Modeling effect of anomalies

Several types of anomalies or flaws occur during manufacturing and service of composite structures. Excluding holes that were discussed in Section 6.3, impact damage and delaminations that are discussed within the context of damage tolerance in this 

Porosity is discussed here briefly as an example. The size of individual pores or voids is assumed to be small so each of them is completely encased by matrix in the composite. The voids are assumed to be spherical and are modeled as cracks of the same size. Then, the matrix properties in the presence of porosity can be determined by considering a new material with the basic matrix properties and randomly interspersed cracks. This problem has been solved by Budiansky and O Connel [26] within 

The Young s and shear moduli Ey and Gy of the porous matrix, respectively, can be found to be  

It is important to note that the size of the voids Ry does not affect the values of the stiffness properties of the porous matrix because as Ry changes, the number of voids per unit volume n changes accordingly, thus canceling out this effect. 

Once the new matrix properties accounting for porosity are known, the ply-level stiffnesses can be determined using micromechanics, and then the classical laminated plate theory outlined in previous sections can be used. 

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