Micromechanical modeling of long-term creep behavior of quasi-brittle rocks considering thermo-mechanical coupling effects

A spectral study is performed to gain insight into the effects of relaxation times and thermomechanical coupling on dynamic thermoe Iastic responses in generalized thermoelasticity. The hyperbolic thermoelastic theories of Lord and Schulman (LS) and Green and Lindsay (GL) are selected for the study. A generalized characteristic equation is derived to investigate dispersion behavior of thermoelastic waves as functions of thermomechanical coupling and relaxation time constants. Thermomechanical coupling is found to impose a significant influence on phase velocities. The GL model implicitly indicates that the order of magnitude of the thermomechanical relaxation time can never be greater than that of thermal relaxation time.

Theoretical and numerical study of the thermo-mechanical coupling effect on the fluid viscous damper

In view of the thermo-mechanical coupling effect that commonly exists in the loading zone of angular-contact ball bearings while the bearings are operated, several process parameters are analyzed, including coordination condition of thermal expansion–deformation load, interaction relationship of contact stress, friction heat, and temperature raised in the loading zone of bearings. Based on the dynamic method of rolling bearings and finite element analysis method, the thermo-mechanical coupling calculation model of angular-contact ball bearings is established and solved. Based on the model, the influences of coupling effect on temperature field, loading characteristics, and fatigue life of bearings are analyzed. Then, the influence of geometric parameters and working conditions of bearings on the thermo-mechanical coupling effect are discussed. The results show that there are differences in the results of temperature distribution, loading characteristics, and fatigue life while the thermo-mechanical coupling effect is considered or not in the bearings analysis; furthermore, the mentioned differences vary with the different geometric parameters and working conditions.

The phenomenon of three “high” and one “disturbance” in deep rock masses is a prominent problem with the increase of the mining depth, which seriously threatens the stability of the rocks surrounding roadways and mining workplaces. For this study under thermo-hydro-mechanical (THM) coupling effect, the deep gneiss rocks in Hong Tou Shan Copper mine were chosen as the subject to explore the mechanical character of deep mining rocks. The experiment involved triaxial loading and unloading on the rocks under different conditions, and the failure mechanism of deep mining rocks under THM coupling effect was revealed. The research showed that the mechanical responses of gneiss in different experimental conditions were significantly diverse. The maximum strength, damage stress strength, and residual strength of gneiss during triaxial loading and unloading under THM coupling effect were the smallest. Also, under conditions of triaxial loading and unloading under hydro-mechanical coupling effect, thermo-mechanical coupling effect, and the conventional condition of triaxial loading and unloading, the strength of gneiss increased successfully. However, the deformation parameters of gneiss shifted clearly towards failure phase when this experiment was performed using THM coupling effect. That is, the drop in elastic modulus and the increase in Poisson’s ratio were the largest. Meanwhile, a reduction in the shifting of deformation parameters of gneiss towards failure was seen in the following order: when the experiment was performed under triaxial loading and unloading with hydro-mechanical coupling, then under thermo-mechanical coupling and then under conventional triaxial loading and unloading. Also, the gneiss failure characteristics in every experimental condition were markedly different. Shear failure of conjugate oblique section happened in conventional triaxial loading and unloading condition, shear failure of the X-conjugate oblique plane happened in triaxial loading and unloading condition under thermo-mechanical coupling effect; tensional shear failure happened in triaxial loading and unloading condition under hydro-mechanical coupling effect, and shear failure of a single slope happened in condition of triaxial loading and unloading condition under THM coupling effect. Based on the coupling effect, the three fields formed on various conditions such as temperature, stress, and seepage impact, interact and constraint, influence each other mutually during deep mining of rocks. Reduction coefficient of confining pressure in relation to water pressure is introduced to build a mechanical model of THM coupling in deep mining rock. Then, gneiss failure characteristics are further discussed and analyzed, which provides a theoretical basis for deep engineering rock mass control under complicated environments.

A dual-scale elasto-viscoplastic constitutive model of metallic materials to describe thermo-mechanically coupled monotonic and cyclic deformations

The effect of thermo-mechanical coupling is a key factor that needs to be fully considered during the construction, operation, and maintenance of tunnels in high ground temperature areas so that measures could be taken to reduce the frequency of damages and accidents. However, research methods and theoretical results for tunnel support structures under high temperature conditions and layered soft rock environment are insufficient, therefore, to fill in this research blank, this paper aims to study the damage deterioration mechanism of tunnel structure under thermo-mechanical coupling effect and its maintenance. In the second chapter, this paper gave a diagram showing the coupling mechanism of several physical fields, including the stress field, the seepage field, and the temperature field, and proposed control equations for the coupling of these fields during the damage deterioration process of the tunnel structure. In the third chapter, this paper applied two yield failure criterions, namely the Mohr-Coulomb criterion and the maximum tensile stress strength criterion to the analysis of the evolution of compression shear failure and tensile failure, and built scientific evolution equations for the permeability coefficient and the thermal conductivity coefficient. At last, experimental results verified the effectiveness of the constructed model and the analysis method.

A hybrid method combining infrared metrology and numerical simulation enables the investigation of thermo-mechanical field coupling effects in the vicinity of the crack tip.The temperature fields are analysed as a function of the loading rate, the specimen geometry and the crack evolution using infrared thermography.The experimental results are used for adjusting and verifying FE-calculations.

Materials with different coefficients of thermal expansion (CTE) are usually bonded together to form laminated stacks in IC and MEMS. However, the thermomechanical coupling effect because of CTE mismatch will greatly affect the reliability and performance of the devices. In this paper, a theoretical model for warpage distribution of the chip surface in multi-layered microelectronic packaging structure is proposed. And a novel optical measurement approach named digital speckle correlation method (DSCM) was applied to study the actual warpage in this stack structure under certain temperature excursions. The test data are compared with the calculated out-plane displacements of both the theoretical model and FEM simulations

Thermo-mechanical coupling effect on surface residual stress during ultrasonic vibration-assisted forming grinding gear

High Performance Cutting of Titanium Alloy Based on the Thermo-mechanical coupling effect

With the long-term decay, releasing a large amount of heat is one of the main characteristics of high-level radioactive waste. Safe operation of high-level radioactive waste repository must consider the effect of thermo-mechanical coupling on repository stability. In this paper, core drilling samples and in-situ stress tests were performed systematically on clay rock in Tamusu area. Thermal conductivity and triaxial tests were operated on samples near the depth of target layer of repository, to obtain the thermal and mechanical characteristics parameters. According to these parameters, a repository model was established in FLAC 3D to simulate excavation of repository and thermo-mechanical coupling of surrounding rock within 100 years after it closed. Results reveal that thermo-mechanical coupling effect has a significant impact on stability of repository. Thermal field reaches a steady state when high-level radioactive waste releases for 20 years, and the temperature in surrounding rock decrease as negative exponential with the distance from the gallery increases of. Due the temperature of the surrounding rock increases, thermal stress is generated, and the stress level in the near field of repository is growing as a whole, thus, strain increases. After heating without support for 100 years, there is the possibility of shear failure at the top and bottom of the chamber. It is necessary to reinforce the chamber lining to ensure the safe and stable operation of the repository.

Thermomechanical coupling effect on the stability of nonconservative elastic continuous systems

Theoretical and experimental studies on the compressive mechanical behavior of 4-harness satin weave carbon/epoxy composite laminates under in-plane loading are conducted over the temperature range of 298–473 K and the strain rate range of 0.001–1700/s in this article. The stress–strain curves of 4-harness satin weave composites are obtained at different strain rates and temperatures, and key mechanical properties of the material are determined. The deformation mechanism and failure morphology of the samples are observed and analyzed by scanning electron microscope (SEM) micrographs. The results show that the uniaxial compressive mechanical properties of 4-harness satin weave composites are strongly dependent on the temperature but are weakly sensitive to strain rate. The peak stress and elastic modulus of the material have the trend of decrease with the increasing of temperature, and the decreasing trend can be expressed as the functional relationship of temperature shift factor. In addition, SEM observations show that the quasi-static failure mode of 4-harness satin weave composites is shear failure along the diagonal lines of the specimens, while the dynamic failure modes of the material are multiple delaminations and longitudinal splitting, and with the increasing of temperature, its longitudinal splitting is more serious, but the delamination is relatively reduced. A constitutive model with thermomechanical coupling effects is proposed based on the experimental results and the increment theory of elastic–plastic mechanics. The experimental verification and numerical analysis show that the model is shown to be able to predict the finite deformation behavior of 4-harness satin weave composites over a wide range of temperatures.

A general framework for the analysis of heterogeneous media that assesses a strong coupling between viscoplasticity and anisotropic viscodamage evolution is formulated for-impact related problems within the framework of thermodynamic laws and nonlinear continuum mechanics. The proposed formulations include thermo-elasto-viscoplastici- ty with anisotropic thermo-elasto-viscodamage, a dynamic yield criterion of a von Mises type and a dynamic viscodamage criterion, the associated flow rules, non-linear strain hardening, strain-rate hardening, and temperature softening. The constitutive equations for the damaged material are written according to the principle of strain energy equivalence between the virgin material and the damaged material. That is, the damaged material is modeled using the constitutive laws of the effective undamaged material in which the nominal stresses are replaced by the effective stresses. The evolution laws are impeded in a finite deformation framework based on the multiplicative decomposition of the deformation gradient into elastic, viscoplastic, and viscodamage parts. Since the material macroscopic thermomechanical response under high-impact loading is governed by different physical mechanisms on the macroscale level, the proposed three-dimensional kinematical model is introduced with manifold structure accounting for discontinuous fields of dislocation interactions (plastic hardening), and crack and void interactions (damage hardening). The non-local theory of viscoplasticity and viscodamage that incorporates macroscale interstate variables and their higher-order gradients is used here to describe the change in the internal structure and in order to investigate the size effect of statistical inhomogeneity of the evolution-related viscoplasticity and viscodamage hardening variables. The gradients are introduced here in the hardening internal state variables and are considered to be independent of their local counterparts. It also incorporates the thermomechanical coupling effects as well as the internal dissipative effects through the rate-type covariance constitutive structure with a finite set of internal state variables. The model presented in this paper can be considered as a framework, which enables one to derive various non-local and gradient viscoplasticity and viscodamage theories by introducing simplifying assumptions.

Ultrasound thermography detects defects by radiating 20 ~ 30 kHz ultrasound waves to the samples and capturing the heat generated from the defects with the use of an infrared thermographic camera. This technology is being spotlighted as a next-generation NDE for the automobile and aerospace industries because it can test large areas and can detect defects such as cracks and exfoliations in real time. The heating mechanism of the ultrasound vibration has not been accurately determined, but the thermomechanical coupling effect and the surface or internal friction are estimated to be the main causes. When this heat is captured by an infrared thermographic camera, the defects inside or on the surface of objects can be quickly detected. Although this technology can construct a testing device relatively simply and can detect defects within a short time, there are no reliable data about the factors related to its detection ability. In this study, the ultrasound thermography technique was used to manufacture gasoline and diesel engine piston specimens, and nondestructive reliability tests to verify the applicability and validity of the ultrasound thermography technique.