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Richard M. Christensen |
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Looking Ahead
The subsequent future section will be on cumulative damage in general materials, not necessarily composites. The term cumulative damage has a somewhat similar connotation as progressive damage but traditionally the former term applies broadly while the latter one is usually taken in the composites context. As developed here, cumulative damage will be considered to be a continuous or quasi-continuous process, as in cyclic fatigue, rather than a collection of discrete, local failure processes. Like progressive damage, cumulative damage is a very challenging topic. The use of fracture mechanics deserves explanation here. It will be found to play a major role in the coming 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 covering other related topics. The homepage is now in its second iteration, after a major redesign. Such changes will continue to occur from time to time. |
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The next section to be given will be on progressive damage in fiber composite laminates. The idea behind it is quite simple. Both “matrix controlled” and “fiber controlled” types of failures can separately and sequentially occur during loading of the various lamina within a laminate. At some point so much damage has accumulated in the form of these local failures that the laminate can no longer sustain load. This then comprises the ultimate load, actually failure in the broad and total sense. However, what sounds simple in concept is anything but simple in practice, no doubt due to the inherent nonlinearity of the processes. The field is evolving; final methods and results are scarce. It is not so much that the field is a generator of controversy as that it is in a state of serious uncertainty. An introductory treatment of progressive damage will be given here. The online form should appear within a matter of some months, after considering the many alternative approaches. |
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Copyright© 2008 |
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