Innovative Structural and Joining Concepts for Lightweight Design of Heavy Vehicle Systems

Recent advances in the area of Metal Matrix Composites (MMC's) have brought these materials to a maturity stage where the technology is ready for transition to large-volume production and commercialization. The new materials seem to allow the fabrication of higher quality parts at less than 50 percent of the weight as compared to steel, especially when they are selectively reinforced with carbon, silicon carbide, or aluminum oxide fibers. Most of the developments in the MMC materials have been spurred, mainly by applications that require high structural performance at elevated temperatures, the heavy vehicle industry could also benefit from this emerging technology. Increasing requirements of weight savings and extended durability are the main drivers for potential insertion of MMC technology into the heavy vehicle market. Critical elements of a typical tractor-trailer combination, such as highly loaded sections of the structure, engine components, brakes, suspensions, joints and bearings could be improved through judicious use of MMC materials. Such an outcome would promote the DOE's programmatic objectives of increasing the fuel efficiency of heavy vehicles and reducing their life cycle costs and pollution levels. However, significant technical and economical barriers are likely to hinder or even prevent broad applications of MMC materials in heavy vehicles. The tradeoffs between such expected benefits (lower weights and longer durability) and penalties (higher costs, brittle behavior, and difficult to machine) must be thoroughly investigated both from the performance and cost viewpoints, before the transfer of MMC technology to heavy vehicle systems can be properly assessed and implemented. MMC materials are considered to form one element of the comprehensive, multi-faceted strategy pursued by the High Strength/Weight Reduction (HS/WR) Materials program of the U.S. Department of Energy (DOE) for structural weight savings and quality enhancements in heavy vehicles. The research work planed for the first year of this project (June 1, 2003 through May 30, 2004) focused on a theoretical investigation of weight benefits and structural performance tradeoffs associated with the design, fabrication, and joining of MMC components for heavy-duty vehicles. This early research work conducted at West Virginia University yielded the development of integrated material-structural models that predicted marginal benefits and significant barriers to MMC applications in heavy trailers. The results also indicated that potential applications of MMC materials in heavy vehicles are limited to components identified as critical for either loadings or weight savings. Therefore, the scope of the project was expanded in the following year (June 1, 2004 through May 30, 2005) focused on expanding the lightweight material-structural design concepts for heavy vehicles from the component to the system level. Thus, the following objectives were set: (1) Devise and evaluate lightweight structural configurations for heavy vehicles. (2) Study the feasibility of using Metal Matrix Composites (MMC) for critical structural components and joints in heavy vehicles. (3) Develop analysis tools, methods, and validated test data for comparative assessments of innovative design and joining concepts. (4) Develop analytical models and software for durability predictions of typical heavy vehicle components made of particulate MMC or fiber-reinforced composites. This report summarizes the results of the research work conducted during the past two years in this projects

Innovative Structural and Joining Concepts for Lightweight Design of Heavy Vehicle Systems

The extensive research and development effort was initiated by the U.S. Department of Energy (DOE) in 2002 at West Virginia University (WVU) in order to investigate practical ways of reducing the structural weight and increasing the durability of heavy vehicles through the judicious use of lightweight composite materials. While this project was initially focused on specific Metal Matrix Composite (MMC) material, namely Aluminum/Silicon Carbide (Al/SiC) commercially referenced as ''LANXIDE'', the current research effort was expanded from the component level to the system level and from MMC to other composite material systems. Broadening the scope of this research is warranted not only by the structural and economical deficiencies of the ''LANXIDE'' MMC material, but also by the strong coupling that exists between the material and the geometric characteristics of the structure. Such coupling requires a truly integrated design approach, focused on the heaviest sections of a van trailer. Obviously, the lightweight design methods developed in this study will not be implemented by the commercial industry unless the weight savings are indeed impressive and proven to be economically beneficial in the context of Life Cycle Costs (LCC). ''Bulk Haul'' carriers run their vehicles at maximum certified weight, so that each pound saved in structural weight would translate into additional pound of cargo, and fewer vehicles necessary to transport a given amount of freight. It is reasonable to ascertain that a typical operator would be ready to pay a premium of about $3-4 for every additional pound of cargo, or every pound saved in structural weight. The overall scope of this project is to devise innovative, lightweight design and joining concepts for heavy vehicle structures, including cost effective applications of components made of metal matrix composite (MMC) and other composite materials in selected sections of such systems. The major findings generated by this research effort in its first two years have been summarized in the 2003 and 2004 Annual Progress Reports of DOE's Freedom Car and Vehicle Technologies Program. Consistent interactions with producers of heavy trailers, such as Great Dane and Wabash, as well as with their users, such as Old Dominion Freight Lines, have continued during this period to ensure that the research conducted at WVU will yield practical results that will benefit the industry in the near future. Furthermore, Dr. Gergis William and Mr. Thomas Evans participated in the 2005 Technology and Maintenance Council (TMC) annual meeting held in Tampa, Florida, in February 2005. This event offered the WVU researchers an effective opportunity to explore various technical needs and concerns of the industry, both from the performance and maintenance viewpoints, as well as to assess realistically potential benefits and barriers associated with practical implementation of lightweight materials and design technologies in heavy vehicle structures

Analytical and experimental methodology for evaluating passively damped structural joints

Ph.D.Lawrence W. Rehfiel

Fatigue of Quasi-Isotropic Laminated Composite Cylinders Under Tension-Tension Loading

Life prediction techniques for structural composites are based on test data obtained from coupon specimens. A tension fatigue life prediction methodology based on a through-thickness damage accumulation model is used to predict the fatigue failure of composite coupon specimens. Its applicability to thin-walled cylindrical specimens is in vestigated by comparing the fatigue behavior of composite coupon specimens to that of composite thin-walled cylindrical specimens. AS4/3501-6 graphite-epoxy coupon speci mens and thin-walled cylinder specimens with the same layup sequence of [0/ ± 45/90]s were tested under static and fatigue loading conditions. Reasonably good agreement is found between the measured and predicted lives of the coupon specimens. Although the ultimate stresses of coupon and cylindrical specimens are different, it is observed that their fatigue lives at the same percentage of ultimate stress are nearly identical, independent of the coupon edge effect. It is concluded that the fatigue life prediction methodology for coupon specimens could be extended to estimate the fatigue life of the thin-walled graphite/epoxy composite cylinders used in this study