Dynamic Split Tensile Strength of Basalt, Granite, Marble and Sandstone: Strain Rate Dependency and Fragmentation

The aim of this study is to understand the strength behaviour and fragment size of rocks during indirect, quasi-static and dynamic tensile tests. Four rocks with different lithological characteristics, namely: basalt, granite, sandstone, and marble were selected for this study. Brazilian disc experiments were performed over a range of strain rates from ~ 10<jats:sup/>–5 /s to 2.7 × 10<jats:sup/>1 /s using a hydraulic loading frame and a split Hopkinson bar. Over the range of strain rates, our measurements of dynamic strength increase are in good agreement with the universal theoretical scaling relationship of (Kimberley et al., Acta Mater 61:3509–3521, 2013). Dynamic fragmentation during split tension mode failure has received little attention, and in the present study, we determine the fragment size distribution based on the experimentally fragmented specimens. The fragments fall into two distinct groups based on the nature of failure: coarser primary fragments, and finer secondary fragments. The degree of fragmentation is assessed in terms of characteristic strain rate and is compared with existing theoretical tensile fragmentation models. The average size of the secondary fragments has a strong strain rate dependency over the entire testing range, while the primary fragment size is less sensitive at lower strain rates. Marble and sandstone are found to generate more pulverised secondary debris when compared to basalt and granite. Furthermore, the mean fragment sizes of primary and secondary fragments are well described by a power-law function of strain rate

Dynamic Compressive Strength and Fragmentation in Felsic Crystalline Rocks

Brittle deformation in rocks depends upon loading rate; with increasing rates, typically greater than ~102 s‐1, rocks become significantly stronger and undergo increasingly severe fragmentation. Dynamic conditions required for rate‐dependent brittle failure may be reached during impact events, seismogenic rupture, and landslides. Material characteristics and fragment characterization of specific geomaterials from dynamic loading are only approximately known. Here we determine the characteristic strain rate for dynamic behavior in felsic crystalline rocks, including anisotropy, and describe the resulting fragments. Regardless of the type of felsic crystalline rock or anisotropy, the characteristic strain rate is the same within uncertainties for all tested materials, with an average value of 229 ± 81 s‐1. Despite the lack of variation of the critical strain rate with lithology, we find that the degree of fragmentation as a function of strain rate varies depending on material. Scaled or not, the fragmentation results are inconsistent with current theoretical models of fragmentation. Additionally, we demonstrate that conditions during impact cratering, where the impactor diameter is less than ~100 m, are analogous to the experiments carried out here, and therefore that dynamic strengthening and compressive fragmentation should be considered as important processes during impact cratering

Dynamic compressive strength and fragmentation in sedimentary and metamorphic rocks

Brittle deformation at high strain rates results in intense fragmentation and rock pulverisation. For rocks, the critical strain rate at which this behaviour occurs is ~102 s−1. The mechanical properties of rocks at these strain rates can also be very different from their quasi-static properties. Deformation of rocks at these strain rates can occur during fault rupture, landslide events, and meteorite impacts. In this study, we present the results of high strain rate mechanical tests to determine the characteristic strain rate for rate-dependent brittle failure, and the fragment size and shape distributions that result from failure at these conditions. We investigated sandstone, quartzite, limestone, and marble and considered whether the fragment characteristics can be used as diagnostic indicators of loading conditions during brittle failure. We find that the characteristic strain rates, where the dynamic strength is twice the quasi-static strength, range between ~150 and 300 s−1 for rate-dependent brittle failure in the investigated lithologies. Furthermore, we use our results to demonstrate an empirical inverse power-law relationship between fragment size and strain rate for dynamic failure under uniaxial compression. On the other hand, we show that fragment shape is independent of strain rate under dynamic uniaxial loading.<br/

Granular Materials Under Shock and Blast Loading

This volume discusses the fundamental dynamic behaviour of granular materials, in particular cohesionless sand, when subjected to shock and blast wave loading. The contents of the book are mainly divided into three parts based on the type of loading imparted to the granular materials: Shock-wave loading (step pulse); Air-blast loading (Friedlander wave); Buried-blast loading. It provides a comprehensive review of the available testing methods, along with the necessary diagnostic measurements for material characterization, making it useful for researchers working in the area of blast protection and Impact engineering

Shock wave attenuation by geotextile encapsulated sand barrier systems

This paper presents a laboratory scale experimental technique to study the performance of the encapsulated sand barrier systems in mitigating shock waves. The geotextile encapsulated sand barrier systems are made of cubical wire mesh formwork lined with geotextile and form a thick protective barrier when filled with granular materials. In the present study, dry sand particles of size varying from microns to few millimeters (fine and coarse) are used as infill granular material. Spherical shaped glass beads are also used as the infill material to study the influence of shape of the infill particle on the attenuation behavior. The process of shock wave attenuation by the sand barrier, with and without the geotextile facing formwork is examined. The experiments are performed using a conventional shock tube, where shock waves with incident Mach number in the range of 129-1.70 are generated. The experimental results show that the presence of geotextile layer has contributed significantly towards shock wave attenuation. The geotextile also plays an important role as a regulator, which is able to deliver gradual pressure rise at the downstream end of the barrier. (C) 2017 Elsevier Ltd. All rights reserved

Laboratory scale investigation of stress wave propagation and vibrational characteristics in sand when subjected to air-blast loading

The main objective of this study is to develop a new approach for evaluating the effects of air-blast on protective barrier made of sand. The air-blast loading is simulated experimentally laboratory using the shock tube test facility. The stress wave propagation in medium dense and dense sand medium are investigated under simulated air-blast loading. Synchronised pressure and accelerometer measurement system is used to capture peak stress wave pressure and peak particle velocity (PPV). The blast wave impact generates a stress wave in the medium leading to the compaction of the soil skeleton, which has led to stress enhancement (4-5 times of peak over-pressure) in top most sand layer, following which the high-pressure gas behind the shock front permeates through the sample. The intensity of stress waves and gas permeation rate gradually decrease with depth. Further, from the result of the simulated air-blast experiments, an empirical equation has been developed with a power law index of 1.88 and 1.36 for medium dense and dense sand respectively, to predict PPV against scaled blast distance. Visualisation of the sand deformation was possible with the help of a high-speed camera; displacement trajectories and strain contours are obtained through digital image correlation (DIC) analyses

Sand ejecta kinematics and impulse transfer associated with the buried blast loading: A controlled laboratory investigation

An experimental test facility has been developed for performing laboratory studies on shallow buried blast loading. The shock tube based test facility offers an alternative method for generating blast wave in a controlled and repeatable manner, without the use of explosives. In this paper, we consider a spherical expanding blast wave of moderate shock strength with relatively low driving pressure. A confined dry sand bed prepared with a constant density, is exposed to a blast wave from the embedded shock tube. The principal objective of this paper is to understand the various events involved during the interaction of leading blast wave with the soil medium, followed by the expansion of the entrained gas. The process initiates with the formation of stress wave in the sand media, followed by the gas bubble expansion and terminates with sand ejection. The variation in the output of the sand ejecta is investigated with the help of high speed photography. The velocity of the sand ejecta front is found to decrease with the increase in the burial depth (DoB). Further, the impulse (using vertical pendulum) and peak pressure (using transducers) imparted to the rigid target are evaluated. The target is located at different stand-off distances (SoD) above the top surface of the sand bed. It is found that the peak pressure values are influenced by the presence of dome-cap of the ejecta, expanding vertically upwards generating a point-load impact. Irrespective of the depth of burial (DoB = 32 mm-64 mm), maximum impulse is observed around the zone of bubble expansion (close to the sand bed surface). Sand ejecta does however have a greater influence on the impulse at higher SoDs (> 40 mm). Moreover, the maximum momentum transfer is observed when SoD to DoB ratio is 2.5. In conclusion, the shock-driven sand test facility is found to be a simple and efficient tool to study the complex dynamics of sand ejecta, including the post- impact on the target structures. (C) 2017 Elsevier Ltd. All rights reserved

Systemic Sclerosis Associated Interstitial Lung Disease: A Conceptual Framework for Subclinical, Clinical, and Progressive Disease

OBJECTIVES: Establish a framework by which experts define disease subsets in systemic sclerosis associated interstitial lung disease (SSc-ILD). METHODS: A conceptual framework for subclinical, clinical, and progressive ILD was provided to eighty-three experts, asking them to use the framework and classify actual SSc-ILD patients. Each patient profile was designed to be classified by at least 4 experts in terms of severity and risk of progression at baseline; progression was based on 1-year follow-up data. A consensus was reached if ≥ 75% of experts agreed. Experts provided information on which items were important in determining classification. RESULTS: Forty-four experts (53%) completed the survey. Consensus was achieved on the dimensions of severity (75%, 60 of 80 profiles), risk of progression (71%, 57 of 80 profiles) and progressive ILD (60%, 24 of 40 profiles). For profiles achieving consensus, most were classified as clinical ILD (92%), low risk (54%), and stable (71%). Severity and disease progression overlapped in terms of framework items that were most influential in classifying patients (forced vital capacity, extent of lung involvement on high resolution chest CT (HRCT)); risk of progression was influenced primarily by disease duration. CONCLUSIONS: Using our proposed conceptual framework, international experts were able to achieve a consensus on classifying SSc-ILD patients along the dimensions of disease severity, risk of progression, and progression over time. Experts rely on similar items when classifying disease severity and progression: a combination of spirometry and gas exchange and quantitative HRCT