A new analysis method was presented to explain asymmetrical weld marks occasionally observed in the section of symmetrically molded products of FRP. At first, a possibility of initial deformation before material flow was calculated by eigenvalue analysis. Next, a model which could simulate the part of infinitesimal deformation was proposed, and by using this model the initial deformation mode was calculated by linear incremental analysis considering the above result. This showed that the

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... l flow might be asymmetrical even if the flow canal is symmetrical. Finally, the flow analysis employing a conventional technique for composite materials was performed considering the above result of linear analysis. As an application of this method, the effect of interface which existed in hybrid lamination, on flow pattern was investigated numerically and experimentally. The numerical analysis that was developed in this paper could simulated the growth of weld line. The numerical model which contains isotropic lamina between each laminates was effective to simulate the behaviour of laminated materials such as hybrid lamination during compression molding process. And both are phenomenologically in good agreement. The numerical analysis also suggests that hybrid lamination, that is, the combined use of sheet molding compounds of different rigidity is a useful way to minimize weld marks in the molded product.