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ABOUT Work done by a pressure applied to a system

Submitted by Lianhua Ma on
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Work done by a pressure

I have one question  about work done by a pressure applied to a system.  The book of Thermodynamics often always present pdV (where dV is the change in the volume of the system. )but never Vdp, Why is that? Is it because we don't treat p as a variable? In a grand canonical ensemble is pressure constant for any system?

Acording to Thermodynamics first law,  du=dq-dw , where dw denotes work done by pressure and external force.  dw=pdv+dw' .   dq=Tds (Thermodynamics second law)

so, dU=TdS-Pdv-dw' 

2nd spatial derivatives from isoparameteric elements

Submitted by Wenbin Yu on
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Computational Mechanics Forum
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FEM

Based on my limited knowledge of FEM, I find it is difficult to use isoparametric elements for any problem whose governing
functional involve the second (or higher) partial derivatives of the unknown
functions. I hope some computational mechanicians can help me on this. Currently, I have a formulation derived from micropolar elasticity which has a functional involving second partial derivatives of the displacements. Thanks a lot for any of your suggestions.

Material model for high cycle fatigue

Submitted by Chali Alindunesiy on
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finite element analysis
Fatigue
numerical simulation

In fatigue analysis, it is common to use S-N curve from database for spesific material, and some time for spesific way of loading. Is there any way to predict fatigue from direct simulation? For example, giving cyclic loading (10^5 times) and the material will suffer damage and eventually failed. In some FEM codes (MARC, LSDYNA, etc) there is Lemaitre-Chaboche model used to analyze material behavior under low cycle cyclic loading.

 Thanks in advance

Chali

ABAQUS unit conversion for nanometer length.

Submitted by wanbot on
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Hi all,

I ran a pre-buckling analysis using ABAQUS.  I chose nanometer as my length unit. So for the Young's modulus, since my sample has 100 GPa for the Young's modulus, I put 0.0000001 as the value for the Young's modulus under the material property in the ABAQUS.

However, the resulted eigenvalue (~2 nN) was not as what I expected (~2uN). Based on the calculation based on the Euler buckling theory, the critical load should be around 2 uN. 

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