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The transverse strength of 90? plies located in cross‐ply laminates subjected to transverse tension is investigated numerically. To reach this aim, it is assumed that the transverse cracking is formed by coalescence of fiber–matrix debonding, which propagates along the planes parallel to the fibers. The two‐dimensional finite element model (FEM) investigates the dominant micromechanical damage mechanisms, fiber–matrix debonding, and matrix cracking using the cohesive zone model (CZM) and plasticity, respectively. The numerical simulation is according to the extended computational micromechanics (ECMM) approach, which can be applied as a useful virtual test method instead of performing costly characterization tests. The results obta
This paper aims to construct a lightweight and durable structure with different designs and construction methods using materials with low-weight characteristics and appropriate strength. In this regard, sandwich panels were made in filled and unfilled sine and square corrugated core, and for comparison of some mechanical behaviors of made specimens with each other, three-point bending tests were performed. Obtained results indicated that the use of polyurethane foam will significantly increase the energy absorption of the structure and extend the life of the structure. The amounts of absorbed energy of the foam-filled samples are 2 and 2.5 times of the foam-free ones for sine and square corrugated cores, respectively. Finally, a numerical a
Composite lattice structures are widely used in the aerospace, automobile and marine industries due to their benefits such as high stiffness and strength with light weight. In this study buckling strength after impact of grid stiffened composite panels was investigated experimentally. For this purpose, grid stiffened composite panels with iso-grid reinforced lattice and three types of skin thickness of 6, 12 and 18 layers were designed, fabricated and tested. E-glass fibers and epoxy resin was used for both ribs and skin. At first, the specimens were subjected to a low velocity impact and then the buckling test was carried out. From results it is concluded that with increasing the thickness of skin, failure mechanisms such as fiber breakage
In this study, the growth of induced delamination in off axes composite laminates has been investigated. Glass-Epoxy composite laminates and Glass-Kevlar-Epoxy hybrid composite laminates with cross-ply [04/90n]s and angle-ply [304/90n]s and [454/90n]s composite layup, containing a low density matrix crack in 90? layers have been made. Then they have been subjected to tensile loading in experimental tests in order to investigate the growth delamination from the location of the matrix cracking and to measure the stiffness degradation. The experimental observations reflect the effects of hybridization and staking sequences on the induced delamination growth for the first time. In addition, the growth of delamination in the considered composite
In this study, the effect of multi-layering in sandwich panel composite structures with different configurations of corrugated cores under the effect of quasi-static indentation loading is investigated experimentally and numerically. Composite plates and corrugated cores with equal weight fraction were manually made using ML506 epoxy resin with 15% hardener and the overall volume fraction of 45% for woven glass fibers. Experiments were performed using a cylindrical indenter with a diameter of 20?mm and a semi-spherical nose shape, and the behavior of the composite structure was evaluated in the case of energy absorption, contact force, and fracture mechanisms for different corrugated cores (rectangular, trapezoidal and triangular). Progress
In this research, the effects of induced delamination on the variation of the mechanical properties of composite laminates subjected to bending loads are investigated using a micromechanical model. For this purpose, the variation of the mechanical properties of delaminated laminates is determined using stress analysis of damaged ply and classical laminate theory (CLT) relationships. Using the proposed model and CLT, the fracture toughness due to induced delamination formation is presented in cross-ply laminates. Subsequently, the variation of strain energy release rate (SERR) is calculated in terms of crack density using analytical and finite element models to detect dominant failure modes in different crack densities. The results are compa
The purpose of the present study is to analyze fiber‐matrix debonding and induced matrix cracking formation as two major micromechanical damage modes in cross‐ply composite laminates using a two‐dimensional numerical approach. To this aim, the cross‐ply laminates containing 90‐degree layers are modeled, where the fibers are arranged randomly in transverse plies. Damage modes in this numerical model are simulated by the cohesive surface method. The performed analyses reveal that in the laminates with 90‐degree layers located in the outer positions, the primary micro damage mode is micro matrix cracking which is initiated from the fiber‐matrix debonding damage mode and will be followed by matrix cracking. The main benefit of th
This study investigates experimentally and numerically the resistance to separation between composite skins and different complex geometries of the corrugated core filled with PVC foam. To this purpose, three different geometries including simple foam core without any corrugated composite, longitudinal trapezoid, and square cores are considered and manufactured as waved (corrugated) composite core. In each specimen, an artificial pre-crack is located between the skin and core and then the effect of the skin's thickness and the core shaped on the debonding growth are examined for the first time. Three-point bending tests are carried out using ENS (End Notch Shear) fixture. Furthermore, the nonlinear response due to separation initiation and
In this study, mechanical behavior of multilayer corrugated core laminated composite sandwich panel subjected to quasi-static three-point bending is investigated experimentally as well as numerically. Parameters such as contact force, energy absorption and specific absorbed energy (unit mass energy) for different geometries of corrugated core (rectangular, trapezoidal and triangular) studied during loading process and failure. Composite plates and corrugated cores have been manually made using ML506 epoxy resin with 15% hardener and 45% volumetric woven glass fibers. Experimental results show that multilayer sandwich composite panels not only strengthen the structure in the quasi-static three-point bending process, but also make the absorbe
In the present study, a new interface model based on continuum damage mechanics (CDM) is developed to investigate the fiber-matrix interfacial debonding in the composite material. This model differs from Voronoi cell finite element and cohesive zone element method. To this purpose, a 2D classical elasticity formulation with non-interactive strength-based criteria and complex variable method with non-interactive energy-based criteria are applied for the analysis of the debond onset and propagation in an RVE with a single fiber, respectively. Then, the CDM approach is used to bridge between analytical and numerical methods. The developed model based on CDM is implanted into ANSYS commercial software to compare the accuracy of the proposed met
In this study a crack density based micromechanics methods in the framework of shear lag approach will be presented. This method is able to establish a dependent relationship for calculating the stiffness degradation and crack density evolution in each applied remote loading. Using this method by considering the effects of out of plane shear stresses, the stress-strain fields, displacement as well as the strain energies of different off-axis composite laminates with the stacking sequences of [?θ/904]s will be calculated. Furthermore, the damage parameters of each damage modes including the matrix cracking and induced delamination will be applied. Using an appropriate fracture criterion, a closed-form analytical relationship will be derived
In the present study, a novel theoretical model is developed, based on classical laminate theory, to predict the equivalent mechanical properties of the re-entrant lattice structures, which composed of continuous fiber reinforced composite struts. Three main mechanism of stretching, flexing and hinging are considered and a general closed-form formulation is derived to estimate the auxetic honeycomb’s elastic and shear modulus as well as Poisson’s ratios. In spite of previous studies in which the response of honeycomb structures is modeled using beam theory, here, each strut of unit cell is expressed as a composite laminate with orthotropic mechanical properties and classical laminate theory is implemented to calculate the mechanical con