To address a critical aspect of the fast growing use of composites in aircraft and aerospace industry, the influence of the porosity on the shear strength of composites property was investigated as a mean for determining the critical values of porosity. Acid digestion techniques were applied to determine the void volume ratio of two families of carbon epoxy laminates (8 and 16 plies). Ultrasonic inspections revealed the corresponding attenuation coefficients. The void morphology was investigated by optical microscopy. Results from Interlaminar shear and Iosipescu shear tests were correlated with the attenuation coefficient to determine critical values of porosity using a modified Mar-Lin fracture criteria. It has been shown that the shear strength decrease with the increase of void volume ratio and the effects are more significant in thicker laminates. This work showed that by using the Mar-Lin criteria the singularity order, which is an indicative of the sensibility to voids in composites, is dependent of type of loading and void distribution.

Resumo: O principal objetivo do presente trabalho foi a determinação do módulo de cisalhamento G12 e a máxima resistência ao cisalhamento (ô12) utilizando o ensaio de cisalhamento losipescu. Os testes foram conduzidos com dois tipos de compósitos, fibra de carbono/epóxi e fibra de vidro/epóxi utilizados na indústria aeroespacial e também uma matriz de resina moldada. Os resultados indicam a efetiva contribuição das fibras de reforço para a resistência ao cisalhamento (ô12) e para o módulo de cisalhamento (G12) comparado com a matriz polimérica sem reforço.

Abstract: The main aim of the present work was the determination of the shear modulus (GI2) and the maximum shear strength (ôI2) using the losipescu Shear Test. Tests were carried out on two types of composites, carbon fiber/epoxy and glass fiber/epoxy, used in the aerospace industry, and also a molded epoxy resin matrix. The results indicate the effective contribution of fiber reinforcements to the shear strength (ô12) and shear modulus (G12) compared to the no reinforcement polymer matrix.

This paper shows different aspects related to the application of different thermal analysis techniques in the study of energetic materials. The criteria used to choose the best technique and an exact approach to adjust the experimental data with a proper model are here discussed. The paper shows how to use the different thermal analysis results to help develop new compounds, to study the stability of some energetic materials and their compatibility, and the conditions necessary for a secure storing environment.