Application of SFEM Method to Analyse Crack Parameters of Ultra High Molecular Weight Polyethylene Material (original) (raw)
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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.
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.
Polymer Testing, 2008
Fracture of Ultra High Molecular Weight Polyethylene (UHMWPE) components used in total joint replacements is a clinical concern. UHMWPE materials exhibits stable crack growth under static loading, therefore, their fracture resistance is generally characterized using the J-R curve. The multiple specimen method recommended by ASTM for evaluation of the J-R curve for polymers is time and material intensive. In this study, the applicability of a single specimen method based on load normalization to predict J-R curves of UHMWPE materials is evaluated. The normalization method involves determination of a deformation function. In this study, the J-R curves obtained using a power law based deformation function and the LMN curve based deformation function were compared. The results support the use of the power law based deformation function when using the single specimen approach to predict J-R curves for UHMWPE materials.
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, 2005
In this paper it is shown that the resistance to slow crack propagation in polyethylene can be predicted from a simple tensile measurement performed at 80 8C. It is shown that for different types of polyethylene homopolymers and copolymers the slope of a tensile curve above its natural draw ratio (i.e. strain hardening) correlates well with the measured stress crack resistance. The data presented in this paper confirm that the slow crack resistance in polyethylene is determined by the failure of the fibrils within the craze, which is shown to be determined by the strain hardening of a tensile curve. A material with a strong strain hardening will reduce the strain rate and consequently the time to failure will be strongly increased. Considering the fact that the slow crack resistance of polyethylene is usually assessed by tedious and time consuming testing methods performed on the notched samples in contact with specific fluids, the findings reported in this publication offer a possibility to assess the information on slow crack propagation in much simpler and faster way. q Polymer 46 (2005) 6369-6379 www.elsevier.com/locate/polymer 0032-3861/$ -see front matter q
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
Experimental and FE Modeling of Mixed-Mode Crack Initiation Angle in High Density Polyethylene
Periodica Polytechnica Mechanical Engineering, 2018
In this paper, an experimental and a numerical analysis were carried out using High density polyethylene (HDPE). Sheets with an initial central crack (CCT specimens) inclined with a given angle are investigated and compared to the loading direction. The kinking angle is experimentally predicted and numerically evaluated under mixed mode (I+II), as a function of the strain energy density (SED) around the crack-tip, using the Ansys Parametric Design Language (APDL).According to the experimental observations and numerical analysis, the plan of crack propagation is perpendicular to the loading direction. Moreover, as suggested by Sih in the framework of linear elastic fracture mechanics (LEFM), the minimum values Sminof the factor S are reached at the points corresponding to the crack propagation direction. These results suggest that the concept of the strain energy-density factor can be used as an indicator of the crack propagation direction.
Annales de Chimie - Science des Matériaux, 2020
In the present paper, we propose a numerical modeling of fracture behavior of High Density Polyethylene (HDPE) using different fracture mechanics approaches as well as a simulation of the static behavior by calibrating the static traction curves in order to highlight the feasibility of the model in reproducing the results of the EWF. The numerical determination of the fracture parameters by the global approach which will be validated by a simulation by means of DENT specimens and results obtained are compared to those of experimental results.
Crack layer analysis of nonmonotonic fatigue crack propagation in high density polyethylene
Polymer, 1987
The rate of fatigue crack propagation (FCP)in high density polyethylene (HDPE) is a nonmonotonic function of the energy release rate, a phenomenon previously noted for other semicrystalline polymers. Microscopic observations reveal a single craze-like active zone preceding the crack during the initial crack acceleration. Subsequently crack deceleration is associated with a circular active zone. Ultimate failure occurs by crack reacceleration preceded by large scale yielding through an elongated damage zone accompanied by large scale deformation. Thus, FCP involves two mechanisms: quasibrittle and ductile. The former dominates the initial acceleration regime and the latter dominates subsequent nonmonotonic crack propagation. This anomalous crack propagation behaviour is well described by the 'crack layer' (CL) theory according to which the specific enthalpy of damage for the brittle and ductile mechanisms are found to be about 0.1 and 1 cal/g, respectively.
Journal of Materials Science, 1986
Crack propagation in polycrystalline specimens is studied by means of a generalized finite element method with linear elastic isotropic grains and cohesive grain boundaries. The corresponding mode-I intergranular cracks are characterized using a grain boundary brittleness criterion that depends on cohesive law parameters and average grain boundary length. It is shown that load-displacement curves for specimens with the same microstructure and for various cohesive law parameters can be obtained from a master loaddisplacement curve by means of simple linear elastic fracture mechanics scaling relations. This property is a consequence of the independence of intergranular crack paths from cohesive law parameters. Perfect scaling is obtained for cases characterized by the same grain boundary brittleness number, irrespective of its value, whereas scaling is approximated for cases with differ