Analysis of Multi-layer Isotropic Materials

The Plate Constitutive equations can be used for curved plates provided the radius of curvature is large relative to the thickness (typically r/h 50). They can also be used to analyse laminates made up of materials other than unidirectional fibres, eg layers which are isotropic or made from woven fabrics can be analysed by inserting the relevant properties for the local 1-2 directions. Sandwich panels can also be analysed by using a thickness and appropriate properties for the core material. These types of situation are considered in the following Examples. 

Example 3.14 A blow moulded plastic bottle has its wall thickness made of three layers. The layers are  

If the diameter of the bottle is 160 mm, calculate the hoop and axial strains in the bottle wall when an internal pressure of 200 kN/m is applied. Calculate also the stresses in the individual layers. 

Solution Although the composite wall is curved, the r/h) value is large and so it can be analysed using the method illustrated for laminates. In this case, each ply is isotropic and so the properties do not vary with 6. It is thus necessary to get Q for each ply relative to the centre line of the wall thickness 

The values of stress may be checked by simple equilibrium analysis. 

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