The studied material was uncured thermoset prepreg 8552/AS4 for all standard (ST) experiments and Hexply 8552/IM7 for the slit tape (SL) experiments. The prepreg roll was cut into smaller sections and then piled up depending on the number of plies (16, 24, or 32) and the ply configuration. Two configurations were studied: unidirectional (UD) and cross-ply (CP). The stacked laminates were then cut with a digital cutting system (Zünd M-1200 CV) into pieces of 20x20 mm. A similar procedure was followed for the preparation of slit-tape samples. However, the first layer was created by parallelly positioning the tapes on a plastic film. The second layer of tapes was placed with a 50 % staggering between the layers. Two sets of experiments were carried out. The first one, involved a full factorial test to study the effect of temperature (25-85 oC with 10 oC intervals) and pressure magnitude (0,1-0,8 MPa with 0,1 MPa intervals), as well as their interaction, on the thickness variation of a UD aerospace qualified prepreg stack (HexPly 8552/AS4). The second set consisted of executing a fractional factorial test to examine the influence of the number (16, 24, 32 plies) and configuration of plies (UD and CP), as well as the width of the tapes (standard UD or slit tapes) on the compaction behavior of the prepreg stack. For this experiments the temperature was set to 55 oC and the compaction pressure to 0.5 MPa. The compaction was carried out in a customized compaction program using the Rheometer (Anton Paar MCR 302). During this program the sample is heated to the desired temperature for 5 min. Then, the initial thickness is measured by applying a force of 0,1 N for 1 min. Afterward, a compaction cycle was executed for each of the plies on the stack. Each compaction cycle comprises: (1) application of force until it reaches 105% of the desired force, (2) compaction for 3 s, (3) release of force, and (4) release time for 30 s. The results were exported directly from the rheometer as tables in csv file type. It must be noted that the files with a pressure level of 0,1 and 0,2 (until 55 oC) MPa did not reach the sample during the initial thickness measurement. This change only had an impact on the first stage of the rheometer, which included heating the sample and measuring the initial thickness. Therefore the initial thickness for these samples was calculated using a mean value from the samples within the same laminate. The average initial thickness of the samples cut from the same laminate was 3.53 mm, with a standard deviation of 0.025.     «

The studied material was uncured thermoset prepreg 8552/AS4 for all standard (ST) experiments and Hexply 8552/IM7 for the slit tape (SL) experiments. The prepreg roll was cut into smaller sections and then piled up depending on the number of plies (16, 24, or 32) and the ply configuration. Two configurations were studied: unidirectional (UD) and cross-ply (CP). The stacked laminates were then cut with a digital cutting system (Zünd M-1200 CV) into pieces of 20x20 mm. A similar procedure was foll...     »