Numerical and experimental validation of a theoretical model for bimaterial helical springs

This article deals with the numerical and experimental validation of a theoretical elastic model for bimaterial helical springs developed by the authors in a recently published article. The numerical validation is performed on finite element models involving one half turn of several springs identified by three spring indices (c=D/d= 3, 5, 10) and three section types (solid homogeneous, solid bimaterial and thin hollow). The experimental validation involves compression tests on two polymer (acrylonitrile butadiene styrene) spring configurations produced by rapid prototyping and cladded by ionic infiltration with CrNiCo alloy. For the larger prototype spring, the stresses are measured on the outside of the coil by means of miniature strain gauges. The numerical results confirm the theoretical stress concentration factors within an error of 5%. The experimental results closely agree with the predicted spring rates of all springs, either fully polymeric or bimaterial. In addition, the strain gauge measurements on the instrumented spring correlate well with the theoretical stresses calculated for that particular geometry.