2024-T351铝合金搅拌摩擦搭接焊接头疲劳性能与寿命预测

通过实验观察2024-T351铝合金搅拌摩擦搭接焊接头焊缝附近区域的焊缝横截面形貌及金相组织。观察表明搅拌摩擦搭接焊接头前进侧与后退侧存在形状不对称的钩状缺陷。将搅拌摩擦搭接焊接头在MTS材料实验机上进行恒幅疲劳加载,得到名义应力幅S-N曲线。根据实验结果建立搭接接头的弹塑性有限元模型,利用SWT疲劳损伤公式和应力集中区域循环应力应变有限元分析结果数据,预测搭接接头疲劳寿命,并将寿命预测结果与实验结果进行对比。结果表明:在低周疲劳寿命范围内,采用SWT疲劳损伤公式对搅拌摩擦搭接焊接头的预测结果与实验结果接近,误差均在2个因子内,但对高周疲劳寿命的预测结果存在较大误差。分析表明,搭接接头的应力集中程度比有效厚度对疲劳寿命的影响更大。     

某燃气发生器壳体的结构可靠性分析与评估

对某燃气发生器壳体的可靠性进行了分析，应用应力和强度均服从正态分布时结构可靠度的置信下限公式，得到了壳体在整个工作期间内的可靠度的置信下限，说明壳体温度的变化对其结构可靠度的影响不可忽视。     

复合材料接头三维有限元技术研究

介绍了复合材料三维单元刚度矩阵，用三维有限元方法计算了复合材料层压耳片接头拉伸、剪切、弯曲载荷的问题；给出了孔边应力分布及弯曲时层间剪应力分布。结果表明：当载荷平行于铺层且沿厚度均匀分布时，应力沿厚度方向变化不大，主要与铺层角度有关；当载荷不平行铺层时，层间剪切应力和拉伸应力较大，是接头破坏的主要原因。     

固体火箭发动机连接结构接触应力研究

应用接触理论和有限元方法，分析固体火箭发动机法兰连接结构的接触问题。建立了法兰连接结构的有限元模型，充分考虑了连接螺栓预紧力对结构刚度的影响，将其合理地转化为等效节点初载荷。推导出在法兰对接面上有气密性要求时求解最佳预紧力的公式。最后通过实例进行了接触应力计算。结果表明，采用的分析方法和由此得出的结论具有一定的工程意义。     

航空发动机高负荷涡轮盘双辐板结构优化设计

转速高负荷重的涡轮盘是发动机重量大户,采用单辐板结构设计难以有效减轻重量。提出并建立了涡轮盘双辐板结构优化设计数学模型及方法,筛选了涡轮盘子午面形状设计参数,建立了应力约束条件,利用AN-SYS优化平台,编制了轮盘结构优化程序。针对典型高负荷涡轮盘结构优化问题,分别进行了单辐板盘和双辐板盘结构优化设计,结果表明,在满足轮盘变形、强度要求的条件下,双辐板盘比单辐板盘重量可减少25.3%,应力分布更均匀,说明对于高负荷涡轮盘,双辐板盘具有明显的优势。     

Evaluation of tool wear and cutting performance considering effects of dynamic nodes movement based on FEM simulation

An accurate estimation of tool wear morphology can provide the opportunity to investigate the influence of tool wear on cutting performance as well as reduce the overall production cost. However, tool wear prediction is still a very challenging research issue. In this paper, a novel method for simulating the actual chip formation and wear evolution thorough the 3D finite element model has been carried out. In order to improve the accuracy of simulation results, the influence of worn tool, stress and temperature distribution on wear rate are considered. Then cutting experiment has been conducted by turning AISI1045 with uncoated carbide tools to validate the accuracy of the proposed model. The comparison between experimental and simulation results show good agreement which proves the ability of the proposed model in forecasting the tool wear. The validated finite element model has been further utilized studying how the worn tool affects the cutting performance including actual cutting rake, stress distribution, cutting force and temperature. The results of this paper not only provide a clear understanding of wear evolution between tool rake face and chip, but also are meaningful to optimize tool design and cutting parameters.     

Effect of stress ratio on HCF and VHCF properties at temperatures of 20 °C and 700 °C for nickel-based wrought superalloy GH3617M

This paper attempts to investigate the effects of stress ratio and high temperature on the HCF(high-cycle-fatigue) and VHCF(very-high-cycle-fatigue) behaviors of nickel-based wrought superalloy GH3617 M. Fatigue tests over the full HCF and VHCF regimes were conducted on superalloy GH3617 M subjected to constant-amplitude loading at five stress ratios of -1, -0.5, 0,0.4, and 0.8 in environments of 20 °C and 700 °C temperatures. From experimental observation and fractographic analysis, fatigue mechanisms were deduced to reveal the synergistic interaction between high temperature and stress ratio on the HCF and VHCF behaviors of superalloy GH3617 M. A phenomenological model was crafted from available fatigue design knowledge to evaluate the synergistic interaction, and a good correlation between predictions and experiments has been achieved.     

基于LCP基板的射频子阵共形一体化制造技术

为解决共形相控阵雷达中组件与共形天线平台不匹配以及线缆插拔带来的系统不稳定等问题,对基于LCP基板的柔性T/R组件封装技术开展研究。分析了基板层压质量控制及有源芯片埋置方法,通过ANSYS软件仿真了基板不同弯曲角度下的应力分布。结果显示叠加层压辅材后的优化层压过程可以有效去除层间气泡,MMIC埋置的气密性可达7.4×10^-7 Pa·m³/s。仿真结果表明在-55~80 ℃的温度循环下,当基板弯曲角度大于10°时,弯曲应力随着弯曲角度的增加迅速增长。当基板弯曲角度小于10°时,T/R共形组件保持优良性能。     

Effects of dry/wet ratio and pre-immersion on stress corrosion cracking of 7050-T7451 aluminum alloy under wet-dry cyclic conditions

The stress corrosion cracking (SCC) behavior and mechanism of 7050-T7451 aluminum alloy under wet-dry cyclic conditions were investigated. Slow strain rate tests (SSRTs) and electrochemical tests were used to study the effects of dry/wet ratio (DWR) and pre-immersion on SCC. Fracture and side surface characterizations were observed by scanning electron microscopy (SEM). The results demonstrate that SCC susceptibility decreases with an increase of the DWR. With an increase of the pre-immersion time, both continuous pre-immersion (CP) and wet-dry cyclic pre-immersion (WDP) samples are more sensitive to SCC, and the cracking mode in the SCC fracture region is intergranular. Furthermore, the effect of WDP on SCC is greater than that of CP when the total time immersed in solution before an SSRT is the same with each other. In fact, each single wet-dry cycle can be divided into three processes with respect to the change of solution on samples’ surface. Volatilization of water on the surface results in an increase in solute concentration, thus accelerating corrosion.     

SCC investigation of low alloy ultra-high strength steel 30CrMnSiNi2A in 3.5wt%NaCl solution by slow strain rate technique

To evaluate stress corrosion cracking(SCC) mechanism of low alloy ultra-high strength steel 30CrMnSiNi2 A in environment containing NaCl, SCC behavior of the steel in 3.5wt% NaCl solution is investigated by slow strain rate technique(SSRT) with various strain rates and applied potentials, surface analysis technique, and electrochemical measurements. SCC susceptibility of the steel increases rapidly with strain rate decreasing from 1 · 10 5s 1to 5 · 10 7s 1, and becomes stable when strain rate is lower than 5 · 10 7s 1. SCC propagation of the steel in the solution at open circuit potential(OCP) needs sufficient hydrogen which is supplied at a certain strain rate.Fracture surface at OCP has similar characteristics with that at cathodic polarization 1000 mVSCE, which presents characteristic fractography of hydrogen induced cracking(HIC).All of these indicate that SCC behavior of the steel in the solution at OCP is mainly controlled by HIC rather than anodic dissolution(AD).