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Nondestructive investigation of the VHCF-endurance on cyclically loaded CFRP by X-Ray-Refractography

  • Carbon fiber-reinforced-plastics (CFRP) are already used under high-cycle- (HCF) and very-high-cycle-fatigue (VHCF) at relatively low loads not only in aerospace industry, but also in other growing markets like especially wind energy and increasingly also automotive industry. While the static strength of CFRP is satisfyingly predictable by means of layerwise-strenght-analysis and material data from single layers, it is more and more uncertain to predict residual strength or lifetime as the design lifetime increases. Previous studies showed that local minor cracks and inter-fiber-fracture (IFF) originate long before total failure of single layers. Reliable fatigue estimation for fiber-reinforced-plastics is not available at present. Subsequently safety-related primary structures made out of FRP are over dimensioned. It is possible to detect the change of inner surface in a specimen by means of X-Ray-Refractography. This includes voids, intact fiber-matrix-interfaces as well asCarbon fiber-reinforced-plastics (CFRP) are already used under high-cycle- (HCF) and very-high-cycle-fatigue (VHCF) at relatively low loads not only in aerospace industry, but also in other growing markets like especially wind energy and increasingly also automotive industry. While the static strength of CFRP is satisfyingly predictable by means of layerwise-strenght-analysis and material data from single layers, it is more and more uncertain to predict residual strength or lifetime as the design lifetime increases. Previous studies showed that local minor cracks and inter-fiber-fracture (IFF) originate long before total failure of single layers. Reliable fatigue estimation for fiber-reinforced-plastics is not available at present. Subsequently safety-related primary structures made out of FRP are over dimensioned. It is possible to detect the change of inner surface in a specimen by means of X-Ray-Refractography. This includes voids, intact fiber-matrix-interfaces as well as defective ones, cracks and all interfaces in plane with the X-Ray-beam. As the crack-density (including IFF) increases, the inner surface of the material correspondingly increases. The borderline where even at high cycles no early cracks were detected was identified for selected laminates out of woven and non-crimped fabric with epoxy-matrix. When no micro-cracks were detected up to 106 cycles, the specimens also lasted in the VHCF-regime. Furthermore for the epoxy resin LY556 in combination with carbon fiber it was distinguished that at a load minor to 50% IFF-load level, no micro cracks were detected and consequently the VHCF-endurance reached. The integration of the set-up small-sized testing machine into the X-Ray buildup in order to achieve in-situ non-destructive detection of the crack initiation while loading the specimens (CFRP and GFRP- woven fabric and non-crimped-fabric) at the same time will increase the performance of the studies. In earlier investigations at BAM it was shown, that the matrix has a strong influence on the micro-crack formation and finally on the total lifetime. In order to determine the influence of the matrix properties on the boarderline to infinite life, research is done on laminates while replacing the epoxy-based matrix with an equivalent one with different fracture mechanical properties. With the evolution of early cracks and IFF monitored as well as the influence of the matrix on the crack propagation investigated we are working on an appropriate model to improve lifetime prediction in CFRP. This work is done within the priority program “infinite life” (SPP 1466) funded by Deutsche Forschungsgemeinschaft (DFG).zeige mehrzeige weniger

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Metadaten
Autoren/innen:Alexander Müller
Koautoren/innen:Volker Trappe
Dokumenttyp:Vortrag
Veröffentlichungsform:Präsentation
Sprache:Englisch
Jahr der Erstveröffentlichung:2016
Organisationseinheit der BAM:5 Werkstofftechnik
5 Werkstofftechnik / 5.3 Mechanik der Polymerwerkstoffe
DDC-Klassifikation:Technik, Medizin, angewandte Wissenschaften / Ingenieurwissenschaften / Ingenieurwissenschaften und zugeordnete Tätigkeiten
Freie Schlagwörter:CFRP; FRP; Micro cracking; X-Ray
Themenfelder/Aktivitätsfelder der BAM:Material
Veranstaltung:MSE 2016
Veranstaltungsort:Darmstadt,Germany
Beginndatum der Veranstaltung:27.09.2016
Enddatum der Veranstaltung:29.09.2016
Verfügbarkeit des Dokuments:Datei im Netzwerk der BAM verfügbar ("Closed Access")
Datum der Freischaltung:13.01.2017
Referierte Publikation:Nein