Implications of Interlaminar Stresses

The existence of interlaminar stresses means that laminated composite materials can delaminate near free edges whether they be at the edge of a plate, around a hole, or at the ends of a tubular configuration used to obtain material properties. In all cases, delamination could cause premature failure so must be considered in specimen design because othen/vise the specimen does not represent the true physical situation. 

In Boundary-Layer Region vs. z (After Pagano smd Pipes [4-15]) 

In summary, three classes of interlaminar stress problems exist  

The significance of interlaminar stresses relative to laminate stiffness, strength, and life is determined by Classical Lamination Theory, i.e., CLT stresses are accurate over most of the laminate except in a very narrow boundary layer near the free edges. Thus, laminate stiffnesses are affected by global, not local, stresses, so laminate stiffnesses are essentially unaffected by interlaminar stresses. On the other hand, the details of locally high stresses dominate the failure process whereas lower global stresses are unimportant. Thus, laminate strength and life are dominated by interlaminar stresses. 

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