Abstract: Quasi-isotropic laminates have isotropic elastic properties in all yn-plane directions.Therefore,this kind of laminate is widely used for structural elements.The simplest stacking sequence of quasi-isotropic laminates is[0/-60/60]s.When the direction of applied axial lood to[0/-60/60]s laminate is inclined at a 30-degree angle,we have the other quasi-isotropic laminate [30/-30/90]s under axial load.The failure mecha-nisms of these two lamibnates are,however,entirely different from each other because these two laminates have different distribution of the interlaminar stresses.It was confirmed by tensile fatigue tests that the [0/-60/60]s laminate does not show any vis-ible fatigue damage,but the[30/-30/90]s laminate develops edge-delamination

Key words: composite, delamination, fracture,