TY - THES

T1 - Characterization of the in-situ effect in cross-ply laminates using acoustic emission analysis and optical crack detection

AU - Paulczinsky, Laurin

N1 - no embargo

PY - 2024

Y1 - 2024

N2 - The master thesis investigates the in-situ effect on cross-ply laminates made of a carbon fibre reinforced (CFRP) and a glass fibre reinforced (GFRP) plastic prepreg with the same matrix. The cross-ply laminates have a [0°/90°n/0°] ply structure. The in-situ effect refers to the fact that 90° plies embedded in a multidirectional laminate have a higher strength than unidirectional laminates transverse to the fibre direction. To investigate the damage behavior of the 90° plies in the cross-ply laminates, quasi-static tensile tests and fatigue tests are performed in combination with optical crack detection and acoustic emission analysis. While optical crack detection can only be used for transparent GFRP laminates, acoustic emission analysis is possible for GFRP and CFRP. In particular, the influence of the number of embedded 90° plies (n = 1, 2, 3 and 4) on the in-situ strength is investigated and compared with the strength of unidirectional laminate samples transverse to the fibre direction. In summary, it can be said that both optical crack detection and acoustic emission analysis can detect the development of damage during quasi-static and cyclic loading. Due to the different measurement principles of the methods, the results must be interpreted accordingly and can be influenced by different potential sources of error. Optical crack detection provides a quantitative measure for crack density but does not take into account other types of damage, such as delamination. One potential source of error is artifacts in the test specimen from laminate production that are mistakenly detected as cracks. The acoustic emission analysis detects any type of damage and associated mechanisms, e.g. friction of crack flanks under cyclic loading. Possible sources of error are, for example, sensors that are not coupled well enough to the test specimen surface. The in-situ effect is observed in the CFRP, but not in the GFRP cross-ply laminates. One possible explanation why the in-situ effect is observed in CFRP laminates and not in GFRP laminates could be the higher stiffness of the outer 0° CFRP layers compared to 0° GFRP layers. The higher the stiffness of the 0° layers, the more likely crack initiation and growth is suppressed in the 90° layers.

AB - The master thesis investigates the in-situ effect on cross-ply laminates made of a carbon fibre reinforced (CFRP) and a glass fibre reinforced (GFRP) plastic prepreg with the same matrix. The cross-ply laminates have a [0°/90°n/0°] ply structure. The in-situ effect refers to the fact that 90° plies embedded in a multidirectional laminate have a higher strength than unidirectional laminates transverse to the fibre direction. To investigate the damage behavior of the 90° plies in the cross-ply laminates, quasi-static tensile tests and fatigue tests are performed in combination with optical crack detection and acoustic emission analysis. While optical crack detection can only be used for transparent GFRP laminates, acoustic emission analysis is possible for GFRP and CFRP. In particular, the influence of the number of embedded 90° plies (n = 1, 2, 3 and 4) on the in-situ strength is investigated and compared with the strength of unidirectional laminate samples transverse to the fibre direction. In summary, it can be said that both optical crack detection and acoustic emission analysis can detect the development of damage during quasi-static and cyclic loading. Due to the different measurement principles of the methods, the results must be interpreted accordingly and can be influenced by different potential sources of error. Optical crack detection provides a quantitative measure for crack density but does not take into account other types of damage, such as delamination. One potential source of error is artifacts in the test specimen from laminate production that are mistakenly detected as cracks. The acoustic emission analysis detects any type of damage and associated mechanisms, e.g. friction of crack flanks under cyclic loading. Possible sources of error are, for example, sensors that are not coupled well enough to the test specimen surface. The in-situ effect is observed in the CFRP, but not in the GFRP cross-ply laminates. One possible explanation why the in-situ effect is observed in CFRP laminates and not in GFRP laminates could be the higher stiffness of the outer 0° CFRP layers compared to 0° GFRP layers. The higher the stiffness of the 0° layers, the more likely crack initiation and growth is suppressed in the 90° layers.

KW - in-situ Effekt

KW - Kreuzlagenlaminaten

KW - GFK

KW - CFK

KW - quasistatische Zugversuche

KW - Ermüdungsversuche

KW - optischer Rissdetektion

KW - Schallemissionsanalyse

KW - in-situ

KW - cross-ply laminates

KW - static tensile tests

KW - fatigue tests

KW - optical crack detection

KW - acoustic emission analysis

U2 - 10.34901/mul.pub.2025.022

DO - 10.34901/mul.pub.2025.022

M3 - Master's Thesis

ER -