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Material Damage (material + damage)
Selected AbstractsAccident risks in disturbance recovery in an automated batch-production systemHUMAN FACTORS AND ERGONOMICS IN MANUFACTURING & SERVICE INDUSTRIES, Issue 4 2002G. Toulouse Accident risks in automated production systems occur mainly during system disturbance. However, few studies have dealt with this issue. We were able to investigate it by studying accident risks during the recovery of incidents occurring in the running of an automated bread production system in an industrial bakery. This problem was examined through worker interviews. The main results indicate that the accident risks associated with system disturbance are due to accessibility problems and the need to operate quickly to avoid production shutdowns or material damage. Different solutions have been implemented to reduce the disturbances and accident risks. The development of these solutions seems related to the managers' and operators' concepts of what constitutes a disturbance. © 2002 Wiley Periodicals, Inc. [source] Creep of saturated materials as a chemically enhanced rate-dependent damage processINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2007Liang Bo Hu Abstract Material behaviour that exhibits characteristics of creep induced by a spontaneous mineral dissolution enhanced by material damage is studied. It is believed that the characteristic rates of the chemical processes involved determine the time-rate dependence of the resulting strain. A basic model of a combined chemo-plastic softening and chemically enhanced deviatoric strain hardening for saturated geomaterials is presented. Chemical softening is postulated to occur as a consequence of the net mass removal resulting from dissolution and precipitation of specific minerals occurring at the damage-generated inter-phase interfaces. Closed and open systems are discussed. In the former case, deformation at constant stress results entirely from a local compensation mechanism between the chemical softening and strain hardening. The classical three stages of creep are interpreted in terms of mechanisms of dissolution and precipitation, as well as the variation in the reaction surface areas involved in the mass exchange. In an open system, the above local mechanism is enhanced by the removal of mass via diffusion of species affecting the mass balance. Such a system is addressed via a boundary value problem as shown in an example. Copyright © 2007 John Wiley & Sons, Ltd. [source] Modelling of elastoplastic damage in concrete due to desiccation shrinkageINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 8 2002F. Bourgeois We present a numerical modelling of elastoplastic damage due to drying shrinkage of concrete in the framework of mechanics of partially saturated porous media. An elastoplastic model coupled with isotropic damage is first formulated. Two plastic flow mechanisms are involved, controlled by applied stress and suction, respectively. A general concept of net effective stress is used in take into account effects of capillary pressure and material damage on stress-controlled plastic deformation. Damage evolution depends both on elastic and plastic strains. The model's parameters are determined or chosen from relevant experimental data. Comparisons between numerical simulations and experimental data are presented to show the capacity of model to reproduce mains features of concrete behaviour under mechanical loading and during drying shrinkage of concrete. An example of application concerning drying of a concrete wall is finally presented. The results obtained allow to show potential capacity of proposed model for numerical modelling of complex coupling processes in concrete structures. Copyright © 2002 John Wiley & Sons, Ltd. [source] Wear Mechanisms of TiB2 and TiB2,TiSi2 at Fretting Contacts with Steel and WC,6 wt% CoINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2010Golla Brahma Raju Unlubricated fretting wear tests on TiB2 and TiB2,5 wt% TiSi2 ceramics against two different mating materials (bearing grade steel and WC,6 wt% Co balls) were performed with a view to understand the counterbody-dependent difference in friction and wear properties. The fretting experiments were conducted systematically by varying load (2,10 N) at an oscillating frequency of 4 Hz and 100 ,m linear stroke, for a duration of 100,000 cycles. Adhesion, abrasion, and three-body wear have been observed as mechanisms of material damage for both the TiB2/steel and TiB2/WC,Co tribosystems. The third body is predominantly characterized as tribochemical layer for TiB2/steel and loose wear debris particles for TiB2/WC,Co tribocouple. An explanation on differences in tribological properties has been provided in reference to the counterbody material as well as microstructure and mechanical properties of flat materials. [source] The Role of Dynamic Material Properties in the Performance of Ceramic ArmorINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2004James Lankford Jr. The penetration of ceramic armor by a kinetic energy penetrator is complex, involving a continual process of material damage, micro-crack nucleation, growth and coalescence, and multiaxial failure, all under conditions of high loading rate and inertial confinement. It will be shown that at sufficiently high stress, which usually requires either high loading rates or confinement (these conditions are known to prevail in the region just beneath a penetrator dwelling at the surface of an armor), plastic deformation occurs in ceramics. This deformation appears to limit the strength of most ceramics, since micro-cracks are subsequently nucleated at the sites of the deformation defects and these immediately begin to coalesce into fragments. The constraint/rate-limited flow of these fragments is the physical event that permits the penetration of ceramic armor. This paper considers the implications for modeling armor penetration of laboratory experiments involving both intact and fragmented ceramics tested under compressive loading at high strain rates and under confining pressure. [source] Modeling UHMWPE wear debris generationJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2007H. Baudriller Abstract It is widely recognized that polyethylene wear debris is one of the main causes of long-term prosthesis loosening. The noxious bioreactivity associated with this debris is determined by its size, shape, and quantity. The aim of this study was to develop a numerical tool that can be used to investigate the primary polyethylene wear mechanisms involved. This model illustrates the formation of varying flow of polyethylene debris with various shapes and sizes caused by elementary mechanical processes. Instead of using the classical continuum mechanics formulation for this purpose, we used a divided materials approach to simulate debris production and release. This approach involves complex nonlinear bulk behaviors, frictional adhesive contact, and characterizes material damage as a loss of adhesion. All the associated models were validated with various benchmark tests. The examples given show the ability of the numerical model to generate debris of various shapes and sizes such as those observed in implant retrieval studies. Most of wear mechanisms such as abrasion, adhesion, and the shearing off of micro-asperities can be described using this approach. Furthermore, it could be applied to study the effects of friction couples, macroscopic geometries, and material processing (e.g. irradiation) on wear. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2007 [source] Bipolar Fatigue Caused by Field Screening in Pb(Zr,Ti)O3 CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2007Nina Balke Bipolar cycling of lead zirconate titanate ceramics can lead to massive material damage in regions close to the electrode. The damaged region can be identified by color changes, and the microstructure in this region shows signs of interface melting. This damaged region can screen the sample volume from the applied voltages and reduced fields are applied to the undamaged part of the sample. This has two effects. The first one is that the bulk is effectively subjected to smaller fields, but the measured parameters are assigned to the applied field, yielding apparent fatigue curves. The second effect is that with further cycling, field screening protects the bulk of the sample from fatigue due to the reduced effective fields. If the damaged region is mechanically removed and the ferroelectric hystereses are measured again, nearly unfatigued parameters are obtained. [source] | |||||||||||||