Abstract
This paper deals with the theoretical aspects of laminated composite materials subjected by torsional stress and the effect of the void in matrix on their static strength. Three kinds of internal resisting moments in the materials take place when the torque moment act on the laminated composite materials perpendicular to the direction of laminated layers.
(1) The moment caused by the inter-laminae shear stress.
(2) The moment due to the distortion of each layer.
(3) The moment due to the bending of the laminated layers apart from the center of torque moment applied on the materials.
The torsional strength and the torsional rigidity of the laminated materials are calculated by summing up these three moments.
The calculated results were compared and in good agreement with the observed ones.
An empirical formula to predict the internal damage of the materials subjected to the stress is given as the result of the water immersion tests in order to examine the effect of void upon the static strength.
