Laminated plate theory (LPT)

Laminated plate theory (LPT) or classical lamination theory (CLT) is the basic design tool for evaluating different laminates when experimental data are not available. LPT can be used to combine properties and the orientation of each ply in a predetermined stacking sequence to predict the overall performance characteristics for a laminate. LPT is based on the assumptions that the laminate deforms under conditions of plane stress and that the strains experienced by the individual layers of the laminate are compatible with the strains in the neighbouring layers. The mechanical properties (i.e. the moduli and poisons ratios)of the unidirectional composite are required before LPT can be applied and these are best obtained from mechanical tests. In-plane loading and loading from bending can be considered. LPT can also be used to assess the stresses that arise through temperature and moisture changes. This theory provides the in-plane stresses and strains for each lamina of the laminate and can be combined with failure criteria for individual plies.

Key aspects of LPT include:

• Used in situations where loading is uniform in-plane or from bending
• Used to analyse stress fields that are free from local stress concentrations
• Easily combined with failure criteria to identify first ply failure
• Rapid solutions can be extracted allowing multiple designs to be analysed
• Implemented in many software packages