共查询到13条相似文献,搜索用时 0 毫秒
1.
J.-H. Yan M. A. Sutton X. Deng Z. Wei Pablo Zavattieri 《International Journal of Fracture》2009,160(2):169-188
Ductile thin-sheet structures, such as fuselage skin or automobile panels, are widely used in engineering applications. These
structures often-times are subjected to mixed mode (I/II/III) loading, with stable crack growth observed prior to final fracture.
To characterize specific specimen deformations during stable tearing, a series of mixed-mode I/III stable tearing experiments
with highly ductile thin-sheet aluminum alloy and steel specimens have been measured by using three-dimensional digital image
correlation (3D-DIC). Measurements include (a) specimen’s deformed shape and 3D full-field surface displacement fields, (b)
load-crack extension response and (c) crack path during stable tearing, (d) angular and radial distributions of strains and
(e) the mixed mode crack-opening displacement (COD, measured at 1-mm from crack tip along crack surface) variation as a function
of crack extension. Results indicate that for both aluminum alloy and steel at all mixed-mode I/III loading conditions (Φ
= 30°, 60° and 90°), the crack tip fields have almost identical angular and radial polar strain distributions. The mixed mode
I/III fields were different from those observed for the nominal Mode I loading case (Φ = 0°). The effect of the Mode III loading
component is that it lowers the magnitude of the dominant strain component ε
θθ
ahead of the growing crack tip and increases the singularity of the strain as compared with that in the mode I case. In addition,
measurements indicate that the average mixed mode I/III stable COD for AL6061-T6 (GM6208 steel) is 4×(3×) greater than the
average Mode I stable COD. 相似文献
2.
This study describes a 3-D computational framework to model stable extension of a macroscopic crack under mode I conditions in ductile metals. The Gurson-Tvergaard dilatant plasticity model for voided materials describes the degradation of material stress capacity. Fixed-size, computational cell elements defined over a thin layer at the crack plane provide an explicit length scale for the continuum damage process. Outside this layer, the material remains undamaged by void growth, consistent with metallurgical observations. An element vanish procedure removes highly voided cells from further consideration in the analysis, thereby creating new tractionfree surfaces which extend the macroscopic crack. The key micro-mechanics parameters are D, the thickness of the computational cell layer, and f
0
, the initial cell porosity. Calibration of these parameters proceeds through analyses of ductile tearing to match R-curves obtained from testing of deep-notch, through-crack bend specimens. The resulting computational model, coupled with refined 3-D meshes, enables the detailed study of non-uniform growth along the crack front and predictions of specimen size, geometry and loading mode effects on tearing resistance, here described by J-a curves. Computational and experimental studies are described for shallow and deep-notch SE(B) specimens having side grooves and for a conventional C(T) specimen without side grooves. The computational models prove capable of predicting the measured R-curves, post-test measured crack profiles, and measured load-displacement records. 相似文献
3.
This paper discusses techniques for the automatic construction of numerical analysis models for multiple scale analyses which employ interacting models at two, or more, physical scales. Consideration is given to the methods to define the geometric representations and generate the discretizations needed by the numerical analysis procedures. The application of the techniques to multichip modules and composite structures, with interacting macromechanical and micromechanical level analyses, is demonstrated. In the multichip module analyses both heat conduction and thermomechanical analysis are performed using different numerical analysis techniques, and the two interaction of the analyses at the through levels is through a basic global/local methodology. The composite structure analysis considers crack propagation at the micromechanical level interacting with the macromechanical analysis through finite element based adaptive multiscale analysis. In both example applications the focus of the discussion is on the automatic construction of the required geometric models and their automatic discretization. 相似文献
4.
This work describes the formulation and application of a 3-D, interface-cohesive finite element model to predict quasi-static, ductile crack extension in thin aluminum panels for mode I loading and growth. The fracture model comprises an initially zero thickness, interface element with constitutive response described by a nonlinear traction-separation relationship. Conventional volumetric finite elements model the nonlinear (elastic-plastic) response of background (bulk) material. The interface-cohesive elements undergo gradual decohesion between faces of the volumetric elements to create new traction free crack faces. The paper describes applications of the computational model to simulate crack extension in C(T) and M(T) panels made of a 2.3 mm thick, Al 2024-T3 alloy tested as part of the NASA-Langley Aging Aircraft program. Parameters of the cohesive fracture model (peak opening traction and local work of separation) are calibrated using measured load vs. outside surface crack extensions of high constraint (T-stress > 0) C(T) specimens. Analyses of low constraint M(T) specimens, having widths of 300 and 600 mm and various a/W ratios, demonstrate the capabilities of the calibrated model to predict measured loads and outside surface crack extensions. The models capture accurately the strong 3-D effects leading to various degrees of crack front tunneling in the C(T) and M(T) specimens. The predicted crack growth response shows rapid convergence with through-thickness mesh refinement. Adaptive load increment procedures to control the rate of decohesion in the interface elements leads to stable, rapidly converging iterations in the globally implicit solution procedures. 相似文献
5.
In polycrystal materials the intergranular decohesion is one important damage phenomena that leads to microcrack initiation. The paper presents a mesoscale model, which is focused on the brittle intergranular damage process in metallic polycrystals. The model reproduces the crack initiation and propagation along cohesive grain boundaries between brittle grains. An advanced Voronoi algorithm is applied to generate polycrystal material structures based on arbitrary distribution functions of grain size. Therewith, the authors are more flexible to represent realistic grain size distributions. The polycrystal model is applied to analyze the crack initiation and propagation in statically loaded samples of aluminium on the mesoscale without the necessity of initial damage definition. 相似文献
6.
E. Smith 《International Journal of Fracture》1981,17(5):443-448
Wnuk's application of the Dugdale-Bilby-Cottrell-Swinden model to stable crack growth in ductile materials, is extended to incorporate a simplified idealization of the fracture process zone. The results, when considered with Rice and Sorensen's recent analytical and finite element results, provide further support for the use of crack tip opening angle as a viable characterising parameter for plane strain stable crack growth.
Résumé L'application faite par Wnuk du modèle de Dugdale-Bilby-Cottrell et Swinden relatif à la croissance stable d'une fissure dans un matériau ductile est étendue de manière à incorporer dans une idéalisation simplifiée la zône où se produit la rupture. Les résultats, lorsqu'ils sont examinés à la lueur des résultats analytiques récents ainsi que des résultats par éléments finis obtenus par Rice et Sorensen, fournissent un support complémentaire à l'utilisation de l'angle d'ouverture de l'extrémité d'une fissure en tant que paramètre caractéristique pour décrire la croissance stable d'une fissure en état plan de déformation.相似文献
7.
A tensile crack bridged by strong and tough fibers is modeled in such a manner that it can be analyzed based on concepts from the mechanics of inclusion. Analytical expressions for the energy release rate, stress intensity factor and crack opening are derived. It is shown that the presence of the supporting fibers reduces the values of those quantities which saturate at a certain level determined by the size and spacing of the fibers. 相似文献
8.
A criterion for crack initiation in unidirectional composite materials is presented. It includes two assumptions:
1. (1) crack initiation occurs in the direction of fibers;
2. (2) rapid crack growth occurs when the energy release rate reaches a critical value, the resistance to crack growth in the direction of fibers.
Then a model of energy release rate for crack growth in unidirectional composites is presented. The model is applied to characterize the fracture of off-axis, unidirectional glass-epoxy and graphite-epoxy composites. The results indicate that the loads corresponding to crack growth predicted by the present model agree well with the experimental results. 相似文献
9.
Summary An approximate analytical 2-D solution for the strain field components 11, 12 and 22 occurring in a cubic material due to a coherently bonded shear eigenstrained inclusion of cylindrical geometry was obtained by means of Continous Fourier Transforms (CFT). A Discrete Fourier Transform (DFT) based numerical model was used in order to test the validity of the results. For the case where the cylindrical inclusion and the surrounding media are elastically homogeneous and the orientation of their principal crystal axes are the same, a correlation between the analytical and numerical models is demonstrated, both for strongly and weakly anisotropic materials. Moreover, the strain fields within the inclusion are shown to be of homogeneous isotropic type. Finally, an expression for the closed-form strain energy of two cylindrical inclusions at arbitrary radius and angle was derived, and then used to determine the minimum energy configuration for the system.Dedicated to Professor Krzysztof Wilmanski on the occasion of his 60th birthday 相似文献
10.
In view of the fact that non-coplaner crack growth is a common characteristic of crack propagation in fiber reinforced composite materials, an attempt is made to derive the equation of the energy release rateG for non-coplaner crack extension in orthotropic linear elastic solids. Combining the idea developed in our previous paper and the analysis by Sihet al., the equation ofG is obtained for the cases of plane symmetric loading, plane skew-symmetric loading, antiplane shear loading, and a combination of these. The result will serve as a basic tool for developing a fracture mechanics approach to composites. 相似文献
11.
C. Y. Liao S. N. Atluri 《International journal for numerical methods in engineering》1991,32(6):1339-1361
An efficient method, based on the Schwarz–Neumann alternating technique, is presented for computing weight functions of a general solid (3-D as well as 2-D), with embedded or surface-flaw configurations. The total rate of change of the crack-opening displacements, due to simple perturbations of crack-dimension characteristics, is conveniently decomposed into the infinite-domain and boundary-correction parts. The former is determined from available analytical solutions of ideal-shaped cracks, whereas the latter is computed numerically by imposing nil boundary-traction requirements for the displacement field corresponding to the weight functions. Numerical examples, with solutions for 3-D weighted-average and local stress intensity factors, indicate that the proposed method is very accurate and efficient. 相似文献
12.
A mathematical model using an integral-equation/singularity-method approach is derived for determining the magnetic field and electromagnetic forces induced by current-carrying conductors in a region bounded by 3-D material-body surfaces which have complex configurations. Special analytical and numerical techniques that eliminate near-field computational difficulties and bypass the cumbersome matrix manipulations required by other integral-equation approaches are described. A comprehensive computer program package has been developed using this approach for obtaining the 3-D solutions in the end region of a turbine-generator due to armature end windings. Special computational techniques for handling the complex end-winding and surface geometry are described and detailed numerical results are presented for the 3-D field solution and the forces acting on the conductors. 相似文献