The effect of drilled and moulded-in circular holes of woven fabric composites on failure strength have been examined in flexural test. Three types of woven fabric-reinforced composite systems were used: glass fiber (E glass), Kevlar fiber, and glass- Kevlar hybrid in polyester matrix. All these types are of (30%) volume fraction, and hole diameter of (1, 2, 3, 4 and 5 mm) for each type. ISO standard flexural specimens were tested and repeated three times.
It is noticed that the specimens with moulded-in holes exhibit failure strengths higher than those of drilled specimens by (7- 24%). Also the values of stress concentration factors (Kt) increase with increasing the hole size for all types of laminates, and they were arranged in an ascending order as follows: Kevlar/ polyester, glass-kevlar hybrid/ polyester, and glass/ polyester.