Design of a sustainable and economical composite structure is challenging due to the often contradicting design drivers such as energy consumption and cost. Therefore, predicting the environmental and economic impact in the early stages of product design results in the significant reduction of energy consumption and cost. Consequently, the impact of contrasting objectives on an optimized carbon fibre reinforced polymer (CFRP) demonstrator is evaluated in this study. This evaluation is performed by integrating a predictive life-cycle assessment and costing framework in a multi-objective optimization methodology. The varying design configurations include designs with and without stiffeners. Furthermore, the impact of end-of-life allocation on the optimized design is also evaluated in this study. The results show a marked difference between the energy consumption of the various optimized designs with energy optimization producing the most efficient solution. However, the mass of the demonstrator increases by 7–9 kg across the different design configurations when the closed loop allocation model is implemented. Consequently, the results show the importance of selecting an appropriate EOL allocation methodology in evaluating the energy consumption of a product. The results also show that the parameters driving the energy consumption (mass and material configuration) and cost (complexity and manufacturability) are varied and often contrasting. The differences in mass, cost, and energy optimized designs further reinforces the importance of coupling cost and energy evaluation in design of sustainable products. Finally, the study demonstrates the need for a holistic life-cycle based assessment in early stage sustainable product design.

This work investigates the role of fibre orientation on interply friction. Interply friction tests were performed on a novel snap-cure unidirectional (UD) carbon/epoxy prepreg for five fibre orientations over a broad range of normal pressures and sliding speeds. The test method used closely mimicked the actual processing condition of the prepreg prior to forming including consolidation of the interface. The results show that fibre orientation of the prepreg has a large influence on interply friction. In fact, interply friction for various fibre orientation combinations varies substantially both in magnitude and behaviour of the curve. Further, the range of this variation is dependent on processing conditions such as consolidation, normal pressure and sliding speed. These findings make a strong case for including direction dependent friction models in forming simulations and presents opportunities to tailor the laminate stacking sequence for better forming outcomes.

The intensified pursuit for lightweight solutions in the commercial vehicle industry increases the demand for method development of more advanced lightweight materials such as Carbon-Fiber-Reinforced Composites (CFRP). The behavior of these anisotropic materials is challenging to understand and manufacturing defects could dramatically change the mechanical properties. Voids are one of the most common manufacturing defects; they can affect mechanical properties and work as initiation sites for damage. It is essential to know the micromechanical composition of the material to understand the material behavior. Void characterization is commonly conducted using optical microscopy, which is a reliable technique. In the current study, an approach based on optical microscopy, statistically characterizing a CFRP laminate with regard to porosity, is proposed. A neural network is implemented to efficiently segment micrographs and label the constituents: void, matrix, and fiber. A neural network minimizes the manual labor automating the process and shows great potential to be implemented in repetitive tasks in a design process to save time. The constituent fractions are determined and they show that constituent characterization can be performed with high accuracy for a very low number of training images. The extracted data are statistically analyzed. If significant differences are found, they can reveal and explain differences in the material behavior. The global and local void fraction show significant differences for the material used in this study and are good candidates to explain differences in material behavior.

Lightweight design is important for Battery Electric Vehicles (BEVs), to minimize the effects from the added weight of the batteries. The study looks at the benefits and  disadvantages of choosing a Carbon Fiber Reinforced Polymer (CFRP) material in comparison to metallic material for a specific battery electric commercial vehicle component. A Life Cycle Energy (LCE) and weight analysis are the basis for the comparison. Other aspects that could be considered important for the industrial implementation, such as cost, are also discussed. The LCE is assessed using a combination of engineering process modelling, available data from industrial partners, and data available in the literature. The analysis is aimed to support a holistic comparison, which means the modelling is performed on an overarching level of detail.

Fatigue strength dictates life and cost of welded structures and is often a direct result of initial manufacturing variations and defects. This paper addresses this coupling through proposing and applying the methodology of predictive life-cycle costing (PLCC) to evaluate a welded structure exhibiting manufacturing-induced variations in penetration depth. It is found that if a full-width crack is a fact, a 50% thicker design can result in life-cycle cost reductions of 60% due to reduced repair costs. The paper demonstrates the importance of incorporating manufacturing variations in an early design stage to ensure an overall minimized life-cycle cost.

Fatigue testing of a Carbon Fiber Reinforced Polymer (CFRP) in tension-tension loading has been conducted. In-situ surface strain measurements were performed to examine the gradual elongation of the specimen as this relates to stiffness loss and fatigue damage. A methodology capturing the specimen at peak load has been developed, including an automated trigger mechanism that activates the camera at the desired cycle count. The material tested was a Unidirectional (UD) Non-Crimp Fabric (NCF) with carbon fibers and an epoxy matrix. The fatigue test results revealed a wide scatter in the mid-range of the high cycle fatigue region. By studying the strain in the early fatigue loading cycles and the stiffness loss over time, benchmark of the fatigue performance between different material samples could be carried out, explaining the scatter in the fatigue testing. It could be observed that the fatigue limit of the UD CFRP material in the fiber direction is in the magnitude of 80 % of the material’s Ultimate Tensile Strength (UTS).

This study focuses on comparing the life-cycle energy required for Conventional Steel and HYBRIT (Hydrogen Breakthrough Ironmaking Technology) Steel. The application chosen for this comparison was a bogie beam of Volvo's articulated hauler A30. HYBRIT is a new generation of a fossil-free steel technology developed by SSAB (Swedish Steel Company) which aims to replace coal with hydrogen during steel production to reduce CO2 emissions. The different phases analysed where; material extraction, steel production, component manufacturing, use and end of life phases. Where the use phase is predominantly fatigue loading. It is concluded that HYBRIT Steel consumed 8-10% less energy than Conventional Steel over the entire lifecycle. For applications with less dominant use phases, the percentage of energy saved by HYBRIT Steel would be even larger.

rev2021 was the first edition of the conference on Resource Efficient Vehicles, held online on 14-16 June 2021. This vehicle-centric conference aims to bring together participants from academia, industry and public agencies to discuss research from all relevant fields connected to resource efficiency in all motorised modes of transport and interdependent surrounding systems. 

The theme of this multidisciplinary conference is Resolving Functional Conflicts in Vehicle Design, a theme explored through topics including modelling for multifunctional design; making trade-offs; efficient use of materials and space; integrating new solutions; transforming the product system; transforming the vehicle-transport system; sustainable design; and early-stage design. 

The 2021 edition of the conference consisted of 40 selected papers for presentation at the conference, complemented with four workshops, five keynote lectures from invited speakers, and a concluding panel discussion with four invited participants. It was organised by the Centre for ECO² Vehicle Design at KTH Royal Institute of Technology in Stockholm.

The design of a composite material structure is often challenging as it is driven by the trade-off between lightweight performance and production costs. In this paper, the boundaries of this design trade-off and its implications on material selection, geometrical design and manufacturability are analysed for a number of design strategies and composite material systems. The analysis is founded on a methodology that couples weight-optimization and technical cost modelling through an application-bound design cost. Each design strategy is evaluated for three levels of bending and torsional stiffness. The resulting stiffness-versus-cost-range together constructs the design envelope and provides guidelines on the suitability and improvement potential of each case. Design strategies researched include monolithic, u-beam-, sandwich-insert- and sandwich-stiffened plates. Considered material systems include carbon-, glass, recycled carbon-, lignin- and hemp-fibre reinforced composites. Optimized sandwich designs are shown to have lowest design cost. Glass-, recycled carbon-, lignin- and hemp-fibre reinforced composite materials are all shown to reduce costs but at lower stiffness performance. Ultimately, the case study demonstrates the importance of early structural design trade-off studies and material selection and justifies introducing novel fibre systems in low-cost applications of moderate stiffness levels.

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.