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This article deals with the influence of the polymeric matrix, such as isotactic polypropylene (iPP), polyethylene (PE-HD), and isotactic polybutene-1 (iPB-1), and the glass fiber content on the material behavior of short glass fiber reinforced thermoplastics. The glass fiber content of all materials ranged between 0 and 50 wt %, which corresponds to a volume content between 0 and approx. 0.264. To describe the mechanical properties of all materials, the stiffness, strength, hardness, and toughness behavior were determined. The crack toughness behavior regarding unstable crack propagation was also assessed by applying fracture mechanics concepts. It was found that the energy-determined J-values for the PP material system reach their maximum at a glass fiber content of 0.135. In contrast, the crack toughness of the PE-HD materials increases continuously with increasing glass fiber content due to the unchanged deformation ability at simultaneously increasing strength. The toughness level of the PB-1 materials is nearly the same independent of the glass fiber content due to the opposite trend of the load and the deformation ability.

Abstract:The hygrothermal aging of short glass fiber-reinforced polyamide 6 materials (PA6 GF) represents a major problem, especially in thin-walled components, such as in the automotive sector. In this study, therefore, the thickness and the glass fiber content of PA6 GF materials were varied and the materials were exposed to hygrothermal aging. The temperature and relative humidity were selected in the range from´40˝C up to 85˝C, and from 10% up to 85% relative humidity (RH). In the dry-as-molded state, the determined Poisson's ratio of the PA6 GF materials was correlated with the fiber orientation based on computer tomography (MicroCT) data and shows a linear dependence with respect to the fiber orientation along and transverse to the flow direction of the injection molding process. With hygrothermal aging, the value of Poisson's ratio increases in the flow direction in the same way as it decreases perpendicular to the flow direction due to water absorption.