Mechanical Response Characteristics Research Articles

Development of nuclear fuel assembly finite element model for mechanical integrity evaluation

This paper proposes a finite element model that can accurately simulate the mechanical behavior of a fuel assembly (FA). An FA is a structure that can be subjected to vibrations and shocks in various environments such as earthquakes or transportation and handling. A reliable model is essential to predict the precise mechanical response characteristics of an FA and evaluate its integrity. A consistent model that eliminates extreme simplifications and model variations due to environmental conditions is required. To accomplish this objective, a three-dimensional finite element model was initially developed to simulate the static and dynamic mechanical behavior of an FA. The model was created using ABAQUS v6.14 based on a 17 × 17 type FA and consists of top and bottom nozzles, top, bottom, mid, and intermediate flow mixer spacer grids, guiding tubes, and fuel rods. Here, beam and spring elements were used to reduce analysis time and hardware cost. To verify the proposed model, static compression and impact tests of the spacer grids and static axial compression and lateral bending, axial and lateral impacts, and vibration tests of the FA were performed. Then, the analysis and test results were compared. The proposed finite element model of the FA agreed very well with the test results, and we confirmed that both the static and dynamic mechanical characteristics were simulated effectively by the proposed FA model. We expect that the proposed model can be utilized to evaluate the mechanical integrity of FAs under vibration or drop conditions during seismic events, transportation, and handling.

Mechanical Response Characteristics and Law of Instantaneous Energy Conversion for Water-Bearing Coal–Rock Masses Subjected to Mining-Induced Stress

Mechanical Response Characteristics and Law of Instantaneous Energy Conversion for Water-Bearing Coal–Rock Masses Subjected to Mining-Induced Stress

Structural Design and Controllability of Magnetorheological Grease Buffers under Impact Loading.

Shock loads can pose a great threat to personnel or instruments, and efficient control of the buffering process is an effective means of reducing damage from shock energy. In this paper, magneto-rheological grease was used as the internal controllable material of the buffer to address the turbulence and settling problems of conventional magneto-rheological fluid. A bending and folding back magnetic circuit is proposed, and the magnetic circuit simulation was verified. The corresponding dynamic mechanical model was established, and the mechanical response characteristics of the buffer under impact load were also simulated dynamically. The mechanical properties of the designed and processed device were tested, and a variable current control method was used to improve the performance of the shock resistance of the buffer. The response of the magnetorheological grease buffer under different drop hammer impacts was investigated. The buffering effect and controllability of the buffer were analyzed by comparing the acceleration, velocity, and top-end cap displacement at the same drop hammer height for different current magnitudes. The results show that the buffer performance of the buffer gradually improved as the current increased. The response time of the designed new magnetorheological buffer was determined by the jump time of the peak damping force to be 9 ms. Lastly, the controllability was verified by manually and automatically adjusting the current magnitude, and the results were compared with those at 300 mm drop hammer height and 0.5 A current magnitude, and the continuous variable current control was found to be effective. This provides a feasible reference for scholars to study optimal buffer control.

Creep properties and energy evolution characteristics of weakly cemented rock under step loading

The contact mode of particles in weakly cemented mudstone (WCM) and the persistence of cemented materials, as well as the cemented particulate matter composed of them, lead to different mechanical response characteristics from general soft rock during loading, that is, rheological failure occurs under low stress. In order to study the creep characteristics and energy evolution characteristics of weakly cemented rock (WCR) in the western mining area of China, based on the triaxial graded loading creep test of WCR, the creep deformation and failure law of WCM under graded loading was studied, and the energy evolution characteristics of WCR in each creep stage were revealed by energy dissipation theory. The results show that with the increase of confining pressure, the fracture angle decreases, but the failure strength and volume expansion point show the opposite trend. In addition, due to the strong heterogeneity of WCR samples, the contact force between particles is different after loading, which makes the slip between particles and cements and then produces a completely different fracture form from other rocks. The energy growth in the deceleration and steady creep stages is mainly affected by the confining pressure. With the increase of confining pressure, the growth rate of dissipation energy Ud and total energy U gradually tends to be constant, but the growth rate of strain energy Ue remains at a high level. In the accelerated creep stage, the growth rate of strain energy Ue decreases rapidly, and the residual energy storage capacity does not change significantly with the increase of confining pressure. These results revealed the unique creep properties and energy evolution characteristics of the WCR, providing a theoretical basis for long-term stability control of roadways that are built with WCR.

The Influence of Cyclic Load Amplitude on Mechanical Response and Acoustic Emission Characteristics of Granite

Cyclic loading and unloading tests with varying stress amplitudes were carried out to study the evolution trends of the elastic modulus, plastic strain, dissipated energy density, and acoustic emission events for granite under cyclic loading with accidental extreme stress. The results were as follows: (1) The loading deformation modulus before and after extreme stress is different. In addition, at extreme stress levels, the loading deformation modulus of granite specimens decreases by approximately 5~13%, but the unloading deformation modulus does not change significantly. (2) When extreme stress causes rock damage, most of the plastic deformation potential of the rock at this stress level is released in advance. The stress constantly varies in the subsequent low-amplitude cycle, and the plastic strain caused by the extreme stress is partly recovered. (3) As the extreme stress increases, the cumulative dissipated energy density of granite increases significantly. Compared with the control group without a stress extremum, the cumulative dissipated energy density of samples in two groups with stress extrema of 20 kN and 40 kN increased by 48% and 153%, respectively. (4) A significant acoustic emission event occurs only when the rock is subjected to a load exceeding the maximum historical stress for the first time, and the acoustic emission intensity is positively correlated with the difference between this stress and the historical maximum value. (5) Extreme stress values below the crack damage threshold reduce the crack growth potential of the rock in advance, and extreme stress above the crack damage threshold aggravates rock damage.

Study on dynamic mechanical response characteristics and fracture energy dissipation mechanism of sandstones with different saturations under real-time low temperature

It is of great significance to study the mechanical properties of rocks with different saturations for safe and efficient development of geotechnical engineering in low-temperature environments, such as open-pit mining and tunnel excavation in winter in cold areas, and etc. In this paper, the LT-SHPB test system was used to carry out impact loading tests for sandstones with various saturations at − 20 °C environment. SEM was used to observe the cross-sectional characteristics of the specimens. The distributions of fragments were obtained by screening after impact failure. The energy dissipation model was established during the failure process. The research results indicated that the failure strength, elastic modulus, and peak strain of sandstones showed significant strain rate strengthening. Under the fixed strain rate, as the increase of the water content, the failure strength and elastic modulus and the sensitivity increased first and then decreased, while the peak strain showed the opposite change characteristics. 75% saturation was the turning point of the change. The sandstones under saturated water content exhibited remarkable ductile failure characteristics, while the brittle failure dominated in other conditions. The fundamental reason for this change was the difference between the freezing and frost heave effects of water-bearing specimens under low temperature conditions. The change characteristics of the macroscopic damage degree of sandstones with the strain rate and water content were basically the same as the characteristics of mechanical properties. The higher the internal density, the more the dissipated energy and surface specific energy for the whole failure of the specimen. The energy dissipation difference could directly change the macroscopic failure characteristics.

Dynamic mechanical response characteristics and cracking behavior of randomly distributed cracked sandstone

Dynamic mechanical response characteristics and cracking behavior of randomly distributed cracked sandstone

Dynamic compression behavior of TiZrNbV refractory high-entropy alloys upon ultrahigh strain rate loading

In this study, the dynamic compressive response behavior of a body-centered cubic (BCC) single-phase TiZrNbV refractory high-entropy alloy (RHEA) was investigated under impact at speeds of 313–1584 m s–1 using two-stage, gas-gun-driven, high-speed plate-impact experiments; recovery sample analysis; and theoretical calculations. The strain rate and pressure were approximately 107 s−1 and 5.07–29.37 GPa, respectively. The results showed that the TiZrNbV RHEA had a Hugoniot elastic limit of 4.12–5.86 GPa and a spall strength of 1.84–2.03 GPa. The initial yield strength of the alloy showed a strong strain-rate dependence and could be described by the modified Zerilli–Armstrong model, while the phonon-damping effect was the main reason for its high strain-rate sensitivity. Microstructural analysis showed that the dynamic deformation of the TiZrNbV RHEA was controlled by the dislocation slip, dislocation proliferation, intersection of the deformation bands, and grain refinement. The analysis also showed that the intergranular, transgranular, and mixed-type cracks dominated the spall failure of the material. The dynamic Hall–Petch effect and pinning from the lattice distortion led to high dynamic yield strength. The critical strain rate for the phonon drag effect was positively related to the relative atomic mass and local strain field of the metals. Within the experimental loading range, the RHEA showed good structural stability, and simultaneously, the theoretical calculation method for the equation of state based on a cold-energy mixture could accurately predict its shock-response behavior. The valence-electron concentration (VEC) had a direct effect on the shock-compression properties of the HEAs; higher VEC implied more difficulty in compressing the HEAs. The findings of this study provide insights into understanding the mechanical response characteristics of RHEAs under extreme conditions such as high-speed impact and ultrahigh strain-rate loading.

Effect of strain rate on mechanical response and failure characteristics of horizontal bedded coal under quasi-static loading

Strain rock burst is one of the main types of rock bursts. Studying the mechanical response and acoustic emission characteristics of coal under quasi-static loading is significant to control and prevent strain rock bursts. In this paper, coal’s strength, deformation, energy evolution, and failure characteristics were analyzed with different strain rates under quasi-static loading. The strength characteristics of coal show a strain rate effect to a certain extent and the elastic modulus decreases first and then increases with stain rate increasing. Moreover, the elastic strain energy of coal samples always accounts for a high proportion before failure and the failure of coal presents a combined failure mode of tensile and shear under the dominance of tensile failure. The contribution of the shear failure to coal failure increases correspondingly when strain rate increases. Under quasi-static loading, There is a range where the strain rate effect does not appear, named as strain rate effect invisible area. The high static loading stress, and direct action of high strain rate loading should be avoided to reduce the risk of rock burst, especially for isolated coal pillars. The research achievements deepen the understanding of strain rock burst and provides critical support for the prevention of strain rock burst induced by high static loading.

Dynamic tensile mechanical properties of water-saturated and frozen sandstone after freeze-thaw fatigue damage treatment

To study the physical properties and dynamic mechanical response characteristics of rock materials in seasonally frozen regions, density, P-wave velocity, nuclear magnetic resonance, and dynamics Brazilian disc tests were carried out on sandstones treated with different numbers of freeze-thaw cycles. The experimental results show that the water-saturated density and P-wave velocity of sandstone decrease and the Nuclear magnetic resonance porosity increases as the number of freeze-thaw cycles increases. Under a certain loading rate, the dynamic tensile strength of water-saturated sandstone gradually decreases and that of frozen sandstone gradually increases as the number of freeze-thaw cycles increases; at the same time, the dynamic tensile strength of both water-saturated and frozen sandstone increases as the loading rate increases under the same number of freeze-thaw cycles. The reason for the variability of dynamic tensile strength between water-saturated and frozen sandstones with the increase in the number of freeze-thaw cycles can be attributed to the change in porosity. On this basis, the concept of relative dynamic tensile strength of sandstones was introduced and regression analysis was carried out with the increase ratio of porosity, and it was found that the correlation between the relative dynamic tensile strength and the increase ratio of porosity was strong. The relative dynamic tensile strength of water-saturated sandstone decreases exponentially with the increase ratio of porosity; the relative dynamic tensile strength of frozen sandstone increases exponentially with the increase ratio of porosity.

Evidence-based uncertainty quantification for bending properties of bimetal composites

Bimetal or laminated metal composites consisting of several metal or alloy layers can efficiently absorb the advantageous properties of each metal when utilised as raw materials for future remanufacturing. Their mechanical response characteristics and failure modes face uncertain challenges during the processing owing to the existence of heterogenous interfacial transition zones between layers. This work aims to study the uncertainty quantification in bending processing of a novel bimetal composite as a result of uncertain interfacial zones using an efficient evidence-based reliability analysis method. An analytical model for bending characteristics of bimetal composite was first established based on the deterministic material properties of each component layer, and it was employed to quantitatively analyse the bending uncertainty properties of 2205 duplex stainless steel/AH36 carbon steel bimetal composite (2205/AH36 BC) considering the epistemic uncertainty in geometric dimensions and mechanical properties of component 2205 and AH36 layers. The variation ranges of tangential stress and bending moment along the thickness direction of composite during bending process were effectively estimated, and the confidence level of each possible in the corresponding upper and lower boundaries was given for the tangential stress at each position. The analysis results illustrated that the uncertainty quantification for bending deformation properties of bimetal composite can more comprehensively understand the mechanical behaviors of composite, and provide an effective guidance for the forming fabrication of bimetal composite structure.

Effects of Midsole Hardness on the Mechanical Response Characteristics of the Plantar Fascia during Running.

High long-term stress on the plantar fascia (PF) is the main cause of plantar fasciitis. Changes in the midsole hardness (MH) of running shoes are an important factor leading to the alteration of the PF. This study aims to establish a finite-element (FE) model of the foot-shoe, and investigates the effects of midsole hardness on PF stress and strain. The FE foot-shoe model was built in ANSYS using computed-tomography imaging data. Static structural analysis was used to simulate the moment of running push and stretch. Plantar stress and strain under different MH levels were quantitatively analyzed. A complete and valid 3D FE model was established. With an increase in MH from 10 to 50 Shore A, the overall stress and strain of the PF were decreased by approximately 1.62%, and the metatarsophalangeal (MTP) joint flexion angle was decreased by approximately 26.2%. The height of the arch descent decreased by approximately 24.7%, but the peak pressure of the outsole increased by approximately 26.6%. The established model in this study was effective. For running shoes, increasing the MH reduces the stress and strain of PF, but also imposes a higher load on the foot.

A prediction method for oblique load stability of multi-cell tubes based on SVM

This paper aims at oblique load stability of multi-cell tubes and proposes a fast prediction method for fast judging the deformation mode of multi-cell tubes under oblique loads based on support vector machines (SVM). Firstly, the finite element model of multi-cell tubes under oblique load is established and verified by the compression experiments. According to the mechanical response and deformation characteristics of multi-cell tubes under oblique loads, a quantitative criterion for determining the deformation of tubes is proposed. Through the combination of finite element data and SVM, the prediction models of four types multi-cell tubes with oblique crushing is established, with the accuracy above 91%. A fast prediction method of critical load angle of tubes is proposed. The analysis of the critical load angle instability hyperplane shows that the cross-section length and structure height are the main sensitive parameters, and the response of the critical load angle is nonlinear. The prediction model proposed in this paper can quickly predict the stability of the multi-cell tubes and provide directions for the optimization of the stability of the multi-cell tubes.

Numerical Simulation on Structural Integrity of Grain with Large Increased Area Ratio for Solid Rocket Motor

To evaluate the structural integrity of a type of solid rocket motor grain with a largely increased area ratio using free-loading modified double-base grain, the Schapery integral nonlinear viscoelastic constitutive equation with damage is derived, and the numerical simulation model of solid rocket motor grain is constructed. According to the mission profile of the grain during the equipment period, the numerical simulation research on the mechanical response characteristics of the grain under three typical working conditions, namely, platform vibration, underwater explosion impact, and ignition pressurization during the launch is carried out. The simulation results show that under the three typical working conditions, the grain will not produce structural damage and defects, and the mechanical response of the grain under the platform vibration and explosion impact load is far less than that under the launch ignition pressurization. The ignition pressurization should be considered in the grain structural integrity design of this type or similar structure solid rocket motor.

Macro Meso Response and Stress Wave Propagation Characteristics of MCT High-Voltage Switch Under Shock load

In order to study the dynamic and electrical coupling response characteristics of Metal Oxide Semiconductor Controlled Thyristor (MCT) high-voltage switch under the synergic action of mechanical load and high voltage, the separated Hopkinson pressure bar (SHPB) test system was used to simulate different impact load environments, and combined with the multi-layer high-voltage ceramic capacitor charging and discharging system, the instantaneous electrical signals of MCT high-voltage switch were collected. Combined with numerical simulation and theoretical analysis, the failure mode and stress wave propagation characteristics of MCT high voltage switch were determined. The mechanical and electrical coupling response characteristics and failure mechanism of MCT high voltage switch under dynamic load were revealed from macroscopic and microscopic levels. The results show that the damage modes of MCT high-voltage switches can be divided into non-functional damage, recoverable functional damage, non-recoverable damage and structural damage. Due to the gap between the metal gate and the oxide layer, the insulating oxide layer was charged. After placing for a period of time, the elastic deformation of the metal gate partially recovered and the accumulated charge disappeared, which induced the recoverable functional damage failure of the device. In addition, obvious cracks appeared on both sides of the monocrystalline silicon inside the MCT high-voltage switch, leading to unrecoverable damage of the device.

Mechanical response and gas flow characteristics of pre-drilled coal subjected to true triaxial stresses

Many gas pre-drainage boreholes are generally constructed in coal seams to ensure safe underground operation. True triaxial experiments were conducted to study the mechanical response and gas flow characteristics of pre-drilled coal to reveal the in-situ behavior at pre-drilled regions in coal seams. The mechanical parameters, failure modes, and flow rate evolutions of pre-drilled coal samples were collected. The gas flow rate of pre-drilled coal samples showed an S-shaped trend with the increase of strain, and no obvious descending progress was found in the flow rate-strain curves. The typical failure mode for pre-drilled coal samples was shear-type during the true triaxial stress compression. V-shaped macro-fractures around the boreholes were observed when boreholes were perpendicular to bedding planes and parallel to face cleats. In contrast, single shear macro-fractures around the boreholes were observed when boreholes were parallel to butt cleats. The pre-drilled coal samples exhibited lower peak strength values when boreholes were parallel to butt cleats, induced by the relatively low cohesion parameter. Pre-drilled coal's initial flow rates perpendicular to bedding planes and parallel to butt cleats directions were only 33.33% and 41.67% of values measured along face cleats. More complex macro-fractures were formed, and up to a 39.30% decrease in strength was observed in pre-drilled coal samples under true triaxial unloading stress paths. The variations in volumetric strain level and the flow rate evolution were further discussed with an anisotropic conceptual failure model. These mechanical responses and flow characteristics of pre-drilled coal would guide the design of borehole layout and prevention of coal dynamic disasters.

Mechanical Response and Failure Characteristics of Granite under Unloading Conditions and Its Engineering Application

Excavation in engineering significantly changes the initial stress state of rock, which makes rock inevitably in complex unloading conditions, thus it is of great significance to make a profound investigate of the mechanical characteristics of rock under unloading condition. This paper carried out two different stress paths including conventional triaxial compression and unloading confining pressure tests on granite specimen from Sanshandao gold mine, and systematically analyzed the strength characteristics, deformation characteristics and energy evolution laws. Results show that the brittle failure characteristic of granite under unloading confining pressure are more obvious, and the peak strength, axial deformation and other parameters are smaller than those of triaxial compression test. Especially the deformation modulus decreases with the increase of unloading confining pressure, which is no longer a constant parameter in the sense of continuum. Therefore, the unloading-induced weakening coefficient of engineering rock mass is proposed, and the relationship between the coefficient and the reduction ratio of confining pressure is quantified. Then, the unloading-induced weakening algorithm is developed in FLAC3D to simulate the stability of a deep mine stope. It is found that results of the unloading-induced weakening model are much closer to the engineering practice, which has certain theoretical and practical reference significance for the stability analysis of rock mass engineering.

Experimental study on characteristic and mechanism of simulated lunar rock destruction under high energy laser irradiation

The large load and poor heat dissipation of moon rock core drilling leads to the difficulty of rock breaking and low drilling and sampling efficiency. As a new auxiliary rock breaking method, laser rock breaking is expected to be applied to perturbation sampling in lunar rock drilling. Revealing the fracture characteristics and mechanism of rock under laser irradiation is an important basis for realizing laser-assisted lunar rock sampling. Basalt was used as simulated lunar rock sample, and its mechanical response characteristics under laser irradiation were analyzed from macro to micro point of view, and the failure law under different laser power and different irradiation time was explored. The results show that the failure of the sample under laser irradiation is mainly characterized by local rock melting and dynamic crack propagation, and the surface temperature of the sample follows the characteristics of Gaussian distribution. The laser power has a greater influence on the degree of rock weakening than the irradiation time. Laser irradiation of rocks can significantly reduce rock strength, and has obvious effects on improving rock breaking efficiency and reducing in situ disturbance. It is expected to provide theoretical and technical support for assisting lunar rock drilling and sampling in the future.

Mechanical Response Characteristics Analysis of Tunnel Surrounding Rock during Near-Fault Construction

Mechanical Response Characteristics Analysis of Tunnel Surrounding Rock during Near-Fault Construction

Exploring electromechanical utility of GaAs interdigitated transducers; using finite-element-method-based parametric analysis and experimental comparison

Analysis of interdigitated transducers often relies on phenomenological models to approximate device electrical performance. While these approaches prove essential for signal processing applications, phenomenological models provide limited information on the device’s mechanical response and physical characteristics of the generated acoustic field. Finite element method modeling, in comparison, offers a robust platform to study the effects of the full device geometry on critical performance parameters of interdigitated transducer devices. In this study, we fabricate a surface acoustic wave resonator on semi-insulating GaAs (100), which consists of an interdigitated transducer and acoustic mirror assembly. The device is subsequently modeled using fem software. A vector network analyzer is used to measure the experimental device scattering response, which compares well with the simulated results. The wave characteristics of the experimental device are measured by contact-mode atomic force microscopy, which validates the simulation’s mechanical response predictions. We further show that a computational parametric analysis can be used to optimize device designs for series resonance frequency, effective coupling coefficient, quality factor, and maximum acoustic surface displacement.