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This paper presents a close-form solution for the anti-penetrating postbuckling problem of fiber reinforced, rectangular laminates. The laminate has a through-width debonded region buried at the center position and is simply supported at its four edges subjected to the in-plane compressive load. Based on the previous analysis of the contact kinematics from micro mechanics of composite material, the nonlinear contact effects at the interfaces of the debonded region are considered and characterized by a contact factor. Governing equations are established and are solved using the perturbation approach. Asymptotic solutions from perturbation analysis are presented. It is found that for fiber reinforced, debonded laminates the postbuckling deformation involves global deflection and local buckling with amplitude of the global one 10⁴ times larger than the local one. The global deflection is induced by the postbuckling load and the local buckling is caused by the anti-penetrating contact effects. Due to the contact effects, the load carry capacity of the delaminated laminate is tremendously enhanced. Further examination indicates that both the buckling load and the contact performances are intrinsic properties of the laminates. Parametric analyses show that (i) the buckling load decreases with the increasing of the delamination length and the delamination depth and is very sensitive to the changing of the aspect ratio, (ii) the contact performances, including the location and size of the contact areas, rely only on the geometries of the debonded region and the material properties but are hardly affected by the aspect ratio. The analysis is in effect by comparing with the well established results.

The paper presents an analysis of the vibration behavior of glass fiber reinforced composites with two overlapping delaminations. The effect of delamination length on the vibration parameters is studied. Throughout a series of vibration tests, the change of natural frequencies and modal damping due to delaminations is evaluated. A numerical simulation considering finite element analysis allows to predict the change of natural frequencies for a known damage size. Modal damping was established which evaluates the different energies dissipated in the material layers direction of the fiber reinforced composites. A comparison of the different results was performed. Next, strain energy of layers directions were established by a numerical analysis and discussed.

Penetration of flat-ended cylindrical projectiles into thin laminated composite plates was investigated analytically and experimentally. An analytical modeling was carried out for thin laminated composite plates by developing a new function for deflection by computing Von Karman nonlinear strains and by using the principle of energy balance. During the perforation process, different regions were considered for the plate, such as fracture region, elastic deformation region, delamination region, and undeformed region. The energy absorbed by each region was measured in small time intervals. To validate this model, the ballistic experiment is performed on the thin laminated composite plate near and beyond ballistic limit velocity. The samples were made from plain woven glass/epoxy using a hand lay-up method. In addition to the initial velocity, the residual velocity of the projectile was also measured using two parallel laser curtains. A comparison drawn between analytical and experimental results demonstrated a good consistency in the residual velocity of the projectile. Finally, the distribution of strains along the plate thickness direction over time, the different amounts of absorbed energy of the failure modes, delamination radius, and energy are assessed at near and beyond ballistic limit velocity.

Stiff thin films supported by pressure sensitive ductile solids are an ubiquitous architecture appearing in a wide range of applications. The film rupture and delamination of films are important reliability issues of such an architecture. In this study, we investigate the synergistic effects of plastic deformation of substrates and fracture properties of film/substrate interface on the delamination of films. The focus of this study is on the interplay between the debonding of the interface and the plastic deformation of substrates. Finite deformation analyses are carried out for a stiff film deposited on a soft substrate with the substrate subjected to stretching. The fracture process of film/substrate interface is represented by a cohesive zone model, and the substrate is modeled as an elastic–plastic solid with pressure sensitive and plastically dilatant plastic flow. It is found that increasing the degree of pressure sensitivity of substrate can generate large plastic deformation, promoting crack tip blunting and thereby retarding delamination of film/substrate interface. Whereas, the increase in the degree of plastic dilatancy of substrate gives rise to the limited plastic deformation and leads to poor resistance to interface delamination. The strain hardening of substrate also affects the film/substrate debonding; the substrate with weakly post-yield strain hardening behavior contributes to enhanced resistance to interface delamination. It is further identified that the fracture properties of interface play an important role in activating plastic deformation of substrates. The film/substrate interface with high stiffness, large cohesive strength and high toughness enables the substrate to undergo significant plastic deformation, which suppresses the film/substrate delamination.

The influences of crack and delamination on the natural frequency and strain energy release rate of the laminated doubly curved shell structure are computed via a commercial finite element tool (ABAQUS). The effect of individual damages (crack and delamination) is modeled using the virtual crack closure technique (VCCT), considering the curvature effect. Initially, the model validity is established by comparing the results with the available results in the open domain. Additionally, the model validity has been verified via in-house experimentation for frequency responses. Further, the natural frequency and strain energy release rate (SERR) have been calculated for the structure to examine the influences of the individual or combined effect of damages by varying the design-dependent input geometrical parameters. The inclusive characteristics of the current model in conjunction with geometrical configurations are summarized for subsequent references.

Carbon fiber-reinforced polymer (CFRP) composite laminates have the characteristics of orthogonal anisotropy and heterogeneity, so the failure mechanism under low-energy impact is very complex. As a supplement to the experiment, it is necessary to develop numerical tools to predict the mechanical behavior of composite laminates under low-energy impact. In this paper, the mechanical behavior analysis framework of composite laminates under low-energy impact load is established by using the micromechanics of failure (MMF) theory and the mixed mode exponential cohesive zone model (CZM). The failure modes of intralaminar components in composite laminates are determined by MMF theory. The damage onset and evolution process of interlaminar delamination is described by the mixed mode exponential CZM. The finite element model of composite laminates under low-energy impact is developed using the Python scripts on ABAQUS/Explicit platform. The user-defined material subroutine VUMAT is written in Fortran language. The impact responses of composite laminates with several impact energies are predicted. The intralaminar failure modes and interlaminar delamination behavior are discussed in detail. The results show that the tensile failure of matrix and interlaminar shear delamination failure are the main failure modes of composite laminates under low-energy impact load. The experimental results present better consistency with the numerical analysis, indicating that the constructed multiscale analysis method is efficient and accurate. This study expands the analysis method of mechanical behavior of composite laminates under low-energy impact. The constructed mixed mode exponential CZM also has guiding significance for the failure analysis of other bonding materials.

With the widespread use of fiber reinforced polymer (FRP) composite pipes, their susceptibility to impact damage remains a significant cause of concern. This work investigates the structural response and damage propagation of glass-fiber reinforced epoxy (GRE) pipes under large-surface low-velocity impacts. A series of drop-weight impact tests of varying heights is conducted and compared to numerical finite element (FE) simulations. Then, plies are individually modeled and assigned with properties obtained from the authors’ earlier work. Utilizing composite failure theories and mixed-mode delamination theories, the simulated structural responses including the load–displacement, strain–displacement response and damage propagation are compared and validated with the experimental results. It was found that the structural response is well predicted at higher drop heights and there is a significant change in damage type and propagation with increasing drop heights. The proposed approach builds on the authors’ earlier work and provides a modeling approach for the prediction of structural response, inter- and intra-laminar damage with just pipe level properties.

A customized MATLAB algorithm is developed for internally separated laminated composite panels experiencing large geometric deformations. The algorithm is designed to calculate nonlinear deflection responses under the effect of combined hygro-thermo-mechanical (HTM) loading. The hygrothermal (HT) load on the panel is in-plane, whereas the mechanical load acts upon the structure transversely. The analysis has adopted various kinematic theories and finite element (FE) techniques to determine the deformations computationally. The deflection behavior of the composite is characterized through a macro mechanical model considering the nonlinearity in geometry with and without accounting for the stretching effects across the panel thickness. Additionally, the changes in composite properties due to the environment and/or loadings are adopted to achieve a realistic response, preserving continuity assumptions between the individual layers of the weakly bonded structure. Moreover, various numerical examples are examined through different models to illustrate the influences of environmental factors and design-specific parameters on the flexural strength of weakly bonded structures. The findings strongly emphasize the necessity of employing diverse kinematic models when examining laminated structures, both with and without HT loading, while also acknowledging the potential for debonding.