Volume 10, Issue 3, 2001

STIFFNESS REDUCTION OF COMPOSITE LAMINATES UNDER COMBINED CYCLIC STRESSES

T. P. Philippidis, A. P. Vassilopoulos

University of Patras, Department of Mechanical Engineering & Aeronautics, Section of Applied Mechanics, P. O. Box 1401, 265 00 Patras, Greece,  (Tel./Fax +3061-997235, e-mail:philippidis@mech.upatras.gr)

(Received 1/01; accepted 6/01)

ABSTRACT

Stiffness reduction due to fatigue of a [0/(±45)2/0]T Glass/Polyester (GRP) laminate under combined cyclic stress is investigated in this experimental study. Stress states combining all three components of in-plane stress tensor are induced by uniaxially testing specimens cut off-axis at various angles from the principal material co-ordinate system. Modulus reduction is related to the various failure modes exhibited under different states of combined stress. It is verified that shear and transverse normal stress induce more severe stiffness degradation compared to stress states where normal stress in the main fibre direction is dominant. For every loading condition and stress state, it is observed in general that stiffness decrease is more pronounced under lower stress levels than these inducing low cycle fatigue.