Abstract This study aimeds at investigating the mechanical behavior of an E-glass fiber-reinforced epoxy resin of a laminated composite sandwich with honeycomb core and a central hole, used in the aeronautics industry submitted to bending loading. Three analytical failure models applied to laminated composites were compared in order to study the influence of stress concentration due to a central hole. The following criteria were assessed: Average Stress Criterion (ASC), Point Stress Criterion (PSC) and the Inherent Flaw Model (IFM). These models were applied to experimental data obtained in a four-point bending test in samples of the sandwich laminate. Finally, modifications on failure prediction models were proposed and appied in sandwich laminates with a central hole. The results obtained showed the applicability of the proposed formulation and that the suggested changes to the model more adequately fit it to the experimental data.

Natural fibers are increasingly used as composite reinforcement in different fields of engineering. Caraua fiber stands out for its good mechanical properties and adherence to resin; however, little is known about its behavior in the manufacture of a composite or whether classic failure theory applies in this case. The present study assesses the mechanical properties of two laminas reinforced with unidirectional curaua fiber containing fiber volume fractions of 30 % and 22 %, and compares the results with the values obtained for four failure criteria, using analysis of variance (ANOVA). To that end, tensile tests were conducted along the fiber direction and at other loading angles, in addition to iosipescu shear tests. The results show that the Hashin criterion was the best and the maximum stress criterion does not represent the failure behavior of these materials.

ABSTRACT This study aimed to assess the effect of hybridization on thermomechanical properties and water absorption of composite materials, by introducing sisal fiber tissue into the material. To that end, two composite material plates were manufactured, the first with five layers of E-glass reinforcement mat and the second with three layers of E-glass fiber interspersed with two layers of sisal fibers, both used as an orthophthalic polyester resin matrix. The material was then submitted to tensile, three-point bending and water absorption tests. It was observed that hybridization causes a change in both the final strength and stiffness of the material.

Over the last few years, great interest has been shown by researchers in presenting alternative proposals for the design and fabrication of materials with good mechanical properties and low cost for a variety of applications. With this in mind, a study was carried out on the addition of curaua fibers in a polypropylene (PP) matrix. These were extruded in the pellets form with curaua fiber content of 5, 10 and 20% (mass percentage). An injector was used to make the test specimens from these pellets, which were then subjected to mechanical tests (tensile and three point bending), physical and thermal tests (fluidity index and HDT). As a consequence, it was noted that the incorporation of fibers in composites of PP with curaua resulted in an increase in the elastic modulus and tensile strength improving therefore the mechanical properties of these materials. Another important point was to check if there was an increase in heat deflection temperature as the fibers were added. As a result, it has been found that it is feasible to use these materials in industry, facilitating its recycling and improving its final mechanical properties.