Design and Analysis of Composite Structures for Automotive Applications

9Equivalent Beams of Helical Anisotropic Springs

9.1 Helical Compression Springs Made of Composite Materials

9.1.1 Statics of the Equivalent Beam for an Anisotropic Spring

For the substitution of helical compression springs, a filamentary‐wounded composite helical compression spring was primarily developed. With a circular cross‐section, a weight reduction of around 50% compared to a steel compression is realistic. The fibers are wound over a thin fiber core in a +45° and −45° arrangement until the finished cross‐section is produced. The cross‐section is then wrapped around the negative mold. The blanks must harden in the autoclave under high pressure and temperature. The finished spring can simply be removed from the negative mold. Frequently, the so‐called “lost form” principle is used, whereby the negative form is no longer used after one occasion. An advantage of the winding process is the hardening of the springs in the autoclave, which allows a large number of springs to harden in parallel.

On the actual compression spring (helical or meander‐shaped) and the hypothetical beam, the equal force and moment act. Under these conditions, the axial s and lateral s_Q displacement of a spring element (coil or meander) correspond to the displacements of the hypothetical beam. Therefore, the hypothetical beam is also referred to as the equivalent beam. An equivalent beam deforms exactly like a compression spring under the same load (Figure 9.1). Analysis of space‐curved beams and, ...