Overview: Damage in brittle layer structures from concentrated loads

Abstract

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 usingpost mortem(“bonded-interface”) sectioning and directin situviewing 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.

Microscale interpretation of tribological phenomena in Ti/TiN soft-hard multilayer coatings on soft austenite steel substrates

“…2a): The system behaves as a brittle monolith, with the stresses concentrated at the top surface. Fracture occurs as a near-axisymmetric cone crack close to the contact circle, where the tensile stresses are maximum [38]. 2.…”

“…Membrane stresses come increasingly into play. Although detailed fracture mechanics descriptions for all three regions are complex [38], conservative relations can be obtained by considering fracture to occur when the tensile Hertzian stresses in region (1), the flexural (bending) stresses in region (2) or thin film tensile stresses exceed coating strength [42]. Diminishing substrate deformation would increase resistance to coating fracture in regimes (2) and (3), which are of main interest for PVD coatings.…”

Design maps for failure of all-ceramic layer structures in concentrated cyclic loading

“…In our experiments we have used polycarbonate with a modulus E s = 2.35 GPa for experimental expediency (transparency). Dental crowns are usually seated onto tooth dentin, which has a modulus closer to E s = 16 GPa [7,46]. Such an increase in E s is equivalent to an increase in P R for core failure in Eq.…”

“…Considerable recent work has been done on the way brittle layer structures consisting of a weak and relatively compliant "veneer" joined to a strong and stiff "core" and glued to a polymeric base fail in contact loading with spheres [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Such configurations are representative of occlusal loading of all-ceramic veneer/core dental crowns fixed to tooth dentin [18][19][20][21].…”

Fatiga por contacto esférico en materiales multicapa de alúmina circona

“…Sin embargo, para materiales cerámicos con tenacidad más elevada aparece daño "casi-plástico", debido al crecimiento y coalescencia de microgrietas situadas bajo el indentador por tensiones de cizalladura [25]. Cuando se indenta un bimaterial (por ejemplo un recubrimiento o una multicapa), aparecen otros tipos de daño, como delaminación o grietas radiales, dependiendo de las propiedades mecánicas de los materiales y de las dimensiones relativas de las capas del material y del indentador, tal y como demostraron Lawn y el grupo de Guiberteau, entre otros, para materiales modelo y materiales biomédicos [26,27,28,29,30]. Para el caso específico de materiales cerámicos multicapas, por ejemplo, An y col. combinaron una primera capa de Al 2 O 3 (rotura frágil) con una segunda capa de Al 2 O 3 :30Ca Al 12 O 19 (rotura casi-plástica), consiguiendo un aumento de la resistencia mecánica del multicapa [31], y Jitcharoen y col. inhibieron el crecimiento de grieta hertziana utilizando un material con función gradiente de alúmina y vidrio de silicato de aluminio [32].…”