不锈钢板翅结构钎焊残余应力及其高温蠕变松弛行为三维有限元分析

利用有限元软件ABAQUS,对不锈钢板翅结构在钎焊过程中产生的残余应力及其高温下的蠕变松弛行为进行三维有限元分析,得到了残余应力的变化规律.结果表明,由于镍基钎料BNi-2和不锈钢母材304力学性能的差异以及夹具的约束作用,钎焊后在接头处产生了较大的残余应力.在高温环境下,由于蠕变松弛,残余应力大幅度下降.在蠕变稳态阶段,钎缝处仍然存在一定的残余应力;钎角处蠕变应力和应变集中,易萌生裂纹,成为最薄弱环节.研究结果为板翅结构的高温强度设计提供参考.     

BT20钛合金高温应力松弛行为研究

通过高温应力松弛实验对BT20钛合金在700～850℃,不同初应力条件下短时应力松弛行为进行研究。结果表明:随着温度升高,BT20钛合金应力松弛速率加快,但长时间应力松弛后剩余应力趋向于一极限值。相同温度下,不同初应力作用的应力松弛极限相同。     

Thermal Relaxation of Residual Stresses in Shot Peened Surface Layer of SiCw/Al Composite

The residual stress relaxation of the shot peened layer on the SiCw/Al composite during isothermal annealing was investigated. The results showed that the residual stresses relaxed in the whole deformation layer especially when the annealing temperature was higher than 200?°C. The relaxation process during isothermal annealing could be described precisely using Zener-Wert-Avrami function. Because of high intensity dislocation around reinforcements producing a large amount of stored energy, the residual stress relaxation activation enthalpy of shot peened SiCw/Al was smaller than self-diffusion activation enthalpy of pure aluminum. According to the analysis of full-width at half-maximum (FWHM) of the shot peened composite in different annealing temperatures, it can be concluded the recovery and recrystallization behavior became intensely when anneal temperature was larger than 200?°C. The small relaxation of residual stress in low annealing temperature was mainly due to partly recovery and recrystallization in a very low level.     

时效及冷热循环对Al2O3增强2A12铝合金尺寸稳定性的影响

采用压铸方法制备了体积分数为30%的Al₂O₃/2A12复合材料,对其残余应力松弛及尺寸变化进行了研究,分析了时效和冷热循环处理对复合材料尺寸稳定性的影响规律。结果表明,复合材料的残余应力松弛量随时效时间的延长而增加;冷热循环处理不仅能导致高密度位错的形成,还能够促进时效析出,并能够降低复合材料中的残余应力,从而提高了复合材料在交变温度场下的尺寸稳定性。伴随着冷热循环处理循环下限温度的降低,即上下限温差越大,复合材料中的残余应力持续减小,微变形抗力提高,对基体析出的加速作用增大,复合材料的尺寸稳定性获得明显改善。本文提出的3种工艺中,160℃×10 h时效+（-196～160℃）冷热循环4次是提高Al₂O₃/2A12复合材料尺寸稳定性的最佳工艺。      

Modeling and Simulation for the Stress Relaxation Beha- vior of Ti-6Al-4V at Medium Temperature

应力松弛是钛合金在升高温度和加载条件下的一个显著特性,也是热校形和热处理的理论基础。因此研究了一种Ti-6Al-4V钛板在923~1023 K温度范围内、几种应变水平下的拉伸应力松弛行为。结果表明,应力松弛速率随着温度的升高而增加,材料中的残余应力经过一段时间之后趋向应力松弛极限;另外,在相同温度下,不同应力水平的应力松弛极限相同。进而,建立了一种描述应力松弛行为的显式三次延迟函数,本构精度高达97%,可用于工艺设计及理论分析。最后,基于应力松弛和蠕变的关系,提出了一种隐式蠕变型本构方程描述应力松弛行为,并将识别的材料参数输入ABAQUS,数值模拟了Ti-6Al-4V的热应力松弛行为,发现模拟的应力变化规律符合应力松弛曲线,证明了蠕变型本构方程对应力松弛模拟的适用性。     

K417材料激光冲击强化残余应力松弛预测

针对某型发动机涡轮叶片材料K417激光冲击强化后残余应力在高温下松弛的现象,分析了残余应力松弛的机理,并运用灰色理论建立了温度作用下残余应力松弛的灰色预测模型.该模型的计算结果和实验结果吻合良好,精度较高,为激光冲击强化后残余应力松弛的预测提供一种可行的方法.     

Residual stress relaxation during heating of bearing rings produced in two different manufacturing chains

Bearing rings produced in two different manufacturing chains have been investigated in terms of residual stress relaxation behavior during heating. Cold rolled rings present almost constant compressive residual stresses at the external periphery and completely affected cross sections. Machined rings show high tensile residual stress with periodic variations along the outer periphery caused by clamping during machining. Residual stress states then are confined in a very thin layer. With increasing temperature residual stresses relax. Machined rings present a progressive loss of the residual stress periodicity with increasing temperature. The cold rolled rings show a different relaxation behavior between surface and core. Complementary investigations revealed that recrystallization occurs at a higher temperature in the core compared to the surface. The surface of cold rolled rings and machined rings present a similar behavior: recovery processes induce a decrease of residual stresses at temperatures up to 500 °C and recrystallization starts above 500 °C which causes a complete residual stress relaxation. In the core of cold rolled rings, recovery processes are still active until 600 °C where recrystallization begins. However, residual stresses in the core are already completely relaxed at 600 °C.     

材料复杂残余应力的高温松弛行为

介绍了材料表面应力状态的X射线测量方法，研究了低碳钢交叉焊缝残余应力状态及其热松弛行为。结果表明，焊缝表面残余应力状态比较复杂，加热处理不但可有效降低应力幅度，对应力状态也产生一定影响。加热温度及时问是决定应力松弛的关键因素。在加热退火期间，Mises等效残余应力按幂指数方式松弛．并遵循蠕变机制。     

三种高钢级油井管温矫温度特性的研究

对三种高钢级油井管（C90、G105、P110）的应力松弛特性进行了研究,并测量了这些材料制造的无缝钢管经不同温度温矫后残余应力的变化。结果表明,钢材的化学成分对其应力松弛特性有明显的影响,含碳量低及合金元素铬、钼高的C90钢中的残余应力不易消除,而P110的应力稳定性最低。所以在制订钢管的温矫工艺时,材料的化学成分是不容忽视的因素。     

铝合金薄壁圆筒纵直缝焊接残余应力数值模拟

利用热弹塑性有限元方法对薄壁铝筒纵直焊缝TIG焊进行了数值模拟计算,建立了分析模型,定量地描述了准稳态温度场和残余应力场计算数值以及在整个圆筒上的分布情况,并进行了试验验证.结果表明,焊接时热源周围极窄区域温度高、梯度大,离开热源,温度峰值急剧下降;纵向残余应力在焊缝及热影响区为拉应力,最大值位于焊缝长度中心截面上;纵向残余应力在圆周上表现出拉压区交替变化的趋势.利用应力释放法对焊接件进行应力测量,测量结果与模拟计算结果吻合良好.     

温度场下17-4PH钢喷丸表面残余应力松弛及疲劳强度

采用喷丸处理对17-4PH不锈钢进行表面强化,研究了温度场对其残余应力和疲劳性能的影响。结果表明,结合扫描电镜等微观结构分析,采用X射线无损检测技术对室温下17-4PH不锈钢在不同喷丸参数处理后的表面残余应力进行了评价,利用旋转弯曲疲劳试验机测试了喷丸后样品的S-N疲劳曲线。然后,采用优化的喷丸处理方法,研究了17-4PH材料在150、300和450 ℃不同温度场下的高温疲劳性能和表面残余应力松弛特性。实验结果表明,17-4PH不锈钢的最佳室温喷丸工艺应选用低强度喷丸参数。同时,针对此最佳喷丸强化工艺的高温疲劳试验表明,当环境温度T<300 ℃时,喷丸能显著提高17-4PH不锈钢的疲劳寿命,当温度T>450 ℃时,17-4PH的疲劳性能反而显著降低。进一步分析表明,对于喷丸后17-4PH的高温服役,其疲劳性能降低机理是由于残余应力的严重松弛和表面完整性的降低。     

Ti-4Al-1.5Mn合金高温应力松弛本构模型及应用验证

研究了Ti-4Al-1.5Mn合金在500~700℃的应力松弛特性,首先在蠕变试验机上开展了该合金500、600和700℃条件下的松弛试验,基于松弛数据分别建了双曲正弦和时间硬化两类本构模型,并对模型的预测精度进行了预测。随后把2类本构模型应用于ABAQUS软件对板材V形弯曲过程进行了仿真分析。结果表明,应力松弛的影响因素主要有温度和时间,松弛过程可以分为2个阶段,第1阶段应力快速下降,第2阶段缓慢下降并逐渐稳定于松弛极限。双曲正弦和时间硬化模型均可以对松弛过程进行较准确地预测,V形弯曲后回弹结果表明双曲正弦比时间硬化模型具有更高的预测精度。研究结果对利用应力松弛进行精确成形的工艺设计具有指导意义。     

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 Modeling in Orthogonal Machining

A predictive model for residual stresses in orthogonal cutting is presented. It uses process conditions as inputs and predicts surface and sub-surface residual stress profiles due to machining. The model formulation incorporates cutting force and cutting temperature predictions and utilizes those parameters to define the thermo-mechanical loading experienced by the workpiece. The stresses at the cutter edge hone and in the shear plane are considered in a rolling/sliding contact algorithm which admits kinematic hardening for non-proportional plasticity with subsequent stress relaxation to meet boundary conditions. Model predictions are compared to experimentally-measured residual stresses under various cutting conditions for validation.     

Finite Element Simulation for Welding Residual Stress and Creep Damage of Welded Joint

基于大型有限元软件Abaqus及其用户子程序(Umat)功能, 开发了焊接残余应力与蠕变损伤耦合计算程序, 对高温用焊接接头残余应力作用下的蠕变损伤行为进行有限元模拟, 并与无焊接残余应力状态下的蠕变损伤情况 进行比较. 研究结果表明, 在炉管焊接状态下, 焊接残余应力最大值集中在焊缝和热影响区处, 并且轴向与环向 残余应力较高. 在高温环境下, 焊接接头初始态焊接残余应力较高, 虽然在短时间内应力松弛到较低的水平, 但 其蠕变损伤仍较大程度地受焊接残余应力的影响, 蠕变损伤分布与焊接残余应力的分布基本一致.     

真空压力浸渗制备CF/Al复合材料热收缩与残余应力数值模拟与实验研究

针对连续碳纤维增强铝基复合材料(CF/Al复合材料),采用细观力学数值模拟与热性能试验结合的方法,研究了真空压力浸渗制备过程中的热收缩行为和热残余应力分布。结果表明,复合材料的横向热收缩应变量远大于轴向热收缩应变量,且具有横观各向同性,纤维随机分布的单胞有限元模型能够准确地预测复合材料轴向与横向热收缩行为曲线;复合材料制备完成后纤维和基体合金分别处于压应力和拉应力状态,基体和纤维的横向残余应力均小于其轴向残余应力,且均表现出横观各向同性;基体合金在轴向残余拉应力作用下会出现不同程度的损伤现象,特别是纤维间距较小部位过高的残余应力会引发界面的局部失效,从而不利于发挥复合材料承载性能,减少纤维局部偏聚是进一步改善提高复合材料力学性能的重要技术手段。     

Residual stress relaxation in typical weld joints and its effect on fatigue and crack growth

Many factors influence the fatigue and crack growth behavior of welded joints. Some structures often undergo fairly large static loading before they enter service or variable amplitude cyclic loading when they are in service. The combined effect of both applied stress and high initial residual stress is expected to cause the residual stresses relaxation. Only a few papers seem to deal with appropriate procedures for fatigue analysis and crack growth by considering the combined effect of variable amplitude cyclic loading with residual stresses relaxation. In this article, some typical welded connections in ship-shaped structures are investigated with 3-D elastic-plastic finite element analysis. The effect of residual stress relaxation, initial residual stress, and the applied load after variable amplitude cyclic loading is revealed, and a formula for predicting the residual stress at hot spot quantitatively is proposed. Based on the formula, an improved fatigue procedure is introduced. Moreover, crack growth of typical weld joints considering residual stresses relaxation is studied.     

残余应力对高速列车A7N01铝合金焊接接头疲劳行为的影响

研究了残余应力在疲劳加载过程中的应力松弛行为,采用预拉伸、表面喷丸等表面预制残余应力的方法预制了表面残余应力,并研究了焊接接头的疲劳性能. 结果表明,在经过1×105周次循环载荷后,各个部位残余应力发生较大松弛,在经过2×105周次后,应力松弛较1×105周次时松弛幅度降低. 在2×105周次后,应力松弛不再明显,最终残余应力分布在拉应力20～40 MPa之间. 当引入残余应力后,各种条件下的实际应力循环比发生了明显的变化,当应力比R≥0时,随着R的增大,平均应力增大,试样的疲劳周次显著下降. 残余压应力会使裂纹萌生的周期缩短,同时加快疲劳裂纹扩展速率.     

难加工材料铣削残余应力研究进展

镍基高温合金、钛合金等材料具有良好的高温强度、耐热性和耐腐蚀性等优异性能,已广泛应用于航空航天领域,然而这些材料属于典型的难加工材料,其相对切削加工性能很差,且已加工表面易产生显著残余拉应力,严重影响零部件使用寿命及性能。通过适当的方法调整和控制已加工表面的残余压应力,可以明显提高零件疲劳强度和耐腐蚀性。压应力制造技术是指以获得残余压应力为目标的制造技术,是一种典型的抗疲劳方法。将超声技术与其他加工方法复合实现残余压应力的主动控制,是目前抗疲劳制造技术的主要方法之一。然而,由于受超声加工的临界速度限制,超声与高速复合加工的研究相对较少,但两者均是目前压应力制造领域高度关切的先进加工方法,如果两者能有效复合,必将使核心部件制造在保证更加优良的抗疲劳性能的同时,获取更高的效率。通过分析铣削加工、高速加工以及超声振动加工中残余应力的研究现状,提出可将高速加工和超声振动加工相结合,从而实现难加工材料的高效压应力制造。     

Q345钢激光熔覆的残余应力分析

针对因残余应力而出现的熔覆层表面开裂等问题,设计了合理的试验方案,获得熔覆与冷却过程中工件的残余应力值。根据残余应力值比较不同工艺路线的优劣,发现工件预弯能够显著降低残余应力。同时使用ANSYS进行仿真分析,模拟工件的温度场与应力场。分析得到,工件因纵向塑性畸变而产生的纵向应力是残余应力的主要成分。