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1.
为了揭示高频振动时效消除残余应力的微观机理,探讨了高频振动载荷作用下的位错密度演化特性对残余应力松弛的影响规律。分别采用Williamson-Hall(WH)法和小孔法分析高频振动前后Cr12MoV钢淬火试样的位错密度和残余应力。在实验研究的基础上,采用微观动力学理论,建立晶粒多自由度系统,分析高频振动激活位错运动的机制,进一步采用晶体塑性理论,建立高频振动作用下的位错密度演化控制方程,分析高频振动时效消除残余应力的微观机理。结果表明:材料内的位错在高频振动的作用下激活运动,产生位错累积和位错湮灭2个演化过程,其中材料内的位错湮灭过程占据主导地位,从而降低了材料内的位错密度;位错密度的降低减小了材料内的晶格畸变程度,从而松弛了材料内的残余应力。  相似文献   

2.
高欢  李正阳  彭青  闫世兴 《表面技术》2021,50(3):198-205
目的 针对航空铝合金构件维修加工后存在残余拉应力,进而影响部件使用寿命的难题,研究一种基于低能量输入激光辐照消减构件表面残余应力的方法.方法 采用激光辐照材料残余应力集中区域,通过激光热作用诱导弹性内能转化为塑性功,从而降低残余应力.为了验证该方法的可行性,对2A12铝合金试样进行四点弯曲加载,通过不均匀塑性变形产生残余应力,再通过激光扫描应力集中区域诱导表面残余应力局部释放.结果 采用X射线衍射法测量表面残余应力的结果表明,激光扫描后,试样表面的残余拉应力完全消除,当激光功率增大到95 W时,残余应力可以消除77%左右.通过理论分析和微观形貌对比,发现材料在激光辐照前后并没有相变.通过分析材料Al(311)晶面X射线衍射峰半高宽的变化,发现激光辐照使材料表面位错密度下降,随着激光功率增大,位错密度下降幅度增大,这也是残余应力降低的原因之一.结论 在不改变材料微观组织的前提下,采用低功率激光辐照可以显著降低材料表面残余应力分布.  相似文献   

3.
采用预压缩CT试样的方法研究了残余应力对Super304H奥氏体不锈钢焊缝金属再热裂纹敏感性的影响。通过ABAQUS模拟结合EBSD表征分析了不同残余应力下的焊缝金属的塑性应变分布和位错密度分布,并从残余应力诱导焊缝金属晶内析出相的方面解释了残余应力对焊缝金属再热裂纹敏感性的影响。结果表明:高预压缩载荷的CT试样具有更高的残余应力,更容易产生再热裂纹。随着残余应力的增加,焊缝金属拉伸试样的抗拉强度逐渐降低。焊缝金属CT试样靠近U型口的高残余应力区域具有更高的位错密度和更高比例的亚晶,促进了晶内小颗粒相的析出,使得晶内硬化更为严重,再热裂纹更容易产生。  相似文献   

4.
目的 提高航空发动机叶片的抗疲劳性能。方法 采用高功率密度短脉冲激光冲击某型发动机TC17钛合金整体叶盘叶片模拟件,并采用飞秒激光在进气边预制缺口。通过扫描电子显微镜和透射电子显微镜表征激光冲击前后的表层微观组织。通过X射线衍射和三坐标测量仪分别测量激光冲击强化过程中的残余应力演变和宏观塑性变形,并由一阶弯曲振动疲劳对激光冲击强化效果进行评价。结果 激光冲击在TC17钛合金叶片表层诱导产生了高密度位错组织,但由于冲击次数的控制,未产生明显的晶粒细化效应。激光冲击叶盆面后,叶盆面呈现压应力状态,残余应力为330.5 MPa,叶背面呈现拉应力状态,其值为55.5 MPa。进一步激光冲击叶背面后,叶背面的拉应力转变为压应力,其值达到了267.0 MPa,叶盆面残余压应力减小,由330.5 MPa变为261.9 MPa。激光冲击叶盆面后,进气边与叶尖交点偏离初始位置0.119 1、0.129 1 mm;冲击叶背面后,位移偏离初始位置减小,分别为0.071 08、0.099 mm。激光冲击强化后,缺口振动疲劳寿命显著提升,平均循环次数由56 696周次增加到199 515周次,出现了明显的裂纹闭合效应。结论 激光冲击强化在TC17钛合金表层引入了高密度位错组织和双面贯穿式残余压应力,并将叶片宏观塑性变形控制在0.1 mm以内,在疲劳性能上获得了显著的提升。  相似文献   

5.
1 INTRODUCTIONDuetothedifferenceofcoefficientsofthermalexpansionbetweenreinforcementandthematrixinSiCw/Alcomposites,thethermalresidualstressisnotavoidedwhenthetemperatureischanged[1,2].Thethermalresidualstresscanlargelyaffectthepropertiesofthecomposites,s…  相似文献   

6.
Based on the measurements of the dependences of the coercive force of ferromagnetic steels on elastic tensile stresses, its minimum values and the positions of these minima have been found. Using the method of thermal neutron scattering, it has been experimentally proved that the stresses at which the coercive force is minimum is equal to the average value of the residual body stresses (internal stresses of the first kind). The latter were varied over wide limits with the aid of either a preliminary tensile plastic deformation to different degrees (steel St3) or using different tempering regimes after quenching (steel U8). In the first case, large residual compressive stresses arise in a significant part of grains along the direction of loading, which are caused by the anisotropy of Young’s modulus of iron. As a result of compensating these stresses by external tensile stresses, there appears a minimum of the coercive force, whose value is determined by an increase in the dislocation density at the stage of plastic deformation.  相似文献   

7.
陈禹锡  高玉魁 《表面技术》2019,48(6):167-172
目的 研究经喷丸强化处理后Ti2AlNb材料表层残余应力的分布特征,并预测残余应力对材料疲劳性能的影响规律。方法 通过贴应变片逐层钻孔法,对使用喷丸强化处理后的Ti2AlNb试样进行残余应力测试分析,得到引入残余应力场各方面的测试数据,结合ABAQUS数值模拟方式,对比分析试验与模拟残余应力场结果,获取材料的最终残余应力梯度。利用FE-SAFE软件,通过叠加残余应力场的方式,预测喷丸强化前后试样的疲劳寿命。结果 在文中加工参数下,实验测试和软件模拟结果的重合度良好。喷丸强化可在Ti2AlNb金属间化合物靶材内引入300 MPa左右的最大残余压应力,深度达到了0.12 mm左右。材料表面塑性应变分布不均匀,且造成的塑性应变距表面深度可达0.1 mm。通过喷丸强化引入残余压应力,预测的Ti2AlNb材料疲劳极限可提高12%,高低周疲劳寿命均有明显的延寿效果。结论 验证了有限元数值模拟此材料喷丸强化的准确性和可靠性,得到了Ti2AlNb材料喷丸强化的残余应力场。由于塑性变形诱发机制的限制,喷丸造成塑性应变分布不均匀,塑性应变层深小于残余压应力层深。此外,强化后材料的疲劳性能显著提高,疲劳极限有可观的提升,且高低周疲劳均有较好的延寿效果。  相似文献   

8.
Abstract

Flexural vibration was applied to specimens during the welding process to observe its effect on welding residual stresses. The study was carried out in three phases, namely, (i) investigation of the effect of amplitude of vibration, (ii) investigation of the effect of time of vibration, and (iii) investigation of the effect of high frequency vibration. The results of the present study provide a basis for relieving the residual stresses in practice. It has been shown that there is an optimum applied stress that will maximise the reduction in both longitudinal and transverse residual stresses. The effect of time of vibration on residual stresses was found to be negligible. After high frequency vibration, the change in longitudinal and transverse residual stresses showed no consistent trend.  相似文献   

9.
The effect of a pulsed electric current on the residual stress evolution of metal materials has been investigated.It was found that the surface and internal residual stresses in the as-quenched samples were reduced dramatically by electropulsing.A large number of experimental data show that the residual stress reduction is proportional to the initial residual stress and related to the material properties and electropulsing parameters.Under the combined actions of drift electrons,Joule heating,and residual stress,the dislocation mobility was enhanced,resulting in plastic strain and the decrease in residual stress.Drift electrons played a unique role in the electropulsing treatment,acting as an additional force pushing dislocations forward.The dislocations ultimately accumulated at a grain boundary,forming a parallel arrangement.Finally,the phenomenological equation of the residual stress evolution under electropulsing was derived from the experimental data.  相似文献   

10.
Strengthening of aluminium alloys 7xxx through the imposition of severe plastic deformation supplemented by ageing treatments is a challenge due to the limited workability of these alloys in cold deformation regimes. This study aims to comprehensively investigate the strengthening of aluminium alloy 7005 through the imposition of severe plastic deformation supplemented by two different ageing treatments: pre-deformation artificial ageing or post- deformation natural ageing. For this purpose, microstructure evolutions of the alloy processed through mentioned procedures were studied using X-ray diffraction and scanning electron microscopy while the alloy strengthening was evaluated using Vickers hardness measurement. Results show that a superlative strengthening is obtained through the imposition of severe plastic deformation supplemented by post-deformation natural ageing. For instance, the yield strength of the alloy increases to more than 400 MPa, about one-third greater than the counterpart amount after the usual T6 treatment. This superlative strength mainly occurs due to refinement of grains, an increase of dislocation density and an increase of volume fraction of the precipitates that appeared during natural ageing. Considering the applied models, it is inferred that the increase of volume fraction of precipitates that appeared during natural ageing has a determinative role in the strengthening of the alloy.  相似文献   

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