Resistance welding of glass fiber reinforced thermoplastic composite: Experimental investigation and process parameter optimization

The utilization of fiber reinforced thermoplastics (FRTP) is expected to fulfill lightweight demand in mass-produced aerospace products. Facing the unavoidable assembly of FRTP parts, fusion bonding methods such as resistance welding are promising compared with mechanical joint and adhesive bonding. In this paper, a procedure has been brought out to understand the relationship between processing conditions and performance of the FRTP welding joints. The adherends were continuous glass fiber reinforced polypropylene (GF/PP) laminates fabricated by hot-pressing method. The influences of time, current and pressure on the bending strength of the resistance welding joints were investigated. A processing window was drawn based on the optical observation of welded surfaces. The quantitative relationship between process parameters and mechanical property of GF/PP welding joint was established by Response Surface Method (RSM) with high accuracy. It was found that bending strength of GF/PP welding joint was improved by 31% compared with hot-pressing benchmark.     

Ti_2AlNb基合金电子束焊接头的显微组织

利用透射电子显微镜和能谱,研究电子束焊接过程中Ti_2AlNb基合金显微组织演变过程以及焊缝区组成、焊后热处理对接头显微组织的影响.结果表明:焊接过程中焊缝区Al元素损失较为严重,这有利于B_2相的形成而不利于O相的形成,使得接头焊缝区主要由B_2和α_2两相组成;在随后的热处理过程中,焊缝区的B_2相转变为β相和板条状的O相,使焊缝区由α_2、O和β相组成.     

飞机机体损伤抢修的研究与应用

阐述实施飞机机体抢修时的关键问题,指出对飞机机体损伤的抢修应综合考虑检测与评估方法、修理方案、维修原则、修理前的准备、修理方法、人员组织结构和人员素质等多种因素的影响。     

一种新的民用飞机修理级别优化模型

修理级别分析(LORA)是飞机保障性分析的一个重要内容,是在设计阶段评估维修对飞机成本影响的一种系统分析方法。现有的LORA经济性分析模型对于系统寿命周期的维修费用考虑不够,且不适合民用飞机维修特点,基于此,提出了一个适合民用飞机维修规划三层三级的LORA经济性分析的数学模型,在此基础上,以最小化维修成本为目标建立了维修级别优化模型,并利用免疫粒子群算法超强的多变量、非线性及全局优化能力,对所提出的民机维修级别优化模型进行了求解。最后通过算例的比较分析,说明了本文LORA经济性分析模型的合理性以及模型求解算法的高效性。     

0018Ni马氏体时效钢电阻点焊工艺试验研究

研究了不同的工艺制度对0018Ni高强度马氏体沉淀硬化时效钢电阻点焊接头显微组织及力学性能的影响.结果表明采用固溶+焊接+固溶+时效的工艺制度,电阻点焊接头的金相组织和单点剪切力较为理想.     

辅助加热温度对铝合金厚板FSW焊缝成形的影响

对铝合金厚板搅拌摩擦焊（FSW）而言,焊缝底部金属温度低、流动能力差是导致焊缝成形困难的主要原因。为此,本研究采用辅助加热的方式对待焊母材底部进行预热,分析辅助加热温度对厚板搅拌摩擦焊焊缝成形的影响。结果表明,随着辅助加热温度从20℃升高至80℃时,焊缝成形质量先变好后变差,宏观表现为焊缝内部焊核区宽度、高度及面积呈现先增大后减小的趋势,而疏松区面积呈现先减小后增大的趋势。其中,当辅助加热温度为40℃时,焊缝成形质量最好,焊核区尺寸最大,疏松区消失;而当辅助加热温度升高至80℃时,焊缝成形质量最差,疏松区面积最大。研究认为,其主要原因是添加合适的辅助加热温度可显著提高焊核区塑性金属的峰值温度及高温停留时间,塑性金属流动能力明显提高,焊缝成形质量得到极大改善。焊核区塑性金属的迁移方式由沿搅拌针表面向焊缝上部高温区迁移向挤压焊核区周边冷金属横向迁移转变。但是,当辅助加热温度太高时,焊核区塑性金属迁移方式开始转变为原始的沿搅拌针表面向焊缝上部高温区迁移,且此迁移程度有明显增大的趋势,导致焊缝内部疏松区缺陷再次出现。     

镁合金铸件缺陷搅拌摩擦修复工艺方法

针对航天器铸件缺陷率高,修复难度大的现状,提出采用搅拌摩擦加工技术实现缺陷修复的新方法。首先制备了含缺陷的AZ91D镁合金试板,并以此作为实验材料进行了搅拌摩擦修复工艺实验,在旋转速度为500r/min,前进速度100mm/min,下压量为1.5mm的工艺参数下,修复区域成形良好。修复前后X射线照片表明,搅拌摩擦加工技术有效修复了镁合金试板中的铸造缺陷。最后对航天器铸件中常见的T形结构和角形结构开展了对应的实验研究,在现有条件下,采用自制简易夹具,可以完成T形结构和角形结构的搅拌摩擦加工。研究结果表明,采用搅拌摩擦方法修复航天器铸件缺陷从技术上是可行的。     

有限维修能力下舰载机可修复件库存优化模型

舰载机保障受维修渠道约束,维修能力有限.为使Palm定理和Metric理论适用于舰载机可修复件优化配置,基于排队理论,将有限维修渠道的实际维修时间与维修等待时间之和等效为无限维修渠道的平均维修时间,建立专业渠道、通用渠道和混合渠道的维修供应渠道修正模型.根据维修供应渠道修正模型,给出了两层级备件项的供应渠道备件数均值和方差模型.结合实例应用,分析了备件需求率和维修渠道数对维修时间的影响.对比分析了"有限维修渠道模型"和"无限维修渠道模型"库存方案的应用效果,并给出了各自的适用条件,结果表明了修正模型的有效性.      

Ti—15—3钛合金点焊工艺及性能研究

对我国新研制的β型Ｔｉ－１５－３新型钛合金进行了点焊工艺及性能研究,并与进口材料进行比较,从而对我国研制的Ｔｉ－１５－３钛合金的点焊焊接性作出评价为其在新机上的应用和该材料的国产化提供了可靠的依据。     

Residual stress determination in friction stir butt welded joints using a digital image correlation-aided slitting technique

This paper presents an incremental cutting method for evaluating the longitudinal residual stresses in a butt welded thin plate via combining the traditional residual stress measurement methods and the advanced optical technique.The proposed approach,which can be called digital image correlation (DIC)-aided slitting technique,introduces a successive extension slot to a speci men and employs the DIC technique to measure the released displacement profiles of the cutting sections after each cutting increment.Then the displacement profiles are used to directly calculate the residual stress distributions up to the slot tip and hence,a stress distribution can be obtained after a cutting increment.Finally,all of the stress distributions are averaged to ultimately determine the original residual stress field.This method does not include any complex experimental operations or tedious derivation,and the resolution of stress variation is greatly improved by the continuous measurement of the released displacements.The presented method has been preliminarily verified by a specimen with residual stress introduced by a four-point bending test.The results show that residual stresses determined by the DIC-aided slitting technique agree well with those from finite element (FE) prediction.The residual stress in a friction stir welded aluminum specimen obtained by the presented technique is also consistent with the evaluations given by X-ray diffraction.Fur thermore,the residual stresses obtained by the DIC-aided slitting technique demonstrate higher accuracy and stability than the evaluations derived by the DIC-aided contour method.