- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
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
-
Effect of Laser Shock Peening on Fatigue Life at Stress Raiser Regions of a High-Speed Micro Gas Turbine Shaft: A Simulation Based Study
摘要： Fatigue failure due to stress raiser regions on critical rotating components in gas turbine engines, such as the shaft, is a crucial aspect. Methods to reduce these stresses and improve fatigue life are a source of ongoing research. Laser shock peening is a method where compressive residual stresses are imparted on the stress raisers of such components. However, numerical based studies on multiple laser shock peening applied to stress raisers is under-researched. Hence, this study will attempt to predict the fatigue life at fillet radii step induced stress raiser regions on a high-speed gas turbine engine shaft by utilization of laser shock peening. The objective of this study was achieved by developing a more computational efficient finite element model to mimic the laser shock peening process on the fillet radii step induced stress raiser regions of a shaft. A modified laser shock peening simulation method for effective prediction of the residual stress field was introduced. Furthermore, the fatigue life improvement due to laser shock peening was predicted by employing Fe-safe fatigue software. From the results, the modified laser shock peening simulation method provided accurate prediction of the residual stress field with a reduced computational time of over 68% compared to conventional methods. The fatigue life revealed an improvement of 553% due to laser shock peening, which is comparable to similar findings in the literature. Hence, from the findings and results achieved, the developed finite element model can be an appropriate tool to assist in the fatigue life estimation of laser shock peening applied to stress raisers.
关键词： Fatigue,laser shock peening,Fe-safe software,stress raiser regions,finite element model
更新于2025-09-16 10:30:52
-
Evaluation of Fatigue Resistance of Laser Welded High Pressure Vessels Steel P355 Considering Fracture Mechanics Approach
摘要： Laser welding is an innovative technology of joining metallic materials. In comparison with conventional arc welding, it has numerous advantages, like high energy of laser beam and high effectiveness, very good reproducibility, possibilities of automation, low energy consumption etc. High pressure vessels and high pressure pipeline industry represent perspective new fields of application. However, since pressure vessels and pipelines are usually operated at conditions of repeated or cyclic loading, an acceptable resistance to fatigue loading of the welds has to be demonstrated. In this contribution, results of an experimental programme aimed at an evaluation of high-cycle fatigue resistance in and near laser welds of a P355 pressure vessel steel are presented and discussed. Particular attention is paid to evaluation of crack initiation mechanisms in connection to laser weld character and welding imperfections. The programme is completed by measurement of fatigue crack growth rates and threshold values in the weld. Results of high-cycle fatigue tests of some groups of specimens were characteristic by a considerable scatter. The reason of the scatter was found in welding defects in some parts of the welds. Fatigue results are discussed also from the viewpoint of fracture mechanics and threshold values of fatigue crack growth.
关键词： fracture mechanics,pressure vessel steel P355,High-cycle fatigue,laser welds
更新于2025-09-16 10:30:52
-
Influence of Work Media on Surface Property of Compacted Graphite Cast Iron Processed by Laser Local Processing
摘要： In order to enhance surface property of brake materials, compacted graphite cast iron (CGI) with non-smooth surface was processed by laser local processing. This study focuses on the influence of the work media on wear resistance and thermal fatigue resistance of specimens. The results showed that when the work media were air and water respectively, laser local processing could enhance surface property of CGI. Changing work media could not change phase compositions of the laser processing area, but refined their microstructures, which enhanced their micro-hardness. By this way, the specimens’ wear resistance and resistance to thermal crack initiation were further improved, while their resistance to thermal crack propagation was influenced by cracks on bionic units.
关键词： Work media,Laser,Compacted graphite cast iron,Wear resistance,Thermal fatigue resistance
更新于2025-09-16 10:30:52
-
Test Results for Wrought and AM In718 Treated by Shot Peening and Laser Peening Plus Thermal Microstructure Engineering
摘要： Fatigue life improvement by shot peening (SP) and laser peening (LP) on metals is already well known. However, we are short of information about results on manufacturing (AM) parts, which are characterized by bad surface finishing, micro-porosities and structural defects. This paperstudies the effects of SP and LP on AM In718. Residual stress profiles, fractures surface, fatigue results will be detailed. Different thermal microstructure and surface preparations are compared: raw AM, SP, LP, polished.
关键词： Fatigue,Thermal,Shot Peening,Additive Manufacturing,Laser Peening
更新于2025-09-16 10:30:52
-
On the Effectiveness of Different Surface Finishing Techniques on A357.0 Parts Produced by Laser-Based Powder Bed Fusion: Surface Roughness and Fatigue Strength
摘要： Laser-based powder bed fusion (L-PBF) is an additive manufacturing (AM) technique that uses a computer-controlled laser beam as the energy source to consolidate a metal powder according to a layer-upon-layer strategy in order to manufacture a three dimensional part. This opens the way for an unprecedented freedom in geometry, but the layer-wise build-up strategy typically results in a very poor surface ?nish, which is a?ected by the staircase e?ect and by the presence of partially molten particles. Surface ?nishing treatments are therefore necessary to obtain an adequate surface ?nish, to improve the fatigue behavior and to meet mechanical and aesthetic needs. The present contribution systematically compares numerous surface ?nishing techniques, including laser shock processing, plastic media blasting, sand blasting, ceramic shot peening and metal shot peening with steel particles of di?erent sizes (φ = 0.2 mm and φ = 0.4 mm). The results show that all the proposed methods improve the surface quality and the fatigue life of A357.0 L-PBF parts. However, the achievement of the lowest surface roughness does not necessarily correspond to the best fatigue performance, thus suggesting that multiple mechanisms may be active and that besides surface roughness also residual stresses contribute to increase the fatigue strength.
关键词： laser shock processing,additive manufacturing,fatigue,shot peening,surface ?nishing,plastic media blasting,sand blasting,surface roughness,A357.0,laser-based powder bed fusion
更新于2025-09-16 10:30:52
-
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
-
Influences of Horizontal and Vertical Build Orientations and Post-Fabrication Processes on the Fatigue Behavior of Stainless Steel 316L Produced by Selective Laser Melting
摘要： In this paper, the influences of build orientation and post-fabrication processes, including stress-relief, machining, and shot-peening, on the fatigue behavior of stainless steel (SS) 316L manufactured using selective laser melting (SLM) are studied. It was found that horizontally-built (XY) and machined (M) test pieces, which had not been previously studied in the literature, in both stress-relieved (SR) or non-stress-relieved (NSR) conditions show superior fatigue behavior compared to vertically-built (ZX) and conventionally-manufactured SS 316L. The XY, M, and SR (XY-M-SR) test pieces displayed fatigue behavior similar to the XY-M-NSR test pieces, implying that SR does not have a considerable effect on the fatigue behavior of XY and M test pieces. ZX-M-SR test pieces, due to their considerably lower ductility, exhibited significantly larger scatter and a lower fatigue strength compared to ZX-M-NSR samples. Shot-peening (SP) displayed a positive effect on improving the fatigue behavior of the ZX-NSR test pieces due to a compressive stress of 58 MPa induced on the surface of the test pieces. Fractography of the tensile and fatigue test pieces revealed a deeper understanding of the relationships between the process parameters, microstructure, and mechanical properties for SS 316L produced by laser systems. For example, fish-eye fracture pattern or spherical stair features were not previously observed or explained for cyclically-loaded SLM-printed parts in the literature. This study provides comprehensive insight into the anisotropy of the static and fatigue properties of SLM-printed parts, as well as the pre- and post-fabrication parameters that can be employed to improve the fatigue behavior of steel alloys manufactured using laser systems.
关键词： fracture,fatigue,selective laser melting,defect,stainless steel 316L
更新于2025-09-16 10:30:52
-
Fatigue behaviour of a laser beam welded CoCrFeNiMn-type high entropy alloy
摘要： Laser beam welding was used to produce butt joints from the CoCrFeNiMn-type high entropy alloy. The alloy in the initial condition had an fcc single-phase coarse-grained structure. Laser welding resulted in the M7C3-type carbides precipitation in the fcc matrix. The carbide particles precipitation resulted in a considerable increase in microhardness from 150 HV 0.5 for the as-sintered condition to 205 HV 0.5 in the fusion zone. Laser beam welding had a negligible effect on both static mechanical properties and fatigue behaviour of the alloy. The endurance limit of either type of specimens (i.e. with and without welding seam) was 200 MPa. Fracture of all specimens with the laser beam welded seams occurred in the base material area during both tensile and fatigue testing. Weak effect of welding on static/fatigue behaviour of the alloy can be attributed to the higher hardness of the fusion zone, resulting in strain localization in the base material area. An increase in load resulted in activation of secondary slip systems and formation of deformation twins in fatigue specimens.
关键词： Fatigue,Tensile strength,Microstructure,Laser beam welding,High entropy alloy
更新于2025-09-16 10:30:52
-
Effects of laser peening on the fatigue strength and defect tolerance of aluminum alloy
摘要： The effects of laser peening (LP) on the bending fatigue strength of the 7075-T651 aluminum alloy were investigated. Accordingly, the defect tolerance of the aluminum alloy subjected to LP is discussed on the basis of fracture mechanics. The results indicate that a deeper compressive residual stress was induced by LP compared with the case of shot peening (SP). The fatigue strengths increased when both peening types were used. Semicircular slits with depths less than 0.4 and 0.1 mm were rendered harmless on the basis of the applications of LP and SP, respectively. The apparent threshold stress intensity factor range ΔKth,ap increased by approximately five and two times owing to LP and SP, respectively. The increase of the ΔKth,ap was caused by the compressive residual stress induced by the peening. The Kitagawa-Takahashi diagram of the laser-peened specimens shows that the defect tolerance of the aluminum alloy was improved by LP.
关键词： fatigue strength,laser peening,residual stress,shot peening,defect tolerance,aluminum alloy
更新于2025-09-16 10:30:52