Overview: Damage in brittle layer structures from concentrated loads
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Overview: Damage in brittle layer structures from concentrated loads Brian R. Lawn Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
Yan Deng Department of Materials and Nuclear Engineering, University of Maryland, College Park, Maryland 20742-2115
Pedro Miranda Departamento de Electro´nica e Ingenierı´a Electromeca´nica, Escuela de Ingenierı´as Industriales, Universidad de Extremadura, 06071 Badajoz, Spain
Antonia Pajares Departamento de Fı´sica, Facultad de Ciencias, Universida¨d de Extremadura, 06071 Badajoz, Spain
Herzl Chai Department of Solid Mechanics, Materials and Systems, Faculty of Engineering, Tel Aviv University, Tel Aviv, Israel
Do Kyung Kim Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Yusong, Taejon 305-701, Korea (Received 12 April 2002; accepted 10 September 2002)
In this article, we review recent advances in the understanding and analysis of damage initiation and evolution in laminate structures with brittle outerlayers and compliant sublayers in concentrated loading. The relevance of such damage to lifetime-limiting failures of engineering and biomechanical layer systems is emphasized. We describe the results of contact studies on monolayer, bilayer, trilayer, and multilayer test specimens that enable simple elucidation of fundamental damage mechanics and yet simulate essential function in a wide range of practical structures. Damage processes are observed using post mortem (“bonded-interface”) sectioning and direct in situ viewing during loading. The observations reveal a competition between damage modes in the brittle outerlayers—cone cracks or quasiplasticity at the top (near-contact) surfaces and laterally extending radial cracks at the lower surfaces. In metal or polymeric support layers, yield or viscoelasticity can become limiting factors. Analytical relations for the critical loads to initiate each damage mode are presented in terms of key system variables: geometrical (layer thickness and indenter radius); material (elastic modulus, strength and toughness of brittle components, hardness of deformable components). Such relations provide a sound physical basis for the design of brittle layer systems with optimal damage thresholds. Other elements of the damage process—damage evolution to failure, crack kinetics (and fatigue), flaw statistics, and complex (tangential) loading—are also considered.
I. INTRODUCTION
Laminate structures are often formed with brittle outerlayers (typically hard ceramics) to shield soft or compliant supporting underlayers or interlayers (metals, polymers, or even soft ceramics) from potentially deleterious external forces. Brittle outerlayers may also provide essential function, e.g., wear, corrosion, and thermal J. Mater. Res., Vol. 17, No. 12, Dec 2002
and electrical resistance. This notion of a protective outerlayer is a critical aspect of many engineering laminate structures, cutting tools, thermal barriers coatings (engine c
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