Static fracture resistance of ultra high molecular weight polyethylene using the single specimen normalization method (original) (raw)
Related papers
2008
Fracture of ultra high molecular weight polyethylene (UHMWPE) total joint replacement components is a clinical concern. Thus, it is important to characterize the fracture resistance of UHMWPE. To determine J-initiation fracture toughness (J Q) for metals and metallic alloys, ASTM E1820 recommends a procedure based on an empirical crack blunting line. This approach has been found to overestimate the initiation toughness of tough polymers like UHMWPE. Therefore, in this study, a novel experimental approach based on crack tip opening displacement (CTOD) was utilized to evaluate J Q of UHMWPE materials. J-initiation fracture toughness was experimentally measured in ambient air and a physiologically-relevant 37°C PBS environment for three different formulations of UHMWPE and compared to the blunting line approach. The CTOD method was found to provide J Q values comparable to the blunting line approach for the UHMWPE materials and environments examined in this study. The CTOD method used in this study is based on experimental observation and, thus, does not rely on an empirical relationship or fracture surface measurements. Therefore, determining J Q using the experimentally based CTOD method proposed in this study may be a more reliable approach for UHMWPE and other tough polymers than the blunting line approach.
This paper presents a cohesive methodology for quantifying the fracture behavior of structural polymers. We accomplish this task by reviewing the complexities of polymer fracture mechanics and associated J-integral fracture toughness testing as well as by conducting appropriate nonlinear-elastic fracture mechanics measurements with comprehensive analysis. J-based crack-initiation and crack-growth fracture toughness testing is performed on ten clinically relevant formulations of ultra-high molecular weight polyethylene (UHMWPE). This polymer is chosen for its extensive literature base in terms of its mechanical properties and fracture toughness behavior, as well as its safety-critical importance and broad use in total joint replacements. One of the current limitations in the fracture toughness characterization of polymers is the use of " engineering " constitutive behavior to determine the crack-initiation toughness, as compared with the " true " constitutive properties. UHMWPE offers a plethora of true tensile stress-strain data that serves as a template and predicate base for fracture analysis. This paper aims to demonstrate why using true stress-strain behavior for polymer fracture mechanics is so important and why a justified comprehensive analysis method is needed in order to reliably measure the fracture toughness of polymeric materials.
Polymer Engineering & Science, 2007
Deformation and fracture toughness of high-density polyethylene (HDPE) in plane-stress tension was studied using the concept of essential work of fracture (EWF). Strain range for necking was determined from uniaxial tensile test, and was used to explain the deformation transition for 2-staged crack growth in doubleedge-notched tensile test. Through work-partitioning, EWF values for HDPE were determined for each stage of the crack growth. Appropriateness of these EWF values to represent the material toughness is discussed. The study concludes that the EWF values for ductile polymers like HDPE may not be constant, but vary with the deformation behaviour involved in the crack growth process.
Biomaterials, 2005
Medical grade ultra high molecular weight polyethylene (UHMWPE) has been used as the bearing surface of total joint replacements for over four decades. These polymeric devices are susceptible to accumulated cyclic damage in vivo. Wear debris formation that ultimately leads to a need for revision surgery is linked to the plasticity, fatigue and fracture mechanisms of UHMWPE. This paper examines the deformation, yielding, fracture and fatigue behavior of conventional and highly cross-linked medical grade UHMWPE. Such properties play an important role in determining the long-term success of orthopedic devices. The mechanical properties discussed include the deformation behavior of UHMWPE, the yielding associated with quasi-static tension and compression, fracture toughness, cyclic loading, and fatigue resistance.
Biomaterials, 2006
Ultra High Molecular Weight Polyethylene (UHMWPE) total joint replacement components under certain conditions are at risk of fatigue fracture. Thus, the fatigue crack inception/propagation resistance of UHMWPE is of interest. During fatigue crack propagation tests of UHMWPE, crack growth is often followed visually; however, this approach can be time consuming and requires that the specimen be accessible during testing. The objective of this study was to demonstrate the applicability of the compliance method for fatigue crack propagation tests of UHMWPE. We hypothesized that the standard calibration coefficients developed for metals may not be appropriate for UHMWPE and that different UHMWPE materials would require different compliance calibration coefficients. Three UHMWPE materials: sterilized (30 kGy); highly crosslinked and annealed (100 kGy, 130 1C); and highly crosslinked and remelted (100 kGy, 150 1C) were examined under ambient conditions. The results support the applicability of the compliance method for determination of crack length during fatigue crack propagation testing of UHMWPE. As hypothesized, the standard calibration coefficients were found to be inaccurate for UHMWPE. New UHMWPE-specific calibration coefficients were determined which predicted the crack growth behavior accurately. Also, as hypothesized, the compliance calibration coefficients for the three materials were significantly different. This is the first reported study to demonstrate the applicability of a compliance method to measure crack length in UHMWPE. r
Icf11 Italy 2005, 2013
This work examines the role of microstructure on the fatigue and fracture properties of ultra high molecular weight polyethylene (UHMWPE). The aim of this work is to develop optimized microstructures that provide both fatigue and wear resistance for implant applications. Recent studies have shown that bulk cross-linking improves the wear resistance of UHMWPE. However, cross-linking degrades fracture properties such as ultimate tensile stress and strain, Jintegral fracture toughness and fatigue crack propagation resistance. One problem with bulk cross-linking is that they employ a melting process. Recrystallization after melting is obtained without any application of pressure and results in a decrease in crystallinity and concomitant mechanical properties. Crystallinity can be restored with the utilization of to utilize high-pressure crystallization on the cross-linked UHMWPE. High crystalline PE has been shown to have a substantial increase in fracture and fatigue crack propagation resistance. This work examines the coupled effects of cross-linking and enhanced crystallinity via high-pressure methods to improve the mechanical properties of UHMWPE. The role of various microstructures on the fatigue and fracture properties are examined and discussed in the context of total joint replacement design.
Journal of Biomedical Materials Research Part B: Applied Biomaterials, 2012
Ultra high molecular weight polyethylene (UHMWPE) has been successfully used as a bearing material in total joint replacement components. However, these bearing materials can fail as a result of in vivo static and cyclic loads. Crack propagation behavior in this material has been considered using the Paris relationship which relates fatigue crack growth rate, da/dN (mm/cycle) versus the stress intensity factor range, K (K max-K min , MPa√m). However, recent work suggests that the crack propagation velocity of conventional UHMWPE is driven by the peak stress intensity (K max), not K. The hypothesis of this study is that the crack propagation velocity of highly crosslinked and remelted UHMWPE is also driven by the peak stress intensity, K max , during cyclic loading, rather than by K. To test this hypothesis, two highly crosslinked (65 kGy and 100 kGy) and remelted UHMWPE materials were examined. Frequency, waveform and Rratio were varied between test conditions to determine the governing factor for fatigue crack propagation. It was found that the crack propagation velocity in crosslinked UHMWPE is also driven by K max and not K, and is dependent on loading waveform and frequency in a predictable quasi-static manner. The current study supports that crack growth in crosslinked UHMWPE materials, even under cyclic loading conditions, can be described by a relationship between the velocity of crack growth, da/dt and the peak stress intensity, K max. The findings suggest that stable crack propagation can occur as a result of static loading only and this should be taken into consideration in design of UHMWPE total joint replacement components.
Journal of Polymer Science Part B-polymer Physics, 1996
Load separation is the theoretical basis for the single-specimen J-integral experiment and the incremental calculation of J-integral crack growth resistance (J-R) curves. This criterion has been experimentally studied in nongrowing crack records in several materials, and more recently a new method to extend the applicability to growing crack experiments has been proposed in testing steel. This article examines the applicability of the load separation criterion for evaluating ductile fracture mechanics parameters in rubber-modified polystyrenes and thermally treated polypropylene in the bending configuration. This criterion allows the load to be represented as the multiplication of two independent functions: a material deformation function and a crack geometry function. Its validity is evaluated with both stationary and growing crack experiments. q-factor calculation for smooth and sidegrooved specimens was also tried using the simple method of Sharobeam and Landes, in order to identify material dependency. This article also investigates the applicability of the normalization method, based on the load separation criterion for evaluating J-R curves on PP and PS. A simple approach which combines a blunt notched and a precracked specimen experiment is proposed to determine the J -R curve of the materials studied. The resulting J -R curves are compared with multiple specimen results available in the literature for these materials. A good agreement between the J -R curves obtained from this simple method and from the multiple specimen technique was found. 0 1996 John Wiley & Sons, Inc. periment for different configurations where the remaining ligament, b = Wa is the only significant length parameter.
International Journal of Applied and Structural Mechanics, 2023
The application of numerical methods, today occupies a much needed place for modeling, and for finding solutions to any problem related to fatigue and damage to materials. This article deals numerically with the evolution of the stress intensity factor and the integral of the contour J in I mode, of an initial rectilinear crack of languor a=0.7, 1.4, 2.1, 2.8 and 3.5mm, with different ratio, a/w=0.1, 0.2, 0.3, 0.4 and 0.5mm. By the stretching finite element method (SFEM) of the (UHMWPE) Ultra High Molecular Weight Polyethylene material. On the other hand, the creation of the parametric mesh based on the computer language (FORTRAN) and to create a model of the square crack front with 5 contours of size L=1mm. In addition, the simulation was done by Abaqus 16.3.1 code. The maximal circumferential stress criterion MCSC were applied. Other materials like Alu20-17 and Steel XC65-90 were used to make the comparison. Crack parameters, such as stress intensity factors KI, KII and J-contour integral were evaluated. The results obtained in our work have justified that there is proportionality between the three materials.
Biomaterials, 2003
Highly crosslinked UHMWPEs have demonstrated improved in vitro wear properties; however, there is concern regarding loss of fracture resistance and ductility. The goals of this study were to evaluate the micromechanisms of failure under uniaxial tension and to determine the effect of gamma radiation-induced crosslinking and post-irradiation thermal processing on the estimated fracture toughness (K c) of UHMWPE. K c was estimated for two conventional and two highly crosslinked UHMWPE materials from tensile tests. A 32% decrease in K c was found following crosslinking at 100 kGy. The highly crosslinked materials also exhibited less ductile fracture behavior. K c was slightly dependent on displacement rate but was insensitive to changes in crystallinity (and thus, to thermal processing). The same basic failure mechanism, microvoid nucleation and slow coalescence followed by comparatively rapid fracture after the defect reached a critical size, was observed for all of the conventional and highly crosslinked UHMWPE specimens. These observations will be used in the development of a theoretical failure model for highly crosslinked UHMWPE, which, in conjunction with a validated constitutive model, will provide the tools for predicting the risk of failure in orthopaedic components, fabricated from these new orthopaedic bearing materials.