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UBC Theses and Dissertations

Spring-in of angled thermoset composite laminates Albert, Carolyne I.


Advanced fibre-reinforced thermoset polymers are primarily used in the aerospace industry for their excellent mechanical properties and low weight. T o justify the use of these materials, low processing and manufacturing cost must counterbalance their high base cost. The necessity to produce parts within tight dimensional tolerances in the aerospace industry constitutes a challenge to cost-effective manufacturing as process-induced distortions are encountered in production. The current work focuses on spring-in, a change in angle occurring during processing of curved thermoset composite parts. Spring-in is encountered for virtually all curved thermoset composite parts and there is currently poor understanding o f the variables and mechanisms that affect this phenomenon. This thesis examines the effect of a number of design and process parameters on spring-in. The parameters studied include part geometry, lay-up, tool material, tool surface condition, cure cycle, and the use of a rubber caul sheet. The results show that process parameters have a significant impact on spring-in, in some cases more than doubling the value. Close examination of the parts made in this study reveals that spring-in can be decomposed into two components: a true corner component and a warpage component. The corner component is shown to be mainly the result of chemical and thermal strain anisotropy during processing. This component is repeatable with little variability for a given part design. Parameters affecting the corner component are the initial part angle and the part lay-up. The warpage component, on the other hand, is found to be driven by mechanical interaction between the tool and the part. This component is affected by the laminate thickness, the flange length, the cure cycle, the tool material, and the tool surface condition.

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