Investigation on the crack evolution in glass-fiber laminates depending on the stacking sequenceMittwoch (26.06.2019) 13:40 - 14:00 Uhr
The aim of this work is to investigate the fatigue behavior of Glass Fiber Reinforced Plastics (GFRP) of flat and tubular specimens. Static tension and fatigue tests are performed to investigate the mechanics which lead to the first failure (transverse crack) as well as the fatigue life until crack saturation (CDS).
Using the roving filament winding and resin transfer moulding technique flat and tubular specimens with three different layups ([0/90/90/̅0̅]s, [0/905/0], [02/͞9͞0]s) are manufactured. Flat specimens are tested under tension-tension loading. Tubular specimens are multiaxially loaded under tension-torsion loading with three different load vectors (0°, 30° and 60°). Prior to fatigue testing a crack evolution curve is recorded for each layup and specimen type. Fatigue tests are performed, load controlled, on servo hydraulic testing devices with a load ratio of R = 0.1 and a frequency of f = 5 Hz. The crack evolution curves from the static tests are used to define three load levels for each specimen layup to obtain S-N curve data. Each fatigue load level is below the value of static first crack nucleation.
Three different techniques are used for damage monitoring. For measuring the degradation during fatigue testing the specimen stiffness is characterized at the beginning and after several load cycles. After each characterization transmitted light photography is used to determine crack length growth data for crack density evaluation. To prevent specimen heating cooling techniques are used. Additionally infrared camera imaging is used for monitoring hot spot formation on the tubular specimen.
The phenomenological stiffness degradation model of Adden  is used for predicting specimen degradation on basis of the crack density data. Due to the fact that all testing is aborted after reaching CDS the shear lag model of Garrat and Bailey  is adopted for predicting specimen failure.
 S. Adden, Schädigungsverhalten von glasfaserverstärkten Kunststoffen aus Multiaxilgelegen unter biaxialer Ermüdungsbelastung, Dissertation, TU Braunschweig, Inst. f. Flugzeugbau und Leichtbau, 2009
 J.M. Berthelot, Transverse cracking and delamination in cross-ply glass-fiber and carbon-fiber reinforced plastic laminates: Static and fatigue loading, Appl. Mech. Rev 56(1), pp. 111-147, 2003