Axial Stress Research Articles

Mechanical testing and numerical simulation of intelligent terminal structure of rockbolt used as a deformable support and for safety monitoring in rock engineering

The nonlinear mechanical behavior perception and deformation control of engineering rock masses are crucial technical challenges in the fields of underground engineering support and safety monitoring. An intelligent terminal structure (ITS) of rockbolts was designed for deformable support systems and safety monitoring in rock engineering applications. It is a type of device installed at the end of a traditional bolt. The ITS comprises two key components: a memory tooth and a yielding ring. This study introduces the design principle of an ITS in deformable rockbolt support systems. It proposes design parameters for the ITS in relation to the deformations encountered by engineering rockbolts. Tests were conducted to measure the ultimate bearing capacity and deformation of the ITS under pull-out conditions. The results demonstrate that the ITS of rockbolt undergoes deformation in the form of elongation as opposed to conventional bolts. Furthermore, finite element numerical simulations were conducted to investigate the mechanism of interaction between the memory tooth and yielding ring of the ITS. The numerical simulation results are consistent with the experimental results. The load capacity of the yielding ring exceeded that of the memory tooth. The field test results indicate that the dilatation of the surrounding rock mass causes ITS deformation in the diversion tunnel. The axial stress load exerted on the rockbolt is transferred to the ITS, leading to memory tooth breakage and compression deformation of the yielding ring. This mechanism allows the load and deformation of the surrounding rock mass to be reflected. The ITS not only serves as a deformable support system but also plays a significant role in monitoring the stress and deformation of the rock mass.

Electrochemical-Thermal-Mechanical Coupling Analysis of Lithium-Ion Batteries under Fast Charging

Thermal runaway and volume expansion caused by temperature rise under fast charging of lithium-ion batteries (LIBs) are the major reasons of battery explosion and cycle performance degradation. In this work, considering the radiation heat transfer on the battery surface, an electrochemical-thermal-mechanical coupling model of cylindrical LIBs under fast charging (state of charge (SOC) ≤80%) is developed in order to investigate the distributions of the temperature and stress. Then, choosing 18650 LIBs as the object, the charge efficiency, temperature, and stress distributions are compared between fast charging and galvanostatic operation under SOC≤80%, respectively. Finally, the influences of the thickness, particle radius, the maximum lithium-ion concentration of the cathode, and initial electrolyte concentration on the temperature, radial stress, and hoop stress of LIB during charge are explored, respectively. Numerical results show that fast charging improves 20.8% of the charge efficiency. Increasing the cathodic thickness and decreasing the cathodic maximum lithium-ion concentration or initial electrolyte concentration can reduce the temperature of LIB during the charge. The results of this work will provide some reference value for the design of LIBs under fast charging.

A new method for visually and real-timely measuring stress and load distributions in bolt with photoelastic technology

After analyzing the stress characteristics of the bolt, we determined that it can be regarded as experiencing a planar stress state due to the absence of circumferential stress. Consequently, a photoelastic bolt specimen was fabricated by taking a slice across its diameter. Using a photoelastic bench, we collected interference fringe images of the photoelastic specimen under different loads. This method enabled us to visually and continuously measure the stress distributions within the specimen in real-time. Additionally, the load distribution ratio of each tooth was derived. By comparing these results with those obtained through numerical simulation, we were able to validate the reasonability of the theoretical assumption regarding the load distribution of each tooth in the bolt. Our method establishes a solid foundation and can be effectively utilized for precise thread connection design.

High-speed photoelastic tomography for axisymmetric stress fields in a soft material: Temporal evolution of all stress components

This study presents a novel approach for reconstructing all stress components of the dynamic axisymmetric fields of a soft material using photoelastic tomography (PT) and a high-speed polarization camera. This study focuses on static and dynamic Hertzian contact as an example of transient stress field reconstructions. For the static Hertzian contact (a solid sphere pressed against a gel block), all stress components in the urethane gel, which has an elastic modulus of 47.4 kPa, were reconstructed by PT using the measured photoelastic parameters. The results were compared with theoretical solutions and showed good agreement. For the dynamic Hertzian contact (a sphere impacting gel), a high-speed polarization camera was used to reconstruct the transient stress field within the gel. PT was used to quantitatively measure the shear and axial stress waves and showed different propagation speeds on the substrate. The technique allowed the simultaneous measurement of stress fields ranging from O(10−1) to O(101) kPa during large deformations, demonstrating its accuracy in capturing rapidly changing stress tensor components in dynamic scenarios. The scaling laws of the calculated impact force agreed with theoretical predictions, validating the accuracy of PT for measuring dynamic axisymmetric stress fields in soft materials.

The Influence of CO2 Physical Properties on Casing and Its Prediction Method

In order to reveal the physical properties of CO2 under actual formation conditions, this paper establishes a mathematical model of the temperature field and pressure field in the wellbore under CO2 injection conditions, optimizes the state equation of CO2 physical-property parameters, calculates the change trend of CO2 density, viscosity, and compression factor along the wellbore, and obtains the influence law of CO2 corrosion on the casing and interface. The viscosity showed a downward trend along the well depth; the compression factor showed an upward trend. The surfaces of the three casings were smooth and flat without obvious defects, the cement structure was dense, and there was no obvious pore structure. After corrosion, with the increase of Cr content, the change of interfacial corrosion decreases. The morphology of the Q125 and 3Cr interface is loose after corrosion, while there is no obvious change in the 13Cr interface. With the prolongation of corrosion time, low wellbore internal pressure easily causes casing yield, and high wellbore internal pressure easily causes cement-sheath compression failure. The circumferential stress of the casing increases with the corrosion time extension, and the radial stress of the casing and cement sheath decreases first and then increases with the corrosion time. The compressive strength of the cement sheath does not exceed the compressive strength.

Experimental study on durability of steel-basalt fiber reinforced concrete under multiple factors coupling

A series of durability tests were conducted using varying composite salt solutions (5% Na2SO4 + 3.5% NaCl, 10% Na2SO4 + 3.5% NaCl, and 3.5% NaCl) and stress levels (F-0.3, F-0.6) to investigate the durability of concrete reinforced with steel and basalt fibers. Specimens were extracted after 0, 25, 50, 75, 100, 125, and 150 wet-dry cycles to explore the changes in the appearance, mass loss, relative dynamic modulus of elasticity, and compressive strength with the number of wet-dry cycles and different coupling effects. Mathematical models correlating mass and compressive strength with wet-dry cycles and stress levels were separately established. The concrete microstructure under coupling effects was observed using Environmental Scanning Electron Microscopy (ESEM). The results indicated that the inhibitory effect on the increase in concrete mass was higher in the F-0.6 group than in the F-0.3 group, showing that concrete under F-0.3 exhibited faster mass growth. As the axial compressive stress ratio increased, steel-basalt fiber reinforced concrete's relative dynamic modulus of elasticity changed less. Concrete degradation was more pronounced in the 10% Na2SO4 + 3.5% NaCl solution and F-0.6 loading environment. The calculated results from the established models agreed with the experimental results, demonstrating a certain degree of feasibility.

Nonlinear Static Bending and Forced Vibrations of Single-Layer MoS2 with Thermal Stress.

Single-layer molybdenum disulfide (MoS2) has been a research focus in recent years owing to its extensive potential applications. However, how to model the mechanical properties of MoS2 is an open question. In this study, we investigate the nonlinear static bending and forced vibrations of MoS2, subjected to boundary axial and thermal stresses using modified plate theory with independent in-plane and out-of-plane stiffnesses. First, two nonlinear ordinary differential equations are obtained using the Galerkin method to represent the nonlinear vibrations of the first two symmetrical modes. Second, we analyze nonlinear static bending by neglecting the inertial and damping terms of the two equations. Finally, we explore nonlinear forced vibrations using the method of multiple scales for the first- and third-order modes, and their 1:3 internal resonance. The main results are as follows: (1) The thermal stress and the axial compressive stress reduce the MoS2 stiffness significantly. (2) The bifurcation points of the load at the low-frequency primary resonance are much smaller than those at high frequency under single-mode vibrations. (3) Temperature has a more remarkable influence on the higher-order mode than the lower-order mode under the 1:3 internal resonance.

Elliptic Rigid Inclusion in Soft Materials of Harmonic Type

Abstract We investigate finite plane deformations of an elliptic rigid inclusion embedded in a soft matrix that is made of a particular class of harmonic-type hyperelastic materials. The inclusion is assumed to be perfectly bonded to the matrix, which is subjected to a constant remote in-plane loading. Utilizing the Cauchy integral techniques associated with conformal mappings, we derive closed-form solutions for the full-field deformation, Piola stress, and Cauchy stress in the entire matrix. Numerical examples are presented to illustrate the current solutions in comparison with those established from linear elasticity theory. We find that in terms of the Cauchy stress around the inclusion, the maximum normal stress component always appears at the endpoints of the major axis of the inclusion, irrespective of the magnitude of the remote loading, while the maximum hoop stress component occurs not exactly at the above-mentioned endpoints when the remote loading exceeds a certain value. In particular, we identify an exact explicit formula for determining the relative rotation of the inclusion during deformation induced by a remote uniaxial loading of arbitrarily given magnitude and direction.

A New Design Method for Obround Shells

Abstract The design of obround components has been difficult and complex due to the absence of a suitable theoretical solution. Current design codes use empirical formulas based on assumptions to determine the minimum required thickness for obround components. The design process involves iteration. The results obtained are far from accurate. Based on a recently proposed closed-form solution, a new design method for obround components is developed. In the new method, an obround shell is imagined as being stretched laterally from a cylindrical shell or parent cylinder. With the flattened shell increasing, the thickness of the obround shell should increase accordingly, to keep the maximum hoop stress of obround shell consistent with the maximum hoop stress of the parent cylinder. The minimum requested thickness (MRT), of the obround shell is related to the MRT of the parent cylinder and the flattened shell length of the obround shell. Through parametric studies, those relationships are investigated. Empirical expressions are used to describe those relationships. Using the proposed design method, the determination of the MRT of obround members becomes the determination of the MRT of the parent cylinders and additional parameters. The MRT of obround members is determined directly. The case study demonstrates that the proposed method is an efficient and accurate design process for obround members. The use of new method for fitness-for-service was explored. The new method can be used to reassess operational safety in the event of vessel materials' deterioration.

Value of information from fatigue monitoring of the monopile foundation of an offshore wind turbine

Value of information (VoI) allows quantifying benefits of adopting structural health monitoring (SHM) even before implementation by altering the prior risk of structural failure using the probabilities of damage detection from SHM data. The VoI is the reduction in the expected failure cost when SHM data becomes available. In this study, an optimized time of SHM deployment for fatigue crack growth in an offshore wind turbine (OWT) monopile foundation is achieved by maximising VoI. The prior probabilities of failure are obtained from stochastic analysis of dynamic responses to random wind and waves characteristic of North Sea environment. Short-term stress time histories are statistically processed to determine the probability distribution functions of their extrema and ranges and statistical extrapolation techniques are then implemented to analyse the long-term probability distributions of axial stresses. The long-term stress ranges and numbers of cycles are determined by the rainflow count and used in fatigue reliability analysis. The probability of detecting a fatigue crack by SHM is modelled and used for calculating the OTW failure risk after repair is conducted based on SHM outcome. The optimal deployment time of the fatigue crack monitoring system for the analysed 5-MW OWT is determined as 21 years past erection.

Key role of surface defects in the multiaxial fatigue life of additively manufactured unmachined 18Ni300 maraging steel

The study aims to estimate the role of surface defects in the fatigue life of age-hardened and unmachined additively manufactured 18Ni300 maraging steel and to verify the effectiveness of stress-based life prediction models. Axial-torsional cyclic loading paths involving in-phase and out-of-phase cases are applied. Scanning electron microscopy and micro-computed tomography are performed to detect the fatigue crack initiation sites and paths. The effectiveness of the classic models and a physics-constrained Gaussian process for regression in fatigue life prediction is estimated. Results show that the intrinsic orientation of the surface defects affects the fatigue mechanism by increasing the material sensitivity to axial stress. Additionally, the steel is insensitive to the phase shift between the axial and torsional loading components. The hydrostatic stress and the integrated shear stress amplitudes over the critical plane are pointed as the most effective load-related quantities for life prediction.

Mechanical behaviors and rupture processes of a typical granitic stratum

Granitic veins (GVs) have a significant influence on the mechanical responses of tunnels excavated in granitic strata. Distinguishing the mechanical properties of host granites (HGs), GVs and vein-granite interfaces (VGIs) is critical. For this, this paper analyzed the mechanical behaviors and rupture processes of typical HG, GV, and VGI samples under uniaxial compression condition. For the rocks studied, although the linear axial stress‒strain relation can be identified and the deformation modulus can be determined, the transverse deformation developed nonlinearly with axial stress. As a result, the instantaneous Poisson's ratio increases continuously and may even exceed 0.5, making it extremely difficult to accurately determine the Poisson's ratio. In addition, the studied GV samples were found to be significantly brittle, indicating that large-scale GVs cannot be ignored when assessing rockburst hazards in granitic strata with brittle GVs. In terms of the rupture process, the HG and GV samples were gradually damaged by the formation of small-scale cracks and then ruptured by large cracks formed from small-scale cracks, whereas the VGI samples ruptured along large cracks with significant energy release. By examining the characteristic stress thresholds of these three granites, it is noted that the crack closure stress σcc exceeds both the crack initiation stress σci and the crack damage stress σcd for the HG and VGI samples. The transverse damage to a tested sample appears to be significantly greater than the axial damage, which is essentially related to the rock grain size and grain size distribution.

Response to internal pressure shock and hoop strength of SiCf/SiC cladding

This study investigated the mechanical behavior of silicon carbide fiber-reinforced silicon carbide matrix (SiCf/SiC) cladding using expanding plug tests at 0.5 and 2 mm/min. A three-stage mechanical response for SiCf/SiC was observed, with significant differences in Stage 3 between specimens tested at different rates. Specimens tested at the slower rate (0.5 mm/min) exhibited a characteristic hoop strength of 112.4 MPa and homogeneous destruction behavior, indicative of uniform stress distribution. In contrast, the hoop stress in SiCf/SiC became unsteady at the faster rate (2 mm/min), leading to cracking at a lower nominal proportional limit stress (PLS), structural instability, non-uniform fiber pull-out, and a lower characteristic hoop strength of 92.4 MPa. This suggests that similar phenomena might occur at higher loading rates during internal pressure shock. Therefore, considering the application of SiCf/SiC, to conduct hoop strength testing at faster rates was recommend, such as 2 mm/min.

Multiphysics simulations of uniaxial compression applied to various rock samples subject to microwave pretreatment

PurposeAmong the various applications involving the use of microwave energy, its growing utility within the mining industry is particularly noteworthy. Conventional grinding processes are often overburdened by energy inefficiencies that are directly related to machine wear, pollution and rising project costs. In this work, we numerically investigate the effects of microwave pretreatment through a series of compression tests as a means to help mitigate these energy inefficiencies.Design/methodology/approachWe investigate the effects of microwave pretreatment on various rock samples, as quantified by uniaxial compression tests. In particular, we assign sample heterogeneity based on a Gaussian statistical distribution and invoke a damage model for elemental tensile and compressive stresses based on the maximum tensile stress and the Mohr–Coulomb theories, respectively. We further couple the electromagnetic, thermal and solid displacement relations using finite element modeling.Findings(1) Increased power intensity during microwave pretreatment results in decreased axial compressive stress. (2) Leveraging statistics to induce variable compressive and tensile strength can greatly facilitate sample heterogeneity and prove necessary for damage modeling. (3) There exists a nonlinear trend to the reduction in smax with increasing power levels, implying an optimum energy output efficiency to create the maximum degradation-power cost relationship.Originality/valuePrevious research in this area has been largely limited to two-dimensional thermo-electric models. The onset of high-performance computing has allowed for the development of high-fidelity, three-dimensional models with coupled equations for electromagnetics, heat transfer and solid mechanics.

PHÂN TÍCH TĨNH VỎ TRỤ FG-CNTRC CHỊU TẢI TRỌNG CƠ NHIỆT VỚI TÍNH CHẤT VẬT LIỆU PHỤ THUỘC VÀO NHIỆT ĐỘ

This article presents a thermo-elastic static analysis of the FG-CNTRC cylinderical shell subjected to a thermo-mechanical load. The temperature is assumed to vary through the thickness, and the temperature distribution is derived from the heat transfer formula. The gorvening equations of thermoelastic analysis are established by using the higher-order shear deformation theory, including the transverse normal stress effect. The material properties of FG-CNTRC are temperature-dependent. Using an analytical solution that used the single trigonometric series and the Laplace transformation to solve these equations of shell with the different boundary conditions. The present approach is validated by comparing the results with published results. The effects of different boundary conditions and temperatures on the displacement and stresses of the FG-CNTRC cylindrical shells are investigated. The results show the jumping variation of the stress components at the boundary position. Besides, when the temperature increases, the maximum absolute value of the axial stress increases while that of the circumferential stress decreases.

Mechanical Properties and Microscopic Evaluation of Heat Treated D6A Ultra High-Strength Steel

This investigation aims to evaluate the influence of heat treatment on the hardness and microscopic characteristics of a specific grade of medium carbon steel, namely, the American standard D6A Ultra High-Strength Steel, which contains 0.47% carbon in its composition. After preparation, specimens were heated in a muffle furnace at a temperature of 830°C and held for 90 minutes, followed by quenching. Subsequently, the specimens underwent tempering at a temperature of 600°C for 60 minutes. The hardness and microscopic evaluation of the heat-treated steel were determined. The results also indicate a rapid increase in hardness with a decrease in thickness for the heat-treated material. For HRA (Rockwell Hardness A Scale) times of 5s and 10s, the hardness enhancement percentages were 29% and 103%, respectively, compared to specimens without heat treatment. Furthermore, a chamber pressure test assessed the suitability and optimal design of Ultra High-Strength Steel for a pressure vessel in a mortar gun. As the outer radius increases, there is a corresponding decrease in axial stress, hoop stress, and the maximum limit of ultimate stress for both internal pressures within the pressure vessel. For internal pressures of 100 MPa and 85 MPa, the optimal inner radius for the pressure vessel is determined to be 0.053m and 0.051m, respectively.

Axial compressive stability design of longitudinal asymmetrical shuttle-shaped columns

Longitudinal asymmetrical shuttle-shaped column (LA-SSC) has found its wide application when subjected to combined axial compression and horizontal point load in practical engineering. This paper focuses on elastic and elasto-plastic buckling behaviors of the LA-SSC only under axial compression and the resulting outcome could provide an indispensable basis for further establishing buckling strength prediction of LA-SSC under axial compression and horizontal point load. At first, the elastic buckling behavior of tapered columns (TC) and longitudinal symmetrical shuttle-shaped columns (LS-SSC) are derived in theory and verified by finite element numerical results, and corresponding elastic buckling modes are discussed. Subsequently the elastic buckling load prediction of LA-SSCs is established first and the corresponding normalized slender ratio, as a key design parameter, is generalized. Finally, the stability capacity of LA-SSCs is involved in theoretical analysis and finite element (FE) numerical calculation under axial pressure. Through investigating the axial load-lateral displacement curves and axial stress distributions the buckled LA-SSCs, the effects of different parameters (such as overall length, plate thickness, and steel strength) on the axial compression stability capacity of LS-SSCs are explored. As a result, the complete design formulas for axial compression stability capacity of LA-SSCs are presented first and compared with current major design codes in various countries. It is observed that the proposed strength design formulas are in good correspondence with the FE numerical results. The proposed formulas could provide references and guidance for the axial compression buckling strength of LA-SSCs under axial compression and they further supply fundamentals for establishing the strength design recommendation of LA-SSCs under axial compression and bending moments.

Combined effect of pore water pressure and axial stress level on the unloading mechanical properties of sandstone

Combined effect of pore water pressure and axial stress level on the unloading mechanical properties of sandstone

Regional shear wave speeds track regional axial stress in nonuniformly loaded fibrous soft tissues

Ligaments and tendons undergo nonuniform deformation during movement. While deformations can be imaged, it remains challenging to use such information to infer regional tissue loading. Shear wave tensiometry is a promising noninvasive technique to gauge axial stress and is premised on a tensioned beam model. However, it is unknown whether tensiometry can predict regional stress in a nonuniformly loaded structure. The objectives of this study were to (1) determine whether regional shear wave speed tracks regional axial stress in nonuniformly loaded fibrous soft tissues, and (2) determine the sensitivity of regional axial stress and shear wave speed to nonuniform load distribution and fiber alignment. We created a representative set of 12,000 dynamic finite element models of a fibrous soft tissue with probabilistic variations in fiber alignment, stiffness, and aspect ratio. In each model, we applied a randomly selected nonuniform load distribution, and then excited a shear wave and tracked its regional propagation. We found that regional shear wave speed was an excellent predictor of the regional axial stress (RMSE = 0.57 MPa) and that the nature of the regional shear wave speed-stress relationship was consistent with a tensioned beam model (R2 = 0.99). Variations in nonuniform load distribution and fiber alignment did not substantially alter the wave speed-stress relationship, particularly at higher loads. Thus, these findings suggests that shear wave tensiometry could provide a quantitative estimate of regional tissue stress in ligaments and tendons.

An elliptical compressible liquid inclusion in an infinite nonlinearly coupled thermoelectric matrix

We study the plane strain problem associated with an elliptical thermoelectrically insulated and compressible liquid inclusion embedded in an infinite homogeneous and isotropic nonlinearly coupled thermoelectric matrix under uniform remote electric current density and energy flux. With the aid of conformal mapping and analytic continuation, an exact closed-form solution to the problem is derived. In particular, an elementary expression for the internal uniform hydrostatic tension within the compressible liquid inclusion is obtained. Our result shows that the internal uniform hydrostatic tension is unaffected by the remote energy flux and is proportional to the square of the two components of the remote electric current density vector. Also presented is the hoop stress distribution along the elliptical interface on the matrix side.