Numerical and experimental stiffness evaluation of CFRP leaf and coil springs

This paper presents the design, manufacturing and testing of Carbon Fibre-Reinforced Polymer (CFRP) springs for lightweight automotive applications. A first test case consists of a leaf spring, which was optimized for the use in a small car. A design method made guided by a multilevel numerical modelling is developed to evaluate the influence of the chassis-leaf spring connection on the suspension stiffness. Experimental tests showed good accordance with the numerical prediction, justifying the goodness of the spring design, in terms of both static stiffness and strength. As a second test case, a low-pressure Resin Transfer Moulding is proposed for the manufacture of composite coil springs with non-flattened, open ends. A non-conventional fixture is here presented for the experimental measure of the stiffness of multiple coil springs with different geometries, with a sustainable cost. The experiments show that numerical predictions overestimate the experimental stiffness by at most 34%, suggesting that the manufacturing process might still be tailored for better predictability.