控锻控冷工艺对GCr15轴承钢力学性能的影响

探究不同控锻控冷热处理工艺对GCr15钢力学性能的影响,测试了它的回火稳定性、冲击性能、滚动接触疲劳寿命。结果表明,采用控锻控冷工艺可提高试样的抗回火稳定性,冲击性能提高50%以上,接触疲劳寿命提高40%以上。     

Multi-Scale Analysis of Fretting Fatigue in Heterogeneous Materials Using Computational Homogenization

This paper deals with modeling of the phenomenon of fretting fatigue in heterogeneous materials using the multi-scale computational homogenization technique and finite element analysis (FEA). The heterogeneous material for the specimens consists of a single hole model (25% void/cell, 16% void/cell and 10% void/cell) and a four-hole model (25% void/cell). Using a representative volume element (RVE), we try to produce the equivalent homogenized properties and work on a homogeneous specimen for the study of fretting fatigue. Next, the fretting fatigue contact problem is performed for 3 new cases of models that consist of a homogeneous and a heterogeneous part (single hole cell) in the contact area. The aim is to analyze the normal and shear stresses of these models and compare them with the results of the corresponding heterogeneous models based on the Direct Numerical Simulation (DNS) method. Finally, by comparing the computational time and % deviations, we draw conclusions about the reliability and effectiveness of the proposed method.     

氮含量对HPD-1双相不锈钢组织及力学性能的影响

通过显微组织观察与力学性能测试研究了氮含量(0.08%~0.22％,质量分数)对HPD-1双相不锈钢硬度、拉伸性能、低温冲击性能及疲劳性能的影响。结果表明,氮含量变化可显著影响试验钢γ/α相比例,当氮含量由0.08％升高到0.22％,γ相含量由38.1％提高至56.5％。α相的硬度由273 HV10提高到343 HV10,γ相的硬度由238 HV10提高到299 HV10,试验钢强度明显提升。氮元素对两相比例和奥氏体相韧性的双重影响导致试验钢低温冲击性能呈先上升后下降的趋势;更高的氮含量抑制疲劳裂纹萌生与拓展,是影响HPD-1双相不锈钢室温疲劳性能的主要因素。撕裂棱是疲劳断口的显著特征。     

某轻型载货车储气罐支架振动断裂分析与优化

为了有效解决某轻型载货车储气罐支架的断裂故障,首先基于建立的储气罐支架有限元模型进行振动特性分析,分析结果表明其前三阶固有频率接均处于发动机激励频率范围之外,不会产生共振。其次测试各种道路的时域载荷,测试结果表明其中角度搓板路的激励频率与储气罐支架第一阶固有频率相接近,从而引起共振,不满足振动特性要求。然后对其进行振动强度分析,分析结果表明其应力水平不达标,其最大应力点与开裂处一致。再对其进行振动疲劳寿命预测分析,分析结果表明其疲劳寿命也不达标,其危险点也与失效位置相同。再采用集成平台对储气罐支架的结构进行优化设计,优化之后其模态频率、振动强度和振动疲劳均符合性能要求,并且其重量也有所减轻,总体优化效果较佳。最后整车试验结果表明优化之后储气罐支架的振动大幅度降低,并且没有发生失效。     

柱塞卡滞原因分析

某柱塞泵工作中发生柱塞卡滞,经显微形貌观察、光谱分析、电子探针面扫描分析和显微硬度分析等,确定柱塞卡滞的根本原因为原材料组织中存在严重的网状共晶碳化物,降低了强度和韧性,增大了柱塞球面表层的脆性,进而导致了球面部位的接触疲劳抗力下降。严重的疲劳磨损与接触疲劳造成了柱塞球面脱层破坏,由此产生的金属碎屑进入柱塞与衬套的配合间隙处,进而限制了柱塞的自由运动。     

Yield stress distribution in injection‐moulded glassy polymers

A methodology for structural analysis simulations is presented that incorporates the distribution of mechanical properties along the geometrical dimensions of injection‐moulded amorphous polymer products. It is based on a previously developed modelling approach, where the thermomechanical history experienced during processing was used to determine the yield stress at the end of an injection‐moulding cycle. Comparison between experimental data and simulation results showed an excellent quantitative agreement, both for short‐term tensile tests as well as long‐term creep experiments over a range of strain rates, applied stresses, and testing temperatures. Changes in mould temperature and component wall thickness, which directly affect the cooling profiles and, hence, the mechanical properties, were well captured by the methodology presented. Furthermore, it turns out that the distribution of the yield stress along a tensile bar is one of the triggers for the onset of the (strong) localization generally observed in experiments. © 2015 Society of Chemical Industry     

Effect of retained austenite – Compressive residual stresses on rolling contact fatigue life of carburized AISI 8620 steel

In this study the rolling contact fatigue (RCF) of case carburized AISI 8620 steel was numerically and experimentally investigated. For the numerical study, a two dimensional finite element (FE) RCF model based on the continuum damage mechanics (CDM) was developed to investigate the fatigue damage accumulation, crack propagation and final fatigue life of carburized AISI 8620 steel under various operating conditions. A randomly generated Voronoi tessellation was used to model the effects of material microstructure topology. The boundaries of the Voronoi elements were assumed to be the weak planes where damage accumulates, cracks initiate and propagate to simulate inter-granular cracks. A series of torsional fatigue tests were conducted on carburized AISI 8620 steel specimens containing 0% and 35% retained austenite (RA) to determine fatigue load (S) vs. life (N) of the material. The S–N results were then used to determine the material parameters necessary for the rolling contact fatigue model. The torsional fatigue test results indicate that the carburized AISI 8620 specimens with higher RA demonstrate higher life than the specimens with lower RA. The RCF model also indicates that the material with higher level of compressive residual stresses (RS) and retained austenite demonstrates higher RCF life. In order to corroborate the results of RCF model, a three-ball-on-rod rolling contact fatigue test rig was used to determine the RCF lives of carburized AISI 8620 steels with different amounts of RA. The fatigue life and cracks evolution pattern from the numerical and experimental results were corroborated. The results indicate that they are in good agreement.     

Investigation into eddy current pulsed thermography for rolling contact fatigue detection and characterization

This paper reports on the use of eddy current pulsed thermography (ECPT) for detection and characterization of rolling contact fatigue (RCF). Detection mechanisms with eddy currents and heat propagation effects were discussed with RCF modeled as a simple angled defect. Two different angled defects were studied through numerical simulations and experimentally by using uniform magnetic field (UMF) excited by Helmholtz coils. Finally, a rail sample with RCF defects was inspected using UMF excitation. It is shown that ECPT with UMF excitation provides an efficient and robust method to detect angled defects, compared with nonuniform magnetic field (NUMF) excitation.