2195-F态铝锂合金TIG焊和FSW焊后残余应力分析

采用盲孔法和压痕法,分别对2195-F态铝锂合金手工TIG焊和FSW焊后残余应力进行测量. 结果表明,盲孔法的测量值普遍高于压痕法. 两种焊接方法,近焊缝区的纵向应力均高于横向应力;横向应力整体表现为压应力或小于50 MPa的拉应力;纵向应力在热影响区附近表现为大于焊缝的拉应力. 焊缝区附近,手工TIG焊纵向残余应力大于FSW,且纵向残余应力表现为较大的拉应力,最大值接近于接头的屈服强度;焊缝区外,手工TIG焊和FSW残余应力值相差不大,其横向残余应力基本表现为很小的拉应力或者压应力.     

热轧高强度钢板矫直前后残余应力分布的研究

针对热轧钢板产品常出现的旁弯、翘曲等板形质量问题,通过盲孔法测量钢板矫直前以及粗矫直、精矫直后的残余应力分布来分析矫直工艺对钢板残余应力分布的影响,以便改善热轧钢板产品的质量。实测结果表明：矫直前钢板宽度方向残余应力很不均匀,并且在钢板边部存在残余压应力使钢板出现边浪等板形不良的情况;经过粗矫直后应力值分布不均减小;在精矫直后应力值进一步减小并且分布趋于均匀。而同一矫直工序中钢板长度方向不同位置残余应力分布也不同,其中钢卷中部的残余应力值为最小。     

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 本文针对热轧钢板产品常出现的旁弯、翘曲等板形质量问题,通过盲孔法测量钢办矫直前以及粗矫、精矫后的残余应力分布来分析矫直工艺对带钢残余应力分布的影响,以便改善热轧钢板产品的质量。实测结果表明：矫直前钢板板宽方向残余应力很不均匀,并且在钢板边部存在残余压应力使钢板出现边浪等板形不良的情况;经过粗矫后应力值分布不均减小;在精矫后应力值进一步减小并且分布趋于均匀。而同一矫直工序中钢板长度方向不同位置残余应力分布也不同,其中钢卷中部的残余应力值为最小。     

300M钢电子束预热与焊接复合加工后的残余应力测试

采用盲孔法测量了电子束预热与焊接复合加工300M超高强度钢板的残余应力分布。结果表明,垂直于焊缝方向的纵向残余应力以拉应力为主,横向残余应力以压应力为主,焊缝中心的最大纵向和横向残余应力分别为34.3和9.2 MPa;最大残余拉应力峰值出现在母材区,其应力值约为208.3 MPa,远低于母材屈服强度。沿焊接方向残余应力变化不大,可近似认为其分布基本稳定。     

屈服状态下盲孔法测量残余应力孔边应变释放系数修正

盲孔法测量残余应力计算公式是在弹性条件下推导出来的。为了测量材料屈服状态下的残余应力,必须对盲孔释放法进行修正,以消除孔边塑性变形对测量精度的影响。通过使用基于孔边形状改变比能S的A、B系数修正法,使盲孔法测量焊接残余应力的精度得到提高,并且扩大了应力值的测量范围。与其它的修正方法相比,结合有限元数值计算的基于孔边形状改变比能S的A、B系数修正法简单易行,更适合于实际的工程应用。     

热沉影响钛合金薄板焊接残余应力的试验分析

采用切条应力释放法测量了钛合金TC4薄板常规钨极氩弧焊(GTAW)和动态控制低应力无变形GTAW对接试件中的纵向残余应力和纵向残余塑性应变的分布。测量结果表明,钛合金常规GTAW缝中残余拉应力峰值小于其母材屈服强度,焊缝附近存在残余压缩塑性应变;动态控制低应力无变形GTAW焊技术中热沉的冷却作用使得热源与热沉之间的高温金属承受强烈的拉伸作用,产生拉伸塑性变形,部分抵消了焊接过程中已产生的缩短的塑性变形,使得试件中纵向残余塑性应变减小,焊接残余拉应力峰值降低,残余压应力水平降低。切条应力释放法是一种简便有效的薄板焊后残余应力测量方法,能够满足工程应用的精度要求。     

焊接工艺对30mm厚Q690钢板焊接残余应力的影响

为了得到焊接工艺对30 mm厚Q690钢板焊后残余应力分布及大小的影响,实施了不同工艺条件下的焊接试验,并通过盲孔法对试板焊后应力进行测定,得到了不同工艺条件下的焊接残余应力。结果表明,在焊缝区,横向应力为压应力,最大为569 MPa,纵向应力为拉应力,最大为57 MPa;在热影响区,横向应力为拉应力,最大为143 MPa,纵向应力由压应力逐步变为拉应力,最大拉应力为75 MPa。焊材和焊接热输入对接头残余应力有一定影响,其中,焊接热输入增加,残余应力也逐步变大。采用"X"形坡口可以改善焊接接头残余应力分布,残余应力多为压应力,但残余压应力的存在会降低接头的局部稳定性,需进行焊后热处理,以减小其不利影响。在实际生产中优选药芯焊材和热输入为20.8 k J/cm的焊接工艺。     

盲孔法测量LiH残余应力

采用盲孔法对烧结、机加成形的SR40超半球和Φ60圆柱的LiH材料测试件进行残余应力测量。结果表明:SR40超半球测试件球面45°处残余应力值最大,径向σr达到-9.5670 MPa,周向σt达到2.2352 MPa;球面各点径向σr残余应力均为压应力,而周向σt残余应力均为拉应力,且径向σr大于周向σt,测试件呈压应力状态。Φ60圆柱测试件端面中心残余应力值最小,从端面中心到端面边缘,径向σr和周向σt残余应力是先增大后减小。     

预拉伸变形量对7055铝合金厚板表面残余应力的影响

为了系统性地研究预拉伸变形量对淬火残余应力的消减规律,采用基于cosα法的μ-X360s型X射线残余应力分析仪,表征7055铝合金厚板经不同预拉伸变形量(0%、0.5%、1.2%、1.5%、2.5%、3.3%、3.9%)的表面残余应力水平,并通过基于sin2Ψ法的X射线衍射法和钻孔法验证测试结果。结果表明:7055铝合金厚板经过固溶淬火处理后,残余应力水平较高,轧向分应力略小于横向分应力,在厚板边缘区域残余应力水平波动较大,波动区域大约在距边部27mm的位置。当预拉伸变形量为1.5%时,轧向分应力的明显减小,继续增大拉伸量,残余应力稳定在60~70 MPa;而当预拉伸变形量大约为1.5%时,横向分应力由压应力状态转变为拉应力状态;经超过2.5%的预拉伸变形后,残余应力稳定在20~30 MPa。     

GEVO16型柴油机机体残余应力的测量及分布规律研究

采用盲孔法对铸态和退火态GEVO16型柴油机机体残余应力进行测量,并讨论了退火工艺对GEVO16机体残余应力的消除作用。结果表明,铸态机体残余应力值较大并且以拉应力为主,最大应力值为60 MPa;退火后机体残余应力减小并且分布比较均匀、以压应力为主,机体表面残余应力的最大消除率达到50.63%。     

基于同步辐射衍射技术的5A06铝合金焊接残余应力的测量研究

利用同步辐射X射线衍射技术测量了变极性等离子弧(VPPA)焊接5A06铝合金试样表面的残余应力,获得了该试样表面残余应力的分布规律,结合金相组织观察、EBSD、显微硬度测试等方法,分析了焊缝区、热影响区、母材区残余应力的产生及演化机制。结果表明:VPPA焊接5A06板材焊缝区晶粒粗大,热影响区晶粒细小,残余应力呈现出焊缝区域为压应力,热影响区为拉应力的"M"形状;在垂直于焊缝(TD)方向上存在75.79MPa的最大拉应力和159.34 MPa的最大压应力;在平行于焊缝(LD)方向上存在132.33 MPa的最大拉应力和89.38 MPa的最大压应力。相比于传统X射线仪器测量获得的残余应力变化趋势,同步辐射衍射测量的残余应力分布趋势与试样不同焊接区域显微硬度的变化趋势更加吻合。实验结果表明,相比于传统的X射线仪器测量残余应力,同步辐射X射线衍射测量的残余应力数据一致性更好。     

Evolution of residual stresses in dissimilar steel surfacing layers during process of post-weld heat treatment

Abstract

Residual stress relaxation during post-weld heat treatment (PWHT) is a thermodynamic process, which is affected not only by the heat treatment process, but also by the welding residual stress. In this study, the residual stresses in as welded and heat treated surfacing metal were measured using blind hole and X-ray method. The results reveal that the welding residual stresses are compressive at the surface of the weld and tensile at inner weld. However, after PWHT, the residual stresses at surface and inner weld change to the opposite state. Finite element simulations show that the differences of expansion coefficients between base metal and filler material are the main factor to the changes of stress state. The experimental results verify that the expansion coefficients of base metal and filler materials have been changed greatly after long soaking at high temperature.     

Residual stress analysis of an aircraft landing gear part using neutron diffraction

The residual stress of a landing gear part of a fighter jet that has a frequent practice of takeoff and landing was evaluated for the safety. The sample was a cylindrical steel bar with a 22.2 mm diameter and 55 mm length used to fix the main landing gear to the aircraft body. For a deep measurement up to 6 mm, we used a neutron beam. From the measurements, the tensile and compressive strain in the axial direction were observed around one side of the pin hole which was across the steel bar vertically with an 8 mm diameter. The strain distribution along the length of the bar presented a similar tendency through the thickness and a larger value on the surface. The maximum value of the residual stress around the pin hole was about 100 MPa. However, there was no strain on the opposite side of the pin hole. From the results, it may be surmised that the steel bar received a steady force in one direction around the pin hole, however the force was weak and affected a small limited area and thus not influence on the steel bar on the whole.     

超音速等离子喷涂FeCrBSi涂层组织和残余应力分析

采用超音速等离子喷涂技术制备了FeCrBSi涂层,利用扫描电子显微镜(SEM)、X射线衍射仪(XRD)和纳米压痕仪等研究了涂层的微观组织和力学性能。采用X射线应力仪对不同厚度及不同温度退火后涂层的表面残余应力进行测试。结果表明涂层表面的残余应力为拉应力,且随着涂层厚度的增加而增加;对试样进行退火处理可以有效地缓和涂层表面的残余应力,随着温度的升高涂层表面的残余应力不断降低,到260℃左右变为压应力;压应力值随着退火温度的升高而变大,但当温度升高到大约400℃以上时,保持在80 MPa左右。     

Characterization and residual stresses of WC-Co thermally sprayed coatings

The present investigation has been conducted in order to determine the residual stresses of an as-ground WC-12Co coating of two different thicknesses, by means of two different methods. Firstly, X-ray diffraction techniques, which allowed the determination of the surface residual stresses of the coating by means of the method called “sin²ψ” method. Secondly, an incremental hole drilling technique together with the integral method, which allowed the analysis of the non-uniform through-thickness residual stresses present in the coatings. It has been determined that the surface residual stresses are of a compressive nature, which could be due to the grinding that was applied to the coatings in order to achieve the desired thicknesses. On the contrary, the results of the incremental hole drilling tests indicated that the through-thickness residual stress distributions are not uniform and are characterized by the presence of tensile peak stresses, at depths in the range of ~ 50-125 μm. Such stresses were observed to decrease towards the coating-substrate interface where the compressive component of the stress state becomes greater than the tensile component. It has been found that the mean residual von Mises stress is higher in the thinner coating than in the thicker one, of approximately 180 and 107 MPa, respectively.