Interlaminar fracture toughness of consolidated, continuous glass fiber reinforced polyamide‐6 tapes, as well as its sensitivity to process parameters are investigated in this study. Therefore, consolidated plaques are manufactured, varying consolidation temperature and pressure, and their delamination behavior in mode I and mode II is analyzed by means of DCB and ENF tests. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Flax fibers are superior to E-glass fibers in terms of specific Young modulus. Many researchers have recently tried to exploit this feature and use flax fibers in polymeric composites to compete with glass fiber composites. In this work, a new type of unidirectional flax/paper reinforcement obtained after resin transfer molding with epoxy is investigated. Reinforcement's parameters (paper ply and flax ply surface densities) and manufacturing parameters (forming pressure and drying temperature) are optimized to obtain the best possible composite strength and modulus. Internal bond strength between flax and paper layers is also investigated. Results show that at equivalent Vf the new flax/paper/epoxy composite is superior, in both specific strength and modulus, to another flax/epoxy composite (without the paper layer). It also surpasses the specific stiffness of a unidirectional E-glass/epoxy composite and the specific strength of a commercially available similar reinforcement.

Principal in-plane permeabilities of a unidirectional flax/paper reinforcement are characterized in terms of reinforcement material and manufacturing parameters at a constant fiber volume fraction (Vf). ANOVA result shows that surface density of the unidirectional flax layer is the most important parameter on the mean and variance of the K1 permeability. On the other hand all four studied parameters are concluded to affect the K2 permeability. The K1 permeability is found close to that of a twill weave flax fiber fabric reported in the literature and only one order of magnitude lower than a plain weave glass fiber fabric. Impregnation of the reinforcement with epoxy resin shows that a large area of the molded plaques was dominated by capillary forces during resin injection. This means capillary number and subsequently the resin injection velocity should be optimized for reducing void content in the final composite.

In this paper a new process to manufacture unidirectional reinforcements for eco-composite materials, made of natural fibers, is presented. Starting with flax rovings of different sizes, an apparatus was developed to feed and align the rovings over the wet-end section of a paper machine. The short kraft paper fibers are therefore mixed with the long flax roving as the machine is running, and at the end of the process, a sheet of the hybrid dry reinforcement is obtained and cut to size for impregnation with various resins, using different processes. This novel manufacturing process allows for high volume production of reinforcement. It is very flexible, and many different combinations of long and short fibers can be exploited for the production of a vast variety of dry reinforcements. In this paper, composite samples are obtained out of these reinforcements, using the resin infusion (RI) molding process with a commercial epoxy resin. The results are compared with those of usual glass fiber reinforcement. An interesting aspect is that the large variability, typical for natural fibers, is largely reduced when the short kraft fibers are present in the composite. In terms of permeability to resin, reasonably comparable values can be obtained compared to that of glass fabrics, if a low surface density of reinforcement is chosen.

The composite pipes manufactured by filament winding technology have anisotropic behavior owing to different reinforced ply angles. Composite pipes can be exposed to the thermomechanical loading due to hot fluid that flows into them. In this paper, based on the three-dimensional anisotropic elasticity, an exact elastic solution for thermal stresses and deformations of the pipes under internal pressure and a temperature gradient has been studied. Giving heat convection conditions the variation of temperature field within the pipe is obtained by solving the conduction equation at the wall. The influence of temperature field in the governing equations of thermoelasticity has been considered via a constitutive law. The shear extension coupling is also considered because of lay-up angles. Stress, strain and deformation distributions for different angle-ply pipe designs are investigated using the present theory.