Stress analysis of composite material structures

In the application of composite materials where the stateof stress may not be predictable or where it is known that thestresses are approximately equal in all directions,unidirectional composites may not be suitable. suchapplications require composites that have approximately equalstrengths in all directions. Multilayered composites can beconstructed from layers of unidirectional laminates havingdifferent fiber orientations so that the resulting composite is.essentially isotropic in a plane. Such composites have thedisadvantage that, although the overall composite is equallystrong in all directions, the surface layers, where the failureis quite often initiated, are still very weak in the transversedirection. In applications where protection from a corrosiveenvironment is an important factor, such as in storage tanks inchemical industries, and in many applications in the automobileindustries, composites of unidirectional laminates do not solvethe problem completely. Thus, it is advantageous to have eachlayer or lamina isotropic in some applications. An effectiveway of producing an isotropic layer is to use randomly orientedfibers as the reinforcement.In the present work we studied the mechanical ·behaviourand the manufacturing quality parameters for in-plane randomglass fiber/polyester composite plates produced by a handlay-up technique for a wide range of fiber weight ratio (Wf*=15-55%).A statistical analysis based on 2 and 3-parameter weibullfunctions were used to predict a new empirical relationsbetween the fiber volume ratio V f and the other manufacturingquality parameters fiber weight ratio Wf, void content V,density p & moisture content H, also a new relations betweenc