TAILIEUCHUNG - Lifetime-Oriented Structural Design Concepts- P8

Lifetime-Oriented Structural Design Concepts- P8: At the beginning of 1996, the Cooperative Research Center SFB 398 financially supported by the German Science Foundation (DFG) was started at Ruhr-University Bochum (RUB). A scientists group representing the fields of structural engineering, structural mechanics, soil mechanics, material science, and numerical mathematics introduced a research program on “lifetimeoriented design concepts on the basis of damage and deterioration aspects”. | 168 3 Deterioration of Materials and Structures Fig. . Electrical potential - plain specimen Fig. . Electrical potential - circular specimen The distribution of the electrical potential across the plain and circular specimen for different crack length is given in Figures and . The results of both the finite element analysis and experiments for both types of specimen are represented in Figure as a dimensionless plot of electrical resistance ratio R R0 against a w where R0 is the electrical resistance at the initial crack length a0 R is the electrical resistance at the crack length a and w is half width of the specimen at the crack height. A good agreement between experimental result and the numerical solution of evolution of the electrical resistance with the crack propagation can be observed. The obtained evolution of the electrical resistance shows at the same time a high level of similarity to the measured crack propagation behaviour under cyclic fatigue load. Based on this results it can be concluded that the method of the resistance measurement detects the appearance of the damage in the early phase and it confirms the development of a damage evolution on the basis of microscopic crack incubation and initiation. Experiments 169 Fig. . Evolution of electrical resistance vs. crack length during fatigue - plain and circular specimen Acoustic Emission The mechanisms by which metals absorb and release strain energy under stress the modelling of which is the basis of fracture mechanics analysis can be different and complicated. Acoustic emission is the elastic energy that is spontaneously released by materials when they undergo deformation. The stress waves which result from this sudden release of elastic energy due to micro-fracture events are of most interest to the structural engineer. These events are typically 10pm to 100pm in linear dimension. Sources of acoustic emission include many different mechanisms of deformation .

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