Abstract
In this experimental work, the quasi static and fatigue properties of a 40 wt.% long carbon fiber reinforced partially aromatic polyamide (Grivory GCL-4H) were investigated. For this purpose, microstructural parameter variations in the form of different thicknesses and different removal directions from injection-molded plates were evaluated. Mechanical properties decreased by increasing misalignment away from the melt flow direction. By changing the specimen thickness, no change in the general fiber distribution pattern transversal and normal to the axis of melt flow was observed. It has shown that with increasing specimen thickness the quasi static properties along the melt flow direction decreased and vice versa resulting in superior properties normal to the melt flow axis. At around 5 mm, an intersection suggests quasi-isotropic behavior. In addition, the fatigue strength of the material was significantly higher in the flow direction than normal to the flow direction. No change in fatigue life was observed while changing specimen thickness. The Basquin equation seems to describe the effect of stress amplitude on the fatigue strength of this composite. Scanning electron microscopy was used to investigate fracture surfaces of tested specimens. Results show that mechanical properties and morphological structures depend highly on fiber orientation.
Highlights
Long fiber reinforced thermoplastics (LFT) are being used in a variety of industry sectors due to their good combination of processability and high specific mechanical properties (Ref 1)
The prevalent fiber orientation of injection-molded LFTs is mainly affected by the thickness of the specimen and the removal direction of specimens from the plate
The Young’s modulus, ultimate tensile strength (UTS) and fatigue strength exhibited a decrease with increasing extraction angle with reference to the melt flow direction
Summary
Long fiber reinforced thermoplastics (LFT) are being used in a variety of industry sectors due to their good combination of processability and high specific mechanical properties (Ref 1). Due to an intrinsic anisotropic behavior of injection-molded LFTs, specimens for mechanical testing in one particular direction are not sufficient to describe the mechanical properties comprehensively In such cases, the extent of anisotropy is mainly affected by the fiber orientation distribution and thickness of the specimen. Increasing misorientation angles led to a distinct decrease in quasi static and fatigue properties In the latter case, the specimens exhibited a typical skin-core layer structure with fibers being aligned with melt flow directions in the peripheral areas of the part and perpendicular to it in the Journal of Materials Engineering and Performance core regions. In LFTs, long initial fiber lengths and high fiber volume fractions lead to fiber–fiber interactions generating dense fiber networks and morphologies exhibiting high looped and interconnected fibers
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