Dynamic Mechanical and Microstructural Properties of Outburst-Prone Coal Based on Compressive SHPB Tests

Understanding the dynamic mechanical behaviors and microstructural properties of outburst-prone coal is significant for preventing coal and gas outbursts during underground mining. In this paper, the split Hopkinson pressure bar (SHPB) tests were completed to study the strength and micro-structures of outburst-prone coal subjected to compressive impact loading. Two suites of coals—outburst-prone and outburst-resistant—were selected as the experimental specimens. The characteristics of dynamic strength, failure processes, fragment distribution, and microstructure evolution were analyzed based on the obtained stress-strain curves, failed fragments, and scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) images. Results showed that the dynamic compressive strength inclined linearly with the applied strain rate approximately. The obtained dynamic stress-strain responses could be represented by a typical curve with stages of compression, linear elasticity, microcrack evolution, unstable crack propagation, and rapid rapture. When the loading rate was relatively low, fragments fell in tension. With an increase in loading rates, the fragments fell predominantly in shear. The equivalent particle size of coal fragments decreased with the applied strain rate. The Uniaxial compressive strength (UCS) of outburst-prone coal was smaller than that of resistant coal, resulting in its smaller equivalent particle size of coal fragments. Moreover, the impact loading accelerated the propagation of fractures within the specimen, which enhanced the connectivity within the porous coal. The outburst-prone coal with behaviors of low strength and sudden increase of permeability could easily initiate gas outbursts.

A review of hydrogen embrittlement of martensitic advanced high-strength steels

The martensitic advanced high-strength steels (MS-AHSS) are used to create fuel-efficient, crashworthy cars. Hydrogen embrittlement (HE) is an issue with high-strength steels; thus, the interaction of hydrogen with MS-AHSS needs to be studied. There are only a few published works on the HE of MS-AHSS. The current literature indicates that the HE susceptibility of MS-AHSS is affected by (i) the strength of the steel, (ii) the applied strain rate, (iii) the concentration of hydrogen, (iv) microstructure, (v) tempering, (vi) residual stress, (vii) fabrication route, (viii) inclusions, (ix) metallic coatings, and (x) specific precipitates. Some of the unresolved issues include (i) the correlation of laboratory results to service performance, (ii) establishing the conditions or factors that lead to a certain HE response, (iii) studying the effect of stress rate on HE, and (iv) a comprehensive understanding of hydrogen trapping in MS-AHSS.

Static-Dynamic Properties of Reactive Powder Concrete with Blast Furnace Slag

Reactive powder concrete (RPC) containing blast furnace slag prepared for hydraulic structure with a designed strength of 150 MPa is examined. We first investigate mixture proportions of RPC to fit the strength requirement, and then, concentrate on the material with 50% replacement of silica fume by blast furnace slag to study seismic resistant properties. Results indicate that curing process and steel fiber can enhance the compressive strength, flexural strength, shear strength and fracture toughness. With 210°C curing, flexural strength of RPC containing 2% steel fibers reaches 91 MPa, almost three times without the fibers. Meanwhile, the shear strength is 47.8 MPa. Dynamic stress-strain curves determined by SHPB test display that the compressive strength of RPC increases with increasing applied strain rate. Applied strain rate dominates the stress-strain behavior and fracture energy of RPC. Toughness index of RPC is improved powerfully by adding a few steel fibers. The fracture toughness of RPC with 50% slag replacement comes to 1.08 MPa·m1/2, and reaches 2.67 MPa·m1/2 as 2% steel fibers are added.

Do loading path and specimen thickness affect the brittle compressive failure of ice?

Compressive experiments were performed on square (160 mm × 160 mm) prismatic specimens of columnar-grained, S2 freshwater ice, biaxially loaded across the columns at −10°C. The work focused on brittle behavior, achieved by deforming the specimens at an applied strain rate of 4.5 ± 1.2 × 10 3s 1 in the direction of shortening. The results show that the specimen thickness (25–150 mm) has no detectable effect on the terminal failure strength of the ice. Likewise, the strength of the ice when loaded under proportional loading, where the minor stress varies during the test, was similar to that when loaded under a constant minor stress, implying that terminal failure depends only on the stress state and not on the path taken.

Strain Enhanced Corrosion in the Iron-Caustic System

Straining electrode experiments were performed to investigate the nature of strain enhanced corrosion of iron in caustic electrolyte. The strain enhanced corrosion rate was generally linearly dependent on applied strain rate, and its potential dependence paralleled that of steady-state polarization behavior on non-straining electrodes. Data was presented as ratios, in which is the corrosion rate in cm/s and is the corresponding strain rate. This ratio, which was shown in a previously published theory to be numerically equal to the crack advance per film rupture event during film rupture SCC, depended on electrochemical variables such as electrolyte concentration and temperature in a manner similar to the kinetics of caustic cracking. Conditions which are known to be marginal in producing caustic cracking resulted in values for of about 10−7 cm, in excellent agreement with a previously developed theory. It was concluded that strain enhanced corrosion in this system results from repetitive film rupture and repair during straining.