Microstructural Examinations of Copper Antimony Alloys

Among other materials, fahlores were used in the Bronze Age copper ore smelting process. These contain, apart from sulfur, arsenic and antimony. Therefore, these elements can be found in Bronze Age copper casting ingots or artifacts. In order to study the behavior of Sb more closely, two copper alloys containing 10 and 30 wt. % Sb were melted and subjected to a metallographic examination. On the one hand, microstructures with copper dendrites and homogeneous interdendritic areas primarily composed of intermetallic phase could be found. On the other hand, at higher Sb concentrations, first Cu3Sb precipitated which, in turn, transformed to Cu10Sb3 upon cooling. The crystals in these microstructures were characterized by numerous parallel cracks. No further phases were observed by XRD.

Progressive Failure and Acoustic Emission Characteristics of Red Sandstone with Different Geometry Parallel Cracks under Uniaxial Compression Loading

The geometric distribution of initial damages has a great influence on the strength and progressive failure characteristics of the fractured rock mass. Initial damages of the fractured rock were simplified as parallel cracks in different geometric distributions, and then, the progressive failure and acoustic emission (AE) characteristics of specimens under the uniaxial compression loading were analyzed. The red sandstone (brittle materials) specimens with the parallel preexisting cracks by water jet were used in the tests. The energy peak and stress attenuation induced by the energy release of crack initiation were intuitively observed in the test process. Besides, three modes of rock bridge coalescence were obtained, and wing crack was the main crack propagation mode. The wing crack and other cracks were initiated in different loading stages, which were closely related to the energy level of crack initiation. The propagation of wing crack (stable crack) consumed a large amount of energy, and then, the propagation of shear crack, secondary crack, and anti-wing crack (unstable crack) was inhibited. The relationship between the crack propagation mode and the geometric distribution of existing cracks in the specimen was revealed. Meanwhile, the strength characteristic and failure mode of fractured rock with the different geometric distributions of preexisting crack were also investigated. The energy evolution characteristics and crack propagation were also analyzed by numerical modeling (PFC2D).

The Interaction between an Edge and an Embedded Parallel Crack in a Structural Component

Parallel cracks are often detected in various structural components using non-destructive methods. In the case of non-aligned parallel cracks, on-site service needs to decide whether they should be treated as coalesced or separate multiple cracks for Fitness-for-Service. Criteria and standards for the adjustment of multiple nonaligned cracks are very different from one another in existing resources. Furthermore, those criteria and standards are often derived from on-site service experience without rigorous and systematic verification. Based on this observation, the interaction between an edge and an embedded parallel crack is investigated to correlate criteria and standards from various resources in order to recommend the usage of those standards for the purpose of Fitness-for-Service. In this study, depending on the crack ratio a1/a2, what may be deemed conservative by one standard, leading to aligned cracks for a given separation distance, H/a2 and S/a2, may be deemed non-conservative, or non-aligned, by another standard. Examples are given to show this phenomenon.

Numerical Analysis of Dynamic Responses of Rock Containing Parallel Cracks under Combined Dynamic and Static Loading

Open-pit slopes contain numerous nonpenetrating, intermittent joints which maintain stability under blasting operations. The tip dynamic response coefficient (DRC) of parallel cracks in a typical rock mass under combined dynamic and static loading conditions was calculated in this study based on the superposition principle. The dynamic response law of the intermittent joint in the slope under blasting was determined accordingly. The influence of many factors (the disturbance amplitude of dynamic load, the lateral confining pressure, the length of rock bridge, the length between cracks, the staggered distance between cracks, and the crack inclination angle) on the dynamic response was theoretically analyzed as well. The ABAQUS numerical assessments were conducted on simulation models with parallel cracks under combined dynamic and static loading conditions. The results show that a larger dynamic load amplitude and smaller crack inclination angle/confining pressure result in greater Type II dynamic strengthening effect on the crack tip. When the length of the rock bridge between cracks (s) is smaller than the half length of the crack (a), the dynamic strengthening effect at the crack tip weakens gradually with increase in s; whens/a≥1, the strengthening effect is almost unchanged. With the increase in the staggered distance between cracks (h), the dynamic strengthening effect of the crack tip weakens at first and then strengthens; the strengthening effect is weakest when h/a=0.4; the crack propagation under combined dynamic and static loading is the most sensitive to the lateral confining pressure (σ3) and is the least sensitive to the inclination angle of the cracks (α). Theoretical results are validated by comparison with numerical simulation results. Such information regarding the dynamic response law of the parallel cracks in rock masses under dynamic and static loading conditions is conducive to further research on the mesofailure mechanism of open-pit mine jointed rock slopes under blasting operations.