Nonlinear Mechanical Characteristics Research Articles

3D numerical study of axial compression behavior of concrete-filled steel tubular columns from mesoscopic perspective

This study investigates the axial compression behavior of Concrete-Filled Steel Tubular (CFST) short columns from a mesoscopic perspective. Concrete is regarded as a three-phase composite material consisting of aggregates, mortar, and interfacial transition zones (ITZs). The Concrete Damaged Plasticity (CDP) model was employed to simulate the nonlinear mechanical response and fracture characteristics of concrete. Verified against experimental results, the numerical model excels in realistically simulating the uniaxial compression behavior of CFST short columns. Subsequently, factors influencing the macroscopic behavior of CFST short columns were investigated. Results indicate that the random aggregate model adopted for concrete enables a more realistic prediction of the behavior of CFST short columns. Additionally, circular section steel tubes demonstrate a stronger confinement effect compared to square ones. With increasing lateral confinement, the properties of CFST short columns, such as bearing capacity and ductility, are significantly enhanced.

Simplified nonlinear model and 3D printing model experiment verification of longitudinal joints of shield tunnel segments

The segment joints represent vulnerable and core-bearing areas within shield tunnel structures. Their flexural stiffness, starting from the contact surface of longitudinal joints to the bolt hole, exhibits continuous changes under bending loads, typically demonstrating nonlinear mechanical characteristics. This study investigates the influence of joint contact surfaces on flexural stiffness, extending from the joint contact surface to damaged concrete in the compressed zone. A new simplified model for the variable nonlinear stiffness of longitudinal segment joints in shield tunnels is proposed, considering the flexural stiffness of the joint contact surface and the width of the damaged concrete zone in the segment ring while simulating the flexural stiffness decay induced by the opening of segment joints. Based on the minimum potential energy principle, a design calculation method for joint flexural stiffness is derived, establishing the nonlinear bending stiffness coupling relationship between the segment and the joint. Through similarity theory, 3D printing technology, and indoor loading tests, the theoretical model's accuracy regarding tunnel segment joints is verified. This theoretical model provides a basis for designing and assessing the performance of tunnel-segment joints.

Nonlinear Dynamic Mechanical Characteristics of Air Springs Based on a Fluid–Solid Coupling Simulation Method

The use of air springs has become widespread in various industries due to their exceptional superelastic properties; however, their strong nonlinear characteristics have become a hindrance to numerical simulations of air springs and have garnered increasing attention. This paper examined the nonlinear dynamic mechanical characteristics of air springs from a fluid–structure interaction perspective and verified the accuracy of the simulation analysis model through quasistatic tension and compression experiments. The average relative errors for air spring load and gas pressure were found to be 8.1% and 7.7%, respectively, which supports the validity of the model. The impact of frequency and amplitude excitations on the axial load characteristics of air springs was investigated through tension and torsion testing. The results showed that increasing the excitation frequency improves the stability of the axial load, while increasing the excitation amplitude enhances the axial load value. The change in axial compression was found to be more significant than that in axial tension, as it was affected not only by the axial load but also by the radial load, which is a key factor affecting the dynamic characteristics of air springs. A radial load analysis model was established to study the influence of frequency and amplitude excitations on the axial load characteristics of air springs. The simulation results indicated that under different amplitudes, the radial load of air springs goes through four stages: a steady period, rising period, steady period, and falling period. Additionally, under the same amplitude, the radial load value increases with an increase in frequency. This research on the dynamic load characteristics of air springs under amplitude and frequency excitations is important for their application in low-frequency and low-amplitude vibration environments, and its findings can be utilized to improve the technical parameters of air springs for suspension damping.

Numerical evaluation of shear strength of CFS shear wall panel with OSB sheathing

Outside of the American Iron and Steel Institute AISI S400-15 limitations of Shear Wall Panel (SWP) height-to-width (h/w) aspect ratio, the present paper puts forward a sufficiently detailed Finite Element Modeling (FEM) using “Abaqus” software, capable to evaluate with a reasonable precision the shear strength of Cold Formed Steel (CFS) SWP with Oriented Strand Board (OSB), under lateral load. In terms of nonlinear response, shear strength and failure modes, the numerical results of the SWP with and without an opening are validated against available experimental data, accounting for nonlinear mechanical and geometrics characteristics, as well as the nonlinear behavior of connection. Subsequently, the conducted comprehensive parametric studies have revealed that the variation of the screw spacing, from 50.8 mm up to 152.4 mm, provides a nonlinear variation of shear strength that cannot be extrapolated for different screw spacings. In addition, the shear strength of a two-sided OSB-sheathed SWP is less than twice one-sided OSB-sheathed SWP. Furthermore, the door’s and window’s openings’ position between the center and the edge of the SWP provide the best performance in terms of shear strength up to 33 % and 24 % than the center and edge openings’ positions respectively.

DYC Design for Autonomous Distributed Drive Electric Vehicle Considering Tire Nonlinear Mechanical Characteristics in the PWA Form

This paper presents a novel direct yaw moment control (DYC) strategy for autonomous distributed drive electric vehicle (DDEV) to improve path-following driving stability under critical maneuvers. Due to the fact that the tire mechanical characteristics show highly nonlinear under those critical conditions, the piecewise affine (PWA) identification method is chosen in this work to model the tire nonlinear mechanical characteristics since it shows best model accuracy/simplicity compromise for system control design. On this basis, to properly reflect the coupling behaviors between longitudinal motion and lateral motion, the vehicle dynamics model which considers the tire nonlinear mechanical characteristics in the PWA form is established. By analyzing the phase plane of vehicle nonlinear model, a novel external yaw moment calculation method based on global fast terminal sliding mode (GFTSM) control method is applied to the upper layer of DYC architecture for eliminating the errors of yaw rate and sideslip angle. Then, different weight coefficients are allocated to obtain the final external yaw moment. In the lower controller, the optimal four-wheel torque is distributed according to a concise and accurate algorithm in which adaptive weight coefficients are considered. The simulation results verify the effectiveness of the proposed control strategy in improving the driving stability performance of autonomous DDEV against two other control strategies under three extreme conditions.

Characterizing fatigue damage behaviors of concrete beam specimens in varying amplitude load

In this paper, the random and nonlinear mechanical characteristics of the composition distribution of concrete in each phase are investigated to solve the difficulty of fatigue damage test of concrete beam specimens under variable amplitude loading. A three-dimensional (3D) concrete composite random aggregate meso-model of concrete beam specimens is built with Digimat as a composite modeling tool. Subsequently, the bending-tensile strength and fatigue life of the model under four-point bending loading is analyzed and calculated using Abaqus finite element analysis model based on the concrete elastic-plastic damage criterion. The mechanical behaviors of concrete materials under static load failure, multistage fatigue loading, and random fatigue loading are studied. Finally, compared with the test results, the following conclusions are obtained. The random aggregate model and elastoplastic damage mechanics model of concrete composite constructed by concrete in Abaqus and Digimat can better describe the geometric and distribution characteristics of composite structure and aggregate in concrete beams and the mechanical behavior of fatigue and static load failure. The difference is 4.08 % with the experimental results, which verifies the validity and reliability of the numerical simulation model, and the fatigue life of concrete beams under random loading Sra and Srb is 1622 and 164 times, respectively. The research results have certain guiding significance and reference value for accurate calculation of bending and tensile strength of concrete beams under specified raw material and mix ratio and prediction of fatigue damage cracking in airport cement concrete pavement structure.

Uncertain natural characteristics analysis of laminated composite plates considering geometric nonlinearity

In order to achieve the fine and high reliability design of laminated composite plates, the randomness of geometric and material parameters, along with the nonlinear mechanical characteristics is taken into deliberately account. A novel method for solving the uncertain natural characteristics is proposed, in which the uncertain natural frequencies first cover effects of the geometric nonlinearity and are obtained with a multiscale feature extraction and fusion network (MFEFN). Theoretical analytical solutions of the nonlinear natural frequencies and nonlinear frequency ratios are derived and then the statistical properties of the two uncertain natural characteristics are obtained. Influences of the random geometric parameters and material parameters on the two natural characteristics are further studied based on the sensitivity analysis. The accuracy of the present uncertain natural characteristics analyses is demonstrated by comparing linear natural frequencies, nonlinear natural frequencies and their statistical properties numerical results with those provided using other models available in the open literatures. The solving efficiency advantages of the proposed MFEFN-based procedure are clearly shown by comparing with MCS. The present research results provide theoretical basis and technical means for accurate analysis and optimal design of the laminated structures.

Experimental study on nonlinear mechanical behavior and sampling damage characteristics of rocks from depths of 4900–6830 m in Well Songke-2

Experimental study on nonlinear mechanical behavior and sampling damage characteristics of rocks from depths of 4900–6830 m in Well Songke-2

A Quantitative Method to Predict the Shear Yield Stress of Rock Joints

The shear mechanical properties of rock joints are crucial in assessing the stability and safety of rock structures, including slopes, rock dams, and tunnels. The yield stress serves as a pivotal point that distinguishes the linear and non-linear mechanical characteristics of rock joints. Due to its significance in risk monitoring and safety evaluation, this paper first provides an overview of the commonly employed methods for identifying the yield stress. Then, a novel displacement reduction method based on the displacement reduction coefficient is proposed and systemically examined. The comparison between the proposed method and existing methods based on shear experimental data suggests that the former is more adept at accurately determining the yield stress without subjective interference. Finally, this innovative method is employed to estimate the effects of external environmental factors on the yield stress of rock joints.

Non-linear mechanical characteristics of tailings in large-scale high tailings dams

The non-linear mechanical characteristics of tailings under high pressure are the research foundation of large-scale high tailings dams. Considering the high stress caused by high tailing ponds, consolidated drained triaxial shear tests were carried out. The deterioration mechanism of non-linear mechanics was revealed by particle crushing. The test results show that sample density has a great influence on volumetric strain under low pressure. However, volumetric strain is not related to sample density under high pressure. The shear strength of the tailings is significantly non-linear. The internal friction angle under low pressure can still be obtained by the traditional linear Mohr–Coulomb criterion and the internal friction angle under high pressure by the power function of the Mohr criterion. The particle crushing of tailings occurs not only at high pressure but also at low pressure. The value of the breakage index increases with sample density. The non-linear mechanics of shear strength are affected by particle breakage. The breakage index value increases linearly with increasing shear strength, indicating that the high density of the deep part of the tailings dam is prone to particle crushing, which affects the stability of the large-scale high dam.

Nonlinear vibration analysis for bolted CFRC plates based on displacement-dependent surface spring-damping model of bolted joint

Under the effect of external excitation, bolted structures are prone to stiffness weakening and damping energy dissipation at the bolted joint, which makes the structures show nonlinear vibration behavior. In this paper, the displacement-dependent surface springs and tangential surface damping expressed by the S-curve model are proposed to simulate the nonlinear mechanical properties of the bolted joint. The non-uniform distribution of the mechanical parameters for the bolted joint is given to simulate the actual joint interface pressure distribution. Based on these, a nonlinear semi-analytical model for bolted carbon fiber reinforced composites (CFRC) plates considering the nonlinear mechanical characteristics of the bolted joint is established. Combined with the experimental results for a bolted CFRC beam, the specific S-curve expressions for the relevant mechanical parameters of the bolted joint are obtained by the inverse identification technology and numerical fitting method. After that, the bolted joint model is transplanted to the dynamic model of a bolted CFRC plate for numerical calculation. The comparison with the corresponding measured results shows that the proposed modeling method can well reproduce the soft nonlinear vibration of the actual bolted CFRC plate, which verifies the correctness and applicability of the proposed modeling method.

A new quasi-dynamic method for the prediction of tendon tension of TLP platform

The assessment of tendon mechanics for the tension leg platform (TLP) is crucial to the safety of the whole TLP system. The tendon design includes nonlinear mechanical characteristics such as set-down and various dynamic effects such as slow drift and springing. In this study, a new quasi-dynamic method dedicated to the dynamic tension of tendon and global motion of TLP is established by employing two primary assumptions, i.e. the separation of the hull’s horizontal and vertical response, and the separation of low-frequency, wave-frequency, and high-frequency excitations due to waves. An analytical tendon model is proposed, and the simultaneous time history of tendon tension can be obtained through the post-treatment after carefully handling the hull’s various dynamic responses. A remarkable efficiency is achieved since the time-consuming convolution integral, finite element model of the tendon, etc., are avoided. A comprehensive validation regarding the TLP system, global motion, and tendon tension is conducted by the comparisons with model test measurement and fully coupled analysis using OrcaFlex. An excellent agreement is achieved no matter the cycles and phases in the time series or the extremes in the statistics. The study has proven the quasi-dynamic method a reliable approach with satisfactory accuracy and superb efficiency, which should be a useful method in the design of the TLP platform.

Mesoscale modeling and failure mechanism of concrete considering pore structures and actual aggregate shapes

This contribution focuses on the modeling and failure mechanism of concrete which is constituted by aggregates, mortar matrix, interfacial transition zones (ITZs) and pore structures. Firstly, actual geometrical shapes of aggregates were obtained by laser scanning technique. Secondly, a random aggregate placement algorithm and a pore structure generation algorithm were proposed to generate 2D concrete models which could realistically reflect the highly heterogenous meso-structure of concrete. Then, zero-thickness cohesive elements with traction - separation laws were embedded in the finite elements to simulate the complex fracture process and nonlinear mechanical characteristics. Finally, uniaxial compression simulations were carried out, and the effect of porosity and aggregate volume content on carrying capacity, elastic modulus and fracture process of concrete were investigated and compared with similar experimental results. The parametric study for cohesive elements is also conducted. Results showed that porosity and aggregate content have a significant influence on the mechanical properties of concrete, the mesoscale model is capable of simulating the failure process and mechanical behavior of concrete. The effect of each cohesive element parameter is clearly identified.

Facile fabrication of Bi-layered perfusable hydrogel tubes as biomimetic 3D arterial construct

Small-diameter arterial conduits with native physiological and biological equivalence continues to be a constant global demand posing critical challenges in fabrication. Advent of various strategies towards mimicking the structural hierarchy of a native blood vessel, often involve complex instrumentation and template-assistance with post-processing complications eventually compromising structural fidelity. In the present research, we report a template-free, facile strategy- ‘3D wet writing’ by peripheral-core differential ionic gelation to fabricate perfusable customizable constructs of any dimension, thickness and length in <5 mins. Dual-crosslinking using di-diol complexation of borax with Alginate- poly (vinyl alcohol) was performed to enhance the stability of fabricated bi-layered tubular constructs (BLT). These fabricated BLTs demonstrated non-linear mechanical characteristics of native blood vessels in withstanding physiological (120/80 mmHg) hemodynamic loading conditions with cyclic strain (5.82 ± 0.88%). The BLTs also ensured adequate longitudinal (0.176 ± 0.03 MPa) & circumferential (0.29 ± 0.012 MPa) tensile strength and burst pressure strength of 353.875 ± 22.69 mmHg. Hemocompatible characteristics of BLT were clearly evident with lower hemolytic index (0.21 ± 0.03%) and maintenance of erythrocyte structural integrity under dynamic conditions. Further, non-thrombogenic and non-inflammatory characteristics of BLTs were confirmed by in-activated platelets and monocytes under dynamic conditions. The developed wet-writing technique exhibited facile integration of layer-specific cells concurrently with the BLT fabrication. The spatial cell-specific expressions of smooth muscle (α-SMA) and endothelial (CD-31) cells in BLT were comparable to native hierarchical cellular organization with the multi-layered medial and mono-layered intimal layers. Further, ex-vivo dynamic studies on anastomotic interface between BLT and rat abdominal aorta clearly evidenced the functional efficacy of fabricated BLTs as physiologically relevant small-diameter vascular construct.

Nonlinear Energy Evolution Characteristics of Diorite Examined by Triaxial Loading-Unloading and Acoustic Emission Tests.

Acoustic emission (AE) is often accompanied by the propagation of internal microcracks in loaded rock samples, and it essentially reflects microinstability phenomena driven by energy redistribution under stress. In this paper, loading and unloading tests were carried out to investigate the internal nonlinear damage evolution characteristics of diorite samples under different unloading confining-pressure rates. The nonlinear mechanical characteristics of the strain energy sequence of diorite were studied by applying nonlinear dynamics and basic chaos theory and MATLAB software. Moreover, the evolution characteristics of AE counts and AE energy of rock samples were investigated, and their microcrack-propagation modes were analyzed based on the RA–AF scatter distribution of AE and a two-dimensional Gaussian mixture model. Finally, according to the evolution characteristics of energy and AE, the nonlinear damage evolution mechanism of diorite under loading and unloading conditions was revealed. The results show that, before the loading and unloading peak strength, when the strain-energy-promotion coefficient, r, is equal to 1 or changes in the ranges of 1–3, 3–3.57, and ≥3.57, the strain-energy evolution of diorite presents the characteristics of supercritical stability, nonlinear stability, period-doubling stability, and chaos, respectively. Meanwhile, the greater the rate of the unloading confining pressure, the earlier the period-doubling bifurcation and chaotic mechanical behavior will occur. After loading and unloading peak strength, the sudden decrease of high-density AE counts and AE energy or the sudden transition of the strain-energy-promotion coefficient from >0 to <0 can be used as an important criterion for the complete failure of rock samples.

Nonlinear mechanical characteristics and damage constitutive model of coal under CO2 adsorption during geological sequestration

Geological sequestration of CO2 is an effective way to achieve the goal of reducing global warming and carbon neutralization. The complex CO2–coal interaction will lead to the change of mechanical properties of coal. Therefore, evaluating the mechanical characteristics of deep coal seam after CO2 adsorption is of great significance for analyzing the geological characteristics and structural stability of deep strata and storage site selection. In this study, the triaxial compression test and acoustic emission (AE) test were used to evaluate the effect of CO2 adsorption pressure on the mechanical properties of coal mass. On the basis of the evolution characteristics of AE ring down count (RDC), fractal theory was used to analyze the deformation and fracturing evolution of coal. Besides, an elastic damage constitutive model describing the nonlinear stress-strain relationship of coal under CO2 adsorption is established. Results show that the growth of adsorption pressure develops the risk of damage and fracturing of coal. With the increase in adsorption pressure, the value of singularity index width Δα presents a downward trend, indicating the development of internal cracks and the increase in the complexity of microunit fracturing process. When the adsorption pressure is low, the gas in large cracks and pores leads to the generation of small AE signal that occupies the dominant position. High adsorption pressure increases the complexity and nonlinearity of coal deformation, strengthens the proportion of large AE signal, and leads to the increase in the average value of multifractal spectrum width Δf. With the increase in adsorption pressure, the fracturing degree of coal is higher, a mass of large-size cracks appears, and more AE spectrum presents intensive distribution. In the plastic stage, the load level is close to the strength limit, the microcracks intersect with each other, and the average value of Δα in this stage is the smallest.

Study on the collision characteristics of a subway coupler

Derailment accidents caused by coupler buffer devices should not be underestimated. In this study, a particular type of subway was considered the research object, and a nonlinear finite element model of train collisions with a detailed coupler was established to study the collision characteristics of the coupler under different working conditions. First, the nonlinear mechanical characteristics of the coupler were analyzed. Then, a finite element model, including the energy absorption characteristics of the buffer and the collapse tube, the failure characteristics of the overload protection device, and the motion characteristics of the nodding and shaking head, was established and its reliability was verified. On this basis, a collision finite element model of a subway with four sections was developed. The attitude motion of the couplers and its influence on the derailment behavior of the vehicle was studied under the condition of initial vertical deviation or lateral deviation of the active and passive head couplers during their operation period. The results show that when the collision velocities are equal, the initial state of the head coupler barely affects the axial action characteristics and the pitching deflection angle attitude of the middle couplers; however, it has a certain effect on the yaw deflection angle. Furthermore, the initial state of the head coupler has a significant influence on its motion. The initial vertical deviation of the head coupler increases the derailment risk of the second section of the active subway. Moreover, the initial lateral deviation of the head coupler increases the derailment risk of the active subway and the first section of the passive subway. When the utilization rate of the head coupler is approximately 69%, the derailment risk of the vehicle is reduced.

Modeling and control of helicopter flight control system with a controllable Semi-rotary fluid viscous damper

To improve the handling comfort of Helicopter Flight Control System (HFCS), an adaptive particle swarm optimization optimized variable universe fuzzy proportional-integral-derivative (APSO-VUFPID) strategy for damping force control is proposed. First of all, by the results of the controllable semi-rotary fluid viscous damper (CSFVD) mechanical tests, a hyperbolic tangent model is developed. Afterwards, an equivalent model of HFCS is established. In the next part, aiming at improving the vibration suppression performance of the joystick system, an APSO-VUFPID is proposed to generate the desired damping force in real-time. Finally, numerical simulation and experimental tests are carried out to verify the vibration reduction effect of the proposed APSO-VUFPID method with respect to passive, proportional-integral-derivative (PID), adaptive particle swarm optimization optimized proportional-integral-derivative (APSO-PID) and adaptive particle swarm optimization optimized fuzzy proportional-integral-derivative (APSO-FPID) methods. The results show that the hyperbolic tangent model can accurately describe the nonlinear mechanical characteristics of the CSFVD. Moreover, under the proposed APSO-VUFPID control method, the amplitude of acceleration and velocity of the joystick system are smaller than those obtained from passive, PID, APSO-PID and APSO-FPID methods. Therefore, the proposed APSO-VUFPID controller has better handling comfort compared to passive, PID, APSO-PID and APSO-FPID controllers and can be employed in real applications.

Seismic Response and Nonlinear Mechanical Characteristics of Bridge Pile Foundation in Yushu Permafrost Area

In order to analyze the application effect of bridge pile foundation in Yushu permafrost area, this paper uses the research methods of theoretical analysis, model testing, and numerical simulation to collect soil samples in the Yushu area, study various indicators of frozen soil, simulate different frozen soil foundations in the Yushu area, and study different seismic waves under the influence of different temperatures. The seismic response mechanism of bridge pile foundations in the Yushu permafrost region under the influence of loading mode, soil material, and single pile in different permafrost regions is analyzed, and the dynamic response and mechanical nonlinear characteristics of displacement and deformation under different seismic forces are obtained. The simulation results show that under the influence of different temperatures, different seismic wave loading methods, and different soil quality single piles, the bridge pile foundation in the Yushu permafrost area has obvious seismic response laws and obvious mechanical nonlinear characteristics. Under the influence of permafrost material, most single piles have response coefficients of between 0 and 1.

Coupling Characteristics of Creep Fracture of Rock Foundation on Wind Turbine under Wind-Induced Vibration

In view of the nonlinear mechanical characteristics of rock foundation creep fracture and its influence on the stability of wind turbine under wind load, based on the influence of wind load, this paper proposed the elastoplastic creep fracture and rock foundation bearing capacity on wind turbine. Considering the superstructure concrete with rock foundation and its boundary conditions, the wind load standard value was obtained and wind turbine system composition was constructed. The two grades of freedom system of viscous damping vibration model was proposed. Furthermore, the frequency characteristic equations and the relations of the first- and second-order natural frequencies were obtained. Considering plastic yield theory on power hard rock base material, the analytical expressions of principal stress distribution, plastic zone, and plastic state of I-II composite crack were obtained and used for coupling Mohr–Coulomb plastic yield condition and creep fracture characteristics. Furthermore, the nonlinear creep model equation and accelerated creep fracture time were also obtained, to be used for the modified Kelvin nonlinear accelerated creep model. Combined with the calculation examples, it is verified that the accelerated creep displacement and crack propagation of rock foundation are obvious, taking full account of the wind bracing and creep characteristics of rock foundation. Final, the failure mode of rock foundation is of compressive shear, local shear, and bending-shear; so, it is necessary to reinforce the interface of the rock foundation in a timely manner.