ANSYS非线性屈曲分析例子命令流.ppt

Buckling is the failure of columns and rods when under a compressive load. The rod/column/beam bends before the load reaches the materials yield point. Buckling occurs due to the structures imperfections. Beams Rods Columns Crankshafts Piston and Cylinders Synthetic bones and prosthetics. Any mechanism that undergoes compression Finite Element Analysis allows the Solution of buckling problems. The Column is divided into different nodes and a small preload is added. ANSYS offers 2 buckling modes, Eigenvalue (Linear) and a non-linear solution method. For this solution method, ANSYS uses the linear Eigenvalue method to solve for the buckling load. The Following is a command prompt used to run the Eigenvalue method on ANSYS. ANSYS can also produce non-linear results. This is done by using sub-stepped loads, to calculate the strains and getting a new Youngs Modulus with the given strain. An initial deformation is placed in the model, so that ANSYS may bend the model and simulate buckling (otherwise the load would show only compressive results). The next is a command prompt to input in ANSYS to produce the analysis. It is important to understand what the NLGEOM command does, and how it does it. This command allows ANSYS to engage in a non-linear elastic modeling of the beam. The first Equation is the Plastic strain equation: Where the super script “pl” represents the plastic strain, and “el” represents the linear strain, and n is the original strain. To calculate the linear strain the following equation is used: In the previous equation Represents the equivalent total strain measure and is calculated using the following equation: As can be seen in the equation, as the number of iterations are increased, the magnitude of the plastic deformation decreases (in a new iteration, the results for the plastic strain is used as the initial strain). The rate of the decrease also decreases with an increasing number of iterations, until the answer for the strain converges. This however does not take into account Non-linear Young modulus, and more complicated methods must be used in order to compute the stress-strain of a model with a non-linear Youngs modulus. ANSYS produces Favorable results for buckling Analysis. The non-linear Buckling analysis tends to give