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Zachary Liu
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Hi, if I'm using the 3d element, I'm wondering how to detect the tensil and compression for a known stress state? the hydrostatic pressure p has been used before, but i don't think it is correct to all the cases.
Emreth said:Can you elaborate more on what you are trying to do?So you're running finite element analysis(3d element?) or you're referring to something else?
Basically, if you know the stress state, you still need to define an orientation to find stresses; stress is a tensor, it varies with angles. After that, use a 3d mohr circle to calculate them at any orientation. Positive means tensile, negative means compressive.
Emreth said:Wikipedia?
http://en.wikipedia.org/wiki/Stress_(mechanics )
From your stress state, find the principal stresses and then calculate 3d mohr circle, its there in wiki. Like i said, positive values mean tensile, negative means compressive.
Brian_C said:No offense, but you should already know Mohr's circle like the back of your hand if you're doing any kind of structural analysis. This is really basic stuff.
Emreth said:Ok i'll give this one more try. Previous post is not a calculation example, you don't really calculate, just assume stresses.
Say you have those as your principal stresses, they are all negative. As you change the orientation, shear stresses will appear within the planes along that orientation.(look at the stress transformation in wiki) Wherever you have the largest shear will be your failure point since materials don't fail under compression, as long as stresses are not equal, you'll always get some shear along some directions. Now, if the three princ. stresses are not just all negative but also equal, you'll get pure hydrostatic stress state where you won't have any shear stresses in any direction and the mohr circle becomes a point. You cannot have failure in that case.
Studiot said:One of the big problems that ground engineers and scientists face is that the properties of ground materials, including the ice you mentioned, vary greatly with the applied stress.
Since bulk material in the real world can be very big bulks the interior of such a mass can have significantly different properties from the outer layers.
Ice does not have the pore fluid of normal soils, but often has entrained air. This air causes slip weakness to shear.
Further real world ice often overlies weaker material such as water, whereas normally encountered soils usually overlie stronger harder materials.
The foundation is as always all important.
Studiot said:What I don't know is whether you are trying to develop your model for laboratory test specimens or bulk material mass.
You did quote a result from the Mohr-Coulomb yield function.
Do you understand the derivation of this and the way yield functions (which is what you seek) are built up?
A 3D element uses mathematical equations and algorithms to calculate the tensile and compression forces within a material. These equations are based on the material's mechanical properties and the applied loads.
3D elements can be used to test a wide range of materials including metals, plastics, composites, and even biological tissues. As long as the material can be modeled accurately, it can be tested using 3D elements.
While 3D elements are a powerful tool for testing materials, they do have some limitations. They may not be suitable for highly nonlinear materials or materials with complex microstructures. Additionally, the results may not be accurate if the model is not properly calibrated or if the element size is too large.
The results from a 3D element analysis will typically include stress and strain values, as well as displacement and strain energy. These values can be compared to the material's yield strength and other mechanical properties to determine if it can withstand the applied loads without failing.
Some tips for using 3D elements include properly calibrating the model, using a fine enough mesh to capture the material's behavior, and verifying the results with experimental data. It is also important to consider the boundary conditions and loading conditions to accurately simulate real-world scenarios.