Reference - Process-induced shape distortions in aerospace thermoplastic composites
| Type | Thesis |
|---|---|
| Title | Process-induced shape distortions in aerospace thermoplastic composites |
| Abstract | Thermoplastic composite materials are of great interest in aerospace structures due to their potential for shorter manufacturing cycle times, high production rates, and their ability to be re-heated and shaped multiple times. Thermoplastic resins offer many new possibilities in their ease of repair, recycling, and welding capabilities. Aerospace-grade thermoplastic composites such as carbon fibre-reinforced polyether-ether-ketone (PEEK) are processed well above their melting point at temperatures as high as 390ºC to allow proper forming and consolidation of the material to take place. During subsequent cool-down from the process temperature, residual stresses develop due to effects of material anisotropy, part geometry, and tool-part interactions that eventually lead to undesired shape distortions in the final part geometry. As observed with thermoset composites, common distortions include spring-in of corner angles and warpage of flat sections. The tight dimensional tolerances required for aerospace parts demand that process-induced shape distortions be well understood in order to eliminate scrap parts and fitting problems during the assembly stage of the components. In this project, L-shape flanges with a corner designed at 90° are manufactured from aerospace-grade AS4/PEEK thermoplastic composite in a hot press using a matched-die tooling configuration. A thermoforming technique is employed that involves heating previously-manufactured flat panels of the material to the processing temperature prior to transfer and consolidation within a relatively cold tool held at constant load and temperature. L-shape flanges consisting of a quasi-isotropic layup of unidirectional plies as well as short randomly-oriented strands of AS4/PEEK are thermoformed at 105°C, 215°C, and 290°C. Spring-in angles of the manufactured parts are quantified using a coordinate measuring machine and the results are compared with predictions from the Nelson-Cairns expression based on material thermal expansion anisotropy. The spring-in angles are also evaluated against measurements of change in part corner angle as a function of temperature due to thermo-elastic effects during heat-up from ambient temperature in a quasi-isotropic and ROS part. The parts are further assessed in terms of thickness measurements, surface quality observations, cross-section optical microscopy, and mechanical strength testing. |
| Authors |
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| Department | Materials Engineering |
| Date | 2016 |
| University | The University of British Columbia, Vancouver |
| Issue | April |
| Websites | |
| DOI | 10.14288/1.0300417 |
| Keywords | Thesis/Dissertation |
Welcome
Welcome to the CKN Knowledge in Practice Centre (KPC). The KPC is a resource for learning and applying scientific knowledge to the practice of composites manufacturing. As you navigate around the KPC, refer back to the information on this right-hand pane as a resource for understanding the intricacies of composites processing and why the KPC is laid out in the way that it is. The following video explains the KPC approach:
Understanding Composites Processing
The Knowledge in Practice Centre (KPC) is centered around a structured method of thinking about composite material manufacturing. From the top down, the heirarchy consists of:
- The factory
- Factory cells and/or the factory layout
- Process steps (embodied in the factory process flow) consisting of:
The way that the material, shape, tooling & consumables and equipment (abbreviated as MSTE) interact with each other during a process step is critical to the outcome of the manufacturing step, and ultimately critical to the quality of the finished part. The interactions between MSTE during a process step can be numerous and complex, but the Knowledge in Practice Centre aims to make you aware of these interactions, understand how one parameter affects another, and understand how to analyze the problem using a systems based approach. Using this approach, the factory can then be developed with a complete understanding and control of all interactions.
Interrelationship of Function, Shape, Material & Process
Design for manufacturing is critical to ensuring the producibility of a part. Trouble arises when it is considered too late or not at all in the design process. Conversely, process design (controlling the interactions between shape, material, tooling & consumables and equipment to achieve a desired outcome) must always consider the shape and material of the part. Ashby has developed and popularized the approach linking design (function) to the choice of material and shape, which influence the process selected and vice versa, as shown below:
Within the Knowledge in Practice Centre the same methodology is applied but the process is more fully defined by also explicitly calling out the equipment and tooling & consumables. Note that in common usage, a process which consists of many steps can be arbitrarily defined by just one step, e.g. "spray-up". Though convenient, this can be misleading.
Workflows
The KPC's Practice and Case Study volumes consist of three types of workflows:
- Development - Analyzing the interactions between MSTE in the process steps to make decisions on processing parameters and understanding how the process steps and factory cells fit within the factory.
- Troubleshooting - Guiding you to possible causes of processing issues affecting either cost, rate or quality and directing you to the most appropriate development workflow to improve the process
- Optimization - An expansion on the development workflows where a larger number of options are considered to achieve the best mixture of cost, rate & quality for your application.
