engleski

Advanced Methods of Structural Damage Analysis

Damaging process analysis is significant for determination of reliability of mechanical components while the numerical simulations of crack appearances and growing will process phenomena of structural damages. In recent years, substantial advances in the understanding of the basic principles governing dynamic structural damage, coupled with the development of new, relatively easy to use verifiable computational methodologies have made it possible to utilize the concepts of fatigue and fracture analysis to a wide spectrum of very diverse applications. They are relevant to technical problems, such as accident prevention, manufacturing processes, and reliability in design. Advanced experimental and numerical analysis will provide the verification of behavior of structural elements. Numerical analysis of dynamic loading and its optimization is important even in the designing of the structure to reduce possible damages, preferably combined by the experimental verification. In electrical transmission line severe damage or even breakdown of the conductor can occur due to material fatigue caused by the Aeolian vibrations. In order to examine accuracy of the developed computational program, as well as correctness of the estimation of the data used (wind power, data on the damper's mechanical impedance, and mechanical characteristics of the conductor), results generated using the developed computer program and data from field measurements are compared. Maximum stresses in the conductor at the suspension clamp and at the damper clamp can be significantly reduced by choosing the optimal damper position, among other parameters, depends on the span length also, the best results can be achieved by determining the damper position for each span inside the line section. Crack growth is interesting to be studied for the proper evaluation of the reliability of structural parts. Fatigue cracking of stiffened panels is an important issue for aged aircraft and ship structures. Under a variety of loading and environmental conditions fatigue cracks may initiate at sites of stress concentration due to geometrical discontinuities. Fatigue crack propagation tests with cyclic stress of constant amplitude and frequency were carried out on stiffened panel specimens damaged with a single crack or an array of collinear cracks, until fracture occurred. FEM numerical simulation procedure for determination the stress intensity factors and multiple propagating cracks was introduced, which takes into account the crack interaction and bending effect due to the cut stiffeners. The optical method of caustics is established for the application to mechanically isotropic materials through the process of evaluation of stress intensity factors and is advantageously improved for the application to fiber-reinforced composites characterized by the significant mismatch in the directions of the principal axes of orthotropy. Comparison of the simulations of the optical effect and the experiments indicated that for the anisotropic materials size and shape of caustic curve not only depend on the loading condition but also on the mechanical material properties. The analysis of the shape and size of experimental caustics can estimate the risk of crack propagation and advantageously makes possible the material modeling during the process of construction design (e.g. the adaptation of the material to the shape of the designed structural part). Research is nowadays extended to the application of the method of caustics in body contact (bearings, meshed gears), both in static and dynamic loading conditions. This makes the caustics method widely applicable to the analysis of any high stress gradient locations in a structure. Composite structures such as fiber-reinforced plastic laminates and sandwich panels made with laminate skins and lightweight cores (e.g. PVC foam) have great potential for use in aggressive environments. The high specific strength of composites offers weight savings and their corrosion resistance gives advantage over traditional metallic materials. When subjected to the high-speed impacts by semi-spherical end-cap projectile of a low velocity gas gun, we investigate possible dynamic failure mechanisms (crack propagation) in a transmission arrangement, resulting from the effects of disintegrating machinery. One can conclude that structural life management requires the integration of design and analysis, materials behavior and structural testing. Assessment of service life of a structure should be given due to accumulated fatigue degradation effects, based on an engineering evaluation of areas particularly susceptible to structural damage. The valuable information gathered by the analysis of critical structural components should be important for making decision about the structural repairing or stopping the plant production.

Risk assessment; Optical method of caustics; FEM model; Aeolian vibrations

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