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Achieving methods to improve the failure behavior of composite multilayer plates has always been of interest to researchers. In this article, in order to delay the collapse of composite multilayers in a brittle and sudden manner, a layer of elastomeric foam is inserted between glass-vinyl ester composite plates and the change of the failure pattern and ultimate strength of sandwiched plates with different layering of fibers, compared to single composite plates, is observed. In the examined layers, firstly, the failure pattern was observed in different types of multilayers with different layering including a stronger alignment, orthogonal layering and woven layers under concentrated loading, and the effect of interlayer foam in changing the pattern of rupture hinges in the plates and parameters of bearing capacity and the amount of absorbed energy was observed. Then, a layer of elastomeric foam was placed between the composite plates, which was able to absorb significant energy in the panels before the final collapse by distributing the stress from the upper plate to the lower plate, and delayed the moment of complete rupture. The results showed that the use of interlayer elastomeric foams causes a change in the formation pattern of rupture hinges in the composite panel and significant softening before the final collapse. This increases energy absorption, especially in the case of panels with lower bending stiffness, up to about 115%, which is a satisfactory result.The objective for application of an elastomeric foam was omission of disadvantage by inflexible crushable foams. Although, the elastomeric foam supplied aa lower flexural modulus for the sandwich composite panels due to its lower shear rigidity, it could distribute stress concentration areas from the top to the bottom composite panels, to create a considerable fuselage to reach the ultimate strength via absorption of considerable energy. The results showed promising performance for failure response of elastomeric foam cored sandwich panels. Application of the interlayer elastomeric foam in the case of composite panels with lower stiffness showed larger enhancing effect.

Delamination or interlayer cracking is one of the most important imperfections in composite materials. The existence of this defect in a structure reduces the strength and, as a result, disables the structure. To analyze the effective factors in interlayer separation, it is necessary to analyze the effective loading parameters. In this paper, the effect of the change in loading rate on the failure mechanism in I failure mode was analyzed using an acoustic emission for unidirectional samples made of glass fiber/epoxy resin. At first composite, samples were made according to standard and placed at different rates of displacement under loading. Force data, displacement and crack growth rate for different loading rates were used to calculate the exact strain energy release rate. In addition to the extensometer, the Dino camera was used. In this paper, a high-reliability method was proposed to evaluate the separation between the layered composites using acoustic emission method. By comparing mechanical data and acoustic emission signals, the mechanical behavior obtained for each loading rate was determined so that the mechanical behavior of the composite material varied with the change in loading rate. The results show that, with increasing loading rates, the resin lost its elastic properties, and the specimen exhibited a more rigid behavior and is quite rigorous so that the fracture failure process is changed. The failure processes and crack growth rate was validated by use of acoustic emission signals. There was good agreement between the fracture toughness of accretion of acoustic emission signals with the experimental values. [ABSTRACT FROM AUTHOR]

Delamination is one of the major failure modes of the laminated composite material, which is responsible for the stiffness degradation of these materials. Hence, it is necessary to investigate this damage mechanism in these types of materials in order to distinguish their behaviors and their effects on the residual strength of the composite laminates. In this paper, a very capable procedure is proposed to assess delamination using Acoustic Emission (AE) method in composite laminates. Firstly, a novel procedure was established to decompose the fundamental Lamb wave modes in small size specimens. The damage mechanisms in End Notched Flexure (ENF) in woven and unidirectional specimens were then distinguished using Fuzzy Clustering Method (FCM). Subsequently, the crack-arrest phenomenon was inspected in each specimen. Next, experimental and Cohesive Zone Modeling (CZM) methods were done to characterize the delamination using ENF specimens. The results displayed how, it is possible to effectively reduce the effect of propagating media such as attenuation of AE signals using the new proposed procedure. In conclusion, the results of this research could lead to proficiently distinguishing different damages in laminated composite using AE Lamb-based technique. [ABSTRACT FROM AUTHOR]

Roll forming of amorphous PVC based composite laminates were studied in this paper for the first time. For this, [0/90]6 and [45/-45]6 lay-ups of this composite laminates with dimensions of 80×12 cm were fabricated using film stacking and hot pressing processes. The suitable forming temperatures of the composites were determined and then, the laminates were roll formed at 170ᵒC with a single stand and also multi stand roll forming process into channel sections. Geometrical defects including warping, flange waviness and spring back of the roll formed profiles were evaluated. Finally it was concluded that [0/90]6 lay-up results in very lower defects in comparison with [45/-45]6 lay-up, and also the final stand of roll forming process has dominant role on the defects of multi stand roll forming [ABSTRACT FROM AUTHOR]

The residual stresses in composite laminates depend on several factors including the conditions of fabricating process, property of materials, direction and lay-ups of the layers. However the thermo-elastic behavior of composite is one of the most important parameters affecting the magnitude of residual stresses. The elastic properties and residual stresses do not remain constant under cyclic thermal loading and vary in a non-linear manner. The study of these non-linear variations of modulus and strength and their effects on residual stresses in laminates while experiencing thermal load cycles is the main goal of this paper. An experimental device is designed and manufactured conveniently to exert defned thermal load cycles with different temperatures and cycle time on composite laminates. Then orthotropic glass-epoxy composite laminates made by hand lay-up are tested under cyclic thermal loading. The elastic modulus and fracture strength of the samples are measured before and after experiencing defned number of thermal shocks. The residual stresses in composite laminates are calculated and compared based on the actual behavior of composite and by means of a modifed classical laminate theory. The results of this study demonstrate that the non-linear behavior of composites infuences the residual stresses signifcantly. In addition, if the sample becomes more brittle, the residual strains remain constant; while the elasticity modulus and residual stresses decrease.