Experimental Determination of the In Situ Transverse Lamina Strength in Graphite/Epoxy Laminates

The uniaxial tensile load at which transverse cracking initiated in the 90 deg. laminae of (0 2/90 n ) s , (±30/90 n ) s and (±60/90 n ) s , n =1,2,4,8, T300/934 composite laminates was determined experimentally using DIB enhanced x-radiography. "In situ" transverse strengths of the 90 deg. laminae corresponding to these loads were then calculated based upon lamination theory predictions including the effects of residual thermal stresses. These in situ strengths, which were as high as 2.5 times the unidirec tional transverse strength, were found to depend strongly on both the 90 deg. laminae thickness and orientation of adjacent laminae suggesting that transverse strength should not be considered as an intrinsic lamina property.

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