Richard M. Christensen |
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Looking Ahead
A future section will be on probabilistic aspects of failure behavior and related failure criteria. In the physical world nothing is absolutely, purely deterministic. There is always variability. For most practical purposes the variability can be smoothed over and only mean value effects considered. There are situations however where the variability is so great, or the design requirements so narrow, that variability cannot be ignored. Examples of these situations will be given and rules or classes of problems will be identified where the probabilistic aspects of the failure problem represents the major challenge to be confronted. Of particular interest will be Weibul statistics. Reasons will be sought to explain the special relationship of Weibul type behavior to the classes of material failure problems of interest here. The use of fracture mechanics deserves explanation here. It was found to play a major role in the section on cumulative damage. Infact, the importance and use of fracture mechanics is suffused throughout this website. It is crucially important in the isotropic material presentation in Section II, and it certainly is pervasive in its general importance, especially for structures. The view here is that the two subjects (i) failure criteria for homogeneous materials, and (ii) fracture mechanics for materials and structures are complementary, stand alone disciplines. The basic properties for both fields are needed in order to completely characterize the performance capability for any particular material in any particular application. A separate section on fracture mechanics is not planned here since it already is so widely and effectively treated. Future possibilities for this website include such interrelated topics as:
Other related interests and topics may evolve. |
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Can Atomic/Nano Scale |
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Copyright© 2010 |
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One of the longest standing problems in materials characterization is how to define, assign, determine both the yield stress and the failure stress (strength) from experimental records. There are many definitions related to yield stress but all or nearly all are quite arbitrary and devoid of a meaningful physical interpretation. Strength determination, as commonly practiced, is equally unsatisfactory, at least in the case of ductile materials. The situation is more clear-cut in the case of brittle materials, in a brittle mode of failure. General, physically based methods for determining both the yield stress and the failure stress will be given. Such definitions are needed in order to make optimal use of failure criteria.
