A Probabilistic High-Pressure Zone Model of Dynamic Ice Structure Interactions and Associated Ice-Induced Vibrations

During ice-structure interactions that are dominated by ice compressive failure, the majority of the ice loads are transmitted through localized contact regions known as high-pressure zones (hpzs). This paper presents a probabilistic modelling framework for dynamic ice-structure interaction based on the mechanics of hpzs. Individual hpzs are modelled as a nonlinear spring-damper system where the stiffness is modelled as a function of nominal strain, with the degree of softening depending on the average strain-rate. Both spalling and crushing failure mechanisms were assessed in the context of periodical sinusoidal response. For spall dominated failure, the model structure showed presence of frequency lock-in in the speed range of 100–125mm/s, beyond which the failure was found to be random in nature with lower amplitude of structural response. The amplitude was also found to be significantly influenced by structural parameters with structural damping having the highest contribution. For pure crushing, an estimated equilibrium layer thickness based on theoretical calculations also showed presence of frequency lock-in. The work highlights the importance of understanding the interplay between these mechanisms, as well as the role of ice conditions and structural parameters on the processes that dominate an interaction.

Research on the Mechanical Properties and Energy Consumption Transfer Law of Cement Tailings Backfill Under Impact Load

The cemented tailings backfill (CTB), which plays a significant role in the stability of mine structure, is made of cement, tailings, and water in a certain proportion. When blasting and excavating an underground mine, the CTB will be disturbed by blasting. The impact load of blasting has an impact on the stability of the CTB, which is directly related to the safety of mine construction. The mechanical behaviour of CTB is generally affected by the cement-tailings ratio (C/T) and average strain rate (ASR). Therefore, a series of impact experiments were carried out on three CTB specimens with different C/T using a SHPB. Combined with the experimental results, this account reports studies on the effects of C/T and ASR on the mechanical properties of CTB, and on the energy transfer laws of CTB during impact compression. The research results show that when the ASR is less than 70 s−1, the peak stress and the peak strain have the same trend, and both of them continue to increase with the increase of ASR.When the ASR exceeds 70 s−1, as the ASR increases, the peak stress continues to increase, but the peak strain decreases gradually. Afterwards, the law of energy transfer of the CTB specimen was analyzed. It was found that as the incident energy increased, the energy reflection ratio of the CTB increased. Both the energy transmitted ratio and the energy dissipation ratio decreased. The volumetric energy showed a sharp increase first and then a trend Because of the slowly increasing trend. Finally, according to the failure morphology of the CTB, it is found that the ASR and the C/T together affect the failure of the CTB. The failure model of the CTB is mainly split failure and crush failure.

MICROFRAGMENTATION OF CAST MICA-CRYSTALLINE MATERIAL UNDER DYNAMIC COMPRESSION

The study aimed at assessing the prospects of using mica-crystalline material of the fluorophlogopite type (the main phase corresponds to the compound KMg3(Si3AlO10)F2) for use in the manufacture of armored products. To carry out such an assessment, the study established the features of the deformation of cast mica-crystalline material of the fluorophlogopite type under dynamic compression by the method of the split Hopkinson-Kola rod. It was revealed that the destruction of cast mica crystalline material at an average strain rate of 250-1500 s-1 occurs with the formation of finely divided fragments. The exposure rate was chosen by analogy with the well-known tests of materials of a similar purpose with a glass crystal structure. For a quantitative assessment of the fracture intensity, the fractional composition of the fracture fragments was analyzed by analyzing the images obtained by scanning electron microscopy. In the course of the analysis of the experimental data, it was found that a characteristic indicator in the analysis of the fractional composition of fracture fragments is the proportion of those whose size is from 1 to 100 μm in the total mass of fragments up to 1000 μm (larger fragments are not considered, since they are formed again as fragments destruction arising after the formation of main cracks), for the material studied, this indicator under the specified exposure conditions ranged from 83 to 87%, which, based on a comparison with similar materials used in the manufacture of elements of armored products, allows us to evaluate it as a material promising in this field of application, since in addition to the optimal indicators of fractional fracture upon impact, this material has a lower density in comparison with analogues and products from it may have a lower mass, which is a competitive advantage.

Plate-impact-driven ring expansion test (PIDRET) for dynamic fragmentation

A new experimental set-up mounted at the muzzle of a singlestage gas gun has been designed in order to study the fragmentation of metallic rings under dynamic radial expansion. This concept takes advantage of the quasi-incompressibility of HDPE whose radial flow under plate impact-like loading is used to apply a pressure boundary condition at the ring’s inner surface. For the experimental configurations considered in the present work, the average strain rate in the ring reaches values close to 104 s-1. The repeatability and the reliability of the experiments are verified for rings made of steel and aluminium.

Experimental Investigation of Dynamic Compression Mechanical Properties of Frozen Fine Sandstone

Aiming at the dynamic mechanical properties of weakly cemented fine sandstone in the rich water-bearing strata in western China under dynamic loading, a 50 mm rod diameter separation Hopkinson pressure bar (SHPB) test was used to study the Paleogene fine sandstone in a coal mine in Ningxia. The system carried out the impact compression tests of −15°C, −20°C, and −30°C and the average strain rate of 28 s−1–83 s−1 and obtained the dynamic compressive strength of the frozen fine sandstone specimens under different test conditions. The strain curve and the fracture morphology were analyzed for the relationship between dynamic peak stress, peak strain, dynamic strength growth coefficient (DIF), and fracture morphology and strain rate. The results show that the peak stress of frozen fine sandstone increases from the decrease of freezing temperature under the same average strain rate. The peak stress of the specimen increases from the increase in the average strain rate of the same freezing temperature. The failure modes of specimen are mainly divided into axial splitting tensile failure and compression crushing failure. To the splitting tensile failure and the compression crushing failure, the main factors determining the two failure modes are the strain rate, while the temperature affects the severity of the impact damage. In the load strain rate and temperature range, the DIF of the frozen fine sandstone is linearly correlated with the strain rate, and the lower the temperature, the slower the growth rate of the DIF.

Use of Average Temperature in Fen Calculations

The effect of the light reactor water environment on fatigue damage is referred to as environmentally assisted fatigue (EAF). This effect is accounted for by applying an environmental fatigue correction factor, Fen, to calculated fatigue usage. In providing guidelines for calculation of Fen, Revision 0 of NUREG/CR-6909 [1] permits temperature averaging for the case of a constant strain rate and linear temperature response, and permits it in other cases as well, but only if the average temperature used produces results that are consistent with the modified rate approach [1, p. A.5]. Revision 1 of NUREG/CR-6909 [2] modifies this slightly, requiring that the threshold temperature be used in averaging instead of the minimum if the minimum is below the threshold [2, p. A-6]. In both cases, the benchmark for accuracy is the modified rate approach [2, Section 4.4]. In this paper, we use real world examples to compare Fen values based on the modified rate approach with those using average strain rate and temperature. We also examine how to select the rise time used to calculate average strain rate in those cases where it is not obvious. We find that temperature averaging is conservative if rise time and other parameters are correctly selected.

High strain rate and low temperature effects on the compressive behaviour of concrete

Temperature and strain rate are important factors when considering the mechanical properties of engineering materials, as they can greatly influence the material behaviour. The research presented here is an experimental investigation to determine the effects of low temperatures and high strain rates on the compressive behaviour of concrete. The primary purpose of the research is the development of experimental stress–strain relationships under these conditions, as this is a largely unexplored research topic. Thirty-five 101.6 mm × 203.2 mm concrete cylinders were tested in uniaxial compression at the University of New Brunswick. The specimens were loaded either under static conditions or dynamically with an average strain rate of approximately 1 s−1, while being exposed to temperatures from 20°C to −70°C to simulate extreme climatic temperature and those attainable within industrial storage facilities. The compression strain of the specimens was obtained using digital image correlation. The mechanical properties studied were the compressive strength, strain associated with the peak stress and general stress–strain behaviour due to the increased strain rate and temperature variations.

Dynamic Splitting Experimental Study on Sandstone at Actual High Temperatures under Different Loading Rates

The tensile failure of rocks is a common failure mode in rock engineering. Many studies have been conducted on the tensile strength and failure mode of rocks after high-temperature treatment under dynamic loading. However, research on the effects of high temperature on the dynamic splitting tensile characteristics of sandstone at actual high temperatures is lacking. To investigate the dynamic tensile characteristics of rocks at actual high temperatures, split Hopkinson pressure bar (SHPB) test apparatus and high-temperature environment box were used to perform dynamic splitting tensile tests under six striker velocities for sandstone specimens at 25°C–800°C. The dynamic splitting tensile strength, radial strain, average strain rate, and failure mode of sandstone under different test conditions were investigated. Test results revealed that the brittleness of sandstone specimens is enhanced at 200°C and 400°C, but slight ductility is observed at 600°C and 800°C. The strain rate effect of dynamic tensile strength is closely related to temperature. When the striker velocity exceeds 2.3 m/s, the dynamic radial strain first decreases and then increases with rising temperature. A quadratic polynomial relationship between the dynamic radial strain and temperature was observed. The temperature effect on the average strain rate is strong at low striker velocity and weak at high striker velocity. In the dynamic splitting tensile tests, high-temperature sandstone specimens are split into two semicylinders along the radial loading direction.

Coupled Static-Dynamic Tensile Mechanical Properties and Energy Dissipation Characteristic of Limestone Specimen in SHPB Tests

To investigate the dynamic splitting tensile mechanical property of limestone under coupled static and dynamic state, the dynamic split tensile tests of limestone under one-dimensional coupled static and dynamic load with different strain rates were performed with the help of modified split Hopkinson pressure bar (SHPB) equipment. The dynamic splitting tensile mechanical property and energy dissipation characteristic under two stress states were also compared in this research. Test results indicated that the dynamic tensile strength of the limestone specimen increased with the increase of average strain rate, exhibiting an obvious strain rate effect. In addition, dynamic tensile strength under uniaxial state was higher than that under one-dimensional coupled static and dynamic load state under the same test condition. Moreover, the deformation modulus increased with increasing average strain rate under uniaxial state, while it decreased with increasing average strain rate under coupled static and dynamic state. Both the reflected energy and absorbed energy linearly increased with increasing incident energy. The preload in the radial direction could increase the reflected energy and decrease the absorbed energy. Moreover, the transmitted energy with preload state was slightly lower than that under uniaxial state. Finally, the dynamic tensile strength of limestone specimen increased as a power function with increasing absorbed energy.

New Insight into the Recent Earthquake Activity in North Cambay Basin, Western India: Seismological and Geodetic Perspectives

The intraplate Gujarat region located at the trijunction of three failed rifts, Kachchh, Narmada, and Cambay, is one of the most seismically active intraplate regions of the world. Among these three, the Cambay basin has been investigated thoroughly for petroleum. However, the basin has not been studied from a seismotectonic perspective. For the past few years, the northern part of the Cambay basin is becoming active with reasonably frequent earthquake occurrences. In the past 10 yr, ∼995 earthquakes have been recorded from the region with a maximum magnitude up to 4.2. Most of the earthquakes are in the magnitude range 1–3. Since 2009, four Global Positioning System (GPS) stations have been in operation in the vicinity of the Cambay basin, and a maximum deformation of 1.8±0.1 mm/yr has been estimated. The GPS‐derived strain rates of ∼0.02–0.03 microstrain/yr are prevalent in the region. An average strain rate of 0.02 microstrain/yr in the region can generate an earthquake of magnitude 6.4. The focal mechanisms of the earthquakes have been mostly normal with strike‐slip component and corroborated by the geodetic strain tensors. Most of the seismicity is clustered in the basement ridges, striking along pre‐existing Precambrian trends that cross the Cambay basin. Complex geodynamics have developed around the northern part of the Cambay rift because of the various movements along several faults, presence of basement ridges, and subsurface plutonic bodies in a failed rift, which are creating stresses and causing earthquakes in this part of the rift. We postulated that the highly heterogeneous subsurface structure beneath the northern part of the Cambay rift is creating additional stress, which is superimposing on the regional stress field substantially, and this mechanism is plausibly facilitating the localized extensional tectonics in the region where compression is expected.