Cyclic Loading Research Articles

Sub‐assemblage testing and fragility analysis of connections of continuous‐plasterboard suspended ceiling systems

AbstractPast earthquake reconnaissance reports highlighted extensive seismic damages to suspended ceiling components and connections, including instances of complete ceiling failures. The seismic qualification of these nonstructural elements typically requires comprehensive evaluation through full‐scale shake table testing. However, such experimental evaluation is ordinarily not possible for every change made in various components and connections of ceiling systems due to the cost and effort involved. A feasible alternative is to obtain the behavior of components and connections from sub‐assemblage testing and incorporate them in appropriate numerical ceiling models to derive mechanical responses for developing alternative or new installation schemes. This paper considers critical connections of three continuous‐plasterboard suspended ceiling systems that were evaluated using shake table‐generated motions. The connections were classified according to their attachment to typical floors and walls of building structures, and sub‐assemblage testing was conducted using both monotonic and cyclic displacement loading. The observed failure modes in each connection were detailed, and appropriate damage states were assigned as the basis for constructing connection fragility curves. The results of the sub‐assemblage testing were presented in terms of the hysteresis responses, envelope curves, nonlinear backbone curves, and cumulative energy dissipation curves. Additionally, multilinear models of the connections were derived by approximating nonlinear backbone curves’ initial‐ and post‐yield behaviors. These multilinear models were further idealized to derive three equivalent linearized models for simplified yet reasonably accurate results for linear structural analyses. Finally, fragility curves were derived for all connections, considering their cyclic displacement failure capacities.

Machine learning-based shear bearing capacity of concrete columns confined by transverse reinforcement subjected to lateral cyclic loading

Machine learning-based shear bearing capacity of concrete columns confined by transverse reinforcement subjected to lateral cyclic loading

A novel approach to enhance the structural integrity of a bottom-edge cracked I-beam with piezoelectric actuators

Structural health monitoring and repair have become increasingly crucial in confirming the safety and longevity of damaged structures. This study presents a novel approach to enhancing the structural integrity and extending the fatigue life of a bottom-edge cracked I-beam by applying piezoelectric actuators strategically placed along the crack location by actively suppressing crack propagation. An innovative actuation system induces controlled deformations in the I-beam, effectively reducing the Stress Intensity Factor (SIF) and preventing crack propagation. The efficacy of the proposed approach is validated through a series of numerical results on the ABAQUS platform, including static loading, fatigue loading, and crack growth monitoring. Various parameters, like maximum loading capacity under static loading, interpretation of crack growth rate, and service life, are monitored and analyzed throughout the cyclic loading process. The results demonstrate that the application of 500 V to the piezoelectric actuators significantly reduces the SIF by 16.62% under a 2 kN total load, a 2.86% enhanced maximum load-carrying capacity is obtained, delayed crack propagation is found after repair, and a 72.67% extended service life is achieved under a load range of 0.2 kN to 2 kN. Overall, the outcomes of this research lead to the development of innovative and efficient techniques for delaying the propagation of cracks, thereby preventing the premature onset of catastrophic failure of cracked I-beams.

Investigating the behavior of vertical trapezoidal CSSWs stiffened with flat steel plate

Steel shear wall (SSW) is an efficient system used to construct and improve many structures over the past decades. The main weakness of the traditional flat plate SSW is the premature buckling of the plate, for which the corrugated steel shear wall (CSSW) is a suitable alternative. However, the reduced resistance of CSSW compared to flat SSWs is a disadvantage. In this research, their reinforcement by flat steel plates with different dimensions and thicknesses has been used to improve the behavior of vertical trapezoidal steel shear walls (VTSSW). The samples studied in this research were subjected to cyclic loading after verification in Abaqus finite element software. The outcomes showed that reinforcing CSSWs with flat plates increased strength and energy absorption between 6 to 63% and 16 to 92%, respectively. Also, the equivalent viscous damping has increased between 5 and 82%. Also, due to strengthening the CSSWs, the pinching phenomenon in the hysteresis curves has been reduced, and the sudden decrease in strength after buckling in the CSSWs without stiffener has been significantly reduced.

Fatigue Strength Analysis of Rail Fastening Baseplate

Superstructural elements of a railway track experience dynamic loads varying over time. As a consequence, this is accompanied by the initiation and accumulation of fatigue damages. Defects in intermediate rail fastening are quite difficult to identify using flaw detection methods, and some can be destructed. In particular, rail fastening baseplates often fail due to insufficient fatigue strength.Purpose: To investigate the fatigue strength of rail fastening baseplate.Methodology: Development of the mathematical model of deformation based on the finite element method (FEM). Strength analysis of the baseplate using the model of a variable-thickness slab resting on a nonlinear elastic foundation. The latter is modeled by a set of rods with nonlinear deformation and parameters determined by compression tests of the baseplate. A mathematical model developed in COSMOS software for the FE analysis of the stress-strain state of the baseplate at a time-varying load from rolling equipment and assembly forces from attaching the baseplate to the sleeper and rail.Research findings: The cyclic loading parameters are obtained at dangerous points of the baseplate and its durability is analyzed at different loads with respect to unevenness of track settlement and failure of bolt connections of rail fasteners. The influence of these factors on actual loads on the rail fastener is determined. It is found that the service life of the baseplate mainly depends on the dynamic load.

New insights into physical origins of dynamic strain aging in Ti-2Al-2.5Zr alloy and influence on LCF and HCF behaviors

The multi-step strain aging tests were meticulously designed in this work to reveal the physical mechanisms of static strain aging (SSA) and dynamic strain aging (DSA) behaviors in Ti-2Al-2.5Zr alloy for the first time. It was revealed that the shuffling mechanism of interstitial oxygen atoms combined with the pinning effect of locally-generated cross-slip on the movement of screw dislocations were responsible for the occurrence of strain aging. Furthermore, the effects of DSA on the low-cycle fatigue (LCF) and high-cycle fatigue (HCF) properties were elucidated in Ti-2Al-2.5Zr alloy. Results showed that the sensitivity of DSA to cyclic loading was attributed to the generation of numerous residual edge dislocation segments through local cross-slip, facilitating the formation of dislocation veins which inhibited the formation of persistent slip bands (PSBs) and led to the significantly cyclic hardening. Finally, it was emphasized that the phenomenon of DSA should be carefully considered for the structural integrity assessment of Ti-2Al-2.5Zr alloy and several suggestions were provided.

Induced magnetic field and thermal regulation of synovial fluid flow through irregular surfaces with first-order slip and gold nanoparticles

ABSTRACT The current computational exploration develops a poroelastic model of the knee cartilage to elevate its temperature under cyclic sinusoidal loading. A contributing factor to the rise in temperature is this tissue’s viscous dissipation, which converts some of the mechanical energy supplied into heat. The manipulation of cartilage temperature is mostly reliant on the movement of synovial fluid inside the space between joints and within the permeable cartilage. We developed the region flow model in the presence of induced magnetic fields and gold nanoparticles, which enhanced the efficiency of joint lubrication by boosting the load-carrying capacity. We dealt with the problem for two different models. Model 1 assumes that viscosity is exponentially dependent on concentration. The shear thinning index in Model 2 is regarded as a concentration-dependent variable. We introduce these models for a complex wavy surface, where the first-order slip effect occurs. We modified the governing problem by assuming a long wavelength and a low Reynolds number. We followed up with a computational analysis utilizing the Rung–Kutta–Merson approach with Newton iteration in a shooting and matching strategy. We have conducted detailed comparisons between Model 1 and Model 2. The graphical findings have been shown for the distributions of velocity, temperature, and nanoparticle concentration. Additionally, the pressure gradients, streamlines, and axially generated magnetic fields have also been included. These results are presented for numerous physical parameters. The mechanics of trapping are thoroughly examined through the use of streamlines.

Effect of Constant Cyclic Stress Coupling on the Fatigue Behavior of 304LN Stainless Steel.

The stress state of the primary circuit main pipeline is very complex mixed constant stress and periodic cyclic stress during the operation of nuclear power plants, which often affects the failure behavior of the stainless steel (SS) pipe. The fatigue behavior of 304LN SS under mixed constant stress and cyclic stress was investigated, and it was found that the coupling effect of constant stress and cyclic stress has a significant collaborative acceleration on the fatigue behavior. The research results showed that the cracks in the 304LN SS did not propagate even after 78 days under both constant load conditions of 5 KN and 7.5 KN, while the crack growth rate (CGR) of the specimen increased by about an order of magnitude when coupled with a cyclic fatigue load. The fatigue life of 304LN SS was the longest under 200 °C high-temperature water, and its life was roughly the same under 250 °C and 300 °C water. In a 300 °C high-temperature water environment, the fatigue life under the coupling of constant stress and cyclic fatigue stress is significantly lower than that under symmetric cyclic stress alone. There is a synergistic acceleration effect on the fatigue life of 304LN SS when constant stress is coupled with periodic cyclic stress, which is attributed to the combined effect of a corrosion environment and mechanical factors.

Coupled hydro-mechanical model for underground hydrogen storage undergoing cyclic injection and production

ABSTRACT Excess renewable energy can be used to generate and store hydrogen underground, offering a secure and econimical solution to the intermittency challenges of renewable energy sources. The success of underground storage relies on understanding and controlling the geo-mechanical integrity of storage sites during cyclic loadings. While geological deformation during natural gas and carbon dioxide storage is well studied, few have investigated pore pressure and in-situ stress variations during cyclic loading, which is unique to underground hydrogen storage sites. This paper presents a predictive analytical model for the pore pressure and stress changes during cyclic loading. The model was derived based on continuous point source injection, a basic hydro-mechanical model while applying the superposition to consider the cyclic loading. The developed model was evaluated for hydrogen and natural gas subjected to cyclic injection and production. Comparing hydrogen and natural gas storage cases can offer valuable insights into the behavior of hydrogen since the deformation of natural gas storage is more studied. Finally, analytical solutions for both storage cases were validated by numerical models with discrepancies between the models amounting to less than 1%. Comparative analysis of the results from 3 to 99 cycles of injection and production for both hydrogen and methane demonstrates that rise in cycle numbers leads to a corresponding rise in stress accumulation in the system. Neglecting the stress accumulation during these cycles can lead to significant geomechanical issues, potentially compromising the storage system’s safety and integrity.

Development patterns of the dynamic elastic modulus of saturated coral sand under different drainage conditions

Long-term cyclic loading can have a significant effect on the modulus of sand, and the influence on saturated coral sand has yet to be established. In this paper, the significant influence of non-plastic fines content (FC) and relative density (Dr) on dynamic elastic modulus (E) of saturated coral sand has been evaluated by a series of cyclic triaxial drainage tests. The results show that the dynamic elastic modulus increases rapidly at the beginning of loading; then the growth slows down and finally stabilizes. In general, the development of E is influenced collectively by FC, Dr and cyclic stress ratio (CSR). The initial dynamic elastic modulus Ed-1 and steady-state dynamic elastic modulus Ed-s increase with the increase of Dr, and decrease as FC increases. The linear fitting equations are given by introducing the equivalent skeleton void ratio esk*. Furthermore, the relative dynamic elastic modulus Er is defined as the ratio of Ed-N to Ed-s, and the prediction equation for Er was developed to provide a basis for the engineering mechanical parameters of coral sands under long-term loads.

Mechanical properties and restoring force model of Squeezing Rub-type Particle Damper

The sliding effect of isolation bearings has been proven to effectively mitigate the seismic effects on large-span bridges. However, it also results in excessive relative displacement between the main girder and piers during earthquakes. In this study, a pioneering Squeezing Rub-type Particle Damper (SRPD) is developed to address this issue. In order to verify the damping characteristics of SRPDs and investigate the working principle of squeezing friction energy dissipation, five quasi-static tests were conducted on SRPDs using two particle damping materials with different compactness levels. In order to compare the energy dissipation performance, comparative tests were conducted on Non-Squeezing-type Particle Dampers (NSPDs) and SRPDs. Utilizing regression analysis, two skeletal curve models for SRPDs were proposed, alongside a detailed restoring force model that incorporates considerations for both the pinching effect and stiffness degradation phenomena observed during the loading and unloading phases. The experimental results demonstrate that the maximum damping force of SRPDs can reach 16 times that of NSPDs, and the energy dissipation of each loading cycle can reach 21.06 times that of NSPDs. SRPDs exhibits improved energy dissipation performance when using high-density blended quartz sand. After sand replenishment repairs,damping force and energy dissipation per cycle of SRPDs were significantly enhanced. The proposed restoring force models of SRPDs aligns well with the experimental curves, underscoring its efficacy in accurately characterizing the hysteresis performance of SRPDs.

Experimental study on degradation of proton exchange membrane fuel cells for eco-friendly heavy equipment

Proton Exchange Membrane Fuel Cells(PEMFC) are considered the main power source for eco-friendly mobility. The degradation of PEMFCs in eco-friendly heavy equipment is analyzed. The target heavy equipment is 4.5 tons track loader of Doosan Bobcat. The complex movement of heavy equipment causes extreme dynamic load cycling in the powertrain. An electrochemical analysis of its Membrane Electrode Assembly(MEA) is conducted to clarify its degradation feature in this work. Dynamic load cycles are obtained from field tests using earth-moving machinery. A 2000 h durability test for a PEMFC single cell is conducted using the obtained dynamic load cycles. According to polarization curve analysis, the maximum power decreases from 19.95 to 13.82 W. This is mainly caused by the degradation of the catalytic activity of the Pt catalyst layer, as confirmed by cyclic voltammetry(CV). The electrochemical surface area(ECSA) decreases by 70 %.

Seismic evaluation of plan irregular reinforced concrete building equipped with comb teeth metallic passive damper

Active and passive damping devices exhibit significant energy dissipating behavior under seismic loads and are being used to control vibration in buildings worldwide. Comb Teeth Damper (CTD) is one of the most promising recent types of passive dampers which consist of steel plates with multiple teeth designed to dissipate seismic energy by in-plane flexural yielding. In this study, the CTD was modeled and analyzed under lateral cyclic load using the finite element analysis software, ABAQUS. The first phase of this investigation was a comprehensive parametric study on CTD with two different numbers of teeth, namely 4 teeth (4 CTD) and 5 teeth (5 CTD); each model with six different thicknesses, namely 5, 10, 15, 20, 25, and 30 mm. The parametric study showed that by increasing the number of teeth, the load-carrying capacity, initial stiffness, and energy dissipation capacity have increased considerably. A similar trend was observed when the thickness of the damper was increased. From the results of the parametric study, 5CTD with 15 mm thickness damper model was identified as a suitable model for utilizing in Reinforced Concrete (RC) buildings using optimization algorithm. In the second phase, a G + 14 storey plan irregular RC building was modeled in the structural engineering software ETABS and subjected to six different strong earthquake ground motions. The non-linear time history analysis was performed on the building with and without identified CTD and found that the building equipped with dampers reduced 56% top displacement, 60% inter-storey drift, and 33% energy dissipation.

Experimental and numerical study on the cyclic behavior of web dumbbell-shaped damper fabricated of low-yield-point steel

Current double-conical steel dampers, mainly made from low-carbon steel, stainless steel or high-strength steel, do not perform well in terms of fatigue, energy dissipation, and plastic deformation. To address these limitations, this study proposes a web dumbbell-shaped damper fabricated of LYP225 low-yield-point steel (LYP-WDP). This innovation aims to significantly improve the hysteretic behavior and fatigue performance of double-conical steel dampers. Given the limited experimental research on the hysteretic behavior of LYP-WDP under cyclic loading, this study conducts tests to evaluate its performance. Seven full-scale LYP-WDP specimens with different structural parameters were designed using LYP225 steel and subjected to low-cycle loading tests to assess their behavior under shear deformation. The effects of various design parameters on the performance of LYP-WDP were thoroughly analyzed. Finite element models of the specimens were created, and the simulation results were compared with experimental data. Additionally, formulas for calculating the elastic stiffness and yield strength of the LYP-WDP were proposed. The findings reveal that LYP-WDP has high ductility and stable energy dissipation capacity. The elastic stiffness and load-carrying capacity of LYP-WDP increase with the internal shrinkage ratio when the inner diameter and length of the energy dissipation segment are constant, while a negative correlation is found when the outer diameter and length are fixed. Increasing the length of the straight segment greatly enhances the energy dissipation capacity of LYP-WDP. The test results validate the accuracy of the proposed formulas and provide valuable insights for the design and application of LYP-WDP, marking a significant advancement in the field of damping technology.

An optimization DEM modelling method for soil-fibre undrained cyclic loading tests model based on the influence range of fibre

The computational cost of discrete element modelling is high owing to the limitations of particle size and contact in fibre modelling. This paper proposes an optimised discrete element method (DEM) for a hybrid model of soil and fibres based on the fibre influence range. First, a relative velocity state function is established based on the relative motion state between the fibres and soil particles under undrained cyclic loading. Subsequently, the influence range of the fibres is determined using the relative velocity function based on the first few cycles of the undrained cyclic loading numerical tests. Cluster and clump models of the fibre are then generated based on the influence range of the fibre. Finally, a symmetrical shape of the optimised model is developed by extracting the distribution length of the edge curve of the influence range along the vertical direction of the axis. In this study, the proposed optimised DEM was validated through a series of undrained cyclic loading numerical tests on fibre-reinforced soil. The results of the optimised model were highly consistent with those of the traditional model, and the computational time was significantly reduced. The cyclic loading timing for determining the range of influence of the fibre was analysed. The optimised model based on the influence range of the 15th cycles not only restored almost the same results but also saved the calculation cost by nearly eight times. The optimised model established based on the influence range after the 15th cycles had a slight influence on the results. In addition, the applicability of the optimised model is discussed. This paper provides new insights into the establishment of a hybrid model of soil and fibres.

Study on the evolution rules of coal deformation and failure characteristics caused by multiple mining disturbances

During coal mining operations, the coal will be deformed and damaged due to multiple mining disturbances (MMD), often resulting in disasters, like rock burst. To understand the evolution rules of coal deformation under MMD and its final fracture characteristics after impact dynamic load loading, reduce the adverse effects of mining disturbances, and improve disaster prevention and control capabilities, quasi-static uniaxial cyclic loading-unloading (L-U) and dynamic axial compression tests were conducted on large-sized coal-like samples. During the tests, three-dimensional (3D) laser scanning and acoustic emission (AE) monitoring technology were utilized to accurately capture the full-field deformation and AE response data, facilitating a systematic analysis of deformation and fracture characteristics. The results show that: (1) Under the cyclic L-U effect induced by MMD, each loading cycle causes compression deformation with partial recovery during unloading, presenting an overall “wavy” variation trend. (2) The maximum load is the most critical factor affecting the damaged coal deformation, with smaller load resulting in less overall sample deformation. (3) After the impact dynamic loading, the damaged samples suffered large-scale impact splitting failure, with the compressive-shear layer failure mainly occurred inside the holes. (4) Lower loading during cyclic L-U process correlate with reduced damage degree, and smaller debris particles with a higher fractal dimension when impact failure occurs, indicating a more severe impact failure. (5) With multiple cycles of L-U, the cracks inside the sample gradually extend and expand from around the hole to the outside. The greater the load and the number of cycles, the more serious the crack damage will be. (6) In the practical mining process, it is crucial to reinforce roadway interiors while minimizing low-loading cyclic disturbances induced by MMD. The study has obtained the deformation evolution rules and failure characteristics of coal under MMD, providing a theoretical basis for the prevention and control of corresponding engineering disasters.

Investigation of the large-diameter monopiles response under flow-controlled loading

The mechanical behavior of monopile support systems for offshore wind turbines under current-induced loads was investigated through numerical simulations. Using the Large Eddy turbulence model, the fluid-structure coupling was analyzed in both unidirectional and bidirectional directions. In the unidirectional coupling, the pressure and velocity profiles of the fluid around the pile were determined. While in the bidirectional coupling, the force distribution, pile displacement, and moment distribution were obtained, along with the current-induced load transmitted from the pile to the soil. The coupling analysis revealed that the fluid flow around the pile exhibited cyclic loading behavior due to the interaction between the fluid and the pile, effectively resulting in an oscillating pile within a steady flow. Additionally, the pile’s stress distribution remained within the tensile yield limit of the steel, indicating a stable state in the fluid-pile model within the given flow conditions. Furthermore, the soil reaction forces obtained from the fluid-pile-soil coupling model validated the accuracy of the current-induced load calculations. This study introduces a novel approach that considers the fluid-pile-soil coupling, offering valuable insights for pile foundation design. The findings of this research have significant engineering implications and practical value, providing a robust foundation for future offshore wind turbine installations.

A Preisach Model Defining Correlation between Monotonic and Cyclic Response of Structural Mild Steel

This article delivers a new Preisach model representing the correlation between the elastoplastic behavior of structural mild steel under axial monotonic and cyclic loading with damage. The newly formed model is based on the experimentally defined correlation between axial monotonic and cyclic behavior of structural mild steel. To examine the monotonic and cyclic behavior of structural mild steel and find fitting material properties for the model, monotonic and cyclic axial tensile tests are performed. Tests are executed on coupons of the commonly used European structural steel S275. The model represents a mathematical description of modified single-crystal material behavior under monotonic loading. Two different approaches were used to describe damage in the multilinear mechanical model. The excellent agreement with experimental results is achieved by infinitely linking many single-crystal elements in parallel, forming the polycrystalline model. This model provides a good solution for everyday engineering practice due to its geometric representation in the form of the Preisach triangle and the lower costs of monotonic tests used to define material properties compared to cyclic tests.

Industry-Scalable Reusable Textile Electrodes for Neurostimulation Applications.

Neurostimulation delivers electrical pulses to modulate neuromuscular activity. Commonly used in medical interventions from pain relief to rehabilitation, neurostimulation typically uses manually placed hydrogel electrodes over the treated region. However, this method limits interventions requiring frequent, long-term daily use. To address this, novel fully textile electrodes are developed using industrial programmable knitting machines. These electrodes are designed to be washable, reusable, flexible, and breathable, with embedded interconnects. Textile electrodes are made of yarns with stainless steel and PEDOT-coated stainless steel conductive components. The electrodes' performance are compared with gel electrodes, characterizing impedance, sensorimotor stimulation thresholds, recruitment of induced movements, sensation levels, and perceived sensations. The effects of residential wash cycles and continuous use duration are also investigated. The proposed electrodes are found to perform similarly to hydrogel electrodes in all characterized metrics. No degradation in electrode performance is found after at least 30 wash cycles. Electrodes remained functionally intact after 1000 cycles of stretch loading at 50% of break strain. The textile electrodes consistently induced comfortable sensorimotor responses for at least six hours after donning. The proposed textile electrodes offer a novel and effective solution for neurostimulation interventions, paving the way for integration into smart garments and long-term wearable health technologies.

Study on the effect of variable laser power on residual stress distribution in laser directed energy deposition of Ti6Al4V

In the laser directed energy deposition (LDED) process, cyclic thermal stress loading induces significant temperature variations on the surface and subsurface of the workpiece during repeated heating, leading to the formation of residual tensile stress during cooling. This adversely affects the mechanical properties of the parts, causing deformation and defects. In this study, a heat transfer model and a three-dimensional stress model were established based on finite element analysis. A variable laser power (VLP) deposition strategy was proposed to dynamically simulate the temperature and stress fields of Ti6Al4V titanium alloy under different deposition strategies. The model was validated by collecting substrate temperature variations using thermocouples and measuring residual stress with an X-ray diffractometer (XRD). Experimental results showed that the temperature error between the simulation and the experiment ranged from 6.25 % to 10.12 %, with an average stress simulation error of 6.92 %. Among the four strategies, the samples using the VLP strategy showed a reduction in the average substrate temperature by 12.68 % to 15.08 % compared to the other three strategies. The maximum principal stress in the layer was reduced by 7.8 % to 32.14 %, and the residual stress distribution was more uniform in all directions. The microstructure of the deposition layer further indicated that the VLP strategy improves residual stress distribution and leading to better deposition quality.