engleski

Advanced Experimental Techniques of Stress Concentration Analysis in Damaged Regions

The assignment of mechanical structures design is to avoid any kind of hazardous situation, which is directly influenced to the safety of living and preservation of human environment. A sudden increase of deformations is significant for the regions around the stress concentrators, e.g. the crack tips and/or contact loading points. The task of experimental stress analysis is to prevent material damages and to predict the future of the inspected mechanical part, usually resulting by structural optimization. The great number of numerical and experimental techniques in fracture mechanics (e.g. multi-parameter methods of fringe analysis in photoelasticity) is employed for determining the stress intensity factors (SIF) of the cracks in deformed structures. The optical method of caustics is established for the application to mechanically isotropic materials, through the process of SIF&#8217 ; ; ; ; s evaluation reduced to the epicycloidal dark spot measuring. As the singularity at the crack tip is successfully solved, the method of caustic finds recently its application to the contact force problem. The reflection method of caustics is advantageously improved for the application to nontransparent mechanically anisotropic materials such as fiber-reinforced composites. The experimental optical effects are compared to the simulated ones for different types of contacts and different crack opening modes. The analysis of dynamic failure process in composites is performed by using high-speed photography and optical interferometric methods. It is possible to observe the phenomena of the formation of the damaged regions in the individual plies and high-speed delamination. Crack growth in bimaterial interfaces is interesting to be studied for the proper evaluation of the reliability of structural parts made of fiber-reinforced composites. The application of coherent gradient sensor (CGS) interferometry is suitable for recording the moment of dynamic crack initiation. CGS interferogram represents the registry of the real time near-tip deformation and shows the emission of stress waves during crack propagation. The results of evolution of the interfacial cracks between the core and the skins in light core sandwich material are significant for the physical process of shear crack initialization and extensive damage afterwards.

experimental mechanics; optical methods; fracture mechanics

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