Topology Optimization Algorithms Of Compliant Mechanisms With Geometrical Nonlinearity And The Design Of Typical Compliant Mechanisms Undergoing Large Displacements

There are many compliant mechanisms undergoing large displacements.They includes bistable mechanisms,energy-absorbing mechanisms,constant-force mechanisms and energy harvesters.These compliant mechanisms have a wide range of applications in biomedical,microelectromechanical systems,and aerospace.However,most studies about the compliant mechanisms undergoing large displacements only focus on the relation between size parameters and performances.Few studies proposed new topology of the compliant mechanisms undergoing large displacements.This study designs compliant mechanisms undergoing large displacements by topology optimization.First,the instabilities in topology optimization considering geometric nonlinearity are studied.A self-adapting time step method is proposed to decide the step size in Total Lagrangian method.An energy interpolation algorithm is proposed to avoid the oscillation in low-density elements.The numerical examples are given to validate the methods.In addition,for the topology optimization of fusiform muscle,it is also necessary to use the improved constitutive model to aviod the instabilities in intermediate density elements.Second,commercial finite element analysis software is utilized to improve the speed.For excessive deformations in low stiffness regions,an additive hyperelasticity algorithm is presented.For the difficulty of sensitivity extraction from commercial software,an approximate expression of the sensitivity is proposed,which greatly reduces the amount of extracted data when calculating the sensitivity.An ANSYS-aided geometrically nonlinear topology optimization algorithm is presented.The algorithm is valided by the minimum compliance problem and the inverter design problem.In addition,a reanalysis algorithm for acceleration is proposed.Third,a bistable compliant mechanism is designed using topology optimization.Considering the contradiction between the space occupied by the bistable compliant mechanism and its robustness to the external forces,the difference between the switching forces is maximized in a given size.Geometric constraints of the minimum length scale in topology optimization are employed to reduce the requirement on fabrication.An approximate expression of the sensitivity is deduced to obtain the derivatives from ANSYS.The experimental studies indicate that the optimized mechanism is more stable than the conventional mechanisms based on straight beams or preshaped curved beams.Last,buckling-induced energy-absorbing mechanisms are designed using topology optimization.Considering the contradiction between the mass and the dissipated energy of the unit cells,the dissipated energy is maximized in a given mass.A two-phase algorithm is proposed to find the optimized result from a uniform initial guess.A minimun post-buckling force constraint is added to design the self-recoverable energy-absorbing mechanisms.The high-energyabsorption unit cells,high-usage-ratio unit cells and the self-recoverable unit cells are designed resprctively.The optimized unit cell absorbs more energy than the conventional unit cells.The experimental studies validate the accuracy of the finite element simulations.