In the framework of a collaborative project between ASME, NASA, and NIST, quasi-static fracture toughness tests were performed at liquid nitrogen temperature (77 K, or 196 °C) and liquid helium temperature (4 K, or -269 °C) on precracked SEN(B) specimens extracted from the centers of four separate lots of welded 316L stainless steel plates. Although the plates were produced in accordance with the same specifications from the same material (316L), large differences in fracture toughness have been observed, with the toughest weld exhibiting almost twice the critical toughness of the least tough at 77 K (219 kJ/m2 vs. 113 kJ/m2), and about seven times the critical toughness of the least tough at 4 K (146 kJ/m2 as compared to 21 kJ/m2). Charpy absorbed energies previously obtained at 77 K for three of the four welds were found to be strongly linearly correlated with fracture toughness at both test temperatures, with an exception represented by the fourth weld, which provided the highest impact toughness and the second lowest quasi-static fracture toughness. Dynamic toughness measurements at impact loading rates were also performed on precracked SEN(B) specimens, in order to deconvolute the roles of strain rate and notch sensitivity on the fracture properties.
EXTENDED ABSTRACT

Slip-critical bolted connections are prone to developing fretting damage between the contacting surfaces. In this study, the effect of two different bolt preload values, 90 and 145 kN, on the fretting fatigue behaviour of steel double-lap bolted joints with a Class B (shot-blasted) surface under high-cycle fatigue conditions is investigated experimentally and numerically. The experimental results show that increasing the bolt preload decreased the total fretting fatigue life significantly. Moreover, the proposed numerical method was able to predict crack initiation and crack propagation behaviours successfully.
EXTENDED ABSTRACT

The strength loss due to welding process poses a high risk of catastrophic rolling contact fatigue failure in the heat affected zones of flash-butt rail welds. Accurate characterisation of fatigue crack growth behaviour in such regions can provide a database for developing safer and more efficient maintenance strategies. This extended abstract details an experimental study on fatigue crack growth behaviour in flash-butt welds in a hypereutectoid rail steel with a hardness level of over 400 HV. Groups of mixed mode fatigue crack growth tests were carried out at parent rail region, partially spheroidised region, fully spheroidised region, re-austenitised region and bond line region. Fractographic analysis was performed to aid the application of the marker band method as well as to analyse the morphology of fracture surfaces. Once all experiments are finished, an equivalent stress intensity factor formula will be fitted to quantify the mixed mode crack driving force in different regions, and modifications of crack growth direction prediction criteria will be proposed for crack growth under the influence of microstructural variation. The current work will provide a reliable database for predicting rolling contact fatigue crack growth at different regions in flash-butt rail welds.
EXTENDED ABSTRACT