共查询到20条相似文献,搜索用时 31 毫秒
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The authors develop an eigth-order model for bending of transversally isotropic plates and use integral transforms and a collocation
method to form a line-spring model for a cracked plate. The eigth-order model allows satisfaction of the three standard plate
bending boundary conditions; the normal moment, twisting moment, and transverse shear force, and an additional shear stress
resultant that allows analysis of transverse normal stresses near the crack tip. The line-spring model is used to develop
geometry correction factors for bending of finite-thickness plates, accounting for transverse shear deformation and pressurization
of the plate near the crack tip. The line-spring model is then applied to the problem of a plate with a reinforced crack,
and the results are used to validate an interpolation solution based on an energy method. While not explicitly analysed, the
models are applicable to many problems, including bending of bonded repairs, fracture and fatigue of composite and layered
materials, surface cracks, crack tip plasticity and crack closure or crack face interaction. 相似文献
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This work extends the analytical solution of an interface crack in straight layered structures to circular layered structures. A small segment at the vicinity of an interface crack tip in a circular laminated beam is analyzed by a novel shear deformable bi-layered circular beam theory. Two concentrated forces are found existing at the crack tip due to the requirement of the equilibrium condition. Closed-form solution of the total energy release rate of the interface crack is obtained as the half of the product of the concentrated forces and the corresponding displacement gradient discontinuities at the crack tip. Closed-form expressions of the mode I and II components of the energy release rate are also obtained by global and local methods. Numerical verifications are conducted by analyzing the interlaminar delamination of a circular beam with an edged crack and comparing with the baseline results obtained through finite element analysis. Excellent agreements between the present method and finite element analysis on the predictions of total energy release rate and mode partition verify the accuracy and efficiency of the present solution. 相似文献
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《Composites Science and Technology》1986,25(1):49-67
Quasi-static fracture of laminated composite plates with circular or elliptic delaminations due to transverse shear stresses is considered. The system is modeled as two laminated plates bonded everywhere except over the area of the disbond. A laminated plate theory with the effects of surface tractions and shear deformations is used for each plate and the problem is reduced to a set of integral equations. Because of the nature of the model, stress singularities along the disbond periphery appear as concentrated line forces, which are different from those obtained from three-dimensional elasticity analysis. Physically meaningful quantities such as strain energy release rates for mode I, II and III types of deformation are evaluated. Failure loads for catastrophic fracture are computed based on firstly a point criterion and secondly a physically realistic growth pattern. Results are compared with test data for disbonds located in the midplane. For such disbonds the mode I component of energy release rate is absent and, therefore, fracture is due to mode II and III interactions. 相似文献
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A simplified method for determining the individual mode components of the strain energy release rate of free-edge delaminations in composite laminates is proposed. Interlaminar stresses are evaluated as an interface moment and interface shear forces obtained from equilibrium equations of stress resultants at the interface between the adjacent layers. The deformation of edge-delaminated laminate is calculated by using a generalized quasi-three dimensional classical laminated plate theory developed by the authors. The analysis provides closed-form expressions for the Mode-I, Mode-II and Mode-III component of the strain energy release rate by combining the deformation of the edge-delaminated laminate with the interface moment and the interface shear forces. The presented method is compared with existing method suggested by Li for the asymmetry laminate. Comparison of the results with a finite element analysis using the virtual crack closure technique shows good agreement. 相似文献
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Thermal buckling of cross-ply laminated composite and sandwich plates according to a global higher-order deformation theory 总被引:4,自引:0,他引:4
A two-dimensional global higher-order deformation theory is presented for thermal buckling of cross-ply laminated composite and sandwich plates. By using the method of power series expansion of continuous displacement components, a set of fundamental governing equations which can take into account the effects of both transverse shear and normal stresses is derived through the principle of virtual work. Several sets of truncated Mth-order approximate theories are applied to solve the eigenvalue problems of a simply supported multilayered plate. Modal transverse shear and normal stresses can be calculated by integrating the three-dimensional equations of equilibrium in the thickness direction, and satisfying the continuity conditions at the interface between layers and stress boundary conditions at the external surfaces. Numerical results are compared with those of the published three-dimensional layerwise theory in which both in-plane and normal displacements are assumed to be C0 continuous in the continuity conditions at the interface between layers. Effects of the difference of displacement continuity conditions between the three-dimensional layerwise theory and the global higher-order theory are clarified in thermal buckling problems of multilayered composite plates. 相似文献
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Mathematical models, for the stress analysis of unidirectional (0°) fiber-reinforced laminated composite double cantilever beam (DCB) specimen using classical beam theory, first and higher order shear deformation beam theories, have been developed to determine the mode I strain energy release rate (SERR) for unidirectional composites. In the present study, appropriate matching conditions at the crack tip of the DCB specimen have been derived by using variational principles. SERR has been calculated using compliance method. In general, the performance of shear deformation beam models of DCB specimen with variationally derived matching conditions at the crack tip is good in determining the SERR for medium to long crack lengths. Performance of higher order shear deformation beam model (having quadratically varying transverse displacement over the thickness) of DCB specimen, with non-variationally derived matching conditions at the crack tip, is good in determining the SERR for all the crack lengths in comparison with the available theoretical and finite element solutions in the literature. Higher order shear deformation beam theories having varying transverse displacement over the thickness are more appropriate to analyze DCB specimen as they predict the appropriate nature of the interlaminar normal stress at the crack tip and its distribution ahead of the crack tip. 相似文献
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《Composites Science and Technology》2003,63(3-4):517-529
This paper presents a novel approach of modeling the delamination phenomenon experienced by laminated composite plate and shell structures by using a previously developed layerwise shell finite element in conjunction with some transformations. This layerwise element is formulated by stacking some single-layered shell elements through a transformation of displacements of the mid-surface of a layer to those on the mid-surface of the laminated composite shell structure. It can accurately model the overall displacements and interlaminar stresses of a laminated composite shell structures whose layers are perfectly (rigidly) bonded. The novelty of the present approach, however, lies in the fact that two different transformations are used so that interlaminar displacements as well as interlaminar stresses can be represented in the finite element model. The transformations allow for displacement mismatches across the normal direction of the layer interfaces (the normal mode of delamination) and between layers (the shear mode). As a result, the proposed methodology can be used to model the open and shear modes of delamination. A two-layered simply supported composite beam and a two-layered simply supported cross-ply square plate are then chosen for numerical studies. These examples demonstrate how the present approach can be applied to accurately model delamination phenomena such as shear slip and normal separation. The paper concludes with suggestions for future work. 相似文献
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《Composites Science and Technology》2002,62(10-11):1407-1414
A new test method is presented for Mode I delamination fracture toughness testing of laminated composites containing a high density of stitches or translaminar reinforcements. The test set up, which is similar to the standard Double Cantilever Beam test, induces an axial tension in the specimen in addition to the transverse forces responsible for propagation of delamination. The tensile stresses reduce the compressive stresses in the vicinity of the crack tip caused by the large bending moments required for crack propagation. The nonlinear differential equations of equilibrium of the new specimen are solved using an iterative procedure to obtain the strain energy release rate as a function of load and crack length. Experiments were conducted using carbon/epoxy specimens containing 6.2 stitches per square centimeter (40 stitches per square inch). Results include Mode I fracture toughness, crack tip bending moment, transverse deflection and slope as a function of crack length. It is found that the apparent fracture toughness of the specimens tested remains constant as the stitches break and crack propagates, and is about sixty times that of unstitched specimens. 相似文献
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This paper deals with the 3D finite element analysis of superimposed thermo-elastic effect on embedded interfacial delamination crack growth characteristics in fiber-reinforced laminated composites. Interlaminar fracture at the delamination front is found to be a mixed-mode phenomenon due to the anisotropy and heterogeneity of thermo-physical properties of composite materials. This leads to the requirement of finite element evaluation of energy release rates, based on the principles of linear elastic fracture mechanics. The strain energy release rate components along the delamination front due to a uniform temperature drop, during the manufacturing stages of composite laminates, to room temperature and subsequent mechanical loading is obtained by superimposing their respective effects based on the assumptions of linear elasticity. Numerical calculations are carried out for multi-layered cross-ply and angle-ply composite laminates and energy release rate plots demonstrate large asymmetries along the delamination front due to the interaction of residual stresses and superimposed transverse loading. 相似文献
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层间弱粘贴复合材料层板的热弹性脱层 总被引:1,自引:1,他引:0
本文建立了一个层间弱粘贴复合材料层板热弹性脱层模型.该模型建立在两个描述层间弱粘贴的基本假设基础上.层间位移不连续由层间粘贴的物理关系来描述,表现为层间位移跳跃值与层间残余横向应力的关系;层间温度不连续由层间传热薄层来描述,并据此给出一个计算层间温度跳跃值的计算公式,表现为温度跳跃值与层间横向张开量之间的关系.在此假设基础上,根据平衡方程和静态传热方程导出了正交柱面弯曲层板热弹性脱层解.算例显示了层间弱粘贴对层板热弹性响应的影响. 相似文献
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The influence of specimen twisting during global anti-plane shear loading in composite split beam specimens is studied. Tests were conducted on specimens with different thicknesses and delamination lengths to produce different amounts of specimen twisting prior to fracture. It is shown that specimen twisting causes mode I stresses to develop, thereby producing mixed mode I–III conditions along the delamination front. This causes near-tip transverse cracks to initiate, prior to delamination advance, at an orientation related to the mode mix. Unlike in homogeneous materials, transverse crack extension is accompanied by planar delamination advance, and transverse crack rotation during extension is restricted by the laminate’s fibers. The overall fracture surface evolution is therefore strongly controlled by specimen geometry. The influence of these findings on the apparent delamination toughness as obtained from composite split beam and other types of mode III tests is discussed. 相似文献
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Prediction of initiation and growth of single level delaminations in a transversely loaded composite specimen using fracture mechanics 总被引:1,自引:1,他引:0
Zoltan Mikulik Donald W. Kelly B. Gangadhara Prusty Rodney S. Thomson 《International Journal of Fracture》2008,149(2):119-141
The behaviour of a composite test specimen with an embedded delamination subjected to transverse tension has been investigated
through experimental testing and finite element (FE) analyses. The testing program consisted of specimens in two geometrical
configurations; square and rectangular delamination. The initiation and growth of the delamination was numerically predicted
by fracture mechanics. FE models were analysed with both MSC.Nastran and Abaqus FE codes. The MSC.Nastran model was used to
calculate strain energy release rates employing a crack tip element methodology. The Abaqus model was evaluated using the
virtual crack closure technique. Both approaches accurately predicted failure initiation locations as observed in the test
specimens. Failure loads were also well predicted. The mode mix at the crack tip in the proposed specimen was found to be
similar to the mode mix expected in a conventional in-plane compression specimen. 相似文献
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SHAW MING LEE 《Journal of Materials Science》1997,32(5):1287-1295
The failure process of mode II delamination fracture is studied on the basis of the microscopic matrix failure modes (microcracks
and hackles) as well as fracture mechanics principles. The crack tip matrix stresses leading to delamination is analysed by
examining an adhesive bond with a crack analogous to a delamination crack in the resin layer of a composite. Such crack tip
stresses induce matrix microcracks involving two major events: (a) single microcrack initiation and (b) development of multiple
microcracks with regular spacing. The microcrack initiation shear stress τ* is found by the use of fracture mechanics to be
related to certain resin properties (shear modulus G and mode I fracture toughness GIC) and microcrack length of the order
of the resin layer thickness t (related to resin content).
The more or less regular microcrack spacing S deduced from shear lag considerations can be related to resin properties GIC,
G, τy (resin yield strength) and t. The multiple microcracks reduce the effective resin modulus and strongly affect the subsequent
microcrack coalescence process. As a result of the detailed analysis of the failure process, mode II laminate fracture toughness
GIIC can be quantitatively expressed as a function of resin GIC and (τ2y/G). The failure process modelled is used to interpret
the mode II delamination behaviour of several carbon/epoxy systems studied here and that reported in the literature. This
study reveals the critical importance of resin fracture (GIC related) and deformation (yielding) mechanisms in controlling
mode II delamination resistance of laminated composites.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
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One of the widely used geometrically complex parts in advanced commercial aircraft is the L-shaped composite. Due to the sharp curved geometry, interlaminar opening stresses are induced and delamination occurs under considerable mode-mixities in L-shaped beams. Dynamic phenomena during delamination initiation and propagation of L-shaped beams are investigated using dynamic (explicit) finite element analysis in conjunction with cohesive zone methods. The 2-D model consists of 24 plies of unidirectional CFRP laminate with an initial 1 mm crack at the center of the laminate at the bend. Loading is applied parallel to one of the arms quasi-statically. The loading type yields different traction fields and mode-mixities in the two sides of the crack in which delamination occurs under shear stress dominated loading on one crack tip and opening stress dominated loading on the other. The speed of the delamination under shear dominated loading at one side is 800 m/s and under normal stress dominated loading is 50 m/s. In addition radial compressive waves at the interface are observed. Finally, as the thickness is changed, a different failure mode is observed in which a secondary crack nucleates at the arm and propagates towards the center crack. 相似文献
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In interfacial fracture modeling of composite delamination, mode mix is typically specified in terms of energy release rates.
Other near-tip quantities can be used to designate mode mix, however. This paper considers the designation of mode mix in
terms of energy release rates, stress intensity factors, stresses ahead of the crack tip and crack face displacements and
the consequences of using different near-crack-tip quantities to designate mode mix in analyzing composite delamination. The
problem addressed is two-dimensional debonding between plies or ply groups modeled as in-plane orthotropic materials; however,
the conclusions discussed apply to general composite delamination problems. It is shown that use of different quantities to
designate mode mix can give significantly different results in matching composite applications to mixed-mode toughness tests.
For cases where measured interfacial toughness increases with increasing mode II deformation, it is demonstrated that use
of a mode mix designation based on energy release rates could be non-conservative. Based on these findings, it is suggested
that practitioners consider the differences in failure load predictions that would result if different near-tip quantities
were used to relate composite applications to measured toughnesses. To this end, methods for converting mode mix designations
in terms of energy release rates into designations in terms of other fracture quantities are outlined and applied.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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In this paper, a C0-type higher-order theory is developed for bending analysis of laminated composite and sandwich plates subjected to thermal/mechanical loads. The total number of unknowns in the present theory is independent of number of layers. The continuity conditions of transverse shear stresses at interfaces are a priori enforced. Moreover, the conditions of zero transverse shear stresses on the upper and lower surfaces are also considered. Based on the developed higher order theory, the typical solutions are presented for comparison. It is very important that the first derivatives of transverse displacement w have been taken out from the in-plane displacement fields of the proposed model, so that its finite element counterparts may avoid using the C1 interpolation functions. To assess the developed theory, the C1-type higher-order theory is chosen for comparison. Numerical results show that the present model can accurately predict the thermal/mechanical response of laminated composite and sandwich plates. Moreover, the present model is able to accurately calculated transverse shear stresses directly from constitutive equations without any postprocessing methods. 相似文献
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This work deals with an enhanced analytical model for the analysis of typical edge debonding problems in concrete or steel beams strengthened/repaired with externally bonded composite laminated plates induced by beam/adhesive interface fracture phenomena. The strengthened system is viewed as composed by three physical different layers: the strengthened beam, the adhesive layer and the bonded plate. On the other hand, the structural model consists of two shear deformable mathematical layers, the upper one representing the beam and the lower one incorporating the adhesive layer and the bonded plate. Bonding conditions between layers are simulated by using the Lagrangian multipliers method and governing equations are obtained by a variational approach. In the context of a fracture mechanics approach, analytical solutions for both total and mode components of energy release rate are obtained by using stress resultant and strain discontinuities across at the crack tip. Closed form solutions are obtained for specific loading conditions and geometric configurations. Comparisons with predictions from very careful FE investigations point out the effectiveness of the proposed results which may form the basis for a design process taking into account properly of debonding failure modes triggered by interface fracture at the edge of the repairing composite plate. Finally, the significance of the paper relies in the analytical approach to the problem, which avoids the complexities commonly shared by FE-based methodologies, related to stress singularities and differences in length scales and in mechanical properties of the single components of the system. 相似文献