Interfacial energy states of moisture-exposed cracks in mica

1990 ◽  
Vol 5 (1) ◽  
pp. 172-182 ◽  
Author(s):  
Kai-Tak Wan ◽  
Nicholas Aimard ◽  
S. Lathabai ◽  
Roger G. Horn ◽  
Brian R. Lawn
Keyword(s):  
Mechanical Energy ◽  
Crack Tip ◽  
Solid Substrate ◽  
Interface States ◽  
Equilibrium States ◽  
Work Of Adhesion ◽  
Equilibrium Crack ◽  
Adhesion Zone ◽  
Reversed Loading ◽  
Gibbs Formalism

Results of crack growth observations on mica in water-containing environments are described. The study focuses on equilibrium crack states for reversed loading cycles, i.e., for initial propagation through virgin solid and subsequent retraction-repropagation through healed or misoriented-healed interfaces. Departures from these equilibrium states are manifest as steady-state forward or backward crack velocities at specific applied loads. The equilibria are thereby interpreted as quiescent, threshold configurations G = WE, with G the Griffith mechanical-energy-release rate and WE the Dupré work of adhesion, on crack velocity (v-G) diagrams. Generally, WE is found to decrease with concentration of water, in accordance with a Gibbs formalism. Hysteresis is observed in the forward-backward-forward crack propagation cycle, signifying a reduction in the adhesion energy on exposure of the open interface to environmental species prior to healing. This hysteresis is especially marked for those interfaces that are misoriented before healing, indicating that the structure of the underlying solid substrate as well as of the intervening fluid is an important consideration in the interface energetics. The equilibrium states for different environments can be represented on a simple energy-level diagram, as differences between thermodynamic end-point states: initial, closed-interface states refer to crystallographic bonding configurations ahead of the crack-tip adhesion zone; final, open interface states refer to configurations behind the crack-tip zone. The significance of this diagram in relation to the fundamental atomic structure of interfaces in fracture and other adhesion geometries, including implications concerning kinetics, is discussed.

A Crack Close to and Perpendicular to an Interface: Resolution of Anomalous Behavior With a Cohesive Zone

2019 ◽  
Vol 86 (3) ◽  
Author(s):  
George G. Adams
Keyword(s):  
Cohesive Zone ◽  
Cohesive Zone Model ◽  
Applied Pressure ◽  
Stress Singularity ◽  
Crack Tip ◽  
Anomalous Behavior ◽  
Work Of Adhesion ◽  
Bimaterial Interface ◽  
Zone Model ◽  
Finite Distance

In this investigation, we consider a crack close to and perpendicular to a bimaterial interface. If the crack tip is at the interface then, depending on material properties, the order of the stress singularity will be equal to, less than, or greater than one-half. However, if the crack tip is located any finite distance away from the interface the stress field is square-root singular. Thus, as the crack tip approaches the interface, the stress intensity factor approaches zero (for cases corresponding to a singularity of order less than one-half) or infinity (for a singularity of order greater than one-half). The implication of this behavior is that for a finite applied pressure the crack will either never reach the interface or will reach the interface with vanishing small applied pressure. In this investigation, a cohesive zone model is used in order to model the crack behavior. It is found that the aforementioned anomalous behavior for the crack without a cohesive zone disappears and that the critical value of the applied pressure for the crack to reach the interface is finite and depends on the maximum stress of the cohesive zone model, as well as on the work of adhesion and the Dundurs' parameters.

Micromechanics-Based Modeling of Interfacial Debonding in Multilayer Structures

1999 ◽  
Vol 594 ◽  
Author(s):  
P. A. Klein ◽  
H. Gao ◽  
A. Vainchtein ◽  
H. Fujimoto ◽  
J. Lee ◽  
...  
Keyword(s):  
Fracture Energy ◽  
Plastic Flow ◽  
Fracture Process ◽  
Process Zone ◽  
Crack Tip ◽  
Multilayered Structure ◽  
Interfacial Debonding ◽  
Work Of Adhesion ◽  
Small Scale ◽  
Fracture Characterization

AbstractClassical approaches to modeling fracture have proved successful in applications for which the highly deformed region near a crack tip is small compared to any other relevant dimensions in the structure. The classical theory relies on phenomenological criteria for material failure that lack a physics-based description of the fracture process itself. Small scale, thin film structures pose difficulties for analysis by these approaches because they contain complicated geometry and many interfaces within the fracture process zone itself. Moreover, plastic flow in metal layers is often severely constrained by the surrounding structure, causing the plastic dissipation part of the overall fracture energy consumed by debonding to be a strong function of geometry. Therefore, it can no longer be regarded as an intrinsic material property. To improve the fracture characterization of these structures, one must develop a physically sound methodology capable of separating the contribution of plastic flow, and other sources of dissipation, from the work of adhesion consumed at the crack tip. In this study, we investigate the parameters affecting energy dissipation by interfacial debonding in a multilayered structure. Interlayer decohesion is modeled using the Virtual Internal Bond constitutive model. We compare our predicted variations in the macroscopic fracture energy with experimental results for varying layer geometry. We also characterize the effect of variations in material properties and other experimental uncertainties in the resulting debonding behavior.

Crack propagation thresholds: A measure of surface energy

1986 ◽  
Vol 1 (6) ◽  
pp. 852-860 ◽  
Author(s):  
Robert F. Cook
Keyword(s):  
Surface Energy ◽  
Crack Propagation ◽  
Crack Extension ◽  
Mechanical Energy ◽  
Crack Tip ◽  
Surface Force ◽  
Energy Term ◽  
Propagation Characteristics ◽  
Applied Loading ◽  
Work Done

Crack propagation thresholds in brittle materials are explained by consideration of the work done by the applied loading and that needed to create new surfaces as a crack propagates. The threshold mechanical energy release rate is shown to be a measure of the equilibrium surface energy of the material, dependent on the chemical environment. For applied loadings greater than those needed to maintain equilibrium the surface energy term introduces nonlinearities into the crack propagation characteristics. Any surface force or lattice trapping behavior at the crack tip will not influence the observed threshold provided the crack tip remains invariant on crack extension. A simple indentation/strength technique is demonstrated that permits the surface energy in the equilibrium state to be estimated. The technique is applied to the propagation of cracks in sapphire and the surface energy in water estimated as 1.42 J m−2, suggesting that the surfaces in water are stabilized by interactions stronger than van der Waals forces or hydrogen bonding alone.

Stretched Polymer Nanohairs by Tailored Capillarity and Adhesive Force

2006 ◽  
Vol 948 ◽  
Author(s):  
Hoon Eui Jeong ◽  
Sung Hoon Lee ◽  
Pilnam Kim ◽  
Kahp Y. Suh
Keyword(s):  
Polymer Film ◽  
Polymer Melt ◽  
Adhesive Force ◽  
Solid Substrate ◽  
Work Of Adhesion ◽  
Thin Polymer Film ◽  
Urethane Acrylate ◽  
Simple Method ◽  
Polymer Interface ◽  
Thin Polymer

ABSTRACTWe present a simple method for fabricating high aspect-ratio polymer nanostructures on a solid substrate by sequential application of molding and drawing of a thin polymer film. In this method, a thin polymer film is prepared by spin coating on a solid substrate and the temperature is raised above the polymer¡¯s glass transition while in conformal contact with a poly(urethane acrylate) (PUA) mold having nano-cavities. Consequently, capillary forces induces deformation of the polymer melt into the void spaces of the mold and the filled nanostructure was further elongated upon removal of the mold due to tailored adhesive force at the mold/polymer interface. The optimum value of the work of adhesion at the mold/polymer interface ranged from 0.9 to 1.1 times that at the substrate/polymer interface. Below or above this range, a simple molding or detachment occurred, corresponding to earlier findings.

scholarly journals A mechanism for enhanced static sliding resistance owing to surface waviness

2011 ◽  
Vol 467 (2132) ◽  
pp. 2209-2223 ◽  
Author(s):  
J. F. Waters ◽  
P. R. Guduru
Keyword(s):  
Contact Area ◽  
Flat Surface ◽  
Mechanical Energy ◽  
Wavy Surface ◽  
Work Of Adhesion ◽  
Rigid Sphere ◽  
Surface Waviness ◽  
Additional Energy ◽  
Normal Separation ◽  
Sliding Resistance

This paper presents an analysis of static sliding resistance of a rigid sphere on a soft elastic material with axisymmetric waviness. When the sphere is loaded laterally under a fixed normal force, the contact area is subjected to mixed-mode loading. It is shown that, as the lateral loading increases, the decrease in contact area involves unstable jumps; and each unstable jump dissipates mechanical energy. The additional energy dissipation increases the peak force required for gross sliding of the interface compared with that of a flat surface. Thus, a mechanism is proposed for enhanced static sliding resistance on the surface of a soft material owing to surface waviness-induced instabilities. Such an increase in sliding resistance is analogous to a similar increase in the detachment force between a sphere and a wavy surface during normal separation, which was reported elsewhere. The influence of mode-mixity-dependent work of adhesion on the static sliding resistance of a wavy surface is also considered.

scholarly journals Spherical Droplet Deposition—Mechanistic Model

Coatings ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 248
Author(s):  
Jacek A. Michalski ◽  
Slawomir Jakiela
Keyword(s):  
Experimental Data ◽  
Liquid Drop ◽  
Mechanistic Model ◽  
Mechanical Energy ◽  
Single Point ◽  
Solid Substrate ◽  
Physical Models ◽  
Droplet Deposition ◽  
Spherical Droplet ◽  
Wetted Area

In the currently existing physical models of wetting a solid substrate by a liquid drop, the contact angle is determined on the basis of the equilibrium of forces acting tangentially to the wetted surface at any point in the perimeter of the wetted area, ignoring the forces (or their components) acting perpendicular to this area. In the solution shown in the paper, the equilibrium state of forces acting on a droplet was determined based on the minimum mechanical energy that the droplet achieves in the state of equilibrium. This approach allows one to take into account in the model, in addition to the forces tangential to the wetted surface, also forces perpendicular to it (also the force of adhesion), moreover, these may be dispersed forces acting on the entire interface, not on a single point. The correctness of this approach is confirmed by the derived equations concerning the forces acting on the liquid both tangentially and perpendicularly to the wetted surface. The paper also identifies the areas of solutions in which the obtained equilibrium of forces is stable and areas of unstable equilibrium of forces. The solution is formulated both for isothermal and isochoric system. Based on the experimental data accessible in the literature, the condition that has to be met by the droplets (and their surroundings) during measurements performed under gravity conditions was formulated.

Simulation and Contrast Analysis of tem Images of Cracks

1990 ◽  
Vol 48 (1) ◽  
pp. 578-579
Author(s):  
D. Goyal ◽  
A. H. King
Keyword(s):  
Displacement Vector ◽  
Crack Tip ◽  
Perfect Crystal ◽  
Operating Conditions ◽  
Displacement Fields ◽  
Fringe Contrast ◽  
Orthogonal Geometry ◽  
Moire Fringe ◽  
Moiré Fringe

TEM images of cracks have been found to give rise to a moiré fringe type of contrast. It is apparent that the moire fringe contrast is observed because of the presence of a fault in a perfect crystal, and is characteristic of the fault geometry and the diffracting conditions in the TEM. Various studies have reported that the moire fringe contrast observed due to the presence of a crack in an otherwise perfect crystal is distinctive of the mode of crack. This paper describes a technique to study the geometry and mode of the cracks by comparing the images they produce in the TEM because of the effect that their displacement fields have on the diffraction of electrons by the crystal (containing a crack) with the corresponding theoretical images. In order to formulate a means of matching experimental images with theoretical ones, displacement fields of dislocations present (if any) in the vicinity of the crack are not considered, only the effect of the displacement field of the crack is considered.The theoretical images are obtained using a computer program based on the two beam approximation of the dynamical theory of diffraction contrast for an imperfect crystal. The procedures for the determination of the various parameters involved in these computations have been well documented. There are three basic modes of crack. Preliminary studies were carried out considering the simplest form of crack geometries, i. e., mode I, II, III and the mixed modes, with orthogonal crack geometries. It was found that the contrast obtained from each mode is very distinct. The effect of variation of operating conditions such as diffracting vector (), the deviation parameter (ω), the electron beam direction () and the displacement vector were studied. It has been found that any small change in the above parameters can result in a drastic change in the contrast. The most important parameter for the matching of the theoretical and the experimental images was found to be the determination of the geometry of the crack under consideration. In order to be able to simulate the crack image shown in Figure 1, the crack geometry was modified from a orthogonal geometry to one with a crack tip inclined to the original crack front. The variation in the crack tip direction resulted in the variation of the displacement vector also. Figure 1 is a cross-sectional micrograph of a silicon wafer with a chromium film on top, showing a crack in the silicon.

Reduction of structural vibrations with the piezoelectric stacks ring

2020 ◽  
Vol 64 (1-4) ◽  
pp. 729-736
Author(s):  
Jincheng He ◽  
Xing Tan ◽  
Wang Tao ◽  
Xinhai Wu ◽  
Huan He ◽  
...  
Keyword(s):  
Vibration Control ◽  
Mechanical Energy ◽  
Electrical Energy ◽  
Structural Vibrations ◽  
Rotor Systems ◽  
Fea Model ◽  
Piezoelectric Stacks ◽  
Shunt Damping ◽  
Reduction Effect ◽  
Euler Bernoulli Beam

It is known that piezoelectric material shunted with external circuits can convert mechanical energy to electrical energy, which is so called piezoelectric shunt damping technology. In this paper, a piezoelectric stacks ring (PSR) is designed for vibration control of beams and rotor systems. A relative simple electromechanical model of an Euler Bernoulli beam supported by two piezoelectric stacks shunted with resonant RL circuits is established. The equation of motion of such simplified system has been derived using Hamilton’s principle. A more realistic FEA model is developed. The numerical analysis is carried out using COMSOL® and the simulation results show a significant reduction of vibration amplitude at the specific natural frequencies. Using finite element method, the influence of circuit parameters on lateral vibration control is discussed. A preliminary experiment of a prototype PSR verifies the PSR’s vibration reduction effect.

Macroeconomic Equilibrium Theory in the Context of Methodological Problems of Contemporary Economic Science

2008 ◽  
pp. 77-88
Author(s):  
M. Likhachev
Keyword(s):  
Empirical Analysis ◽  
Equilibrium States ◽  
Equilibrium Theory ◽  
Economic Systems ◽  
Economic Science ◽  
The Real ◽  
Theoretical Status ◽  
Methodological Problems ◽  
Real Stability

The article is devoted to the analysis of methodological problems in using the conception of macroeconomic equilibrium in contemporary economics. The author considers theoretical status and relevance of equilibrium conception and discusses different areas and limits of applicability of the equilibrium theory. Special attention is paid to different epistemological criteria for this theory taking into account both empirical analysis of the real stability of economic systems and the problem of unobservability of equilibrium states.

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