EFFECTS OF DELAMINATION AND PLY FIBER WAVINESS ON EFFECTIVE AXIAL ANDBENDING STIFFNESSES IN COMPOSITE LAMINATES

An analytical method based upon a sublaminate modeling approach was de veloped to quantify the loss of the effective axial and bending stiffn esses due to defects in laminates. Defects considered were single and multiple delaminations as well as ply fiber waviness. Laminates with ( 45 degrees, -45 degrees, 0 degrees, 90 degrees, 0 degrees, 90 degrees) (s) layup of AS4/35016 graphite/epoxy were used to investigate the sti ffness loss due to defects at various interfaces and with various perc entages of overlap in the multiple delaminations. It was found that th e reductions of the stiffness in a given direction is more pronounced if the thinner sublaminate of the delaminated laminate contains a ply which contributes more stiffness in that direction. For multiple delam inations, reduction of stiffness increases as the overlap percentage o f two delaminations decreases. The loss of axial and bending stiffness is significant if a ply contributing more stiffness in the laminate c ontains a fiber waviness.