Block Shape Research Articles

Experimental study on strength and failure characteristics of sandstone rock mass with complex cataclastic structure using 3D printing models

A cataclastic rock mass is a poor type of engineering geological rock mass. The determination of the shear failure characteristics and shear strengths of cataclastic rock masses can provide key basis for the design and construction of infrastructure. Physical model samples of a sandstone cataclastic rock mass were first produced by a combination of three-dimensional (3D) printing technology and manual pouring. Shear tests were conducted with respect to the shear stresses parallel to the trace line plane and perpendicular to the trace line plane of the cataclastic rock mass model. Based on an extensive analysis of the shear failure characteristic, shear stress evolution characteristic curve and shear strength. When the shear stress was parallel to the trace line plane, and when the rock block that was cut and confined by the trace line exhibited a significant tip, the end stress concentration effect of the cataclastic rock mass was more significant during the shear process with the anisotropy of the rock block increased. In addition, the shapes of the rock blocks that were confined and cut by the joints were the main influencing factors of the strength of the cataclastic rock mass. When the shear stress was perpendicular to the trace line plane, the structure of the rock wall was the main influencing factor of the deformation and failure process of the shear failure plane and the shear strength. The physical and mechanical properties of the shear failure plane of the cataclastic rock mass were found to be closely related to the joint–rock wall system characteristics of the cataclastic rock mass. Therefore, when determining the shear strength of cataclastic rock mass, the shape and combination form of the rock block, shear direction, and structural failure characteristics of the rock wall should be comprehensively considered during the shear process.

Effectiveness of High-Damping Rubber (HDR) Damper and Tuned Mass—HDR Damper in Suppressing Stay-Cable Vibration

High-damping rubber (HDR) dampers have the advantages of convenience for various shapes of pressure blocks, aesthetic installation, easy maintenance, temperature stability, etc.; thus, they present good application prospects in the vibration reduction of stay cables. Hence, a model of a taut cable equipped with two types of HDR damper—i.e., HDR damper and tuned mass–high-damping rubber damper (TM-HDR-D)—is established herein. Then, based on this theoretical model, the effect of each damper acting alone and in combination on the cable’s additional modal damping is studied. Finally, an actual cable of a cable-stayed bridge is used to study the effectiveness of two dampers for practical engineering. The results show that, when the TM-HDR-D has a small mass, the total additional modal damping of the cable approximates the superposition of the respective effects of the two dampers. The damping effect of HDR mainly depends on its stiffness and installation position; meanwhile, the damping contribution of TM-HDR-D is mainly related to its tuning frequency and installation position. In practical engineering, the smaller installation mass of TM-HDR-D can make up for the lack of damping enhancement of the cable-end HDR damper.

Wear mechanism and debris analysis of PEEK as an alternative to CoCrMo in the femoral component of total knee replacement

The polyetheretherketone (PEEK)-highly cross-linked polyethylene (XLPE), all-polymer knee prosthesis has excellent prospects for replacing the traditional metal/ceramic-polyethylene joint prosthesis, improving the service life of the joint prosthesis and the quality of patients’ life. The long-term wear mechanism of PEEK-XLPE knee joint prosthesis is comprehensively evaluated from wear amount, wear morphology, and wear debris compared to that of CoCrMo-XLPE joint prosthesis. After 5 million cycles of in vitro wear, the wear loss of XLPE in PEEK-XLPE (30.9±3.2 mg) is lower than that of XLPE in CoCrMo-XLPE (32.1±3.1 mg). Compared to the XLPE in CoCrMo-XLPE, the plastic deformation of XLPE in PEEK-XLPE is more severe in the early stage, and the adhesive peeling and adhesion are lighter in the later stage. The size distribution of XLPE wear debris in PEEK-XLPE is relatively dispersed, which in CoCrMo-XLPE is relatively concentrated. Wear debris is mainly flake and block debris, and the wear mechanism of XLPE was abrasive wear. The wear volume per unit area of PEEK femoral condyle (10.45×105 µm3/mm2) is higher than that of CoCrMo (8.32×105 µm3/mm2). The PEEK surface is mainly furrows and adhesions, while the CoCrMo surface is mainly furrows and corrosion spots. The PEEK wear debris is mainly in flakes and blocks, and the CoCrMo wear debris is mainly in the shape of rods and blocks. The wear mechanism of PEEK is abrasive wear and adhesion, and that of CoCrMo is abrasive wear and corrosion.

Static friction coefficient depends on the external pressure and block shape due to precursor slip

Amontons’ law states that the maximum static friction force on a solid object is proportional to the loading force and is independent of the apparent contact area. This law indicates that the static friction coefficient does not depend on the external pressure or object shape. Here, we numerically investigate the sliding motion of a 3D viscoelastic block on a rigid substrate using the finite element method (FEM). The macroscopic static friction coefficient decreases with an increase in the external pressure, length, or width of the object, which contradicts Amontons’ law. Precursor slip occurs in the 2D interface between the block and substrate before bulk sliding. The decrease in the macroscopic static friction coefficient is scaled by the critical area of the precursor slip. A theoretical analysis of the simplified models reveals that bulk sliding results from the instability of the quasi-static precursor slip caused by velocity-weakening local friction. We also show that the critical slip area determines the macroscopic static friction coefficient, which explains the results of the FEM simulation.

Effect of Cu on the Formation of Reversed Austenite in Super Martensitic Stainless Steel.

We investigated the effect of Cu on the formation of reversed austenite in super martensitic stainless steel by using X-ray diffraction (XRD), a transmission electron microscope (TEM) and an energy-dispersive spectrometer (EDS). Our results showed that the microstructure of the steels comprised tempered martensite and diffused reversed austenite after the steels were quenched at 1050 °C and tempered at 550-750 °C. The volume fraction of reversed austenite in the steel with 3 wt.% of Cu (3Cu) was more than that with 1.5 wt.% of Cu (1.5Cu). The transmission electron microscope results revealed that the reversed austenite in 1.5Cu steel mainly had the shape of a thin strip, while that in 3Cu steel had a block shape. The nucleation points and degree of Ni enrichment of reversed austenite in 3Cu steel were higher than those in 1.5Cu steel. The reversed austenite was more likely to grow in ε-Cu enriched regions. Therefore, Cu can promote reversed austenite nucleation and growth. The mechanical properties of 3 Cu steel are obviously better than those of 1.5Cu steel when tempered at 550-650 °C.

Determining the size and shape of a dimension stone block under consideration on the spatial relationship of joint sets

Dimension stone not only represents the quality, including strength, color, and polish indexes but also shows the size and shape to obtain standard requirements for the processing plant. One of the issues affecting the size and block recovery ratio is discontinuities inside the stone, dividing into specific sizes and shapes. Therefore, the paper shows a relationship among three main joint sets, existing in the quarries, influencing the size and shape of a stone block generated by intersections of these joint sets. Each joint set is characterized by dip, dip direction, and spacings. Modelling discontinuities from three main joint sets generated a stone block with a specific size and shape. The paper carried out at stone quarries in Phu Yen, Binh Dinh, and Khanh Hoa Provinces. The results showed that when changing one of the geometry parameters of these joint sets, the size, and shape will be correspondingly changed. These sizes and shapes depend on the spatial intersection of these joint sets. In addition, the recovery ratio of each block for processing was calculated regarding its shape to assess which quarries have a good relationship with joint sets. From the minimum size for the processing plant is a rectangular parallelepiped of 0.4 m3, the minimum spacing of joints in a set was defined to satisfy such requirements. This contributes to showing which quarries have a favorable condition on stone size and shape the plant requires. From this, the spacings are equal or more than the minimum spacing in each joint set for quarries determined to calculate the reverse of the rectangular parallelepiped of equal or more than 0.4 m3.

Study on the precipitation mechanisms of TiC particles in steel matrix composites fabricated by eutectic solidification

The precipitation mechanisms of TiC eutectic particles in steel matrix composites prepared by eutectic solidification are studied through thermodynamic calculations and experimental analyses. The results indicate that the eutectic TiC particles begin to precipitate when the concentrations of Ti and C in the residual molten steel reach a eutectic point during the solidification process. The mass fractions of Ti and C in SMCs play significant roles in the precipitation time, particle characteristics and precipitation mechanism characteristics of TiC eutectic particles. When the mass fractions of Ti and C in SMC are low, TiC particles precipitate in the form of divorced eutectic solidification, showing strip, block and irregular shapes that are mainly distributed on the grain boundaries. When the mass fractions of Ti and C are high, TiC particles precipitate in the form of eutectic solidification, showing flake and dendritic shapes that are distributed on the grain boundaries and also in the grains. There are orientation relationships between the eutectic particles and the matrix.

Design and Experimental Investigation of an Ultra-Low Frequency, Low-Intensity, and Multidirectional Piezoelectric Energy Harvester with Liquid as the Energy-Capture Medium

Traditional piezoelectric vibration energy harvesters (PVEHs) usually adopt a rigid energy-capture structure, which can achieve efficient energy harvesting in single-directional, high-frequency, and high-intensity vibration environments. However, efficient harvesting with the use of low-frequency, low-intensity, and multidirectional vibration energy remains a challenge for existing harvesters. To tackle this problem, we proposed a PVEH with liquid as the energy-capture medium. Our previous research verified that this set up can show a good energy harvesting performance under low-frequency, low-intensity, and horizontal multidirectional vibration excitation. In this paper, we further studied the possibility of vertical multidirectional energy harvesting using this device, as well as the influence of several important parameters (rope margin, liquid level height, and floating block shape) on the output performance. The results showed that the proposed PVEH can realize energy harvesting in three-dimensional space and that the output characteristic is adjustable.

Deformation mode in 3-point flexure on pantographic block

Pantographic blocks are metamaterials made of a finite number of parallel pantographic sheets interconnected by cylindrical pivots. In this paper, a pantographic block subjected to 3-point flexure, where the prescribed displacements are parallel to the pantographic plane, shows essentially monoclastic deformation (i.e., one of the principal curvatures of the top surface is found to be negligible wrt. the other one). Pantographic blocks are modeled herein with a second gradient 3-dimensional continuum model that is valid at the length scale of pantographic cells. This reduced order model allows for predictive numerical simulations whose computational burden is relatively small. Second gradient effects (i.e., higher-order terms contributing to the strain energy) are limited to the second derivatives along the fibers of their transverse displacements. Digital Volume Correlation (DVC) techniques are employed to measure deformed shapes of pantographic blocks. A model-driven initialization procedure of DVC is followed to quantify the shape of such pantographic blocks in large displacements and strains.

Evaluations of corrugated macro-structure porous heat sinks for the combined heat dissipation and noise reduction performance

In compact air convection cooling applications, it is desirable to satisfy noise reduction and heat dissipation within same functional space. Designing a solution for such application need to consider thermal, acoustic and flow aspects. The corrugated arrangement of porous material is utilized for the combined thermal-acoustic function, as it is known to offer a lesser mean-flow pressure drop than other geometries such as block shape, wedge shape. It consists of air channels separated by porous walls which conduct the heat away from base of the heat sink. The porous walls are considered to be consisting of a periodic foam material. The effect of higher-than-ambient temperatures on the acoustic performance of the corrugated arrangement is observed experimentally using a custom-built test setup. Two designed, additively manufactured corrugated porous heat sink samples with octet truss periodic foam are tested within the heat sink operating conditions observed typically in electronics cooling applications (<70 °C). A coupled thermal-acoustic model is presented to predict and study the performance of the corrugated porous heat sinks for the combined application. The relevant performance parameters are pressure drop, overall thermal resistance and transmission loss (TL). Using this model, a simple parametric design study is enabled with variations in porosity and different macro-geometric parameters of the corrugated arrangement.

Semi-automatic extraction of dangerous rock blocks from jointed rock exposures based on a discontinuity trace map

Using a rock slope surface model generated from unmanned aerial vehicle (UAV) digital photogrammetry, this study develops a new semi-automatic dangerous rock blocks extraction approach. It consists of four steps: (1) three dimensional trace map extraction and projection; (2) convex polygon searching using a depth-first search algorithm and a sign consistency test; (3) true block formation analysis based on the geometric topology; and (4) block removability, failure mode and stability analyses using the edge vector, active resultant vector and limit equilibrium method, respectively. Compared with existing block identification methods, the proposed approach considers the contribution of line-type discontinuities on block formation and integrates geometric and mechanical modelling processes in one program. This approach is suitable for rockfall sources quantitative assessment. The locations, geometric parameters, and stability results of all identified blocks can be automatically obtained, and these could provide a reference for rockfall hazard assessment. The proposed approach is applied to a railway bridge case in China, and the corresponding rockfall hazard is evaluated. At the end of this paper, the joint sets related to block formation, uncertainties of block shapes, and discontinuity size effect are discussed.

Ferrohydrodynamics Mixed Convection of a Ferrofluid in a Vertical Channel with Porous Blocks of Various Shapes

Numerical simulations of (water-Fe3O4) ferrohydrodynamics (FHD) mixed convection inside a vertical channel are performed. The magnetic field is produced by three sources positioned outside the channel’s right wall. The latter is provided with localized heat sources surmounted by variously shaped porous blocks: rectangular, trapezoidal, and triangular. The general model of Darcy-Brinkman-Forchheimer is employed to describe the fluid flow in the porous regions, and the resulting equations are numerically solved by the finite volume approach. The influence of significant parameters, including the magnetic number (Mn), the Richardson number (Ri), and the shape of blocks, is examined. The results essentially reveal that the enhanced heat transfer brought by the magnetic field and its intensity increase is suppressed by the augmentation of Ri until a critical value, rising with Mn, beyond which the global Nusselt number increases again. The mean friction coefficient increases with increased Mn and reduced Ri. Compared to the case with no magnetic field, the maximum enhancement in heat transfer rate is around 132% for the rectangular blocks, 146% for the trapezoidal blocks, and 160% for the triangular blocks, while the maximum increase in pressure drop is approximately 45% for all the shapes. The triangular shape seems the most efficient because it leads to high heat transfer rates and low mean friction coefficients; its performance factor is 2.32 for a dominant magnetic field and 2.62 for a dominant buoyancy force. The current research's conclusions will help optimize the operation of various thermal engineering systems, including electronic devices, where the improved heat removal rate will keep the electronic components at a safe operating temperature.

Investigation of the effective hydro-mechanical properties of soil-rock mixtures using the multiscale numerical manifold model

This study focuses on determination of the effective hydro-mechanical properties of a widespread geological mélange, the Soil-Rock Mixture (SRM), using the multiscale Numerical Manifold Method (NMM). Influences of the Volumetric Block Proportion (VBP), block size, block shape, block orientation angle and micro-dynamics on the effective properties are investigated thoroughly. The SRM structural models are generated within the NMM framework in a statistical manner. The effective properties are extracted using the multiscale theory where micro-dynamics is fully considered based on the extended Hill-Mandel lemma. Through numerical simulations, the VBP and block orientation angle prove to be the first and second most influential factors. A growing VBP leads to increasing deformation moduli but decreasing effective permeability and Biot’s factor. Normal components of permeability and deformation tensors are positively proportional to the corresponding normal intersecting areas formed by sample cross-sections and blocks while shear components are positively proportional to sums of the normal and shear intersecting areas. Introducing micro-dynamics and diminishing the time step make the effective permeability and deformation moduli rise while Biot’s coefficient decrease. The accuracy and stability of the multiscale NMM are validated by comparing present results with those of empirical formulae and single-scale numerical methods.

Tectonic setting of metamorphism and exhumation of eclogite-facies rocks in the South Beishan orogen, northwestern China

AbstractHigh-pressure metamorphic rocks occur as distinct belts along subduction zones and collisional orogens or as isolated blocks within orogens or mélanges and represent continental materials that were subducted to deep depths and subsequently exhumed to the shallow crust. Understanding the burial and exhumation processes and the sizes and shapes of the high-pressure blocks is important for providing insight into global geodynamics and plate tectonic processes. The South Beishan orogen of northwestern China is notable for the exposure of early Paleozoic high-pressure (HP), eclogite-facies metamorphic rocks, yet the tectonism associated with the HP metamorphism and mechanism of exhumation are poorly understood despite being key to understanding the tectonic evolution of the larger Central Asian Orogenic System. To address this issue, we examined the geometries, kinematics, and overprinting relationships of structures and determined the temperatures and timings of deformation and metamorphism of the HP rocks of the South Beishan orogen. Geochronological results show that the South Beishan orogen contains ca. 1.55–1.35 Ga basement metamorphic rocks and ca. 970–866 Ma granitoids generated during a regional tectono-magmatic event. Ca. 500–450 Ma crustal thickening and HP metamorphism may have been related to regional contraction in the South Beishan orogen. Ca. 900–800 Ma protoliths experienced eclogite-facies metamorphism (~1.2–2.1 GPa and ~700–800 °C) in thickened lower crust. These HP rocks were subsequently exhumed after ca. 450 Ma to mid-crustal depths in the footwall of a regional detachment fault during southeast-northwest–oriented crustal extension, possibly as the result of rollback of a subducted oceanic slab. Prior to ca. 438 Ma, north-south–oriented contraction resulted in isoclinal folding of the detachment fault and HP rocks. Following this contractional phase in the middle Mesozoic, the South Beishan orogen experienced thrusting interpreted to be the response to the closure of the Tethyan and Paleo-Asian Ocean domains. This contractional phase was followed by late Mesozoic extension and subsequent surface erosion that controlled exhumation of the HP rocks.

Structural Changes in Block-Shaped WEBAM’ed Ti6Al4V Samples after Friction Stir Processing

In this paper, the structure and mechanical properties of workpieces made of Ti6Al4V alloy in the shape of blocks manufactured by wire-feed electron beam additive manufacturing and processed by friction stir processing were investigated. Samples were cut from the upper and lower parts of the additive block and processed in the layer deposition direction using different tool loading forces. Studies have shown that the processing of such material forms a clearly defined thermomechanically affected zone represented by nanosized α-grains. In the stir zone, the material is characterized by a fine-dispersed structure with a content of α- and nanosized α″-phase plates. The material after processing demonstrates 24% higher values of the ultimate tensile strength as compared to the base metal in the as-built state.

Heat-prone neighbourhood typologies of European cities with temperate climate

• Compact mid-rise areas are the most heat-prone in Amsterdam, London, and Paris • Within one local climate zone, morphological variance needs to be considered. • Combinations of seven morphological parameters are analysed. • Four neighbourhood typologies are developed using K-means cluster analysis. • Street orientation and Height-to-Width ratio are the most variant parameters. Outdoor microclimates vary among different urban neighbourhoods depending on their morphological variations. The Local Climate Zone (LCZ) framework is a well-developed typomorphological classification used to capture the variation that characterises neighbourhood microclimates. However, it does not include detailed morphological parameters within neighbourhoods that have synergistic effects on microclimates. It is thus essential to develop neighbourhood typologies with detailed spatial descriptions. This study first identifies the LCZ in Amsterdam, London and Paris with the highest Land Surface Temperature (hereinafter referred to as the most heat-prone areas). Subsequently, parameters which are not covered by the LCZs were analysed, including building block's floor area ratio and shape factor, street canyon's orientation and Height-to-Width ratio, street total length, green space area, and tree cover ratio. The results show that LCZ 2-compact mid-rise areas are the most heat-prone. Employing K-means cluster analysis, four neighbourhood typologies are distinguished within the LCZ 2: mainly wide streets with N-S and E-W orientations, mainly narrow streets with N-S and E-W orientations, mainly narrow streets with NE-SW and NW-SE orientations, mainly wide streets with four orientations divided by 45°. These generalised neighbourhood typologies can be used as the basis for design interventions aiming at climate adaptation in heat-prone urban areas.

Macro-meso shear properties of alluvial-diluvial soil-rock mixture (ADSRM) subgrade fillers based on field investigation and N-method

Alluvial-diluvial deposit (ADSRM) is a special soil-rock mixture, which is composed of gravels, boulders, pebbles, and fine-grained soils carried by rivers or temporary floods. Its mechanical properties are quite different from regular soils and rocks. Based on the investigation results of alluvial-diluvial deposits in Luonan, Shaanxi Province, China, and the theory of the N-method, the shear mechanical properties of ADSRM samples with different N-values were analyzed using large-scale direct shear tests and image processing technology (IPP). Investigation results show that alluvial-diluvial deposits in the Luonan area are widely distributed, and most of complex origins and structures. The fractal dimension values of ADSRM samples only have one scale range of particle size and decrease with the increasing n value. The equivalent cohesion, internal friction angle, shear strength, and dilation value of the ADSRM sample with n = 0.55 are higher than those of other samples. The proportion of pore area, pore abundance, total crushing area, the fractal dimension of rock block contour, and equivalent diameter and abundance of rock blocks were used to characterize the pores and rock block morphology on the shear plane. The shape of most pores on the shear plane is oblate, secondly near-equiaxed, and the least long-strip. The crushing area of rock blocks on the shear plane of n = 0.55 sample is the highest, and the shape of most rock blocks is oblate and tends to develop to near-equiaxed. In summary, the macro-meso shear properties and engineering characteristics of the n = 0.55 sample are better than those of other samples designed by the N-method.

Morphology Effects on Structure-Activity Relationship of Pd/Y-ZrO2 Catalysts for Methane Oxidation

Pd/Y-ZrO2 catalysts were prepared by Y-ZrO2 with different morphologies (flower-like, spherical, reticulated, and bulk-specific morphology), which were prepared by hydrothermal synthesis. Activity evaluation and characterization results show that the morphology influences the microstructures of Y-ZrO2 and the chemical states of active Pd species, thus affecting the activity of methane oxidation. Bulk Pd/Y-ZrO2 exhibits the best CH4 oxidation activity and thermal stability due to the block shape exposed (101) surface, and the single tetragonal phase structure maintained after high-temperature aging. The relatively large-sized Pd particles and Pd0 jointly promote the catalytic oxidation of CH4.

A Model for Sound Propagation Through Corrugated Porous Structures With Mean Flow

Abstract For applications of porous materials where mean pressure drop is a concern, packaging the material into a corrugated structure is better compared to other geometries such as block or wedge shapes. The goal of this study is to integrate noise reduction functionality within that material, which requires an understanding of sound propagation through corrugated porous structures, including flow effects. The corrugated porous structure involves porous partitions separating inlet and outlet fluid channels. The porous materials considered are periodic octet-truss and body-centered cubic unit cells, and sound propagation across these porous partitions is modeled using the Johnson–Champoux–Allard model. The predicted transmission loss (TL) is benchmarked using designed additively manufactured corrugated structures measured using a flow duct. The laminar flow regime is maintained across the porous structure to reduce flow-noise effects. It is shown that the TL for a given corrugated structure increases with a decrease in porosity, and the impact of flow becomes significant as the porosity decreases. The influence of flow on TL also depends on the unit cell configuration. Furthermore, the model provides insights into pressure and acoustic particle velocity distributions within the corrugated structure and reveals regions of the porous material that effectively participate in noise reduction.

Characterization of dust produced during the 2021 first campaign in EAST tokamak

• The dust collected from 2021 first experimental campaign in EAST was characterized and analyzed. • By using the diagnostic observation window, dust was collected during the campaign for several times. The local dust production rate decreases as the plasma operation goes. • Ferromagnetic dust with the shape of strips, flakes, irregular blocks and spheroids has been found in EAST. Dust has been collected and characterized by various methods during the 2021 first experimental campaign in EAST tokamak. It was found that the weight of the in-vessel dust collected at the mid-plane port varied from about 265 mg to about 966 mg. And the dust appeared mainly in the shape of spheroids, flakes, stripes and irregular-shaped particles with the sizes ranging from micrometers to several millimeters. The dust consisted of different elements, which was from the wall-conditioning, erosion of plasma-facing materials (PFMs) as well as the flaking of deposits. The dust collected from the lower port K contained different elements from those collected from the in-vessel port K, with more Fe in the lower port and more Li in the vacuum vessel. The ferromagnetic dust with different shape has been found, and different shape has different O content and size. By using the diagnostic observation window, dust was firstly collected during the campaign and the local dust production rate is calculated, which is found to decrease as the plasma operation goes.