Vehicles used to be predominantly made of steel, but to reduce weight and cost today’s vehicles are now built from a mixture of materials including steels, aluminum and fiber-reinforced plastics. Highly stressed load-bearing structures and crash components constructed from composites are designed to buckle on impact to help reinforce the body and protect the vehicle‘s occupants in the event of a collision. But these materials tend to chip into sharp-edged splinters on impact. Researchers have now found a way for the automotive industry to mass-produce a particularly safe class of materials that can absorb the enormous forces generated in a collision without splintering.

Currently used composites constructed using a thermoset matrix not only tend to splinter, they are also difficult to mass produce efficiently and cannot be recycled. Researchers from the Fraunhofer Institute for Chemical Technology (ICT) claim to have now found a solution to these problems by developing a new class of materials designed for large-scale use in vehicle construction called thermopastic fiber composites.

Not only can they be shredded, melted down and reused to produce high quality parts, they have also been found to perform significantly better in crash tests. When reinforced with textile structures they absorb the forces generated in a collision through viscoelastic deformation of the matrix material – without splintering.

Mass production process

Researchers had previously failed to come up with a suitable manufacturing technique for thermoplastic composite structures made from high performance fibers, but the ICT engineers say they have now developed a process suitable for mass production which makes it possible to manufacture up to 100,000 parts a year.

“Our method offers comparatively short production times,” sayss Dieter Gittel, a project manager at ICT. “The cycle time to produce thermoplastic components is only around five minutes. Comparable thermoset components frequently require more than 20 minutes.”

The Fraunhofer researchers have named their technique “thermoplastic RTM” (T-RTM). It is derived from the conventional RTM (Resin Transfer Molding) technique for thermoset fiber composites and forms the composite in a single step.

“We insert the pre-heated textile structure into a temperature-controlled molding tool so that the fi ber structures are placed in alignment with the anticipated stress. That enables us to produce very lightweight components,” Gittel explains.

The researchers say they have developed some highly specialized structures but the preferred methods of reinforcement comprise carbon or glass fibers. The next step involves injecting the activated monomer melt into the molding chamber. This contains a catalyst and activator system – chemical substances that are required for polymerization. Researchers can select the system and the processing temperature in a way that enables them to set the minimum required processing time.

Porsche demonstrator part

The team constructed the trunk liner for a Porsche Carrera 4 as a demonstration part to confirm the benefits of the material. To improve the crash behavior of the vehicle’s overall structure, the ICT engineers also calculated the optimum fiber placement. The trunk liner weighs 50 percent less than the original aluminum part and will be exhibited at the Composites Europe fair in Essen, Germany from June 14 – 16.

The researchers say that the cost of the thermoplastic matrix material and the cost of its processing are up to 50 percent lower than the equivalent costs for thermoset structures. Over the next few years the researchers anticipate that these kinds of components will start to be used in vehicle and machine construction as well as in the leisure industry.