1,721,207 research outputs found
The role of microconstituents on the fatigue failure of bone cement
No full textImplant fixation via the use of acrylic bone cement is now a well-established practice in orthopaedics. Excellent long-term clinical results are evidenced in national joint registers based on over 5 decades of clinical experience. Increased life expectancies, patient BMI, together with the need to remain active in later life, are expected to put greater demands on the materials used in load bearing joint arthroplasty. Failure of bone cement and its interfaces with the implant and bone often leads to loosening, requiring revision surgery. This is a particularly invasive procedure, with lower long-term success rates compared to the primary procedure. To reduce the incidence of bone cement failure, it is necessary to understand the origins of failure in vivo. In the past, bulk failure of bone cement has been attributed to damage accumulation originating at pores. Advances in imaging technology now mean that we are able to observe cement microconstituents readily and identify crack-initiating defects more precisely as we attempt to understand origins of failure. The role of radiopacifier particles within the bone cement has not been examined extensively to date, and the present study demonstrates that this microconstituent could be involved in crack formation due in part to its ability to agglomerate and not bond with the surrounding matrix. To verify this hypothesis, explanted bone cement and laboratory tested bone cement are compared and correlations in failure mechanisms are discussed
Data for: Image-enhanced modelling of residual compressive after impact strength in laminated composites
No full textTabulated data for: Image-enhanced modelling of residual compressive after impact strength in laminated composites
Results contain the following outputs from simulations:
•Damage area vs. force and out-of-plane deflection data
•Load vs. strain energy release rate data
•Failure load predictions
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Image-enhanced modelling of residual compressive after impact strength in laminated composites
No full textThis study implements key mechanisms and parameters observed from the previous compression after impact (CAI) experimental studies into finite element models, to study their effects parametrically on residual compression strength. The mechanisms and parameters include: impact damage area, the role of intact interfaces within the overall damaged region (identified here as the “undamaged cone”), interlaminar toughness, and the extent of permanent out-of-plane deformation. The findings highlight that within the limits observed experimentally, in addition to the size of the damaged area, interlaminar toughness and the extent of permanent out-of-plane deformation strongly affect CAI strength (by up to ~100% for a given damage area), with toughness playing a more significant influence than permanent out-of-plane deformation. For the first time, and contrary to much of the literature, the significant role of the undamaged cone is evidenced and quantified
A finite element study on the effects of toughness and permanent out-of-plane deformation on post-impact compressive strength
No full textThis study applies mechanisms observed from previous work (the undamaged cone, toughness and extent of permanent out-of-plane deformation) to parametrically study their effects on residual compression after impact (CAI) strength using finite element models. Based on previous experimental work, tougher material systems exhibited up to 30% greater CAI strength for a given damage area. Based on this, it is necessary to understand what other parameters, beyond damage area, contribute to a loss in CAI strength. Finite element models were conducted in ABAQUS explicit. Delamination growth was modelled using the virtual crack closure technique (VCCT). This study found that systems containing an undamaged cone led to an increased load prior to buckling resulting in lower 0° peak compressive stresses and lower strain energy release rates forming at the outer edges of the delamination zone. In certain configurations, delamination growth into the undamaged cone occurred and was shown to negatively affect the post-buckled response. Overall, the effects of both toughness and permanent out-of-plane deformation was shown to affect CAI failure load by up to ~50% for a given damage diameter. It is also apparent that toughness played a more significant influence than the extent of permanent out-of-plane deformation
Comparing cone beam laminographic system trajectories for composite NDT
No full textWe compare the quality of reconstruction obtainable using various laminographic system trajectories that have been described in the literature, with reference to detecting defects in composite materials in engineering. We start by describing a laminar phantom representing a simplified model of composite panel, which models certain defects that may arise in such materials, such as voids, resin rich areas, and delamination, and additionally features both blind and through holes along multiple axes. We simulate ideal cone-beam projections of this phantom with the different laminographic trajectories, appling both Simultaneous Iterative Reconstruction Technique (SIRT) and Conjugate Gradient Least Squares (CGLS) reconstruction algorithms. We compare the quality of the reconstructions with a view towards optimising the scan parameters for defect detectability in composite NDT applications
A comparison of quasi-static indentation and low velocity impact on hybrid composite-metallic structures using micro-focus computed tomography
No full textFinite element and analytical modelling of crack closure due to repeated overloads
No full textIn this paper, investigations of crack closure due to repeated overloads are presented using finite element (FE) and simplified analytical modelling approaches. In particular, attempts are made to study the effects of overload spacing on closure levels and the underlying physical mechanisms involved. Overload closure behaviour is functionally similar for both FE and analytical approaches used and is seen to be in reasonable accord with relevant available experimental observations. In the first instance, it is noted that for double overload interactions, crack closure influence of an initial overload upon the unloading conditions of a second overload can explain much of the observed enhancement in crack growth retardation; however, for successive (repeated) overloads in plane strain, a critical influence of in-plane constraint arises to attenuate closure interactions
Understanding the mechanisms of root-reinforcement in soils: soil shear tests using X-ray computed tomography and digital volume correlation
No full textSoil containing plant roots may be expected to exhibit a greater shearing resistance compared with the same ‘unreinforced’ soil, providing enhanced stability and effective erosion control, particularly for earth slopes. To be able to rely on the improved shearing resistance and stiffness of root-reinforced soils, it is important to understand and quantify the effectiveness of root reinforcement. This requires sophisticated multiscale models, building understanding at different length scales, from individual soil-root interaction through to full soil-profile or slope scale. One of the challenges with multiscale models is ensuring that they are representative of real behaviour, and this requires calibration to detailed high-quality experiments. The focus of the work presented was to capture and quantify root-reinforcement behaviour and associated soil and root deformation mechanisms during direct shear at the macroscopic to millimetre length scales. A novel shear box was developed to operate within a large-scale X-ray computed tomography (CT) scanner. Tests were interrupted to be scanned at a series of shear displacements from 0-20 mm to capture the chronology of behaviour in three-dimensions. Digital volume correlation (DVC) was applied to the CT dataset to obtain full-field 3D displacement and strain component information. The study demonstrates feasibility of the technique and presents preliminary DVC results
Roughness-and plasticity-induced fatigue crack closure under single overloads: finite element modelling
No full textResults from finite element modelling of plasticity-induced crack closure (PICC) and roughness-induced crack closure (RICC) of fatigue cracks subjected to single overloads are presented. Effects of L/r(p) ratios on RICC, where L and r(p) represent crack asperity length and plastic zone size, respectively, are seen to be functionally similar to results presented previously for constant amplitude fatigue loading [Kamp N.. Parry MR, Singh KD, Sinclair I. Acta Mater 2004;52:343-53], particularly in the saturation of the influence of RICC for L/r(p(OL)) >= I, where r(p(OL)) is the overload plastic zone size. The present work is seen to map out overload regimes where RICC and PICC effects may be expected to influence crack growth transients. Comparisons of modelled and experimental closure levels, and growth rate studies are presented, with the accompanying paper [Singh KD, Khor KH, Sinclair I. Acta Mater (in press)] considering a simplified analytical representation of the effects presented here
Some issues on finite element modelling of plasticity induced crack closure due to constant amplitude loading
No full textAn investigation of plasticity induced crack closure (PICC) behaviour using finite element (FE) method is presented for cracks subjected to constant amplitude loading and small scale yielding (SSY) conditions. Undeflected cracks have been examined under both plane strain and plane stress conditions. Anomalous near-tip closure in FE models has been identified to occur under both plane stress and plane strain conditions and is seen to vary with baseline load levels and crack propagation algorithms. In the case of plane strain models, propagation algorithms are seen to influence pre-crack closure. In general terms it may be said that none of the plane strain models showed crack closure that could be related to ongoing/steady-state crack growth: crack closure in all cases was dominated by pre-crack contact, and/or anomalous near-tip contact, even for the relatively long crack propagation used in the low loading range models
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