Fracture theory

The parameter is a crack propagation velocity and n(e) is a crack activation law driven by the bulk tensile strain e and specified by the Weibull fracture theory... 

X-Ray irradiation of quartz or silica particles induces an electron-trap lattice defect accompanied by a parallel increase in cytotoxicity (Davies, 1968). Aluminosilicate zeolites and clays (Laszlo, 1987) have been shown by electron spin resonance (e.s.r.) studies to involve free-radical intermediates in their catalytic activity. Generation of free radicals in solids may also occur by physical scission of chemical bonds and the consequent formation of dangling bonds , as exemplified by the freshly fractured theory of silicosis (Wright, 1950 Fubini et al., 1991). The entrapment of long-lived metastable free radicals has been shown to occur in the tar of cigarette smoke (Pryor, 1987). 

The fracture theory is the most widely applied theory in studying mucoadhesion mechanisms. It accormts for the forces required to separate two sttrfaces after adhesion. The maximttm tensile stress (a) produced dttring detachment can be determined by Eq. (6) by dividing the maximiun force of detachment by the total surface area A ) involved in the adhesive interaction ... 

The same theories relevant to adhesion, developed to explain and predict the performance of glues, adhesives, and paints, have also been applied to bioadhesive systems [44], These include the electronic, absorption, wetting, diffusion, and fracture theories. 

Several mechanisms by which mucoadhesives adhere to biological surface have been suggested, including the electronic, adsorption, wetting, diffusion, and fracture theories. It is likely that water movement from the mucosa to the polymer and physical entanglement of the adhesive polymer in the mucus glycoprotein chains are important in obtaining adherence. 

Several mechanisms of the polymer/mucus interaction have been suggested, including the electronic, adsorption, wetting, diffusion, and fracture theories. 

An explanation for the anomalous behavior of the most highly crosslinked DGEBA/DDS network may be that it was chemically unstable at the high test temperatures (25(K260 °C) required to reach the rubbery range for this network. Also, the threshold fracture theories may simply fail to describe the structure-fracture relationship of this very highly crosslinked network. 

The fracture theory does not take into account biological phenomena such as stress caused, for example, by movement of the tissue. 

Bueche and Halpin (126, 203, 215-217) have developed a fracture theory for amorphous rubbers. Their model pictures rupture as the result of the propagation of tears or cracks within the material. The growth of a tear is viewed as a process in which molecular chains at the tip of the tear stretch viseoelastieally, under the influence of a high stress concentration, until they rupture. The failure process is a non-equilibrium one, developing with time and involving consecutive rupture of molecular chains. The principal result of the theory is embodied in the equation... 

The mechanisms of bioadhesion have been reviewed by Kaelble and Moacanin [62] and by Peppas and Buri [84] and may be classified as chemical (electronic and adsorption theories) and physical (wetting, interpenetration and fracture theories). 

The starting point of the fracture theory is the Griffith-Irwin theory of cohesive fracture. It has been extended to the adhesive fracture According to this theory the fracture strength a of an adhesive bond is related to the fracture energy e and the critical crack length 1. It is... 

There are two principal theories, or models, that attempt to describe what happens during brittle fracture, the Griffith fracture theory and the Irwin model. Both assume that fracture takes place through the presence of preexisting cracks or flaws in the polymer and are concerned with what happens near such a crack when a load is applied. Each leads to the definition of a fracture-toughness parameter and the two parameters are closely related to each other. The Griffith theory is concerned with the elastically stored energy near the crack, whereas the Irwin model is concerned with the distribution of stresses near the crack. Both theories apply strictly only for materials that are perfectly elastic for small strains and are therefore said to describe linear fracture mechanics. 

Xing, S.R. Xiao, L. Zhang, J.P. 2010. An Analysis of Fracture Theory on the Expansion of Complex Macroscopic Cracks Caused By Pre-fracturing of Coal Seams. China Coal 36(10) 107-111. 

The polymer chain undergoes fracture if the maximum force along the contour exceeds a critical value, (the critical-stress-to-fracture theory)... 

According to the critical-stress-to-fracture theory (assumption 2), the chain is fractured at up- The scaling of the critical fracture strain rate cp on and can be derived from (13) as... 

Some researchers also speculate that the primary factor governing chain scission in FTP is not the frictional force at break (critical-stress-to-fracture theory, assumption 2) but the elastic energy stored in the deformed molecule [110]. A few experimental results seem to support the argument [146, 147]. 

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