Search results for "Fracture"
showing 10 items of 873 documents
The global cracking laws for a finite-element model of no-tension material
1992
Abstract For perfect no-tension materials (NRT) the validity of the local stability postulate of Drucker, well known in plasticity, has been assumed so far and utilized to derive the local cracking laws, which relate cracking strain states and stress states to each other. On this base a finite-element (FE) model with suitable constitutive behaviour for the single FE is presented. Classical FE approaches enforce the cracking laws at the Gauss points of the FEs. In this work it is shown that taking into account cracking strains, suitably modelled, over the whole domain of the FE and making use of an energy approach lead to general cracking laws describing the constitutive behaviour of the who…
Effect of exercises with weight vests and a patient education programme for women with osteopenia and a healed wrist fracture: a randomized, controll…
2015
Background Exercise programmes have shown to be important for the prevention of fractures in patients with established osteoporosis. However, few studies have evaluated the effect of such programmes for women with low bone mineral density (BMD) (osteoporosis or osteopenia) who have already suffered a fracture. Studies have indicated that exercise programmes concentrating on muscular strength and dynamic balance have a positive effect on significant risk factors for falls such as quadriceps strength and balance. The aim of the present study was to assess the effect of a 6-month exercise programme and a patient education component (OsteoACTIVE) on quadriceps strength, BMD, dynamic balance, wa…
FATIGUE FAILURE CRITERIA FOR MATERIALS UNDER RANDOM TRIAXIAL STATE OF STRESS
1984
SUMMARY Five fatigue failure criteria are formulated for a random triaxial state of stress whose components have zero mean values. It is assumed that fatigue failure is determined by the stress and strain components that act on an expected fracture plane. It is shown that in some special cases the proposed failure theories reduce to classical theories applied for sinusoidal stresses.
Vertical root fracture in endodontically treated teeth: A review of 25 cases
2001
Abstract Objective: We sought to examine the clinical conditions under which 25 endodontically treated teeth underwent vertical root fracture (VRF) and to relate this condition to the time elapsed from endodontic treatment to fracture. Study Design: This was a retrospective study in which we reviewed 25 case histories of patients with postendodontic VRF and studied the effect of various pretreatment and posttreatment factors as they related to VRF. Results And Conclusions: The mean time to VRF was 54 months; this was not significantly influenced by the presence or absence of prior restoration or by the presence or absence of a crown fitting. The use of a prefabricated, cylindrical, cemented…
Influence de l'orientation des fibres sur un essai Arcan = Influence of fiber orientation on Arcan test data
2009
National audience; Ce papier présente les résultats d'une étude expérimentale portant sur le comportement d'éprouvettes ‘papillon' en verre/époxy, soumises à des chargements de cisaillement pur et de traction-cisaillement combinés, au moyen d'un dispositif Arcan. Des éprouvettes dont les fibres sont orientées parallèlement à la direction des entailles et d'autres pour lesquelles les fibres sont perpendiculaires à cette direction, respectivement désignées Mat31 et Mat32, ont été testées pour différents angles de sollicitation, dans une plage comprise entre 0° et 90°. Le mode de rupture observé pour les éprouvettes Mat31 est répétitif, alors qu'il dépend de la direction de la sollicitation po…
Orthogonal cutting simulation of OFHC copper using a new constitutive model considering the state of stress and the microstructure effects
2016
International audience; This work aims to develop an orthogonal cutting model for surface integrity prediction, which incorporates a new constitutive model of Oxygen Free High Conductivity (OFHC) copper. It accounts for the effects of the state of stress on the flow stress evolution up to fracture. Moreover, since surface integrity parameters are sensitive to the microstructure of the work material, this constitutive model highlights also the recrystallization effects on the flow stress. Orthogonal cutting model is validated using experimental designed cutting tests. More accurate predictions were obtained using this new constitutive model comparing to the classical Johnson-Cook model.
Fracture of Honeycombs Produced by Additive Manufacturing
2022
Publisher Copyright: © 2021 World Scientific Publishing Europe Ltd. Lattice materials, such as honeycombs, are remarkable in their ability to combine high stiffness, strength and toughness at low density. In addition, the recent and pervasive development of additive manufacturing technologies makes it easier to produce these cellular materials and opens new possibilities to improve their properties by implementing small modifications to their microstructure. Such developments open new opportunities towards the design of new classes of architectured materials. For example, recent computational studies have shown that honeycombs with lattice density gradients have a fracture energy under tens…
Particularités de l'imagerie des traumatismes de l'appareil locomoteur chez l'enfant et l'adolescent (crâne et rachis exclus)
2013
Les lésions traumatiques du squelette en pratique pédiatrique sont fréquentes, faites de macrotraumatismes et de microtraumatismes répétés. Le diagnostic et le bilan de cette pathologie sont, dans l'immense majorité des cas, réalisés grâce aux clichés standards, surtout pour le squelette appendiculaire. Les fractures de l'enfant sont plus souvent diaphysométaphysaires incomplètes qu'épiphysométaphysaires. Elles touchent principalement le membre supérieur par ordre de fréquence. Il existe de nombreuses images pièges, variantes de la normale ; la consultation d'ouvrages de référence est fondamentale. Les clichés standards en incidences orthogonales sont la règle et permettent de diagnostiquer…
Impact of the coronavirus pandemic on maxillofacial trauma:a retrospective study in southern Spain
2022
The coronavirus pandemic has impacted health systems worldwide, with Spain being one of the most affected countries. However, little is known about the extent to which the effects of staying home, social distancing, and quarantine measures have influenced the epidemiology of patients with maxillofacial trauma. The aim of this study was to analyze the impact of the coronavirus pandemic on the incidence, demographic patterns, and characteristics of maxillofacial fractures in the largest hospital in southern Spain. Data from patients who underwent surgery for maxillofacial fractures during the first year of the pandemic between 16 March 2020 and 14 March 2021 (pandemic group) were retrospectiv…
Effects of defects on the tensile strength of short-fibre composite materials
2014
Abstract. Heterogeneous materials tend to fail at the weakest cross-section, where the presence of microstructural heterogeneities or defects controls the tensile strength. Short-fibre composites are an example of heterogeneous materials, where unwanted fibre agglomerates are likely to initiate tensile failure. In this study, the dimensions and orientation of fibre agglomerates have been analysed from three-dimensional images obtained by X-ray microtomography. The geometry of the specific agglomerate responsible for failure initiation has been identified and correlated with the strength. At the plane of fracture, a defect in the form of a large fibre agglomerate was almost inevitably found.…