Science topic

Mechanical Behavior of Materials - Science topic

Explore the latest questions and answers in Mechanical Behavior of Materials, and find Mechanical Behavior of Materials experts.
Questions related to Mechanical Behavior of Materials
  • asked a question related to Mechanical Behavior of Materials
Question
4 answers
I would like to to know, is there any change in stacking fault energy with varying strain rate during deformation? 
Relevant answer
Answer
yes stacking fault energy does depend on strain rate and you will find many research article to support it.
  • asked a question related to Mechanical Behavior of Materials
Question
11 answers
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
Relevant answer
Answer
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.
  • asked a question related to Mechanical Behavior of Materials
Question
7 answers
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.
Relevant answer
Answer
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.
  • asked a question related to Mechanical Behavior of Materials
Question
5 answers
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? 
Relevant answer
Answer
the grade of the steel is important in order to compromise properties.... but totally 24 hours is suitable
  • asked a question related to Mechanical Behavior of Materials
Question
7 answers
 Thanks in advance for your replies.
Relevant answer
Answer
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.
  • asked a question related to Mechanical Behavior of Materials
Question
7 answers
Young's Modulus and Poisson's' ratio is not known for the material (in literature).
Relevant answer
Answer
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.
  • asked a question related to Mechanical Behavior of Materials
Question
2 answers
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?
Relevant answer
Answer
That is a good question.
  • asked a question related to Mechanical Behavior of Materials
Question
5 answers
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).
  • asked a question related to Mechanical Behavior of Materials
Question
8 answers
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
Relevant answer
Answer
If there is still interest, you might also consider Franc3D. It creates well-configured crack tip meshes, works well with ABAQUS, and calculates very accurate SIFs using M-integrals from the results.
  • asked a question related to Mechanical Behavior of Materials
Question
3 answers
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?
Relevant answer
Answer
Hi Ghanbar,
You can use the spring for your model.
  • asked a question related to Mechanical Behavior of Materials
Question
6 answers
Thickness and diameter shrinkage percentage of the Al2O3 sample (after sintering):
Diameter 20%
Thickness 18%
Relevant answer
Answer
thanks for your important question
  • asked a question related to Mechanical Behavior of Materials
Question
2 answers
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.
Relevant answer
Answer
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
  • asked a question related to Mechanical Behavior of Materials
Question
11 answers
Hi everyone;
I am doing a contact simulation within ABAQUS;
I want to apply a concentrated force on the reference point of rigid body. But the results shows that it just does not have any effect, (the rigid body should have a rigid displacement along the direction of the force)?
If you have encoded the same case with me, please reply me!
Thanks so much!
Liang
Relevant answer
Answer
Chao Liu Did you solve this problem? I met the same problem with you. When I add the pressure on the surface of the rigid body(tied into rigid body), it's OK. Adding concentrated force will get the same error: displacement increment for contact is too big.
  • asked a question related to Mechanical Behavior of Materials
Question
4 answers
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.
Relevant answer
Answer
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
  • asked a question related to Mechanical Behavior of Materials
Question
5 answers
Does a single-valued description exist for isotropic materials?
Relevant answer
Answer
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.
  • asked a question related to Mechanical Behavior of Materials
Question
9 answers
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,
Relevant answer
Answer
I am searching the same problem.
I think this article will be useful.
It explain PCI 2010 material model and Power Formula model.
  • asked a question related to Mechanical Behavior of Materials
Question
4 answers
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.
Relevant answer
Answer
Has anyone stored the digitize.opk for Origin V.75 and earlier. It is not available anymore on the fileexchange site. Thanks!
  • asked a question related to Mechanical Behavior of Materials
Question
9 answers
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.
Relevant answer
Answer
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.
  • asked a question related to Mechanical Behavior of Materials
Question
4 answers
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?
Relevant answer
Answer
Yes , I have used this in my thesis for modelling of composite
  • asked a question related to Mechanical Behavior of Materials
Question
8 answers
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 !
Relevant answer
Answer
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.
  • asked a question related to Mechanical Behavior of Materials
Question
11 answers
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
Relevant answer
Answer
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.
  • asked a question related to Mechanical Behavior of Materials
Question
3 answers
e.g. if f'c = 35MPa (AS3600) what would fcu =  ? MPA (BS8110)
Relevant answer
Answer
Neville proposed the following formula
f'c = [ 0.76 + 0.20 log10 (fcu/19.59) ] fcu
  • asked a question related to Mechanical Behavior of Materials
Question
9 answers
My "Concrete Damaged Plasticity" model in ABAQUS can't simulate the behavior of reinforced concrete structures in cyclic loading.
Relevant answer
Answer
you can find sample records for Abaqus umat subroutine in:
  • asked a question related to Mechanical Behavior of Materials
Question
4 answers
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.
Relevant answer
Answer
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
  • asked a question related to Mechanical Behavior of Materials
Question
4 answers
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?
Relevant answer
Answer
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.
  • asked a question related to Mechanical Behavior of Materials
Question
9 answers
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?
Relevant answer
Answer
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.
  • asked a question related to Mechanical Behavior of Materials
Question
29 answers
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.
Relevant answer
Answer
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.
  • asked a question related to Mechanical Behavior of Materials
Question
13 answers
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
Relevant answer
Answer
Please find the attached file.
  • asked a question related to Mechanical Behavior of Materials
Question
9 answers
.
Relevant answer
Answer
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).
  • asked a question related to Mechanical Behavior of Materials
Question
3 answers
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.
Relevant answer
Answer
HI,
I think, from FEMFAT Material Data! It is a nice way to get input parmeters for ANSYS Strain Life calculation.
Best regards, László
  • asked a question related to Mechanical Behavior of Materials
Question
3 answers
Please explain with reference to that of an undergrad level.
Relevant answer
Answer
I recommend this article, because it is simple and so perfect.
  • asked a question related to Mechanical Behavior of Materials
Question
13 answers
Please share your thought.
Your opinion is highly appreciated
Regards
Relevant answer
Answer
The joint region should have the same cross section of the rest of the gauge length portion of the tensile specimen. Hence, it is MANDATORY to remove flash (in case of solid state welding processes like friction welding, linear friction welding, friction stir welding etc.) and excessive reinforcement (in case of fusion welded joints). If they are not removed, the additional flash and reinforcement will increase the area of the cross section and shift the failure location from weld zone to HAZ or base metal. A flash or reinforcement is never retained on the welded component in practical use. Therefore, it is necessary to find out the failure location accurately which requires removal. Otherwise, the original strength of the welded joint will also be unknown.
  • asked a question related to Mechanical Behavior of Materials
Question
11 answers
Deseo cambiar mi nombre inicial de Ariel  por César
Relevant answer
Answer
Como modificar el apellido de mi perfil?
  • asked a question related to Mechanical Behavior of Materials
Question
4 answers
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 ?
Relevant answer
Answer
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.
  • asked a question related to Mechanical Behavior of Materials
Question
7 answers
  • 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?
Relevant answer
Answer
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
  • asked a question related to Mechanical Behavior of Materials
Question
13 answers
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
Relevant answer
Answer
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.
  • asked a question related to Mechanical Behavior of Materials
Question
3 answers
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.
  • asked a question related to Mechanical Behavior of Materials
Question
7 answers
Large wire wedge bonding 
Aluminum wire
Relevant answer
Answer
Not yet. But Im planning to have one.
  • asked a question related to Mechanical Behavior of Materials
Question
18 answers
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
Relevant answer
Answer
I think the cooling rate is an important parameter to participate alloy, you can try slow cooling rate
  • asked a question related to Mechanical Behavior of Materials
Question
17 answers
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.
Relevant answer
Answer
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
  • asked a question related to Mechanical Behavior of Materials
Question
5 answers
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?
Relevant answer
Answer
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
  • asked a question related to Mechanical Behavior of Materials
Question
4 answers
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.
Relevant answer
Answer
Nadeem, can you share how to use UMATHT subroutine ?
  • asked a question related to Mechanical Behavior of Materials
Question
14 answers
I have diagram of cyclic voltammogram, seeking to understand how to define the diagram voltammogram.
Relevant answer
Answer
I found the following video link very informative - although I assume there is bit of anomaly in the definition of anodic and cathodic current.
  • asked a question related to Mechanical Behavior of Materials
Question
4 answers
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.  
Relevant answer
Answer
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.
  • asked a question related to Mechanical Behavior of Materials
Question
9 answers
Aim is to introduce different amounts of oxygen into Zr and study its deformation behaviour.
Relevant answer
Answer
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.
  • asked a question related to Mechanical Behavior of Materials
Question
29 answers
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?
Relevant answer
Answer
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
  • asked a question related to Mechanical Behavior of Materials
Question
4 answers
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?
Relevant answer
Answer
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.
  • asked a question related to Mechanical Behavior of Materials
Question
10 answers
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.
Relevant answer
Answer
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)
  • asked a question related to Mechanical Behavior of Materials
Question
13 answers
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
Relevant answer
  • asked a question related to Mechanical Behavior of Materials
Question
6 answers
Hello to all the members of the world of science!
It's a tensile-related question and kind of a basic one; but I'd really like to know the answer. So here we go:
Notwithstanding the fact that for most of the iron-based alloys, a rapid fall from upper yield point to lower yield point is witnessed (in addition to the Lüders bands), some iron-based "superalloys" exhibit an almost straight, fall-free form of curve. What is the reason?
Thanks in advance!
Relevant answer
Answer
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.
  • asked a question related to Mechanical Behavior of Materials
Question
3 answers
Specifically electropolishing reagent and conditions.
Relevant answer
Answer
Thanks to both of you. I shall try these methods.
-bharat
  • asked a question related to Mechanical Behavior of Materials
Question
4 answers
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?
Relevant answer
Answer
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.
  • asked a question related to Mechanical Behavior of Materials
Question
6 answers
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.
Relevant answer
Answer
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.
  • asked a question related to Mechanical Behavior of Materials
Question
17 answers
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.
Relevant answer
Answer
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.
  • asked a question related to Mechanical Behavior of Materials
Question
26 answers
Is there any extensive literature, dataset or open source/free software for generating CCT and TTT diagrams for steels
Relevant answer
Answer
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):
  • asked a question related to Mechanical Behavior of Materials
Question
4 answers
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.
Relevant answer
Answer
see the attached file.
  • asked a question related to Mechanical Behavior of Materials
Question
3 answers
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?
Relevant answer
Answer
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!
  • asked a question related to Mechanical Behavior of Materials
Question
6 answers
I am currently investigating the load-carrying mechanism of a driven pile (hollow bar) and trying to install strain gauge on the pile for measurement of stress distribution.  I have tried to install the strain gauges on both outer and inner surface of the pile with sealant and protective tape on but they all fail due to the large driving force applying on the pile. Most of the gauges broke at the lead wire connections. Is there a way to install the gauges that can withstand large driving force?
Regards, Philip
Relevant answer
Answer
I am also working with strain gauges pasting it on circumference of the hollow circular pile. I am currently grooving the outside the layer of pile with the thickness of the gauge length of the strain gauges. The wires soldered to the strain gauges were sent from the holes made on the pile above the strain gauges and the strain gauges are then protected with the protective layer given by the HBM. Thus, driving the pile by hammering does not affect the strain gauges and the wires attached to it.
  • asked a question related to Mechanical Behavior of Materials
Question
3 answers
Hello all ! I'm working on the formability of different aluminium alloys by ironing process. And I want to know how does the strain hardening exponent 'n' influence the formability by this process?
Thank you !
Relevant answer
Answer
When one does the ironing process, the plastic deformations are very high, especially at the bottom of die's edges. These plastic deformations causes the sheet to tear apart. Now, if the sheet is made of a metal with higher 'n', then it can withstand larger plastic deformations before being damaged. Also, larger 'n' helps more uniform plastic deformation in metal forming process, such as ironing leading in a better quality.
  • asked a question related to Mechanical Behavior of Materials
Question
2 answers
Where is the stress-strain diagram of brass forging at different temperatures and strain rates?
Relevant answer
You can found it in the ASM Atlas of stress-strain curve, pages 523 foward.
If you don't find it, ask me.
  • asked a question related to Mechanical Behavior of Materials
Question
5 answers
Does anyone have experience in writing UMAT Subroutine in Abaqus?
Relevant answer
Answer
Hi,
There are numerous articles available where 2D Puck's theory and 3D have been implemented. For instance in this article, 2D version has been implemented:
BR
  • asked a question related to Mechanical Behavior of Materials
Question
47 answers
I wish to open a discussion on the way that Plastic Instabilities influence the results of Mechanical Tests. For example, tensile tests, creep tests, torsion tests, pressurised tubes test, etc..
It might be interesting to also discuss tests that are not affected by plastic instabilities; this category might include high cycle fatigue and fracture toughness tests. However, it would be interesting to hear any views to the contrary, such as the need to use side grooves in fracture testing being because of plastic instabilities.
Finally, perhapse I should have re-phrased this question as:
Do plastic instabilities influence the outcome of all mechanical property tests?
Relevant answer
Answer
Perhaps one should first define what one means by plastic instabilities. As long as we stick to tension, there is no confusion, because the manifestation of instability (necking) is both easily observed and well-defined mathematically.
On the other hand in a test like torsion, it is difficult to establish any geometric instability since the geometry is in principle invariant. Failure simply occurs when a certain condition is reached (consider for instance the max. shear stress criterion); do we consider this point as a plastic instability?
Going further to tests such as compression, where the geometry does change, but in a beneficial manner, making failure less likely. 'Instabilities' in this case would arise from the experimental setup, non-conservation factors like friction, and so on. These are very indirectly related to plasticity.
So at a macroscopic level, the definition is difficult.
At a microscopic level, we may observe certain manifestations; such as flow localisation. People have put forward instability criteria for such cases. These include empirical criteria (eg. Semiatin) as well as criteria developed on energy input/output considerations (eg. rate of energy storage to rate of energy dissipation).But the question again is, at what point do we call it an instability? Stage-I fatigue crack growth is governed by plasticity considerations and Stage-II is governed by fracture mechanics -which of these two is better described as a plastic instability? On one hand it should be Stage-I, because that is 'plastic', on the other hand Stage-II is a more evident 'instability'.
  • asked a question related to Mechanical Behavior of Materials
Question
12 answers
Angle of internal friction of sand is found to decrease with increased overburden pressure (see attached figure). The curved nature of actual Mohr-Coulomb failure envelope (the straight line that we plot for Mohr-Coulomb failure envelope is merely a linear approximation) also indicates the same, i.e. a decrease in friction angle at higher normal stress. 
In physical terms friction angle represents particle interlocking. Greater the interlocking between the particles, larger should be the friction angle and vice versa. At higher normal stress better interlocking is to be expected, which should translate into a higher friction angle but it isn't the case (considering the density remains constant). Particle crushing at high normal stress, might be one reason leading to low friction angle. My question is what are the other physical explanations of the decrease in friction angle at higher normal stress/overburden pressure?
Relevant answer
Answer
First of all, the critical state friction angle does not change with the overburden pressure and soil density and thus, the discussion must be about the peak friction angle.
Many ordinary stress-dilation rules based on the balance between the input and dissipated energies (e.g., Taylor’s stress-dilatancy rule) highlight a clear direct linkage between the mobilized friction and dilation angles. Considering that the increase in the overburden pressure mitigates dilation, one can expect decrease in the peak friction angle with the increase in overburden pressure.
  • asked a question related to Mechanical Behavior of Materials
Question
6 answers
I performed a Crack Propagation analysis using XFEA in Abaqus. The result is showing that the crack is propagated and the crack length is increased, however when I plot the result, I see the crack is all the way propagated. I could not see the crack propagation gradually. I think my visualization setting needs to be adjusted and then I will be able to see the crack propagation element by element. Any help will be appreciated.
Hamid
Relevant answer
Answer
I think that you need to put check mark for "PHILMS, Level Value phi" while you recording macro and then insert that code to main python code.
  • asked a question related to Mechanical Behavior of Materials
Question
5 answers
I have problems to running data of damage parameter (dt)  coming from formula of Birtel article (2006 ABAQUS Users’ Conference )[1].
But, with   formula below ABAQUS running very well and, i take result in figure attached.
  • dt = 1-exp(-strain inelastic * ac) ....... Bashar [2]
or
  • dt = 1 - tension / fcm ........................ Jankowiak [3]
Someone can tell me how can i make data made with Birtel formula running in ABAQUS?
[3] Identification of parameter of Concrete Damaged Plasticity Model
Relevant answer
Answer
@ Hamid, if I am correct you suggest to use Engineering stress and Engineering strain values and find the point where yielding occurs. Then, use the simple formula to calculate 'dc' i.e. the damage parameter in compression. How to obtain 'dt' ?
  • asked a question related to Mechanical Behavior of Materials
Question
2 answers
In Abaqus I have an axisymmetric model of the rotor for a steel seal with a thin ceramic face. I want to get the circumferential stress induced by friction on the rotor face, when the seal is spinning at steady state, to determine interfacial stresses between the main body of the seal and the film. I see that this can be done in Abaqus, but I can't seem to find a way to specify spinning along the correct axis of rotation.
Relevant answer
Answer
Here's what I found. Abaqus has what is called generalized axisymmetric elements. In regular axisymmetric elements CAX4 no deformations are included in in the circumferential direction. In generalized axisymmetric elements CGAX4 circumferential deformation is allowed, as long as all planes can be assumed to deform circumferentially in the same manner. This is used infrequently, so there is not much out there on it in the help forums. Using this type of element it then becomes possible to apply moments about the axis of symmetry, or specify rotational displacements. This element type is really convenient if you have an axisymmetric model that experiences circumferential forces as it is spinning. It makes it possible to model this without a full 3D model, and the accompanying larger number of elements.
  • asked a question related to Mechanical Behavior of Materials
Question
8 answers
I have a question about cyclic hardening .
Are the values of Yeild stress at zero plastic strain and equiv stress  identical?
Relevant answer
Answer
If I have the Cyclic curve for a material (Single hysteresis loop). How to enter this material data in abaqus ??
  • asked a question related to Mechanical Behavior of Materials
Question
9 answers
The experimental data test will be used in conjunction with the numerical results of a counterpart model in an optimization procedure. The cost function will be built using the difference between the numerical and experimental data then minimized in a least squares sense.
Relevant answer
Answer
With impulse excitation technique you would be able to identity most of the elastic moduli, however it is necessary to prepare more than one sample Please, see image attached and the white paper below:
  • asked a question related to Mechanical Behavior of Materials
Question
15 answers
let's say we are after strength and ductility of a structure with gradient of grain size (bimodal microstructure), and micro tensile test setup is not available. Is it possible to somehow manage to get stress-strain curve that represent mechanical behavior of all the microstructure from micro-hardness test or nano-indentation test? I know it is possible to get several indentation test along the sample and get a stress-strain curve for each point. However, the sample has gradient of grain size lets say from 400nm up to 5um, so depending on the indent location we are expecting different mechanical behavior. Also I am not sure if just averaging all these curves would be a very scientific way of getting the final stress-strain curve. Any idea along these thoughts is highly appreciated.
Thanks
Relevant answer
Answer
In fact, we are discussing the problem of adequate averaging. This procedure may be performed in two ways, namely, 1) by mathematical (statistical) averaging, 2) by physical averaging. For second way you may use macroindentation without nanoindentation. Then you will realize physical averaging because of contact area (and deforming volume of material) become essentialy larger than grain size.
  • asked a question related to Mechanical Behavior of Materials
Question
7 answers
Which theory is used to calculate shear stress in Ansys workbench?
because I like to determine shear stress for a brittle material through Ansys.
Relevant answer
Answer
Tresca criterion (ie. max shear stress) is for ductile materials. Brittle materials need Galileo-Rankine criterion (ie. max principal stress)
  • asked a question related to Mechanical Behavior of Materials
Question
16 answers
Dear all researchers,
I observed that Fracture Strain and Fracture Toughness of Aluminum Alloys depends upon the strain rate, as we increase the stain rate Fracture Strain and Fracture Toughness also increases. I don't able to find the reason behind this.
Relevant answer
Answer
Hi Purnashis,
Have you checked the temperature of specimen in your experiments.
It could be that in higher strain rates the temperature of the specimen increase by adiabatic heating. So, the increase in the fracture stain might be caused by the temperature effect.
  • asked a question related to Mechanical Behavior of Materials
Question
20 answers
In mechanics of materials the engineering stress & strain (Cauchy) are defined by the original area and original gauge length respectively. Is this by definition, at room temperature at which the original measurements are likely to be made?
During tensile testing (creep testing etc) at elevated temperatures thermal expansion will affect the area and gauge length. However, it is common practice to use the values measured at room temperature to calculate the engineering stress and engineering strain.
It is clearly, possible to take this thermal expansion into account and I often do so when calculating true stress and strain (Hencky).
However, I don't do so for engineering stress and strain and instead use the room temperature values. Thereby treating the engineering definitions as approximations and the true stress and strain as the more "correct" definition of stress and strain.
In my mind I consider the engineering stress and strain to use the original area and original gauge length as measured at room temperature as a definition of "engineering" stress and strain. However, I have never seen this written down explicitly and wondered if anybody knew if the "engineering" stress and strain were actually defined differently such as "original area and original gauge length, measured under appropriate conditions".
Please note for the calculation of "true stress" and "true strain" I am fairly convinced that the correct thing to do is to use the "original area and original gauge length, measured under appropriate conditions". My question is about the engineering definitions!
I know this is very pedantic!
Relevant answer
Answer
I totally agree that testing standard do not provide the real answer sometimes. They put you in a mode that you can not innovate. In the real world we should think of them as restricted methods, but good enough to establish certain protocol and try to understand the whole concept of temperature and error in our case. Therefore true stress and strain depend on other variables. Thank you for a good and helpful discussion.
  • asked a question related to Mechanical Behavior of Materials
Question
15 answers
In prestressed concrete, additives always are used. There are different types of them. There effects should be known. 
Relevant answer
Answer
Any used material with the ordinary concrete composition, (cement, fine aggregate, coarse aggregate and water), shall have positive or negative side effect on the concrete properties (physical, chemical and mechanical) and that will affect positively or negatively the reinforcement performance.
A. Some of additives increase the heat of hydration that for sure increase the initial prestressing losses for pretensioned strands due to the difference of temperature between the sections inside (i.e.,through the span) and outside (i.e.,at anchorages).
B. Some of additives decrease the shrinkage of concrete that will minimize the time-dependent losses of strands (pretensioned or posttensioned).
C. Some additives are increasing the corrosion resistance of reinforcing steel to reduce the risk of rusting steel that causing cracking of concrete.
I think the question should be specific not general (i.e., for a specific type of additives what is the side effect of using it).
Thank you colleagues
  • asked a question related to Mechanical Behavior of Materials
Question
9 answers
I have developed a 3D half symmetric scratch model using Abaqus/Explicit consisting of two parts an analytically rigid conical indenter and an elastic-plastic deformable specimen. I have NOT defined any failure criterion for the material. The normal load is applied on the indenter along –Y (load control), indenter moves along –X to generate the scratch in the specimen (displacement control). I have the following questions and I would be grateful if someone could help me out
1.      At higher loads (say > 10 N), when the linear displacement of the indenter begins, the job gets aborted due to Excessive element distortion.  I have implemented ALE adaptive mesh but the mesh moves along the -Y (probably because the load is applied in that direction). Is there a way to allow the mesh to adapt in –X direction? If yes, how should it be implemented?
 I have tried mesh constrains but the following error message is displayed as soon as the job is submitted:
Spatial adaptive mesh constraints cannot be specified on nonadaptive nodes.
Adaptive mesh constraints cannot be applied to more than one degree of freedom on nodes that lie on a Lagrangian or geometric edge
2.      Secondly, sliding velocity of the indenter is 0.5 mm/s so I implement a timeperiod based on scratch length and sliding velocity.
For example Scratch length = 3 mm; Sliding velocity = 0.5mm/s; Timeperiod = (3/0.5) +2 = 8s; 2 seconds for loading and unloading the indenter. Is this correct?
3.      If time scaling needs to be implemented to reduce the KE of the model to < 10% of Total Energy of the model then should the time period of simulation be increased or decreased?
Please let me know if any further explanation is required regarding the model or the questions.