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Questions tagged [solid-mechanics]

Studies the behavior of solid materials, and deformation under the action of forces

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33 views

Non-intuitive FEM simulation of a 4 point bend

I am conducting some finite element analyses of beams under 4 point bend mechanisms. The boundary conditions are set up such that there are 2 fixed locations, 2 displacement driven locations, and the ...
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1answer
33 views

Given co-ordinates of 8 vertices, how to calculate the outward normal and surface area for each face of a irregular hexahedron?

I am working on an FEA mesh of hexahedron elements. The elemental level calculations involve finding the surface normals and area for each surface of a hex element. I preferred the vector cross ...
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1answer
75 views

Is steady linear elasticity inherently ill-conditioned?

Compared to the transient PDE for linear elasticity, the steady equations appear to less well-conditioned. Are they inherently ill-conditioned without the transient term? The condition number for ...
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1answer
39 views

Strain from FEM simulations to strain gauge measurements

I am looking for some intuition in making comparisons of FEM simulations to experimental measurements. In particular, I am interested in comparisons to strain gauge readings, and perhaps even LVDTs. ...
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0answers
29 views

Is it possible to obtain a 'relaxing lengths' for 8 node hexaedral element

I am using 3D FEM with 8-node brick elements to model a certain type of growth/expansion, which is not a plastic deformation. First, I apply a pressure/load and I get displacement and the new position ...
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0answers
41 views

Thermal stress to displacement through finite volume method

I am attempting to solve for a displacement field where I know the thermal stresses on my discretized domain, which consists of hex cells. My first question is: is easier way to solve for the ...
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1answer
104 views

What is the difference between Abaqus and Calculix contact input?

I would like to say first that am new at using Calculix. I'm using Abaqus/CAE to create a cup deep drawing simulation and everything worked perfectly but my objective is to run the same exact ...
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1answer
57 views

Purpose of compatibility equations in linear elasticity

I have a vague understanding of the compatibility equations for linear elasticity. They appear to be necessary in obtaining a unique displacement field. However, why is it that, in my papers I've come ...
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29 views

Combining fluid flow solver based on lattice Boltzmann method with a mechanical deformation solver based on finite element method

I'm thinking to couple my fluid flow solver based on lattice Boltzmann method with a mechanical deformation solver based on finite element method to take account for solid deformation in my models. In ...
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0answers
85 views

What is the mathematical and physical principle behind of RBE2 element?

I am writing a 3d linear finite element code to solve the standard linear elasticity equation on a tetrahedron mesh of a gearbox. Notice that, the two rectangular plates above the gearbox are fixed, ...
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0answers
37 views

Simplest meaningful PDE/FEM calculation for mechanical stress due to heat

W have a complicated structure on which we do some FEM calculations regarding electrical potentials and heat distribution. The equations have the form $\nabla\kappa\nabla u = f + g\rvert_{N}$ where $...
3
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1answer
82 views

Why are the linear elasticity equations referred to as the “equilibrium” equations?

I asked this question previously on the physics board (LINK: https://physics.stackexchange.com/questions/404539/linear-elasticity-governing-equation), but I thought I'd post it here and see if anyone ...
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1answer
54 views

Modeling orthotropic materials with isotropic assumption

This is really a general question, but my interest is primarily for structural mechanics. Say you are modeling an elastic solid material that is orthotropic. You have the orthotropic properties (...
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0answers
75 views

Strange behavior when modeling deflection (e.g., cantilever) problems using linear elasticiy

I am observing some strange behavior in my code as I model deflection such as cantilever problems. I am using the linear elasticity equations with finite volume methods. I am attaching a figure at ...
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1answer
72 views

Boundary conditions in a four point bend test

I am looking into the four-point bend test, such as one in this YouTube video. Sample screenshot from the video illustrating the problem: I am a little confused as to how the loads are prescribed ...
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0answers
42 views

How does atmospheric pressure correspond to a traction BC for structural mechanics?

If you have some object that's just sitting on a table, some of its surfaces will be exposed to the ambient conditions, say at standard pressure and temperature. In computational modeling, would you ...
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1answer
81 views

Well-posedness of linear elasticity boundary conditions

I have several questions regarding suitable boundary conditions for linear elasticity. I have read that in order for modeling linear elasticity to be well-posed, the entire boundary cannot be ...
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1answer
93 views

Are mixed boundary conditions possible in structural mechanics?

For structural mechanics, such as linear elasticity, I am aware of BCs such as a prescribed displacement (Dirichlet) or a prescribed traction (Neumann). Is it possible that a boundary can have a ...
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2answers
985 views

How does one calculate reaction force in FEA?

I wrote a UEL (User Element in Abaqus) for one element and compared to a reference UEL which used standard FEM, where the results agreed satisfactorily, except the reaction force. The stress, strain, ...
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1answer
73 views

Structural mechanics simulation using FLUENT compared to analytical solution

This is a continuation of my previous post, 1D analytical solution vs FEM solution for a bar under compression. For some reason, I cannot comment in it. The analytical solution to the 1-D static ...
2
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1answer
124 views

1D analytical solution vs FEM solution for a bar under compression

I simulated the compression problem in ANSYS and compared to the analytical solution and found some discrepancies. The classical solution to the 1-D compression problem is: \begin{align} u(x) = Cx ...
3
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1answer
220 views

Traction -> stress; stress->displacement gradient

If given a displacement gradient tensor, we can easily obtain the stress tensor (using Hooke's law and the strain-displacement relationship), as well as the traction vector. If given a traction, and ...
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1answer
165 views

Can we simulate rigid body motion using finite element analysis?

I was wondering if we could model rigid body motion of bodies using finite element models. Particularly I'm interested to know if we can model motion of objects with no constraints or with some ...
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1answer
57 views

Simulation of a complicated projectile motion

I'm trying to model a projectile motion, considering every detail such as projectile aerodynamics, effects of wind, air temperature etc. What is a good software to model it in with good graphics? I ...
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0answers
54 views

Discretization used for steady linear elasticity - followup to previous question

This is a follow-up of my previous scicomp question (https://scicomp.stackexchange.com/posts/28863/edit). I figured I'd start a new thread on this as the question is a bit different from my previous ...
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0answers
112 views

Solving linear elasticity equations for a cantilever problem

Has anyone successfully used the linear elasticity equations to model a cantilever problem? The equation I am solving is simply: $$\nabla \cdot \boldsymbol{\sigma} = 0$$ subject to boundary ...
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1answer
763 views

Structural mechanics - traction free = Zero displacement gradient?

This is a follow up question to my question yesterday Structural mechanics traction boundary condition question Does a traction free boundary condition also mean that the displacement gradient is 0 ...
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0answers
143 views

Structural mechanics traction boundary condition question

In structural mechanics, are the boundary conditions "free surface," "Traction free", "stress free" all equivalent Neumann boundary conditions?
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1answer
119 views

stiffness matrix for 3D regular grid in FEM

I have understood the stiffness matrix for 3D truss, and programmed Ku=f from scratch (in Java) to find the displacements. Then I moved to 3D solid but lost in too many concepts and equations, such ...
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1answer
328 views

Finite Element Analysis for Laminated Plates with Holes or Patches

As the title says, I am trying to code in FEM a plate structure that either has a hole in one of the layers or one of the layers is made of patches of plates, rather than one whole plate. However, ...
3
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0answers
81 views

Piecewise Constant Enrichment of the continuous galerkin method

I am interested to study crack propagation in a hyperelastic material in a variational setting. The crack surface exhibits a jump discontinuity. The function space for displacement field should ...
4
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1answer
157 views

Initialize arc length control in Riks' method

I'm trying to use Riks' method and I'm not sure how to set the initial values for the loading coefficient, nor the tangent vector (i.e. the derivative of the displacements and loading coefficient with ...
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0answers
157 views

Solution to 1D consolidation problem python implementation

A solution to the 1D consolidation problem is given by $$\frac{\partial}{\partial t} p = c_{v} \frac{\partial^{2}}{\partial y^{2}} p$$ where $p$ is the pore water pressure, $c_v$ is the ...
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1answer
105 views

How to determine if Kelvin-Voigt elements are dissipating stress correctly?

I am using a program that creates viscous/absorbing boundaries by implementing Kelvin-Voigt elements. The theory behind 1-D Kelvin Voigt elements is given in this Wikipedia page. In my case I am ...
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1answer
117 views

Euler-Bernoulli beam element versus continuum beam element

I am using OpenSees to model a simply supported beam with a point load in the middle. The model is in consistent units. The beam is made up of bilinear quad elements. I have used 30 elements along the ...
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1answer
55 views

Dynamic Analysis and Visualization of Laminate Mindlin Plate

I am trying to make the jump from a FEM plot of a static load applied to Mindlin laminate plate to a surface visualization of various Mode Shapes of the Laminate Plate. For that, I understand that the ...
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1answer
124 views

Well-posedness of Elasticity Boundary Conditions

For geotechnical engineering problems, it is common to fix a single component of displacement along a boundary as a Dirichlet boundary condition (roller boundary condition). However, I'm having ...
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0answers
65 views

Modelling fracture flow in stress field in COMSOL [closed]

I am new to COMSOL and I want to model fluid flow in stress field. As starting point I want a simple 2D box having a fracture from right to left while pressure gradient vertically. I want to know the ...
3
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1answer
109 views

Extracting system matrices from FEM software

I work in the field of Finite Element Methods, specifically, developing algorithms to speed up the computational time in structural mechanics problems. Till now I have been developing my code in ...
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2answers
217 views

Time step relationship with number of elements or material properties

When looking at the output file of my solver, I have been told that the time-step taken by the solver depends on parameters like the total number of elements and their relative size in my geometry, or ...
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2answers
223 views

Why does the displacement have to be small to use the infintesimal strain elasticity equations?

In all the sources I have that discuss the elasticity equations, they start by saying that the strain tensor, $\epsilon$, is related to the displacement gradient, $\nabla u$, where $u$ is the (vector ...
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2answers
409 views

Derivative of the inverse of the Right Cauchy-Green Deformation Tensor wrt itself

In continuum mechanics, we define the Right-Cauchy-Green Deformation Tensor as $\boldsymbol{C}=\boldsymbol{F}^T\boldsymbol{F}$ I want to compute $\frac{\partial \boldsymbol{C}^{-1}}{\partial \...
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1answer
96 views

Damping for Dynamic Problem using FEM

I came across this form of damping implemented in an elastodynamics problem. The stress tensor without the damping would look like: $ \sigma = 2 \mu \epsilon + (\lambda \, \text{tr} (\epsilon)) I $ ...
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1answer
102 views

How to use non-dimensional form in open source codes instead of Units

I am using an open source FEM platform, which requires you to convert your equation system to non-dimensional form. So, there are no units specified for the parameters in the problem. If you use ...
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2answers
752 views

Developing a C++ solid mechanics program

I am a beginner in computational science and programming. I am doing research in non linear solid mechanics analysis and using C++ for coding. I have been exploring various finite element open source ...
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3answers
198 views

Stability criterion for waves in anisotropic solids

The equations of motion for an elastic solid are given by $$\begin{align} &\nabla \cdot \boldsymbol{\sigma} + \mathbf{f} = \rho \ddot{\mathbf{u}}\\ &\boldsymbol{\sigma} = \mathbb{C}\...
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1answer
154 views

Buckling reference using the FEM

I want to analyze buckling in a composite using the FEM. So far I have studied this references Zdenek P Bazant, Luigi Cedolin. Stability of Structures: Elastic, Inelastic, Fracture and Damage ...
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3answers
719 views

Help choose Finite Elements (FEM) software for elastic, multi body system!

I would appreciate help choosing a software for the Finite Elements Method (FEM). I wish to model items like ropes, bull whips and fishing rods. (I intend to transfer the model into bio-mechanics, ...