In this study, ultrasonic pulse velocity (UPV) and ultrasonic shear-wave tomography are combined to measure the residual compressive strength (RCS) of small-scale lining concrete blocks and to detect inner defects in the lining structure. The characteristics of and variations in the RCS of test blocks after being exposed to elevated temperatures (200–800 °C) and constant heating times (2 h, 3 h, and 4 h) were studied. At 800 °C, the RCS values reduced by 64.4%, 69.2%, and 74.6% at heating times of 2 h, 3 h, and 4 h. Scanning electron microscopy (SEM) was used for the micro-phase analysis of the samples that had been exposed to high temperatures. The heating time and RCS as well as the SEM micro-structure relationship were compared. Finally, a tunnel lining slab sample was designed to simulate the post-fire damage inside the blocks. Additionally, shear-wave tomography with 32 probes was able to detect the ϕ10 mm void defects at a depth of 200 mm.
The strain rate-related creep-fatigue (CF) interactions on the long-term service damage of 9%Cr steel-welded joint were investigated at low-strain amplitude (0.2%). Initially, the average CF life gradually increased from 1,103 to 2,185 cycles as strain rate increased from 0.0001 to 0.002 s À1 , and then it slowly decreased from 2,185 to 1,503 cycles as continuously increase the strain rate from 0.002 to 0.005 s À1 . By increasing strain rates, the microscale observation indicates the CF fracture location could be shifted from the fine-grained heataffected zone (FGHAZ) to the base metal (BM) region. Meanwhile, the local microscale mechanical properties including hardness, elastic modulus, creep resistance, and strain rate sensitivity on the fractured specimens with a series of strain rates were detected by instrumental nanoindentation. With increasing CF strain rates, the nanoindentation hardness and creep resistance evidently dropped. Based on the characteristics of microstructural evolution and the variation in local mechanical properties, strain rate effects of CF interaction on fracture mechanism of the welds were systematically discussed.
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