## General Mechanical

#### Load Multiplier in Nonlinear Buckling Analysis

• Nikke
Subscriber
Hi,I have a couple of questions regarding the load multiplier value in the nonlinear buckling analysis in Ansys Mechanical Eigenvalue Buckling analysis system.n1) What does it mean if I get a negative load multiplier in nonlinear buckling analysis? Might it mean that the loading should be applied to the opposite direction in order the structure to buckle?n2) According to Mechanical User's Guide section Eigenvalue Buckling Analysis, the nonlinear buckling analysis load multiplier works so that we take the initial pre-stress load which has been used in the static analysis and add to that the load multiplier value multiplied by the perturbation load used in the buckling analysis . So in other words the buckling force is F_BUCKLING = F_RESTART + λ_i · F_PERTRUB. How about such situation when my load multiplier is for example λ_i = -0.5 and F_RESTART = F_PERTURB = 1000 N? Does it mean that the critical buckling load for the structure would be half of the load in static structural i.e. F_BUCKLING = 1000 N - 0.5 * 1000 N = 500 N? With the same logic does it mean if λ_i = -3 then F_BUCKLING = 1000 N - 3 * 1000 N = -2000 N where negative sign means the loading in opposite direction?nThanks and looking forward for your answers,nNiklasn
• 1shan
Ansys Employee
Hello Array,nYes, a negative load factor means that loading should be in opposite direction. Also, if you are performing a non linear based eigen value buckling the loads that are to be reversed depend on whether the keep pre-stress load option is set to yes or no. If you read the documentation further you would find an example with a bullet point mentioning 'If you receive all negative buckling load factor values for your Eigenvalue Buckling analysis and you wish to see them in the positive values, or vice versa, reverse the direction of all of the loads you applied in the Static Structural analysis when the Keep Pre-Stress Load-Pattern property is set to Yes. If this property is set to No, reverse the direction of all of the loads that you applied in Eigenvalue Buckling analysis.nRegards,nIshan.n