Using Simulation for Accurately Modeling Fiber-Reinforced Composites

Designing lighter products, whether they’re as large as jet liners or as small as mobile phones, has always been smart business. Less material means less cost and lower energy consumption, both in production and operation. Lower production costs mean higher profit margins for manufacturers. Lower operational costs lead to broader customer acceptance and higher market share.

These days, the “smart business” in lighter products has been upgraded to “essential ingredient.” Lower weight and material efficiency are mandatory for companies that expect to succeed in markets coping with volatile energy prices and increasing environmental regulations. Higher energy prices cause sharp swings in production costs. Manufacturing a product and its component materials means more predictable costs and higher profit margins.

End products are also subject to more scrutiny during their operational lives. Vehicles have to squeeze more miles out of every gallon to satisfy mandates such as U.S. corporate average fuel economy (CAFE) standards

For decades, making a product lighter meant optimizing designs to cut out mass that wasn’t needed to achieve engineering goals. Now, extensive use of fiber-reinforced composites has introduced a new weight-saving measure into product design. Especially in vehicle design but also in appliances and industrial machinery, composites offer comparable strength to metal at a fraction of the weight.

However, introducing composites into product design requires extensive testing. Composites’ plasticity means they do not perform as predictably as metals under real-world conditions. Many manufacturers qualify composites through extensive physical testing on prototypes. This is expensive, time consuming, and can be replaced by simulation – provided that simulation evolves to accommodate composites. Otherwise, they will not yield accurate material allowables, and inaccurate allowables can lead to poor product performance or outright failure.

Simulation technology has traditionally focused on metals. Composites, however, have different properties from metals. For example, a metal-stamped part will behave the same way regardless of how it is manufactured. 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.

Those additional variables complicate engineers’ tasks. They can optimize a design for maximum lightness but end up with a different set of problems because the composite won’t perform the way they expected. Engineers must be able to simulate the strength of composites in different configurations and through various manufacturing processes down to the microstructure level. However, simulation technology hasn’t accommodated them so far.

Most simulation solutions depict composites as “black aluminum.” They represent a composite part’s geometry, but not the full range of its properties. Composite suppliers provide their customers with property data, but that data seldom takes into account the manufacturing process’ influence on the material. Entered into a simulation, these data points will not produce accurate results.

Without accurate material modeling and simulation, designers have to approximate how the composite will perform under real-world conditions. That often 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.

Many simulation technology vendors have incorporated some level of non-uniform material behavior into their solutions. However, these solutions only simulate composite behavior on the surface. A truly realistic model requires an intelligent handle on:

• individual 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.

Giving engineers that precision opens a new range of possibilities for making products lighter without sacrificing performance. For example, 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. The mount weighs 1.2 kilograms. Simulation reveals that the engine mount performs its function under normal loads and in normal operating conditions.

Through virtual simulations to analyze the composite’s behavior in that shape and function, the design team does a series of iterations, analyzes 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 composites with the same precision they have for simulating metals. It’s the approach that manufacturers need to incorporate in bringing composites into their designs while keeping prototyping costs. The result will be lower material use and energy consumption in production and operation, and more accurate material and part performance. These essential qualities will enable manufacturers to meet the new economic realities of rising energy costs and the societal obligations of sustainability through lighter, better products.

This article was contributed by Dr. Roger Assaker, PhD,  founder and CEO of e-Xstream Engineering, and also chief material strategist at MSC Software. Please see http://www.mscsoftware.com/product/digimat for more information.)

Tags: composites, Digimat, fiber-reinforced composites, MSC Software, Roger Assaker, simulation

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