Autohesion model for thermoplastic composites

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Virginia Polytechnic Institute and State University

A non-isothermal autohesion model was developed by combining a transient finite element heat transfer model with the isothermal autohesion model. Heat transfer analyses and the interfacial strength development analyses were conducted using the non-isothermal autohesion model on a polysulfone (Udel P1700) compact tension specimen, a 64-ply graphic (Thomel T300)/P1700 unidirectional composite, and a 192-ply graphite (Hercules AS4)/P1700 unidirectional composite. A 64-ply T300/P1700 unidirectional composite was processed in a matched metal mold. Temperature data were taken and compared with the calculated values. Good agreement was observed between the calculated and the measured temperature values.

A healing test which aimed at studying the interplay bond development in AS4/P1700 unidirectional composites was performed. The double cantilevered beam (DCD) Mode l fracture toughness test was selected. The DCB specimens were fractured and healed in a special fixture with different combinations of temperature pressure, and time. The healed DCB specimens were refractured and the critical strain energy release rates (GIC) were measured. The pressure was found to be a key factor in the healing process. Temperature and time dependencies of the interply bond development were also observed.

The non-isothermal autohesion model predicted a higher strength achieved in a shorter time. This was due to the extra time which was needed for the fracture interface to achieve intimate contact, and the assumption of the initial intimate contact achievement of the non-isothermal autohesion model.