Macroscopic Mechanics Research Articles

Study on the mechanical properties and microstructure of a rich-watered grouting material

The effective method of mine gas control and efficient development is gas extraction technology. The sealing effect of grouting material on borehole directly affects the efficiency of gas extraction. The new type of rich-watered sealing material with suitable mechanical strength and significant plastic characteristics was developed based on the addition of accelererant, alkali activator, expansion agent and reinforcing agent to Portland cement for mining. The effect of reinforcing agent on the mechanical properties of materials under different w/c ratios was tested by RMT. By means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and other test methods, the microstructure evolution of grouting materials and its influence mechanism on macroscopic mechanics were revealed. The results show that the crystal structures of hydration products AFt, Ca(OH)2 and C-A-H regulate the development of mechanical strength of materials. The uniaxial compressive strength of rich-watered grouting materials can reach 3.5–5.6 MPa and the residual strength is greater than 3 MPa in the range of rich-watered ratio of 0.9–1.3. The new rich-watered grouting material developed has significant plastic deformation characteristics under high rich-watered ratio conditions, which can greatly adapt to borehole deformation and reduce the gap width of slurry-coal interface, and can meet the technical requirements of long-term sealing of gas extraction boreholes.

Failure analysis and engineering mechanics modeling methods of a stitched ceramic sandwich structure

Stitched ceramic sandwich structures attract much attention in the aerospace field due to their advantage of heat insulation/load-bearing integration. In this study, the industrial camera and strain gauges were applied to perform out-of-plane tensile, compressive, interlaminar shear and 4-point bending tests of a stitched sandwich structure. Different specimens were fixed on the corresponding fixtures of a universal testing machine, and the loading rates referred to related standards. The images were captured at 1 Hz and analyzed by digital image correlation method. Based on macroscopic properties and microscopic damage mechanisms, progressive damage analysis was conducted to simulate mechanical behaviors of the structure. The representative volume element model was established for tensile, compressive and shear simulations, and several full models were proposed for bending simulations based on different degrees of simplification. The experimental results indicate that: The stitched sandwich structure shows approximately linear macroscopic mechanical behaviors under out-of-plane tensile and interlaminar shear loads, but exhibits bilinear behaviors under out-of-plane compression and 4-point bending loads. Core-related damage typically occurs first under external load, including interface debonding between the core and panel, shear delamination, collapse of holes, and densification of matrix; the sutures is the main load-bearing constituent. The precise model can describe nonlinear and bilinear behaviors, and characterize the damage evolution of the sandwich structure. The simplified model without considering the sutures is able to simulate 4-point bending behavior efficiently and accurately. The research demonstrates that, sutures can be ignored when simulating 4-point bending behavior, while they (especially out of plane) are necessary for vibration analysis. The mechanical effect of constituents during loading should be fully considered in the finite element model simplification.

Mechanism of attapulgite processed by calcination and grinding on hydration process and mechanical properties of cementitious materials

In this paper, the effects of attapulgite processed by two different methods, burning and grinding attapulgite (BGA) and grinding and burning attapulgite (GBA), on the macroscopic mechanical properties and microscopic hydration mechanism of cement paste were systematically studied. The application potential of these two materials in the field of cement-based materials was analyzed and evaluated. The results indicated that both BGA and GBA inhibited the hydration of cement to varying degrees at 7th day of age. Due to the competitive adsorption of water by the nanorod crystal structure of BGA and GBA, the amount of water used for cement hydration decreased, thus reducing the hydration degree of cement. The decrease of hydration product content increased the porosity and leaded to the decrease of mechanical strength. At the age of 28th days, due to the slow-release effect of the nanorod crystal structure and the pozzolanic effect, the macroscopic mechanical strength of the admixture ratio except for 20 % BGA all exceeded that of control paste. The mass generation of hydration products of the paste formed a dense micro structure and thus reduced the porosity. The structure and morphology of Calcium silicate hydrate (CSH) formed by BGA and GBA were distinctive by SEM-EDS at 28th days, because Ca/Si in CSH decreased to different degrees. In general, the performance of GBA on cement hydration kinetics and macroscopic mechanical strength was better than that of BGA at 7th and 28th day, and 20 % GBA was the optimal ratio of all mixture ratios.

Investigation of progressive failure mechanism of tunnel lining with material defects using discrete element method

Material defects in the concrete lining are common due to factors such as poor construction quality and environmental erosion. Material defects can exacerbate the stress status, give rise to microcracks accumulation and may bring out a failure of the concrete lining. Thus, investigating the performance of concrete lining with material defects is essential for evaluating the safety of operating tunnels. In this paper, the discrete element method (DEM) is adopted to investigate the influence of material defects on the mechanical performance of the concrete and the progressive failure process of the lining structure. For this purpose, a numerical approach is adopted for modeling concrete with randomly distributed defects. After that, the mechanical performance and micro-fracturing evolution process of concrete specimens influenced by material defects are examined. Then, a numerical model of lining concrete structure containing aggregate and mortar is established to investigate the impact of material defects on the progressive failure mechanism and bearing capacity of the concrete lining structure. Findings show that the stress concentration caused by material defects damages concrete when the load is much lower than its strength. Macroscopic fracture bands formed from the interconnection of microcracks among defect sites, which not only accelerates the damage process but also changes the failure model of concrete specimens. These characteristics of defective concrete decrease its macroscopic mechanics, such as compressive strength and elastic modulus. At the structure level, material defects degrade the stress state of the lining structure, causing localized damage to the lining structure and dramatically lowering the safety of tunnels. The distribution of material defects has a prominent influence on the failure model of concrete lining structures, where the content of material defects significantly impacts the bearing capacity of the concrete lining structure.

Micro-damage evolution and macro-mechanical property of preloaded sandstone subjected to high-temperature treatment based on NMR technique

Sandstone is an important natural building material. Due to blasting, excavation disturbance and other geological disasters, the rock usually continue to work with initial damage in engineering projects. Moreover, geological high temperatures and sudden fire have a significant influence on the internal structure and mechanical stability of sandstone containing initial damage. Therefore, to study the micro-damage evolution and macro-mechanical properties of the preloaded sandstone after thermal treatment, the mechanical testing system (DSZ-1000) was used to carry out the uniaxial cyclic loading–unloading test with different stress amplitudes. Three kinds of sandstone with different initial damage were formed, and then heated at different temperatures (25 °C, 200 °C, 400 °C, 600 °C and 800 °C). Based on macroscopic mechanics and deformation analysis, the microstructure evolution of the sample was analyzed by using nuclear magnetic resonance (NMR). It is found that the preloading and high-temperature lead to mechanical properties degradation and the change of microstructure, and the energy dissipation increases with the rise in stress amplitude during cyclic loading and unloading. Meanwhile, the coupled mechanical-thermal treatment can promote significantly the development of the pore and crack of sandstone relative to the single treated method of the cyclic preloading or high-temperature. Moreover, based on the comprehensive analysis of mechanical parameters, T2 spectrum, NMR imaging, X-ray diffraction patterns and porosity, the macroscopic mechanical and microscopic damage evolution laws of the preloaded sandstone under high temperatures were determined.

Numerical simulation model of reciprocating rod seal systems with axial wear texture on rod surface

AbstractIn this paper, a simulation model of reciprocating rod seal systems when there is axial texture on the rod surface due to wear is studied. The model includes macroscopic solid mechanics analysis, microscopic contact mechanics analysis and fluid mechanics analysis, and on this basis, the change of surface pressure when the sealing ring fall into a texture is calculated by the micro‐deformation mechanics analysis of the seal surface. Then, the stiffness matrix method is used to find the film thickness when the three pressures in the sealing area are in equilibrium, completing the fluid–solid coupling calculation. Combined with the above simulation process, the performance parameters of the sealing system such as leakage and friction can be obtained. Results show that axial texture will degrade sealing performance, which increases leakage and friction. The simulation results can quantitative characterise the influence of rod wear on sealing performance and provide some theoretical basis for the study of seal failure mechanism and prediction of seal life.

Recent advances toward mesoscopic quantum optomechanics

We present a number of approaches, currently in experimental development in our research groups, toward the general problem of macroscopic quantum mechanics, i.e., manifestations of quantum noise and quantum fluctations with macroscopic (engineered and microfabricated by man) mechanical systems. Discussed experiments include a pendulum, a torsion pendulum, a ng-scale phononic-crystal silicon nitride membrane, a μ g-scale quartz resonator, and mg-scale mirrors for optical levitation. We also discuss relevant applications to quantum thermometry with optomechanical systems and the use of squeezed light to probe displacements beyond conventional quantum limits.

Photo-induced stress relaxation in reconfigurable disulfide-crosslinked supramolecular films visualized by dynamic wrinkling

Stress relaxation in reconfigurable supramolecular polymer networks is strongly related to intermolecular behavior. However, the relationship between molecular motion and macroscopic mechanics is usually vague, and the visualization of internal stress reflecting precise regulation of molecules remains challenging. Here, we present a strategy for visualizing photo-driven stress relaxation induced by infinitesimal perturbations in the intermolecular exchange reaction via reprogrammable wrinkle patterns. The supramolecular films exhibit visible changes in microscopic wrinkle topography through ultraviolet (UV)-induced dynamic disulfide exchange reaction. In accordance with the trans-scale theoretical models, which quantitatively evaluate the chemical-dependent mechanical stresses in the supramolecular network, the unexposed disordered wrinkles evolved into highly oriented patterns and underwent subsequent mutations after thermal treatment. The stress-sensitive wrinkle macro-patterns can be repetitively written/erased through network topology rearrangement using different stimuli. This strategy provides an approach for visualizing and understanding the molecular behavior from dynamic chemistry to mechanical changes, and directly programming wrinkle patterns with regulated structures.

The importance of intermediate filaments in the shape maintenance of myoblast model tissues.

Liquid and elastic behaviors of tissues drives their morphology and their response to the environment. They appear as the first insight into tissue mechanics. We explore the role of individual cell properties on spheroids of mouse muscle precursor cells and investigate the role of intermediate filaments on surface tension and Young's modulus. By attening multicellular myoblast aggregates under magnetic constraint, we measure their rigidity and surface tension and show that they act as highly sensitive macroscopic reporters closely related to microscopic local tension and effective adhesion. Shedding light on the major contributions of acto-myosin contractility, actin organization and intercellular adhesions, we reveal the role of a major component of intermediate filaments in the muscle, desmin and its organization, on the macroscopic mechanics of these tissue models. Implicated in the mechanical and shape integrity of cells, intermediate filaments are found to be crucial to the mechanics of unorganized muscle tissue models even at an early stage of differentiation both in terms of elasticity and surface tension.

Mechanical Properties of Polyaniline/Polyvinyl Alcohol Composite Gels Utilized in Strain Sensor

In order to determine the mechanical properties of polyaniline/polyvinyl alcohol composite gels used in strain sensors, both microstructure and macroscopic mechanics experiments are conducted on the specimen. Firstly, the preparation process for this material will be explained. Then, the microstructure of this material showing the wrinkles and small holes caused by water loss is discussed. Based on the static tension test, the final equivalent elastic coefficient and relaxation time are obtained. Then, the fatigue parameters like the asymptotic temperature increment, asymptotic dissipation, and energy tolerance to failure are determined by the thermal-graphic technique.

Friction Behavior of Rough Surfaces on the Basis of Contact Mechanics: A Review and Prospects.

Contact and friction are closely related as friction cannot happen without contact. They are widely used in mechanical engineering, traffic, and other fields. The real contact surface is not completely smooth, but it is made up of a series of tiny contact asperities as viewed in the micro-scale. This is just the complexity of the contact and friction behaviors of rough surfaces: the overall mechanical behavior is the result of all asperities which are involved during the contact. Due to the multiplicity of surface topography, the complexity of contact scale, and the nonlinearity of the constitutive material, there are still many open topics in the research of contact and friction behavior of rough surfaces. Based on the perspective of the macroscopic and micro-nano scale contact mechanics, this review gives a brief overview of friction for the latest developments and points out the existing issues and opportunities for future studies.

Study on Mechanical Properties of the Compound Soil of Feldspathic Sandstone and Sand Based on Micro – level

It is of great practical significance to study the mechanical properties of composite materials of arsenic and sandstone to control the ecological environment in soft sandstone area. In order to understand the material and structural characteristics of composite materials under different compound proportions, the microstructure and the composition of the material elements were analyzed by the microscopic test and the test of mercury injection from the microscopic level. The dynamic three axis instrument was used to carry out the mechanical test under the different mixing ratio. The results showed that the main mineral components of feldspathic sandstone are quartz, albite, montmorillonite and calcite. The structure has the strength in the anhydrous state. When the water is saturated, the structure collapses, the cohesive force decreases rapidly, and it has the collapsibility; Due to the complexity of the structure and the optimization of the gradation, the permeability is greatly reduced; the macroscopic mechanics exhibits strain hardening and nonlinear characteristics.

Shape-programmable cantilever made of a magnetoactive elastomer of mixed content

This work presents an approach to the macroscopic field-controlled mechanics of magnetoactive elastomers of mixed content, which are a special type of smart materials made of an elastic composite and a combination of two essentially different ferromagnetic fillers. High-coercive particles of NdFeB-alloy powder for the magnetically hard (MH) filler and carbonyl iron powder particles with nearly zero coercivity for the magnetically soft (MS) filler are usually used. The MH particles are tens-of-micron in size and impart to the elastomer a remanent magnetisation, whereas due to the MS particles of several microns in size, the elastomer acquires a high magnetic susceptibility. Since large MH particles once magnetised in a strong field possess their own fields to which the MS particles are susceptible, the overall elastomer magnetisation as well as its mechanical response greatly depends on the relative concentration of both fillers. This work particularly studies the bending deformation of horizontally fixed magnetoactive cantilevers with the permanent magnetisation along the length axis under the action of gravity and a vertically applied uniform magnetic field. The cantilevers of the same geometry and fixed NdFeB content but different carbonyl iron concentration are considered. The magnetomechanical model is developed based on the finite-strain theory assuming the plane-stress approximation of the two-dimensional cantilever of infinite width. The magnetic energy comprises two magnetic terms, one of which is qualitatively linear and the other one is quadratic in the applied field strength. The numerically calculated field-programmed equilibrium bending shapes of the cantilevers are compared with the experimentally observed shapes. The model provides good agreement with the experiment up to moderate concentrations of the MS filler, when the coefficients of customary interpolation formulas for the concentration dependencies of elastic modulus and magnetic susceptibility are properly adjusted.

Human Visual System involves macroscopic scaleinvariants and microscopic quantum mechanics single-photon sensitivity

“A half Century has gone by; the general public seems to be lacking a simple Readers’ Digest knowledge about human visual system (HVS). In order to ward off wolf eyesight emitting few photons in a dark cavern, we have evolved to separate the energy from the information, as well as adopt the negation of the converse detection logic. To achieve the sensitivity, HVS uses the dark (no light yet) current, discovered by NIH Hagins, to inhibit 100 rods' bundled together by Ganglion integrator by using its own energy firing. We have applied the dark current to inhibit firing, until a detection of a single photon of wolf eyesight by any of the rod bundle. In this short communication, we shall give 2 theorems: macroscopic scale invariants and microscopic quantum mechanics. Now we know why we can see red color while the other animal cannot and why we can detect a single photon while the other cannot. Given the basic deep learning algorithm and possible experiments to verify Quantum Mechanics Uncertainty Principle for HVS single photon detection capability according to the Gold Standard: Double Blind, Negative Control and Sufficient Statistics.”

Probabilistic failure mechanisms via Monte Carlo simulations of complex microstructures

A probabilistic approach to phase-field brittle and ductile fracture with random material and geometric properties is proposed within this work. In the macroscopic failure mechanics, materials properties and spatial quantities (of different phases in the geometrical domain) are assumed to be homogeneous and deterministic. This is unlike the lower scale with strong fluctuation in the material and geometrical properties. Such a response is approximated through some uncertainty in the model problem. The presented contribution is devoted to providing a mathematical framework for modeling uncertainty through stochastic analysis of a microstructure undergoing brittle/ductile failure. Hereby, the proposed model employs various representative volume elements with random distribution of stiff inclusions and voids within the composite structure. We develop an allocating strategy to allocate the heterogeneities and generate the corresponding meshes in two- and three-dimensional cases. Then the Monte Carlo Finite Element Method (MC-FEM) is employed for solving the stochastic PDE-based model and approximate the expectation and the variance of the solution field of brittle/ductile failure by evaluating a large number of samples. For the prediction of failure mechanisms, we rely on the phase-field approach which is a widely adopted framework for modeling and computing the fracture phenomena in solids. Incremental perturbed minimization principles for a class of gradient-type dissipative materials are used to derive the perturbed governing equations. This analysis enables us to study the highly heterogeneous microstructure and monitor the uncertainty in failure mechanics. Several numerical examples are given to examine the efficiency of the proposed method.

Mechanical response and damage mechanism of 2D woven SiCf/SiC ceramic matrix composites under tension-shear coupling load

The macroscopic mechanical behavior and coupling damage mechanism of 2D woven SiCf/SiC ceramic matrix composites (CMC) prepared by chemical vapor infiltration (CVI) process under tension-shear coupling load were experimentally analyzed. At macroscale, the uniaxial tension, uniaxial shear and off-axis tension tests were completed and the results were compared. The tensile modulus and proportional limit have no significant difference with the increase of off-axis angle, while failure strength decreases by 22.3% compared the 45° tensile (165.4 MPa) with the 0° tensile (212.8 MPa). Based on the strain-difference analysis, the coupling damage effect of SiCf/SiC-CMC was characterized. At microscale, the main damage types of SiCf/SiC-CMC during loading were analyzed by scanning electron microscope (SEM), and the corresponding laws between micro damage development and macro mechanical behavior under different loading conditions were revealed by cluster analysis of acoustic emission (AE) signals. The test results show that the micro damage caused by tensile and shear stress components promote each other. The macro mechanical behavior of SiCf/SiC-CMC under complex loading is controlled by basic micro damage forms such as matrix cracking, interface debonding and fiber fracture. The tension-shear coupling load affects the evolution process of the basic damage forms, and then change the macro properties of SiCf/SiC-CMC.

Plasma Oscillatory Pressure Sintering of Mo-9Si-8B Alloy with ZrB2 Addition.

Oscillatory pressure sintering is a novel crystal refinement technology. The doping of different concentrations of ZrB2 under oscillatory sintering technology (9 Hz) is discussed here, focusing on its macroscopic mechanics and oxidation resistance. In particular, doping 2.5 wt% ZrB2 can effectively increase the hardness of the alloy, slightly increase the fracture toughness of the alloy and have an outstanding effect on the oxidation resistance of the alloy at 1300 °C, achieving the effect of reducing mass loss by 80.3%.

Macroscopic quantum mechanics in gravitational-wave observatories and beyond

The existence of quantum correlations affects both microscopic and macroscopic systems. On macroscopic systems, they are difficult to observe and usually irrelevant for the system's evolution due to the frequent energy exchange with the environment. The world-wide network of gravitational-wave (GW) observatories exploits optical as well as mechanical systems that are highly macroscopic and largely decoupled from the environment. The quasi-monochromatic light fields in the kilometer-scale arm resonators have photon excitation numbers larger than 1019, and the mirrors that are quasi-free falling in propagation direction of the light fields have masses of around 40 kg. Recent observations on the GW observatories LIGO and Virgo clearly showed that the quantum uncertainty of one system affected the uncertainty of the other. Here, we review these observations and provide links to research goals targeted with mesoscopic optomechanical systems in other fields of fundamental physical research. These may have Gaussian quantum uncertainties as the ones in GW observatories or even non-Gaussian ones, such as Schrödinger cat states.

Prediction of the Macroscopic Mechanics Properties of Recycled Aggregate Concrete Based on the Mesoscopic Equivalence Theory

Prediction of the Macroscopic Mechanics Properties of Recycled Aggregate Concrete Based on the Mesoscopic Equivalence Theory

Particle Flow Analysis of Macroscopic and Mesoscopic Failure Process of Salt Rock under High Temperature and Triaxial Stress

In order to reveal the mechanism of thermal-induced deformation and fracture development of salt rock under high temperature, the particle flow program PFC2D was used to study the triaxial compression failure process of salt rocks under different temperatures; at the same time, a combination model of Burge and Linearpbond was proposed to simulate plastic deformation and heat conduction of salt rock. Finally, the simulation results were compared with the experimental results to verify the validity of the conclusion. The simulation results show that the elastic limit points of rock gradually descend, the dilatancy points rise gradually, and the plastic deformation characteristics of salt rock become more obvious with the increase of temperature. Due to the damage of the sample, the strong chains break and disappear, increasing the proportion of the weak chains, and the high temperature intensifies the rupture of the contact between the particles in the salt rock. As the temperature increases from 50°C to 120°C, the strong chains in the rock sample decrease significantly, and the damage gradually increases; when the temperature is 150°C, the contact force decreases sharply, and the damage of salt rock is significant. According to the particle displacement cloud diagrams, it is found that the expansion direction from the middle part of the rock sample to the left and right ends is 12.08°, 9.55°, 8.2°, 6.33°, and 0°, respectively. The displacement directions of the rock sample show obvious radial expansion tendency, and the higher the temperature, the more obvious the “drum-shaped” failure phenomenon in the middle of the rock sample. During the heating process, the thermal cracks are mainly tensile cracks, and transverse cracks are gradually formed in the middle of the model. The cementation failure points at the top and bottom of the model expand in an oblique direction and form oblique cracks of about 45°. From the three different mathematical models of macroscopic and mesoscopic views, it is concluded that the effect of temperatures on salt rock is more significant after 90°C. This research is important for exploring the macroscopic and microscopic mechanics evolution of salt rock and provides a reference for determining the long-term mechanical strength of salt rock.