Simulating Composites for Lighter Designs

Cargo pallet made from composite material. (Image courtesy of Carbon Freight.)

When Carbon Freight set out to design and engineer the world’s lightest air cargo pallet, it turned to computational simulation to bring the product to market quickly and inexpensively. The goal was to take advantage of new composite materials in designing a durable and lightweight pallet that would save the airline industries millions of dollars in fuel costs. According to CEO Glenn Philen, “Simulation enables us to innovate our solution and get our products to market faster with the confidence that they will be right the first time.”

Carbon Freight is not alone in this pursuit. Designing innovative components and products through novel, lightweight materials continues to be one of the key enabling technologies for both aerospace and automotive sectors in their pursuit of reduced energy usage and emissions. The aerospace industry has evolved from metal parts and structures to long-fiber composite materials over the course of the past 40 years. In fact, more than half of the airframe for the Boeing 787 is made from advanced composites, including carbon fiber reinforced polymers, contributing to that the fact that it is the industry leader in fuel efficiency. The automotive industry has been slower to adopt new materials, but progress is being made, as evidenced by Ford switching the body of its F-150 pickup from steel to aluminum in 2015.

In reducing structural weight though, designers cannot compromise safety, as structural integrity and designing for crashworthiness are key design drivers. Understanding how aluminum or composite structures and materials perform over their lifecycles under static and dynamic loading requires expertise in a range of areas. Successful composite use is far more complicated than a drop-in replacement. As these factors suggest, and as new material technologies emerge, there is a growing need for advancements in computational prototyping and simulation to enable composite-specific design.

What is unique and challenging about composites is that product architecture, material, manufacturing and assembly are much more closely coupled than with traditional materials and must be considered simultaneously in overall relation to weight, performance and cost. To understand design tradeoffs in product architecture, a designer must first have a firm understanding of the material properties and behaviors available. While the properties of many common composites have been cataloged, for example by MatWeb, the infinite possibilities of material combinations and production approaches mean your ideal composite might not be cataloged yet. To make matters worse, the fiber orientations assumed in the as-designed composite structure are frequently different from the fiber orientations in the as-built composite structure. This means the fundamental material properties of the composite structure are often misunderstood because the orientation of the fibers is central to their definition.

Residual stresses and distortion during a curing process. (Image courtesy of ANSYS.)

One useful computational tool to help designers better understand the dynamic properties of composite products in development is ANSYS Composite Cure Simulation (ACCS). ACCS works with ANSYS Composite PrepPost to simulate the curing process. Together, both tools are capable of simulating the entire composite manufacturing process, including layup and curing, resulting in a detailed material variability specification.

Richard Mitchell, lead product marketing manager for structures at ANSYS, describes the software this way: “ACCS was developed in response to the growing market demand for a reliable simulation platform to support manufacturing and tooling engineers throughout the process design cycle. The platform has been comprehensively validated and subsequently used to compensate millions of pounds’ worth of rib, spar and wing-skin tools across the aerospace and wind energy industries, where previously the only method of achieving parts of sufficiently high tolerance to meet strict aerospace assembly rules was to re-machine finished tooling after molding the first part.”

ACCS prediction of polymerization, glass transition temperature and exothermic heat in curing process. (Image courtesy of ANSYS.)

Once the material specification is complete, the ANSYS Composite PrepPost software provides all of the necessary functionalities to execute a finite element analysis of layered composite structures in a “model as you build it” approach. In a recent example, KTM Technologies used the ANSYS Composite PrepPost software to reduce the weight of its composite KTM X-Bow race car, the world’s first monocoque production car.

The KTM X-Bow. (Image courtesy of ANSYS.)

According to KTM CEO Peter Martin, “The first monocoque designs of the KTM X-Bow were engineered without the use of ANSYS Composite PrepPost. When we did employ the ANSYS software for composites, we were able to reduce the monocoque’s weight—a very important aspect of sports car design—by 20 percent.”

In conclusion, composite materials in engineering are gaining popularity with manufacturers due, in part, to their lightweight properties, strength and durability. The design of composite parts involves more unknowns and interdependencies than does that of a metallic part design, and serial design processes can necessitate inflated design allowances and safety factors that act to negate the inherent material advantages. Concurrent simulation tools enabling optimization of closely coupled product architectures, materials, manufacturing and assembly are evolving in order to enable these innovators to achieve more fully optimized designs and shorter lead times.

ANSYS has sponsored this article and provided access to their products and people. They have provided no other editorial input. All opinions are the authors, except what is quoted.

About the Author

Stewart Bible is a principal engineer at Resolved Analytics. His interest in computational fluid dynamics began with his undergraduate and graduate research at the University of Kentucky, where he encountered his first commercial CFD code, CFD2000, ironically enough, in the year 1999. His current interests are in the areas of multiphysics and uncertainty quantification, with particular emphasis on medical devices, renewable energy and air pollution control systems.