SAE - Automotive Carbon Fiber Composites From Evolution to Implementation

Organization: SAE
Publication Date: 29 November 2011
Page Count: 130

Executive Summary

The advantages of carbon fiber composites (CFCs) in automotive design are high stiffness, high specific strength (strength-to-weight ratio), excellent fatigue endurance, corrosion resistance, generally good impact resistance, and flexibility in design that permits them to be tailored to design requirements. Composites also facilitate a lower parts count by reducing the number of subassemblies and fasteners. Replacing metal with CFCs can provide significant weight reduction, which has become particularly important in our current society that is facing high fuel prices and much more stringent emissions standards. Aside from passenger vehicles, heavy-duty on-highway trucks and military vehicles are also exploring the use of CFC components to enable better fuel economy and/or increase payload. Unfortunately, CFCs also have notable disadvantages, including relatively high material and fabrication costs, poor compressive and shear properties, and the necessity for non-destructive inspection techniques to detect flaws or damage.

The main factors in the automotive industry driving fiber development and resin development center around cost, performance, cure time, and processing method. The years 2010 and 2011 have seen an incredible amount of cooperation and partnerships between companies operating at different points in the value stream to bring new materials and processing technologies to market quicker. Carbon fibers and matrix resins, and their developments, are not independent of the other aspects of manufacturing a carbon fiber composite component, nor are they necessarily independent of each other. Different resins process differently with regard to the time, temperature, and pressure required for fiber wet-out and consolidation. Additionally, different fiber-resin constructions require different processing methods. Selecting the right fiber, resin, and construction for a particular application requires knowledge of not only the fiber and resin material properties, but also of the method of manufacturing. The method of manufacturing influences the composite construction and end properties, while the surface quality of the finished part (Class A or non-Class A) and the production volumes to be made in turn dictate what manufacturing methods are technically and economically viable. One must also factor in the commercial competitiveness with other materials with regard to vehicle installation, maintenance, and lifecycle issues. There is usually more than one way to make a carbon fiber composite automotive part, and all factors should be considered to make the best decision.

Both the aerospace and automotive industries are driving changes in carbon fiber composite technology to produce components that have lower material cost and targeted performance. Those developments will in turn lead to some developments in the manufacturing processes. For example, changes in processing temperatures can result in changes in tooling materials and heat sources, and changes in composite construction can lead to changes in material handling during component manufacture. Such future advancements driven by raw material and construction improvements will be additive to the advancements driven directly by the manufacturing process to improve areas such as part-to-part cycle time and energy efficiency.

One of the most challenging aspects of implementing CFC components in vehicle design is attaching them to the rest of the vehicle. This usually requires machining and joining, which must be done in a manner that retains the mechanical properties of the CFC component as well as possible, provides a strong and durable joint, is cost-effective, and fits with the OEM assembly process and vehicle production rate.

Worldwide, automotive companies are facing some challenging energy and environmental issues. In the U.S., the 2010 Corporate Average Fuel Economy (CAFE) regulation that increased fuel economy from 27 to 35 miles per gallon by 2016 has already resulted in concerted efforts to implement more lightweighting materials, including CFCs, in vehicle design. Means to recycle CFCs and other lightweighting materials must be developed to just maintain the current level of recyclability of vehicles made predominantly with steel. The CFC recycling industry is still in its infancy and the processes are expensive and complicated. The industry has formidable requirements, including consistent scrap availability, appropriate size reduction technologies, established process parameters, the infrastructure for material collection, and standardization of recyclate properties. The technical and economic issues with recycling/reusing CFCs are best developed during vehicle design to aid in both the recovery of the material as well as potential implementation of the recyclate back into a vehicle.

Implementation and longevity of CFC components in mainstream vehicles hinge on a multitude of technical issues, covering raw materials, fabrication, assembly to other (CFC or non-CFC) components, and in-vehicle performance. However, addressing all the technical issues will not guarantee first-use or long lasting use of CFCs in mainstream vehicles. Acceptance of the material is also key - the acceptance of CFCs by OEMs through the inclusion of CFCs in their portfolio of materials from which they can design mainstream vehicles, and acceptance by the consumers with regard to cost and performance throughout the vehicle life, which inevitably includes damage and repair.

This is an exciting time for the carbon fiber composites and automotive industries. The current need to drastically lightweight the U.S. vehicle fleet in the next few years provides a great opportunity for CFCs to find prominence in mainstream vehicles. Their advantageous high specific modulus and strength can result in weight savings up to 60% compared to conventional steel designs. However, before CFCs find prominence, significant inroads in reducing the relatively high material and fabrication costs, long part-to-part cycle times, and slow assembly/attachment to other vehicle components will need to be made. Progress will also be needed in the areas of damage detection, repairability/replaceability, and recycling.

The combined chapters of this book highlight current activities surrounding automotive carbon fiber composites and the anticipated direction of developments in the next 5-10 years. The objective is to provide a high-level view as opposed to technical treatises, preparing the reader for meaningful discussions with composites engineers and technicians, fiber suppliers, resin suppliers, tool and equipment manufacturers, as well as business development and lifecycle workers. The possibilities of carbon fiber composites in automotive applications are plentiful - and more promising than ever before in the history of the automobile.