JEC COMPOSITES MAGAZINE - Issue #70 - January/February 2012 - 50

thermoplastics

Fig. 4: Single-rib part failure

Fig. 6: Dual-rib part failure

ribs or areas in contact with support structures. In this study, structural FEA was also used in combination with mould flow analysis (MFA) to understand the fibre orientation and weld line locations in the tray arm and predict their impact on the mechanical performance of the tray arms. The stress distribution information obtained from the FEA was utilized for the design improvements. The goal was to reduce stress in critical areas and better accommodate the as-moulded material properties (e.g., fibre orientation and weld line) in the part. Once we were confident in the analysis results, these design changes were translated to tooling, and then the parts were moulded for testing and validation.

tray arm to predict the stress levels at different locations of the arm (Figure 5a). FEA indicated that with the 8-mm side support, the maximum stress concentration was close to the new rib and the side support location, and the maximum stress value (273 MPa) was very close the tensile strength of the PEI compounds. In order to reduce the stress on the rib location, further FEA was performed with increased side supports. As the side support width was increased from 8 mm to 20 mm, the maximum stress was still close to the rib and the side support location, but the maximum stress was reduced from 273 MPa to 261 MPa (Figure 5b). The tray arm tool was modified to add the second rib. The location of the gate was kept unchanged for the dual-rib design. Tray arms were moulded with the PEI and PPS materials (EC006PXQ, EC008PXQ, OC006XXQ and OC008XXQ) and tested with the modified MTS system as described in the experimental section. The tray arms were tested with 8-mm and 20-mm stainless steel side supports. All the samples failed along the new rib (Figure 6), which was in line with the FEA prediction.

Results and discussion
As mentioned in the introduction and depicted in Figure 1, the bottom part of the tray arm designed by Vaupell was open-ended with a single rib. The failure location of this open-ended single-rib tray arm is shown in Figure 4. As a starting point, SABIC Innovative Plastics suggested that a rib be added to the location where the failure was observed. Before modifying the tray arm tool, FEA was performed on this open-ended, dual-rib

The open-ended, dual-rib tray arm test data is summarized in Table 2, which shows the maximum loads that the tray arms were able to withstand before they failed. As predicted by the FEA, the tray arms performed better and were able to withstand about 10% higher load with the 20-mm side support. The PEI-based compounds survived higher loads than the PPS-based compounds, but in both cases the peak load/break load was Fig. 5: Stress distribution in open-ended, dual-rib tray arms with 120 lbs load and (a) 8-mm stainless steel side not close to the target peak support and (b) 20-mm stainless steel side support. Maximum stress is 273.1 MPa and 260.1 MPa for situation (a) and (b), respectively load of 120 lbf. Although the

50 jec composites magazine / No70 January - February 2012

JEC COMPOSITES MAGAZINE - Issue #70 - January/February 2012

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #70 - January/February 2012