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# Applied Mechanics - Science topic

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This subject is important because evidence of conoidal rough cracks is observed experimentally on various macrographs of broken specimens, under fatigue for instance. Our recent works (see below in answers) provides associated physical quantities.
Again with this work at hand, it becomes possible to follow the evolution (propagation) of highest complexity cracks that nucleate from defects (such as heterogeneities, inclusions ...) located inside materials. The provided G (the crack extension force per unit length of the crack front) is function of highest number of variables and parameters.
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Greeting Researchers
It is well known that within the linear range, the in-plane and transverse motion of a plate are independent of each other i.e. the equations governing the in-plane and transverse motions are uncoupled. The stiffening/softening effect of the in-plane loads on the transverse vibrations of the plates is then accounted for by considering the work done by the in-plane loads during the transverse motion. In FEM, the work done by the in-plane loads is used to obtain the geometric stiffness matrix. The FEM equations can be given as
Ma + (K + Kg)u = f ... (1)
where u is the vector of nodal displacements, a is the vector of nodal accelerations, K is the stiffness matrix and Kg is the geometric stiffness matrix.
When the range of motion is no longer linear, the equations of motion for the in-plane and transverse motion are inherently coupled. In this case, incorporating geometric nonlinearity in the Von Karman sense, the FEM equations may be written as
Ma + (K + Knl)u = f ... (2)
where Knl is the nonlinear stiffness matrix.
Now my question is whether it is necessary to include Kg in eq. (2) i.e. whether the correct dynamic equation of motion with the incorporation of nonlinearity is as shown below in eq. (3)
Ma + (K + Kg + Knl)u = f ... (3)
My opinion is that since in the nonlinear case, the equations of motion are inherently coupled and thus, there is no need for the inclusion of matrix Kg as done in eq. (3). The coupling is incorporated through the matrix Knl and eq. (2) is the correct dynamic equation of motion. In the linear case, since the equations of motion are uncoupled, it is necessary to add the matrix Kg to incorporate the effect of the in-plane loads on the dynamics of the transverse motion.
I would like to have your valuable opinions on the same.
Best Regards,
Jatin
Thank you, Aziz Khan and Stephan D A Hannot for your valuable suggestions.
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I have written a numerical model for calculating the elastic deformation of two elastic bodies in 3D static contact. The code takes the applied laod, Young's Modulus, Poisson ratio, and surface profile of each body. Calculates influence coefficients based on the equation provided by Love [1]. The problem is solved by conjugate gradient descent and elastic deformation is calculated by Discrete Fourier Transform- Discrete Convolution method.
I tested the model on ball-on-flat and ball-on-ball geometries with the same material properties of each body. I am facing the problem that the elastic deformation contour is diagonal instead of concentric in these cases. The pressure distribution normalized at Hertz Contact pressure and contact width is correct, but the deformation is not. I have double-checked by Kernal/influence coefficient matrix but can not seem to understand this behavior. I have attached the 3D plots of the example (ball-on-ball), the 3D plot of the influence coefficient at 1 point, and the contour of calculated deformation.
Any help, guidance to solve, or help in understanding the problem would be greatly appreciated.
Thanks.
A.E.H. Love. Stress produced in a semi-in nite solid by pressure on part of the boundary. Philosophical Transactions of the Royal Society of London, 377:54{59, 1929.
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.
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i am searching for new sensors that is used in cars for effective performance of motor.
can you give me a book or paper or introduce me a site?
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.
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Hello,
I have several structures which is composed of an upper body and an under body. I want to compare different upper body with each other (therefore several different structures) with Finite element software. I also want to lower the stiffness of these under body to have the same stiffness on the different models and thus be able to compare upper body between them. For this the solution is to vary the Young's Modulus of these different under body. The problem is that some are longer than others in terms of length. How to take this parameter into account?
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?
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Wake formation has been largely observed behind objects in real use e.g pillars, vehicles, buses, cars and building.
It has also been regions of large interest over decades.
So the question here is ? what are disadvantages of wake formation?
why they are so important?
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.
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Hello ResearchGate,
I'm simulating a blanking process in 2D using Abaqus Explicit with ALE. When the Johnson-Cook criterion is satisfied, elements start to be deleted, thus simulating the fracture at the end of the process. However, no matter how much I try to initially distort the mesh so that it gets more structured by the time fracture starts, the element deletion propagates "diagonally through the elements" (see attached screenshots), which leaves some of the not deleted elements connected by just one node (again, see attached screenshots). This stretches those elements to the point where my stable time increment gets pretty low, my burr is distorted and large, unrealistic stresses appear. I've tried to make the mesh finer, which hasn't really solved the problem. I've also tried to activate DELETE DISTORTED ELEMENTS, but this option doesn't seem to work, as the elements get stretched but their characteristic length remains large, as well as their area. I've tried applying the minimium dt option of this tool with no success (as the only parameter that seemed to be altered by these distorted elements was the stable dt).
I've attached a couple of screenshots that showcase the problem. If anyone knows a workaround or has any suggestion they will be very welcomed.
Have a nice day :)
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:
1. Check the mesh quality: One of the primary reasons for highly distorted elements is poor mesh quality. Ensure that the mesh is refined in areas of high-stress gradients and curvature. This can be done using adaptive meshing or manually refining the mesh.
2. Adjust the element type: Different elements behave differently under varying loading and boundary conditions. Switching to a more suitable element type may help reduce element distortion.
3. Consider changing the material model: Material instability can also cause element distortion. Try using a more robust material model that is better suited to the properties of the material being analyzed.
4. Increase the number of integration points: Sometimes, distorted elements can be a result of insufficient integration points. Increasing the number of integration points can help resolve the issue.
5. Use element deletion: If an element is highly distorted and causing convergence issues, it may be necessary to delete it. This can be done manually or by using the element deletion feature in Abaqus.
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Can an elliptic crack (small enough to remain a single entity, with no internal pressure or shear force) inside an isotropic material (no boundary effect) be expanded in its own plane under externally applied shearing stresses only?
If yes, how did you show that? Do we have experimental evidence for the process?
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)?
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Greetings researchers!
I am using FEM to obtain the time response of the nonlinear forced vibration of plates. I am using plate elements based on Reddy's HSDT and Newmark time integration in conjunction with the Newton-Raphson iteration to obtain the time response.
It is well known that multiple steady-state solutions can exist in the case of nonlinear forced vibrations. Also, all steady-state solutions are not stable. In practice, unstable solutions are not realizable and the system assumes any one of the stable solutions depending on the initial conditions.
I was curious to know whether the FEM predicts only stable steady-state solutions. Or does it predict stable and unstable solutions and the stability of the predicted solutions needs to be determined through other means?
Thank you for your valuable time.
With best regards,
Jatin
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.
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Hallo every one,
I did nanoidentation experiment :
1 photoresist with 3 different layer thicknesses.
My results show that the photoresist is harder when it has thicker layer..
I can't find the reason in the literature.
Can any one please explaine me why is it like that??
is there any literature for this?
best regards
chiko
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
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Hello.
I am trying to do a static analysis of a torque box using shell elements and I have the following issue.
I have modeled the Boeing 737 wing (torque box) in Autodesk Inventor using surfaces.
Then I transferred it in Ansys Workbench to start the FEA analysis.
However, I want the inner structure of the wing to be made using composite materials.
So, I opened an ACP module. In that module, I cannot hide some surfaces and here's where the problem is.
If I can't hide them, then I cannot select the ribs and apply an Oriented Selection Set.
I tried, also, making three different ACP modules and then assembling them in static structural (transferring shell data) however that results into an error.
I have attached my project file, without the ACP module.
Hello, I have a problem with Ansys for composite prototyping. Does anyone know how to add the ACP (pre) module in Ansys 2018?
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The uniaxial (direct) tensile test is not commonly used for masonry structures. Researches mostly rely on bond wrench or bending tests for masonry structures. My questions are:
1. What are the main reasons for the direct tensile test being used so little for masonry structures (the brittleness of the material? the low tensile strength? complexity in the boundary conditions, i.e. chances of introducing flexure in the specimen)?
2. Are there additional complicating factors with performing direct tensile tests on specimens retrieved from existing structures? Let's say one is able to retrieve a vertical drill core from a masonry structure, what are the additional problems one faces with performing a direct tensile test on such a specimen (compared to a lab made couplet specimen)? Is it perhaps the loaded faces being not completely parallel to each other?
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Regular polygons of trigonal and hexagonal symmetry are used as yield criteria in theory of plasticity:
References for regular icositetragon (24-gon) as yield criterion are sought for a systematization of yield and strength criteria.
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.
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The beam has a varying cross section. Also one of the sides is loaded uniformly by a force. See attached file for more clarification.
Dear colleague
the research in title may help to find the answers
'Serviceability of Reinforced Concrete Gable Roof
Beams with Openings under Static Loads '
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Hello Researchers,
Say that I have 'p' number of variables and 'm' number of constraint equations between these variables. Therefore, I must have 'p - m' independent variables, and the remaining variables can be related to the independent ones through the constraint equations. Is there any rationale for selecting these 'p - m' independent variables from available 'p' variables?
Bob Senyange Sir and Victor Krasnoshchekov Sir, thank you for your comments.
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I am trying to determine the maximum true contact pressure [Cylinder on flat body model]. I only have the Vickers hardness value (500 HV for 10 kgf load). Is there a way to correlate them?
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.
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i mean do some thing make abaqus understand that if i put a mass on a point in space , if that point move anywhere mass will also moves with it , that what i mean , if that can done by just put that mass in a datum point for example ??
if i defined mpc link between that point which i defined mass on it , is that mean that mpc link is work with point only and mass together ???
property module>special (at top of screen)>inertia>create>anisotropic
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hello
I want to simulate a triboelectric nanogenerator by COMSOL MULTYIPHYSICS.
How to apply mechanical force for contact separation mode?
in tutorial files or articles just sweep the gap between the triboelectric layer for measuring Voc and don't use solid mechanics to apply mechanical force and when I use that facing an error: Failed to find a solution for the initial parameter.
is there any way for direct measurement of the output voltage of TENG in terms of applied forces by COMSOL MULTYIPHYSICS simulating?
Theories for triboelectric nanogenerators: A comprehensive review (https://doi.org/10.1515/ntrev-2020-0049)
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I would like to know if the SUPG method has any advantages over the least squares finite element method?
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
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Does a single-valued description exist for isotropic materials?
When the crack (be it planar or non-planar) is associated with crack-tip plasticity, the relations between the failure stresses in specimens tested in tension, compression and bending given above (see our answer 1) remain valid, except that σT is now multiplied by a quantity that contains the crack-tip plastic zone size, crack-front shape and orientation of average crack surface. Please see “NON-PLANAR CRACK WITH CRACK-FRONT PLASTIC YIELDING UNDER GENERAL LOADING” in our contributions in ResearchGate.
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Hi all,
I am designing an electrosorption experiment using the 3 electrode system (Working electrode-WE, Counter-CE, and Reference-RE) , and I want to compare the results with OC adsorption. In order to perform an OC experiment, I just need to remove the CE from the potential-stat (still applying the voltage in my solution), am I correct?
Also, for electrosorption, can I apply magnetic stirring? If so what is a good rpm range for it? In cyclic voltammetry (CV) experiment, the electrolyte is kept unstirred to make sure mass transport can occur only by diffusion due to concentration gradients created around the electrode surface. However, this is different so I think applying mechanical mixing by magnetic stirring might enhance the adsorption efficiency of the WE. However, I am not sure what is the good rpm range for it which will not interfere with the electrosorption process.
Thanks!
P.S. I am not an electrochemist, so this might sound silly for the experts.
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.
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Hi, I'm working on a mechanical behavior of a new material analytically. For the purpose of verification, I need to obtain stress distribution on the cross section of a curved beam with rectangular cross section. Due to the lack of familiarity with Abaqus, I can't obtain it. How can I find it?
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??
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Hello
To validate the results of modeling by Abaqus software with experimental results, how can estimate the Chaboche hardening coefficients from the hysteresis curve?
The material is steel.
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Dear fellows,
i am looking for an elasto/mechanochromic material that can undergo color change already at low applied mechanical load. Ideally the color change is reversible upon unloading and color change in visible light spectrum.
No matter if the material is polymer, metal, or ceramic.
I am very thankful for your help or hint.
kind regards
Al.
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
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We are working on the frictional mechanics and need to see this source.
Attached is the paper.
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Hey there,
I want to simulate & analyze the fracture and fatigue (crack growth) in the rear axle housing of heavy tracks (Volvo company) in Abaqus.
My question is which method is suitable for this research and how I can find the geometry and the mechanical & fatigue properties for this specific vehicle?
(If there is any related paper/thesis or anyone can help me, please let me know.)
Thank you
Also, you need to findout the Hashin Damage model parameters for the axle material from the previously published experimental studies.
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Hi all,
I am dealing with quasi-static compression simulations on topology-optimized lattice structures using the Abaqus Explicit solver.
By the way, I have not modeled material failure model for several reasons and the material model I've used includes Johnson-cook plastic parameters for AM-SS316L. Now here is my question:
How important and effective is modeling material failure in this case? does it effectively change the stress-strain (force-displacement) curves trend?
If yes, what is your suggestion for material failure model of SS316L in Abaqus? Is there any easier way rather than finding J-C damage parameters for SS316L?
It would be great if anyone can help me to find these parameters.
Regards,
Mohsen
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.
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i want to move a parabolically varying load according to time in ansys apdl. this should be written with codes because i want to apply this load for many cycles.
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
!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
*DO,K,1,100,1
*USE,FORCE,TIM*(K),(K)*delta
*ENDDO
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Hi everyone,
To put this in context, , I am making a Matlab algorithm for topology optimization that consider fatigue breaking. I am basing on the Ole Sigmund algorithm, which discretices the 2D piece into a rectangular mesh.
For analysing the fatigue resistance of a piece candidate (discreticed on little squares), I need the stress tensor everywhere, so I decided to compute the stress on the center of each squared element, with FEA analysis, because displacements of the nodes are already computed .
Then, I apply the standard 4-node quadrilateral element stress analys: I know the 2 displacements (u,v) of each 4 node, and I apply interpolation to know the deformation on the center of the element, and so the 3 stress components. I do it with the B matrix and C matrix:
B=0.5/l*[ -1 0 1 0 1 0 -1 0; 0 -1 0 -1 0 1 0 1; -1 -1 -1 1 1 1 1 -1];
(l=side of the element)
C=(E/(1-nu^2))* [ 1 nu 0;
nu 1 0;
0 0 (1-nu)/2 ];
Stress=C*B*nodes_displacements
The problem is that once I compute those stresses, and so the Von Misses stress, the final result doesn't seem to be correct, mostly on parts of the piece being flected.
I also tried taking the 16 closer elements for interpolating the stress on the center of the element, but it didn't work either. I did that last thing with a much bigger B matrix, that has as "input" the 32 displacements of those 16 points around the element:
B=[ -0.0013 0 0.0352 0 -0.0352 0 0.0013 0 -0.0117 0 -0.0117 0 0.0013 0 -0.0352 0 0.0352 0 -0.0013 0 0.0117 0 0.0117 0 -0.3164 0 0.3164 0 0.3164 0 -0.3164 0;
0 -0.0013 0 0.0117 0 0.0117 0 -0.0013 0 0.0352 0 -0.0352 0 0.0013 0 -0.0117 0 -0.0117 0 0.0013 0 -0.0352 0 0.0352 0 -0.3164 0 -0.3164 0 0.3164 0 0.3164;
-0.0013 -0.0013 0.0117 0.0352 0.0117 -0.0352 -0.0013 0.0013 0.0352 -0.0117 -0.0352 -0.0117 0.0013 0.0013 -0.0117 -0.0352 -0.0117 0.0352 0.0013 -0.0013 -0.0352 0.0117 0.0352 0.0117 -0.3164 -0.3164 -0.3164 0.3164 0.3164 0.3164 0.3164 -0.3164 ]/(2*l);
So my question is, what would be the simpliest way to fix this problem, and so to get the correct stress values?
I would prefer a way to fix it using only the 4 nodes around the element, because using 16 makes everything more complicated.
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.
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Hi Everyone,
My attempt to use the drapability and stretching behavior of knitted composites(just fiber without matrix) in die forming. At this moment, I am only interested in the behavior of the fiber.
I ran 2 models (geometrically, constraints and interaction are identical).
Job 68-
Material model used (Steel with plasticity defined).
Results: Are converging. The behavior is as expected.
Job 69- Material model used (Carbon fiber-MAT-1 in .inp and material orientation defined based on texgen software algorithm). Added orientation by calculating the normal for each element using the node data. I have defined the material parameter based upon the property sheet from attached Hexcel-tow data.
The error I get is ratio of deformation speed is too high. I have tried a number of possibility as mentioned in this forum earlier. Any help would be highly appreciated:-)
-Sangram
I think the mentioned error comes from element dimensions, run the simulation by default element and check the results.
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I want to measure the hardness of particles that are smaller than 120 micrometers. Do you think we can use depth sensing nano indentation method to measure the hardness of this material?
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.
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The simulation involves Rigid body + Polycarbonate Flexible body. The Flexible body penetrates into the rigid body upto some extent and doesn't show up any stress and plastic strains. But when reversed the conditions, i.e. Fix the flexible body and drop rigid body onto it, stress and other results come up, Why does this happens?
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I am writing a new plasticity model in Ansys Explicit Dynamics using AUTODYN as solver for Bilinear Isotropic Hardening model but any how unable to add this particular material model code, as I need MATDEF code for above model.
It will be a great help if anyone can help me to write that particular code. So as to define my model and get in continuation with my research.
Hi Karan,
Aside from the suggested answers, you can also use AceGen in Mathematica.
Best,
Romik
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Hello, I am performing an undergraduate finite element analysis research project, and my current task is to find the shear center for an asymmetric C beam. Out of curiosity, how does one go about doing this? (picture of profile attached, I am also just taking a mechanics of materials course at my university as we speak)
I wish you all a wonderful day
Corresponding Python script
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There is an open access journal (IJCESA) to call for research paper related to the civil engineering.
The journal is related to structural engineering, construction technology, building materials and structures, coastal and harbor engineering, construction management, earthquake engineering, environmental engineering, renovation of building, geotechnical engineering, highway engineering, hydraulic, road and bridge engineering, transportation engineering, tunnel engineering, urban engineering, water resources engineering, urban drainage and etc.
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 :-(
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We are preparing a material list for a low temperature service (-40 degree C) due to natural gas choking downstream a drain valve. We need to choose the accepted material to suit this application other than ASTM A105. Is  there any reference standard which explains the material temperature limitation for low temperature service?
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.
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If global warming cannot be resolved by controlling/minimising gas emissions, then extraordinary measures may be the only viable options, one of such ideas is placing a solar shield between the sun and earth at the L1 lagrangian point to obtain a reduction in solar insolation . It may sound crazy, more like science fiction to know that a disk of 2000km in diameter would be necessary to reduce solar radiation reaching earth by 1.7%. I wonder about the sort of stresses that would be experienced by such an enormous body. Also, what sort of materials' properties would be required to withstand the conditions at L1, for example solar radiation, other rays. While it is possible to calculate the disk's orbital velocity around the sun, its angular velocity (around its axis) is difficult to calculate. I would be grateful if those with relevant experience could share their thoughts about how such calculations could be achieved.
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
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This problem could be used as reference.
The shear modulus can be calculated by using one of the analysis programs, such as Ansys
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The toughness and resilience are calculated when tensile load is applied. Will a material absorb same energy when a impact load is applied such as bullet fired on the material front face? Which material will absorb more energy; whose resilient modulus is more or whose toughness modulus is more or a material which becomes strain hardened?
There is no general valid answer, because materials do not respond equally to different typs of projectiles.
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I have a Scenario where my lock nut is tightend using a prevailing torque of 14 Nm (as mentioned by the manufacturer) on to the rotor placed between bearings (But the tightening direction and the rotor rotating direction is same unfortunately). The lock nut is loosened after particular life cycle of usage as the rotor rotates with a acceleration of 1230 rad/sec and every time it starts, the sudden acceleration loosens the lock nut. Is there a simple approch to calculate a appropriate prevailing torque for this situation, so that the lock nut does not loosen up when the rotor starts accelerating towards it's max RPM of 9400 in 1 second?
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.
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Hello,
A very general question is ahead.
When we find stresses σij corresponding to displacement vector U=grad f, then boundary loads will be piijnj, where n is unit external normal vector to the boundary of the body, and volume loads will be bi=-σij,j. These loads cause the infinitesimal rotation tensor to be equal to zero. The case of symmetric displacement field is only particular.
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This question requires explanation. Discussion on the second day of Galileo’s Two Chief World Systems raises the point.
Simplicio, taking the position of those opposed to Copernicus, doubts the Earth moves; if Earth moved it would have to move at too great a speed. Sagredo and Salviati say this objection has no merit. The fixed stars have a radius far greater than the Earth, and yet the implied speed, much greater than that of the Earth in the Copernican conceptual reference frame, does not undermine the belief of the anti-Copernicans in their objection. Here is an inconsistency.
The inconsistency is not encountered in modern times that takes for granted the heliocentric model of the solar system. This argument, based on the large radius of the distant stars, is one not usually encountered. One supposes that is so, because it is unnecessary. But then the question arises. Does society lose or forget these old insights that are discarded once new conceptual reference frames take hold? Or, perhaps, is nothing lost?
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!
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Hi everybody
I'm using abaqus dynamic implicit solver to analyze hip joint. There is not problem like this with static step. but i have to use time depended loads. so when i use dynamic implicit; there are stresses only in force applied area but no stress or displacement in anywhere else. i also tried with dynamic explicit step and concentrated and pressure loads but the problem didnt solve.
i've used frictionless surface to surface contact and fixed a region far from load applied area. and material properties defined by mimics software.
i'll also add a photo and abaqus files fore details. thanks alot for your help.
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.
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A simple crack system (Figure 1) can be readily studied to estimate the Hertzian conoidal crack angle and length, and also the stress intensity factor.
This is a 3-D brittle elastic half-space on the flat boundary Ox1x3 of which a rectilinear contact pressure along Ox3 is exerted by a cylinder whose axis is parallel to x3; the cylinder lies along Ox3 on the flat boundary. A planar straight-front crack inclined by an angle θ with respect to x1x3 is present under the action of the load along x2 due to the cylinder. The relevance of this modelling may be understood as follows. A slab of cylinder with thickness dx3 at spatial position O’ (0, 0, x3) exerts elastic fields (displacement and stress) proportional to those of a point load at O’ (proportionality coefficient dx3). Physically, this corresponds to the action of a spherical indenter to which is associated a conoidal fracture surface for sufficiently large load (Roesler (1956) as quoted by Frank and Lawn (1967)). The coalescence of conoidal cracks from different slabs of cylinder along Ox3 would produce planar fracture surface envelops parallel to x3 at large crack lengths. Therefore, we expect the modelling in Figure 1 to provide the experimentally observed fracture surface inclination angle θ and crack length l as a function of critical load P by both a spherical indenter and cylinder. This is the essence of the modelling depicted schematically in Figure 1.
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.
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What is the tensor type for Green Lagrange strain tensor and 2nd 2nd piola kirchhoff tensor?
Stress and strain are called 2nd order tensor because they follow the transformation rule: sigma`= R * sigma * R' where R is transformation matrix.
Deformation gradient, rotation matrix and 1st piola kirchhoff are called two point tensor because they relate two configuration. For example deformation gradient is: F(iJ) = xi * XJ where * is dyadic or tensor product and XJ and xi are the element before and after deformation.
What about Green Lagrange strain tensor and 2nd piola kirchhoff tensor?
which they do not change with element rotation
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Using damage model includes the relation between the effective and true stress. The true stress-strain curve is the stress-strain curve measured directly from experimental tests which could include softening part. While the effective stress-strain shouldn't have. Is that right?
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
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I am trying to model the strain-softening behavior of rock mass using UMAT subroutine. And, I am applying the 'static Riks method'. My model is running fine in abaqus under small loading. However, when comparatively large loading is applied the analysis is being aborted after 18% load application with an error msg, 'THE SOLUTION APPEARS TO BE DIVERGING. CONVERGENCE IS JUDGED UNLIKELY'.
I have checked the .msg file, .log file and the UMAT subroutine file, but could not find any thing helpful.
Kindly give me some suggestions for solving this problem.
Regards, Dipaloke
Can you select arc length method in ABAQUS?
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How the total potential energy is a unique function with respect to semi-tangential rotation?
Also how the tangent stiffness matrix of space elements based on semi-tangential moment is symmetric?
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Also when referring to variation in the work (virtual work), we use virtual rotation not rotation variation?
Thanks.
* 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.
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The balance laws could be defined in term of Cauchy stress and 1st Piola-Kirchhoff stress tensor as follow https://en.wikipedia.org/wiki/Continuum_mechanics
But could I define it in term of 2nd PK?
Thank you so much L. Angela Mihai
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For close shaped section, polar moment of inertia can be calculated from perpendicular axis theorem (adding both the 2nd moment of area in cross sectional axis). But how to calculate polar moment of inertia (2nd moment of area in perpendicular direction of the cross section) of I beam?
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)
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Hi All
For an ndof vibration system of mass and dampers, we know the equation of motion for imposed force.
but in finite element codes, it is also possible to apply a constant displacement and calculate the reaction force in the fixed end of the system as the response function .
Anyone could help with how to write the equation of motion for such a vibrating system ?
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It's seems that addition of carbon atoms increase the hardness by solid solution strengthening. However I do not know why it will have more effect on ferrite than on Austenite.
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Can some one give me details for the application of QUICK scheme to 2d lid driven cavity?
Best Regards
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
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I encountered a return-map technique in many papers but I do not understand how it works.
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.
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I got an error in Ls Dyna after solving, says that *** improper format** and error in keyword.
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I am modelling the heat transfer analysis of a wire electrode during the wire EDM process in ABAQUS. Can anyone please help how to apply the wire pre tension in the model as a boundary condition. Do I need to use coupled temperature displacement analysis to apply this mechanical constraint. I am attaching my model of wire electrode.
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
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I don´t have any idea about these two add on softwares for fatigue calculation. I am also new in FE simulation. Any comments or suggestions about the operating of these two softwares.
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.
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Major question.. give me your logical definition and whats the deference in application....
Dear TIZA MICHAEL TORYILA ... Thanks for joining our discussion..
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The beam has unsymmetrical section and is simply supported at its both ends and subjected to forces and moments in all 3 directions at a point.
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.
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I am working on cohesive contact(Between two Aluminium bars). I just have some questions that I am wondering if anyone can help me by answering them.
1. How can I find the the parameters in traction-separation: Knn, Kss, Ktt ( should I consider module of shear and elasticity for them?)
- In damage initiation: normal, shear 1, shear 2 (would I consider tensile and shear strength for these values?)
- In damage evolution: fracture energy. mix-mode ratio 1 and 2
2. From where i can get this parameters ??
I'm looking forward to hearing from you soon.
Thank you,
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.
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The function assumes a direct and reverse law. What do we know about the inverse function? Never mind. This is just the shadow of the direct function. Why don't we use the inverse function, as well as direct? ------------- I propose the concept of an unrelated function as extended concept of reverse function. ------------ There is a sum of intervals, on each of which the function is reversible (strictly monotonic) -nondegenerate function. ---------- For any sum of intervals, there is an interval where the function is an irreversible-degenerate function.
@ Vasiliy Knyshev ,
Kindly state and explain clearly the Newton's Second Law of the third order.
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It seems that when an element (let's say an infinitesimal 3D cube) on earth is not subject to applied forces, the assumed stresses in all dimensions are zero. Why don't we take the atmospheric pressure into account?
In the case of a material whose strength is dependant on the confining pressure, will ignoring atmospheric pressure give a false indication of its actual strength?
Atmospheric pressure is about 0.1 MPa, that is negligible when considering concrete for example, however, it could be significant to other applications.
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There are control strategies like LQR, Positionfeedback control, Negative velocity feedback control, etc.
Which one will provide better active control of vibration ?
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Normally, representative volume element (RVE) of the composite is independent of geometry. There are several homogenization methods available that defines regular shaped like rectangular, quadrilateral with inclusions of rectangular,circular,ellipsoidal, spherical shapes. Is there any analytical methods defined for irregular shaped RVE?
The basic assumption of RVE modeling is that the overall geometry is obtained by an infinite repetition of the RVE in all allowed (depending on specific BCs) directions. You need to tile (fill) the 2D (3D) space by infinitely repeating the RVE without gaps.
Thus, the RVE shape does not need to be regular per se, but it must be such that, when repeated infinite times, it fills the space without gaps. The simplest such geometries are the square, the rectangle and the hexagon. More are available, with different degrees of regularity (a term that should be better specified, we are using it with a quite vague meaning), and one has to look into the research on tessellations. It would be interesting to study how different patterns affect the calculated mechanical behavior. However, you cannot use arbitrary "irregular" shapes or even purely random geometries. It is not compatible with the homogenization method's assumptions.
Furthermore, geometries and size of RVE do affect the mechanical homogenized behavior, especially for composites (and any material with structure at multiple scales). The RVE should in theory be independent of geometry, but in practice you need to investigate which configuration is best to model the homogenized material.
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Hello everyone,
The strain energy of Abaqus neo-Hookean material is:
U = C10 * ( Ibar1 - 3 ) + ( 1 / D1 ) * ( Jel - 1 ) ^ 2
If D1 = 0, then stress values will become infinite. But, there are examples in Abaqus Documentation that D1 is assumed to be zero.
What happens when D1 is set to be zero in Abaqus neo-Hookean material?
Does it change the strain energy function to avoid infinite stress?
What does it mean when D1 is zero?
From Abaqus 6.13 Theory Guide, 4.6.1 Hyperelastic material behavior:
"The Di values determine the compressibility of the material: if all the Di are zero, the material is taken as fully incompressible. If D1=0, all Di 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 Di 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."
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I am doing quasi static and high strain rate compression and tension test but the yield value are different. Compression yield is grater than tensile yield. What is the reason behind it.
The above answer does not seem satisfactory. Indeed, strain hardening, which is due to an increase of the dislocation, will occur whatever the loading direction is (i.e. tension or compression).
In my opinion, the most likely explanation for this asymmetry is the impact of processing. Indeed, during the fabrication of your alloy, a significant amount of plastic deformation has been used for forming (e.g. extrusion, rolling). Because this plastic deformation result in strain hardening, the yield surface of your alloy has significantly been altered by processing. Strain hardening is usually directional (i.e. kinematic hardening), which means that the evolution of the yield strength is direction dependent. The consequence is that, because of processing-induced hardening, the compression and tensile yield strength are different.
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Eigenstrain reconstruction of residual strains in an additively manufactured and shot peened nickel superalloy compressor blade
E Salvati, AJG Lunt, S Ying, T Sui, HJ Zhang, C Heason, G Baxter, ...
Computer Methods in Applied Mechanics and Engineering 320, 335-351
Dear professor Korsunsky,
we are interested in residual stress evaluation in laser material deposition.
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Stress fracture is associated with significant morbidity, attrition, failure to complete training, failure to return to pre-injury level activity as well as increased likelihood of re-injury, specifically within military populations. Pathogenesis of stress fracture is multifactorial in nature. The incremental rate of progression in both volume and intensity of high impact physical activity leading to a breach the bones capacity to tolerate repetitively applied mechanical loading such that repair is exceeded by damage, however, the precise mechanisms are yet to be confirmed.
Stress fractures require some of the longest recovery times and is reported to range from three weeks to several months. The Professional, legal and moral responsibility to investigate causation, management and mitigation of these costly injuries are the property of both organisation and individual clinician.
Our stress fracture protocol consist of 4-6 weeks partial weight bearing, once pain subside, commence 3 phases Rehab programme. Therefore, I am inviting your opinion regarding effective stress fracture rehabilitation method to prevention as well as intervention to enhance bone healing process.
It is a very interested question
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