Sebastian Henschel

Crack initiation at high loading rates applying the four-point bending split Hopkinson pressure bar technique

Dynamic crack initiation with crack-tip loading rates of

Effect of Filter Coating on the Quasi-Static and Cyclic Mechanical Properties of a G42CrMo4 Casting†

\dot{K} \approx 2 \cdot 10^6\,\mathrm {MPa\,m^{0.5}\,s^{-1}}

Study of dynamic crack formation in nodular cast iron using the acoustic emission technique

K˙≈2·106MPam0.5s-1 in a high strength G42CrMoS4 steel was investigated. To this end, a previously developed split Hopkinson pressure bar with four-point bending was utilized. V-notched and pre-cracked Charpy specimens were tested. The detection of dynamic crack initiation was performed by analyzing the dynamic force equilibrium between the incident and the transmission bar. High-speed photography of the tests and analysis of the dynamic stress intensity factor revealed that the vibration of the specimen had to be considered. The dynamic and static analyses of the tests lead to nearly the same results when a force equilibrium was achieved. Fracture-surface analysis revealed that elongated MnS inclusions strongly affected both the dynamic crack initiation and growth. Blunting of the precrack did not take place when a group of MnS inclusions was located directly at the precrack tip. Due to the direction of the elongated MnS inclusions perpendicular to the direction of crack growth, the crack could be deflected. The comparison with a 42CrMo4 steel without elongated MnS inclusions revealed the detrimental effect in terms of resistance to crack initiation.

Microstructure and mechanical properties of bulk TiN–AlN composites processed by FAST/SPS

Abstract The determination of velocity and displacement evolution of the specimen in a low-blow Charpy impact test was critically analyzed. To this end, a laser-based measurement of velocity and displacement was applied in addition to the standard integration procedure. The applicability of this non-contact method was investigated with respect to the measurement of velocity and detection of vibrations. It was shown that the velocity of the specimen could be determined in the case of unnotched specimens as well as of notched and precracked specimens. Utilizing the velocity evolution of the specimen determined by the laser, the dynamic force calibration was possible. The high sensitivity of the laser measurement to changes in velocity enabled the detection of pop-ins and, in some cases, the detection of stable crack initiation. The analysis of the specimen vibration frequency directly after the test could be utilized to estimate the final crack length.