异种金属摩擦焊接头焊后热处理工艺的确定

通过分析NiCr20TiAl与4Cr9Si2摩擦焊的焊接性,对接头焊后热处理制度进行了试验研究。试验结果表明,立即油冷和650℃/45min回火可改善接头的强韧性能,使弯曲角达到67°以上,弯曲载荷达到139kN以上。     

Distribution of Residual Stresses in a Layer Containing a Welded Cylindrical Disk

By the method of conventional plastic strains, we study the distribution of residual stresses in a plane layer containing a welded cylindrical disk. For plastic strains symmetric about the median surface of the layer, we perform the numerical analysis of the distribution of residual stresses. It is shown that the radial stresses on the surfaces of the welded joint decrease and the hoop stresses increase as the radius of the disk increases.     

A Study of the Welding Parameters for High Frequency Welded Pipes

In cold roll forming, steel pipes are welded with different technology parameters in order to improve the steel pipe′s quality, thus we should optimize the technology parameters for producing steel pipes. By means of metallographic examination, scanning electron microscope examination, hardness test, impact test, bend test, tensile test and so on, the microstructure and mechanical properties of the steel pipes were investigated. The test results show that welding defects such as crack and blowholes are not ...     

Optimum Design of Thick-Walled Multi-Layered CFRP Pipes to Reduce Process-Induced Residual Stresses

Process-induced residual stresses may cause cracking in thick-walled multi-layered CFRP pipes during the curing of the pipes, significantly affecting the ultimate structural performance. Several factors influence the amount of the residual stresses, such as thermal and elastic properties of CFRP, and stacking sequences and dimensions of pipes. This paper deals with the optimum design of thick-walled multi-layered CFRP pipes by minimising the process-induced residual stresses under some constraints of structural stiffnesses. An analytic model based on quasi-static thermoelasticity is adopted for the calculation of the residual stresses in the multi-layered CFRP pipes. The numerical results of optimisation show that, in the case of cross-ply pipes, the residual stresses can be reduced to a certain level by controlling ply thicknesses. However, in real process conditions, the optimised pipes are susceptible to cracking because the transverse residual stress is still large in a strength-based sense. To further suppress the residual stresses, the effects of stacking sequence, wall thickness and axial pre-tension on the optimum solutions are carefully examined.     

Thermoelectric Nondestructive Evaluation of Residual Stress in Shot-Peened Metals

This paper presents a noncontacting thermoelectric method that can be used to characterize the prevailing residual stress in shot-peened specimens. This novel method is based on magnetic detection of local thermoelectric currents in the compressed near-surface layer of metals when a temperature gradient is established throughout the specimen. Besides the primary residual stress effect, the thermoelectric method is also sensitive to the secondary ``material' effects of shot peening (local texture, increased dislocation density, hardening), but it is entirely insensitive to its ``geometrical' by-product, i.e., the rough surface topography. Our experimental results in copper indicate that the developed method is more sensitive to residual stress effects than to the secondary material effects, but unequivocal separation of residual stress relaxation from the parallel decay of secondary cold-work effects is generally not feasible. However, since the ratio of residual stress to cold work is primarily determined by the material and the specific surface treatment used, the thermoelectric method still offers the unique capability of nondestructively monitoring thermomechanical relaxation below the treated surface. Preliminary results on IN100 nickel-base superalloy are also presented to demonstrate that the proposed method might be applicable to a wide range of alloys including high-strength, high-temperature engine materials.     

预拉伸条件下铝合金筒体焊接残余应力和变形的数值模拟

利用ANSYS有限元分析软件,分别对施加及不施加拉伸应力的铝合金筒体环焊缝对接焊接过程中的应力场及变形进行了模拟分析。计算结果表明:预拉伸焊接可以有效减小铝合金薄板的焊后残余应力和变形。当预拉伸应力为材料屈服强度的90%时,焊缝残余应力较无预拉伸的降低近52%,同时,铝合金筒体焊接残余变形也大幅减小。     

Thermoelectric Nondestructive Evaluation of Residual Stress in Shot-Peened Metals

Abstract

This paper presents a noncontacting thermoelectric method that can be used to characterize the prevailing residual stress in shot-peened specimens. This novel method is based on magnetic detection of local thermoelectric currents in the compressed near-surface layer of metals when a temperature gradient is established throughout the specimen. Besides the primary residual stress effect, the thermoelectric method is also sensitive to the secondary “material” effects of shot peening (local texture, increased dislocation density, hardening), but it is entirely insensitive to its “geometrical” by-product, i.e., the rough surface topography. Our experimental results in copper indicate that the developed method is more sensitive to residual stress effects than to the secondary material effects, but unequivocal separation of residual stress relaxation from the parallel decay of secondary cold-work effects is generally not feasible. However, since the ratio of residual stress to cold work is primarily determined by the material and the specific surface treatment used, the thermoelectric method still offers the unique capability of nondestructively monitoring thermomechanical relaxation below the treated surface. Preliminary results on IN100 nickel-base superalloy are also presented to demonstrate that the proposed method might be applicable to a wide range of alloys including high-strength, high-temperature engine materials.     

焊接残余应力数值模拟的研究与发展

分析了用有限元法计算焊接残余应力的基本理论,其中包括温度场和应力场的数值模拟,介绍了焊接残余应力数值模拟方法的近期研究成果,并探讨了焊接残余应力数值模拟技术的发展趋势.     

Residual Stresses in Galvanizing

Zinc coating is formed by heterogeneous assembly of phases in which mechanical properties greatly differ. In the galvanizing process the great difference between the linear thermal expansion of the iron substrate and the Zn has proven to be the source of important residual stresses. The primary objective of this paper is to determine the residual stresses which promote crack formation and deterioration of corrosion resistance. Because direct determination by x-ray diffraction has been difficult, three other methods are proposed. The first one led us to calculate an average stress by measuring the variation of crack length with applied load resulting from a Vickers small indentation. The second is an application of the Timoshenko's bimetallic strip method based on the difference in thermal expansion coefficients. The third is deduced from the variation of the curvature of one-face galvanized specimens. These results are compared and the homogeneous value of residual stresses are shown.     

Evaluation of Residual Stresses During Fatigue Test in an FSW Joint

Abstract:  This paper shows an application of the adjusted compliance ratio method (ACR), and the on-line crack-compliance technique for determination of the effects of the residual stress during a fatigue test. The fatigue crack growth tests were carried out on a friction stir welded (FSW) joint in Ti-6Al-4V titanium alloy. On-line crack compliance enables the determination of the residual stress intensity factor in real time from a fatigue test. The ACR methodology was used to separate the residual stress effects from the crack growth rate data. Finally, the residual stress distribution of the FSW joint was found from the knowledge of the residual stress intensity factor through an integral solution. It would have to be noted that both methods are based on ratios of displacements; therefore, the practical application does not require the use of the influence functions needed for the cut-compliance method. Moreover, a specific test, which determines residual stresses, can be avoided because the effect of the same residual stresses on the crack growth is evaluated during the fatigue test. This methodology is more accurate than cut compliance because it reflects the real crack growth behaviour.     

Evaluation of Residual Stresses in Prismatic Rods with Unknown Young's Moduli

We propose a procedure for the evaluation of residual axial stresses in the surface layers of prismatic rods with unknown Young's moduli.     

Thermoelastic Characterization and Evaluation of Residual Stresses in Bi-Directional Fibrous Composites

The thermoelastic behavior of bi-directional fibrous composites will be studied through the use of a finite element-based micromechanical model. The model is used to study the effect of the crossing angle of the fibers on the composite’s coefficient of thermal expansion (CTE) and the residual thermal stresses that develop after a temperature change. The effect of the fiber volume fraction (V _f ) on the same results is also studied. For anisotropic materials, one can see that in addition to normal strains, shear strains will also be developed due to temperature change. This method will lend itself to evaluate the coefficients of thermal expansions not only due to normal expansion, but also due to shear expansion for composites with no principal directions. In this micromechanical model, parallelepiped unit cells incorporating the fibers at different cross angles are created to represent the periodic microstructure of the angular bi-directional composite. The volume averaged stresses per unit temperature of the individual constituents are used to study the residual thermal stresses that develop. Two different sets of materials are used to test this model. Results show that when the fiber’s cross angle is not 0^o or 90^o, shear strains are created. Also, residual stresses in the unit cell are functions of the cross angle between the fibers.     

Methods for Determining Residual Welding Stresses and Their Relief (a Review)

We present a brief analysis of the existing methods for the determination and relieving of residual welding stresses. Among numerous ways of their removal, methods based on surface plastic deformation appear to be the most promising. In addition, we propose a new method of decreasing residual tensile stresses.     

Effect of Residual Stresses on the Fatigue Resistance of Welded Joints of Steels of Different Strength Levels

Strength of Materials - Limiting cyclic stress diagrams of welded joints of a low-carbon and low-alloy steels of different strength levels are analyzed under conditions that they contain the same...     

采用模糊综合评价法设计铜铝管对焊机

以系统的观点进行功能分析,最终采用模糊综合评价法这一现代机械系统设计方法进行决策。通过对总功能的分解和原理解的组合,得到了铜铝管对焊机的形态学矩阵;通过对形态学矩阵中各方案的模糊综合评价,得到了最佳的可行方案。实践证明,用这种设计方法研制出的铜铝管对焊机,整体性能达到了国际先进水平。     

Pulsed Electromagnetic Field Effect on Residual Stresses and Strains of Welded Joints of AMg6 Aluminum Alloy

Strength of Materials - The pulsed electromagnetic field treatment of welded joints is a promising method to improve the mechanical characteristics of metal structures. Its influence on the...     

Thermal Residual Stresses in Bonded Repairs

The number of ageing aircraft is increasing and will further increase considerably in the near future. The control of damage by inspection and repair becomes therefore more and more important. The bonded repair method proved to be a cost-effective way to repair damage. However, this method has some disadvantages. One of them is the introduction of thermal residual stresses in the repair, due to the mismatch in coefficients of thermal expansion between the skin material and the repair material. Two analytical models are available to determine these residual stresses in the repairs, i.e., the Wang–Rose model and the Van Barneveld–Fredell model. A new computer program CalcuRep2000 [1] is being developed. This computer program will be used to calculate the stresses in bonded repairs, and is developed by the US Air Force in co-operation with the faculty of Aerospace Engineering of Delft University of Technology in The Netherlands. For this program an analytical model, which is able to calculate the thermal stresses in a bonded repair accurately, is essential. This paper describes how the most adequate analytical model was identified by comparison with Finite Element (FE) analysis. Two repair configurations were distinguished: The test specimen, i.e., bonded repair specimens used for fatigue tests in laboratories, and the in-field specimen, i.e., a realistic repair. The difference between both repair configurations is that a test specimen is free to expand during curing while in a realistic repair configuration expansion is partly prevented by the cooler surroundings of the heated area. The analytical model of Van Barneveld and Fredell proved to be the most accurate one. The results of this model agree with the results of the FE model of the test specimen and the in-field specimen. The Wang–Rose model calculates the thermal residual stresses accurately in the case of a test specimen, but the stresses calculated in the case of an in-field specimen are less accurate. No useful experimental data are available in literature from measurements of thermal residual strains on bonded repairs. Therefore experiments were conducted to measure thermal residual strains in bonded repairs. The same repair configurations were used for these experiments. The results obtained with the experiments are compared with FE results. Finally, the temperature distribution calculated by the analytical models is compared with the temperature distribution measured during the experiments of the in-field specimen. The influence on the thermal residual stresses of a different temperature field is discussed here, using the FE results.     

Stresses in Pipes Joined by a Circular Weld

We present the solution of the problem of evaluation of residual stresses in welded shells obtained with the help of a numerical-experimental method. By using the function that describes plastic strains, we apply this solution to the case of butt welding of steel pipes with a single-pass weld. The difference between the theoretical and experimental results does not exceed 10%. We also modify the approach to the evaluation of the width of the plastic zone in the numerical analysis of welding stresses by the method of Trochun.