The present work is devoted to the derivation of fundamental equations in generalized thermoelastic diffusion theory. The main aim is to establish a size-dependent model with the consideration of spatial nonlocal effects of concentration and strain fields. The heat transport equation for the present problem is considered in the context of Moore–Gibson–Thompson (MGT) generalized thermoelasticity theory involving linear and nonlinear kernel functions in a delayed interval in terms of the memory-dependent derivative. The medium is considered to be one-dimensional having a spherical cavity where the boundary of the cavity is traction-free and is subjected to prescribed thermal and chemical shocks. The Laplace transform technique is incorporated for the solution of the basic equations. For numerical evaluation, the analytical expressions have been inverted in the space-time domain using the method of Zakian. From numerical results, the effects of the nonlocality parameters in the heat transport law and the nonlocality of mass-flux have been discussed. The effect of different kernel functions, the delay time, and the effect of thermodiffusion are also reported. A comparative study between the MGT theory and the hyperbolic Lord–Shulman theory is also explained.

Rheology-driven sliding is a key contributor to failure; thus, a comprehensive understanding of rock rheological processes is important. In this paper, shear creep on mudstone and sandstone was studied to examine the rock rheological behavior. The creep results show that the creep behavior becomes increasingly nonlinear over time. The plastic part of the Ramberg–Osgood model is improved with a new plastic rheological element, which is incorporated into the classic Nishihara model and Burgers model to fit the creep experimental results. The various viscoelastic–plastic rheological elements provide capabilities to describe the elastic, viscoelastic, viscous, and plastic deformations of the rocks. The models are compared with the Nishihara model and the Burgers model, and are validated by the rheological data. The results show that the new element can describe well the plastic behavior of the rocks. The proposed models provide an increased accuracy in describing the behavior in the three rheological stages (attenuated, steady-state, and accelerated-creep stages), which depend on the stress level and burial depth. The models can also effectively predict the failure time and long-term stability of rock slope.

The present study illustrates the thermoelastic vibrations of a rotating microbeam caused by a laser pulse heat source and sinusoidal heating in the context of three-phase thermoelasticity. Mathematical modeling of the problem was developed using the concept of the Euler–Bernoulli beam theory and the generalized theory of thermal conductivity with three relaxation coefficients of time. It was taken into account that the flexible beam suffers from initial stress at the beginning. The microbeam motion equation was derived by applying the assumptions of the Hamiltonian principle. The closed-form solutions of the studied domains are identified in the Laplace transform domain. After presenting the numerical inversion of the Laplace transform, the numerical results for the studied field variables, such as deflection and temperature, were developed. The influences of the angular velocity of rotation, the initially applied pressure, and the intensity of the laser pulse on the behavior of the physical fields have been demonstrated. In addition, the advantage of the current model has been verified by comparing the results of the field variables of the current model with the results of other thermal conduction theories, whether classical or generalized. It is believed that the results extracted from the present study may be useful for developing some high-quality electromechanical systems.

We investigate the plastic flow stress characteristics for 2A12 aluminum alloy at different strain rates and temperatures through both experiments and constitutive modeling at different strain rates (\(10^{-4}\)–\(10^{-1}\text{ s}^{-1}\)) and temperatures (300—450 K). The experimental results showed that the yield strength and tensile strength of 2A12 aluminum alloy gradually decrease as the strain rate increases at 300 K and a V-shaped strain rate effect at 350–450 K. The quasi-static yield strength decreases significantly with increasing temperature, reaching 250 MPa at 300 K and 207 MPa at 450 K. The Johnson–Cook (J-C) model was found to be insufficient to describe the experimental observations. Consequently, a modified J-C model was developed, validated, and implemented in finite element simulations. The modified model well agrees with the experimental data, indicating that the modified J-C model developed herein can describe the plastic flow stress characteristics of 2A12 aluminum alloy at different strain rates and different temperatures.

Hill’s linear isotropic hyperelastic material models based on the one-parameter (\(r\)) Itskov family of strain tensors (including the Hencky, Pelzer, and Mooney strain tensors generating the H, P, and M material models, respectively) were used to obtain exact solutions of the simple torsion problem for circular cross-section rods from the H, P, and M materials. The “exact” solutions available in the literature for the problem of generalized torsion of cylindrical rods with free edges in the axial direction were analyzed. The objectives of the present study are to develop and implement new formulations of these material models in the commercial MSC.Marc nonlinear FE software and to verify these formulations using the above-mentioned exact solutions. Computer simulations of the simple and generalized torsion of cylindrical specimens were carried out using three material models (H, P, and M) and the standard Mooney–Rivlin model. The results of computer simulations of the resultant moment and the resultant axial force (in the problem of simple torsion) or axial elongation (in the problem of generalized torsion) were compared with exact solutions. For the simple torsion problem, the solutions obtained by the two methods are similar, but for the problem of generalized torsion, these solutions are similar only for sufficiently small values of the torsion parameter. We explain the discrepancy for sufficiently large values of the torsion parameter by the fact that the so-called “exact” solutions cease to be exact because of the assumptions made by other authors in obtaining these solutions. We assume that for all values of the torsion parameter, our numerical solutions are close to the true exact solutions. Computer simulations showed that the Pelzer material model is similar in performance to the Mooney–Rivlin model.

This study aims to describe a toughened adhesive’s ratcheting–recovery behavior under reversed cyclic load using a viscoelastic–viscoplastic model. As most adhesives are based on synthetic polymers, their tensile and compression response can be different. A series of load–Sunload tests were conducted on bulk adhesives and bonded joints involving tension/compression–shear loads to characterize the initial yield surface. The effect of hydrostatic stress was studied by considering the instantaneous response and yield strength under tensile and compression loads. Given the observed modulus degradation and extensive permanent strain during reversed cyclic tests, time-dependent damage factors were considered for both viscoelastic and viscoplastic responses. The model was implemented in a finite element (FE) code and used to model the shear response to reversed cyclic load with varying frequency. Good agreement between the model and experiment was obtained. The consideration of both hydrostatic stress and damage was required to describe the observed adhesive reversed cyclic response.

The joints in a rock mass generally control the stability of the rock mass, and are mostly nonpersistent, and their deformation and failure mechanisms are also relatively complicated. One of the most important mechanisms of rock deformation and failure mechanism is rock creep. Therefore, the research on the mechanism of creep-deformation failure of nonpersistent joints is of great significance to theoretical research and practical engineering research. In this study, A model method derived from practical engineering is proposed and triaxial compression creep tests on nonpersistent joints are performed. The creep characteristics of nonpersistent joints and the relationship between creep rate and time are analyzed. After analysis, it is found that the confining pressure affects the failure mode and mechanical properties of nonpersistent joints and the relationship between the creep rate and time has an exponential function. A fractional viscoelastic element and an accelerated-damage element are introduced, and the three-dimensional (3D) stress state constitutive model suitable for joints is constructed. A parameter-sensitivity analysis study was performed to show the effect of fractional-order \(\beta \), material parameter \(\alpha \), and the rheological index \(\lambda \) on the constitutive model. Also, the Levenberg–Marquardt (L–M) algorithm and global optimization method are used to verify the appropriateness of the constitutive model. After verification, the constitutive model can well reflect the entire creep process of nonpersistent joints and it can provide a certain reference for the deformation and failure of nonthrough slopes.

The unloading effects induced by rock excavation on high slopes are significant, and a prestressed anchor cable is an effective reinforcement method for high-slope safety. In this work, we consider the interaction between rock creep in high slopes and the changing anchoring force of prestressed cables. We then derive theoretical solutions for the unloading rock creep and anchoring force of prestressed cables considering the coupling effect, and verify the solutions using numerical simulation. First, based on the Boussinesq problem in elastic mechanics, we simplify the problem of slope reinforcement with a single prestressed anchor cable to the problem of a concentrated force acting on a boundary of a semiinfinite medium. The concentrated force is affected by the excavation unloading effect from the slope and the anchoring forces from the anchor cables. Based on this simplification, we derive elastic solutions for the slope unloading displacement after excavation and for the anchoring force of prestressed cables. Secondly, considering rock-creep behavior and varying anchoring force, the Burgers model is used for rock masses and the elastic model is used for anchor cables. According to the coordinated deformation between rock masses and anchor cables, we obtain the analytical solutions for the rock displacement and for the anchoring force of the cables under the coupling action in the Laplace space, based on which the viscoelastic solutions for the rock displacement and for the anchoring force considering the coupling effect are solved by the Laplace inverse transform. Finally, we validate the analytical solutions by comparing against numerical simulation results with FLAC3D. A good agreement is achieved, suggesting the fidelity of the analytical solutions. The theoretical model provides a reference for studying slope reinforcement, analyzing slope rock-creep behavior and the long-term prestress of the reinforcement structure.

A hyperelastic–viscoplastic constitutive model is developed to describe the strain-softening behavior of glass-filler-reinforced–epoxy composites under large strain-compression loading. The model’s rheological network comprises two parallel networks; the first consists of a nonlinear elastic spring in series with a nonlinear viscous dashpot, and the other involves a hyperelastic Langevin spring. The postyield strain softening in the model is introduced by a time-dependent shear resistance to molecular deformation, where the shear resistance is varied from an initial value up to a saturation value at large strain. The model is reduced to a one-dimensional incompressible case, and fitted to the experimental data of spherical- and milled-glass-fiber–epoxy composites to retrieve the optimized model parameters. Milled-fiber–epoxy composites exhibit higher values of optimized elastic modulus and shear deformation resistance parameters, which are correlated to outcomes of dynamic mechanical analyses like filler-reinforcement efficiency, polymer chain-entanglement density, and filler–matrix adhesion. The improvement in filler-reinforcement efficiency due to milled fibers leads to better load transmission to the matrix, resulting in enhanced elastic modulus of milled-fiber–epoxy composites. An increase in polymer chain-entanglement density and filler–matrix adhesion results in higher resistance to viscous flow for milled-fiber composites. Semiempirical equations for elastic modulus and shear-deformation resistance parameters are proposed that consider the relative stiffness of filler and matrix, and the shape and volume fraction of fillers. When the fillers are embedded in the polymer matrix, these equations operate as multiplicative factors to the neat polymers. Thus, the model is capable of capturing the stress–strain response of both neat polymer and glass-filled polymer composites.

To determine the long-term Young’s relaxation modulus of composite double-base propellants (CMDB), thermally accelerated aging tests were conducted at 343.15 K for 100 days. Gas chromatography and stress relaxation tests at different aging times were conducted. The aging stress relaxation model has taken into account the change of stabilizer (N-methyl-4-nitroaniline, or MNA) content in accelerated aging. The results show that with the increase of aging time, the MNA content decreases, and Young’s relaxation modulus increases. The time-aging time superposition principle was considered to construct an aging relaxation master curve through a series of short-term stress relaxation curves under different aging times. Based on the master aging relaxation curve and the Prony series models, the conversion time related to the content of MNA was determined. The aging stress relaxation model considering the change of MNA content agrees well with the experimental results and can accurately predict Young’s relaxation modulus of CMDB propellant during thermal aging.

Amongst various avenues being searched for solving the menace of increasing amount of plastic accumulation, its use in hot mix asphalt (HMA) is becoming popular. Several research studies have been conducted since the 1980s on the use of different types of waste plastics in asphalt mixtures through dry and wet processes. While it may seem ‘simple’ and ‘attractive’, incorporation of waste plastic in asphalt mixtures is plagued with many challenges. This paper summarizes the works of the available literature on the use of waste plastics in asphalt mixture. The selection of dry or wet process is highly dependent on type, density, size and melting point of waste plastic, to create a homogeneous mixture. Physical, rheological, and morphological properties of asphalt binder are effectively altered by the use of waste plastics. This is in turn is a function of various parameters such as type of plastic and base asphalt binder, dosages used, use of compatibilizers and other polymers, production process, etc. Similarly, the performance of waste plastic modified asphalt mixture is found to vary considerably. While the stiffness characteristics of HMA is improved by incorporation of waste plastic, more studies on in-field performance and environmental concerns are desirable. To make the use of waste plastic in HMA a ‘success story’, there is a need to carry out fundamental research to generate a unified solution.

Time-dependent characteristics are key factors for the instability and safety in underground engineering projects. Due to geological structure and manual excavation, any rock mass is subjected to true triaxial stress. Therefore, true triaxial tests under the monotonous loading were conducted on sandstones first under different intermediate principal stresses along with a constant pore pressure to simulate rock in situ, and subsequently, the creep experiments were performed at different stress proportions under corresponding conditions. The experimental results show that anisotropic deformation and rates vary with stress levels and the intermediate principal stress. Combined with literature data, the lateral deformation ratio of the intermediate principal strain (\(\varepsilon _{2}\)) to the minimum principal strain (\(\varepsilon _{3}\)), is closely related to the reciprocal of the side stress ratio for instant and creep increments in the penultimate stage. The intermediate principal stresses (\(\sigma _{2}\)) have a significant effect on the creep behavior of sandstone. Based on the experimental results, a new anisotropic creep-damage model is subsequently developed, and anisotropic damage is defined based on statistical damage theory. The parameter values can be obtained using the method of Universal Global Optimization (UGO). The theoretical predictions show good consistency with laboratory data and field data, respectively. The model is reliably used to simulate creep behavior and gives a good account of the effect of intermediate principal stresses. Therefore, it could provide a better understanding of the long-term stability of engineering projects.

Shotcrete technology is widely used in many fields, including municipal engineering, tunnel engineering and mine engineering. However, due to a large number of cementitious materials, the aggregate has a continuous particle size of 5-10 mm and the accelerator speeds up the early hydration process, causing shrinkage cracking to be more serious than in ordinary concrete. This study is focused on the effects of two types of shrinkage-reducing agents (powder and liquid) on the shrinkage deformation of cement mortar with an accelerator. The results show that with the increase in the dosage of the two shrinkage-reducing agents (SRA), the setting time of the cement paste becomes longer, and the compressive strength within 1d decreases to a certain extent. In the 180-day shrinkage test, both autogenous and drying shrinkage deformation decreased, and the liquid shrinkage-reducing agent displayed better shrinkage-reducing effects. These improved shrinkage-reducing effects were most evident for the cement mortar with an alkali-free accelerator. The results also show that external coating of liquid shrinkage-reducing agent can reduce the autogenous and drying shrinkage to some extent. Both the internal mixing and external coating of the shrinkage-reducing agent slow down the water loss and humidity reduction under dry conditions. Microscopic test characterization shows that the incorporation of shrinkage reducing agent delays the early hydration process of cement paste with accelerator, but has little effect on long-term hydration. As such, the appropriate dosage has no effect on the application performance of shotcrete.

Rheological behaviors are widely recognized to be induced by the existence of pre-loading conditions, which should be considered in the constitutive models. In this paper, a fractional-order model is proposed to characterize pre-loading dependent rheological behaviors. The loading-dependent fractional order can be physically interpreted by the master curve and modeled by a power law function. The power-law criterion between material parameter and initial loading is also constructed. Experimental data are employed to validate the effectiveness and predictive abilities of the model. Simulation and prediction results reveal that the proposed model effectively describes initial loading-dependent creep and relaxation responses.

With the increase of the scale of an underground cavern, more and more towering underground side walls are left behind by blasting operation, which leaves a huge hidden danger to the structure safety of an underground cavern. Taking the propagation mechanism and damage distribution characteristics of blasting vibration along the elevation direction as the research subject, the propagation mechanism of blasting vibration along the elevation direction of high side wall of a deep-buried underground cavern can be obtained by comprehensive application of theoretical analysis, dimensional analysis, formula derivation, numerical analysis, and other research methods. Through multiangle comparative analysis, the internal mechanism of blasting vibration under elevation effect in underground caverns is revealed, and combined with the relationship between surrounding rock damage and blasting vibration velocity, the distribution characteristics of blasting vibration and damage under the elevation effect are proposed. In addition, through the establishment of a mechanical model of the response of blasting vibration of underground high side walls, the prediction formula of particle vibration velocity along the elevation direction under blasting vibration condition is analyzed, and the formula is adjusted and modified, which can meet the developing requirements of surrounding rock damage control precision.

Regarding the issue of creep characteristics of the rock mass following excavation or excavation with graded loading and unloading under external forces. This study performs uniaxial compression and step loading and unloading creep tests on rock samples under different wetting-drying cycles with yellow sandstone to investigate the creep characteristics of rock bodies after excavation or excavations with step loading and unloading under external forces. Moreover, it constructs a creep damage model based on the nonlinear rheological theory and damage mechanics to describe the instantaneous elastic strain, instantaneous plastic strain, nonlinear viscoelastic strain, and nonlinear viscoplastic strain of rocks. Besides, it proposes a creep model parameter identification method based on the creep curve characteristics. The results have shown that the action of wetting-drying cycles causes a weakened decrease in elastic modulus, uniaxial compressive strength, and long-term compressive strength of yellow sandstone, in line with the exponential function change relationship. The specimen damage type evolves from shear damage of a single oblique section to conical shear damage of a double oblique section. Additionally, the creep rate is not constant in the steady-state creep stage but constantly changes with time, and the fluctuation range increases with the increase in the wetting-drying cycles. The creep damage model parameters do not differ much under the same stress condition, and each parameter is influenced by the creep stress at a specific law. The instantaneous modulus of elasticity of the elastomer and plastic body and the creep stress have a linear relationship, whereas the modulus of elasticity and viscosity coefficient and the creep stress have an exponential one.

The time-dependent autogenous shrinkage of shotcrete under different alkali content and dosage of accelerators was tested. The adiabatic temperature rise, microstructure, chemical compound, and mercury injection test were characterized to determine the influence of accelerators on the autogenous shrinkage of shotcrete. The previous theoretical model for shrinkage was improved by introducing the influence factor of expansive hydration products. An autogenous shrinkage prediction model suitable for shotcrete was proposed, and the relevant model parameters were calibrated based on experimental results. Compared with the control group, alkali-free or alkaline accelerator significantly accelerates the autogenous shrinkage of shotcrete, which is mainly due to the accelerating effect on the hydration process at an early age and the free water absorption in the hydration process; Compared with the alkaline accelerator, alkali-free accelerator generates a large amount of expansive hydration product Ettringite. Therefore the autogenous shrinkage of shotcrete with alkali-free accelerator was smaller than that with alkaline accelerator. By introducing the influence factor \(p_{1}\) the previous shrinkage model was improved. The new model can better describe the influence of expansive hydration products generated by accelerators on the shrinkage of shotcrete. The theoretical model is suitable to investigate the shrinkage development of the initial tunnel support structures.

Rheological characterization of the rock surrounding the lower wall of Xianglushan No. 2 tunnel was made to investigate the degree of stability for assurance of the long-term stability of the rock. The creep parameters were extracted for the creep model for the rock mass in the fault zone. A micro-element was introduced to describe the accelerated creep deformation and a new accelerated creep model was established. The creep parameters were extracted by allowing the creep modeling results to fit feature points in the creep curves under different creep loads. The role of various creep parameters on creep behavior was identified. The results showed that the creep modeling results agreed with the experimental data, validating the creep model and the associated parameter determination method.

This study evaluated various mechanical responses that evolved as a function of gauge length for PGCL sutures. Gauge length dependency is important to be studied as it directly reflects the possible complications related to suture failure and inadequacy of mechanical properties, which could happen due to inappropriate suture lengths used in incision closure. The results show that the gauge length caused differences in monotonic and cyclic responses of the PGCL samples. However, the stress relaxation response is unaffected by the gauge length. In monotonic responses, most of the mechanical parameters, including elongation at break, load at break, ultimate tensile strength as well as initial modulus, improve with increasing gauge length. The overall stiffness and strain at break decrease as the gauge length increases. Both stress-softening and hysteresis loops are observed in all PGCL samples with varying gauge lengths. As the gauge length increases, the permanent set decreases, whereas the maximum stress level and hysteresis increase. Concerning crystallization behavior, the degree of crystallinity, lattice strain, and crystallite size are altered by the gauge length. As the gauge length increases, the lattice strain decreases, and the crystallite size decreases.

Given a circular economy, wood waste has become an important secondary raw material. For this purpose, an experimental study was conducted to characterize concrete mixes containing wood shavings for structural and nonstructural construction applications. In this study, treated wood shavings (TWS) from woodworking waste were used by replacing natural sand for making sand concrete (SC) with different mixing ratio (0%, 10%, 20%, 30%, 40%, and 50%) by volume of sand. The behavior of sand concrete samples containing wood was then explored. Wood shavings treatment, X-ray diffraction (XRD), resistance, porosity, thermal conductivity, fire resistance, and scanning electron microscopy (SEM) were used to investigate the behavior of SC using TWS (SCWS). The results showed that most of the SCWS samples had acceptable mechanical strength and density. Increasing the amount of (TWS) decreased the density, compressive strengths, and thermal conductivity of the mixtures by up to 38%, 35%, and 35% respectively. However, all the mixtures could be considered structural LWC mixtures as they developed acceptable strength in terms of structural design and use. Additionally, the novel composite reportedly possesses adequate thermal conductivity and fire resistance.Finally, sand concrete based on wood shavings could be used as a fire insulator when combined with other relevant fire-resistant materials.