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Discussion on the Cause of Print-through Phenomenon of FRP and Several Improvement Methods

A print-through phenomenon (PTP) often occurs on the surface of the gelcoat layer of fiber-reinforced plastic (FRP). The fiber prints are visible with the naked eye. According to the scanning profile measured by instruments, the wrinkles indeed exist at the microlevel on the surface. In our previous works, it was concluded that PTP is induced by the nonuniform residual stress that is yielded while the resin hardens. This study further developed this argument regarding the cause of PTP and proved it by experiments. Moreover, several improvement methods to PTP were also tested by changing the configurations of core-mat, gelcoat, and resins to mitigate the tiny-scale deformations on the gelcoat surface. The simulation and experimental results showed that the increase in the thickness of core-mat and gelcoat layers is an effective way of reducing PTP. In addition, from simulation, it was found that searching for a substitution for core-mat, may possibly be another effective way of improving PTP.