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

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.

The Role of Microtexture on Fatigue Lifetime Variability and Crack Initiation Mechanisms (Preprint)

2011 ◽  
Author(s):  
Christopher J. Szczepanski ◽  
S. L. Semiatin ◽  
James M. Larsen
Keyword(s):  
Crack Initiation ◽  
Fatigue Lifetime

Role of plasticity on interface crack initiation from a free edge and propagation in a nano-component

2007 ◽  
Vol 145 (4) ◽  
pp. 261-271 ◽  
Author(s):  
Hiroyuki Hirakata ◽  
Yoshimasa Takahashi ◽  
Do Truong ◽  
Takayuki Kitamura
Keyword(s):  
Crack Initiation ◽  
Interface Crack ◽  
Free Edge

On velocity gradient dynamics and turbulent structure

2015 ◽  
Vol 780 ◽  
pp. 60-98 ◽  
Author(s):  
J. M. Lawson ◽  
J. R. Dawson
Keyword(s):  
Velocity Gradient ◽  
Local Strain ◽  
Turbulent Structure ◽  
Stochastic Estimation ◽  
Spatially Resolved ◽  
Gradient Dynamics ◽  
Layer Structures ◽  
Non Local ◽  
Conditional Averaging

The statistics of the velocity gradient tensor $\unicode[STIX]{x1D63C}=\boldsymbol{{\rm\nabla}}\boldsymbol{u}$, which embody the fine scales of turbulence, are influenced by turbulent ‘structure’. Whilst velocity gradient statistics and dynamics have been well characterised, the connection between structure and dynamics has largely focused on rotation-dominated flow and relied upon data from numerical simulation alone. Using numerical and spatially resolved experimental datasets of homogeneous turbulence, the role of structure is examined for all local (incompressible) flow topologies characterisable by $\unicode[STIX]{x1D63C}$. Structures are studied through the footprints they leave in conditional averages of the $Q=-\text{Tr}(\unicode[STIX]{x1D63C}^{2})/2$ field, pertinent to non-local strain production, obtained using two complementary conditional averaging techniques. The first, stochastic estimation, approximates the $Q$ field conditioned upon $\unicode[STIX]{x1D63C}$ and educes quantitatively similar structure in both datasets, dissimilar to that of random Gaussian velocity fields. Moreover, it strongly resembles a promising model for velocity gradient dynamics recently proposed by Wilczek & Meneveau (J. Fluid Mech., vol. 756, 2014, pp. 191–225), but is derived under a less restrictive premise, with explicitly determined closure coefficients. The second technique examines true conditional averages of the $Q$ field, which is used to validate the stochastic estimation and provide insights towards the model’s refinement. Jointly, these approaches confirm that vortex tubes are the predominant feature of rotation-dominated regions and additionally show that shear layer structures are active in strain-dominated regions. In both cases, kinematic features of these structures explain alignment statistics of the pressure Hessian eigenvectors and why local and non-local strain production act in opposition to each other.

Entrapping an impacting particle at a liquid–gas interface

2018 ◽  
Vol 841 ◽  
pp. 1073-1084 ◽  
Author(s):  
Han Chen ◽  
Hao-Ran Liu ◽  
Xi-Yun Lu ◽  
Hang Ding
Keyword(s):  
Immersed Boundary Method ◽  
Density Ratio ◽  
Liquid Pool ◽  
Diffuse Interface ◽  
Critical Conditions ◽  
Immersed Boundary ◽  
Structure Interaction ◽  
Scaling Models ◽  
The Impact

We numerically investigate the mechanism leading to the entrapment of spheres at the gas–liquid interface after impact. Upon impact onto a liquid pool, a hydrophobic sphere is seen to follow one of the three regimes identified in the experiment (Lee & Kim, Langmuir, vol. 24, 2008, pp. 142–145): sinking, bouncing or being entrapped at the interface. It is important to understand the role of wettability in this process of flow–structure interaction with dynamic wetting, and in particular, to what extent the wettability can determine whether the sphere is entrapped at the interface. For this purpose, a diffuse-interface immersed boundary method is adopted in the numerical simulations. We expand the parameter space considered previously, provide the phase diagrams and identify the key phenomena in the impact dynamics. Then, we propose the scaling models to interpret the critical conditions for the occurrence of sphere entrapment, accounting for the wettability of the sphere. The models are shown to provide a good correlation among the impact inertia of the drop, the surface tension, the wettability and the density ratio of the sphere to the liquid.

Effect of microtubule-destroying drugs on the spreading and shape of cultured epithelial cells

1985 ◽  
Vol 74 (1) ◽  
pp. 267-282
Author(s):  
L.V. Domnina ◽  
J.A. Rovensky ◽  
J.M. Vasiliev ◽  
I.M. Gelfand
Keyword(s):  
Glass Surface ◽  
Cell Shape ◽  
Medium Effects ◽  
Adhesive Surface ◽  
Lipid Films ◽  
Cultured Epithelial Cells ◽  
The Media ◽  
Glass Surfaces ◽  
Cytoplasmic Processes

The role of microtubules in the spreading of cells from the liver-derived IAR2 rat cell line was studied. Cells in the control medium seeded on a flat isotropic glass surface rapidly spread to form discoid shapes. Spreading in colcemid-containing medium was disorganized and delayed; partial reversal of spreading was observed. Nevertheless, even in the presence of colcemid the cells finally spread to discoid flattened shapes. IAR2 cells in medium without colcemid spread not to discoid but to elongated shapes under three different sets of conditions: (1) when the cells were forced to spread on narrow strips of adhesive glass surface between two non-adhesive lipid films; (2) when the cells spread on the poorly adhesive surface of poly(HEMA)-covered glass; (3) when the cells spread on the usual glass surfaces in medium containing cytochalasin D. Addition of colcemid to the media reversed the polarized spreading under the first two conditions; colcemid did not reverse the formation of the elongated cell shape acquired by the cells spreading in cytochalasin-containing medium. Effects of microtubule-destroying drugs on the spreading of epithelial and fibroblast cells are compared and discussed. It is suggested that microtubules are essential for the stabilization of the spread state of those attached cytoplasmic processes and lamellae that do not have numerous and stable-cell substratum contacts, e.g. the processes formed at the early stages of spreading or the elongated processes of polarized cells. Possibly, microtubules stabilize the non-contracted state of the actin cytoskeleton in these processes.

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