Composite materials have been increasingly used in both researches and industries, given their wide range of innovative applications and configurations. High-performance hybrid fabric-reinforced plastics stand out in this sector. In the present research, an epoxy-based vinyl ester resin laminate reinforced with bidirectional hybrid fabric consisting of carbon and Kevlar fibers is developed. In order to determine its mechanical properties and damage mechanism considering the anisotropy and the presence of geometric discontinuity (circular hole), this research focused on both experimental and analytical aspect. Concerning to geometric discontinuity, in the vicinity of the hole (known as a stress concentration area), characteristic distances ao and do associated to ASC (Average Stress Criterion) and PSC (Point Stress Criterion) failure theories, respectively, were determined. All the study of the composite material mechanical behavior was conducted based on uniaxial tensile tests. Their results show higher losses in the mechanical properties of the hybrid laminate, with respect to the anisotropy and the presence of the central hole, mainly when the orientation of the Kevlar fibers coincides with the direction of the applied load.

This study aimed to analyze the mechanical properties and damage characteristics in uniaxial tensile loading of two hybrid composite laminates consisting of an ortho-therephthalic polyester matrix reinforced by bidirectional jute fabrics and E-glass fibers, with different configurations and types of geometric discontinuities in the longitudinal section, characterized by the presence of a circular hole and semicircular notches. A semi-empirical study was conducted using the residual properties obtained in mechanical tests, as well as the Point Stress Criterion (PSC) and Average Stress Criterion (ASC) failure theories. This study is based on the calculation of distances (d0 and a0) in the neighborhood of both the hole and the notches, the area of failure stress. The results show the direct influence of geometric discontinuity and residual and modulus strengths in all the parameters studied. With respect to failure theories, only the PSC showed good agreement when the K equal to 2.36 or 2.58 values was used.

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.

In an effort to show the influence of the hybridization method in hybrid fabric reinforced composites within the characteristic of the fracture and the mechanical properties, two laminate reinforced with bi-directional woven were developed, where one of them was reinforced with a hybrid strand (hybrid strand composite laminate) and the other with a different strands (hybrid fabric composite laminate). Both laminates used polyester resin, Kevlar-49 and glass-E fibers, had four layers and were prepared industrially by hand lay-up manufacturing. The percentages by weight of fiberglass and Kevlar in each type of woven are equal. The hybrid strand composite laminate showed a higher tensile strength, however the hybrid fabric composite laminate showed superior properties in three-point bending test, for example, 41.7 % superiority in flexural strength. The results showed that the hybridization method in hybrid reinforced composites influences the mechanical behavior of laminates and the formation and spread of damage.

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.

The damage mechanism of reinforced plastics may be present in many different ways, since it depends on many factors. Highlights may be given to the effect of stress concentration in of geometric discontinuity in the sections of these structural elements, which in general always leads to certain characteristics of the fracture. In the case of glass fiber reinforced plastics (GFRP) it is expected the same tendency, beyond the influence of reinforcement and its internal orientation in the layers (anisotropy). The aims of this work are detailed study of the influence of the holes (longituninal section) in the characteristic fracture in GFRP submitted to tensile loading. Three different configurations of composite laminates were studied: two reinforced with Eglassfiber bidirectional textil fabric and the other only with short mats, also Eglassfiber. The results showed the influence of all parameters listed above in the final fracture characteristics and residual properties.

Natural fiber reinforced plastics (NFRP) have awakened considerable interest in the area of polymer composites, because of the need to develop new, environmentally friendly materials. One of the most complex ways of manufacturing this type of material is in the form of ultrathin laminar layers; however, this process hinders mechanical testing, mainly three and four-point bending. The present investigation faces this challenge and shows the influence of parameters, such as the grammage of reinforcing fabric and lamination process, on strength, stiffness and fracture characteristics for three-point bending in this type of structural element. The industrially manufactured laminas were composed of orthophthalic polyester resin reinforced with licuri fibers. Macromechanical and micromechanical analyses were conducted in the study of fracture characteristics for all the parameters. The mechanical behavior in the three-point bending of the laminar composite showed that the use of licuri fiber to obtain natural fiber-based plastic is completely viable.

Damaging of composite laminates was monitored during fatigue tests, revealing the formation and propagation stages for compressive, tensile, or alternate cyclic loading. Two different laminate stacking sequences, with different number of layers, were tested. The laminates consisted of E-glass fibers reinforced orthoftalic polyester resin (FGRP) shaped as mats or (bi-direction) woven fabric textile. Preliminary density, calcination tests and static compressive and tensile mechanical tests were carried out. Then, tensile (R = 0.1), compressive (R = 10) and alternate axial (R = - 1) fatigue tests were performed at different maximum stresses. Tensile cyclic loading resulted in crack formation and propagation confirming the findings reported in other studies. On the other hand, damage from alternate and compressive fatigue depicted peculiar features. Less extended damage and better fatigue resistance were observed for the laminate with symmetrically distributed layers.