Effect of off-axis concentrated loading on failure of curved brittle layer structures

2006 ◽  
Vol 76B (2) ◽  
pp. 334-339 ◽  
Author(s):  
Tarek Qasim ◽  
Christopher Ford ◽  
Mark B. Bush ◽  
Xiaozhi Hu ◽  
Brian R. Lawn
Keyword(s):  
Layer Structures ◽  
Brittle Layer ◽  
Concentrated Loading

Overview: Damage in brittle layer structures from concentrated loads

2002 ◽  
Vol 17 (12) ◽  
pp. 3019-3036 ◽  
Author(s):  
Brian R. Lawn ◽  
Yan Deng ◽  
Pedro Miranda ◽  
Antonia Pajares ◽  
Herzl Chai ◽  
...  
Keyword(s):  
Damage Mechanics ◽  
Limiting Factors ◽  
Damage Initiation ◽  
Layer Structures ◽  
Brittle Layer ◽  
Wide Range ◽  
Damage Process ◽  
Analytical Relations ◽  
System Variables ◽  
Process Damage

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.

Role of Adhesive Interlayer in Transverse Fracture of Brittle Layer Structures

2000 ◽  
Vol 15 (4) ◽  
pp. 1017-1024 ◽  
Author(s):  
Herzl Chai ◽  
Brian Lawn
Keyword(s):  
Crack Initiation ◽  
Glass Surface ◽  
Hard Spheres ◽  
Glass Plate ◽  
Critical Conditions ◽  
Transverse Fracture ◽  
Adhesive Interlayer ◽  
Layer Structures ◽  
Brittle Layer

The role of a soft adhesive interlayer in determining critical conditions for fracture in brittle layer structures from indentation with hard spheres is investigated. A model transparent trilayer system consisting of a glass plate overlayer (thickness range 80 μm to 2 mm) joined to a glass plate underlayer (thickness 5.6 mm) by an epoxy adhesive (thickness range 5 μm to 8 mm), loaded at its top surface with a hard tungsten carbide sphere (radius 3.96 mm), facilitatesin situobservations of the crack initiation and propagation. Whereas in bulk glass fracture occurs by inner Hertzian cone cracking immediately outside the contact circle, the soft adhesive allows the overlayer glass plate to flex, initiating additional transverse fracture modes within the overlayer: downward-extending outer ring cracks at the top glass surface well outside the contact, and upward-extending radial cracks at the bottom glass surface (i.e., at the glass/adhesive interface) on median planes containing the contact axis. The top and bottom surfaces of the glass overlayers are given selective prebonding abrasion treatments to ensure uniform flaw states, so as to enable accurate comparisons between crack initiation conditions. The adhesive bonding is strong enough to preclude delamination in our layer system. Of the three transverse crack systems, the subsurface radials generates most easily in systems with large adhesive thicknesses (and smaller overlayer thicknesses). Semi-empirical relations are specified for the dependence of the critical loads for radial and ring cracking on adhesive as well as overlayer thickness, based on the assumption that crack initiation occurs when the maximum tensile stresses in the flexing glass plate exceed the bulk strength of the (abraded) glass. Coupled with the traditional “Auerbach's law” for cone crack initiation, these relations afford a basis for the construction of simple design diagrams for brittle layer systems joined by adhesives.

Role of indenter material and size in veneer failure of brittle layer structures

2007 ◽  
Vol 82B (1) ◽  
pp. 253-259 ◽  
Author(s):  
Sanjit Bhowmick ◽  
Juan José Meléndez-Martínez ◽  
Ilja Hermann ◽  
Yu Zhang ◽  
Brian R. Lawn
Keyword(s):  
Layer Structures ◽  
Brittle Layer

Cracking in Ceramic/metal/polymer Trilayer Systems

2002 ◽  
Vol 17 (5) ◽  
pp. 1102-1111 ◽  
Author(s):  
Hong Zhao ◽  
Pedro Miranda ◽  
Brian R. Lawn ◽  
Xiaozhi Hu
Keyword(s):  
Epoxy Adhesive ◽  
Model Systems ◽  
Fracture Modes ◽  
Aluminum Sheets ◽  
Dental Crowns ◽  
Layer Structures ◽  
Metal Thickness ◽  
Brittle Layer ◽  
Side Walls ◽  
Metal Properties

Fracture and deformation in model brittle-outerlayer/metal-core/polymer-substrate trilayer systems in concentrated loading are studied. Model systems for experimental study are fabricated from glass microscope slides glued with epoxy adhesive onto steel and aluminum sheets, and the resulting laminates glued onto polycarbonate substrate bases. Critical loads to initiate two basic fracture modes in the glass layers—cone cracks at the top surfaces and radial cracks at the undersurfaces—are measured as a function of metal thickness byin situobservation through the glass side walls. Finite element modeling (FEM) is used to quantify these competing fracture modes. The more damaging radial fracture mode is attributed to flexure of the glass layers on soft underlayers. Although much of this flexure can be eliminated by removing the soft adhesive interlayer between glass and metal, yield in the metal limits the potential increases in critical load for radial cracking. Trilayer systems consisting of porcelain fused to Co-, Pd- and Au-alloy core support layers relevant to dental crowns are then analyzed by FEM. The hardness (especially) and elastic modulus of the metal are identified as the primary controlling material parameters, with modulus and strength of the brittle layer as supplemental parameters. Guidelines for improving metal-based crownlike layer structures are thereby developed via optimization of metal properties and relative layer thicknesses.

The Effects of Cyclic Loading on Fracture Modes in Brittle Layer Structures: Relevance to Failure of Dental Crowns

2008 ◽  
Vol 41-42 ◽  
pp. 21-26 ◽  
Author(s):  
Sarah Lam ◽  
Kimble Halliday ◽  
Tarek Qasim
Keyword(s):  
Cyclic Loading ◽  
Hard Spheres ◽  
Vertical Component ◽  
Dental Crowns ◽  
Layer Structures ◽  
Brittle Layer ◽  
Moist Environment ◽  
Loading Tests ◽  
Cyclic Loading Tests ◽  
Radial Cracks

The effects of cyclic loading on contact damage in curved bi-layer systems are investigated. Dome structures consisting of glass shells, filled with epoxy resin, simulate the essential structure of monolithic all-ceramic dental crowns on natural tooth dentine. Cyclic loading, with only a vertical component, was carried out with the Multi-Functional Chewing Simulator (Willytec. Munich, Germany). The specimens were tested by indentation with hard spheres of tungsten carbide, with the load applied axially at the apex of the dome. This project reports some new results on the effect of cyclic loading on curved bi-layer systems. In addition, the effect of aqueous environments is addressed. In both air and water tests, observations taken throughout the cyclic loading course indicated that the outer cone cracks inhibited the propagation of radial cracks. Results confirm that crack initiation occurred more rapidly in wet conditions of testing, emphasizing the influences of the moist environment of the oral cavity. Furthermore, the experiments took into account the evolution of inner cone cracks observed in wet cyclic loading tests. The new results are important since nearly all-dental crowns exhibit some curvature. The implications of the results on the failure of dental crowns are discussed.

Indenter/Coating Modulus Mismatches and Load Location Effects on Contact Damage in Curved Brittle-Based Bi-Layer Structures

2008 ◽  
Vol 41-42 ◽  
pp. 33-39
Author(s):  
Tarek Qasim ◽  
Xiao Zhi Hu ◽  
Mark Bush
Keyword(s):  
Radial Crack ◽  
Fracture Behaviour ◽  
Layered Systems ◽  
Contact Damage ◽  
Layer Structures ◽  
Brittle Layer ◽  
Specimen Axis ◽  
Load Location ◽  
Axis Of Symmetry ◽  
Radial Cracks

This paper summarizes some of the recent advances that have been made as a result of contact damage tests on bi-layer structures containing one brittle layer on a polymeric support base. The effects of indenter modulus (hard/soft indenters) and of the sate of loading (load location reference to the specimen axis of symmetry) on contact damage in bi-layer systems were investigated. Convex specimens having curvature of 12 mm inner coating diameter and 1mm thick were produced, and loaded along the axis of symmetry and off axis at 45o using flat indenters of six different moduli. The influence of indenter modulus on radial crack initiation and damage evolution was examined in respect to the load location, with particular attention paid to the relevance of such damage to lifetime-limiting failures of biomechanical layered systems. The results of this study illustrates that the fracture behaviour of brittle layered structures is not dominated by certain parameters. Critical loads for initiation of radial cracks are sensitive to indenter modulus (hardness) but not sensitive to load location. Load location plays an important role in crack propagation and subsequent damage patterns, especially at specimen margins.

Electron Energy Analysis of Germanium and Silica Layers on Silicon Substrates

1975 ◽  
Vol 33 ◽  
pp. 96-97
Author(s):  
R. W. Ditchfield ◽  
A. G. Cullis
Keyword(s):  
Epitaxial Growth ◽  
Electron Energy ◽  
Silicon Substrates ◽  
Secondary Phases ◽  
Si Substrates ◽  
Transmission Electron ◽  
Layer Structures ◽  
Si Films ◽  
Electron Energy Loss ◽  
Growth Centres

An energy analyzing transmission electron microscope of the Möllenstedt type was used to measure the electron energy loss spectra given by various layer structures to a spatial resolution of 100Å. The technique is an important, method of microanalysis and has been used to identify secondary phases in alloys and impurity particles incorporated into epitaxial Si films.Layers Formed by the Epitaxial Growth of Ge on Si Substrates Following studies of the epitaxial growth of Ge on (111) Si substrates by vacuum evaporation, it was important to investigate the possible mixing of these two elements in the grown layers. These layers consisted of separate growth centres which were often triangular and oriented in the same sense, as shown in Fig. 1.

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