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Crack closure mechanisms in residual stress fields generated by laser shock peening: A combined experimental-numerical approach
摘要： Laser shock peening (LSP) is successfully applied to retard fatigue cracks in metallic lightweight structures by introducing specific, in particular compressive, residual stress fields. In this work, experiments and a multi-step simulation strategy are used to explain the fatigue crack retarding and accelerating mechanisms within these LSP-induced residual stress fields. Crack face contact is identified as main mechanism to retard the fatigue crack as the stress distribution changes and the stress intensity factor range decreases. Crack face contact is experimentally detected by load vs. crack opening displacement (COD) curves and scanning electron microscopy (SEM) of the crack faces, as well as during numerical simulations. The convincing agreement between experiment and simulation, especially regarding the specific crack face contact areas, allowed the proper evaluation of the stress intensity factors depending on the crack length. It is found that crack closure is indeed one of the main reasons for the efficient application of LSP for fatigue crack retardation. Furthermore, the occurrence of crack closure does not indicate a zero value stress intensity factor in complex residual stress fields, as the areas of crack face contact depend strongly on the LSP-induced compressive residual stresses.
关键词： Stress intensity factor,Laser shock peening,Residual stress,Fatigue crack growth,Crack closure
更新于2025-09-16 10:30:52
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Fatigue Behaviour of Laser Spot Welds in Dual Phase 780 Steel
摘要： High cycle fatigue performance was evaluated on circular shaped laser spot welds (LSW) of dual phase DP780 steels. Fibre laser with two different parameter sets were applied to produce the spot welds. The weld size growth is concomitant to laser power. The failure mechanism under fatigue loading, involving crack initiation and propagation till failure, is explained using analytical stress models and experimental data. Interrupted fatigue tests were done and the crack path was captured by observing under scanning electron microscope. Stress models show that during tensile shear loading of overlapping sheets having spot weld, there is a countering effect of shear stress and bending stress; the latter acts perpendicular to the shear stress and arises from the bending moment along the plane of contact during load transfer. The dominant stress depends on the contact area, i.e. the weld size, which largely controls the crack path route and concurrent fatigue life. Incidentally smaller welds show marginally longer life wherein the stronger axial stress component propels the crack through a longer route consuming more number of cycles. Again, with lowering of fatigue load there is a shift in the mode of failure with transition from interfacial to partial to pull-out failure. However, large welds fail in pull-out mode only irrespective of the fatigue load levels. As compared to the size effect, the weld microstructure has less influence on fatigue crack propagation.
关键词： Laser welding,Stress Intensity Factor,High Cycle Fatigue behaviour,Circular weld,Dual phase steel
更新于2025-09-16 10:30:52
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Evaluating the Reduction of Stress Intensity Factor in Center-Cracked Plates Using Piezoelectric Actuators
摘要： Active repairs using smart materials such as piezoelectric actuators can play a significant role in reducing the crack damage propagation in engineering structures. This study analytically and numerically investigated the active repair of center-cracked plates using piezoelectric actuators. First, the stress intensity factor (SIF) for a center-cracked plate due to stress produced by a piezoelectric actuator is analytically modeled. This analytical model is obtained by applying the method of weight functions. In the second step, the solution is found for the center-cracked plate due to external loading from known linear elastic fracture mechanics. These solutions are then superimposed, taking into account the superposition principle to yield the total stress intensity factor for the integrated piezoelectric actuator to the center-cracked plate. Finally, the proposed theoretical model is verified by finite element simulation. The results indicated that the relative errors of the analytical model and the FEA results are less than 5% in all the cases studied in this paper.
关键词： fracture mechanics,stress intensity factor,active repair,piezoelectric actuator
更新于2025-09-09 09:28:46
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Fracture behaviors of a piezoelectric-piezomagnetic sandwich structure under electromechanical loads: plane problem
摘要： The fracture behaviors of a piezoelectric-piezomagnetic sandwich structure with an eccentric internal crack subjected to two kinds of in-plane electromechanical loads have been studied in this paper. A singular integral equation with Cauchy kernel is obtained by means of Fourier transform and further solved by using Gauss-Chebyshev technique. Then the stress intensity factors are obtained and some numerical results are presented to show the e?ects of the material properties, structure geometries, electromechanical loads and the crack location on the stress intensity factors. The conclusions of the present paper may be useful for the design and fracture prediction of layered piezoelectric-piezomagnetic structures.
关键词： sandwich structure,stress intensity factor,plane strain problem,integral transformation,Piezoelectric-Piezomagnetic composite
更新于2025-09-04 15:30:14