Applied Mechanics - Science topic

Again with this work at hand, it becomes possible to follow the evolution (propagation) of highest complexity cracks that nucleate from defects (such as heterogeneities, inclusions ...) located inside materials. The provided G (the crack extension force per unit length of the crack front) is function of highest number of variables and parameters.

Thank you, Aziz Khan and Stephan D A Hannot for your valuable suggestions.

Influence coefficients are used in numerical simulations to determine how much influence a given node or point in the domain has on other nodes or points. These coefficients are often calculated based on the nodes' relative positions and the system's physical laws, such as the heat equation or Navier-Stokes equations for fluid dynamics.

As you've noticed, one common issue with influence coefficients is handling the boundaries or corners of the domain. In many cases, the influence coefficients near the boundaries will differ from those in the interior because the boundary conditions affect the system's behaviour.

One way to handle this is by using different formulas or methods to calculate the influence coefficients near the boundaries and interior. For example, you might calculate the first row of the influence coefficient matrix using x1 and y1 for the corners, and then use a different method for the interior points.

Another potential issue is that some numerical methods assume periodic boundary conditions, meaning that the system wraps around from one domain edge to the other. As you've described, this can result in 'continued influence' on the other edge of the domain. If your system doesn't have periodic boundary conditions, you might need to use a different method that properly handles the actual boundary conditions of your system.

It's hard to give more detailed advice without knowing the specifics of your system and the method you're using. However, I hope this gives you a starting point for understanding and resolving your issues.

There are couple of sensors might be used for different purpose in automobile, for temperature, rain, speed, fuel, break and stability direction, knock, transmission, oxygen, proximation, traffic etc. depends on your requirements. You can use all or call on car is inbuilt with which sensors.

Hi

Does that mean you want to compare different bodies with a fixed underbody? If so, can't you consider the underbody rigid in your software? If not, can you ask your question more clearly?

Thank you Gaurav for your interest.

In aerospace the wake has always been a disadvantage from the design point. But is it possible to use it for solving the problem, or designing a device, may be the cooling mechanism.

Using the problem itself to generate the solution. Reverse engineering if I m correct.

When using Abaqus or other finite element analysis software, it is not uncommon to encounter elements that become highly distorted and remain connected by only one node. This can occur for various reasons, such as meshing errors, modeling inaccuracies, or material instability.

To address this issue, you can try the following steps:

In order to overcome the difficulty for an elliptical crack to expand under applied shearing stresses parallel to the plane of the loop, we just analysed THE ROUGH CONOIDAL CRACK UNDER GENERAL LOADING. These types of cracks are observed in high strength broken specimens (steel, Ni superalloys ...) subjected to long life fatigue experiments.

Please refer to the "Q&A" question How to estimate the average rough conoidal crack shape (angle, height, circular basis) observed in high strength materials (steel, nickel alloys)?

I think Praveen meant stable solutions and not steady. To get unstable solutions you can integrate backward in time or use continuation methods to trace steady-state stable and unstable solutions including bifurcations.

The nano layer thickness is very very small layer, otherwise it's cannot use by Resistivity method and it has VES limitation.

Best regards.

P. Hakaew

Hello, I have a problem with Ansys for composite prototyping. Does anyone know how to add the ACP (pre) module in Ansys 2018?

The regular polygons of trigonal and hexagonal symmetry as yield criteria are summarized in Altenbach, H., Kolupaev, V. A., General Forms of Limit Surface: Application for Isotropic Materials, in Altenbach, H., Beitelschmidt, M., Kästner, M., Naumenko, K., Wallmersperger, Th. (eds.), Material Modeling and Structural Mechanics, Advanced Structured Materials, pp. 1-76, Springer, Cham, 2022. Both 24-gons are called the Rosendahl criteria.

Dear colleague

the research in title may help to find the answers

'Serviceability of Reinforced Concrete Gable Roof

Beams with Openings under Static Loads '

Bob Senyange Sir and Victor Krasnoshchekov Sir, thank you for your comments.

Hello!

You can use the Tabor equation: H=3S, here H (MPa) - hardness & S (MPa) - yield stress.

Also you can use the next equation describing indentation h (mm) of a cylindrical object (indenter) into a material with HV (MPa):

h=(P/HV/l)^2/(2R), here P - load (N), l - length (mm), R - radius (mm) of a cylindrical object. This equation can be easily transformed into a equation for a case of a spherical object (indenter) indentation.

Best regards, Michael.

property module>special (at top of screen)>inertia>create>anisotropic

I think this job will help you

Theories for triboelectric nanogenerators: A comprehensive review (https://doi.org/10.1515/ntrev-2020-0049)

Dear Zmour,

It can be better in term of diffusion convection reaction. My opinion is little different, the least-squares method has better control of the streamline derivative than the SUPG.

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.

Almost all modern instruments have an option to measure the OC potential of solutions (sometimes called the rest potential) in 3 electrode configuration. You don't need to remove or disconnect any electrode. Don't stir the solution during measurements. I don't understand what means "electrosorption" experiment. If this is a kind of bulk electrolysis, you must stir the solution as fast as possible.

I also need to use this feature but the problem is when I use it the values of stress are changing. How can I use the view cut feature without changing the values?? and Is there another way to do it??

Dear Hamid,

I suggest you try the following links:

Best regards,

Dear Al B. Kounga, piezochromic polymers are known with regard to this feature. Please check the following documents. My Regards

10.1007/978-3-642-36199-9_6-4

10.1002/chem.201800194

Attached is the paper.

Also, you need to findout the Hashin Damage model parameters for the axle material from the previously published experimental studies.

Hi, SLM-ed SS316L does not need damage model. Based on numerous experiences working with the compression of SS316L lattices no fracture will occur even up to densification. In addition, bulk SS316L (cylinder) sample does not even fracture up to 80 % compressive strain. A solely bilinear or multilinear plasticity model will work for SS316L.

If you are interested in damage model for a less ductile metal, such as Ti64, high strength steel etc, you can consider the Johnson-Cook damage model nontheless. If you are not planning to obtain them experimentally, you can reference them easily from various lattice papers.

this is a simple Code i have done while ago hope will help :

NDIV=10

PI=3.14

!

VELO=10

TIM=Lbr/NDIV/VELO

delta=1/100

!

*CREATE,FORCE

FDELE,ALL

TIME,ARG1

Force=node(ARG2,Wbr/2,Hbr) !! Load position

amplitude=-1e2*cos(45*2*3.14*ARG1) !! load amplitude

!amplitude=-10e2

F,Force,FZ,amplitude

solve

*END

/SOLU

ANTYPE,4

TRNOPT,FULL,,DAMP

LUMPM,0

OUTRES,ALL,ALL

DELTIM,TIM ! Specifies the time step sizes

TINTP,,0.25,0.5,0.5

KBC,1 ! Ramped load step

*DO,K,1,100,1

*USE,FORCE,TIM*(K),(K)*delta

*ENDDO

Thanks again to you all, you helped me and pushed to keep on researching about the problem. And I finally solved it!

The problem was not on the B matrix, but it was on the order of the 8 displacements of the 4 nodes, on the vector that multiplies B. I called it nodes_displacements.

To be coherent with my B matrix, the order of the nodes have to be physically anti-clockwise: down-left, down-right, up-right, up-left. This is also the order used on many books.

However, as I had all the displacements of all the nodes of the mesh on a big vector, ordered from up to down, I inconsistently took the elements from up to down to build up the nodes_displacements vector, which corresponded to low index to high index and that was incorrect.

All in all, I recommend to anyone having my same problem to verify the order of the indexed displacements.

I think the mentioned error comes from element dimensions, run the simulation by default element and check the results.

Dear Mohammad Reza Amiri,

You can certainly use nano-indentation to measure the hardness of a particle less than 120 um in diameter. First, minimize the mismatch between the modulus of elasticity and yield strength associated with the particle and the modulus and yield strength associated with the mounting resin. Once the material is mounted, use standard polishing and grinding procedures to minimize the surface roughness, achieve a mirror finish, and expose the cross-section of the particle. Once you've calibrated your nanoindenter frame stiffness, compliance, and tip's contact area function using a reference material such as fused silica, determine the particle-dominated depth limit using the criteria proposed by Yan et al. such that indentation depth is less than or equal to 0.02 * R, where R is the radius of a given particle. Otherwise, David Mercier et al. appear to have had success when using the guiding principal established by Constantinides et al., which advocates for a depth limit of 10% of the particle size. From my own experience, when the mismatch between a particle's stiffness and the stiffness of a given mounting material is very large, then Constantinides 10% rule no longer holds and the 2% particle radius rule from Yan et al. remains reasonable.

With the aforementioned in mind you will still face a significant challenge in so far as the indentation size effect is concerned. Depending upon the radius of your particle, when you abide by Yan et al.'s approach then you may not obtain enough values of hardness as a function of indentation depth to apply the Nix-Gao relation before surpassing the particle-dominated depth limit. Therefore, care needs to be taken in interpreting the results. In other words, the hardness will not be the "true" hardness without the Nix-Gao analysis unless your particle is 120 um in diameter, then you could potentially solve for the true hardness by fitting the hardness vs. depth data between depths of 100 nm and 1200 nm. Such a range would likely be sufficient for indentation size effect analysis.

Lastly, one could take an alternative approach. You could acquire a flat-punch indenter tip and compress the micro-particles using an indenter. See Assadi et al. for more information surrounding this alternative approach.

Best,

Bryer C. Sousa

Materials Science and Eng.

Worcester Polytechnic Institute

Yan et al.

Mercier et al.

Assadi et al.

Good Answer Vaibhav Balkrishna Jadhav

Hi Karan,

Aside from the suggested answers, you can also use AceGen in Mathematica.

http://symech.fgg.uni-lj.si/User/AceGenPrint.pdf

Best,

Romik

Corresponding Python script

In Poland, there is now a trend in which we all have to duplicate our research and analysis in magazines that have relevant points on the list from our Ministry of Science and Higher Education - unfortunately I can't find you in our list :-(

Please look at ASME B31.3 Code Table A1 for minimum design temperature of materials. But Low temperature carbon steel ASTM A350 LF2 is very common forging carbon steel rather than A105.

The following article is relevant:

This paper presents a novel method of space-based geoengineering which uses the mass of a captured near Earth asteroid to gravitationally anchor a cloud of unprocessed dust in the vicinity of the L1 position to reduce the level of solar insolation at Earth. It has subsequently been shown that a cloud contained within the zero-velocity curve of the largest near Earth asteroid, Ganymed, can lead to an insolation reduction of 6.58% on Earth, which is significantly larger than the 1.7% required to offset a 2 °C increase in mean global temperature. The masses of the next largest near Earth asteroids are found to be too small to achieve the required level of insolation reduction, however, they are significant enough to be used as part of a portfolio of geoengineering schemes.

Cheers

There is no general valid answer, because materials do not respond equally to different typs of projectiles.

Unfortunately, what you have here is a classic case of "jerk". It will not matter how well you calculate the theoretical torque required for the nut to hold fast, in practice it will always come loose. It is the same principle as the tool used to remove wheel nuts. You have to change the physics of your assembly. If you can, reverse the thread direction of the nut. If you cannot, you have to find a way of clamping the nut. Solutions depend on the size of the nut. How big is it? Knowing this, I can give you a way of locking the nut that does not depend on the torque that you are using.

Hi Newgato Chiro,

When we find stresses σ_ij corresponding to displacement vector U=grad f, then boundary loads will be p_i=σ_ijn_j, where n is unit external normal vector to the boundary of the body, and volume loads will be b_i=-σ_ij,_j. These loads cause the infinitesimal rotation tensor to be equal to zero. The case of symmetric displacement field is only particular.

Hello @Robert Shour,

On the question, "Does society lose or forget these old insights that are discarded once new conceptual reference frames take hold?" Yes, in the sense that too much "knowledge" eclipses common sense. A case in point is what I call the "Wimbledon Phenomenon". A couple years ago, British social scientists conducted a survey among 1) Housewives, and 2) Tennis trainers, asking who would win the next Wimbledon championship. The housewives out-performed the tennis trainers by a large margin.

It could also be argued that the Friedman-Robertson-Walker metric (as "a new conceptual reference frame") and its attendant big bang theory and LambdaCDM cosmological model have eclipsed all common sense about the nature of the universe, insofar as huge contradictions now exist in standard cosmology, for example related to Dark Energy, which has a phantom equation of state p<-rho and therefore behaves like anti-gravity. Yet this does not undermine the Mainstream Physicist's continuing belief in their objections to refutations of LambdaCDM!

Chee Loong Chin Thanks a lot for your helpful answer.

Units were not consistent. The mimics soft had defined density in g/cm3 but because distances was in mm; the consistent unit for density was tonne/mm3.

Problem solved and thank you again.

In a recent work intitled “Fracture Mechanics in a three-dimensional elastic half-space under the rectilinear contact pressure of a cylinder” (see our contribution in ResearchGate), this crack system has been investigated. Expressions of the relative displacement of the faces of the crack, crack-tip stresses and crack extension force G per unit length of the crack front are given. G displays a maximum at an angle θ that is confronted to experiment. dG / dθ = 0, the condition that determines the crack angle, is seen to depend on Poisson’s ratio only.

thanks Abhimanyu Kumar

Khaled Megahed Khaled, there is much to it then stated here. To answer your question, yes, it should not have softening part. By your terminology, it seems you are dealing with concrete or some similar material, since for metals, true stress is the one without softening. True stress could be expressed mathematically (usually without perfect matching), and damage also can be expressed through some sort of function. But it depends on many more parameters, firstly material and type of degradation that is causing damage, than triaxility, Lode parameter, than strain rate etc. Then, you probably need this for numerical analysis, and by using Abaqus or similar software, you will need to make a choice about yield law, hardening law, damage type and law (if any), or simply use damage as a multi-linear for some points you choose. This choice is highly influenced by the experiment you did, for example, is the strain rate important and varied etc, or did you used extensometers so you have only global softening, or you used DIC so you already know the true stress-strain relation for your material. If the latter is not the case, I suggest you follow the advice Charles gave, and iteratively obtain satisfactory P-delta through numerical analysis. Some papers that might help would be:

An Experimental-Numerical Combined Method to Determine the True Constitutive Relation of Tensile Specimens after Necking, You-de Wang, Shan-hua Xu, Song-bo Ren, and Hao Wang

True Stress-True Strain Models for Structural Steel Elements P. Arasaratnam K. S. Sivakumaran and M. J. Tait

Bolted shear connectors vs. headed studs behaviour in push-out tests, Marko Pavlović, Zlatko Marković , Milan Veljković , Dragan Buđevac

ELse, if you used Aramis, then maybe take a look at:

Strain and stress relation for non-linear finite element simulations, Sohren Ehlers , Petri Varsta

Can you select arc length method in ABAQUS?

Thank you Mohammad Qasim Abdullah

* A virtual displacement is any field of displacements, which satisfy the boundary conditions, but is imaginary (do not actually occur). Moreover, a virtual displacement means an instantaneous (time is held constant) change in coordinates so the state of stress does not change (a real displacement would change the state of stress).

Then, the work of all (real) forces on virtual displacements should be zero if the system is in a state of equilibrium.

* The variation in displacement is an infinitesimal change in the displacement field so the change in the state of stress can be neglected. Then, the variation in displacement can be interpreted as virtual dispalcement.

Thank you so much L. Angela Mihai

The statement "I am looking for 2nd moment of area in y direction of this shape." is not correct. Maybe you are looking at the polar moment of the section with respect to y axis:

Iyy =Izz+Ixx

(I assume, although not shown in your drawing, that (xyz) has origin at the barycenter of the section)

It is a very interested question ,see

Muhammad Usman

Maybe you can buy on internet only the Leonard's chapter of the book at a cheaper cost. However, be aware of the fact the the QUICK scheme can be used mainly for the steady formulation, therefore for Re<10^4 in the 2D lid driven cavity. Many years ago I developed an improved version of the Leonard's schemes, suitable for the lid-driven flow unsteady problem, you can see some details here

hi

the following references may be helpful

-Abdolrasoul Ranjbaran "A computer program for the stress analysis of reinforced concrete structures. PhD thesis submitted to UMIST UK, 1992; pages 100-110. The thesis is available in internet.

- A. Ranjbaran "Finite element techniques for the nonlinear stress analysis of metallic and ..." Chapter 4 in Structural Dynamics Systems Computational Techniques and Optimization, Editor C. T. Leondes, Gordon and Breach Science Publishing.

- A. Ranjbaran and M. E. Phipps, "Dena: A finite element program for the nonlinear ..." Computers & Structures, 51 (2) : 191-211, 1994.

Dear Sanghamitra Das,

if you want to have mechanical loading/response as well as thermal loading/response then you have to define a coupled temperature-displacement analysis step. Trying to impose mechanical boundary conditions to a thermal problem is like trying to apply thermal boundary conditions to a mechanical problem. It is possible through thermo-mechanical coupling.

Furthermore, to apply a pre-tension condition, you can define a coupled temperature-displacement step, go to Initial Fields, choose the Initial step and then on the Category -> Mechanical and on the Type -> Stress. In the pop-up window you can define the stress components required.

Regards,

Anargyros

I agree with Nigel. nCODE has done a better job at integrating into ANSYS WB. fe-safe can still read RST files. But you'd have to post-process in ANSYS Classic. SafeTechnology was acquired by Dassault, so it is natural to expect fe-safe to be more integrated with ABAQUS and the 3D Experience Platform. I have used both and I am currently working for DS R&D. My personal opinion is that fe-safe is more transparent, i.e., you know exactly what the software is doing. In areas like fatigue of welds, rubber, TCD, Nitinol, Infinite Life and random vibration fe-safe has the lead. Due to the influence of HBM however I'd say nCODE has more to offer in terms of signal processing.

Dear TIZA MICHAEL TORYILA ... Thanks for joining our discussion..

You need to be more specific, which "source" of asymmetry you have? Is this due to geometry of the cross section? due to a different lamination (in case you are dealing with composites)? or both? In the most general case, considering the Timoshenko's beam model, you may end-up with a fully coupled configuration, i.e. 21 unknowns (cross sectional stiffnesses). As far I understood, you need to change those to satisfy a (or some) prescribed constraint(s) given in terms of maximum deflection(s).

As for the equation for the displacement, you can use the principal of virtual work to evaluate the displacements but for a fully coupled configuration it is a long way to go. You can certainly use superposition as far as the tube works in the linear regime. Seemingly you have a pre-defined set of applied loads, so you need to systematically "link" the geometrical parameters to the the cross sectional stiffnesses (exactly as you do for a simple rectangular section where you know that I=1/12ab^3), and change those parameters to get the response you're looking for. If I understood correctly your problem, you may want to use parametrical analysis or optimization to get meaningful results. In fact, if you just play with the values of the cross sectional stiffnesses, you might have a numerical solution which satisfies your constraint but which in turn is unfeasible.

knn, kss, ktt should be taken as large as possible to avoid collaps of contact point. the usual convention is E/t where E is the modulus and t is the thickness of adjacent layer. similarly G12 and G23 for kss and ktt. for damage initiation both shear can be assumed to be inter-laminar shear strength i.e S12 and normal as strength of matrix. these assumptions are quite appropriate. this is extended for damage energies too.

@ Vasiliy Knyshev ,

What is your question ?

Kindly state and explain clearly the Newton's Second Law of the third order.

Atmospheric pressure is about 0.1 MPa, that is negligible when considering concrete for example, however, it could be significant to other applications.

These links may help you

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.

Hi, Saeed Torbati

From Abaqus 6.13 Theory Guide, 4.6.1 Hyperelastic material behavior:

"The D_i values determine the compressibility of the material: if all the D_i are zero, the material is taken as fully incompressible. If D₁=0, all D_i must be zero."

From Abaqus 6.13 Analysis User's Guide , 22.5.1 Hyperelastic behavior of rubberlike materials:

"If D₁ is equal to zero, all of the D_i must be equal to zero. In such a case the material is assumed to be fully incompressible in Abaqus/Standard, while Abaqus/Explicit will assume compressible behavior with Poisson's ratio of 0.475."

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.

Dear professor Korsunsky,

we are interested in residual stress evaluation in laser material deposition.

It is a very interested question

dear. Fikrat Almahdi.

Do you have a PDF file of book: Modal analysis theory and testing ?

could you share to me ?

thank you so much