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Thermoplastic fiber composite components may soon help keep cars safer in a collision.
Steel used to be the primary material for cars, but modern cars now consist of a mixture of steels, aluminum and fiber-reinforced plastics. Highly stressed load-bearing structures and crash components designed to buckle on impact help reinforce the body in order to protect the vehicle‘s occupants in the event of a collision. Automakers previously constructed these parts from composites using a thermoset (i.e. infusible) matrix. But this approach has a number of disadvantages. In addition to being difficult to mass produce, it can also be potentially hazardous since this material tends to “delaminate” into sharp-edged splinters in a collision. An additional problem is the fact you cannot recycle thermosets.
There is now a solution to the problem, said researchers from the Fraunhofer Institute for Chemical Technology ICT in Pfinztal, Germany. They developed a new class of materials designed for large-scale use in vehicle construction: Thermoplastic fiber composite materials. Once they have reached the end of their useful life, users can shred them, melt them down and then reuse them to produce high-quality parts. They also perform significantly better in crash tests: Thermoplastic components reinforced with textile structures absorb the enormous forces generated in a collision through viscoelastic deformation of the matrix material, without splintering.
It was difficult to create a suitable manufacturing technique for thermoplastic composite structures made from high performance fibers, but the ICT engineers developed a process suitable for mass production which makes it possible to make up to 100,000 parts a year.
“Our method offers comparatively short production times,” said 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 researchers named their technique thermoplastic RTM (T-RTM). It comes from the conventional RTM (Resin Transfer Molding) technique for thermoset fiber composites. The researchers form the composite in a single step.
“We insert the pre-heated textile structure into a temperature-controlled molding tool so that the fiber structures are placed in alignment with the anticipated stress. That enables us to produce very lightweight components,” Gittel said. The preferred types of reinforcement comprise carbon or glass fibers, and the researchers have also developed highly specialized structures. The next step involves injecting the activated monomer melt into the molding chamber. This contains a catalyst and activator system – chemical substances required for polymerization. One of the innovated parts is the researchers can select the system and the processing temperature in a way that enables them to set the minimum required processing time.
A demonstration part confirmed the benefits of this new class of material: The trunk liner for the Porsche Carrera 4 weighs up to 50 percent less than the original aluminum part. To improve the crash behavior of the vehicle’s overall structure, the ICT engineers also calculated the optimum fiber placement. Another advantage of the T-RTM process is 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 these kinds of components will start to see use in vehicle and machine construction as well as in the leisure industry.

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