PSI - Issue 19

Marc J.W. Kanters et al. / Procedia Structural Integrity 19 (2019) 698–710 Marc Kanters et al./ Structural Integrity Procedia 00 (2019) 000–000

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2. Experimental methods 2.1. Materials and geometries

The material used was a polyamide 66 reinforced with 50 wt.% of glass fibers. From the granular material specimens are injection moulded: tensile specimens according to ASTM D638 Type S (referred to as IM) and plaques with dimensions of 270 x 310 x 2 mm. From each plaque samples were milled, one specimen per plate, comprising tensile specimens according to ISO527 1B and ASTM D638 Type S and straight beams (64 x 10 x 2 mm). All geometries were milled at various angles with respect to the flow direction, whilst ensuring their center always at the same position in the plaque where the flow front was fully evolved. To study the sensitivity for stress concentrations, double edge notched specimens are machined from the ISO527 1B tensile bars with radii of 0.1, 0.25, 0.4, 0.8, or 1.5 mm. For validation purposes, an in-house developed DSM demonstrator part was moulded in the same material. 2.2. Mechanical testing Uniaxial tensile tests and creep rupture experiments ( ) were performed on a Zwick Z010 Testing Machine equipped with a 10 kN load-cell. Cyclic fatigue experiments were performed on a servo-hydraulic MTS Testing System equipped with a 25 kN load cell. During all load controlled cyclic fatigue experiments, a sinusoidal stress was applied up to failure, while the maximum load, load ratio (R-value), and frequency were kept constant during each experiment. Frequency was 0.25 Hz for the test samples and 1 Hz for the demonstrator part. A wide range of load ratios was used; load levels were selected to obtain fatigue lives between 10 2 and 10 6 cycles. All mechanical tests were performed at ambient conditions (23 o C/50% RH), and testing times were such that moisture uptake was negligible. This was validated by checking the quasi-static stress-strain behavior after exposure to ambient conditions for similar timescales. 2.3. Microstructure For short-glass fiber reinforced plastics the glass fibers orient during the injection moulding process, and, depending on geometry, gating location, and processing conditions, a specific microstructure will result for each sample type. For the characterization in this work, two geometries are moulded: the injection moulded Type S bar and the plate. Glass fiber orientation of these samples is quantified using X-ray micro-tomography, as illustrated in Figure 1. The injection moulded Type S bars display a strong and homogenous orientation over the cross-section, caused by a plug flow in the narrow section. The plate samples display a distinct shell/core type of morphology due to the expansion flow in the core and the shear flow near the walls of the cavity.

Figure 1: Glass fiber orientation for the injection moulded Type S tensile bar (left) and the injection moulded plate samples (right). a 11 represents the fibers oriented in flow direction, a 22 fibers in-plane and perpendicular to the flow direction, and a 33 the fibers oriented out-of-plane.