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I googled this for a while from another perspective and it seems the problem is caused by the use of Green-Naghdi stress rate, which is not work-conjugate with any finite strain measure and, therefore, causes energy error depending on the problem at hand. I suspect that the first order accurate...

No damping. But I'm pretty sure that is not the problem in this case, since the S4R model and S4RS with second order accuracy give reasonable results. Besides, I think that damping would only have the same effect as plasticity: it would just dissipate the already erroneous energy, making it...

The energies present in this case are: -Kinetic energy -Elastic strain energy -Work done by external forces -Hourglass energy Hourglass energy is negligible and the mesh shows no signs of hourglassing. Kinetic energy and strain energy oscillate and their sum continues to increase. Therefore...

Okay, specifying second order accuracy in "element controls" section for S4RS elements solved the energy balance issue, although it had minimal effect on displacement results (<0.1%). I still don't understand why disabling second order accuracy leads to energy creation from nowhere instead of...

I am trying to compare different shell element formulations in Abaqus/Explicit and I stumbled upon an energy growth issue. Here are the specifics of my test case: -2m x 2m rectangular plate with 5mm thickness -Element size 0.1m x 0.1m (total of 400 elements) -All edges fixed (U1 = U2 = U3 = UR1...

"Concepts and Applications of Finite Element Analysis" by Robert D. Cook et al. It's a good book, one of the most recommended ones for FEM.

An extract from Cook's book: "In static analysis, symmetry of geometry, material properties, boundary conditions, and loads makes it possible to analyze part of a structure as representative of the whole. Symmetry can also be exploited in vibration analysis, but it is easy to overlook modes...

Hi, you are performing an explicit dynamic analysis(?). I got the same error message when I used Abaqus/Explicit. With me the problem was with the element time step. When I manually forced a too large time step, the solution failed to converge. I would suggest you to check your time stepping...

Hi, I am modeling a beam with trapezoidal section in Abaqus/CAE. The default number of integration points for this section is 5 x 5. Is it possible to change the number of integration points in CAE, and if it is possible then how can I do it? -henki

I remembered wrong, the displacements of the middle points in the two models were: -Pure shell model: 11.4mm -Stiffeners modelled as stringers: 8.7mm So the difference wasn't that great after all, but still the pure shell model gives approx. 35% higher displacement value. Is this something that...

Hi. I modelled a 500 x 500mm plate with fixed constraints in edges using ABAQUS/Cae. I included two T-beams (50 x 50mm) to the plate as stiffeners. In my first model I used only 4-node shell elements (in both the plate and the stiffeners). In my second model I included the stiffeners as...

corus, good point. Why didn't I think of that. I have to re-run some analyses. By the way, which one do analysts more use as a design guideline: stresses and strains in critical element nodal point or integration point (as the stresses are more accurate in the integration point)? For example...

Let's take an example. I modelled a 500 x 500 x 500mm steel box (only 1/8 of the box to save time) with a plate thickness of 5mm. An explosion occurs inside the box and the used material model is Johnson-Cook. I performed an explicit dynamic analysis using CalculiX, therefore the only acceptable...

Okay, now I understand. Thank you all for your answers! -henki

IRstuff, okay, now you got me confused. Are you sure you are not talking about implicit procedure? I was under the impression that in explicit analysis no iterations are performed, as the chosen timestep size is so small that the solution is assumed to converge by itself. Explicit method is...

Hi, are there any guidelines for element size/mesh density when performing impact/crash analysis? With plastic material behavior, the stresses do not grow infinitely as the mesh density is increased. However, sometimes very fine mesh is needed to obtain converged solution, which results in...

Drej, I calculated the time step for beam element using the equation that takes into account "I" and "A". The dimensions of the beam cross-section are: -width = 176.8mm -height = 7.1mm Now I haven't found anything of time step with beam elements from ABAQUS documentation, but I will now assume...

btrueblood, what do you mean with this: "i.e. is the matrix solved by decomposition or by direct inversion"? I thought that in explicit method no matrix conversion and equation solving is needed. What matrix do you mean? -henki

I agree, L / c is a gross value. I think the loading rate should also be considered when determining the time step, as the magnitude of the load can change substantially in small time. Also some other things could be considered. What I am trying to find out is that how do the explicit software...

Hi. As far as I know, the time step size in explicit dynamics depends on the characteristic length "L" of an element and the wave speed "c" as follows: delta_t = L / c. This is also explained in the following link: http://www.dynasupport.com/tutorial/ls-dyna-users-guide/time-step-size I have...