Technical cost modelling and efficient design of lightweight composites in structural applications

Abstract: A lightweight transport design reduces fuel costs and emissions and can be achieved through the use of fibre-reinforced composite materials. Although lightweight, the composite raw material can be expensive and the sequential component production challenging and costly. To design weight- and cost-efficient composite structures and find ways to reduce production costs, technical cost modelling must be applied. In this thesis, a technical cost model for composite manufacture, assembly and basic inspection is proposed and implemented to identify cost drivers, evaluate trending design strategies and suggest appropriate composite design guidelines for transport and aeronautical applications. Among identified cost drivers, material costs dominates at 50-90 % of the total part cost also for low annual volumes. Tooling costs are second in importance for slow processes and large parts while the importance of investment and labour depends on degree of automation. Part integration is shown to only marginally reduce cost. Traditional composite assembly is in turn found to potentially reduce costs by 30 % through the elimination of non-value-adding processes such as shimming and part positioning. In comparison to part integration, sandwich design exhibits superior cost- and weight-efficiency for low-to-intermediate stiffness levels. Moreover, the industry impact of a sustainable, circular recycling flow of composite materials is estimated and shown to give up to halved raw material costs as well as cost returns also for virgin carbon fibre users. Low-cost fibres such as glass, lignin-based carbon, hemp and recycled carbon fibres are found to be highly cost-competitive also for structural adaptions.The technical cost model, method and results presented in this thesis provide important composite design conclusions and a foundation for further modelling work needed to reach that elusive weight- and cost-optimal composite design.