Simulation is a natural solution to these problems. But just as design has had to adapt to wider plastic and composite use, so does simulation. Spec ifically, a large blind spot in simulation technology has to be eliminated — namely, accurately representing plastics and composites.

The multi-scale modeling approach starts with an in-depth investigation of composite materials on the microscopic level. Homogenization technology delivers micromechanical models that can take into account the impact of the fiber orientation on the material properties. In structural analyses, be it on dumbbell, part, or system level, such material models can be coupled with results from processing simulations.
Most simulation solutions represent plastic as “black metal” and composite as “black aluminum.” Most vendors have incorporated some level of non-uniform material behavior into their solutions. However, it’s only at the surface level. A truly realistic model requires an intelligent handle on:

• Individuals properties of the fiber and the matrix;
• The composition of the overall materials; and
• Manufacturing processes’ influence.

Conventional simulation tools do an excellent job of modeling a party’s geometry, loading, deformation physics, etc. Incorporating detailed material behavior for composites drives further precision into the simulation lifecycle.

Unlike metal properties, plastic and composite properties can change significantly depending on the manufacturing process they go through. A metalstamped part will behave the same way, for the most part, regardless of how it is produced. By contrast, the manufacturing process can change a fiber-reinforced plastic part’s behavior significantly because the process can affect the orientation of the fibers in the material’s epoxy resin matrix. Properties listed in a material manufacturer’s data sheet often do not take the manufacturing process’ influence on the material into account.

Design engineers must take that into account to guard against failure. Designers can approximate how the new material will perform, but that inevitably leads to over-designing to guard against failure. Over-designing undermines the purpose of designing with plastic or composite in the first place — using less material and reducing weight. It also adds unnecessary cost.

Simulation technology developers must respond with a new generation of simulation tools that accurately represent plastic and composite behaviors in real operational conditions.

Simulate, Don’t Prototype

Multiscale analysis of a frontal car crash incorporating an injection-molded bumper beam. The comparison shows maximum principle stresses obtained with an isotropic and an anisotropic micromechanical material model. As can be seen, switching to a multiscale analysis changes not only the local stresses, but also the failure behavior of the described part.
Automotive OEMs cannot afford to produce physical models to evaluate every iteration of a part of a subsystem. We’ll use the term prototyping to describe this part- and assembly-level testing, though in the automotive industry, that term is usually reserved for complete vehicles assembled for system-level track or crash testing. At the part and assembly level, physical model testing usually consists of production part approval process (PPAP) builds or validation tests as opposed to full prototyping.

Regardless of what you call it, minimizing physical modeling and testing is a key imperative in automotive design. Composites are much more expensive than metals. Their cost is offset by properties that enable engineers to combine many functions and parts into a single assembly. However, if it takes more physical modeling to perfect compositebased designs, their advantages erode.

This is the way designing with composites should work: An automotive OEM wants to re-design a metal engine mount in composite to save weight. Design engineers develop the basic geometry for the new mount in a 3D CAD environment. It weighs 1.2 kilograms. Simulation reveals that the engine mount performs its function under normal loads and in normal operating conditions.

Through finite element analysis to analyze the composite’s behavior in that shape and function, the design team does a series of iterations, simulates the mount’s performance, and reduces its mass by 40 percent without compromising performance. The lower mass shaves 15 percent from the mount’s cost.

This is what design teams can achieve when they have the tools to model and simulate new materials with the same precision they have for modeling metals. Plastic and composite simulation is an essential process for developing the new vehicles that will deliver higher fuel economy and lower costs and carbon emissions.

This year, BMW plans to put its zeroemission i3 sedan into full production. It will be the first mass-market vehicle with a carbon composite body. The light body enables the plug-in hybrid to go farther between charges. BMW is estimated to be three to five years ahead of the industry in large-scale composite vehicle manufacturing.

With the cost of finite element analysis technology dropping and usability improving sharply, other automotive OEMs have a valuable tool for creating their own lightweight vehicles. Highend simulation and analysis will enable them to work with composites and plastics throughout the design cycle, from the idea phase to end-of-life. The key is accurately simulating the behavior of these new materials in actual working conditions on a computer screen and not through an endless string of expensive prototypes.

This article was written by Dr. Roger Assaker, founder and CEO of e-Xstream Engineering (Mont-Saint-Guibert, Belgium) and Chief Material Strategist at MSC Software (Santa Ana, CA); and Dr. Prabhakar Vallury, Director of Business Development at e-Xstream Engineering. For more information, visit http://info.hotims.com/45602-121.

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