共查询到20条相似文献,搜索用时 15 毫秒
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In this paper, resistance spot weldability of high‐Mn steels were investigated in order to get high reliability in welded joints of automotive components. Microstructural characterizations, cross‐tensile test (CTT), microhardness tests of spot welded parts were conducted. The effects of weld current on the microstructural characteristics, mechanical properties, and fracture modes were investigated using optical microscopy (OM) and scanning electron microscopy (SEM). The hardness in the weld nugget was observed to be lower than that in the base metal (BM). In CTT, the failure initiation was observed to occur at the boundary of the weld nugget. Also welding imperfections of welded parts were investigated. Liquation cracking in heat affected zone (HAZ), porosity, and shrinkage cavity were found most common welding defects in welded parts. Furthermore, the effects of welding imperfections on weld quality and failure criteria were identified and discussed. 相似文献
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This paper aims at investigating metallurgical and mechanical characterization of low carbon steel laser spot welds. Microstructural examinations, microhardness tests and quasi‐static tensile‐shear tests were preformed. Mechanical properties of the welds were described in terms of peak load and failure mode. The effects of laser spot welding parameters including pulse frequency, laser energy, welding speed, pulse width and welded circle diameter, on low carbon steel laser spot weld performance were studied using the Taguchi design of experiment method. It was found that the effective laser pulse energy is the controlling factor in the determination of mechanical strength of laser spot welds. 相似文献
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The fatigue crack propagation characteristics of a friction stir welded Al‐Mg‐Si alloy, 6082, have been investigated. The electrical potential drop method was used for measurements. A low and a high load ratio (R) level were tested. At low load ratio (R=0.1) and a low stress intensity δK the propagation rate in the weld was higher than in the parent material by a factor of 3 to 5. However, the propagation rates were approaching each other close to fracture. At high load ratio (R=0.8) the propagation rate was similar in the parent material and weld. The weld crack growth rate was about the same at low and high R (except close to fracture), while the parent material growth rate increased at high R. Paris law was used to describe the measured crack propagation rates in the weld. In the case of the parent material, showing an R‐dependence, Forman's law was used. 相似文献
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In this paper, the results of a recent study aimed at understanding the influence of orientation on high cycle fatigue properties and final fracture behavior of alloy steel Pyrowear 53 is presented and discussed. This alloy steel has noticeably improved strength, ductility, and toughness properties compared to other competing high strength alloy steels having a near similar chemical composition and processing history. Test specimens of this alloy steel were precision machined and conformed to the specifications detailed in the ASTM standards for tension testing and stress‐controlled cyclic fatigue tests. Test specimens were prepared from both the longitudinal and transverse orientations of the as‐provided alloy steel bar stock. The machined test specimens were deformed in cyclic fatigue over a range of maximum stress and under conditions of fully reversed loading, i.e., at a load ratio of ?1, and the number of cycles‐to‐failure recorded. The specific influence of orientation on cyclic fatigue life of this alloy steel is presented. The fatigue fracture surfaces were examined in a scanning electron microscope to establish the macroscopic fracture mode and to characterize the intrinsic features on the fatigue fracture surfaces. The conjoint influence of microstructure, orientation, nature of loading, and maximum stress on cyclic fatigue life is discussed. 相似文献
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Lifetime of hot‐work tools is often limited by the development of crack nets as a consequence of thermal and/or mechanical fatigue loading. In this paper, the isothermal fatigue behaviour of the tool steel AISI H11 (German grade X38CrMoV 5‐1) under stress controlled uniaxial tension‐compression loading with zero mean stress is investigated in the temperature range between room temperature and 500 °C. Different surface conditions (polished, shot peened, hard turned) were taken into account and a small influence of the near‐surface states on the measured plastic strain amplitudes could be detected. In all cases, for the most part, strain softening occurred with increasing numbers of cycles, which is also influenced by the stress amplitude applied. Due to manufacturing induced near‐surface compressive residual stresses and strain hardening, shot peened specimens exhibit higher fatigue lifetimes than hard turned or polished ones. 相似文献
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低温时效对非调质钢组织和耐疲劳性能的影响 总被引:1,自引:0,他引:1
紧固件工作失效多起源于疲劳,利用光学显微镜、透射电子显微镜、洛氏硬度仪和耐疲劳性能试验机等分析测试方法研究时效处理对减面率22.5%的非调质钢MFT8紧固件的组织、硬度和耐疲劳性能的影响。研究结果表明:与未时效处理试样相比,时效工艺为300℃×2h时,其硬度和耐疲劳极限达到最大值。时效强化和耐疲劳性能提高的主要原因是,在时效回复处理过程中,位错之间相互反应而湮灭或逐渐迁移而重排,引起位错墙或位错胞内部位错密度减少,形成具有稳定状态或亚稳定状态的组织结构或亚结构。 相似文献