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Andrew P. Bunger - One of the best experts on this subject based on the ideXlab platform.
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Stochastic Analysis of Core Discing for Estimation of In Situ Stress
Rock Mechanics and Rock Engineering, 2010Co-Authors: Andrew P. BungerAbstract:Extraction of diamond-drilled core from high stress environments can result in the core breaking into discs. Through four decades of research, a variety of computational tools and experimental approaches have been used to analyze the details of the failure processes leading to core-Discing-type breakage of diamond-drilled cores. One motivation for this research is to use these calculations for stress estimation based on, for example, the disc length (i.e., thickness) measured in a particular core. This application requires that the core discs lengths do not deviate much from an average or typical value. This paper presents a stochastic approach, based on analyzis of the entire distribution of disc lengths, that provides a basis for application of existing core Discing models even when it is unclear how to define a typical disc length, for example when the disc length distribution is highly non-Gaussian. The viability of the stochastic approach is demonstrated by comparison with data collected from 900 m of core extracted from a South Australian granite formation.
T. Saito - One of the best experts on this subject based on the ideXlab platform.
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Observation of core Discing and in situ stress measurements; Stress criteria causing core Discing
Rock Mechanics and Rock Engineering, 1995Co-Authors: T Ishida, T. SaitoAbstract:Core Discing was typically observed in cores recovered from near horizontal holes drilled in Palaeogene sandstones at a depth of 1055 m in the Horonai colliery, Hokkaido, Japan. We have observed disc- and ring-like cores and measured in situ stress where they were recovered. We compared the measured stress state with an empirical criterion of core Discing based on Obert and Stephenson (1965) and a theoretical criterion based on Sugawara et al. (1978) and Ishida and Saito (1989). Consequently, we found that disc-like cores were recovered under lower stress state than predicted by both criteria. The stress state where ring-like cores were recovered satisfied the empirical criterion, however, it was below the critical stress state according to the theoretical criterion. These discrepancies indicate that existing stress criteria are not satisfactory and that further experimental, theoretical and field investigations are needed.
Anil Cay - One of the best experts on this subject based on the ideXlab platform.
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effect of different tillage systems on the quality and crop productivity of a clay loam soil in semi arid north western turkey
Soil & Tillage Research, 2006Co-Authors: Sakine Ozpinar, Anil CayAbstract:Abstract A 2-year study was conducted to investigate the effect of three tillage systems on the properties of clay–loam soil (EutricVertisol) planted with winter wheat ( Triticum aestivum L.) in the Canakkale province of north-western Turkey. Crop productivity was also evaluated. The three tillage treatments were: (1) conventional tillage involving mouldboard ploughing followed by two Discings (MT); (2) shallow tillage consisting of rototilling followed by one Discing (RT); (3) double Discing (DD). In the first year of the study, bulk density (BD) was found significantly lower under RT at both 0–10 and 10–20 cm depths with 1.24 and 1.32 Mg cm −3 , respectively, when compared to MT treatment. However, MT at 20–30 cm provided the highest BD, at 1.49 Mg cm −3 . In the second year of the study, DD had the lowest BD at all depths followed by RT and MT. Based on the 2-year mean, aggregate size distribution (ASD) and mean weight diameter (MWD) were significantly influenced by tillage treatments. The greatest MWD was obtained with DD, followed by MT and RT. Increasing MWD and coarse aggregates decreased seedling emergence. Organic carbon increased after RT, DD, and MT by 58%, 30%, and 18%, respectively, when compared to the amount at the beginning of the study. Similarly, the total N in the soil and straw was higher after RT than the other treatments. At 1.76 MPa, penetration resistance at 18–30 cm was significantly higher during the growing period using DD, followed by RT with 1.35 MPa and MT with 1.33 MPa. There was no significant difference between treatments at 0–18 cm. Increasing OC and total N and decreasing BD and PR under RT increased grain yield to 4611 kg ha −1 , followed by MT and DD at 4375 and 4163 kg ha −1 , respectively, according to the 2-year mean.
T W Clyne - One of the best experts on this subject based on the ideXlab platform.
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energy absorption during projectile perforation of thin steel plates and the kinetic energy of ejected fragments
International Journal of Impact Engineering, 2009Co-Authors: J Dean, C S Dunleavy, P M Brown, T W ClyneAbstract:Abstract This paper concerns energy absorption in thin (0.4 mm) steel plates during perforation by spherical projectiles of hardened steel, at impact velocities between 200 and 600 m s −1 . Absorbed energies have been obtained from measured incident and emergent projectile velocities. These tests were simulated using ABAQUS/Explicit, using the Johnson and Cook plasticity model. A strain rate-dependent, critical plastic strain fracture criterion was employed to model fracture. Good agreement is obtained between simulations and experiment and the model successfully captures the transitions in failure mode as projectile velocity increases. At velocities close to the ballistic limit, the plates fail by dishing and Discing. As the incident velocity is increased, there are two transitions in failure mode, firstly to shear plugging and secondly to fragmentation and petalling. The simulations also show that, during the latter mode of failure, the kinetic energy of ejected debris is significant, and failure to include this contribution in the energy balance leads to a substantial over-estimate of the energy absorbed within the sheet. Information is also presented relating to the strain rates at which plastic deformation occurs within the sample under different conditions. These range up to about 10 5 s −1 , with the corresponding strain rate hardening effect being quite substantial (factor of 2–3 increase in stress).
T Ishida - One of the best experts on this subject based on the ideXlab platform.
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Observation of core Discing and in situ stress measurements; Stress criteria causing core Discing
Rock Mechanics and Rock Engineering, 1995Co-Authors: T Ishida, T. SaitoAbstract:Core Discing was typically observed in cores recovered from near horizontal holes drilled in Palaeogene sandstones at a depth of 1055 m in the Horonai colliery, Hokkaido, Japan. We have observed disc- and ring-like cores and measured in situ stress where they were recovered. We compared the measured stress state with an empirical criterion of core Discing based on Obert and Stephenson (1965) and a theoretical criterion based on Sugawara et al. (1978) and Ishida and Saito (1989). Consequently, we found that disc-like cores were recovered under lower stress state than predicted by both criteria. The stress state where ring-like cores were recovered satisfied the empirical criterion, however, it was below the critical stress state according to the theoretical criterion. These discrepancies indicate that existing stress criteria are not satisfactory and that further experimental, theoretical and field investigations are needed.