Mechanical Behavior of Materials - Science topic

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.

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.

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:

In my opinion, Franc3D is the best.

yes stacking fault energy does depend on strain rate and you will find many research article to support it.

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.

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.

the grade of the steel is important in order to compromise properties.... but totally 24 hours is suitable

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.

¿Alguien conoce cómo cambiar el nombre ?

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.

That is a good question.

Dear Vanda Nur Ilmi

It is suggested to read following papers:

Hi Ghanbar,

You can use the spring for your model.

thanks for your important question

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

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

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 σ_T 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.

I am searching the same problem.

I think this article will be useful.

It explain PCI 2010 material model and Power Formula model.

Has anyone stored the digitize.opk for Origin V.75 and earlier. It is not available anymore on the fileexchange site. Thanks!

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.

Yes , I have used this in my thesis for modelling of composite

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.

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.

you can find sample records for Abaqus umat subroutine in:

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

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.

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.

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.

Dear Dhanraj Rajaraman

Please find the attached file.

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).

HI,

I think, from FEMFAT Material Data! It is a nice way to get input parmeters for ANSYS Strain Life calculation.

Best regards, László

I recommend this article, because it is simple and so perfect.

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.

Consistent with the mechanistic arguments in the earlier replies one can say:

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

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.

Not yet. But Im planning to have one.

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

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

Nadeem, can you share how to use UMATHT subroutine ?

I found the following video link very informative - although I assume there is bit of anomaly in the definition of anodic and cathodic current.

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.

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.

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

Dear Andrey Leonov ,

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.

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)

Hello

you can read this link

http://abaqus.software.polimi.it/v6.13/books/usb/default.htm?startat=pt05ch23s02abm20.html

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.

Thanks to both of you. I shall try these methods.

-bharat

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.

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.

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.

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):

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.

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!

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.

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.

You can found it in the ASM Atlas of stress-strain curve, pages 523 foward.

If you don't find it, ask me.

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

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'.

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.

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.

@ 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' ?

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.

If I have the Cyclic curve for a material (Single hysteresis loop). How to enter this material data in abaqus ??

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:

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.

Tresca criterion (ie. max shear stress) is for ductile materials. Brittle materials need Galileo-Rankine criterion (ie. max principal stress)

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.

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.