The Study Of Creep And Ratcheting Behavior Of HA/UHMWPE Composite

Ultra-high molecular weight polyethylene(UHMWPE)has been successfully used as a bearing material in prosthetic replacement for joint for over five decades,owing to its unique mechanical properties.While the weakness of the artificial joint friction pairs result in some problems during clinical application,such as delamination,cracking and loosening,which will affect its service life.In this study,0,5,10 and 20 wt.% hydroxyapatite(HA)and UHMWPE powders were homogeneously compounded and consolidated under hot press,then a series of mechanical tests were conducted to investigate the contribution of HA particles to the mechanical properties of UHMWPE matrix.Results showed that the hardness and Young's modulus of composites increase with the addition of HA content,while the tensile strength and elongation at break have an apparent reduction.Combined with SEM,it was found that the HA particles are uniformly distributed in the UHMWPE matrix and inhibit the movement of the polymer chains,the existence of micro cracks will lead to premature rupture of the specimen.The creep and recovery tests of HA/UHMWPE composites revealed that the creep strain and residual strain of specimens increase with stress and reduce with the content of HA.To quantitative analysis the effect of HA particles on the elastic,viscoelastic and viscoplastic properties of UHMWPE,the Findley model,Burgers model and Weibull distribute function were employed here.And these analytical models were applicable for the creep prediction of the samples.To investigate the cyclic mechanical behavior of UHMWPE,the ratcheting effect under different stress amplitude and rate and HA content were studied and predicted by the ratcheting model.Otherwise,a cross tensile specimen was designed,and the in-plane biaxial tensile ratcheting tests were carried out.The results showed that the modified model can significantly predict the uniaxial ratcheting behaviors,and during the biaxial loading,at each loading path,the specimen have obvious plastic strain accumulation phenomenon in the two directions,because the influence of load waveform,phase,loading rate and peak holding time,samples show different ratcheting accumulate strain and strain rate.