Composite Prepreg Tack Test ASTM D8336, Adhesive Peel Test Fixture is a new peel test has been developed which quantifies the tack and dynamic stiffness of uncured prepreg. The test is designed to simulate the automated tape lay-up (ATL) and automated fibre placement (AFP) processes. It includes a pressure controlled application stage, where contact time is inversely proportional to peel rate. The use of a thin film allows stiffness to be isolated from peel resistance in a continuous two stage test. A repeatability study revealed consistent results with 16% standard deviation. Tack and stiffness variability has been observed across roll width and between faces in commercial hand lay-up prepregs. The overall tack and stiffness values for commercial hand lay-up prepregs were found to be inconsistent with the levels specified by manufacturers.

The ASTM D8336 test fixture consists of two pairs of opposing 25 mm diameter rollers connected to the fixture body via low friction bearings. The first pair of rollers aligns and supports the prepreg sample, while the second pair of rollers provides compaction for the prepreg sample, simulating the layering process. The compaction force is applied by two springs installed at the end of the compaction roller at the lower part. The compression force can be adjusted by rotating the two lifting screws that connect the top of the compression spring to the fixture body. The testing fixture is installed on the base of the universal testing machine. The upper end of the sample is inserted into the mechanical vise fixture connected to the weighing sensor above the fixture.

Two types of prepreg samples can be tested (Figure 2), depending on whether the viscosity measurement is performed between two prepreg layers (Method I) or between the prepreg layer and a rigid metal substrate (Method II). In both cases, the width of the prepreg strip is 75 millimeters (3 inches) and the length is at least 215 millimeters (8.5 inches). A rigid substrate (usually a stainless steel plate) is 80 millimeters (3.15 inches) wide and at least 140 millimeters (5.5 inches) long.