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

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.

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.

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.

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

Layer Structures. 4. Role of Long Alkane Spacers in Poly(ester imide)s Derived fromN-(4‘-Hydroxyphenyl)-4-hydroxyphthalimide

1996 ◽  
Vol 29 (12) ◽  
pp. 4234-4240 ◽  
Author(s):  
Hans R. Kricheldorf ◽  
Nicolas Probst ◽  
Gert Schwarz ◽  
Christoph Wutz
Keyword(s):  
Layer Structures

Metastability in SiGe/Si Strained-Layer Structures

1988 ◽  
Vol 116 ◽  
Author(s):  
Brian W. Dodson
Keyword(s):  
Experimental Data ◽  
Plastic Deformation ◽  
Crystal Growth ◽  
Strain Relaxation ◽  
Dislocation Dynamics ◽  
Strained Layer ◽  
Layer Structures ◽  
Standard Models ◽  
Stability Limits

AbstractThe physics governing growth and stability properties in SiGe/Si strainedlayer structures is reviewed. The role of metastability in crystal growth is outlined. Experimental data on stability limits and rates of strain relaxation are examined. We conclude that essentially all observations on relaxation of semiconductor strained-layer structures can be explained by standard models of plastic deformation adapted to the special conditions controlling dislocation dynamics in these structures.

Dislocation Nucleation in Heteroepitaxial Semiconducting Films

2009 ◽  
Vol 156-158 ◽  
pp. 251-259
Author(s):  
Bernard Pichaud ◽  
N. Burle ◽  
Michael Texier ◽  
C. Fontaine ◽  
V.I. Vdovin
Keyword(s):  
Dislocation Nucleation ◽  
Support Surface ◽  
Atomic Simulation ◽  
Gaas Substrates ◽  
Surface Steps ◽  
Layer Structures ◽  
Classical Models ◽  
Nucleation Centre ◽  
Original Dislocation

The nucleation of dislocation in semiconductors is still a matter of debate and especially in heteroepitaxial films. To understand this nucleation process the classical models of dislocation nucleation are presented and discussed. Two main points are then developed: emission of dislocations from surface steps and the role of point defects agglomeration on dislocation nucleation. Recent atomic simulation of half loops emission from surface steps and experimental evidences of anisotropic relaxation of GaInAs films deposited on vicinal (111) GaAs substrates strongly support surface steps as preferential sites for nucleation. In low temperature buffer layer structures (SiGe/Si) an original dislocation structure is observed which corresponds to the dislocation emission in different glide systems by a unique nucleation centre.

Mechanistic Investigations into the Adhesion between RFL-Treated Cords and Rubber. Part I: The Influence of Rubber Curatives

2007 ◽  
Vol 80 (4) ◽  
pp. 545-564 ◽  
Author(s):  
W. B. Wennekes ◽  
J. W. M. Noordermeer ◽  
R. N. Datta
Keyword(s):  
Adhesion Force ◽  
Resorcinol Formaldehyde ◽  
Scientific Investigations ◽  
Rubber Compounds ◽  
Brittle Layer ◽  
Cure Time ◽  
Rubber Part ◽  
Peel Adhesion ◽  
Peel Force

Abstract The adhesion between virgin textile cords and rubber is always weak, because of significant differences between fiber and rubber in modulus, elongation, polarity as well as reactivity. In order to improve the adhesion, it is customary to use adhesive systems, which act as bridges between elastomer and reinforcement. These are commonly based on Resorcinol/Formaldehyde/Latex (RFL) dips. For polyester and aramid fibers, two dip systems are applied. The first one is an epoxy pre-dip and the second dip is a RFL dip again. Although several mechanisms are proposed to explain the role of RFL, the majority of these explanations are based on assumptions rather than proper scientific investigations. In this paper an attempt is made to understand the role of the rubber vulcanization system on RFL-to-rubber bonding as judged by measuring the H-pullout force, Strap Peel Adhesion Force (SPAF) and the mechanical properties of the compounds. A positive correlation is found between the optimum cure time (t90) of the rubber compounds and the pullout and peel force. In literature this is commonly explained by the lack of curative migration from the rubber into the dip when t90 is low. In the present paper curative migration is monitored by scanning electron microscopy coupled to an energy dispersive X-ray spectrometer (SEM-EDX). A strong enrichment of curatives in the RFL dip near the interface is observed. A high accelerator loading results in a low t90 of the rubber compound as well as a more pronounced enrichment of curatives in the dip near the interface. Therefore the drop in adhesion does not occur because of lack of curative migration from rubber to the RFL layer, but more likely due to overcure of the latex in the dip, causing a brittle layer resulting in low pullout and peel strengths.

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