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 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.     

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.

     

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.     

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   

Development of a new creep specimen for medium and high temperature tests

A new creep sample geometry is presented which has round heads instead of threads to connect to the grips. This reduces high temperature adhesion problems considerably. In addition, the production of samples from materials which are difficult to machine or which requires expensive machining techniques is made easier using this geometry. The successful use of the sample is demonstrated by means of two examples.     

An analysis of dynamic,ductile crack growth in a double edge cracked specimen

Dynamic crack growth is analysed numerically for a plane strain double edge cracked specimen subject to symmetric impulsive tensile loading at the two ends. The material behavior is described in terms of an elastic-viscoplastic constitutive model that accounts for ductile fracture by the nucleation and subsequent growth of voids to coalescence. Two populations of second phase particles are represented, including large inclusions or inclusion colonies with low strength, which result in large voids near the crack tip at an early stage, and small second phase particles, which require large strains before cavities nucleate. The crack growth velocities determined here are entirely based on the ductile failure predictions of the material model, and thus the present study is free from ad hoc assumptions regarding appropriate dynamic crack growth criteria. Adiabatic heating due to plastic dissipation and the resulting thermal softening are accounted for in the analyses. Different prescribed impact velocities, inclusion spacings and values of the inclusion nucleation stress are considered. Predictions for the dynamic crack growth behavior and for the time variation of crack tip characterizing parameters are obtained for each case analyzed.     

Finite element analysis of shear punch testing and experimental validation

In this work, finite element analysis (FEA) of the shear punch testing is carried out to study the specimen deformation up to yielding and the results are compared and validated with experimental data for four different materials. The elastic portion of the FEA generated load–displacement curve overlaps with the corresponding experimental curve only when the fixture compliances are eliminated in experiments. Based on through thickness plasticity in the FEA study, the shear yield stress estimated at an offset of 0.15% of normalized displacement compares well with the experimentally determined shear yield strength and satisfies the von Mises yield relation _σys=1.73_τys${\sigma }_{\mathit{ys}}=1.73{\tau }_{\mathit{ys}}$. The effects of die-punch clearance and specimen thickness on shear yield strength studied using FEA are also discussed.