Understanding and predicting stiffness in advanced fiber-reinforced polymer (FRP) composites for structural applications

This is an updated version of the chapter on the elastic properties of advanced fiber-reinforced composites starting from the basic constituents, i.e., the fiber and matrix. The general structure is the same to preserve the chapter coherence. The number of bibliographic references doubled as a reflex of the performed updates.

The analytical and numerical tools for the prediction of the elastic properties of the composites comprise the micromechanics approaches based on the elastic properties of the basic constituents. It also includes comparative analysis between experimental and predicted final density of composites based on the rule of mixtures. The content was updated to include recent developments using new material examples providing a comprehensive view of the models’ prediction capability. The classical lamination theory is included due to its importance to calculate the elastic properties of multidirectional laminates.

The concept of master ply properties is introduced in this updated version. This new invariant-based theory of composites explores the scaling property of the trace (an invariant) of the plane stress stiffness matrix of composites (now Tsai’s Modulus) leading to the concept of master ply properties. The use of Tsai’s Modulus as a material property reduces the number of variables, the number of tests for composite laminates characterization and simplifies the design of laminates. Initially developed for carbon-reinforced polymer composites, these master ply properties proved inadequate for aramid and glass-reinforced polymer composites. Yet, this strict assessment was revised to extend this for those composite materials. The use of this concept allows a general overview of the in-plane and flexural engineering constants of carbon-reinforced polymer composites laminates, rather than looking for a specific material case as in the original chapter.

The last section provides an updated overview of the methods to identify the elastic proprieties based on full-field measurements. Optical methods allow a new perspective in the mechanical characterization of advanced composite materials. The full-field optical method coupled with a suitable identification strategy can determine several constitutive parameters on single test configurations. This makes these methodologies suitable for the elastic characterization of anisotropic and heterogeneous materials.