Lightweight Suspension Design with Polymer–Metal Hybrids

Researchers are pushing the boundaries of vehicle mass reduction by testing polymer metal hybrid (PMH) suspension components.

Today, compliance with current regulations challenges vehicle manufacturers to reduce the mass of vehicles increasingly. Already, polymers have replaced many metal vehicle components, such as engine mounts and air intake manifolds. Many components, particularly safety-critical components, are still comprised of metal. One such component is the suspension system, which makes up approximately 25% of vehicle mass. Because this is a significant contribution to vehicle mass, the suspension system draws particular interest from designers. Additionally, reducing vehicle mass brings better handling and thus, better comfort for the driver and passengers.

You can also read: Metal 3D Printing in Mold Making: A Technologies Comparison.

In previous studies, researchers have attempted to manufacture suspension components using continuous fiber-reinforced thermosetting polymers. Solutions using carbon fiber-reinforced polymer (CFRP) offered good stiffness and strength-to-weight ratios but were brittle and prone to failure. Composites using polymer metal hybrid (PMH) technology show promise for lightweight automotive applications. Some popular car manufacturers have used PMH in commercially available automotive front-end modules. Researchers developed a demonstrator for a short fiber-reinforced PMH suspension control arm to investigate further automotive uses of this technology.

Demonstrating a Novel Solution

The demonstrator’s main structure comprised 50% by weight short glass fiber reinforced special polyamide-66 (SGFR-PA66) and a 6061-T6 aluminum insert. The composite structure was the load-bearing element, with the insert to prevent complete separation of the demonstrator at failure. Just like a vehicle’s suspension control arm, the demonstrator must withstand a significant load.

The researchers also created a version of the demonstrator without the aluminum insert, referred to as the “polymeric demonstrator”. Then, they injection molded both versions of the demonstrator and extensively tested their load-bearing behavior. Longitudinal load is the typical type of force transmitted by the wheel of a vehicle to the control arm. To characterize the demonstrator’s performance when subjected to longitudinal load, researchers conducted quasi-static, creep, and impact tests.

Setting a Foundation for Research

During the quasi-static tests, the polymeric demonstrators showed consistent failure at about 6.7 kN. The PMH demonstrators, which had the aluminum inset, failed with larger scatter of maximum loads and corresponding deflections. A surface treatment to promote adhesion between the metal and composite may provide better performance. The location of failure predicted by simulations did not correspond with the experimental location. The simulation assumed perfect composite and insert adhesion, which could be a reason as to why this occurred. An overestimation of the composite shell’s strength at the weld lines could also be a contributing factor.

The creep tests showed that temperature had a large effect on both demonstrators. During the impact tests, researchers confirmed that the metal insert prevents complete separation. All observed failure events had a crack triggered by the flow weld lines. Further research may prioritize adjusting the approach to injection molding to confine the weld lines to non-critical areas.

This study sets a foundation for future research for short fiber reinforced PMH in automotive safety components. Though limitations remain, advanced modelling techniques, increased testing, and better adhesion may improve this novel technology.