Design Of Efficient Structures Research Articles

Radiation attenuation of boro-tellurite glasses for efficient shielding applications

The borotellurite glasses whose chemical structure is (29.5–0.4x)CaO + 10CaF2 + (60–0.6x)B2O3 + xTeO2+ 0.5Yb2O3 (where x=10, 16, 22, 31, and 54 % mole. represent TCCBY1-TCCBY5, respectively) are Pb-free, thermally stable, and transparent glasses with attractive optical features for technological applications. The gamma-photons, electrons, protons, neutrons, carbon ions, fast neutrons, and fast neutron interaction parameters of these glasses are presented in this study to better understand the role of TeO2 in influencing their radiation shielding properties and radiation protection applications. The photon mass attenuation coefficient was evaluated by XCOM computation and simulation using the FLUKA code. The FLUKA code was also used to evaluate the mass stopping powers of the charged radiations, while neutrons’ cross sections were evaluated using standard expressions. For 0.015 MeV–15 MeV photons, the mass attenuation coefficients of the glasses fell from 17.9499 to 0.0246 cm2/g for TCCBY1, 20.5628 to 0.0263 cm2/g for TCCBY2, 23.2756 to 0.079 cm2/g for TCCBY3, 26.7487 to 0.0298 cm2/g for TCCBY4, and 33.3591 to 0.0335 cm2/g for TCCBY5. The photon half-value layer at 15 keV is reduced by about 19.57%, 32.68%, 48.84%, and 63.89% when the TeO2 content increases from 10 mol to 16, 22, 31, and 54 mol, respectively. TeO2 was found to suppress photon buildup in the glasses. The mass stopping powers of charged radiation increased as glass density decreased. The addition of TeO2 into the glass structure increased the ability of the TCCBY glass to absorb fast neutrons by up to 54 % mole. The gamma radiation and fast neutron moderating ability of TCCBY5 glass compared to common shields and other materials is exceptional. The glass is recommended for the design of Pb-free, transparent, and efficient radiation protection structures.

Practical application of multi-material topology optimization to performance-based architectural design of an iconic building

With the rapid development of architectural design methods and structural analysis techniques, structural performance-based design approaches have become increasingly important in architectural design. Among these approaches, topology optimization is a significant design method. However, most existing topology optimization research and related applications are based on single-material topology optimization techniques, which have limitations when applied to the design of complex and challenging structures. Building upon our previously proposed multi-material bi-directional evolutionary structural optimization (multi-material BESO) method, this paper presents the approaches for achieving diverse and competitive structural designs and then presents a practical application of the multi-material BESO method to the structural design of the core structure of a long-cantilevered building project called “Xiong’an Wings”. After an evolutionary design process based on the multi-material BESO method, an efficient frame with lower overall material costs, better static and dynamic performance compared to the initial design by experienced engineers is achieved. As the first practical application of the multi-material BESO method to a large-scale architectural design, the example of the “Xiong’an Wings” building demonstrates the tremendous prospects for the application of multi-material topology optimization technology to the generative design of innovative and efficient building structures.

Understanding the behaviour of a new robotic device for next-generation site investigation: A 3D DEM Exploration

Accelerating advancements in robotic engineering provide an opportunity for developing economical and efficient site characterisation devices, particularly for critical offshore applications. A new intelligent robotic device, ROBOCONE (Figure 1), is being developed for site characterisation and design of offshore structures, which would be capable of mimicking the load histories of the soil inside the ground at a desired depth [1]. The obtained soil constitutive properties would support an efficient design of offshore structures, considering “whole life” stress-strain histories. ROBOCONE could apply lateral, shear, and torsional modes (Figure 1(a)) of loading on the surrounding soil, operated remotely from the ground. In the pursuit of developing such a device, a prior understanding of its behaviour is essential. The lateral loading static and cyclic responses of offshore foundations are critical aspects of their design. The present work highlights the lateral module (P-Y Module) behaviour of the ROBOCONE device (Figure 1(a)) under various stresses, using 3D Discrete Element Modelling (DEM). The P-Y module moves horizontally at a desired depth in the ground and this lateral motion is numerically simulated using commercial DEM software, Particle Flow Code (PFC3D) [2].
 The proposed dimensions of the P-Y module are 200mm long and 54mm diameter (DRC). Present DEM model uses rigid walls as P-Y module placed in a rigid monodisperse 3D granular assembly with grain diameter of around 1/3rd DRC [3]. The Hertz contact model micro-parameters for grain-grain (E50 value of 27.4±2.2MPa) and grain-wall contacts are shown in Table 1. A 10 times higher shear modulus of grain-wall contact than the grain-grain contacts is sufficient to have stiffer response. The servo mechanism in PFC enables the model to reach desired average stresses. The primary objective of this work is to understand the ROBOCONE P-Y module behaviour and thus the lateral soil reaction curves without the influence of boundary. For the current testing mode, where the module moves laterally in the soil, the ratio of the moving object to soil bed dimensions for no boundary effects is unprecedented. A simple and innovative method of using periodic boundaries is proposed in the present study. Conventionally, periodic boundaries replicate the representative volume element infinitely at the boundaries. Due to the presence of ROBOCONE in the centre of the model, the required extent reduces to half in X and Y directions, as schematically shown in Figure 1b. This paper discusses the model side to ROBOCONE diameter, L/DRC, (e.g., 9, 18, 30) influence on the P-Y curves (at a given stress level). The effects of random particle generations for different models in PFC software can be minimized using same central core zone of contacts with ROBOCONE for each simulation, while the extent of model side is increased. ROBOCONE wished-in-place rather than driving/jacking in the model reduces the DEM computation costs. Limited amount of lateral displacement of the ROBOCONE (around 2.5mm) is sufficient to establish the effectiveness of the proposed modelling. Optimum loading rate (the lateral velocity of P-Y module) of around 0.8mm/s, which can maintain the inertial number lower than the threshold value of 7.9x10-5[4] further helps the computational efficiency.
 Once the optimum L/DRC value is obtained, the quantitative outcomes from these simulations are the lateral soil reaction curves at different stress levels and also the bending moments on the ROBOCONE P-Y Module. Though the ROBOCONE model in these simulations is a rigid wall and doesn’t mobilize in bending, the moments calculated from the magnitude and locations of each contact force on the P-Y module provide an estimate of bending stresses generated on the module. These results provide a basis for developing an understanding of the physical capacity of the robotic device in sustaining the lateral forces. Figure 1(c) shows preliminary results of soil reaction curve from the P-Y module at 500kPa stress level for L/DRC value of 9. The changes in the contact forces during the P-Y module motion can be qualitatively assessed through the changes in the force chain network (Figure 1(d)). Figure 1(e) shows a representative plot of bending moments calculated at different lateral movement stages of the P-Y module, and the maximum value at a desired displacement of the P-Y module suggests the physical design requirements of the ROBOCONE. The results from these DEM simulations would directly inform the design of the robotic device for ground investigation and hence improve the economical offshore foundation designs.

The softening effect of welding on the mechanical properties of cold-worked stainless steel

Cold-working can occur during production of flat sheet products and during fabrication of structural cross-sections. In both cases, when the material is cold-worked, plastic deformations result in material strength enhancements. These strength enhancements are particularly significant for materials such as stainless steel, which exhibit rounded stress-strain behaviour and pronounced strain hardening, and for hollow structural sections, where the strength increases arise in both the corner and flat regions of the cross-sections. Numerous studies have shown the importance of utilising this strength enhancement for efficient structural design, and predictive models have been derived for harnessing these enhancements. However, if cold-worked material is welded, some of the enhanced strength can be lost due to partial softening in the heat affected zone (HAZ). The extent of this strength loss is investigated experimentally in the present study. The experimental programme comprised ten tensile coupon tests on 1 mm thick austenitic (Grade 1.4301) stainless steel sheet material, with central welds parallel and transverse to the direction of cold-rolling, as well as twelve full cross-section tensile tests on 80×60 mm and 60×60 mm hollow sections with thicknesses varying between 2 and 4 mm. Digital image correlation was utilised to determine the local constitutive properties of the base metal, the heat affected zone, and the weld metal of each specimen. The hardness and microstructure of the welded samples, along with the widths of the weld and heat affected zone, were also characterised.

GMNIA‐based design of stainless steel structural systems

AbstractDesign by GMNIA (Geometrically and Materially Nonlinear Analysis with Imperfections) allows the key behavioural features of structures to be directly captured in the analysis, dramatically reducing the need for subsequent design checks. Since the analysis of frames typically employs beam finite elements, which do not explicitly account for local buckling, cross‐section classification and capacity checks remain necessary. To resolve the step‐wise and overly conservative nature of traditional checks, the alternative use of strain limits, defined using the Continuous Strength Method, has been proposed. The framework allows cross‐sections of all classes to be treated in a consistent manner, and results in an accurate and consistent representation of the true behaviour of structures. To date, the accuracy of the design approach for stainless steel has been comprehensively demonstrated for isolated stainless steel members; the design method is extended to indeterminate stainless steel structural systems herein. The method is included in AISC 370 and prEN 1993‐1‐14; inclusion of this design framework in international codes of practice presents a step change for the future direction of efficient structural stainless steel design.

Structural Performance of Demountable Hybrid Floor Systems Under Monotonic and Cyclic Loading

AbstractThe building sector is actively researching and reviewing technical solutions for de‐construction, driven by the increasing importance of sustainability requirements, as outlined in the EU Commission's ‘Green Deal,‘ which aims to achieve net‐zero greenhouse gas emissions by 2050. Two key research areas in efficient structural design strategies are the performance of hybrid structures, which combine mechanical properties and architectural appearance of different materials, and the techniques and mechanical properties of connections between structural components that enable deconstruction and reuse. However, there is a scarcity of studies and methods focused on demountable and hybrid structural systems, limiting the understanding of their overall structural performance at a real‐structure floor level. In this paper, a finite element model is presented to conduct a comparative study between the traditional floor system with welded stud connections and the demountable floor system with coupler‐embedded bolted connectors. The numerical results showed that the serviceability loading capacity of the demountable floor system was 8% lower, and the difference in ultimate resistance was further enlarged. Reusing a demountable floor system, analysed in the case study, had little effect on the ultimate resistance, but it is difficult to exclude local plastic deformation after the first life cycles.

Surface crack growth in metallic pipes reinforced with Fibre-Reinforced Polymers subjected to cyclic loads: An analytical approach

This paper introduces a novel analytical approach aimed at predicting the growth of surface cracks in metallic pipes reinforced with Fibre-Reinforced Polymers (FRPs) subjected to cyclic bending and/or tension loads. The primary objective of this study is to develop a comprehensive analytical model that accounts for multiple factors influencing crack growth, namely stress reduction, crack-bridging effect, stiffness degradation, and fatigue damage of the FRP-to-metal interface simultaneously. By considering these simultaneous effects, our proposed approach enables accurate evaluations of the stress intensity factors (SIFs) at both the surface point and the deepest point of a surface crack. To facilitate practical implementation, we have developed an in-house program that automates crack growth rate and residual fatigue life predictions. The proposed analytical method has been validated through a series of comparisons with experimental data and finite element results, demonstrating its accuracy in estimating fatigue lives. The key novelties of this research lie in the holistic consideration of multiple dominating and influencing factors, the achievement of precise SIF evaluations, and the development of an automated prediction tool for practical applications. Overall, our findings confirm the suitability of the proposed analytical approach for predicting crack growth and provide valuable insights for guiding the design of FRP reinforcement in surface-cracked metallic pipes. This work contributes to advancing the understanding of crack growth behaviour in FRP-reinforced metallic pipes and opens new possibilities for the safe and efficient design of such structures.

Stress field model for bond in reinforced concrete ties

The interaction of the reinforcing bars and the surrounding concrete plays an important role in structural concrete as it is decisive for the reinforcing bar anchorage and the load-deformation behaviour, including stiffness and deformation capacity. Therefore, understanding this interaction – commonly known as bond – is highly relevant to a safe and efficient structural concrete design. Bond depends on many parameters, which affect the local reinforcing bar-concrete interface as well as the global load transfer between the reinforcing bars and the surrounding concrete. The latter governs the formation of transverse and longitudinal cracks and the activation of transverse confinement, which are as decisive for bond as the local interface characteristics. Nonetheless, most bond models and code provisions focus on the local interface and merely account for the global configuration by means of empirically calibrated factors accounting, e.g. for good or bad bond conditions in confined or unconfined situations, respectively.This study investigates the potential of stress fields for modelling bond based on the lower-bound theorem of plasticity theory. Stress fields facilitate the investigation of the local interface and the global load transfer consistently in one model, providing valuable insight into the flow of forces. For simplicity, the fundamental case of a concrete tie reinforced with one deformed steel bar is studied in this paper, superimposing axisymmetric discontinuous stress fields originating at each reinforcing bar rib. Each stress field consists of a triaxial nodal zone adjacent to a rib and a conical compression field that spreads the bond force radially, and is equilibrated along its outer perimeter by axial tensile stresses and confining hoops. The model relies on geometric parameters and basic material properties. The validation against experiments on reinforced concrete ties shows a good correlation between the predicted and observed bond strength and the crack spacing. The predictions can be improved by assigning stiffnesses to the stress field components and requiring interface compatibility, i.e. ensuring contact between the concrete and the reinforcing bar at every rib. Even when assuming a simplified, linearly elastic constitutive behaviour for concrete, the consideration of interface compatibility allows for reproducing the steel strain dependency of the local and average bond stresses and the occurrence and impact of splitting cracks.

Ultrahigh-efficient material informatics inverse design of thermal metamaterials for visible-infrared-compatible camouflage

Multispectral camouflage technologies, especially in the most frequently-used visible and infrared (VIS-IR) bands, are in increasing demand for the ever-growing multispectral detection technologies. Nevertheless, the efficient design of proper materials and structures for VIS-IR camouflage is still challenging because of the stringent requirement for selective spectra in a large VIS-IR wavelength range and the increasing demand for flexible color and infrared signal adaptivity. Here, a material-informatics-based inverse design framework is proposed to efficiently design multilayer germanium (Ge) and zinc sulfide (ZnS) metamaterials by evaluating only ~1% of the total candidates. The designed metamaterials exhibit excellent color matching and infrared camouflage performance from different observation angles and temperatures through both simulations and infrared experiments. The present material informatics inverse design framework is highly efficient and can be applied to other multi-objective optimization problems beyond multispectral camouflage.

Topology optimization of rib patterns for a freeform composite structure

This paper presents an algorithm for the design of efficient and stable composite freeform shell structures. The design workflow combines form-finding, structural analysis, and optimization techniques. To illustrate it, the paper provides a case study of the design and optimization of carbon fiber-reinforced polymer shell. After form-finding of the the initial structural shape, topology optimization was conducted to develop the reinforcing rib pattern to increase its buckling resistance. The use of optimized rib layouts greatly increased the rigidity of the shell, which was confirmed by finite element simulations.[copyright information to be updated in production process]

Near-term pathways for decarbonizing global concrete production

Growing urban populations and deteriorating infrastructure are driving unprecedented demands for concrete, a material for which there is no alternative that can meet its functional capacity. The production of concrete, more particularly the hydraulic cement that glues the material together, is one of the world’s largest sources of greenhouse gas (GHG) emissions. While this is a well-studied source of emissions, the consequences of efficient structural design decisions on mitigating these emissions are not yet well known. Here, we show that a combination of manufacturing and engineering decisions have the potential to reduce over 76% of the GHG emissions from cement and concrete production, equivalent to 3.6 Gt CO2-eq lower emissions in 2100. The studied methods similarly result in more efficient utilization of resources by lowering cement demand by up to 65%, leading to an expected reduction in all other environmental burdens. These findings show that the flexibility within current concrete design approaches can contribute to climate mitigation without requiring heavy capital investment in alternative manufacturing methods or alternative materials.

A new class of string transformations for compressed text indexing

Introduced about thirty years ago in the field of data compression, the Burrows-Wheeler Transform (BWT) is a string transformation that, besides being a booster of the performance of memoryless compressors, plays a fundamental role in the design of efficient self-indexing compressed data structures. Finding other string transformations with the same remarkable properties of BWT has been a challenge for many researchers for a long time. In this paper, we introduce a whole class of new string transformations, called local orderings-based transformations, which have all the “myriad virtues” of BWT. As a further result, we show that such new string transformations can be used for the construction of the recently introduced r-index, which makes them suitable also for highly repetitive collections. In this context, we consider the problem of finding, for a given string, the BWT variant that minimizes the number of runs in the transformed string.

Research progress of intrinsic polymer dielectrics with high permittivity

AbstractThe high permittivity of polymer dielectrics facilitates their use in the electronics industry. Compared to inorganic ceramics and composites, intrinsic high permittivity polymer dielectrics have the advantages of easy solution processing and better homogeneity. The permittivity of common polymers is generally low, hence it would be worthwhile to explore avenues for augmenting the permittivity of polymer dielectrics via judicious and efficient structural design. The effective strategies used to increase the permittivity of intrinsic polymers encompass elevating local polarisabilities by fortifying electron delocalisation capabilities, exploiting ion pairs to generate atomic clusters with larger dipole moments, amplifying dipole density, augmenting dipole mobility, and so forth. Due to the rigidity and flexibility of the polymer backbone's decisive influence on the dielectric's all‐around performance, its selection also requires a total consideration of the requirements of practical applications. This work provides an overview and a brief evaluation of the dominant design strategies and mentions possible future design paradigms for polymer dielectrics.

Mechanics and properties of fish fin rays in nonlinear regimes of large deformations

Fins from ray-finned fishes do not contain muscles, yet fish can change the shape of their fins with high precision and speed, while producing large hydrodynamic forces without collapsing. This remarkable performance has been intriguing researchers for decades, but experiments have so far focused on homogenized properties, and models were developed only for small deformations and small rotations. Here we present fully instrumented micromechanical tests on individual rays from Rainbow trout in both morphing and flexural deflection mode and at large deflections. We then present a nonlinear mechanical model of the ray that captures the key structural elements controlling the mechanical behavior of rays under large deformations, which we successfully fit onto the experiments for property identification. We found that the flexural stiffness of the mineralized layers in the rays (hemitrichs) is 5-6 times lower than their axial stiffness, an advantageous combination to produce stiff morphing. In addition, the collagenous core region can be modeled with spring elements which are 3-4 orders of magnitude more compliant than the hemitrichs. This fibrillar structure provides negligible resistance to shearing from the initial position, but it prevents buckling and collapse of the structure at large deformations. These insights from the experiments and nonlinear models can serve as new guidelines for the design of efficient bioinspired stiff morphing materials and structures at large deformations. Statement of significanceFins from ray-finned fishes do not contain muscles, yet fish can change the shape of their fins with high precision and speed, while producing large hydrodynamic forces without collapsing. Experiments have so far focused on homogenized properties, and models were developed only for small deformations and small rotations providing limited insight into the rich nonlinear mechanics of natural rays. We present micromechanical tests in both morphing and flexural deflection mode on individual rays, a nonlinear model of the ray that captures the mechanical behavior of rays under large deformations and combine microCT measurements to generate new insights into the nonlinear mechanics of rays. These insights can serve as new guidelines for the design of efficient bioinspired stiff morphing materials and structures at large deformations.

Structural investigation of zinc‐based photoresists with different substituents for high‐resolution lithography

The fineness of the photolithographic pattern depends largely on the composition and structure of the photoresist, and different structures endow metal‐based photoresists with different photon‐absorbing capabilities. Here, we synthesized zinc‐based photoresists with different electron‐effect substituents (amine and bromine) in the ligands and investigated the influence of the ligand groups on the sensitivity and resolution at deep ultraviolet and electron beam. The developed resist patterns exhibit that the sensitivity of the Zn‐based photoresists containing bromine groups (Zn‐PBBA) is nearly seven times higher than the Zn‐based photoresists containing amine groups (Zn‐PABA) at the same resolution under ultraviolet irradiation, which is supported by the density functional theory (DFT) calculations where a smaller HOMO–LUMO gap for Zn‐PBBA is obtained. Analogously, the Zn‐PBBA also showed better sensitivity and resolution than Zn‐PABA at EBL, with a resolution of 70 nm at a dose of 800 mJ cm−2 by characterization with AFM. This work provides an understanding of the efficient structural design of photoresists and future guidance for the development of better‐performing materials.

Structural design of hybrid steel-timber buildings for lower production stage embodied carbon emissions

Using cross laminated timber (CLT) floor panels in combination with steel framing has been identified as a promising new structural configuration that can reduce the embodied greenhouse gas emissions of buildings. This project evaluated efficient structural design of hybrid steel-timber floor sections for a wide range of design parameters to determine the reductions in global warming potential possible relative to a conventional steel-concrete cross section. Each of the structural designs was checked for strength limit states, deflection, and minimum fire rating of either unrated, 1-h, or 2-h for a range of deck spans between 2.3 m and 4.6 m and beam spans between 5.5 m and 13.5 m. For an unrated floor assembly there is little global warming potential benefit to use steel-timber floors if a topping slab is included on top of the CLT slab. Whereas, using steel-timber configurations without a topping slab result in the largest global warming potential reductions. For the 1-h and 2-h ratings, even steel-timber configurations with a 64 mm thick topping slab had up to 20% reduction in global warming potential compared to the steel-concrete alternative. Additionally, several considerations that can drastically affect the global warming potential results were discussed. The results from this project demonstrate the best practices for structural design of hybrid steel-timber buildings to reduce global warming potential of the superstructure frame by between 5% and 35% relative to conventional steel and concrete construction.

Построение распределенных микропроцессорных систем управления движением поездов

High material requirements of new relay systems make it impossible to modernize devices within existing areas and require the construction of new interlocking system buildings, which significantly affects the volume of capital investments. Transitioning to microelectronic and microprocessor electronic platforms allows for the design of more compact systems with expanded functional capabilities. In global practice, there is a trend towards widespread use of microprocessor-based interlocking system. However, there is a slow pace of device updates, mainly due to the high cost of microprocessor-based interlocking system, which exceeds by several times the cost of similar relay-based interlocking system. The high performance of computing resources and fiber-optic data transmission channels allows for the design of efficient structures for microprocessor-based interlocking system. The article presents a comparative analysis of the structures of microprocessor-based interlocking system. The implemented decentralized structures solve the issues of reducing investments for the design and construction of the station’s cable network. The advantages of using these systems from the point of view of controlling the transportation process are described, conclusions are drawn on the effective use of the capabilities of modern control systems with integrated subsystems in relation to field-based train traffic control technologies.

Hydrologic Design of Soil and Water Conservation Structures Using Probability Analysis and Machine Learning Techniques in Saurashtra Region of Gujarat, India

The soil and water conservation structures are constructed to overcome water scarcity as a result of interannual rainfall variability and paucity of the perennial source of water. The present study was aimed to estimate the design runoff for the efficient hydrologic design of various soils and water conservation structures using machine techniques for enabling efficient harvesting of available rainfall with economical design which can support in developing climate resilience for the Saurashtra region of Gujarat, India. The design rainfall at various return periods was predicted by Annual One Day Maximum Rainfall (ADMR) using three technics i.e. Probability Distribution Fitting, Artificial Neural Network (ANN) and Gaussian Process Regression (GPR) for 11 stations. Various goodness of fit tests revealed that ADMR was efficiently predicted by log-logistic (3P) distribution for six stations, generalized extreme value distribution for two stations and lognormal (3P), gamma (3P) and lognormal distribution for one station each. Among ANN and GPR, the performance indicators revealed that GPR has shown a higher capability to predict ADMR as compared to ANN with correlation coefficient ranging from 0.97 to 0.99, mean absolute error from 15 mm to 411 mm and root mean squared error from 40 mm to 494 mm for various stations. The design runoff estimation was demonstrated based on predicted ADMR for return periods suitable for various soil and water conservation structures like field bunding, terrace outlets and vegetative outlets, field diversion, permanent masonry gully control structures, earthen dam, etc. using SCS-Curve Number method for curve number 70 and 85. The study is useful for researchers, planners and engineers to implement the economical, efficient and safe design of various soil and water conservation structures.

Theoretical and Numerical Analysis of Cohesive-Frictional Backfill against Battered Retaining Wall under Active Translation Mode

The appropriate prediction of horizontal earth pressure against retaining walls can lead to a safer and more efficient design of such structures. Retaining walls are among the structures in which the arching phenomenon plays an essential role in distributing horizontal earth pressure. In this research, based on the limit equilibrium condition and considering the arching effect, a new theoretical method is proposed to estimate the earth pressure against a battered wall under translation movement with a cohesive-frictional backfill soil. A parametric study is conducted for assessing the effect of the surcharge pressure, cohesion, internal friction angle, wall–soil friction angle, and wall inclination on lateral earth pressure. In addition, a series of numerical models is employed to implement the finite difference method. The development of shear bands inside the backfill and the changes in earth pressure behind the wall are studied. The outcomes of the suggested analytical solution are compared with the numerical data as well as with some other theories. It is concluded that the proposed method is applicable to a wide range of cohesive-frictional soils retained with walls, covering a variety of batter angles and face frictional conditions.

Characterizing the cracking process of various rock types under Brazilian loading based on coupled Acoustic Emission and high-speed imaging techniques

Tensile strength is one of the important mechanical properties of rock and rock-like materials and its accurate estimation and understanding of its failure mechanism are crucial for efficient design of structures on or within the rock masses. Amongst various approaches developed for estimating this property, Brazilian testing has received considerable attention analytically, numerically and experimentally. The test has been deployed for a wide range of materials such as rock, concrete, and ceramic, however its fracturing process at micro and macro scales has not yet been properly characterized. Thus, in this study, for a full understanding of the fracturing process of different rock types under indirect tensile loading, the coupled Acoustic Emission (AE) and high-speed imaging techniques were used to characterize the generated micro and macrocracks under Brazilian loading. The characteristics of AE parameters and the evolution of micro-macro cracks were investigated for three different rocks including sandstone, coal and granite at different sizes and loading configurations. A systematic framework was developed to exhibit the link between micro and macro fracturing processes under Brazilian loading. It was noted that the tensile microcracks are the first to initiate during the Brazilian failure with high intensity compared to shear microcracks. Transition in microcracking mechanism from tension to shear was evident in the samples with high brittleness. The tensile microcracks showed ascending trends with a decrease in geometrical or volumetric sample size for granite and sandstone, while its trend for coal was inconclusive due to its unique intrinsic fracture network or so-called “cleat network”. At macro scale level, single and multiple cracking mechanisms were observed in the tested samples where those with high shear microcracks mostly revealed failure under multiple cracking. Finally, some insights were provided into the transition from single tensile cracking to multiple tensile/shear cracking based on high-speed image data with high resolution.