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A kind of modified bismaleimide resin, with good processability, heat resistance, and impact strength was developed, using 4,4′-dipropargyloxydiphenyl ether (DPEDPE), N-(4-propargyloxyphenyl)maleimide (4-PPM), and 3-ethynylphenyl maleimide (3-EPM) as modifiers. The DPEDPE, 4-PPM, and 3-EPM were synthesized and characterized by Fourier transform infrared spectroscopy (FTIR) and 1H-nuclear magnetic resonance (1H NMR), and used to modify the N,N′-(4,4′-diphenylmethane)bismaleimide (BDM)/2,2′-diallyl bisphenol A (DABPA) resin system (BD) to obtain the different blend resin systems of DPEDPE-modified BD (BDD), 4-PPM-modified BD (BDP), and 3-EPM-modified BD (BDE). The curing temperature of BD resin increases with increase of the alkynyl-terminated modifier content. The processability of BD resin was improved with addition of the propargyloxy-terminated compounds. The temperature of 5% weight loss, residual yield at 800°C and glass transition temperature of the cured BD resin increase with increase of the alkynyl-terminated modifier content and can reach 443°C, 46.7% and higher than 380°C. The tensile strength of the cured BD resin decreases with increase of alkynyl-terminated modifier content. The impact strength of the cured BD resin increases with increase of the propargyloxy-terminated compound content and can increase by 65%. The tensile strength, elastic modulus, and impact strength of the cured BD resin blended with DPEDPE can be 73.7 MPa, 4.1 GPa, and 19.6 kJ m−2, respectively. Moreover, the cured BD resin blended with DPEDPE has good water absorption resistance.

To explore the characteristics of rock deformation and failure under cyclic loading and unloading, the MTS815 rock mechanics test system and acoustic emission (AE) signal acquisition system were used to perform cyclic loading and unloading tests on red sandstone samples. The results showed that, compared with the uniaxial compression test, cyclic loading and unloading had a certain strengthening effect on the strength of the samples. The plastic deformation of the rock samples increased as the number of cycles increased. Based on AE signals, the cracking mode classification was analyzed on the basis of the average frequency and the rise angle of the waveforms. It was observed that the Felicity ratio gradually decreased with the increase in the stress level, which showed a cumulative damage effect. From the perspective of energy, the obvious increase of AE energy rate was mainly concentrated in the early and late stages of uniaxial compression, while the significant increase of dissipated energy rate occurred in the late stage of uniaxial compression. During the cyclic loading and unloading, most of the work done by external forces in the compaction stage and the elastic stage was converted into elastic strain energy, and dissipated energy began to gradually increase in the stage of stable fracture development. In addition, it was found that the damage evolution of the rock samples changed from slow to fast, and the dissipated energy ratio increased when failure was approaching.

Magnetic shape memory alloys (MSMAs) are materials with strong nonlinearity, which will show hysteresis when it works. In the current paper, a differential model is proposed to describe the hysteresis in MSMAs caused by magnetic field induced martensite reorientation based on Landau theory of phase transitions. First, the three-dimensional model is simplified into a one-dimensional case, and the hysteresis in MSMAs is described by three martensite variant orientations. Then, a traditional Landau free energy is introduced, and the traditional Landau model is obtained by using the Euler–Lagrange equation. However, it is found that the prediction accuracy of the model is not ideal compared with the experimental data. Thus, an improved model is proposed, and the traditional Landau free energy is replaced by a function that can be determined by the easily measured physical quantities in the experimental curve. Numerical experiments show that the prediction effect of the improved model is much better than the traditional Landau model, and the stress dependence is also demonstrated. Moreover, the proposed improved model has the advantages for dynamic analysis and control with its differential form. Therefore, the frequency dependence of the improved model is demonstrated and a feedback linearization control methodology is proposed to make the system develops in the desired trajectory.

To explore the development mechanism of cracks in the process of rock failure, triaxial compression tests with simultaneous acoustic emission monitoring were performed on granite specimens using the MTS rock mechanics test system. The frequency-domain information of the acoustic emission signal was obtained by the fast Fourier transform. The Gutenberg–Richter law was used to calculate the acoustic emission signals and obtain the b-value dynamic curve in the loading process. Combined with the stiffness curve of granite specimens and acoustic emission signal in the time domain and frequency domain, the crack development characteristics in different stages were analyzed. The results showed that the acoustic emission signals of granite samples under triaxial compression can be divided into four stages: quiet period 1, active stage 1, quiet period 2, and active stage 2. b-value attained its maximum value in the active phase 2 when it is close to the sample loss, and then drops rapidly, which means the propagation of cracks and the formation of large cracks. The acoustic emission signal’s dominant frequency was not more than 500 kHz, mostly concentrated in the medium-frequency band (100–200 kHz), which accounted for more than 80%. The proportion of signals in each frequency band can reflect the distribution of the three kinds of cracks, while the change in low-frequency signals can reflect the breakthrough of microcracks and the formation time of macrocracks in granite samples. By fully analyzing the characteristics of acoustic emission signals in the time domain and frequency domain, the time and conditions of producing large cracks can be determined accurately and efficiently.

In order to reveal the influence of prophase stress levels on the fatigue damage characteristics of granite, uniaxial fatigue tests of granite with different prophase stress levels were carried out on the basis of the MTS 815.04 rock mechanics test system. The results show that, under the same number of cycles, the failure degree increases with the increase of the prophase stress level. Under the low upper limit of cyclic stress, the tangent modulus and dissipated energy increase significantly with the increase of prophase stress level at the early stage of the cycle loading, while the increasing trend is not obvious with the increase of prophase stress level at the late stage. Under the high upper limit of cyclic stress, the tangent modulus and dissipated energy are less affected by the prophase stress level. The development trend of elastic release energy is not obvious with the increase of prophase stress level, which is less affected by the number of cycles. From the damage parameters defined by dissipative energy, under the low upper limit of cyclic stress, the initial damage is less affected by the prophase stress level. With the increase of the number of cycles, the influence of the prophase stress level on the development trend of the damage variable increases gradually. And the development trend of damage variables shows “C-shaped” damage.

Shape memory alloy (SMA) is a very important smart material, which has been widely used in many fields, especially in vibration. Phase transformation can be induced by changing temperature and its stiffness changes accordingly. In this paper, the primary resonance vibration of a one-dimensional SMA oscillator is analyzed using the harmonic balance (HB) method. The amplitude-frequency curves of the SMA oscillator with different temperatures are drawn, and the effect of temperature and frequency on the amplitude is discussed. Then, the energy flow of SMA in the vibration process is researched by the power flow analysis (PFA) approach. The time-averaged input power (TAIP) is calculated using the analytical and numerical method, respectively, and the calculation time is compared. It is found that the difference between the analytical and numerical solutions is not significant in most cases, but the calculation time of analytical solution is only about one-tenth of that of the numerical solution, which is very important in saving computational cost, real-time control and so on. Finally, some other characteristics of energy flow in the SMA oscillator are identified.

The well completion and fracturing towards deep unconventional high-temperature (HT) petroleum or natural gas reservoirs is considerably strict to the packer especially packing elements. However, existing packing elements including swellable packers usually are made from Hydrogenated Nitrile (HNBR) or Fluorine rubber (FKM) with drawbacks of great expense and difficult tripping into the horizontal wellbore. This paper proposes a compact isolating solution using swellable Thermo-plastic Vulcanizates (TPVs), which is prepared by blending HNBR, low-cost Polyamide66 (PA66) and Porous Super Absorbent Resin (PSAR) with enhanced nanoparticles. The TPVs were characterized by experiments and the system with Plastic/Elastomer Ratio (PER) of 45:55, tensile strength of 18.6 MPa and elongation at break of 635% upon aging (150 °C) was qualified for the packing element material. A novel enhanced packing element is put forward with corrugated-profile structure to address large-size and over-extrusion issues. The numerical study on packer components was conducted based on TPV constitutive model. The prototype with element length of 2.5–2.6 m was validated in the lab and rated as the sealing of more than 70 MPa. An optional disintegrating casing is adopted to avoid the premature damage risk of packers. For the field trial, the multistage fracturing tubular with improved packers was deployed into the horizontal open hole without severe pipe stuck. The fracturing operation was successfully performed and all packers functioned normally with the maximum pressure differential of 73 MPa. It concludes that the new solution exhibited high strength, heat resistance and structure integrity with low cost over the traditional packers towards HT environment.

This study proposes an active-controlled hydraulic low-frequency vibration isolator. The vibration isolator can achieve large equivalent mass and quasi-zero dynamic stiffness by combining the fluid inerter with the hydraulic active compensation. Thus, good vibration isolation performance at ultra-low frequency can be realised. The model for the dynamics of the device is set up. The principle of low-frequency vibration isolation is explicated. The natural frequency and its influencing factors are analysed. Finally, preliminary experimental research works are carried out. The results indicate that low-frequency vibration can be effectively isolated by the device proposed in this study.

Recently, a novel method for mechanical energy harvesting has been proposed, which is based on stress-induced polarization switching in ferroelectric materials. Compared with the traditional piezoelectric energy harvesters, a huge improvement in the output energy has already been theoretically demonstrated. In this article, the influence of different materials on the energy-harvesting performance associated with this new strategy is further studied. The state-of-the-art phase-field model is adopted to investigate the nonlinear hysteretic energy-harvesting process in two nanoscale ferroelectric energy harvesters, which are respectively based on two typical ferroelectric materials—single-crystal BaTiO3 and PbTiO3. In both cases, the effects of the bias voltage and bias resistance are carefully investigated and the optimum values are obtained. Later, the energy-harvesting process and energy flow details in both harvesters working at the optimum conditions are presented and carefully compared in the context of real applications. Furthermore, the energy-harvesting performance of a BaTiO3-based nanoscale piezoelectric energy harvester with equivalent material size is additionally simulated with the finite element method and compared with the corresponding results of the ferroelectric energy harvesters, where obvious advantages associated with the new strategy are demonstrated.

In the current paper, a macroscopic model is proposed to simulate the hysteretic dynamics of ferroelectric ceramics with creep phenomenon incorporated. The creep phenomenon in the hysteretic dynamics is attributed to the rate-dependent characteristic of the polarisation switching processes induced in the materials. A non-convex Helmholtz free energy based on Landau theory is proposed to model the switching dynamics. The governing equation of single-crystal model is formulated by applying the Euler–Lagrange equation. The polycrystalline model is obtained by combining the single crystal dynamics with a density function which is constructed to model the weighted contributions of different grains with different principle axis orientations. In addition, numerical simulations of hysteretic dynamics with creep phenomenon are presented. Comparison of the numerical results and their experimental counterparts is also presented. It is shown that the creep phenomenon is captured precisely, validating the capa...

In the current paper, energy dissipation via stress-induced polarization switching in ferroelectric material is investigated, and the feasibility of its application in sound wave absorption is analysed. For the system design and analysis, a phenomenological model based on the modified Landau phase transition theory is constructed to describe the polarization switching. A simple and robust energy dissipation prototype is introduced. The hysteretic dynamics associated with the polarization switching process and the energy dissipation process are investigated. The dependence of the energy dissipation on the bias voltage, frequency, and resistance is analysed in detail. The energy dissipation density in one cycle is calculated. It is shown that the resistance has a strong influence on the energy dissipation. Meanwhile, a better energy dissipation effect could be obtained by setting an appropriate resistance for the low-frequency excitation. The feasibility of using ferroelectric materials for low-frequency sound wave absorption is validated. For a specific acoustic energy dissipation device, corresponding design and analysis will be discussed in our future papers.

In the current paper, the coupled hysteretic behaviors of ferroelectric ceramics subjected to combined electromechanical stimulations are modeled. For a single grain, the polarization orientation switching process is modeled by employing the Euler–Lagrange equations and formulated as a coupled differential equation system. For ferroelectric ceramics, the principle axis orientations of the individual grains are assumed to be distributed in a certain profile, the behaviors of the ceramics are modeled as a weighted combination of the response of each grain. The influence of intergranular interactions is carefully discussed. Numerical results for the minor hysteresis loops in strain and polarization are demonstrated. Comparisons between these results and their experimental counterparts are presented to illustrate the attributes of the proposed model.

In the current paper, a nonlinear differential algebraic approach is proposed for the modeling of hysteretic dynamics of polycrystalline ferromagnetic materials. The model is constructed by employing a phenomenological theory to the magnetization orientation switching. For the modeling of hysteresis in polycrystalline ferromagnetic materials, the single crystal model is applied to each magnetic domain along its own principal axis. The overall dynamics of the polycrystalline materials is obtained by taking a weighted combination of the dynamics of all magnetic domains. The weight function for the combination is taken as the distribution function of the principal axes. Numerical simulations are performed and comparisons with its experimental counterparts are presented. The hysteretic dynamics caused by orientation switching processes is accurately captured by the proposed model. Minor hysteresis loops associated with partial-amplitude loadings are also captured. Rate dependence of the hysteresis loops are inherently incorporated into the model due to its differential nature.

In the current paper, the coupled fatigue hysteretic behaviors in ferroelectric ceramics are modeled by a blending a phenomenological hysteresis model with point defects. The time-dependent phenomenological model is employed to capture the hysteresis loops associated with phase transitions. The fatigue hysteresis is modeled by combining the single-crystal model with time functions. The mechanism of fatigue in ferroelectric ceramics is interpreted as an accumulation of residual polarization in the proposed model. Numerical results of static and dynamic hysteretic behaviors are presented and compared to their experimental counterparts. The capability of the proposed model for capturing the fatigue phenomenon is validated.

Many studies have used numerical models, analytical models and laboratory models to investigate the factors influencing the shear strength of bolted rock joints. This study presents the preparation of a reinforced standard cylindrical specimen containing a joint; the jointed specimen was reinforced with a 3D printed (3DP) rock bolt and planting-bar anchorage glue. The surface profile of the 3DP rock bolt was identical to that of an actual rock bolt, and the strength of the 3DP bolt was satisfactory. Afterwards, the digital image correlation (DIC) method was applied to capture the changes in the strain/displacement fields on the surfaces of the specimens during testing. In addition, two pressure sensors (PSs) were attached to the external threaded sections of each 3DP bolt; these PSs recorded the changes in the load at the bolt ends positioned in the upper section above the joint plane and in the lower section below the joint plane. The influences of the joint plane and joint angle on the cracking process, DIC changing pattern, and stress-strain evolution were comprehensively discussed. The research approaches proposed in this study provide new methods with which to investigate the reinforcement effect of bolts on jointed rock masses, the results of this study can be used as a reference in engineering areas where jointed rock masses must be reinforced by rock bolts.

In this paper, a quick response artificial finger actuated by SMA springs was designed. The SMA springs were heated and cooled by water instead of electricity. A mechanical model, temperature model and SMA phase transformation model were used to predict the movement. The phalanx’s response under different situation was simulated in MATLAB to verify our design and test the feasibility of the quick response of our finger.

An optical device is used to scan a cavity. In a single incident the scanner produces what can be considered a blurred image of the intersection curve between a plane and the cavity. Mathematically the image represents an intensity function and that is obtained by integrating a certain kernel along the intersection curve. We suggest methods to determine the kernel and subsequently the intersection curve given the image. The methodology is tested with some success using an artificial, but realistic kernel and some synthetic images produced by this kernel.

Different from the traditional piezoelectric vibration energy harvesting, a new strategy based on stress-induced polarization switching has been proposed in the current paper. Two related prototypes are presented and the associated advantages and drawbacks have been discussed in detail. It has been demonstrated that, with the assistance of a bias electric field, the robustness of the energy harvesters is improved. Furthermore, the real-space phase-field model has been employed to study the nonlinear hysteretic behavior involved in the proposed energy harvesting process. A substantially larger electric current associated with the stress-induced polarization switching has been demonstrated when compared with that with piezoelectric effect. In addition, the effects of bias electric potential, bias resistance, mechanical boundary conditions, charge leakage and electrodes arrangements have also been investigated by the phase-field simulation, which provides a guidance for future real implementations.