). We take ar = a1 / a2 = 1 where aiare the semiaxes of the elliptical crack; R = a1.
P.N.B. ANONGBA, Elliptical crack under arbitrarily applied loadings: dislocation, crack-tip stress and crack extension force, Rev. Ivoir. Sci. Technol., 38 (2021) 388 – 409; see also, http://dx.doi.org/10.13140/RG.2.2.27048.29446
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The ʺstress intensity factorsʺ concept is known from Irwin (1948, 1957) who linked these to the energy release rate (crack extension force per unit length of the crack front) in the case of a crack in a two-dimensional crack analysis. In practice (to be used in three dimensions), the crack is viewed planar (Ox1x3) with a straight front running indefinitely in the x3-direction, perpendicular to the crack propagation x1-direction. In this situation, the utility of the stress intensity factor is apparent. For an arbitrary crack front in three dimensions, please see what follows.
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The GIc method is already outdated by non linear plastic principles such as GF.
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I sam earching a preporcessor program for fracture mechanics analysis using abaqus, I am doubting between zencrack and feacrack, I wonder if someone has experience with these programs and can help me to select which one (or another program) is better.
I want to use it for 3D studies
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In my opinion, Franc3D is the best.
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I would like to to know, is there any change in stacking fault energy with varying strain rate during deformation? 
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yes stacking fault energy does depend on strain rate and you will find many research article to support it.
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Hi, I am working micro mechanical analysis of the composite material by using GTN model. I am encountering the macroscopic and microscopic local phenomenon in the composite is completely depends on the type and arrangement of element. I would like to suppress this mesh dependency of solution in the GTN, could you please let me know is there is any possible method to over this issuse, without using UMAT or UEL. If possible , could any one share their UEL or UMAT code for nonlocal GTN model
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We have released the implementation of a nonlocal GTN model for Abaqus/Standard (UMAT) and Abaqus/Explicit (VUMAT) at http://www.tu-freiberg.de/en/nonlocalGTN . It does not require an UEL but uses the analogy to the heat equation and is thus easy to use.
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I have done the tensile strength test on two kinds of tensile specimens with the same material, but the mechanical behaviors differ from each other.
My considerations are focused on the size effect factor of test specimens, but I don't know how this parameter manipulates the mechanical behavior.
I would be grateful for any suggestions.
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There is no single factor for all materials that reflects the influence of sample size on the result of strength measurement. It is quite natural that small specimens often show higher specific strength than large specimens, since statistically they have fewer structural defects. However, this difference in specific strength depends on many properties of the material, primarily on its deformability: the more plastic the material, the smaller the difference.
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I am doing subzero heat treatment after quenching for en24 steel. And after subzero heat treatment am tempering it for 450c. So is it ok to go for 6 hours for subzero heat treatment or do we have to go for 24 hours only? 
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the grade of the steel is important in order to compromise properties.... but totally 24 hours is suitable
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 Thanks in advance for your replies.
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Dear Ghanbar
I agree with Aliasger. Beam elements can't be used for heat transfer and coupled temp-displacement coupled steps because they don't have a temperature degree of freedom. You must use solid, shell, or truss elements to do so.
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Deseo cambiar mi nombre inicial de Ariel  por César
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¿Alguien conoce cómo cambiar el nombre ?
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Young's Modulus and Poisson's' ratio is not known for the material (in literature).
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If you assume that the load frame always deforms elastically, and that your sample initially deforms elastically, then you can use the springs-in-series reciprocal addition relationship to correct for frame compliance based on the theoretical Young's modulus of your material and your initial sample dimensions. I have attached a MATLAB script that does this in an automated way. Please see the image attached, along with a sample dataset and the MATLAB script. A note - if you use an extensometer to measure strain on the sample, then you do not need to correct for compliance. For this reason, extensometers and digital image correlation are increasingly popular.
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I had a question revolving around the friction hardening law based on UBCSAND model utilized in CY model embedded in FLAC3D-V5. Apropos of CY model, the users are supposed to define a table of the mobilized friction angle in terms of the plastic shear strain. Inasmuch as the ensuing equations, i.e. Eq.1 and Eq.2, were posited for the frictional soils, I have tended to think of modifying the aforesaid equations so as to harness in the cohesive frictional soils medium in light of the fact that the friction hardening table in CY model ought to be adjusted to reflect more realistic behavior for a cohesive material.
Eq.1
Eq.2
Having perused HS model in PLAXIS plus CY model in FLAC3D, the formula concomitant with the elastic shear modulus has been rectified for the clayey soils as follow:
Eq.3
As respects the plastic shear modulus formula, can I have your say whether or not Eq.1 is expected to be modified with the intention of adding the mobilized cohesion?
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That is a good question.
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I am trying to find out how to identify specified parameters of ductile damage material in its stress-strain curve in Abaqus. I could identify the Young's modulus and the yield stress, but not the fracture energy. How do I identify this in my results?
For now I am simulating a simple tensile test in y-direction on a one-element model (1x0.2x1).
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Suppose one side of the rope is closed and the other side is on the pulley. Force is applied to the free side of rope. How can I simulate this, since the rope does not bear shear force? Which element? Beam? Trus?
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Hi Ghanbar,
You can use the spring for your model.
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Thickness and diameter shrinkage percentage of the Al2O3 sample (after sintering):
Diameter 20%
Thickness 18%
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thanks for your important question
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Hello
We have certain high temperature oxidation/corrosion autoclaves for testing in aqueous or gaseous environments. I would like to check the creep resistance (qualitatively) of alloys by exposing the pre-stressed/strained specimens in the autoclave, as it is more demanding to build a creep-tester with load cell and extensometer exclusively for it. Are there any reported procedures to perform qualitative creep tests using pre-stressed/strained specimens (such as U-bend specimens for SCC testing)? I would check the creep damage through the evolution of creep cavities and cracks after the completion of the test. Any suggestions provided will be of great assistance.
Thank you in advance.
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Hi,
Your question takes me back many years, to a collaborative project on reheat cracking in the 1970s.
The test that might help you was developed by Martin Murphy and David Batte at the Charles Parsons turbine manufacturers. It was used in that project, where it is described as a notched-bend relaxation test. See this article:
The second reference in the article, Batte et al 1976, describes the test more fully. It was published by Allianz, the insurance company; I suggest you contact them for a copy.
The test jig comprised a stiff, hollow, rectangular frame in which a Charpy specimen could be loaded in 3-point bend. The inner surface of one long edge carried two ridges, the opposite side was drilled to hold a heavy bolt that pressed the third ridge against the specimen, opposite the notch. The specimen could be pre-stressed to a controlled amount by tightening the bolt. If the rig was made from exactly the same material as the test specimen, then it was self-compensating for thermal expansion.
Once loaded, the jig and specimen can be placed in the furnace / autoclave for a set time at temperature.
On removal, there are several options. First would be to carry out an impact test in the usual way; the properties can be compared with those of virgin material and of a specimen that had seen the same thermal history, but without load. Examinng the fracture surface would reveal the extent of any cracking during the thermal treatment, and metallography would reveal and quantify any associated cavitation.
Please let me know if this works! I'm afraid that after 40 years I have no drawing or photos, but I'm sure you can devise a jig like this.
It may be possible to produce something similar using a small punch specimen.
Two other articles which might help in interpretation are:
Best wishes
John
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I’m searching for possible applications for magnesium wire and rods. I considered fasteners (for example, screws, rivets, and bolts), springs , grids and meshes and bioresorble implants. Also I would like to discuss their potential. I’m not sure if Mg springs could get to industrial use, because of its low Young modulus of 45 GPa. But springs from aluminium with a low Young modulus of 70 GPa is commercially available. In my opinion screws have the best chances because with increasing use of Mg sheets more fasteners of the same material will be needed (e.g. to reduce galvanic corrosion).  Any ideas for other applications would also be appreciated. Thanks in advance.
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Dear Johannes Luft,
Since magnesium alloy retains its strength and elongation after annealing at high temperatures , hence its high innovative demand in production technology. Mostly magnesium alloy fine wire is applicable in couple of potentials areas such as;
1. Surgical as Tension band wiring
2. Biodegradable applications, such as suture materials
3. Medical devices (bioabsorbable medical devices)
4. Cardiology; coil stents- potential applications for magnesium alloys in cardiovascular medicine
5. Orthopedic applications
6. Degradable implants with ligatures for blood vessels
7. Motor paddle shifters
8. High purity Magnesium Wire with the highest possible density for use in semiconductor etc.
Hope information is helpful for you.
Ashish
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Does a single-valued description exist for isotropic materials?
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When the crack (be it planar or non-planar) is associated with crack-tip plasticity, the relations between the failure stresses in specimens tested in tension, compression and bending given above (see our answer 1) remain valid, except that σT is now multiplied by a quantity that contains the crack-tip plastic zone size, crack-front shape and orientation of average crack surface. Please see “NON-PLANAR CRACK WITH CRACK-FRONT PLASTIC YIELDING UNDER GENERAL LOADING” in our contributions in ResearchGate.
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What is commonly used stress-strain material model for prestressed steel tendon/strand reinforcement for computer modelling such as Abaqus?
I have material model for concrete (such as Hognested)  and steel reinforcement (such as Ramberg-Osgood), but would like to know theoretical/ideal material model for prestressed steel reinforcement to be used for nonlinear analysis
Does the curve change in case of prestressed or post tensioning? 
Cheers,
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I am searching the same problem.
I think this article will be useful.
It explain PCI 2010 material model and Power Formula model.
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The material of the specimen is concrete. Three point bending test in my words is synonymous with a Crack mode opening displacement tests with a notch on the bottom surface of the concrete beam.
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Has anyone stored the digitize.opk for Origin V.75 and earlier. It is not available anymore on the fileexchange site. Thanks!
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In hot forging process, when we heat the work piece up-to 1200oC. It surface begin to rupture, due to oxidation of iron. This oxide layer penetrates into the metal surface when we deform it with compressive forces. So, We are in the investigation of a best technique for descaling of hot metal. Our production is mixed and  batch. Our product variety.
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Use high pressure water Descaler. Most of forgings and steel producers are using to remove scale from heated billets / slabs.
Water spray @ 200 bar is applied through flat jet nozzles. This reduces billet / slab temperature @ 5 to 10 degree, which is acceptable in these process.
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I am simulating on adhesive bonded multi-layer protective structure. To capture the adhesive effects, I am advised to use AUTOMATIC_SURFACE_TO_SURFACE_TIEBREAK to model the bonding strength without actually modeling the bulk adhesive. However, the contact surfaces are eroding surfaces due to projectile penetration. Could I use two contact cards simultaneously to simulate an eroding contact surface with initial bonding strength? if not, is there any other suggestion?
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Yes , I have used this in my thesis for modelling of composite
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When a planar crack is loaded in tension (mode I) in brittle materials, the velocity V of the crack is observed to increase from zero to a terminal velocity VT, then follows crack branching on further increasing V. VT falls well below the Rayleigh wave velocity VR.
To our knowledge, one attempt has been made to estimate theoretically VT. This attempt makes use of Mott (1948) extension of the Griffith concept to dynamic fracture. This is expounded by Lawn (1993). This estimate gives VT ≈ 0.38cl where cl is the velocity of longitudinal sound wave.
Does any other estimate exist?
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The conservation of energy corresponds to Griffith Energy-balance concept. This is stated as
G(I)max=2*Gamma
where Gamma is the surface energy. Observe that this is valid at G(I)max only. Here, G(I)max is known independently first, before we can reach the Griffith equation. You are telling nothing new.
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I need very recent (2010 onwards) technological advances that can allow magnesium to be used for Car body shells. Similar to how aluminium is used today at JLR. Thanks !
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I could recommend to pay attention to the Manoj Gupta works regarding Mg metal matrix composites design and investigation. Even about lightweight the Mg alloys.
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Hi guys
I am trying to implement Holzapfel material model (anisotropic hyperelastic) and have to define two families of fibre directions. Initially we ran Abaqus’s benchmark problem input files (section 3.1.7 Anisotropic hyperelastic modelling of arterial layers), but we did not get any of their results! (Keeping in mind the 1/8 th symmetry)!  
Is there a problem with Abaqus input files for the mentioned section? I am planning to follow what they have done in this simulation, specifically with regards to their implementation of fibre directions, but it’s quit depressing to see that they are not working.
Thanks in advance
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Xiaoyao Xu You just need to go the input file and change the gamma there. You can also have control over the number of anisotropic invariants used for instance you want to use just one instead of two,whatever.
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My "Concrete Damaged Plasticity" model in ABAQUS can't simulate the behavior of reinforced concrete structures in cyclic loading.
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you can find sample records for Abaqus umat subroutine in:
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I have been trying to solve Stokes equation in 3D micro - geometrical meshed. I'm currently exploring the Fluid model>Creeping flow>stationary of COMSOL 4.4. Comsol failed to solve my problem. It continue showing me "Failed to find a solution. Divergence of the linear iterations. Returned solution is not converged". Going through discussion forum, someone suggested that unchecking "p" on "solver manager" in "solver paramters" would help solve the problem. Please, can anyone help me on how I can locate this solver manager in COMSOL 4.4? Or what is a suitable approach? Thank you all,
Otaru, A.J.
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I will address the general solution divergence issue in Comsol. You can try following steps to improve the convergence.
Use structural meshes where you think you are getting the error (or use everywhere), Play with adaptive mesh refinement in solver or adapt option inside mesh node ~ Use this everytime to fine your meshes
Use the Generalized Alpha rather than BDF with strict or intermediate time stepping ~ this improves the convergence in many cases for me
Play with the tolerances (relative and absolute both) ~ sometimes if I change from factor to manual absolute tolerance (with enough time-discretization) it works.
Get the Jacobian update on every iteration than minimum ~ very important for non-linear solvers
Increase the number of maximum iterations ~ good option if you are using very fine tolerances
Change from fully coupled to segregated solvers ~ if you have many integrated physics
Use assembly in geometry and play with source to destination mesh refinements ~ when you are defining BCs or ICs inside the domains
Change scaled values of variables to manual and use values of their respective maximums ~ very helpful at the start of simulation fails.
Regards
Noman
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I am currently working on a phenomenological creep damage model that takes account of (i) creep cavity nucleation, (ii) diffusion controlled creep cavity growth and (iii) plastic hole growth.
The model gives a good prediction of a wide range of creep-fatigue test data (164 tests) on; Cast 1CrMoV, Cast ½CrMoV, Wrought Grade 91, Cast Type 304L, Type 347 Weld Metal, Wrought Type 321, Wrought Type 316H and Type 316H Multi-Pass HAZ; Tested at Temperatures ranging from 538 to 650°C. (see attached plots).
(Note: The black lines show 1, 2 and 0.5, which are acceptable scatter bands. The red lines show a linear fit to the data and the upper and lower 95% prediction intervals to demonstrate whether the model meets the acceptance criterion. )
However, to achieve a good prediction for all of the 164 Creep-Fatigue tests I have to make some assumptions. I am therefore looking for other evidence (such as metallography or theoretical modelling) that supports these assumptions:
The main assumption that has been made is about the conditions under which Plastic Hole Growth dominates and when Plastic Hole Growth is negligible.
Are there any metallographic observations or theoretical modelling that suggests that; Plastic Hole Growth can only dominate; (i) when the total strain is monotonically increasing and/or (ii) when the total strain exceeds a certain value; or (iii) any other relevant observation regarding Plastic Hole Growth at elevated temperature?
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Maybe you can focus on the shape of the cavities.
Assume under uniaxial creep testing:
If the plastic hole growth takes control, then the cavities should be more like a standing needles which is perpendicular to the GB. Otherwise if the vacancy diffusion mechanism controls, the cavities should be like cracks that is parallel to the GB.
But to remember, when the constrained diffusional growth mechanism takes control, then the cavities growth rate actually depends on the slow creep deformation on the neighbourhoods matrix. However, the cavities look like the crack-type, since the vacancy diffusion contributes most of the growth but it is constrained by surrounding slow creep deformation rate. This is the most common type of creep cavitation.
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Does Young's modulus of a material change with heat treatment?
Does the chemical composition affect Young's modulus?
If during heat treatment process the chemical composition remains constant and material only has a microstructural change, dose Young's modulus change?
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Since the Young modulus is related to the bonding between the atoms of materials, generally, it doesn't change after heat treatment processes. However, if the nature of an atomic bonding is affected by the HT, via the crystallographic or phase transformations, the value of Young modulus may be changed. Anyway, the other elastic characteristics e.g. the yield stress or the modulus of resilience are certainly changed after the HT.
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I am trying to model friction in a cracked structure by using contact feature. I have used contact pair algorithm option and used Dynamic Explicit analysis method. If you suspect any modeling error, I would appreciate your suggestion.
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One reason could be
STATEV dimension from fortran(UMAT) file is higher than the Depvar dimension in material definition. For e.g., Depvar dimension in material definition is 2, then if you try to access the STATEV(3) in fortran "Illegal memory reference" pops up in during execution at integration point.
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I am using ductile damage in FE model for steel material. the damage evolution law should be specified in terms of equivalent plastic displacement (Upl) or in terms of fracture energy dissipation (Gf)
Is the correct to use the following relation for calculating equivalent plastic displacement (Upl)?
Where L is the characteristic length of element,  "epsilon.f.pl" is the equivalent plastic strain at failure and  "epsilon.0.pl" is the equivalent plastic strain at the onset of damage.
or it should be calculated using this equation?
based on abaqus documentation the fracture energy can be calculated using the following relation
Gf=(Upl*sigmayo)/2
where sigmayo is the value of the yield stress at the time when the failure criterion is reached
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Please find the attached file.
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.
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I would rather plot Force (kN) VS. Displacement (mm) curve and calculate the area which essentially will give Energy (J). You can calculate Energy at any point of your curve. And do not try to go deeper than that.. keep the life simple, it will give a less probability to make a error/s (sometimes fatal).
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In the material assignment section, I am not able to define the strain life properties of materials (i.e. Strength Coefficient, Strength Exponent, Ductility Coefficient, Ductility Exponent, Cyclic Strength Coefficient, Cyclic Strain Hardening Exponent). Please help me for the same.
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HI,
I think, from FEMFAT Material Data! It is a nice way to get input parmeters for ANSYS Strain Life calculation.
Best regards, László
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Please share your thought.
Your opinion is highly appreciated
Regards
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You should remove flash, surface irregularities and all areas of roughness.
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Please explain with reference to that of an undergrad level.
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I recommend this article, because it is simple and so perfect.
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For N-H creep, creep rate is inversely proportional to d2 , whereas for Coble creep, creep rate is inversely proportional to d3 . What can be the possible explanation for d2 or d3 ?
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Consistent with the mechanistic arguments in the earlier replies one can say:
  • Nabarro-Herring creep: If you multiply the grain size by an arbitrary factor p, the creep rate decreases by a factor p because of the increase of the diffusion distance. The creep rate decreases by another factor p because of the decrease of the gradient of the vacancy concentration. The only function of grain size that fulfills this restriction is a power law with the power of -2.
  • Coble creep: In addition to the above, the creep rate decreases a third time by a factor of p because of the decrease of the cross section of the diffusion path. The only function of grain size that fulfills this restriction is a power law with the power of -3.
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  • Generally, fracture mechanics parameters and terms (CTOD, J, C*, stress, load line displacement, plastic zone size) have relevant & respective dimensional units. The physical significance of their units is easily understandable like, energy per unit area or energy rate per unit area of crack growth. In case of K, why its (meter)1/2 i.e. square root of crack size, a and not simple a or 1/a or a-2 ? What is the physical significance of including square root of crack size, a in K formula?
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Mr. Kumar,
As explained by many others, the unit of K is due to the sqrt(r) singularity.
Describing a similar parameter for HRR singularity might have a unit with MPa.m^n, where n can have a fraction value.
The physical significance could be that for an applied stress, K describes by what factor the stress will intensify at a distance of 'r' from the crack tip. The definition of K comes from theory of elasticity, and so it should describe the stress field at the boundary of plastic zone.
As I said another parameter can be described at a boundary of plastic zone and process zone, and that factor would describe the stress field at that boundary.
To make it more fancy, its similar to the Event Horizon, the boudnary of singularity in a Black Hole.
With regards,
Abhishek
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I want to know the reason for the impression as shown in figure after hot forging of composite material. I have done a step wise hot forging of cylindrical shape ingot and after hot forging the rectangular shape as shown in figure has obtained with impression of top and bottom side. I want to know the reason for that if anyone can explain this.
thanks
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dear Abdul Basit, the star-like squared pattern that you see results from the circular (!) face of the cylinder which you want to change into a more or less squared shape. If you dont want it, because it is related to made properties, you can change the material flow by designing the intermediate forming steps in a way to enhance the flow as much as possible towards the straight sides of the square first before puching the material into the corners. Regarding the distribution of material properties, it depends very much on the properties of the initial cylinder and the alloy grade and casting properties. You can improve on some of the material properties by forming but also causing problems. It is hard to say from the scratch. Is also a question of design and application.
By the way in open die forming you should generate a mostly perfect circle pattern until you work towards the squared shape, but the distance from the edges of the former circular face to the final squared side edges can be manufactured constant on all sides as well corners in this way.
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It's seems that addition of carbon atoms increase the hardness by solid solution strengthening. However I do not know why it will have more effect on ferrite than on Austenite.
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Large wire wedge bonding 
Aluminum wire
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Not yet. But Im planning to have one.
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We are trying to manufacture fasteners made of A286 steel. The fasteners were forged and solid solution treated at 900oC for 2.5hours followed by 680, 720, or 740oC aging for 16hours, which is well-known heat-treatment process for gamma' precipitation of A286. After then, hardness in the range of 30-32HRC was obtained.
This result is pretty much unsatisfactory to us because we need to make A286 fasteners with 34HRC or above. I heard that maximum hardness of A286 would be around 35-36HRC but our heat-treatment couldn't lead to the value.
Can anybody suggest any heat-treatment process to improve hardness of A286 steel? Unfortunately, we cannot conduct cold rolling more after solid solution treatment due to client's request. For your information, grain size of our materials is around 12-13 micro meter.
Any assistance would be greatly appreciated.
 
Thank you,
JH Kim
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Controling the cooling rate
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Since strains measured in the middle of the bars of SHPB by gauges don't represent what happens at specimen/bar interfaces, we must establish calibration files for both incident and transmitted bars. These files will be introduced to a post processing program.
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The article, "Evolution of Specimen Strain Rate in Split Hopkinson Bar Test," by H Shin and J-B Kim reports a method of validating the experimental result of the split Hopkinson bar. It cal also be used for the calibration of the instrument. The article can be downloaded at: https://doi.org/10.1177/0954406218813386
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I'm doing the characterization of composites materials at high strain rates by SHPB. I need to know if there is a way to validate the method. In other words how can I know that the Stress-Strain curve is correct?
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A recent paper by H. Shin and J.-B. Kim, "Evolution of Specimen Strain Rate in Split Hopkinson Bar" reports a method for verifying the experimental result of the split Hopkinson bar. It can be downloaded at: https://doi.org/10.1177/0954406218813386
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Can anyone help me to make the user subroutine UMATHT used in ABAQUS simulation for lithiation process in lithium ion battery (LIB)? I am working on anode part of LIB and need to run an FEM simulation. However, I am not aware of the programming part of this subroutine. I would really appreciate comments from people who know about it.
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Nadeem, can you share how to use UMATHT subroutine ?
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I have diagram of cyclic voltammogram, seeking to understand how to define the diagram voltammogram.
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I found the following video link very informative - although I assume there is bit of anomaly in the definition of anodic and cathodic current.
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I model and simulate a simple plate in 2D form, to analysis the tensile test in WB. However, by increasing the load, nothing happened and just stress and deflection increased. Even stress passes the ultimate strength of steel. I defined the plasticity in Engineering material and its ultimate tension strength is defined there too. I am new to Ansys and I do not know how to accomplish the tensile test.  
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I am Aziz from Taiyuan university. I get terrible with doing Tensile strength simulation model of Inconel 718. Could you give me any help?
I want to know the Johnson cook damage (d1,d2,d3,d4,d5) of inconel 718.
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Aim is to introduce different amounts of oxygen into Zr and study its deformation behaviour.
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Heating it in open air for various times will form oxygen layer of various thickness on the surface of Zr. O2 is very eager to get into the surface of Zr :). Than you can anneal the sample in furnace for penetration of O2 content. Though this is not a scientific way of doing it. You may get different results with different experiments.
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Dear engineers, scientists and experts in the field of plasticity,
In the literature, the terms strain hardening and work hardening are often used under the theory of istropic hardening. Mostly these terms are used in the same context or even equated.
Is that always correct, even using Drucker-Prager flow rule?
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Work hardening, also known as strain hardening, is the strengthening of a metal or polymer by plastic deformation. This strengthening occurs because of dislocation movements and dislocation generation within the crystal structure of the material. Many non-brittle metals with a reasonably high melting point as well as several polymers can be strengthened in this fashion. Alloys not amenable to heat treatment, including low-carbon steel, are often work-hardened. Some materials cannot be work-hardened at low temperatures, such as indium, however others can only be strengthened via work hardening, such as pure copper and aluminum.
Work hardening may be desirable or undesirable depending on the context. An example of undesirable work hardening is during machining when early passes of a cutter inadvertently work-harden the workpiece surface, causing damage to the cutter during the later passes. Certain alloys are more prone to this than others; superalloys such as Inconel require machining strategies that take it into account. An example of desirable work hardening is that which occurs in metalworking processes that intentionally induce plastic deformation to exact a shape change. These processes are known as cold working or cold forming processes. They are characterized by shaping the workpiece at a temperature below its recrystallization temperature, usually at ambient temperature. Cold forming techniques are usually classified into four major groups: squeezing, bending, drawing, and shearing. Applications include the heading of bolts and cap screws and the finishing of cold rolled steel. In cold forming, metal is formed at high speed and high pressure using tool steel or carbide dies. The cold working of the metal increases the hardness, yield strength, and tensile strength
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We use Vickers indentation method for estimation of the fracture toughness. We use the following formula, Fig. 1. The calculation requires the average length of cracks. If there is only one 8 μm crack (Fig. 2), then we take the average 8 μm? Or (8+0+0+0)/4 = 2 μm?
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I think the load of indentation, you have used, was not high enough to induce the radial cracks at all corners of indenter's impression. I recommend you to increase the load and repeat the test for 3 or 4 times. In my opinion, you can not rely on only one indentation as well as on the length of only one crack instead of four cracks.
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I want to explore the dynamics of parametrically excited (nonlinear) beam whose material's Young's modulus (E) and loss tangent (tan(delta)) are known. It is convenient to use the simple Kelvin-Viogt model in the evaluation nonlinear dynamics. Hence, I want to find out viscoelastic coefficient (eta) in the model, sigma = E*(epsilon)+eta*(d/dt(epsilon)) where, sigma is time varying stress, epsilon is time varying strain. d/dt is differentiation with respect to time. Please, give me some suggestions for the calculation of viscoelastic coefficient or any other alternative modelings using loss tangent and Young's modulus.
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Dear Manish,
There was a mistake in my last pdf.Please see the revised pdf.
The loss tangent is omega*mu/E. (omega : radial frequency(rad/sec), mu : viscosity(Pa*s), E: Young's modulus (Pa))
Sincerely ,
Ryuzo Horiguchi (Kao Corporation)
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hello
im a new abaqus user and i want to model a viscoelastic material (asphalt) in abaqus . i have uniaxial creep test data for characterize viscoelastic behaviour . my question is how can i enter viscoelastic parameters in abaqus?is there any way to put creep test data directely in abaqus??
in abaqus for modelling viscoelastic material in time domain there are three ways:
1)combined test data
2)shear test data
3)volumetric test data
i have unaxial creep test data so what shoud i do?how can i obtain long-tern normalized shear compliance and elastic modulus for elastic modelling?
i attached my test data .
thank you
best regards
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Hello everyone! I have a question about tensile stress that I'm genuinely curious about:
In many iron-based alloys, we often observe a sharp drop from the upper yield point to the lower yield point—along with the formation of Lüders bands. However, in some iron-based "superalloys," the stress-strain curve appears much smoother, without this pronounced drop.
Could anyone explain why this difference occurs? Thanks in advance!
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Existence of upper and lower yield points is typical for alloyed steels. The reason for that is so called "solute drag", namely: solute atoms' preference to displace in the vicinity of the dislocations (due to an interaction of their stress fields with those of around dislocation core). Thus, when an external stress applied to a sample reaches the vicinity of a yield stress of the material, initially existing dislocations, surrounded (caught) by solute (impurity) atoms, need to additional stress to come off them. This "additional" stress developed onto the loaded sample, is seen as a "higher" yield point. When the majority of dislocations overcome their interaction to solute atoms, the yield point "fall" to its "lower" level. This mechanism works both for interstitial and substitutional solid solutions.
Regarding superalloys, their phase formation should be discussed in details for each specific case separately. For example, for multi-principle alloys (like high-entropy alloys), no "solute" atoms may be defined and then they normally do not demonstrate higher and lower yield points. For intermelallic hardened superalloys, the majority of alloying elements form inermetallide phases, so no "free"solute" atoms exist and then these materials also have no higher and lower yield points.
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Specifically electropolishing reagent and conditions.
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Thanks to both of you. I shall try these methods.
-bharat
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Normally, representative volume element (RVE) of the composite is independent of geometry. There are several homogenization methods available that defines regular shaped like rectangular, quadrilateral with inclusions of rectangular,circular,ellipsoidal, spherical shapes. Is there any analytical methods defined for irregular shaped RVE?
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The basic assumption of RVE modeling is that the overall geometry is obtained by an infinite repetition of the RVE in all allowed (depending on specific BCs) directions. You need to tile (fill) the 2D (3D) space by infinitely repeating the RVE without gaps.
Thus, the RVE shape does not need to be regular per se, but it must be such that, when repeated infinite times, it fills the space without gaps. The simplest such geometries are the square, the rectangle and the hexagon. More are available, with different degrees of regularity (a term that should be better specified, we are using it with a quite vague meaning), and one has to look into the research on tessellations. It would be interesting to study how different patterns affect the calculated mechanical behavior. However, you cannot use arbitrary "irregular" shapes or even purely random geometries. It is not compatible with the homogenization method's assumptions.
Furthermore, geometries and size of RVE do affect the mechanical homogenized behavior, especially for composites (and any material with structure at multiple scales). The RVE should in theory be independent of geometry, but in practice you need to investigate which configuration is best to model the homogenized material.
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Is there any element type available to model viscoelastic material ?
There is only option available to model viscoelastic material in ANSYS is using prony series but that couldn't help me.
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Yes, this is simplest feature and should be available with any software. Please search in the manual for how to define. I have no experience with these two software.
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I am doing quasi static and high strain rate compression and tension test but the yield value are different. Compression yield is grater than tensile yield. What is the reason behind it.
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The above answer does not seem satisfactory. Indeed, strain hardening, which is due to an increase of the dislocation, will occur whatever the loading direction is (i.e. tension or compression).
In my opinion, the most likely explanation for this asymmetry is the impact of processing. Indeed, during the fabrication of your alloy, a significant amount of plastic deformation has been used for forming (e.g. extrusion, rolling). Because this plastic deformation result in strain hardening, the yield surface of your alloy has significantly been altered by processing. Strain hardening is usually directional (i.e. kinematic hardening), which means that the evolution of the yield strength is direction dependent. The consequence is that, because of processing-induced hardening, the compression and tensile yield strength are different.
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Is there any extensive literature, dataset or open source/free software for generating CCT and TTT diagrams for steels
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An excellent online industry-based resource is that from Ovako.
Online software has been developed by:
I believe that combining the excellent previous scientifc work of Kirkaldy reported by JMatPro might allow most of us to build his/her own software for quite "general" steels.
Many years ago ( I believe 2008) we built "3d mensionnal" curves of TTT/CCT curves, they were good looking but seems no-one have been using seriously them to date for practical issues..
So a more recenta nd serious option is:
or directly here (for researchgate users):
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I collect data concerning Poisson's ratio of different types of geopolymer concrete. I would appreciate if you recommend any articles that include the results of tests in which the value of Poisson's ratio of geopolymer concrete is determined.
Thank you.
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Please refer to the following books:
1. Geopolymer, Green Chemistry and Sustainable Development Solutions by Joseph Davidovits . Please refer to page 136. You can find the book at google book.
2. Concrete Construction Engineering Handbook by Edward G. Nawy . Please refer to page 26-10. You can find the book at google book.
Hope this will help.
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I am trying to correlate the experimental and modeling results of micro-indentation. The indent shapes are not matching because the amount of springback and material rise the model is predicting is different than that from the experiment. I tried changing the BCs, refining the mesh in the region of indentation. I didn't experiment with the contact behavior yet. But,these solutions didn't help. I am guessing the differences are due to improper material definition (using Abaqus for modeling). I am using tensile test data for the same. I wanted to know if Al 1100 H14 behaves differently in compression. If yes, how to incorporate that in Abaqus material definition?
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There are several possible sources for the experimental-simulation mismatch, which seem to me more likely than a mismatch in the tension and compression behavior of Al 1100 H14, which I expect to be rather small, if it exists at all.
1.) Modelling the specimen undergoing indentation, geometry and boundary conditions:
The size of the simulation box (halfspace) should be sufficiently large both in width and depth directions to properly reflect the elastic effects.
If the halfspace is sufficiently large in lateral direction, the chosen boundary conditions (free or fixed) at the lateral boundaries do no longer play a significant role for the microindentation results. You can check that simply by comparing the results for different conditions.
If the simulation box size in depth direction is chosen too small, the (structural) stiffness of the indented halfspace will be larger than the real one, such that plastic yielding commences at an earlier stage of indentation.
2.) Finite element modeling:
In order to avoid artificial stiffening effects („locking“) it is recommended to use rather hexahedral/brick-type solid elements than tetrahedral ones, better quadratic shape functions (e.g. C3D20) than linear ones.
A sufficiently fine resolution not only of the indentation volume but also of its surroundings is crucial – you mentioned the measurement of mesh refinement in that region.
Hint: For the existing isotropy you can exploit symmetry and reduce the indented halfspace e.g. to one fourth, or even less, of course. (You could even exploit rotational symmetry.) Then a mucher finer discretization can be invested for the same costs compared to the full model.
- Modeling frictional contact comes on top of that, I would start out with a rigid indenter, zero friction.
3.) Material model.
The choice of isotropic elastoplasticity at finite strains seems to me adequate for that material and the deformation regime (large plastic deformations in the indentation zone).
Accurate material parameters in agreement with the experiments, i.e. yield stress and the hardening behavior. The hardening behavior will strongly influence the behavior of pile-up (low strain hardening rates) or sink-in (for large hardening rates).
Hope there is something helpful in it, good luck and have a great day ahead!
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