Non-destructive measurement of residual stresses in carbon steel weld joints

Abstract

Residual stress measurements have been carried out on 8 and 12 mm thickness carbon steel single V weld joints by X -ray diffraction and ultrasonic techniques. The maximum tensile and maximum compressive stresses on the surface of the 12 mm carbon steel weld joint are higher than those on the surface of the 8 mm carbon steel weld joint. The results also indicate that the variation in the surface residual stress across the weld is different from that for the through thickness residual stresses. The effect of constraint, which depends on the thickness of the weld joint, is found to influence the surface and through thickness residual stresses. The effect of stress relief annealing heat treatment on residual stresses was also studied.     

非破坏性测量焊接残余应力方法的应用现状

介绍了X射线衍射法、中子衍射法、磁声发射法和超声波法等四种非破坏性测量焊接残余应力的基本原理,综述了它们的发展概况及应用现状。通过比较分析各种测量方法的特点和适用范围,指出了选用适宜方法测定焊接残余应力的原则。     

X射线衍射测试PDC表面残余应力的实验研究

作者采用DIMAX2500型X射线衍射仪,通过对入射光狭缝尺寸进行调整,使X射线的照射光斑尺寸缩小为1.5×5 mm,从而实现了对PDC表面沿径向的四个不同位置的应力测量.测量采用sin2ψ法,不但测出了PDC表面不同位置的残余应力,还由此得到了PDC表面应力沿径向的分布规律,而且这一测试结果与通过有限元分析计算出的应力分布趋势基本吻合.作者还对测试值与有限元分析计算值出现偏差的原因从测试方法、有限元分析参数取值及样品表面加工方式等几方面进行了分析讨论.     

Thermal residual stresses in co-continuous composites

The thermal residual stresses in two types of co-continuous composites copper/aluminum oxide (Cu/Al₂O₃) and aluminum/aluminum oxide (Al/Al₂O₃) were measured by neutron diffraction experiments. These stresses were generated during the cooling after high processing temperature. The coefficient of thermal expansion (CTE) mismatch of metal and ceramic phases led to significant amount of thermal stresses. In both the composites, the metallic phase was found to be under tension and aluminum-oxide phase under compression. Even though the magnitude of compressive stress in both the composites was similar; the two metal-phases had very different magnitude of tensile stresses. The difference in volume fraction, CTE, elastic stiffness and plastic flow properties led to this difference. The hydrostatic stresses were found to be predominant in both the phases. Finite element simulations were used to predict the stress distributions inside each phase and at the interfaces. A representative unit cell approach was considered to represent the composite. Concept of effective ΔT was utilized to simulate the thermal stress distribution inside the two phases in the unit cell. This model utilized the neutron diffraction measurements to predict the stress distribution inside each phase and at the interface. The simulations showed that significant amount of tensile stresses develop at the metal–ceramic interfaces.     

薄板结构焊接残余应力的数值分析

运用有限元方法,对大型客车车身薄板结构焊接时采用的电铆焊、连续焊、断续焊及塞焊的残余应力进行了热-弹塑性数值模拟.分析了连续焊缝、电铆焊和塞焊残余应力分布特点.结果表明,电铆焊、塞焊、断续焊所产生的应力场为波浪起伏的不均匀拉应力,不会造成薄板结构的失稳变形.而连续焊时焊缝区域为拉应力,远离焊缝区域为压应力,此压应力造成薄板结构的失稳变形.模拟结果为薄板结构焊后失稳变形的评判提供了理论参考.     

Predicting residual stresses in gas turbine components

This article describes work carried out by a major aircraft-engine builder and one of its suppliers to validate the numerical prediction of heat-treatment-induced residual stresses. For verification, the project used a large-scale, nickel-based super alloy forging-, calculated stresses are compared to those measured using a hole-drilling technique. Even though the analyses were conducted by both companies using different software, the results tie closely with the measurements.     

A study on residual stresses in rolling

Determination of residual stresses in rolled material is important for the design of product and process. Different approaches for determining them and difficulties associated with the methods are discussed. A simplified approach to find the longitudinal residual stress (stress in the direction of rolling) is proposed. A parametric study has been carried out to show the influence of process parameters on the residual stress distribution pattern.     

7075铝合金残余应力与机械载荷交互作用的试验研究

振动时效是一种能有效降低残余应力的工艺技术,但是工件在振动时效过程中微观组织和宏观力学性能都会发生变化。通过激振器和试验机两种装置研究7075高强铝合金板的振动时效发现,残余应力的松弛也伴随着材料力学性能的下降。断口扫描电镜分析表明,杂质相和第二相粒子造成的组织缺陷是疲劳性能降低的主要原因,但两种情况下略有不同。结果认为振动时效除了应合理选择动应力,激振频率对材料残余应力松弛与力学性能也有重要影响,疲劳累积损伤理论是另一重要影响因素。     

拉剪载荷下超高强度钢点焊残余应力试验

点焊后焊接残余应力叠加工作载荷后,内部应力会重新分配.文中选用B1500HS超高强度钢薄板,制备焊接构件,并通过X射线衍射法测量焊核区、热影响区及母材区的表面残余应力.在施加拉剪载荷的情况下,分别从电极端面直径、焊接电流两方面考察点焊构件在施加拉剪载荷前后残余应力的分布情况.结果表明,点焊时电流变化对试件的残余应力有一定影响;电极端面直径增加使得焊核区的残余应力增大.施加拉剪载荷后,残余应力在焊核与热影响区有所释放,远离焊核区的释放较小.     

Change of residual stresses in rolls during operation

Conclusions The redistribution of residual stresses in surface layers of rolls during operation in cold rolling mills is due to the manufacturing technique and operating conditions.The principal means of improving the durability of rolls are the use of new steels with structural stability and rehardening of rolls after a given operating period to reestablish the original stresses.Elektrostal' Factory of Heavy Machine Construction. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 72–75, January, 1975.     

On the proper selection of reflections for the measurement of bulk residual stresses by diffraction methods

The suitability of various reflections for diffraction measurement of bulk residual stresses in austenitic steel after plane-strain deformation is investigated by self-consistent calculations. Earlier findings (for tensile-deformed fcc materials) that 311 is particularly well suited was not confirmed. In the present calculations 111 and 422 turned out to be the best (least bad) reflections. The new results have led us to reconsider the earlier findings.     

Experimental and numerical modelling of the residual stresses induced in orthogonal cutting of AISI 316L steel

Residual stresses in the machined surface layers are affected by the cutting tool, work material, cutting regime parameters (cutting speed, feed and depth of cut) and contact conditions at the tool/chip and tool/workpiece interfaces. In this paper, the effects of tool geometry, tool coating and cutting regime parameters on residual stress distribution in the machined surface and subsurface of AISI 316L steel are experimentally and numerically investigated. In the former case, the X-ray diffraction technique is applied, while in the latter an elastic–viscoplastic FEM formulation is implemented. The results show that residual stresses increase with most of the cutting parameters, including cutting speed, uncut chip thickness and tool cutting edge radius. However, from the range of cutting parameters investigated, uncut chip thickness seems to be the parameter that has the strongest influence on residual stresses. The results also show that sequential cuts tend to increase superficial residual stresses.     

Applied mechanics in grinding-V. Thermal residual stresses

The objective of this part of the series research is to investigate the correlation between the thermal residual stresses and conditions of surface grinding. The heat generated in grinding was modelled by a moving band heat source with a triangular profile. The effect of a coolant was simulated by heat convection. To obtain a reliable figure of thermal residual stresses induced by grinding, temperature-dependent properties of work materials were taken into account and a non-uniform convection model with an effective cooling factor was introduced. A thorough analysis using the finite element method showed that the predictions based on the temperature-independent properties always underestimate thermal deformation, that the effective cooling factor in the grinding zone should be maintained beyond a critical value, and that the Peclet number has a significant effect on the selection of critical grinding conditions. The paper offers an insight into the mechanism understanding of thermal residual stresses induced by surface grinding.     

Effect of residual stresses on hydrogen permeation in iron

The effect of residual stresses on electrochemical permeation in iron membrane was investigated. Four thermal and mechanical treatments were chosen to obtain different surface states in relation to the residual stresses.Residual stresses were determined by X-ray diffraction (XRD) using the Macherauch and Müller method. The results were completed by the microhardness measurements. For all iron membranes, compressive residual stresses were obtained.Electrochemical permeation experiments using a Devanathan and Stachurski cell were employed to determine the hydrogen permeation behaviour of the various iron membranes. The latter was charged with hydrogen by galvanostatic cathodic polarization in 0.1 M NaOH at 25 °C. The experimental results revealed that hydrogen permeation rate increases with increasing residual stresses introduced in iron membranes.     

Relaxation of residual stresses in SiC wafers by annealing

Residual stresses in SiC wafers, which were introduced during production processes including sawing, lapping, mechanical polishing （MP）, and chemical-mechanical polishing （CMP）, were evaluated in terms of changes in radius of curvature and high-resolution X-ray diffractometer （HRXRD） measurements. It was found that annealing was an effective method to reduce stress fields and to improve the wafer flatness. Lapping process generated more residual stresses than other machining processes, and these stresses could be relaxed by thermal treatment. The results showed that annealing was an essential procedure following lapping in the whole production process. The molten KOH etching results accounted for the correlation between the relaxation of stresses and the creation of basal screw dislocations.