In this work, a four-dimensional lattice spring model is developed for studying the mechanical responses of solids. Our results indicate that the Poisson’s ratio limitation of the classical lattice ...spring model defined in three-dimensional space can be released by introducing an extra fourth-dimensional interaction. The fourth-dimensional lattice spring model adopts central interactions only, and it can naturally represent the nonlinear dynamic responses of solids without special treatment of rigid body rotation or incremental integration of non-central/non-local interaction as used in the traditional methods. Applicability of the model is illustrated from a few numerical examples.
•The Poisson’s ratio limitation of classical LSM is released by introducing an extra fourth-dimensional interaction.•The method of constructing 4D lattice spring model is presented.•The method of parameters selection is provided.•The underlying principle is investigated using hyperelasticity analysis.
Innovative technologies are highly pursued for the detection and avoidance of counterfeiting in modern information society. Herein, we report the construction of photo-responsive supramolecular ...polymers toward fluorescent anti-counterfeit applications, by taking advantage of multicycle anthracene‒endoperoxide switching properties. Due to σ-metalation effect, photo-oxygenation of anthracene to endoperoxide is proceeded under the mild visible light irradiation conditions, while the backward conversion occurs spontaneously at room temperature. Supramolecular polymers are formed with cooperative nucleation‒elongation mechanism, which facilitate fluorescence resonance energy transfer process via two-component co-assembly strategy. Fluorescence resonance energy transfer efficiency is delicately regulated by either light-triggered anthracene‒endoperoxide conversion or vapor-induced monomer-polymer transition, leading to high-contrast fluorescent changes among three different states. On this basis, dual-mode anti-counterfeiting patterns have been successfully fabricated via inkjet printing techniques. Hence, cooperative supramolecular polymerization of photo-fluorochromic molecules represents an efficient approach toward high-performance anti-counterfeit materials with enhanced security reliability, fast response, and ease of operation.
Monolayer SixCy constitutes an important family of 2D materials that is predicted to feature a honeycomb structure and appreciable bandgaps. However, due to its binary chemical nature and the lack of ...bulk polymorphs with a layered structure, the fabrication of such materials has so far been challenging. Here, the synthesis of atomic monolayer Si9C15 on Ru (0001) and Rh(111) substrates is reported. A combination of scanning tunneling microscopy (STM), X‐ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and density functional theory (DFT) calculations is used to infer that the 2D lattice of Si9C15 is a buckled honeycomb structure. Monolayer Si9C15 shows semiconducting behavior with a bandgap of ≈1.9 eV. Remarkably, the Si9C15 lattice remains intact after exposure to ambient conditions, indicating good air stability. The present work expands the 2D‐materials library and provides a promising platform for future studies in nanoelectronics and nanophotonics.
2D Si9C15 monolayer is fabricated on Ru (0001) and Rh(111) substrates via the reaction between Si and graphene under high temperatures. The as‐grown Si9C15 layer is micrometer‐scale, high quality, and single crystalline with a bandgap of ≈1.9 eV. Combined measurements and density functional calculations confirm the buckled honeycomb structure. The novel 2D material also shows good air stability.
Digital image correlation (DIC) is used to investigate crack initiation and propagation in discs of transversely isotropic Hawkesbury sandstone subjected to the Brazilian test. To verify DIC's ...validity and precision a simple calibration method is presented. It involves adjusting the size and spacing of subsets of pixels within images of a specimen's surface from which local deformations and strains are quantified, achieving agreement between strains measured by DIC and gauges attached to the surface. Using DIC the tensile and shear strain fields, crack opening displacements (CODs) and displacement vectors are determined at all stages of loading. The development of the fracture process zone is also identified prior to a major crack initiation. Also, a range of load contact configurations is considered, including the loads being applied via flat rigid platens and across finite strips with widths controlled by small (3 mm wide) and big (5 mm wide) wooden cushions placed between the load applicators and discs. It is observed that, for 0° and 90° anisotropy angles (representing layering normal to and parallel to diameters connecting load contacts) and for both the flat platen and small wooden cushion, cracks initiate far from the disc centres. Also, for the 45° anisotropy angle and all load configurations, cracks initiate at the disc centres. Furthermore, when the loads are applied via big wooden cushions, cracks initiate at the disc centres regardless of the anisotropy angle. Also, specimens loaded via big wood cushions exhibited the largest COD while the specimens loaded via small wood cushions exhibited the smallest. Also, specimens loaded via flat platens failed at smaller loads compared to those using wooden cushions. This study confirms transverse isotropy has strong effect on crack development. It also demonstrates important parameters including time and location of initiation, as well as COD, may be determined using DIC.
In this work, an improved domain decomposition method is developed to address workload imbalance when implementing the parallel computing of a four‐dimensional lattice spring model (4D‐LSM) to solve ...problems in rock engineering on a large scale. A cubic domain decomposition scheme is adopted and optimized by a simulated annealing algorithm (SAA) to minimize the workload imbalance among subdomains. The improved domain decomposition method is implemented in the parallel computing of the 4D‐LSM. Numerical results indicate that the proposed domain decomposition method can further improve the workload balance among processors, which is helpful to supersede the limit of computational scale when solving large‐scale geotechnical problems and decrease the runtime of the parallel 4D‐LSM by at most 40% compared to the original cubic decomposition method. This shows the practicability of the proposed method in parallel computing. Two types of target functions of SAA are tested, and their influence on the performance of the parallel 4D‐LSM is investigated. Finally, a computational model with one billion particles for one actual engineering application of using 4D‐LSM is realized, and the result shows the advantages of parallel computing.
•The fracture criterion in DLSM has been validated against LEFM.•Fracture toughness is influenced by the intrinsic length-scale of microstructure.•A simple and unified crack criterion can simulate ...various fracturing conditions.•DLSM can simulate crack propagation and coalescence with pre-existing cracks.•DLSM can easily cope with dynamic crack propagation and 3D fracturing.
With the rapid development of high-performance computing, Lattice Spring Models (LSMs) using a simple fracturing law demonstrate many prospects for simulating crack propagation in brittle solids. In this paper, a comprehensive study on crack propagation in brittle material is conducted using the distinct lattice spring model (DLSM) with high-performance computing and physical tests on crack propagation in brittle material from this work and the literature. The relationship between the simple fracturing law and the fracture criterion based on linear elastic fracture mechanics is investigated for the first time. The work involved includes the correlation between the Stress Intensity Factor (SIF) and spring deformation, the influence of the particle size on fracture toughness, and the relationship between the micro-spring failure and the critical stress intensity factors. Our results indicate that the simple fracturing law based on spring deformation may be easier and more fundamental for understanding crack propagation in brittle materials than fracture-toughness-based criteria. The applicability of the simple fracturing law is further confirmed from numerical modelling of crack propagation and coalescence problems with complex pre-existing cracks. Our results show that models with an appropriate resolution can simulate the crack path reasonably. Finally, the advantages of using the simple fracturing law are highlighted through multiple dynamic crack propagation and three-dimensional fracturing.
Acoustic emission uncovers thermal damage evolution of rock Zhang, Yuliang; Zhao, Gao-Feng; Li, Qin
International journal of rock mechanics and mining sciences (Oxford, England : 1997),
August 2020, 2020-08-00, 20200801, Letnik:
132
Journal Article
Recenzirano
The thermal damage evolution of rock closely relates to many important scientific and engineering problems, such as the mechanisms of earthquake and the effective extraction of deep geothermal ...energy. However, there is lack of rational thermal damage evolution model, and the mechanisms of thermal damage are still unclear especially during cooling. By use of a specially designed acoustic emission (AE) test system, we explored the thermal damage evaluation in a rock and established a thermal damage evolution model which takes into account both heating and cooling processes. The mechanisms of rock damage caused by heating and cooling were analyzed by using a lattice spring model, and two different microstructural explanations were found, i.e. heterogeneous microstructure and microdefect structure. The damage evolution model can be used for more accurate modeling of these problems which involve rock thermal damage, such as induced seismic activity during deep geothermal exploration.
3D printing is an innovative manufacturing technology that enables the printing of objects through the accumulation of successive layers. This study explores the potential application of this 3D ...printing technology for rock mechanics. Polylactic acid (PLA) was used as the printing material, and the specimens were constructed with a “3D Touch” printer that employs fused deposition modelling (FDM) technology. Unconfined compressive strength (UCS) tests and direct tensile strength (DTS) tests were performed to determine the Young’s modulus (
E
) and Poisson’s ratio (
υ
) for these specimens. The experimental results revealed that the PLA specimens exhibited elastic to brittle behaviour in the DTS tests and exhibited elastic to plastic behaviour in the UCS tests. The influence of structural changes in the mechanical response of the printed specimen was investigated; the results indicated that the mechanical response is highly influenced by the input structures, e.g., granular structure, and lattice structure. Unfortunately, our study has demonstrated that the FDM 3D printing with PLA is unsuitable for the direct simulation of rock. However, the ability for 3D printing on manufactured rock remains appealing for researchers of rock mechanics. Additional studies should focus on the development of an appropriate substitution for the printing material (brittle and stiff) and modification of the printing technology (to print 3D grains with arbitrary shapes).
Brazilian tests are used to determine tensile strengths of rocks. Failure mechanisms, and the strengths determined, are influenced by the configuration of the load contacts. Most research on how to ...interpret Brazilian tests is only valid for isotropic rocks. This study addresses Brazilian tests on transversely isotropic rocks, experimentally and analytically, to identify failure conditions for a range of load contact types and anisotropy angles (representing orientations of the transversely isotropic planes with respect to direction normal to the loading). Stress fields are determined analytically and coupled with a failure criterion to infer locations where failure and crack initiations occur. The analytical results are compared with experimental observations using digital image correlation (DIC) for transversely isotropic Hawkesbury sandstone. It is found that anisotropy angles affect the locations of the crack initiations, with agreement between the experimental results and analytical solutions being observed. The study goes on to show that, for a wide range of transversely isotropic rocks and for planes parallel and perpendicular to the loading directions, cracks will always initiate at disc centres as long as the contact area is large (corresponding to a subtended angle at the disc centre of at least 25∘). Failure and cracking at a disc centre enables reliable determination of the indirect tensile strength. The equation for strength, including a stress concentration factor for a range of transversely isotropic elastic properties, is presented for use by practitioners and laboratory technicians.
PDF
