PSI - Issue 68

R. Lach et al. / Procedia Structural Integrity 68 (2025) 1337–1342 R. Lach et al. / Structural Integrity Procedia 00 (2025) 000–000

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based UD tapes investigated and the varied processing parameters are summarised in Table 1. For the PA6/CF based UD tapes the fibres were plasma-treated to activate their surface (see Table 2); furthermore, the processing parameters were varied too. Based on the reference adjustment previously obtained by optimization processes of the laboratory-scale impregnating tool the impact of selected processing parameters and/or fibre treatment on the mechanical and fracture mechanics properties of the UD tapes was investigated. Morphological parameters such as the roughness data were used to trigger morphology–property relationships.

Table 1. Variation of processing parameters of the PP/GF-based UD tapes investigated.

UD tape

Variation of processing parameters

153 157 160 165 172

Reference Increase of the pull-off force Reduction of opening of the mould Increase of the line speed Increase of the pull-off force at higher drive shaft

Table 2. Variation of plasma treatment of the PA6/CF-based UD tapes investigated.

UD tape

Variation of plasma treatment: pressure gas type, flow rate

343 344 345 346 347 348 349 350

Reference Air, 110 l/min Air, 80 l/min

Nitrogen, 100 l/min Nitrogen, 100 l/min

Air, 110 l/min Air, 80 l/min Air 110 l/min

2. Morphology of the UD tapes From micrographs obtained by means of a digital reflected-light microscope using polished cross-sections of selected UD tapes (see Fig. 2a and 3a), the thickness of the UD tapes, the formation of the matrix-rich surface layers and channels within the cross-section, the fibre distribution and the structural homogeneity differ highly depending on processing parameters and/or fibre treatment (Tillner et al., 2020; Lach and Teuscher, 2023). These different structural parameters are strongly affecting the fracture mechanics properties (see below). On example of the UD tape 172, Fig. 2b gives a representation of a 3D surface scan using a profilometer. Already macroscopically, surface features such as fibre bundles are easily visible. Furthermore, inappropriate processing parameters, which result in a pulsating production process, for example, can be detected without problems. Fig. 3b shows a 3D surface scan of a PA/CF-based UD tape using a profilometer.

a

b

Fig. 2. (a) Cross-section of a PP/GF-based UD tape; (b) profilometer-supported 3D surface scan of a PP/GF-based UD tape.

Based on these 3D scans, the line roughness to be composed on the roughness values R a und R z cross to fibre orientation and in fibre orientation was quantified. R a is the mean surface roughness i.e. the mean distance from measuring points on the surface to the mean line. R z is the so-called average peak-to-valley height and is related to