Effects of hot pressing process on fiber compaction of unidirectional composite laminates

To control the degree of fiber compaction, insure the quality of composites and reduce the cost, it is necessary to study how the state of fiber compaction changes and the factors that affect it. A parameter which is called compaction index I_c is used to show the degree of fiber compaction of unidirectional composite laminates. The greater the I_c, the greater the degree of fiber compaction. For the hot pressing process, the effects of pressure, timing of the applying pressure and the number of layers on I_c were analyzed by means of optical microscope along the thickness of the laminates. The results show that I_c increases nonlinearly with pressure, decreases with the increase of resin viscosity at the timing of applying pressure and reduces linearly with the number of layers. These results provide some important experimental evidence to optimize the hot pressing process and establish a short-distance flow model.