Stress analysis of the double cantilever beam specimen

A higher-order plate theory which includes transverse shear deformation and a thickness-stretch mode is utilized to analyze a complete double cantilever beam specimen. Homogeneous, orthotropic materials are considered. The beam is divided into a section along the crack and a second section along the uncracked region. Complete continuity of inplane force resultant, transverse shear force resultant, bending moment, and displacements are satisfied across the boundary between the two sections. This analysis allows one to obtain an approximate distribution of the interlaminar normal stress ahead of the crack. The effect of specimen geometry on energy release rate is investigated numerically. Consideration is also given to the average stress criterion as an alternative to a fracture mechanics approach for characterizing interlaminar peel strength.     

Finite element stress analysis of a notched coupon specimen for in-plane shear behaviour of composites

The results of a linear elastic, plane stress finite element investigation of the stress distribution in a double V-notched coupon specimen are presented for an isotropic material (steel) and five graphite/polyimide laminates ([0], [90], [0/90]_x, [±45]₃ and [0/90/±45]₅). Stress contours, stress profiles, and stress concentration factors are presented for specimens loaded through rigid fixtures. It is shown that the finite element analysis predicts a region of essentially uniform pure shear in the central portion of the specimen for all laminates considered. Stress concentrations vary considerably with laminate configuration. The influences of elastic fixtures and thermal stresses on the stress distribution in [0] laminates are also investigated. The [0] laminate is predicted to exhibit maximum pure shear in the centre of the test section for both rigid and elastic fixtures. It is concluded that the specimen is a practicable candidate for use as a composite shear specimen and should be investigated further, both numerically and experimentally.     

Finite element analysis of a laser-processed fracture specimen

Finite element analysis was used to simulate the static failure of a AISI 4140, three-point bend, Charpy specimen. Non-linear finite element models (FEM) were constructed to represent standard Charpy, fatigue-precracked Charpy, and laser-processed Charpy specimens. For the laser-processed Charpy FEM, a strain-based failure criterion was used to simulate crack propagation through the 0.5 mm thick laser-processed zone. For comparison, a 0.5 mm long crack was used in the fatigue-precracked FEM and similarly loaded. Results showed that the numerically calculated load for crack initation through this zone compared favorably to that reported in earlier experiments. Furthermore, after the crack had propagated through the laser-processed zone within the FEM-comparison of plastic strain contours for this model and that for a fatigue-precracked model showed that similar patterns exist around the crack tip. These results indicate that laser-processing and fatigue-precracking should provide a similar basis for fracture toughness measurements.     

An analysis of a fracture specimen for rough crack in shear

In this paper, a BEM formulation predicting the reduced mode II and the enhanced mode I stress intensity factors of the mode II test specimen caused by fracture surface roughness is presented. The dilatant boundary conditions (DBC) are based on the assumptions of idealized uniform sawtooth crack surfaces and an effective Coulomb sliding law. They are obtained by relating the crack opening displacement and crack sliding displacement through the assumption of rigid body asperity sliding as in Young (1999). Three different types of crack, i.e. (1) non-interfering flat closed crack; (2) DBC with elastic crack tip; and (3) DBC with plastic crack tip are discussed. The results show a good approximation of the present BEM model. This study also shows the potential application of the present method determining the effect of crack face roughness in a realistic experimental specimen.     

An orthotropic shear specimen in computerised stress analysis

The Iosipescu specimen, invented for investigation of shear strength of orthotropic materials, in its original shape did not meet expectations, producing a complex stress pattern. In the present investigation a improved shape of the specimen is presented, which depends sharply on tested material properties. Resulting relations both for the shape of the specimen (1) and calculation of shear strength (2) are given. The research has shown a strong dependence of the shape of the specimen on elastic properties of the tested material.     

Finite strain analysis by a stress-function method

A finite element method for finite inelastic strain analysis of solids and structures is described. The method, which is based on a direct discretization of the equations of compatibility and angular momentum balance, represents a generalization of the mixed stress function approach proposed for linear elasticity by de Veubeke (1975). It captures the main advantages of hybrid-stress, direct stiffness, and reduced integration finite element methods while avoiding their principal drawbacks. Examples are included which demonstrate important features of the method.     

Effect of stress regime‐dependent creep behaviour on measurement of creep strain rate based on small specimen techniques

Small specimen creep testing technique has become a hot topic of research as bulk materials are not available in many occasions. The stress distributions in the small specimens such as small punch and 3‐point bending specimens are essentially nonuniform. As it is known, the creep deformation/damage accumulation mechanisms exhibited at a high stress regime are not the same as the ones at a lower stress regime for many engineering alloys. The potential measurement errors because of stress regime‐dependent creep behaviour, however, has not been considered in the determination of the creep parameters based on small specimen testing in the previous studies. In this paper, 2 kinds of materials that show different Norton's parameters at the corresponding stress regimes are examined. A simple case of 2‐bar structure is firstly adopted to illustrate the measurement error of creep strain rate because of stress regime‐dependent creep behaviour. Furthermore, clamped beam bending testing and small punch testing are investigated to demonstrate the significance of measurement error using the same materials. It is shown that an error of more than 8 times may occur near the transition point of creep deformation mechanism depending on specimen types and materials. Attention should thus be paid to the selection of stress level in the small specimen testing to avoid significant measurement errors.     

Theoretical analysis of the double cleavage drilled compression specimen

A theoretical analysis of stress intensity factors and crack opening displacements for the double cleavage drilled compression specimen (DCDC) is presented. This specimen exploits a well known fact that the stress field around a circular hole in a plate subjected to uniaxial stress reverses sign at points on the hole which are parallel to the applied stress. Under uniaxial compression, tensile stresses exist at the edge of the hole and this tensile stress propagates a crack in the DCDC specimen. Because this tensile region is very localized, catastrophic crack growth cannot occur and it is not necessary to groove the specimen to promote straight crack growth. The controlled crack growth possible with this specimen should make it possible to examine fracture mechanisms in detail. The simplicity of this test specimen also makes it an ideal candidate for studying environmental effects on fracture.

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Résumé On présente une analyse théorique des facteurs d'intensité de contraintes et des déplacements d'ouverture de fissure pour une éprouvette donnée de compression à double clivage (DCDC). Ce type d'éprouvette exploite le fait bien connu que le champ de contraintes autour d'un trou circulaire dans une plaque soumise à contraintes uniaxiale change de signe dans les zones du trou parallèle à la tension appliquée. Sous compression uniaxiale, des tensions existent au bord du trou et ces tensions induisent la propagation d'une fissure dans l'éprouvette DCDC. Comme la zone concernée est trés localisée, il ne peut survenir de croissance catastrophique de la fissure, et il n'est pas nécessaire d'entailler l'éprouvette en vue de provoquer une propagation droite de la fissure. Le fait de pouvoir contrôler la croissance de la fissure dans ce type d'éprouvette devrait rendre possible l'examen en détail des mécanismes de rupture. La simplicité de cette éprouvette d'essai en fait également une candidate idéale pour l'étude de effets de l'environnement sur la rupture.

     

Two- and three-dimensional elastic-plastic stress analysis for a double edge notched tension specimen

This paper describes an elastic-plastic stress analysis for a double edge notched tension specimen, a specimen used for the determination of the microscopic cleavage fracture stress. The analysis was performed numerically using the finite element method. First, a study of the finite element modelling is presented in order to demonstrate the requirements on a three-dimensional finite element structure leading to accurate stress distributions in the whole specimen. On the other hand possible restrictions are shown, if only a certain parameter, e.g. the maximum tensile stress has to be evaluated. Then the global response of the three-dimensional structure is compared with results of two-dimensional calculations assuming plane stress and plane strain, respectively. Subsequently the most interesting stress and strain distributions are discussed. The maximum value of stress concentration in front of the notch is given as a function of the applied stress. Additionally the state of deformation at fracture load is characterized by the plastic zone size, too. All three-dimensional results are compared with results of a plane strain model.     

框架木箱有限元受力分析

介绍了木包装的基本情况,对木包装中使用广泛的框架木箱的结构设计过程进行分析,并设计制做出了一个框架木箱,对其进行了有限元分析。采用大型有限元软件ANSYS和ANSYS-LSDYNA具体分析其在静载、堆码、叉取、跌落等各种情况下的力学性能,为框架木箱的设计做出有益的探索。     

Finite element analysis of creep fracture initiation in a model superalloy material

Detailed finite element analyses were performed for a single edge-cracked specimen geometry under both plane stress and plane strain constraint for a superalloy material that obeys a power-law creep relationship. The objectives of these analyses were to elucidate the stationary creep crack-tip fields and to provide guidance for the experimental measurement of crack-tip deformations. New results demonstrate that, for both plane stress and plane strain, the angular variations in the creep strain fields do not agree with HRR-type predictions, although the radial variations are in agreement with HRR-type creep strain field predictions in a zone very near the crack tip. Thus, the use of experimental measurement of surface displacement and/or strain data for the location of HRR-type fields may not be possible, unless modifications to the existing HRR-type theory are made. It is also noted that the size of the stress-based HRR-dominance zone is only a fraction of the creep zone size in plane stress, and is very small (especially along =0°) compared to the creep zone size in plane strain. Furthermore, the dominance of the singular strain fields are at least two orders of magnitude smaller than the corresponding stress dominance zones. As such, unless the microstructural features of the material are smaller than the dimensions of the dominance zones, the basis for using stress or strain-based fracture parameters derived from the HRR-type fields for prediction of creep fracture initiation is unclear.     

板式剪切型铅阻尼器的试验研究及有限元分析

提出一种新型的剪切型铅阻尼器,该装置中铅块直接嵌于滑动钢板与固定钢板的凹槽之间,构造简单。基于性能试验和有限元分析对该装置的滞回性能及关键参数进行了研究,研究结果表明:该阻尼器的滞回性能可以采用双线性模型加以模拟;阻尼器屈服阻尼力由铅块的剪切面积决定;加载曲线中弹性阶段与完全塑性阶段之间的过渡弧段的曲率半径与剪切铅块的长厚比成反比。     

联合载荷下无裂纹DLC薄膜的内应力有限元分析

本文用有限元分析的方法,对受法向和切向联合载荷作用下的无裂纹类金刚石(DLC)薄膜系统内部应力进行了模拟计算,分析了不同摩擦系数和膜厚比对于内部应力的影响,数值模拟结果表明:较大的摩擦系数可以使得界面处剪切应力和Mises等效应力以及y轴Mises等效应力显著增大,而对于界面处的y向压应力影响不是很大。在一定的范围内(0相似文献