**6. Conclusion**

The problems of interlaminar performance are discussed along with the technique used to measure them and the fracture mechanics principles applied to improve them. The DCB test is a well established test used to measure interlaminar fracture toughness in reinforced composite materials. In this study, interlaminar fracture toughness values are determined by DCB test method Mode I for woven [0°/90°]16 and woven [±45°]16 glass/epoxy composite materials. For investigation of woven angles and specimens width's effect on fracture toughness have been compared. It has been obtained that woven [0°/90°]16 specimens have higher fracture toughness values than, woven [±45°]16 specimens. Some decreases has been eventuated in fracture toughness values by an increase on width. Also, the energy release rate increases with decreasing width length. Therefore, width effect for DCB specimens on fracture toughness value can be neglected. It is also seen that here its no special effect of width on SERR for DCB test specimens. The agreement between the calculated results and the experimental data shows that the finite element analysis method is reliable.

The thickness of material is an important parameter between the state of plane stress and plane strain, and the fracture toughness value can be obtained. For materials with high interlaminar fracture toughness, it may be necessary to increase the number of plies, that is, increase the laminate thickness or decrease the delamination length.
