The Crack-contact and the Free End Problem for a Strip Under Residual Stress

The plane problem for an infinite strip with two edge cracks under a given state of residual stress is considered. The residual stress is compressive near and at the surfaces and tensile in the interior of the strip. If the crack is deep enough to penetrate into the tensile zone, then the problem is one of crack-contact problem in which the depth of the contact area is an unknown which depends on the crack depth and the residual stress profile. The problem has applications to the static fatigue of glass plates and is solved for three typical residual stress profiles. In the limiting case of the crack crossing the entire plate thickness, the problem becomes a stress-free end problem for a semi-infinite strip under a given residual stress state away from the end. This is a typical stress diffusion problem in which decay behavior of the residual stress near and the nature of the normal displacement at the end of the semi-infinite strip are of special interest. For two typical residual stress states the solution is obtained, and some numerical results are given

Fracture of composite panels

The fracture problem in panels consisting of periodically arranged load carrying and buffer strips of different materials is considered. The main emphasis is placed on the problem of a crack terminating at and crossing the interfaces and on the stress free end problem. The problem is formulated in terms of a system of singular integral equations, and numerical solutions are obtained for certain material combinations. With the study of possible crack propagation and delamination in mind, certain stress intensity factors are defined and calculated. A main result is that when the crack touches or intersects a bimaterial interface, the stress state has no longer the standard square root singularity, and, to study further propagation of the crack, the conventional fracture models need to be modified, or new models need to be developed

Crack opening stretch in a plate of finite width

The problem of a uniaxially stressed plate of finite width containing a centrally located damage zone is considered. It is assumed that the flaw may be represented by a part-through crack perpendicular to the plate surface, the net ligaments in the plane of the crack and through-the-thickness narrow strips ahead of the crack ends are fully yielded, and in the yielded sections the material may carry only a constant normal traction with magnitude equal to the yield strength. The problem is solved by neglecting the bending effects and the crack opening stretches at the center and the ends of the crack are obtained. Some applications of the results are indicated by using the concepts of critical crack opening stretch and constant slope plastic instability

Transverse cracks in a strip with reinforced surfaces

The symmetrical problem of two transverse cracks in an elastic strip with reinforced surfaces is formulated in terms of a singular integral equation. The special cases of one central crack or two edge cracks are discussed. Numerical methods for solving the problems with internal cracks are outlined and stress intensity factors are presented for various geometrics and degrees of surface reinforcement

Fracture of composite plates containing periodic buffer strips

Fracture of a composite plate which consists of perfectly bonded parallel load carrying laminates and buffer strips is considered. Fatigue cracks appear and spread in main laminates or in buffer strips or in both perpendicular to the interfaces. The external load is applied to the plate parallel to the strips and away from the crack region. The problem is solved for fully imbedded cracks and for broken laminates or strips. Corresponding stress intensity factors are calculated

Virtual money, practices and moral orders in Second Life

Virtual monies present a limit case in debates about money's moral and political entanglements between sociologists, anthropologists, and economists. Digitized virtual monies seem ephemeral, almost ideal typical examples of money as a pure medium of exchange. This paper begins with the premise that virtual monies are as value-laden and morally entangled as any other form of money. This assertion is demonstrated by exploring how one type of virtual money, the Linden dollar (L$), and some of its associated practices are bound up with research participants' moral categories and judgments in the virtual world of Second Life (SL). Participants' accounts of virtual money practices are linked to moral attributes, sometimes in stark ‘good’ or ‘bad’ dichotomies, but also in more nuanced terms. These framings reproduce classifications of people and practices along a continuum with virtuousness at one end and maliciousness or harm at the other, passing through various states of possible moral dubiousness. For respondents, these two judgments go together; people are what they do with money. As a result, respondents decide what ‘people like that’ deserve. Evaluating someone's money practices means assessing the person. Participants' accounts of Linden dollar practices overlap with explanations of what SL is and how residents should live there. In SL, money is a form of material culture through which appropriate ways of being in the world are debated and reproduced

From Indymedia to Anonymous: rethinking action and identity in digital cultures

The period following the social mobilizations of 2011 has seen a renewed focus on the place of communication in collective action, linked to the increasing importance of digital communications. Framed in terms of personalized ‘connective action’ or the social morphology of networks, these analyses have criticized previously dominant models of ‘collective identity’, arguing that collective action needs to be understood as ‘digital networking’. These influential approaches have been significantly constructed as a response to models of communication and action evident in the rise of Independent Media Centres in the period following 1999. After considering the rise of the ‘digital networking’ paradigm linked to analyses of Indymedia, this article considers the emergence of the internet-based collaboration known as Anonymous, focusing on its origins on the 4chan manga site and its 2008 campaign against Scientology, and also considers the ‘I am the 99%’ microblog that emerged as part of the Occupy movement. The emergence of Anonymous highlights dimensions of digital culture such as the ephemeral, the importance of memes, an ethic of lulz, the mask and the grotesque. These forms of communication are discussed in the light of dominant attempts to shape digital space in terms of radical transparency, the knowable and the calculable. It is argued that these contrasting approaches may amount to opposing social models of an emerging information society, and that the analysis of contemporary conflicts and mobilizations needs to be alert to novel forms of communicative practice at work in digital cultures today