Berner (1997) studied matrix damage of cross-ply laminate by combining a simplified
micro-mechanics model with finite element analysis and showed that the prediction of
damage is improved substantially with the incorporation of residual stresses. Aoki et al.
(2000) modeled and successfully predicted the leakage through the matrix cracks.
The present objective is to investigate options available to minimize the increase in
thickness due to thermal residual strains for laminates designed subject to thermal and
mechanical loads. Deterministic designs were performed to investigate the following
effects: (i) temperature dependant material properties for strains analysis, (ii) laminates
designed to allow partial ply failure (matrix cracking), and (iii) auxiliary stiffening
solutions that reduce the axial mechanical load on the tank wall laminates.
Composite Laminates Analysis under Thermal and Mechanical Loading
Since the properties of composite materials, such as coefficients of thermal
expansion and elastic moduli, change substantially with temperature, classical lamination
theory (CLT) (e.g., Giirdal et al. 1999) is modified to take account of temperature
dependent material properties. The stress-free strain of a lamina is defined as
EF (Ia F = GAT, Where a is the coefficient of thermal expansion (CTE). When a is
a function of temperature T, the stress free strain is given by the expression
aF = a(T)dT (4-1)
where Tero is the stress-free temperature of the material and Tserwce, is the service
temperature. From the equilibrium equation and vanishing of residual stress resultant, the
equilibrium of a symmetric laminate subjected to pure thermal load with uniform
temperature profile through the thickness can be expressed by