A pressure vessel, composed of a welded aluminum liner partially reinforced with thin FRP, has been developed in order to achieve a considerable reduction in weight of a delivery type vessel for liquefied petroleum gas. In this paper, an emphasis is placed on investigation into damage of FRP layer. In case that a penetrated type cut damage in the perpendicular to fiber direction occurs in the FRP layer, unstable cracks to the fiber direction grow from both tips of cut damage by tensile stress in the fiber direction, and a band-like partial separation of FRP layer from the aluminum liner occurs. First, it is indicated that this FRP pressure vessel maintains sufficient strength even though such a band- like separation would occur. Second, a failure criterion of a circumferential crack growth from cut damage introduced into the FRP hoop layer is studied using FEM analyses and experiments of equivalent test pieces to the FRP layer of the vessel. This criterion can be expressed by an average shear stress and a characteristic damage area on the basis of a modified average stress model. Application of this criterion into an actual FRP pressure vessel demonstrates that an allowable size of the penetrated type cut damage could be predicted using the criterion within a practical accuracy.
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