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Influence of laser weld shape on mechanical and fatigue behaviour of single lap laser welded joints
摘要： Traditional manufacturing processes, like arc welding and resistance spot welding, are still the main welding processes to join structural components used across the on/o?-road vehicle industry. Due to the abundance of data, experiences and insights over the decades of usage, lot of fatigue design data has been generated for different joint geometries produced using these methods. The laser welding process has excellent capabilities to join thin sheet metal structures with minimum heat input resulting into lower deformation and improved productivity that offers significant benefit as compared to the arc and resistance welding processes. However, due to the agility of designing joint configurations and limited availability of understanding regarding the fatigue behaviour of laser welded joints, the need arises for the fatigue design data. Most of the research presents the use of straight linear shape laser welds and limited knowledge exist regarding the influence of shape of laser welds on mechanical and fatigue performance of the laser welded joints. The laser welded joints produce small notch like radius at the root of laser weld which could act as a stress raiser causing early crack initiation. For this work, C-shape laser weld has been selected as the geometric shape in comparison to the straight linear shape of laser weld produced on a series of single lap joints. Detailed fatigue experimental investigation has been carried out for linear and C-shape laser welded joints tested in 3 different orientations with respect to the applied cyclic load and several different R-ratio’s and the results are compared. The metallurgical studies have been carried out to understand the failure mode and micro-hardness variations across the weld and heat affected zone. Further, the residual stress profiles have been compared for the C-shape laser weld with the linear welds using detailed X - Ray Diffraction based residual stress measurement.
关键词： Laser Weld,Ultra-high strength steel,C Shape,Crack propagation,High strength low alloy steel,Crack initiation
更新于2025-09-23 15:21:01
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The effect of manufacturing defects on the fatigue life of selective laser melted Ti-6Al-4V structures
摘要： The manufacturing defects introduced by selective laser melting typically lead to lower fatigue strength and a larger variation in fatigue life compared to conventionally manufactured structures. X-ray micro computed tomography (μCT) is used to characterize the porosity and lack of fusion defects in terms of population, morphology, dimension and location. The defect size and location are combined with the NASA/FLACGRO (NASGRO) fatigue crack growth model to predict the likely fatigue life, in which an effective initial crack length is defined using the cyclic plastic zone and the defect radius. An eXtended defect zone (XDZ) describing the propensity for local plasticity during fatigue around a defect has been shown through numerical analysis to be a good indicator of the ranking of the threat to fatigue caused by differently located manufacturing defects. This indicates that the effect of a defect, initial radius, r0, is likely to be pronounced when its center is within 2r0 of the surface and maximal when it lies just beneath the surface.
关键词： Additive manufacturing,High cycle fatigue (HCF),Fatigue crack initiation and growth,Digital printing,Defect tolerance method
更新于2025-09-23 15:19:57
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A new approach to correlate the defect population with the fatigue life of selective laser melted Ti-6Al-4V alloy
摘要： Microstructural features and defects arising from selective laser melting (SLM) determine the in-service performance of additively manufactured near-net-shape components. Here the grain type, shape, size and distribution were characterized using electron backscattered diffraction (EBSD). High-resolution synchrotron radiation X-ray computed tomography was used to quantify the population, morphology and dimensions of porosity and lack of fusion defects. For SLM Ti-6Al-4V alloy, the larger-sized defects in comparison with α′ grains are more important for crack initiation, typically leading to poor fatigue resistance and a pronounced variation in fatigue life. The fatigue strength was then evaluated in terms of the defect population using a combination of the statistics of extremes and the Murakami model. Finally, an extended Kitagawa-Takahashi fatigue diagram was established within the framework of defect-tolerant design, which includes a classical safe-life region and the defect-determined lifetime in the finite life region.
关键词： Defect tolerance assessment,Chapetti model,Fatigue crack initiation and propagation,Kitagawa-Takahashi diagram,Additive manufacturing
更新于2025-09-19 17:13:59
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Analytic Model of Spalling Technique for Thickness-Controlled Separation of Single-Crystalline Semiconductor Layers
摘要： Thickness-controlled separation of a thin layer of single-crystalline semiconductors from its bulk substrate is being developed for co-integration of compound semiconductors with silicon-based integrated-circuit (IC) chips and fabrication of high-performance flexible devices. Recently, a controlled spalling technique that can mechanically separate single-crystalline semiconductor layers has been actively demonstrated because of the process simplicity and the less limitation in materials. Here, we developed an analytic model that can precisely estimate the spalling depth. In this model, the spalling depth was calculated from the thermodynamic equilibrium condition in which total strain energy accumlated in a separated layer is balanced with the crystal binding energy. We empirically investigated the dependence of the spalling depth on the stressor layer thickness and stress, and we compared the empirical results with the suggested analytic model. We also verified that the crack initiation angle of the spalling process is determined by the binding energy contrast in the main crystal orientations in the semiconductor.
关键词： thermodynamic equilibrium condition,analytic model,spalling technique,thickness-controlled layer separation,crack initiation angle
更新于2025-09-12 10:27:22