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1.
The residual stress distribution in the thermally grown oxide (TGO) around holes in thermal barrier coatings has been measured using luminescence piezospectroscopy. Far removed from the holes the residual stress field in the oxide is equi-biaxial and independent of position but in the vicinity of the holes, the mean stress decreases monotonically towards the edge of the hole. The characteristic distance over which the stresses vary is of the order of the half the hole radius, typically 10–100 times the thickness of the TGO, consistent with a shear-lag model for stress redistribution. The measurements also indicate that the stress distribution in the TGO is unaffected by the presence of an as-deposited thermal barrier coating. 相似文献
2.
This paper deals with the study of stress distribution around holes in wedges. Ling and Hsu have reported a theoretical analysis for an infinite wedge of uniform thickness and variable depth (with a circular hole), using stress functions. In the present investigation, a large number of electrical resistance strain gauges of small gauge length (3 mm) were used for obtaining the distribution of stresses in a cantilevered wedge of uniform thickness and variable depth, with a circular hole subjected to end loading. The wedge was made of perspex. The results obtained indicate a maximum stress concentration factor of 1.7 using Timoshenko's method of calculating the nominal stress in the wedge at the hole boundary (using his theory of calculating stresses in a wedge without a hole). The experiments on the cantilevered wedge indicate a lower stress-concentration factor compared with the results obtained theoretically by Ling and Hsu for an infinite wedge. In addition to vertical loading, stress distribution with a load inclined to the vertical was also obtained. 相似文献
4.
Aluminium alloy 6082 (HE30) and aluminium-lithium alloys 8090 and 2091 were examined after holes were cut and cold-expanded by means of an oversized mandrel. The extent of cold working was analysed by two techniques, namely neutron diffraction (ND) and the Sachs cutting method (SM). While the former requires neutron diffraction facilities and is a non-destructive measurement technique, the latter is based on the removal of small layers of material from the inside of the expanded hole while recording the apparent change in strain by the removal of the layer. The stress distributions analysed by ND are compared with the method of Sachs and the results are discussed with respect to distances over which the state of stress changes from compression to tension. These changes are significant in explaining the improvement of service life in mechanical fastener holes from the process of cold expansion. In all alloys examined it was found that the improved fatigue performance was a function of the degree of expansion. All alloys exhibited a maximum in expansion beyond which fatigue life deteriorated. This was due to crack initiation during excessive hole enlargement exceeding the yield strength of the alloys. Crack initiation usually started from inside the hole of the fastener but always perpendicular to the applied load. The initial stages of growth occurred perpendicularly over a short distance but further growth occurred on a plane with normals inclined at about 55–60° to the tensile axis. This behaviour was due to the presence of texture development in the alloys which is beneficial to the resistance of both fatigue crack initiation and propagation. 相似文献
5.
After a change in temperature, high stresses leading to destruction may occur in bonded dissimilar materials near the point of the interface line intersection with the edge. In terms of linear elasticity, these high stresses are described by the singular terms of the stress field expansion at the corner point. In the present paper, the explicit representation of the singular terms and exact values of the stress intensity factors in the case of infinite wedge-shaped joint geometry are obtained by the Mellin transform technique. Systematic comparison with the FEM results for samples of finite size has shown that the values of stress intensity factors are in good agreement if the singularity is not too strong (the singularity orders k<0.2). With the stronger singularity, the analytical solution is in qualitative agreement with the FEM one, such that it can be used for fast parametrical study of finite samples as well. 相似文献
6.
An experimental method for the determination of stress-intensity factors (SIF) at a crack tip under thermal loading is presented. The experimental technique used is thermophotoelasticity. Data were collected from whole-field patterns by means of a digital image analysis system. SIF values were extracted using the stress field equations obtained from Williams' stress function. The photoelastic fringe field corresponding to predicted SIFs was regenerated and superimposed onto the actual fringe field to verify the results.
Résumé On présente une méthode expérimentale pour déterminer le facteur d'intensité de contrainte à l'extrémité d'une fissure sous une sollicitation thermique. La technique expérimentale utilisée est la thermophotoélasticité. A l'aide d'un système d'analyse digitale de l'image, on rassemble des données venant de configuration de l'ensemble du champ. Les valeurs du facteur d'intensité de contrainte en sont extraites au moyen d'équations du champs de contraintes obtenues à partir d'une fonction de contràintes de Williams. Le champs photoélastique marginal correspondant aux valeurs du facteur d'intensité de contraintes prédit est revu et superposé au champs marginal actuel en vue de vérifier les résultats. 相似文献
7.
An analytical thermoelasticity solution for a disc made of functionally graded materials (FGMs) is presented. Infinitesimal deformation theory of elasticity and power law distribution for functional gradation are used in the solution procedure. Some relative results for the stress and displacement components along the radius are presented due to internal pressure, external pressure, centrifugal force and steady state temperature. From the results, it is found that the grading indexes play an important role in determining the thermomechanical responses of FG disc and in optimal design of these structures. 相似文献
9.
We discuss computational aspects of the inverse and ill-posed problem of identifying residual stresses in steel structures under thermal loading. This corresponds to an inverse source problem in linear thermo-elasticity. The studies aim in investigating whether thermal loadings for the excitation of structures are sufficient in order to detect reliably inherent residual stresses. These stresses may result from the construction process or later thermal or mechanical treatment of the structure-like welding. By answering the raised question positively, our method provides an important basis for successful thermal straightenings. The quality of the solution of the inverse problem depends on a series of parameters, like material parameters, noise in the measurements, and the experimental setup. We numerically study the effects of these parameters and quantify the uncertainties in the results of the inverse problems by means of Sobol indices. 相似文献
10.
采用一种新的显微数字散斑相关方法,对微薄层梯度材料在恒温热载荷情况下的应变场进行了实验研究,并与双材料恒温下的应变场进行了比较与分析,从而为优化设计和制备梯度功能材料提供了一种可行的实验方法和有意义的结果。 相似文献
11.
Closed analytical solutions are obtained of steady-state problem of heat conduction and static thermoelasticity for a multilayer hollow spherical body heated by steady sources. 相似文献
12.
通过试验的方法研究制冷剂在系统中的分布规律,提出测试原理及方法。测试数据显示,热泵在稳态运行下,制冷剂主要分布在两器中,在制热工况下,气液分离器中贮存约13%的气态制冷剂。 相似文献
13.
A previous experimental study revealed fatigue life reduction in Al 7075-T6 cold expanded fastener holes exposed to 120 °C for 1 h. The obtained experimental evidence indicated a residual stress reduction associated with material softening at elevated temperatures, termed as thermo-mechanical stress relaxation. In order to identify and characterize the potential features of this phenomenon, FE analysis is carried out in this study and a detailed body of evidence is provided for occurrence of a time-independent thermo-mechanical residual stress relaxation around cold expanded fastener holes due to exposure to elevated temperature. The results of FE simulation demonstrate a good agreement with experimental results obtained earlier. 相似文献
14.
The article suggests a method of determining temperature and of calculating thermal stresses in the range of elastic deformations and of the boundaries of the plastic zones in elastoplastic deformation of the material of a permeable cylindrical wall with porous cooling in steady-state heating.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 49, No. 5, pp. 814–818, November, 1985. 相似文献
15.
Cold working is one method used to enhance the fatigue life of holes in aerospace structures. The method introduces a compressive stress field in the material around the hole and this reduces the tendency for fatigue cracks to initiate and grow under superimposed cyclic mechanical load. To include the benefit of cold working in design the stress intensity factors must be evaluated for cracks growing from the hole edge. Two-dimensional (2D) finite element analyses have been carried out to quantify the residual stresses surrounding the cold worked hole. These residual stresses have been used in a finite element calculation of the effective stress intensity factor for cracks emanating from the hole edge normal to the loading direction. The results of the 2D analysis have been compared with those derived using a weight function method. The weight function results have been shown always to underestimate the stress intensity factor. A three-dimensional (3D) FEA has been carried out using the same technique for stress intensity factor evaluation to investigate the effect of through thickness variation of residual stress. Stress intensity factors calculated with the 3D analysis are generally higher than those calculated using the 2D analysis. 相似文献
16.
In this paper, we use a local thermal non-equilibrium (LTNE) thermo-poroelasticity theory to investigate temperatures, pore pressure and thermal stresses around a spherical cavity in an infinite fluid saturated porous medium. In the LTNE theory, the solid and fluid phases undergo different temperature variations which induce additional pore pressure and thermal stresses. The asymptotic short time solutions of temperature, pore pressure and thermal stresses are obtained using the Laplace transform technique. Numerical results for two porous materials (clay and sandstone) are presented to examine the effects of LTNE on the temperature, pore pressure and thermal stresses around the spherical cavity. The results show that for the clay, the LTNE radial stress has a significantly larger peak value (magnitude) than that of the classical radial stress. The influence of LTNE on the pore pressure and tangential stress, however, are marginal. For the sandstone, both the radial stress (magnitude) and pore pressure are significantly increased by the LTNE effect. 相似文献
17.
Summary Based on Tresca's yield condition and its associated flow rule, a semianalytical method is presented for the calculation of thermal stresses due to steady-state thermal loading in an assembled shrink fit. The calculation is evaluated assuming plane stress conditions, linear elastic-perfectly plastic materials, and linearly temperature dependent yield stresses. Depending on the temperature gradient, different combinations of pure elastic and plastic zones arise in the shaft and in the hub. 相似文献
18.
An analytic solution is presented for stresses induced in an infinite plate with two unequal circular holes by remote uniform loadings and arbitrary internal pressures in the holes. The solution is obtained by using the general expression for a biharmonic function in bipolar coordinates. The Airy stress function is decomposed in the sum of a fundamental stress function for an infinite plate remotely loaded, which gives non vanishing tractions on the circular boundaries, and an auxiliary stress function required to satisfy the boundary conditions on the pressures at the edges of the holes, which produces vanishing stresses at infinity. Correspondingly, the variations of the stress concentration factor are determined in terms of the holes geometry and loading conditions. The path independent Jk- ( k = 1, 2), M- and L-integrals are analytically calculated on a closed contour encircling the two holes, under remote loading, in order to evaluate the energy release rates accompanying unit translation, self similar expansion and rotation of the holes, respectively. Results are then presented for varying loading orientation angle, biaxial loading ratio and holes geometry. 相似文献
19.
This paper presents analytical solutions for maximum temperature drops, and graphs and criterial relationships for the determination of maximum thermal stresses in heated cylinders with initial radial temperature variation.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 20, No. 2, pp. 329–337, February, 1971. 相似文献
20.
In this paper, a technique to study the 3-dimensional stress state around a circular hole in laminated plates is developed. First, the 3-dimensional elasticity problem for a thick plate with a circular hole is formulated in a systematic fashion by using the z-component of the Galerkin vector and that of Muki's harmonic vector function. This problem was originally solved by Alblas[1]. The reasons for reconsidering it are to introduce a technique which may be used in solving the elasticity problem for a multilayered plate and to verify and extend the results given by Alblas. Among the additional results of particular interest, one may mention the significant effect of the Poisson's ratio on the behavior and the magnitude of the stresses. Secondly, the elasticity problem for a laminated thick plate, which consists of two bonded dissimilar layers and which contains a circular hole, is considered. The problem is formulated for arbitrary axisymmetric tractions on the hole surface. Through the expansion of the boundary conditions into Fourier series, the problem is reduced to an infinite system of algebraic equations which is solved by the method of reduction. Of particular interest in the problem are the stresses along the interface as they relate to the question of delamination failure of the composite plate. These stresses are calculated and are observed to become unbounded at the hole boundary. An approximate treatment of the singular behavior of the stress state is presented, and the stress intensity factors are calculated. It is also observed that, the results compare rather well with those obtained from the finite element method. 相似文献
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