Non-linear Analysis Of The Coupling Interface Between Residual Limb And Compression/Release Stabilized Socket

Prosthetic act as a instrument used to replace the limb shape and the function of the limb,and the socket is the only bridge between the residual limb and prosthetic,which its quality directly affects the function of the prosthesis.Therefore,the study of the interface between the lower residual limb and socket was carried out to understand the stress distribution of the interface,which could help to provide great theoretical basis and practical significance for further optimization of the socket and improve the comfort.In this paper,the coupling interface between trans-tibial residual limb and compression/ release stabilized(CRS)socket was studied.The nonlinear finite element model of residual limb and socket was developed by reverse engineering and finite element method.The soft tissues was defined using the hyperelastic constitutive model,The effects of different hyperelastic constitutive parameters and poisson ratio on the surface stress of residual limb were compared;Through the interface stress,the influence of rectifications on the stress distribution of compression/release stabilized socket,then compared with patellar tendon bearing(PTB)socket;Five typical gait phases were used to calculate the stress variation of interface between residual limb and two kinds of socket.The main contents are as follows:1.Combined with the biomechanical properties of soft tissue,such as incompressible,heterogeneous and anisotropy,the nonlinear source of coupling interface between residual limb and socket was analyzed.Based on the incompressible mechanical properties of soft tissue,some constitutive equations of hyperelastic materials used in the finite element software are introduced,which provides a theoretical basis for guiding the subsequent finite element analysis.2.The nonlinear finite element model of residual limb and socket was developed by reverse engineering and finite element method.The Neo-Hookean model,the Mooney-Rivlin model and the three order polynomial model are used to define the soft tissue materials respectively.The difference of calculation results between linear elastic and the hyperelastic material parameters is discussed,and the effect of the poisson ratio on the surface stress of the residual limb is studied.As the poisson ratio increases,the maximum contact surface residual stress and shear stress were increased gradually.The results of the Neo-Hookean constitutive model at the Poisson’s ratio of 0.495 are similar to the reference literature,and the rationality of the finite element modeling of the coupling interface is verified.3.Based on the design principle,the CRS socket is used as the research object to investigate the effect of different rectifications on stress distribution of residual limb.Compared with the PTB socket,the normal stress of PTB socket is the largest,but the stress below residual limb was the smallest.When taking R07 model of CRS socket,the function transfer and comfort of socket can be well realized.4.By applying the load and torque of five typical phases in the gait cycle,the stress distribution and law of the contact interface between residual limb and socket during the walking process were calculated.The surface stresses of CRS and PTB display double-peak curve and reach the local peak at foot flat and the heel off.The mean values of stress at foot flat are compared with that of single leg standing.The stress status of the coupling interface between the limb and socket was studied in this paper,which provides the theoretical basis and reference value for the design and optimization of the structure of socket,as well as the establishment of an expert system for the rapid prototyping of socket.