Fracture modelling of DP780 sheets using a hybrid experimental-numerical method and two-dimensional digital image correlation

This paper is concerned with the construction of fracture envelopes of DP780 sheets using two methods: a hybrid experimental-numerical method; two-dimensional digital image correlation (2D-DIC). For the hybrid method, four types of ductile fracture tests were carried out covering a wide range of stress states on specimens: with a central hole; two symmetric circular notches; flat grooved; and diagonally double-notched. Based on the fracture strain and loading paths identified with finite element simulation, a fracture envelope was obtained by employing the three-parameter modified Mohr-Coulomb fracture model. In addition, the fracture surface strain was directly measured using 2D-DIC. Loading histories of each test were extracted from a surface element of a three dimensional finite element model. The comparison of fracture envelopes constructed by the two methods reveals that there is little difference. Thus, it can be concluded that 2D-DIC is applicable to fracture modelling of DP780 sheets despite the assumption of the plane stress condition even after necking

Inter-observer variation in the diagnosis of coronal articular fracture lines in the lunate facet of the distal radius

Background: Several studies support the use of CT for diagnosing coronal fractures of the distal radius but the inter-observer reliability of these observations is less well studied. We tested the null hypothesis that radiographs alone and the combination of radiographs and two-dimensional computed tomography scans (2DCT) have the same inter-observer variation for the diagnosis of coronal articular fracture lines in the distal radius. Methods: Using a web-based survey, 63 surgeons were randomized to evaluate 16 fractures of the distal radius on radiographs alone or radiographs and 2DCT for the presence or absence of a coronal fracture line of the lunate facet and, if present, the stability of the fracture. The kappa multirater measure was calculated to estimate agreement between observers. Results: The inter-observer variation in diagnosis of a coronal fracture line was fair with both radiographs and 2DCT, as was the diagnosis of instability of the volar lunate facet fracture when present. Conclusion: Two-dimensional computed tomography does not improve observer agreement on the diagnosis of coronal plane articular fracture lines in the lunate facet of the distal radius. © 2012 American Association for Hand Surgery.

Prior fracture as a risk factor for future fracture in an Australian cohort

This study investigated the influence of prior fracture on the risk of subsequent fracture. There was a higher risk of subsequent fracture in both young and older adult age groups when Australian males or females had already sustained a prior fracture. Fracture prevention is important throughout life for both sexes.

Investigating the predictive ability of gait speed and quadriceps strength for incident falls in community-dwelling older women at high risk of fracture

Gait speed is a recommended geriatric assessment of physical performance, but may not be regularly examined in clinical settings. We aimed to investigate whether quadriceps strength tests demonstrate similar predictive ability for incident falls as gait speed in older women. We investigated 135 female volunteers aged mean±SD 76.7±5.0 years (range 70-92) at high risk of fracture. Participants completed gait speed assessments using the GAITRite Electronic Walkway System, and quadriceps strength assessments using a hand-held dynamometer (HHD). Participants reported incident falls monthly for 3.7±1.2 years. N=99 (73%) participants fell 355 times during the follow-up period (mean fall rate 83 per 100 person years). We observed a reduced odds ratio for multiple falls (0.83, 95% CI 0.70-0.98) and a reduced hazard ratio for time to first fall (0.90, 95% CI 0.83-0.98), according to quadriceps strength. There was also a significantly shorter time to first fall for those with low quadriceps strength (<7.0 kg; lowest tertile) compared with those with normal quadriceps strength (estimated means [95% CI] 1.54 [1.02, 2.06] vs. 2.23 [1.82, 2.64] years; P=0.019), but not for those with low (<1.0 m/s) vs. normal gait speed (P=0.15). Quadriceps strength is a significant predictor of incident falls over three years amongst community-dwelling older women at high risk of fracture. Quadriceps strength tests may be an acceptable alternative to gait speed for geriatric assessments of falls risk.

Modeling of shear ductile fracture considering a changeable cut-off value for stress triaxiality

 A macroscopic ductile fracture criterion is proposed based on micro-mechanism analysis of nucleation, growth and shear coalescence of voids from experimental observation of fracture surfaces. The proposed ductile fracture model endows a changeable cut-off value for the stress triaxiality to represent effect of micro-structures, the Lode parameter, temperature, and strain rate on ductility of metals. The proposed model is used to construct fracture loci of AA 2024- T351. The constructed fracture loci are compared with experimental data covering wide stress triaxiality ranging between –0.5 and 1.0. The comparison suggests that the proposed model can provide a satisfactory prediction of ductile fracture for metals from compressive upsetting tests to plane strain tension with slanted fracture surfaces. Moreover, it is expected that the proposed model reasonably describes ductile fracture behavior in high velocity perforation simulation since a reasonable cut-off value for the stress triaxiality is coupled with the proposed ductile fracture criterion.

Modified Mohr-Coulomb fracture model for anisotropic sheet materials under limited triaxial stress conditions

 This paper reviews recent work of the authors to model necking and fracture for anisotropic materials, which requires consideration of the stress conditions that vary through the thickness of the sheet, and in particular, taking into consideration the conditions at individual integration points. Although the prior work adequately addresses the roll of triaxial stress conditions on necking, the fracture model developed in the prior work was limited in its application to analysis of plane-stress conditions. In this work, a fracture model is developed for application to a limited range of triaxial stress conditions, in which the through-thickness shear stresses are assumed to be negligible, but the normal stress is allowed to be non-zero. The model is extended in a way that reduces to the prior anisotropic fracture model under plane stress conditions, but includes the contribution of a triaxial stress condition in a way that retains the desired features
of the Mohr-Coulomb Model.

Age- and sex-related patterns of first fracture and fracture prevalence

There are few data documenting the pattern of prevalent fracture across the entire adult age range, so we aimed to address this gap by investigating the prevalence of fractures in an Australian cohort. All-cause (ever) fractures were identified for males and females enrolled in the Geelong Osteoporosis Study (Australia) using a combination of radiology-confirmed and self-reported data. First fractures were used to generate age-related frequencies of individuals who had ever sustained a fracture. Of 1,538 males and 1,731 females, 927 males and 856 females had sustained at least one fracture since birth. The proportion of all prevalent fractures in the 0-10 year age group was similar for both sexes (~10 %). In males, the proportion with prevalent fracture increased to 34.1 % for age 11-20 year. Smaller increases were observed into mid-life, reaching a plateau at ~50 % from mid to late life. The age-related prevalence of fracture for females showed a more gradual increase until mid-life. For adulthood prevalent fractures, approximately 20 % of males had sustained a first adulthood fracture in the 20-30 year age group, with a gradual increase up to the oldest age group (49.1 %), while females showed an exponential pattern of increase from the 20-30 year age group (6.8 %) to the oldest age group (60.4 %). In both sexes, those who had not sustained a fracture in childhood or early adulthood generally appeared to remain fracture-free until at least the sixth decade. When considering the prevalence of adulthood fractures across the age groups, males showed a gradual increase while females showed an exponential increase.

Application of the embedded element technique to predict interlaminar failure

In this study a modelling technique, namely, the embedded element method is assessed to evaluate its ability to predict Mode I interlaminar failure. The embedded element technique takes advantage of the embedded constraint in ABAQUS and allows the two constituents, fibre and matrix, to be meshed independently. Since the two constituents can be meshed independently a contiguous mesh is not required and the time taken to create an acceptable mesh is significantly reduced. The embedded element technique has been used to model fibre-reinforced composite structures, however, to date no studies have been conducted which combine the embedded element technique with an interlaminar damage model. The work described herein evaluates the ability of the embedded element technique to predict mode I interlaminar failure. DCB specimens were modelled using the embedded element method and a traditional 3D solid FE modelling approach with the predictions compared against experimental data. Both modelling approaches provided good agreement with experimental results. The good agreement demonstrates that the embedded element technique is capable of providing a response that is equivalent to a traditional 3D solid FE models and is particularly suited to modelling thick composite structures with complex geometry.

Adulthood fracture and quality of life : A population-based study of Australian men

Background: Our objective was to investigate associations between adulthood fracture and quality of life (QOL) in men. Methods: For 448 men aged 50-85 years and enrolled in the Geelong Osteoporosis Study, we measured QOL using the validated (Australian) World Health Organization Quality of Life-Brief Version (WHOQOL-Bref) in the domains of physical health, psychological health, social relationships, and the environment. Self-reported adulthood fractures were categorized as recent or non-recent ( ≤ 10 years or > 10 years pre-QOL assessment, respectively). Lifestyle and health information were self-reported. Results: One hundred seventy four men (38.8%) sustained at least one fracture, 26% of which had occurred within the last 10 years. Compared with men who had never had an adulthood fracture, a non-recent fracture was more likely associated with poorer QOL in the physical health domain (age-adjusted odds ratio [OR] 0.47, 95% confidence interval [95%CI] 0.27-0.83), but not in any other domain. Men who had sustained a recent fracture reported a lower QOL in the domain of psychological health (age-adjusted OR 0.48, 95%CI 0.24-0.97), with a trend observed for lower QOL in the domains of physical health and environment. No further associations were observed. All results were sustained in further models that were adjusted for smoking, alcohol, physical inactivity, and body mass index. Conclusions: We present novel data examining associations between fracture status and QOL in a populationbased sample of Australian men using the WHOQOL-Bref. Recent fractures were associated with poorer QOL in the domain of psychological health while non-recent fractures were more likely associated poorer QOL for physical health. These findings have important implications for healthcare post-fracture.

Numerical investigation of influence of the Martensite Volume Fraction on dp steels fracture behavior on the basis of digital material representation model

Development of the methodology for creating reliable digital material representation (DMR) models of dual-phase steels and investigation of influence of the martensite volume fraction on fracture behavior under tensile load are the main goals of the paper. First, an approach based on image processing algorithms for creating a DMR is described. Then, obtained digital microstructures are used as input for the numerical model of deformation, which takes into account mechanisms of ductile fracture. Ferrite and martensite material model parameters are evaluated on the basis of micropillar compression tests. Finally, the model is used to investigate the impact of the martensite volume fraction on the DP steel behavior under plastic deformation. Results of calculations are presented and discussed in the paper.