In Chapter 1 we discussed the durability assessment of composite structures, the
overall goal for the subject of this book. As outlined there in Figure 1.1, the
mechanisms of damage and their effects on deformational response constitute the
main thrust of the field of damage mechanics, which is at the core of durability
assessment. After discussing the physical nature of damage observed
experimentally in Chapter 3, the next two chapters treated the two main
approaches in damage mechanics – micro-damage mechanics (MIDM) and
macro-damage mechanics (MADM), both aimed at predicting deformational response
at fixed damage. Damage evolution was treated in Chapter 6, while Chapter 7 was
devoted to fatigue, a subject that requires special attention due to the
conceptual difficulties it poses.
In closing the book we wish in this chapter to review what has been achieved and
what directions the field of damage and failure of composite materials should
pursue to further advance toward durability assessment and beyond.
Computational structural analysis
Obviously, complex structural geometries require computational structural
analysis. The analytical modeling of damage initiation and evolution, and its
effects on deformational response of composite laminates, discussed in previous
chapters, were developed for idealized simple cases. Direct application of these
models is limited to structures with simple geometry and loading conditions. For
complex geometries, such as an airplane wing or a wind turbine blade, usually
subjected to multi-axial mechanical loads, and possibly combined with thermal
and moisture environments as well as manufacturing-induced residual stresses,
computational approaches are inevitable. In industry, one often uses commercial
software, e.g., ANSYS, ABAQUS, and NASTRAN, and the obvious need is to integrate
damage and failure analyses into these codes. Efforts have been made to attempt
some simple test cases where FE analysis of composites is combined with damage
using failure criteria [1]. A series of World Wide Failure Exercises (WWFE)
[2–4] have been conducted to compare several composite failure models with
experimental data and provide guidance for their usage in composite design.