Critical assessment of methods for evaluatingJ_ICfor a medical grade ultra high molecular weight polyethylene

Abstract

Various methods for the evaluation of the critical J-integral Jfc based on the standard ASTM E813-89 are analyzed by conducting investigations on a ductile medical grade ultra high molecular weight polyethylene (UHMW-PE) at room temperature. Differences in Jfc reaching almost 50% were recorded between the methods investigated. The controversy surrounding the construction of the crack blunting line is discussed in terms of the stretch zone width together with the size requirements of ASTM E813-89. The findings of this investigation suggest that an R-curve construction based on mid-thickness crack growth and ultimate tensile strength (UTS) combined with a blunting line of slope m = 2 and modified exclusion lines provides consistent and conservative Jfc values. Using this technique, a near plane strain value, smaller than previously published data, of 66.5 kJ/m2 was obtained at 23°C.

Evaluation of J-initiation fracture toughness of ultra-high-molecular-weight polyethylene used in total joint replacements

“…The applicability of the blunting line approach depends on: 1) the fitting method; 2) the exclusion lines and; 3) the slope and stress value used to define the blunting line. Pascaud et al [7] justified the validity of equation 3 for a UHMWPE material based on observations of the stretch zone caused by blunting of the crack tip. However, it may not always be straightforward to identify the stretch zone from the fracture surface.…”

“…The blunting line relationship is given by $$J=m{\sigma }_Y\mathrm{\Delta }a$$ where, m is the slope of the blunting line, σ Y is the effective yield strength (an assumed value of uniaxial yield strength that represents the influence of plastic yielding upon fracture test parameters), and Δ a is the crack extension. For tough polymers, equation 1 may overestimate the crack extension associated with crack tip blunting [7]. Therefore, for UHMWPE, a blunting line relationship based on ultimate tensile stress was recommended by Rimnac et al [1].…”

“…Based on stretch zone width measurements following the procedure recommended by Kobayashi et al [8], Pascaud et al [7] recommended the use of a blunting line for UHMWPE that utilized ultimate tensile strength [1] and maximum crack extension with a slope, m = 2: $$J=2(\mathit{\text{UTS}})\mathrm{\Delta }{a}_{\text{max}}$$ This recommendation was based on experiments conducted on one UHMWPE formulation (as-received, ram extruded Hostalen GUR 4150-HP, Westlake plastics, Lenni, PA) tested in ambient air conditions.…”

Compósito de resina poliuretano derivada de óleo de mamona e fibras vegetais

“…Este problema foi abordado por Hashemi e Williams (1986), Huang (1991) e Pascaud et al (1997). De um modo geral, houve um consenso de que muito dos detalhes experimentais aplicados aos materiais metálicos, parecem prover resultados satisfatórios, como o uso de entalhes laterais nos corpos de prova, por exemplo, para aproximar a condição de deformação plana.…”

“…Para as dimensões do corpo de prova utilizadas neste trabalho, este valor foi de 0,8mm. Na curva J-R apresentada, este limite foi um pouco excedido, mas isto não compromete a validade da curva pois este limite é por demais conservativo (Huang, 1991), (Pascaud et al, 1997). Com relação ao valor J máx , a norma ASTM D6068-96 não faz nenhuma referência.…”