Brandt, Robert
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Publication Access status: Metadata only , Experimental Investigation of Unidirectional Glass-Fiber-Reinforced Plastics under High Strain RatesWhen a vehicle leaves the road, crash barriers stop it and prevent significant damage to the vehicle, its environment, and the occupants. Typically, such protection systems are made of simple steel, but fiber-reinforced composites can efficiently absorb and dissipate the impact energy at high-risk locations. In order to design such protective systems, material parameters under dynamic loading are necessary. Here, split Hopkinson pressure bar tests with unidirectional glass-fiber-reinforced epoxy of 58% glass fiber content are performed. The elastic response at strain rates between 300/s and 700/s in the loading direction parallel and perpendicular to the fiber is determined. From the measured data, a model of the time dependence of the elastic modulus is derived to enable the design engineer to lay out protective systems made of such GFRPs.Source Type:Article3 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Torsional fatigue behaviour and damage mechanisms of martensitic spring steel in the HCF regimeThis study investigates the fatigue behaviour and damage mechanisms of the martensitic spring steel SAE 9254, with emphasis on short crack propagation. Shear stress-controlled torsional fatigue tests are performed at stress ratio R = -1 and test frequency f = 79 Hz using structure-sensitive measurement techniques to detect the relevant damage mechanisms. An in-situ torsional fatigue testing device is applied for shear-controlled fatigue tests at two amplitudes of the torsion angle using R = –1 and f = 5 Hz, and the microstructural-dependent short crack propagation path is documented by means of confocal laser microscopy and electron backscattering analysis. It is found that the early development of fatigue damage is characterised by the formation of slip bands, which serve as crack initiation sites. In this process, crack initiation occurs preferentially at or near prior austenite grain boundaries. Furthermore, prior austenite grain boundaries were identified as obstacles for the propagation of short cracks, because of the change of the crystallographic orientation leading to an oscillating propagation rate of short cracks. The short crack density ρCD, which is an important parameter for fatigue damage, is rapidly growing with increasing shear stress amplitude ΔτT/2 and reveals a stress type specific behaviour.Source Type:Article4
