Viscoelastic Behaviors of Ultrahigh Molecular Weight Polyethylene Under Three-Point Bending and Indentation Loading

Abstract

Dynamic mechanical properties under three-point bending and deformation behavior under indentation loading of an ultrahigh molecular weight polyethylene (UHMWPE) were investigated in this study. Dependence of its viscoelastic properties on temperature, frequency, load level, specimen geometry and heating rates were examined. The results showed that temperature and frequency had significant effects on the response of UHMWPE to the dynamic load. With the increase in temperature, the storage modulus (E') was decreased and the loss angle (tan delta) was increased, indicating an increase in the trend in viscoelastic response of the polymer at high temperature. On the other hand, when frequency was increased, higher E' and lower tan delta were observed, suggesting that the material behaved more elastically. While the two heating rates of 5 degrees C/min and 10 degrees C/min had little effect on E' and tan delta, the load level significantly influenced the dynamic mechanical properties of the polymer. UHMWPE showed quite different responses at 0.5 and 20 Hz than at 1-10 Hz, which is worth further investigation. The results from indentation experiment showed that temperature, specimen geometry and load level had significant effects on the response of UHMWPE to the indentation load. With the increase in temperature, the penetration depth was increased, indicating an increase in the deformation trend in the polymer at high temperature. High load led to high penetration. The time-temperature superposition (TTS) method could be used to predict the long-term penetration behaviors of the polymer. From TTS analysis, the activation energy associated with penetration deformation was obtained. Further analysis showed that it might be possible to increase the resistance of UHMEPE to indentation deformation by increasing the thickness and/or decreasing the diameter of the polymer samples.

Ultra High Molecular Weight Polyethylene and its Reinforcement with Carbon Nanotubes in Medical Devices

“…Within certain limits, it was shown that UHMWPE is a thermorheologically simple material (Guedes [2011a]). Remarkably, not many published papers are devoted to study the viscoelastic behavior of UHMWPE (Deng [2010]). However this is an important subject since the components are mounted with tight tolerances and UHMWPE excessive creep limits the long-term survival of TJA (Deng [1998]).…”

“…In this context, the constitutive equations are necessary to calculate the stress and strain under prescribed boundary and loading conditions. UHMWPE has a viscoelastic nature, as any polymer, that can be described by simple models (Deng [2010], Guedes [2011a]). …”

Transient viscoelastic lubrication analyses of UHMWPE hip replacements

“…In order to understand the effects of the retardation time ( ) and mechanical loss factor (the ratio of loss and storage modulus, E1/E2), a wide range of variations (4 s to 100 s for and 0.1 to 0.25 for E1/E2), which were all within a previous experimental test [2], were investigated. When the effect of the retardation time was investigated, mechanical loss factor was kept as a constant (0.14).…”

“…Moreover, viscoelastic materials are also widely used in biomedical devices, such as the ultra high molecular weight polyethylene (UHMWPE) in low modulus artificial hip replacements. The deformation process of soft viscoelastic materials, such as polymers and elastomers, may display significant time lags and the viscoelastic effect may have to be considered in tribological analyses [1,2]. However, due to the complexity of the tribological systems and the time-dependent properties of the materials, it is difficult to include the realistic mechanical behavior of the viscoelastic materials in a lubrication analysis, which intends to predict the pressure distribution and lubricant film thickness of a lubricated system.…”

Determination of Asphalt Binder Creep Compliance Using Depth-Sensing Indentation

“…The indentation technique was initially applied to determine the hardness and Young's modulus of timeindependent elastic materials [5][6][7][8], and it has been used more recently to characterize viscoelastic behavior of polymers and other time-dependent materials [9][10][11][12][13][14][15][16][17]. Lee and Radok [18] obtained expressions for the load and penetration during the spherical indentation of a linear viscoelastic material by replacing the elastic modulus in the classical Hertz solution [19] with a hereditary integral.…”