Numerical Study on Fragmentation Characteristics of Granite Under a Single Polycrystalline Diamond Compact Cutter in Rotary-Percussive Drilling

Fragmentation characteristics of granite in rotary-percussive drilling are studied using the distinct element method. We developed a model to investigate the interaction between the rock and a Polycrystalline Diamond Compact cutter. The micro contact parameters in the model are calibrated by conducting a series of simulated mechanical tests of the rock. Sensitivity analyses are then conducted according the drilling performances which are quantified as the penetration displacement, the fragmentation volume and the specific energy, as well as the lateral force and the particle size distribution. Results show that the model can well represent the typical fracture system under indentation of the cutter, the torque fluctuation phenomenon in drilling and the formation of lateral chips, which verify the reliability of the model. The cutter with a back rake angle of 55°and impact frequency of 30Hz has the best penetration performance in evaluated parameters. Increasing the frequency has a great effect on the rock breaking speed under the coupling effect of impact and cutting in the low frequency range. Considering crushing efficiency, 50 Hz is the recommended impact frequency. This paper provides a useful tool to represent the fragmentation performance of rotary-percussive drilling and sensitivity analyses shed light on the potential ways to improve the performance.

Modelling discontinuity control on the development of Hell’s Mouth landslide

This paper focuses on numerical modelling and back analysis of the Hell’s Mouth landslide to provide improved understanding of the evolution of a section of the north coast of Cornwall, UK. Discontinuity control is highlighted through the formation of a ‘zawn’ or inlet, the occurrence of two successive landslides and evidence of ongoing instability through opening of tension cracks behind the cliff top. Several integrated remote sensing (RS) techniques have been utilised for data acquisition to characterise the slope geometry, landslide features and tension crack extent and development. In view of the structural control on the rock slope failures, a 3D distinct element method (DEM) code incorporating a discrete fracture network and rigid blocks has been adopted for the stability analysis. The onset and opening of tension cracks behind the modelled slope failure zones has also been studied by analysing the displacements of two adjoining landslide blocks, between which, a joint-related tension crack developed. In addition, a sensitivity analysis has been undertaken to provide further insight into the influence of key discontinuity parameters (i.e. dip, dip direction, persistence and friction angle) on the stability of this section of the coastline. Numerical modelling and field observations indicate that block removal and preferential erosion along a fault resulted in the formation of the inlet. The development of the inlet provides daylighting conditions for discontinuities exposed on the inlet slope wall, triggering the initial landslide which occurred on 23rd September 2011. Numerical modelling, and evidence from a video of the initial landslide, suggests that the cliff instability is characterised by a combination of planar sliding, wedge sliding and toppling modes of failure controlled by the discrete fracture network geometry.

Multivariate Statistical Analysis of Multiple-Elements in Anisodus Tanguticus (Maxim.) Pascher from Different Regions to Determine Geographical Origins

Background: Anisodus tanguticus (Maxim.) Pascher, which is an important species used in traditional Tibetan medicine, is grown in the Qinghai -Tibet Plateau. Because the quality of A. tanguticus varies depending on where it is grown, a method for determining the geographical origin of this species is needed.Methods: A quantitative analysis of 18 elements (Al, Ba, Be, Ca, Co, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, P, Sr, V, and Zn) in A. tanguticus and the soil collected from different locations was conducted using an inductively coupled plasma optical emission spectrometer. The elemental contents underwent a principal component analysis (PCA), and an orthogonal partial least-squares discriminant analysis (OPLS-DA). Furthermore, elemental accumulation and elemental transfer coefficients were calculated according to the element concentration gradients.Results: Distinct element fingerprints were detected for the A. tanguticus collected from different regions. Additionally, the PCA and OPLS-DA results indicated A. tanguticus plants can be distinguished on the basis of their geographical origin. The Tibet samples were easily separated from the other samples. Elemental accumulation and transfer patterns differed significantly among the analyzed elements and plant parts. Ca and P were identified as the elements with the highest in elemental accumulation and elemental transfer patterns of A. tanguticus. Conclusions: Our approach can be used to efficiently and accurately distinguish herbs according to their varietal characteristics and geographical origins.

Micromechanical study of potential scale effects in small-scale modelling of sinker tree roots

When testing an 1:N geotechnical structure in the centrifuge, it is desirable to choose a large scale factor (N) that can fit the small-scale model in a model container and avoid unwanted boundary effects, however, this in turn may cause scale effects when the structure is overscaled. This is more significant when it comes to small-scale modelling of sinker root-soil interaction, where root-particle size ratio is much lower. In this study the Distinct Element Method (DEM) is used to investigate this problem. The sinker root of a model root system under axial loading was analysed, with both upward and downward behaviour compared with the Finite Element Method (FEM), where the soil is modelled as a continuum in which case particle-size effects are not taken into consideration. Based on the scaling law, with the same prototype scale and particle size distribution, different scale factors/g-levels were applied to quantify effects of the ratio of root diameter (𝑑𝑟) to mean particle size (𝐷50) on the root rootsoil interaction.

A panoramic perspective of travel and tourism in Iddia during COVID 19

It has always been seen that the cuisine of a respective place has always been considered by a vacationer. Local food has always been considered as an important & a distinct element for a destination. The study focuses on different factors taken into consideration by a vacationer during the local cuisine experimentation. The literature also indicates the different factors like flavor, money value etc. which actually directs the consumption of cuisine of the respective place. The impact of COVID has also been analyzed to get an insight into the effect on an international perspective. At the same time, various policies have also been discussed with respect to various secondary resources.

Systematic Compounding of Ceramic Pastes in Stereolithographic Additive Manufacturing

In this paper, stereolithographic additive manufacturing of ceramic dental crowns is discussed and reviewed. The accuracy of parts in ceramic processing were optimized through smart computer-aided design, manufacturing, and evaluation. Then, viscous acrylic resin, including alumina particles, were successfully compounded. The closed packing of alumina particles in acrylic pastes was virtually simulated using the distinct element method. Multimodal distributions of particle diameters were systematically optimized at an 80% volume fraction, and an ultraviolet laser beam was scanned sterically. Fine spots were continuously joined by photochemical polymerization. The optical intensity distributions from focal spots were spatially simulated using the ray tracing method. Consequently, the lithographic conditions of the curing depths and dimensional tolerances were experimentally measured and effectively improved, where solid objects were freely processed by layer stacking and interlayer bonding. The composite precursors were dewaxed and sintered along effective heat treatment patterns. The results show that linear shrinkages were reduced as the particle volume fractions were increased. Anisotropic deformations in the horizontal and vertical directions were recursively resolved along numerical feedback for graphical design. Accordingly, dense microstructures without microcracks or pores were obtained. The mechanical properties were measured as practical levels for dental applications.