Fatigue crack shielding in plain bearings under large scale yielding

Multi-layered bearing systems used in the automotive industry show shielding and antishielding effects that reduce or amplify the crack driving force under large-scale yielding conditions. Using finite element analysis, it is shown that shielding in such systems results in path deflection and bifurcation despite the absence of mixed-mode loading. As the crack approaches a stiff layer, the tangential strains measured around a blunted crack tip model show a maximum corresponding to the direction of crack propagation. The distribution of such strains indicates the effect of shielding and the likelihood of the tip to deflect or bifurcate.The suitability of bi-layer and tri-layer bearing architectures is assessed through crack path and respective crack driving force prediction

Elasto-plastic finite element studies of fatigue crack shielding in multi-layered systems

Multi-layered systems used in automotive plain bearings show complex patterns of crack growth under service conditions. The studied architecture consists of a steel backing (1.8 mm), a compliant pure-aluminum interlayer (0.04 mm) and a lining of medium-strength aluminum alloy (0.38 mm). Previous experimental studies [1] with flat strip specimens of identical architecture under three point bending indicated similar crack propagation patterns despite the absence of mixed mode loadin

Three-dimensional crack growth in multi-layered architectures for automotive plain bearings

The assessment of shielding and anti-shielding effects on crack growth in multi-layered architectures is achieved using elasto-plastic finite element models. Initially, the evolution of straight, deflected and bifurcated cracks is studied through two-dimensional models with blunted crack tips using the maximum tangential strain as a criterion for deflection and the crack opening displacement as the crack driving force. The methodology is extended to three dimensions assuming only elastic material behavior; some initial analysis results on the effects of shielding along the crack front are presented and discusse

Effects of tangential strains and shielding in large scale yielding in multi-layered architectures for bearings

Multi-layered bearing systems used in the automotive industry show shielding and antishielding effects that reduce or amplify the crack driving force under large scale yielding conditions. Using finite element analysis, it is shown that shielding in such systems results in path deflection and bifurcation despite the absence of mixed-mode loading. As the crack approaches a stiff layer, the tangential strains measured around a blunted crack tip model show a maximum corresponding to teh direction of crack propagation. The asymmetric distribution of such strains indicates the effect of shielding and the likelihood of the tip to deflect or bifurcate. The suitability of bi-layer and tri-layer bearing architectures is assessed through crack path and respectie crack driving force predictions

Plain bearing stresses due to forming and oil film pressure

This paper describes a methodology for assessing critical stress ranges arising in automotive plain bearings during engine operations. An industry-produced and run simulation program provides information on oil film pressure and overall bearing deformation during accelerated performance tests. This code performs an elasto-hydrodynamic lubrication analysis accounting for the compliance of the housing and journal. Finite element analyses of a multi-layer bearing are performed to assess the conditions responsible for possible fatigue damage over the bearing lining. The residual stresses arising from the forming and fitting process are first assessed. The stress analyses over the engine cycle show the intensity and distribution of cyclic tensile and compressive stresses in the bearing. The location of maximum stress range is found to be consistent with the damage observed in accelerated fatigue tests. Critical zones are identified in the lining for possible fatigue crack initiation and growth studie

Assessment of three-dimensional crack growth in ductile layered material systems

Fatigue crack growth in three-dimensions may follow complex patterns that depend on the local and global conditions of the material around the crack front. In layered material systems, crack growth may be enhanced or delayed over portions of the crack front as the latter approaches a dissimilar layer. Three-dimensional elasto-plastic finite element analyses were developed for the study of the effects of dissimilar layers ahead of the crack front on the crack driving force (crack tip opening displacement) and crack growth; the simulation of the latter was based on previous experimental data obtained from a fatigued specimen with identical tri-layer architecture. The efficiency of the model under elastic conditions was first assessed by comparison of its predictions with an exact analytical solution. Crack growth in the top layer was simulated up to a depth of around 95% of its thickness. The modelling was based on a re-meshing scheme and was applied to bi-layer and tri-layer architectures subjected to three-point bending. The crack front was positioned as close as possible to the dissimilar layer so that shielding and anti-shielding effects would be clearly observed. These three-dimensional simulations revealed that such effects are less intense than those predicted by previous 2D analyses that assumed through-width cracks

Progresso e mimesis: ideias políticas, imitação e desenvolvimento Progress and mimesis: political ideas, imitation, and development

A ciência política comparativa vinha ignorando o papel central que ideias e modelos políticos têm na criação e no desenvolvimento das instituições. Com o colapso do bloco soviético e o fervor intelectual que acompanhou esse evento, criou-se uma abertura pela qual os efeitos do pensamento político passaram a ser vistos como importantes. Articuladas por pensadores políticos, as ideias dirigem ações, refletem entendimentos dominantes entre as elites sobre a realidade ou fornecem uma base para a crítica desses entendimentos. Nesse sentido, seu estudo pode revelar alguns aspectos do esforço de constituição de um regime. Este artigo sugere uma forma de abordar o problema: examinar como as ideias são adotadas, adaptadas e assimiladas pelos atores políticos.<br>Comparative political science has ignored the central role that political ideas and models have on the creation and development of institutions. With the collapse of the Soviet bloc and the intellectual fervor that accompanied this event, possibilities of paying attention to the effects of political thought grew. Articulated by political thinkers, ideas direct actions, reflect dominant understandings among elites on the truth or provide a basis for criticism of these understandings. In this sense, their study may reveal some aspects of the effort to set up a regime. This article suggests an approach to the problem: focusing on how ideas are adopted, adapted and supported by the political actors