How is the conduction in composite materials

Car tires of the future: How does stress hardening work in polymer composites?

Scientists at the Max Planck Institute for Polymer Research (MPI-P) have deciphered how the linear and non-linear mechanical properties in polymer composites - polymers with additional fillers - can be individually influenced. The amount of fillers regulates how pronounced the stress hardening of the material is. The results make it possible to design tailor-made materials, for example for car tires, in order to be able to carry both cyclic and static loads.

Car tires are subject to a large number of different material loads. Thanks to their linear elasticity, tires withstand small deformations and can withstand low cyclical loads. However, they also have to cushion large bumps that occur, for example, when a car drives over speed bumps or curbs. It is therefore important that the material also has non-linear, elastic properties.

How will the car tires of the future be developed?

The optimization of the mechanical properties of polymer composites has so far been based on the trial and error principle. In particular, stress hardening, how a material solidifies under severe deformation and thus becomes more resistant, is currently only done through trial and error. The relationship between the linear and non-linear material properties and the amount and size of the respective filler particles has not yet been clarified. In the science journal Proceedings of the National Academy of Sciences of the United States, a research team led by Dr. Sapun Parekh, project manager at MPI-P, how the elastic properties of composite materials can be precisely designed.

Dr. Parekh and his colleagues used various methods to quantify the amount of filler and the orientation of the polymer chains, including transmission electron microscopy and molecular spectroscopy for real-time analyzes during mechanical deformation. Theoretical modeling techniques helped interpret the experimental results. In this way, the scientists were able to show that the nonlinear stress hardening in composites, mediated by polymer chain alignment, only varies with the number of particles, but not with regard to their size. Using the amount of fillers, engineers can now initially set the non-linear elasticity. Thereafter, the desired linear extensibility can be regulated using appropriately large fillers.

What are composites?

Composite materials consist of a flexible, soft material that is combined with very hard particles such as glass. When mixed together, the various components form so-called composite materials and their mechanical properties are superior to those of the individual components. These improved features can be, for example, a higher elasticity or conductivity, but also a lower weight. At best, a material saving ensures a lower price. Depending on what the material will be used for later, the properties can be varied in a targeted manner. Composite materials are often used in aircraft construction or as sealants in internal combustion engines.