A study on the validity of various fracture criteria of angle-ply-laminated composites is presented for in-plane loading. Special emphasis is given to the vectorial presentation of the J-integral as a suitable candidate for fracture characterization of composites under general combined loading. The combined loading which is composed of a simultaneous tension, shear and in-plane bending in any desired proportion, has been produced in a highly computerized fashion by a specially devised apparatus at the U.S. Naval Research Laboratory. The fracture data of several angle ply laminates of carbon/epoxy composite (T300/5208) result from prescribing the foregoing three combined radial loading until fracture. Aided by numerical stress analysis (finite-element program) the data points are cast into more well-known descriptions; namely, crack-opening displacement versus crack-sliding displacement. Mode-I stress-intensity factor (KI) versus Mode-II stress-intensity factor (KII) and energy-release rate vector Jx versus Jy. The main outcome is that the data displayed on the J-integral plane have a highly distinctive nature of aligning the data points along straight lines, thus a clear discrimination between the fracture properties of different angle-ply laminates can be characterized by only two parameters. The ability to infer fracture conditions in subcomponents from tests on small coupons is assessed.

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