金属基复合材料界面残余应力的研究进展

综述了金属基复合材料界面残余应力的各种影响因素、残余应力的实验测试方法和理论分析方法及残余应力对复合材料宏观力学性能的影响,分析讨论了目前研究中存在的问题和不足之处,并指出了今后工作的重点与方向.     

金属基复合材料残余应力测定

分析了金属基复合中热残余应力的形成机理及表现特点，并对几种常用的测定金属基复合材料残余应力的方法进行了分析比较，普通Ｘ射线法虽然简便、经济、但穿透能力有限，所测值仅反映试样表面的残余应力状态；中子衍射的区域较大，测出的仅是残余应力平均值。Ｘ射线能量衍射法虽然穿透能力较强，能测出试样内部较深范围的残余应力，但由于产生衍射法穿透力强，分辩率高，能测出复合材料内部的残余应力场梯度，是测定金属基复合材料残     

纤维缠绕复合材料起伏区域残余应力

针对纤维交叉起伏区域残余应力,建立一种细观分析模型。基于热传导方程、固化反应动力学模型和复合材料层合理论,采用有限元方法和细观分析模型,对缠绕复合材料在固化工艺过程中的残余应力分布及其变化规律进行数值模拟。通过算例,研究纤维起伏区域残余应力的分布特点,结果表明:起伏纤维束不同位置处残余应力差别很大,层合区纤维束呈现拉应力状态,起伏区纤维束呈现压应力状态,富树脂区出现最大压应力;残余应力沿纤维束起伏方向呈现V型变化趋势,在纤维束上不同位置出现拉、压不同的应力状态,起伏角度最大处出现最大压应力。     

X-ray Analysis of Residual Stresses in C/SiC Composites

The residual stress state of C/SiC-composites, which are manufactured by a pyrolytical process is analysed by X-ray diffraction. The residual stress state in the composites results from the superposition of the shrinkage of the matrix material during the pyrolytical process and from effects of the thermal mismatch between fibres and matrix. The dependence of the residual stress state on the fibre coating and the process parameters of the pyrolytical process is determined. Furthermore, the change of the stress state in the samples submitting them to mechanical and thermal loads is analysed.     

树脂基纤维复合材料的热残余应力数值分析

以环氧树脂R368-1/硼纤维复合材料为研究对象,采用柱体单胞结构,建立了三维有限元分析模型。考虑试样加工制备过程和常温使用时的温度差,对残余应力分布特点和应力水平进行了讨论,给出了应力分布云图和应力沿径向的分布规律。进一步考察了纤维体积分数、温度差和附加界面层对残余应力分布的影响,结果表明,基体主要受拉伸应力作用,纤维主要受压缩应力作用,纤维体积分数增加和附加界面层有助于改善复合材料中残余应力的分布,试样制备温度的升高对纤维中应力的增加具有较大影响。     

Efficient 2D Analysis of Interfacial Thermoelastic Stresses in Multiply Bonded Anisotropic Composites with Thin Adhesives

In engineering practice, analysis of interfacial thermal stresses in composites is a crucial task for assuring structural integrity when sever environmental temperature changes under operations. In this article, the directly transformed boundary integrals presented previously for treating generally anisotropic thermoelasticity in two-dimension are fully regularized by a semi-analytical approach for modeling thin multi-layers of anisotropic/isotropic composites, subjected to general thermal loads with boundary conditions prescribed. In this process, an additional difficulty, not reported in the literature, arises due to rapid fluctuation of an integrand in the directly transformed boundary integral equation. In conventional analysis, thin adhesives are usually neglecteddue to modeling difficulties. A major concern arises regarding the modeling error caused by such negligence of the thin adhesives. For investigating the effect of the thin adhesives considered, the regularized integral equation is applied for analyzing interfacial stresses in multiply bonded composites when thin adhesives are considered. Since all integrals are completely regularized, very accurate integration values can be still obtained no matter how the source point is close to the integration element. Comparisons are made for some examples when the thin adhesives are considered or neglected. Truly, this regularization task has laid sound fundamentals for the boundary element method to efficiently analyze the interfacial thermal stresses in 2D thin multiply bonded anisotropic composites.     

Nondestructive Evaluation of Welding Residual Stresses in Dissimilar Welded Pipes

This paper investigates the nondestructive capability of ultrasonic waves in residual stress evaluation of dissimilar welded pipes. Longitudinal critically refracted (L _CR ) waves are employed to measure the residual stresses in a pipe-pipe joint of stainless steel 304 and carbon steel A106. Measuring the acoustoelastic constant is usually accomplished through the tensile test which needs cutting the tested material to extract tensile test specimens. However, cutting the tested pipe to complement the nondestructive ultrasonic measurement was not considered here. Instead, a dissimilar welded plate with the same welding specification, joint geometry, thickness and the same dissimilar materials is used to extract tensile test samples. The measured acoustoelastic constant of the plate along with the measured time of flight of the L _CR wave on the pipe, are utilized for ultrasonic stress measurement. A finite element model of welding process validated by hole-drilling method is used to verify the ultrasonic results. The results show good agreement between finite element and ultrasonic measurements in the pipe measured without any destructive process.     

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.     

Progress in Thermoelastic Residual Stress Measurement

Abstract:  The possibilities of using thermoelastic stress analysis to measure residual stresses are assessed, particularly in the context of the effect of plastic strain on the thermoelastic output. Components manufactured from aluminium and steel were deformed so that they experienced a plastic deformation and in some cases, a residual stress. Thermoelastic data from the components were compared with data from geometrically similar undeformed components. According to well-accepted theory, the thermoelastic data from both components should be practically identical. The results from the deformed components show departures from those of the undeformed components; the possible reasons for this are discussed in detail. A practical application of cold-expanded holes used in aircraft structures is described and recommendations are made for possible future work.     

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.     

Nondestructive Evaluation of Welding Residual Stresses in Austenitic Stainless Steel Plates

This article investigates the nondestructive capability of ultrasonic waves in residual stress evaluation of austenitic stainless steel plates (AISI 304L). Longitudinal critically refracted (L _CR ) waves are employed to measure the residual stresses. Measuring the acoustoelastic constant through the tensile test is eliminated on the main investigated sample to keep it intact. Another welded plate with the same welding specification, geometry, thickness, and the same material is used to extract tensile test samples. To find the acoustoelastic constant of the heat affected zone (HAZ), a metallographic investigation is done to produce microstructure similar to that of the HAZ in a tensile test sample. A finite element model of welding process, which is validated by hole-drilling method, is used to verify the ultrasonic results. The results show good agreement between finite element and ultrasonic stress measurements which is accomplished nondestructively.     

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.     

Effects of Interphase Damage and Residual Stresses on Mechanical Behavior of Particle Reinforced Metal-Matrix Composites

Mechanical behavior of aluminum matrix composites reinforced with SiC particles are predicted using an axisymmetric micromechanical finite element model. The model aims to study initiation and propagation of interphase damage subjected to combination of thermal and uniaxial loading. Effects of manufacturing process thermal residual stresses and interphase de-bonding are considered. The model includes a square Representative Volume Element (RVE) from a cylindrical unit cell representing a quarter of SiC particle surrounded by Al-3.5wt.%Cu matrix. Suitable boundary conditions are defined to include effects of combined thermal and uniaxial tension loading on the RVE. An appropriate damage criterion with a linear relationship between radial and shear stresses for interphase damage is introduced to predict initiation and propagation of interphase de-bonding during loading. A damage user subroutine is developed and coupled to the finite element software to model interphase damage. Overall Stress-strain behavior of particulate metal-matrix composite by considering residual stresses is compared with experimental data to estimate interphase strength. Effects of thermal residual stresses in elastic, de-bonding and plastic zones of composite system are discussed in details. Furthermore, parametric study results show high influence of interphase strength on the overall mechanical behavior of composite material.     

Thermoelastic Determination of Individual Stresses in a Diametrally Loaded Disk

Abstract: In a cyclically loaded structure which experiences adiabatic and reversible conditions, the measured change in temperature is associated with the change in the stresses. For proportional loading and isotropy, the technique measures information on the sum of the principal stresses. As engineering analyses frequently necessitate knowing the individual components of stress, supplementary experimental methods or information is sometimes required to ‘separate the stresses’. This need is circumvented here in that individual stresses are evaluated throughout a loaded disk without additional measured data by hybridising the TSA information with an Airy stress function and some known boundary conditions. Although demonstrated here to a circular aluminium disk under diametral compression, the approach is applicable to more complicated shapes, under more complex loadings and inverse problems. The technique does not pre‐suppose knowing the details. While TSA information has been displayed previously for a loaded disk, the authors are unaware of the stresses being thermoelastically separated for this case.     

Visualizing Residual Stresses in Plastic and Glass

Polariscopes can be used to visualize the residual stress patterns in transparent or translucent materials. Residual stresses contribute to the fracture stress of failed components. This article describes the construction and usage of a lab polariscope made for less than US$150.     

Thermal Residual Stresses in Multilayered Coatings

The mechanical integrity and reliability of coated devices are strongly affected by the residual stresses in thin films and coatings. However, due to the metallurgical complexity of materials, it is rather difficult to obtain a closed-form solution of residual stresses within multilayered coatings (e.g. functionally graded coatings, FGCs). In this paper, an analytical model is developed to predict the distribution of residual stresses within multilayered coatings. The advantage of this model is that the solution of residual stresses is independent of the number of layers. Specific results are obtained by calculating elastic thermal stresses in ZrO2/NiCoCrAIY FGCs, which consist of different material layers. Furthermore, the residual stress distribution near the edges and the stress-induced failure modes of coating are also analyzed. The topics discussed provide some insights into the development of a methodology for designing fail-safe coating systems.     

Thermal Residual Stresses in W Fibers/Zr-based Metallic Glass Composites by High-energy Synchrotron X-ray Diffraction

Thermal residual stresses in W fibers/Zr-based metallic glass composites were measured by in situ high energy synchrotron X-ray diffraction(HEXRD). The W fibers for the composites were 300,500,and 700 m m in diameter,respectively. Coaxial cylinder model(CCM) and finite element model(FEM) were employed to simulate the distribution of thermal residual stress,respectively. HEXRD results showed that the selected diameters of W fiber had little influence on the value of thermal residual stresses in the present composites. Thermal residual stresses simulated by CCM and FEM were in good agreement with HEXRD measured results. In addition,FEM results exhibited that thermal residual stress concentrated on interface between the two phases and area where the two W fibers were the closest ones to each other.