Fracture properties of an acrylic bone cement (original) (raw)
Related papers
2008
This study investigated experimentally the fracture properties, i.e., the fatigue strength, the resistance to crack propagation and the fracture toughness, of an acrylic bone cement (Cemex RX). The mean endurance limit was determined following the staircase method. The endurance limit was estimated at 9.2 MPa. The fatigue crack propagation rate was measured according to the ASTM E647 standard. The equation of the line fitting the crack growth per cycle (da/dN) versus the stress-intensity factor range (∆K), in a log–log graph, was used to calculate the empirical constants of Paris’ law for the selected bone cement: da/dN (m/cycle) = 3.56·10·∆K (MPa·m). This power-law relationship described well (R = 0.96) the growth rate in the stable crack growth region, i.e., in the mid ∆K range. The fracture toughness KIC of the bone cement was determined according to the ASTM E399 standard. The KIC mean value was 1.38 MPa·m. These experimental results provide the set of necessary inputs for numer...
Failure of acrylic bone cements under triaxial stresses
Journal of Materials Science, 1990
Bone cements work under complex triaxial states of stress between the prosthesis and the bone. However, no failure criteria have been formulated for such materials. In the present work two acrylic bone cements have been tested under triaxial stresses up to failure and it has been shown that they behave following the Coulomb-Mohr criterion. Tests have been carried out with moulded thick-wall cylindrical hollow specimens. The samples were unidirectionally compressed whilst a constant internal pressure was provided. Although weaker, one of the bone cements exhibits a similar behaviour to industrial polymethylmethacrylate (PMMA). The different behaviour of these bone cements cannot be related to porosity, which ranges from 1 to 4% in both materials, nor to their different molecular weight. It has been shown that the different morphologies of the bone cement PMMA powders may account for their different mechanical behaviour. It seems that a more homogeneous distribution of sizes, ranging from 10 to 50 {lm, and shapes (practically spherical) gives rise to a material which behaves in a similar way to industrial PMMA.
TESTING AND COMPARISON OF THE MECHANICAL PROPERTIES OF COMMERCIAL BONE CEMENTS
Experimental Techniques, 2008
... ajbarletta@gmail.com) and A. Schonning are affiliated with the Mechanical Engineering, School of Engineering, University of North Florida, Jacksonville, FL, 2 R. Cotton and M ... 7 Krause, W., Mathias, RJ, and Grimes, LW, Fatigue Properties of Acrylic Bone Cement: SN, PN ...
Quantitative Crack Surface Morphology of Bone Cements in Relation to Propagation Rate
Fatigue & Fracture of Engineering Materials and Structures, 2007
Morphology of the crack surface of surgical bone cements has seldom been studied in the past despite the clinical relevance of cement failure. Previous studies on a specific cement type suggest that crack morphology depends on crack propagation rate. The objectives of this work were: (i) to develop a quantitative indicator for describing crack morphology; and (ii) to assess if dependency on crack-propagation rate is affected by cement formulation. Known crack surfaces were obtained from specimens under controlled loading conditions. Crack surface roughness was measured for different crack-propagation rates, and compared against the amount of cleaved pre-cured beads (measured with a semiautomated procedure based on micrographs). Such indicators were extremely robust, operator-independent, highly correlated, and sensitive to the type of fracture. Moreover, it was found that crack surface morphology heavily depends upon cement composition. Thus, crack surface roughness is proposed as a method for quantitatively identifying crack morphology, and finally classifying fracture type. Keywords acrylic surgical bone cement; polymethylmethacrylate (PMMA); crack growth rate; crack growth path; fracture surface roughness; fatigue crack propagation.
A methodology and criterion for acrylic bone cement fatigue tests
Fatigue & Fracture of Engineering Materials & Structures, 2000
A B S T R A C T Acrylic bone cement is used as a fixing device in total hip arthroplasty and it is based on polymethyl-methacrylate. Fatigue failure of the cement is the primary cause of loosening of cemented arthroplasties. Pores form in the acrylic material during mixing and curing, and an analysis of the fatigue life of the cement requires the elimination of the critical macropores, defined as having a diameter >1 mm, which may bias the outcome of tests. Previous workers have rejected fatigue specimens either on a qualitative basis or at a specified pore size level. However various different thresholds have been considered but currently there is no quantitative criterion to define them. This investigation proposes a quantitative criterion for establishing a critical macropore size rejection threshold for fatigue specimens, and discusses the effectiveness of this criterion based on fatigue tests of radiopaque cement specimens.
Influence of specimen molding technique on fatigue properties of a bone cement
Journal of applied biomaterials & biomechanics : JABB
Fatigue failure of the acrylic cement mantle is one of the most common causes of aseptic loosening in cemented femoral prostheses. Cement fatigue properties can be assessed by mechanical in vitro tests, usually performed on properly shaped specimens from standard molds, following a controlled procedure. On the contrary, in the operating theatre the cement mantle is produced in the medullary channel after stem insertion by the surgeon. It is arguable whether the cement properties obtained from the in vitro tests reflect the actual fatigue properties of the cement mantle, as a less controlled procedure can create more defects in the cement. To evaluate the influence of cement preparation, molded specimens for fatigue tests were produced by three different methods. Specimens were molded, using hand-mixed cement, into a standard mold or into a purposely designed device, simulating stem insertion in the medullary channel. Two different specimens were molded with this device, the cement manually or syringe inserted. Fatigue tests were carried out with a sinusoidal uniaxial zero-tension load (15 MPa) and cycle numbers at failure recorded for the three different groups of specimens. The results showed that, in the case of specimens properly manufactured (using a syringe) the fatigue strength reaches values similar to those of standard molded specimens, but it significantly decreases if cement is not inserted according to proper surgical procedures. Therefore, in the operating theatre it is recommended that the correct and complete procedure is followed to limit the risk of early fatigue failure
Polymerisation stress modelling in acrylic bone cement
Journal of Biomechanics, 2010
Fatigue failure of the cement mantle has been proposed as one of the failure processes contributing to aseptic loosening of cemented joint replacements. It has also been suggested that fatigue failure is dramatically accelerated by residual stress generated during the cement polymerisation process. Previous computational models of the polymerisation process have investigated only the latter part of polymerisation by assuming both instantaneous hardening of the material (a stress locking point) and that all residual stress results from thermal shrinkage after this stress locking point. In this study, finite element models which use the local degree of polymerisation to calculate material properties and shrinkage have been used to predict residual stresses in two models of total hip replacement cement mantles. Results indicate that the final value of cement mantle stress may not be the highest stresses that the cement is subjected to during the polymerisation process. Two models are presented, a 2dimensional model, which was adapted from a similar model in the literature (Lennon and Prendergast, 2002) and a 3-dimensional concentric-cylinders model. In both cases a chemical kinetics model was used to predict the progress of the polymerisation reaction and a second linear model used to predict cement mechanical properties and density, and so stress generation and volume change, over time. There was good agreement of the results of the 2D model with its counterpart in the literature. For the 3D model, the final residual stress magnitudes and patterns showed good agreement with similar physical and computational models in the literature.
Journal of Materials Science-materials in Medicine, 1999
Fracture and mechanical characterization of bone composite composed of polymethylmethacrylate and hydroxyapatite (HA) at different contents was carried out. Hydroxyapatite is added in order to improve cement biocompatibility, but it is expected that it also affects mechanical properties. Specimens were either stored in air at 37°C for 120 h or in physiological solution (PhS-37), in order to establish the influence of storage conditions upon mechanical behavior. One set of specimens was also postcured at 120°C for 4 h to take into account the influence of free monomer. Fracture experiments revealed some non-linearity in load–displacement records and differences in trends between initiation and propagation values of the fracture surface energies. The trends in the data shows that HA acts as a rigid filler enhancing fracture resistance, flexural modules and yield stress, up to a certain content. Beyond the latter limit, properties suffer a deterioration because the addition of HA also affects the cement porosity. Absorbed water acts as plasticizer leading to a decrease in mechanical properties. The highest propagation strain energies were exhibited by materials aged in PhS-37. ©1999 Kluwer Academic Publishers
Computational Materials Science, 2010
The mechanical resistance of the total hip prosthesis (THP) and particularly the adhesion quality between the implant and the bone depend primarily on the nature of the cement used and its mechanical and geometrical characteristics. The fracture behavior of the cement is decisive in the failure of the cemented THP. In this work, an analysis of the different criteria of crack propagation in the cement using the finite element method was carried out on various regions of the cement (proximal, medial and distal) with a distributed load on the femoral head of the THP of a 90 kg average body weight. Three orientations of the initial crack were considered: horizontal, vertical and inclined. The two first move in the proximal part towards the distal part, and the third moves in the distal zone. The results show that a crack started in the distal zone of the cement propagates in mixed mode, whilst the one initiated in the proximal zone in mode I.