Experimental investigation of the uncertainty of disordered fiber-reinforced injection-molded components

Short fiber-reinforced composites manufactured by injection molding exhibit an alignment of the fibers superimposed by a manufacturing process induced scatter. As a result, the components possess a scatter in their mechanical properties due to the local scatter in fiber length, fiber orientation and fiber volume content. In this paper, we investigate the scatter of mechanical properties and fiber orientation of a glass fiber-reinforced phenolic resin with a fiber mass content of 37.5 wt.% manufactured by a thermoset injection molding process [1]. Rectangular plates of 2- and 3-mm thickness and a size of 190 x 480 mm² were manufactured. The objective is to investigate the local variation of mechanical properties (Young’s modulus, tensile strength, and fracture strain) and fiber orientation and to evaluate the data statistically. Tensile tests are performed on miniature specimens of 36 mm length, 2 mm thickness and 2 mm width tested in 0° and 90° direction. The local mechanical properties are correlated with the local fiber orientation evaluated on in-plane micrographs taken on every specimen. On the 3 mm plates, tensile tests on specimens with shortened ISO dimensions are performed. The strain is evaluated globally and locally by digital image correlation (DIC). The investigated material shows fiber alignment in flow direction with the sprue positioned in the middle of the plates. The fiber alignment is superimposed by a large local process induced variation of the fiber orientation.