TY - BOOK

T1 - Optimisation of the winding process by minimizing the critical failure potential during fibre roving delivery

AU - Maier, Alexander

N1 - no embargo

PY - 2016

Y1 - 2016

N2 - Polymer matrix composites offer outstanding possibilities of designing and producing load-tailored structures and provide exceptional mechanical properties combined with low specific weight. During the last decades, these materials were mainly applied to the aircraft and the aerospace industry. Within the last ten years the approach to composite materials has changed and now higher quantities also for applications in the commercial automotive sector are aspired. While the material properties and the lightweight potential outweighed economic considerations in the past, the required quantities in the arising product markets set new challenges to the productivity and also the production costs of composite parts nowadays. The manufacturing processes used for continuously fibre reinforced composite structures are by now mostly proved from the industry. One of these manufacturing processes is the winding technology. This technology is mainly used for rotationally symmetrical composite parts such as tanks for storage of alternative fuel media in the automotive industry. During the winding process, dry or with resin pre-impregnated fibres are continuously delivered to a mandrel, on which the fibres are winded in defined patterns. Critical influencing factors on the final part quality are the preload within the fibres, which can be adjusted specifically during the delivery, and the accuracy of fibre positioning on the mandrel. The cycle times are mainly limited by the chosen matrix system and the required, specific curing time. Beyond that, the cycle time itself can be shortened by process optimisation. High processing speed in combination with high fibre pre-loads lead to high mechanical loads in the reinforcing fibres. Consequently, unwanted fibre fracture can occur and result in expensive production downtimes and the production of waste. In the present work, the mechanical behaviour of dry glass fibre bundles was investigated under process-similar conditions in order to optimise the fibre delivery during the winding process and to prevent unwanted fibre fracture in the future. Due to the fact that the mechanical characterisation of dry glass fibre bundles in process-similar dimensions is not a common task at all, a test set-up for mechanical tests was initially developed. Dry fibres were tested in tensile tests with a variety of free gauge lengths and at different strain rates. To reconstruct real complications during the winding process, dry fibre bundles were deliberately twisted and mechanically loaded with off-axis tensile loads. Moreover, tests with dry bundles were compared to tests with resin impregnated samples. In addition to that isolated fibres were separated from the bundles and tested. The results of these various tests showed that the maximum fibre tensile load depended on the free gauge length as a result of the statistical defect influence. This effect was monitored in single fibre tests with short free gauge lengths and also in an intensified way in tests with bundles with process-similar lengths. Furthermore, the results indicated that the tensile load of fibres during the delivery in the winding process was not only affected by the statistical defect probability but also by the interactions within the bundles. In order to analyse these coherences in a systematic way, glass fibres were chemically treated and the standardly present sizing on the glass fibres was removed. Based on the presented investigations conclusive recommendations for the various parameters of the fibre delivery in the fibre winding process such as free gauge length, off-axis loading and shear behaviour or surface properties of the glass fibres could be given. In conclusion the gained results improve the understanding of the factors affecting the tensile strength of glass fibre bundles within the winding process and can help to prevent unwanted fibre fracture in the future.

AB - Polymer matrix composites offer outstanding possibilities of designing and producing load-tailored structures and provide exceptional mechanical properties combined with low specific weight. During the last decades, these materials were mainly applied to the aircraft and the aerospace industry. Within the last ten years the approach to composite materials has changed and now higher quantities also for applications in the commercial automotive sector are aspired. While the material properties and the lightweight potential outweighed economic considerations in the past, the required quantities in the arising product markets set new challenges to the productivity and also the production costs of composite parts nowadays. The manufacturing processes used for continuously fibre reinforced composite structures are by now mostly proved from the industry. One of these manufacturing processes is the winding technology. This technology is mainly used for rotationally symmetrical composite parts such as tanks for storage of alternative fuel media in the automotive industry. During the winding process, dry or with resin pre-impregnated fibres are continuously delivered to a mandrel, on which the fibres are winded in defined patterns. Critical influencing factors on the final part quality are the preload within the fibres, which can be adjusted specifically during the delivery, and the accuracy of fibre positioning on the mandrel. The cycle times are mainly limited by the chosen matrix system and the required, specific curing time. Beyond that, the cycle time itself can be shortened by process optimisation. High processing speed in combination with high fibre pre-loads lead to high mechanical loads in the reinforcing fibres. Consequently, unwanted fibre fracture can occur and result in expensive production downtimes and the production of waste. In the present work, the mechanical behaviour of dry glass fibre bundles was investigated under process-similar conditions in order to optimise the fibre delivery during the winding process and to prevent unwanted fibre fracture in the future. Due to the fact that the mechanical characterisation of dry glass fibre bundles in process-similar dimensions is not a common task at all, a test set-up for mechanical tests was initially developed. Dry fibres were tested in tensile tests with a variety of free gauge lengths and at different strain rates. To reconstruct real complications during the winding process, dry fibre bundles were deliberately twisted and mechanically loaded with off-axis tensile loads. Moreover, tests with dry bundles were compared to tests with resin impregnated samples. In addition to that isolated fibres were separated from the bundles and tested. The results of these various tests showed that the maximum fibre tensile load depended on the free gauge length as a result of the statistical defect influence. This effect was monitored in single fibre tests with short free gauge lengths and also in an intensified way in tests with bundles with process-similar lengths. Furthermore, the results indicated that the tensile load of fibres during the delivery in the winding process was not only affected by the statistical defect probability but also by the interactions within the bundles. In order to analyse these coherences in a systematic way, glass fibres were chemically treated and the standardly present sizing on the glass fibres was removed. Based on the presented investigations conclusive recommendations for the various parameters of the fibre delivery in the fibre winding process such as free gauge length, off-axis loading and shear behaviour or surface properties of the glass fibres could be given. In conclusion the gained results improve the understanding of the factors affecting the tensile strength of glass fibre bundles within the winding process and can help to prevent unwanted fibre fracture in the future.

KW - Filament winding

KW - Winding process optimisation

KW - Glass-fibre mechanics

KW - Mechanical characterisation

KW - Dry fibre bundle mechanical behaviour

KW - Continuous manufacturing process

KW - Kontinuierliche Verbundverarbeitung

KW - Optimierung des Wickelprozesses

KW - Mechanische Charakterisierung von Glasfasern

M3 - Doctoral Thesis

ER -