Design and Analysis of Composite Structures for Automotive Applications

12Hereditary Mechanics of Composite Springs and Driveshafts

12.1 Elements of Hereditary Mechanics of Composite Materials

12.1.1 Mechanisms of Time‐Dependent Deformation of Composites

The stiffness and strength of a composite material forms the basis of the mechanical properties of a laminate. In general anisotropy and spatial stress states, the generalized Hooke's law is used to establish the relationship between stress and strain. However, the material law of linear elasticity law describes the dependence between the stress and strain of a material only at considerably low temperatures. With increasing temperatures, pure elastic, time‐independent deformation is complemented by different hereditary effects, such as viscoelasticity (Kerner 1956). Different deformation processes (e.g. quasi‐static loading, short‐term and long‐term creep, stress relaxation and cyclic loading) can be described by equations with a definite set of parameters (Rabotnov 1980). This approach is known as hereditary mechanics.¹

Composite materials with polymer matrix demonstrate pronounced time‐dependent behavior. Therefore, to make a prediction of long‐term performance of structural members, hereditary effects must be accounted for. Principally, there are two distinct physical mechanisms of hereditary behavior of composite materials. First, there is the “true creep” in the matrix material, because the matrix exhibits distinct viscoelastic behavior, typical for polymer materials (Tschoegl 1990). For temperatures ...