چكيده به لاتين
Abstract
In this research, a new method for manufacturing of composites was developed with the help of the knitted texture technology. The composites obtained from this method has a low weight, strength against low velocity impact, proper tensile strength, recycling ability and resistance to delamination and wrinkles.
In this method, polypropylene yarns and glass fibers using Stoll weaving machine were weaved together by knitting method and a composite preform with a specific geometry was manufactured. Then, based on the shape and geometry of the product, a male-female mold was designed and the preform was laid down in the mold cavity. Subsequently, the molds and samples were subjected to a specific pressure and heat in a hydraulic press. The polypropylene fibers were melted under pressure and temperature to mix with the glass fibers. Then, the cooling operation started and the mold cooled down to ambient temperature. Finally, the composite specimen made of thermoplastic matrix reinforced with glass fibers was extracted from the mold.
In order to characterize mechanical properties of the specimen, flat samples of this composite were subjected to axial tensile tests and mechanical properties including elastic modulus, ultimate strength, ultimate elongation, Poisson’s ratio, and stress-strain diagrams were obtained using the standard tests. Then spherical specimens made with the new thermoplastic composites were subjected to the drop test and the force-time diagram was obtained. These results were compared with the values of pure polypropylene samples. The results showed that the existence of knitted fibers has increased the tensile mechanical properties and toughness of composite material, compared with the material of the pure matrix. Simulation of the drop test on a spherical composite specimen was performed by Abaqus software. The results obtained from the experiments and the simulation were compared and good correlation was achieved. The impact test on a sample with the actual dimensions of a helmet was also modeled using the software and the results were examined.
The strength, impact resistance, weight and price of the designed helmet was compared with a sample made of pure ABS material, which is common in the design of a helmet. The results indicated the superiority of the composites made in the present study.
Keywords: texture composite, thermoplastic, knitted textile, glass fibers, polypropylene yarns
