Design And Study Of The Lifting Aid Bath Device Based On Extended Finite Element Method

The elderly and the disabled are in a certain proportion of the world's population, the disadvantaged group has a huge demand for rehabilitation services, including the need for bathing AIDS in the bath difficulties, which can assist personal mobile and bath by means of mechanical structure and motion .In this process, the bath AIDS will have stress,and after cyclic loading force, the mechanical structure will occur fatigue failure caused by fracture,then cracks will seriously affect the service life of the mechanism, and even endanger the safety of people, so it is very important to study the crack propagation and estimate the crack propagation life of the structure.At present, using the finite element method based on fracture mechanics to simulate and analyze cracks, the extended finite element method developed in recent years is a new method,which improved based on the traditional finite element method, it can solve complex problems such as the discontinuous problems,local deformation and fracture mechanics and so on . Its core idea is to use the shape function which is modified by the jump function and the crack tip displacement function to strengthen the traditional finite element shape function , in order to dispose of the discontinuous problem caused by cracks,and make the discontinuous field be completely independent of the mesh.It solved defects which are caused by figuring out the crack problems used finite element method, simplified the crack propagation analysis process and improved the accuracy of the analysis results.In this paper, based on the extended finite element method, we studied the production and propagation of the crack in the bath auxiliary lifting device due to fatigue in use process,the main research contents are as follows:First we introduced the extended finite element theory, the basic model of the fracture,the basic format of the extended finite element method based on partition of unity,the level set method,the structure of extended shape function, the J integral and stress intensity factor,and finally we introduced the fracture criterion of the crack.Then we did the simple design of the lifting device for bathing aids , determined to choose the ball screw as transmission, and according to the existing bathing bed and ergonomics principle, we confirmed the sizes and the lifting ranges of the supporting plate on lifting device , as the reference sizes to model.Then we did the simple design of the lifting device for bathing aids , determined to choose the ball screw as transmission, and according to the existing bathing bed and ergonomics principle, we confirmed the sizes and the lifting ranges of the supporting plate on lifting device , as the reference sizes to model.After the sizes are determined, we used ABAQUS software as the finite element analysis software, and established the model of bathing AIDS lifting device , then set the parameters of the material, steps,boundary conditions and loads, and meshed the model,after that,we submitted the job.We got the results to make sure the maximum stress value ,in order to determine the initial crack position. Then we created the initial crack and set the XFEM parameters to let the crack automatically extend.At last,we calculated the residual life of the model from generated the initial crack to completely fractured through the stress intensity factor.