Effects of voids on postbuckling delamination growth in unidirectional composites

This work examines the effects of manufacturing induced voids on the postbuckling behavior of delaminated unidirectional composites. In the finite element model developed, a through-width delamination is introduced close to one surface of a flat panel, and a void is placed in the delamination plane ahead of each delamination front. The panel is subjected to compression in the fiber direction. The postbuckling delamination growth is studied by calculating the strain energy release rate (SERR) using the virtual crack closure technique. Local stress analyses of the region near the delamination front are also performed to further investigate the void effects. It is found that although the presence of void does not significantly alter the postbuckling transverse displacement of the delaminated panel, the induced stress perturbation by the void affects the SERR. The Mode II SERR as well as the total SERR increase depending on the size of the void and its distance from the delamination front. Since the Mode I SERR shows non-monotonic behavior with the applied load, the effects of voids are studied on its maximum value.     

Buckling and postbuckling behavior of antisymmetrically angle-ply laminated composite plates

The buckling and postbuckling behaviors of perfect and imperfect antisymmetricallyangle-ply laminated composite plates under uniaxial compression have been studied byperturbation technique which takes deflection as its perturbation parameter.In this paper,the effects of in-plane boundary conditions,angles,total number oflayers and initial geometric imperfection on the postbuckling behavior of laminated plateshave been discussed.     

Elasto-plastic analysis for the buckling and postbuckling of rectangular plates under uniaxial compression

Full-range analysis for the buckling and postbuckling of rectangular plates under in-plane compression has been made by perturbation technique which takes deflection as itsperturbation parameter.In this paper the effects of initial geometric imperfection on the postbuckling behaviorof plates have been discussed.It is seen that the effect of initial imperfection on the inelasticpostbuckling of plates is sensitive.By comparison,it is found that the theoretical results ofthis paper are in good agreement with experiments.     

具有分层损伤的不同加筋形式复合材料层合板的后屈曲性态研究

基于板的一阶剪切理论和V on-K arm an大挠度理论,分别推导了复合材料层合板和层合梁的几何非线性有限元列式,提出了含嵌入分层的复合材料加筋层合板在受压缩载荷作用下的后屈曲有限元分析方法,对在板厚方向具有不同分层位置的加筋板结构进行了有限元数值分析,研究了不同的加筋方式及筋的分布对具有分层损伤的复合材料加筋层合板的后屈曲性态的影响,所得结果对确定在压缩载荷作用下含损伤复合材料加筋层合板的剩余承载能力具有参考价值。     

Nonlocal thermal buckling and postbuckling of functionally graded graphene nanoplatelet reinforced piezoelectric micro-plate

This paper analyzes the nonlocal thermal buckling and postbuckling behaviors of a multi-layered graphene nanoplatelet(GPL) reinforced piezoelectric micro-plate. The GPLs are supposed to disperse as a gradient pattern in the composite micro-plate along its thickness. The effective material properties are calculated by the Halpin-Tsai parallel model and mixture rule for the functionally graded GPL reinforced piezoelectric(FG-GRP) micro-plate. Governing equations for the nonlocal thermal buckling a...     

A novel model of delamination bridging via Z-pins in composite laminates

A new micro-mechanical model is proposed for describing the bridging actions exerted by through-thickness reinforcement on delaminations in prepreg based composite materials, subjected to a mixed-mode (I–II) loading regime. The model applies to micro-fasteners in the form of brittle fibrous rods (Z-pins) inserted in the through-thickness direction of composite laminates. These are described as Euler–Bernoulli beams inserted in an elastic foundation that represents the embedding composite laminate. Equilibrium equations that relate the delamination opening/sliding displacements to the bridging forces exerted by the Z-pins on the interlaminar crack edges are derived. The Z-pin failure meso-mechanics is explained in terms of the laminate architecture and the delamination mode. The apparent fracture toughness of Z-pinned laminates is obtained from as energy dissipated by the pull out of the through-thickness reinforcement, normalised with respect to a reference area. The model is validated by means of experimental data obtained for single carbon/BMI Z-pins inserted in a quasi-isotropic laminate.     

含脱层损伤复合材料层合梁的冲击动力屈曲

针对含初始缺陷和脱层损伤的复合材料层合梁的轴向冲击动力屈曲问题进行了分析。基于Hamilton原理导出了考虑初始缺陷、轴向和横向惯性、横向剪切变形以及转动惯性影响时含脱层损伤复合材料梁的非线性动力屈曲控制方程;基于B-R准则,采用有限差分方法求解了受轴向冲击载荷作用下含脱层损伤复合材料梁的动力屈曲问题;讨论了冲击速度、初始几何缺陷、铺层角度以及脱层长度等因素对复合材料层合梁动力屈曲的影响。     

Nonlinear delamination buckling and expansion of functionally graded laminated piezoelectric composite shells

In this paper, an analytical method is presented to investigate the nonlinear buckling and expansion behaviors of local delaminations near the surface of functionally graded laminated piezoelectric composite shells subjected to the thermal, electrical and mechanical loads, where the mid-plane nonlinear geometrical relation of delaminations is considered. In examples, the effects of thermal loading, electric field strength, the stacking patterns of functionally graded laminated piezoelectric composite shells and the patterns of delaminations on the critical axial loading of locally delaminated buckling are described and discussed. Finally, the possible growth directions of local buckling for delaminated sub-shells are described by calculating the expanding forces along the length and short axis of the delaminated sub-shells.     

Analytical solution approach for nonlinear buckling and postbuckling analysis of cylindrical nanoshells based on surface elasticity theory

The size-dependent nonlinear buckling and postbuckling characteristics of circular cylindrical nanoshells subjected to the axial compressive load are investigated with an analytical approach. The surface energy effects are taken into account according to the surface elasticity theory of Gurtin and Murdoch. The developed geometrically nonlinear shell model is based on the classical Donnell shell theory and the von K′arm′an's hypothesis. With the numerical results, the effect of the surface stress on the nonlinear buckling and postbuckling behaviors of nanoshells made of Si and Al is studied. Moreover, the influence of the surface residual tension and the radius-to-thickness ratio is illustrated.The results indicate that the surface stress has an important effect on prebuckling and postbuckling characteristics of nanoshells with small sizes.     

Numerical analysis of delamination growth for stiffened composite laminated plates

A study of postbuckling and delamination propagation behavior in delaminated stiffened composite plates was presented. A methodology was proposed for simulating the multi-failure responses, such as initial and postbuckling, delamination onset and propagation, etc. A finite element analysis was conducted on the basis of the Mindlin first order shear effect theory and the von-K6rm~n nonlinear deformation assumption. The total energy release rate used as the criteria of delamination growth was estimated with virtual crack closure technique (VCCT). A self-adaptive grid moving technology was adopted to model the delamination growth process. Moreover, the contact effect along delamination front was also considered during the numerical simulation process. By some numerical examples, the influence of distribution and location of stiffener, configuration and size of the delamination, boundary condition and contact effect upon the delamination growth behavior of the stiffened composite plates were investigated. The method and numerical conclusion provided should be of great value to engineers dealing with composite structures.     

Ultimate strength of postbuckling for simply supported rectangular composite thin plates under compression

1.IntroductionAsiswellthnown,thepostbucklingmetalplatescanbesuccessivelysubjectedtotheload.Forsomemetalplates,theultimatestrengthcanreachthirtytimesofthebucklingstressll].Inordertostudythebearingcapacityofthecompositeplatesthroughtestsandtheoreticalanalysis,f'ttiluretestsofthe283specimensofGFRPthinrectangularplatesundercompres.sionarecarriedout.ItisprovedthattheGFRPplatesinpostbucklingstillhavehigherbearingcapacity,forthetestedspecimensshowedultimatestrengthwhichisfourtotwenty-livetiniesth…     

An analysis of axisymmetric buckling and growth of circular-shaped delamination

The buckling and post-buckling of clamped circular plate subjected to distributed radial compressed load is presented by using the high-order perturbation analysis and shooting method. The sixth-order solution shows good agreement with the FEM results in [11]. The results in this paper are applied to investigate the buckling and growth of pressed thin film delamination in the film/substrate system. Under a certain residual pressure in the thin film, two characteristic blister radiiR _c andR _g, the critical radius and growing radius respectively, are obtained. The numerical result shows that the growth criterion of delamination in [9,10] is not perfect. In variant residual stress or interface toughness, the conditions of no growth, stable growth and unstable growth of the delamination are obtained by comparing the driving force at the interface crack tip with the interface toughness.This project is supported by National Natural Science Foundation of China.     

复合材料加筋板壳结构的后屈曲强度及破坏分析程序系统

本文介绍适用于复合材料（含各向同性材料）层合加筋板壳结构的后屈曲强度及破坏分析的程序系统（ＣＯＭＰＯＳＳ程序系统）的功能特点、原理和结构，通过一个受压剪载荷作用的加筋层合矩形板的破坏分析，并与试验结果作了比较，说明该程序系统的正确、可靠性     

F E M analysis of delamination buckling in composite plates and shells

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The Mexican hat effect on the delamination buckling of a compressed thin film

Because of the interaction between film and substrate,the film buckling stress can vary significantly,depending on the delamination geometry,the film and substrate mechanical properties.The Mexican hat effect indicates such interaction.An analytical method is presented,and related dimensional analysis shows that a single dimensionless parameter can effectively evaluate the effect.     

Buckling and postbuckling of stiffened cylindrical shells under axial compression

Buckling and postbuckling behaviors of perfect and imperfect,stringer andorthotropically stiffened cylindrical shells have been studied under axial compression.Based on the boundary layer theory for the buckling of thin elastic shells suggested in ref.[1],a theoretical analysis is presented.The effects of material properties of stiffeners andskin,which are made of different materials,on the buckling load and postbuckling behaviorof stiffened cylindrical shells have also been discussed.     

爆炸冲击下复合材料层合扁球壳的动力屈曲

研究计及横向剪切的复合材料层合扁球壳在爆炸冲击载荷作用下的非线性轴对称动力屈曲问题。通过在复合材料层合扁球壳非线性稳定性的基本方程中增加横向转动惯量项并引入R.H.Cole理论的爆炸冲击力,得到爆炸冲击下复合材料层合扁球壳的动力控制方程,应用Galerkin方法得到用顶点挠度表达的爆炸冲击动力响应方程,并采用Runge-Kutta方法进行数值求解,采用Budiansky-Roth准则确定冲击屈曲的临界载荷,讨论了壳体几何尺寸对复合材料层合扁球壳冲击屈曲的影响;数值算例表明,此方法是可行的。     

Postbuckling growth of a concentric delamination in a circulal plate under axisymmetric compression and bending

Postbuckling growth of a thin circular delamination at the center of a circular plate subjected to axisymmetric edge compression and bending is analyzed. A one-parameter family of solutions of the non-dimensionalized Von Karman's nonlinear equations is obtained by using the shooting method based on the fourth-order Runge-Kutta integration formula. The expression of energy release rate is deduced by means of the path-independent M-integral, and corresponding numerical results are given. The present analysis investigates the various possibilities of bifurcation, snap-through and crack growth.     

Thermo-piezoelectric effects on the postbuckling of axially-loaded hybrid laminated cylindrical panels

IntroductionCompositelaminatedcylindricalpanelhasbeenusedextensivelyasastructuralconfiguration,mainlyintheaerospaceindustry .Oneoftherecentadvancesinmaterialandstructuralengineeringisinthefieldofsmartstructureswhichincorporatesadaptivematerials.Bytakingadvantageofthedirectandconversepiezoelectriceffects,piezoelectriccompositestructurescancombinethetraditionalperformanceadvantagesofcompositelaminatesalongwiththeinherentcapabilityofpiezoelectricmaterialstoadapttotheircurrentenvironment.Therefore…     

Compression-induced stiffness in the buckling of a one fiber composite

We study the buckling of a one fiber composite whose matrix stiffness is slightly dependent on the compressive force. We show that the equilibrium curves of the system exhibit a limit load when the induced stiffness parameter gets bigger than a threshold. This limit load increases when the stiffness parameter is increasing and it is related to a possible localized path in the post-buckling domain. Such a change in the maximum load may be very desirable from a structural stand point.