Dynamic Cyclic Loading Research Articles

Experimental Investigation on Mechanical, Electrical, and Fatigue Properties of Entangled Metal Wires under Cyclic Dynamic Load Test

Experimental Investigation on Mechanical, Electrical, and Fatigue Properties of Entangled Metal Wires under Cyclic Dynamic Load Test

Dynamic Mechanical Performance of Sulfate-Bearing Soils Stabilized by Magnesia-Ground Granulated Blast Furnace Slag

Sulfate soils often caused foundation settlement, uneven deformation, and ground cracking. The distribution of sulfate-bearing soil is extensive, and effective stabilization of sulfate-bearing soil could potentially exert a profound influence on environmental protection. Ground granulated blast furnace slag (GGBS)–magnesia (MgO) can be an effective solution to stabilize sulfate soils. Dynamic cyclic loading can be used to simulate moving vehicles applied on subgrade soils, but studies on the dynamic mechanical properties of sulfate-bearing soil under cyclic loading are limited. In this study, GGBS-MgO was used to treat Ca-sulfate soil and Mg-sulfate soil. The swelling of the specimens was analyzed by a three-dimensional swelling test, and the change in compressive strength of the specimens after immersion was analyzed by an unconfined test. The dynamic elastic properties and energy dissipation of GGBS-MgO-stabilized sulfate soils were evaluated using a fatigue test, and the mineralogy and microstructure of the stabilized soils were investigated by X-ray diffraction and scanning electron microscopy. The results showed that the maximum swelling percentage of stabilized Ca-sulfate soil was achieved when the GGBS:MgO ratio was 6:4, resulting in an expansion rate of 14.211%. In contrast, stabilized Mg-sulfate soil exhibited maximum swelling at GGBS:MgO = 9:1, with a swelling percentage of 5.127%. As the GGBS:MgO ratio decreased, the dynamic elastic modulus of stabilized Ca-sulfate soil diminished from 2.8 MPa to 2.69 MPa, and energy dissipation reduced from 0.02 MJ/m3 to 0.019 MJ/m3. Conversely, the dynamic elastic modulus of stabilized Mg-sulfate soil escalated from 2.16 MPa to 6.12 MPa, while energy dissipation decreased from 0.023 MJ/m3 to 0.004 MJ/m3. After soaking, the dynamic elastic modulus of Ca-sulfate soil peaked (4.01 MPa) and energy dissipation was at its lowest (0.012 MJ/m3) at GGBS:MgO = 9:1. However, stabilized Mg-sulfate soil exhibited superior performance at GGBS:MgO = 6:4, with a dynamic elastic modulus of 0.74 MPa and energy dissipation of 0.05 MJ/m3. CSH increased significantly in the Ca-sulfate soil treated with GGBS-MgO. The generation of ettringite increased with the decrease in the GGBS-MgO ratio after immersion. MSH and less CSH were formed in GGBS-MgO-stabilized Mg-sulfate soil compared to Ca-sulfate soils. In summary, the results of this study provide some references for the improvement and application of sulfate soil in the field of road subgrade.

Fatigue Analysis of a Jacket-Supported Offshore Wind Turbine at Block Island Wind Farm.

Offshore wind-turbine (OWT) support structures are subjected to cyclic dynamic loads with variations in loadings from wind and waves as well as the rotation of blades throughout their lifetime. The magnitude and extent of the cyclic loading can create a fatigue limit state controlling the design of support structures. In this paper, the remaining fatigue life of the support structure for a GE Haliade 6 MW fixed-bottom jacket offshore wind turbine within the Block Island Wind Farm (BIWF) is assessed. The fatigue damage to the tower and the jacket support structure using stress time histories at instrumented and non-instrumented locations are processed. Two validated finite-element models are utilized for assessing the stress cycles. The modal expansion method and a simplified approach using static calculations of the responses are employed to estimate the stress at the non-instrumented locations-known as virtual sensors. It is found that the hotspots at the base of the tower have longer service lives than the jacket. The fatigue damage to the jacket leg joints is less than 20% and 40% of its fatigue capacity during the 25-year design lifetime of the BIWF OWT, using the modal expansion method and the simplified static approach, respectively.

Experimental study on the damage characteristics of cyclic disturbance and acoustic emission characteristics of different types of sandstones under high stress in deep mines

AbstractThree sandstone specimens common in rock engineering were selected to study the differences in the mechanical properties of rocks with different lithologies. The development and expansion of the internal cracks in the specimens were observed by combining the simulation system with the acoustic emission system. Through the combination of dynamic and static stresses, the deformation and damage of rocks under deep rock excavation and blasting were simulated. As the results show, the acoustic emission events of specimens with different lithologies under combined static and dynamic cyclic loading can be roughly divided into three phases: weakening, stabilizing, and surging periods. In addition, the acoustic emission characteristics of specimens with different lithologies show general consistency in different compression phases. The degree of fragmentation of specimens increases with the applied stress level; therefore, the stress level is one of the important factors influencing the damage pattern of specimens. The acoustic emission system was used to simulate the deformation and damage of rocks subjected to deep rock body excavation and engineering blasting. Cyclic dynamic perturbations under sinusoidal waves with a frequency of 5 Hz, a loading rate of 0.1 mm/min, a cyclic amplitude of 5 MPa, and a loading rate of 0.1 mm/min were applied to the three rock samples during the experiments. Among them, the fine‐grained sandstones are the most sensitive to the sinusoidal cyclic perturbation, followed by the muddy siltstone and the medium‐grained sandstones. On this basis, the acoustic emission energy release characteristics were analyzed, and the waveform characteristics in the damage evolution of the specimen under dynamic perturbation were studied by extracting the key points and searching for the main frequency eigenvalues.

Study on physico‑mechanical characterization of rock-like material with bedding planes under coupled static and dynamic cyclic loadings

Study on physico‑mechanical characterization of rock-like material with bedding planes under coupled static and dynamic cyclic loadings

Latarjet procedure: biomechanical evaluation of 2-screw coracoid fixation

Coracoid nonunion is a relevant complication following the Latarjet procedure and is influenced by multiple factors, including the method of graft fixation. The purpose of this study was to evaluate and characterize the biomechanical properties of various two-screw fixation constructs used for coracoid graft fixation in the Latarjet procedure. Forty model scapulae (Sawbones Inc., Vashon, WA, USA) were used for this study. A 15% anterior inferior glenoid bone defect was created. The coracoid was osteotomized at the juncture of the vertical and horizontal aspects, transferred to the anterior-inferior edge of the glenoid, and fixed with either two 3.5mm fully threaded cannulated cortical screws, two 3.5mm fully threaded solid cortical screws, two 3.5mm partially threaded cannulated screws, or two 4.5mm partially threaded malleolar screws (MS). Biomechanical testing was performed with an Instron material testing machine (Instron Corp., Norwood, MA, USA) by applying loads to the lateral aspect of the transferred coracoid graft. The constructs were preconditioned with nondestructive cyclical loading (0N-20N) to determine construct stiffness. After 100 cycles of dynamic loading, the construct was loaded to failure to determine ultimate failure load, yield displacement, and mode of failure. All failures were associated with plastic deformation of the screws and coracoid graft fracture. There was a significantly lower initial stiffness for partially threaded cannulated screws compared to MS (186±49.3N/mm vs. 280±65.5N/mm, P=.01) but no significant differences among the other constructs. There was no difference in ultimate failure load (P=.18) or yield displacement (P=.05) among constructs. Two screw coracoid fixation of the coracoid in a simulated classic Latarjet procedure with 3.5mm fully threaded cortical and cannulated screws is comparable to 4.5mm MS in strength, stiffness, and displacement at failure. On the other hand, partially threaded 3.5mm cannulated screws provide inferior fixation stiffness and could potentially affect clinical outcomes.

Degradation prediction of proton exchange membrane fuel cell based on mixed gated units under multiple operating conditions

The aging process of proton exchange membrane fuel cell (PEMFC) is affected by different operating factors, and its practical application scenarios involve multiple operation conditions. To improve the accuracy and controllability of aging prediction, a mixed recurrent neural network (RNN) model based on Gated Recurrent Unit (GRU) and Minimal Gated Unit (MGU) is proposed. The model dynamically adjusts the mixed weights of GRU and MGU throughout the entire training process to obtain the optimal prediction network structure throughout the entire lifecycle. Furthermore, an attention mechanism is incorporated into the mixed gated unit (MIXGU) model. The effectiveness of the MIXGU model is evaluated by utilizing experimental data from static condition, quasi-dynamic condition, and dynamic load cycling conditions. The predictive performance of MGU, GRU, MIXGU, and MIXGU model with attention mechanism (AT-MIXGU) are compared under different operating conditions. The validation results indicate that MIXGU model exhibits superior predictive performance compared to single gated unit, the attention mechanism enhances prediction accuracy. And the AT-MIXGU model demonstrates strong generalization capabilities, and well-suited for accurately predicting PEMFC aging under diverse operating conditions.

Hybrid self-centering braces with NiTi-SMA U-shaped and frequency-dependent viscoelastic dampers for structural and nonstructural damage control

This study proposes a novel hybrid self-centering brace (HSB) with structural and nonstructural damage-control capabilities for the seismic resilience of building structures. NiTi-based shape memory alloy (SMA) U-shaped dampers and frequency-dependent viscoelastic dampers are included in HSBs to provide self-centering capacity for avoiding structural damage and velocity-proportional damping for nonstructural damage control, respectively. This study includes two major parts, i.e. component-level mechanical behaviour and system-level dynamic response evaluation of HSBs. The working principle and desired nonlinear behaviour of the HSB were first presented. Then, the preliminary design procedures were developed. After validating the efficiency of the modelling of SMA U-shaped and viscoelastic dampers using prior test results, comprehensive 3D finite element model simulations were performed to study the hysteretic responses of HSBs under cyclic loadings, where the influences of loading frequency, loading amplitude and viscoelastic damper’s contribution were considered. Analysis results demonstrated that the designed HSB can attain the desired deformation mechanism and nonlinear hysteretic behaviour during dynamic cyclic loadings. Higher loading frequency and amplitude and more contributions of the viscoelastic damper can introduce higher loading and energy-dissipation capacity. Subsequent dynamic analyses of the single-degree-of-freedom systems were conducted to assess the dynamic performance and advantages of HSBs. Results showed that compared with traditional self-centering systems without velocity-proportional damping, the systems with HSBs can achieve zero residual deformations, lower base shear demands and smaller absolute acceleration responses, confirming the promising potential of HSBs in developing seismic resilient building structures by reducing structural and nonstructural damage.

An undrained dynamic strain-pore pressure model for deep-water soft clays from the South China Sea

With the increasing use of oceans for engineering purposes, such as the installation of suction anchors and pipelines, the stability of seabed structures has become a pivotal concern and is intricately linked to the characteristics of seabed soils. This study focuses specifically on deep-sea soft clay, a predominant seabed soil type distinguished by its high water content, thixotropy, and low permeability. These clays are vulnerable to destabilization and damage when disturbed, thereby posing threats to seabed installations. While the existing literature extensively examines the cyclic behavior of clay, considering factors such as the pore pressure response and strain and deformation characteristics, there is a notable gap in research addressing the behavior of deep-sea soft clay under comprehensive stress levels and prolonged cyclic loading. In this study, cyclic shear tests of the natural marine clay of the South China Sea were conducted, and the cyclic stress ratio (CSR), overpressure consolidation ratio (OCR), consolidation ratio (Kc), and loading frequency were varied. It was found that the CSR, OCR, and Kc significantly impact the cumulative dynamic strain in deep-sea soft clay during undrained cyclic dynamic tests. Higher CSR values lead to increased dynamic strain and structural failure risk. Subsequently, a dynamic strain-dynamic pore pressure development model was proposed. This model effectively captures the cumulative plastic deformation and dynamic pore pressure development, showing correlations with the CSR, OCR, and Kc, thus providing insights into the deformation and pore pressure trends in deep-sea clay under high cyclic dynamic loading conditions. This research not only furnishes essential background information but also addresses a critical gap in understanding the behavior of deep-sea soft clay under cyclic loading, thereby enhancing the safety and stability of seabed structures.

Effect of different water contents on the softening characteristics of clay under intermittent cyclic dynamic loading

Effect of different water contents on the softening characteristics of clay under intermittent cyclic dynamic loading

A monitoring method of rail fastener reaction force based on iron pad strain

This research has successfully explored a monitoring method that does not necessitate modifications to the current structure of the fastening system and ensures that the intrinsic force distribution remains undisturbed, which is the pioneering use of Fiber Bragg Grating (FBG) strain sensors to test the strain of iron pads to reflect the force of fastener support points. Then, through the laboratory single-point loading test and finite element simulation, the feasibility of the monitoring method has been confirmed, and the resolution is higher than the traditional method. Subsequently, based on the experimental environment of high-speed railway commissioning, dynamic long-term monitoring research was conducted, and relevant calibration experiments and finite element simulation analyses were carried out. The experimental research and finite element simulation analysis revealed the superior ability of the method in capturing intricate data details, with the field experiment verifying a high resolution markedly surpassing other existing methods. Furthermore, by monitoring the same train, the data were found to be highly repeatable, which confirmed the ability of the monitoring method to stably reflect the dynamic behavior of the train. Overall, the monitoring method provided in this research could monitor the fastener reaction force in real time for an extended period and accurately record its periodic dynamic loading cycle pattern, which provides important data support for the structural health condition of the ballastless track and the safe operation assessment of trains.

Dynamic cyclic loading tests for investigating the influence of loading rate and axial force on the lateral response of RC columns

AbstractThe material properties of steel and concrete vary depending on the loading rate to which they are subjected. To realistically evaluate the seismic performance of reinforced concrete (RC) columns, it is necessary to simulate the loading rate that structures will experience during seismic events as accurately as possible. Real‐time dynamic testing is preferred over quasi‐static testing for this purpose. On the other hand, the seismic performance of RC columns also depends on the axial force applied to the column. However, due to the large axial stiffness of RC columns, accurately controlling the axial force during the test, particularly in real‐time testing, is challenging. Consequently, only a few component‐level dynamic tests have been conducted for RC columns. This study aims to explore the influence of axial force and loading rate on the seismic performance of RC columns. To this end, both slow and fast cyclic loading tests were conducted on square cross‐section RC columns subjected to four different axial forces. By utilizing a robust actuator control method along with a specially designed load transfer element, the axial force was successfully controlled, while the lateral displacements were imposed on the columns in real‐time. The results include lateral strengths, postyield responses, damage patterns, rebar strains, and their rates, all of which constitute unique experimental data that can contribute to a deeper understanding of the actual seismic response of RC columns.

Study on post-buckling crack propagation in thin-walled cylinders under dynamic cyclic load

Study on post-buckling crack propagation in thin-walled cylinders under dynamic cyclic load

Degradation of Pt-Based Cathode Catalysts Upon Voltage Cycling in Single-Cell PEM Fuel Cells Under Air or N2 at Different Relative Humidities

A major degradation mechanism of polymer electrolyte membrane fuel cells (PEMFCs) in transportation applications is the loss of the electrochemically active surface area (ECSA) of platinum cathode catalysts upon dynamic load cycling (resulting in cathode potential cycles). This is commonly investigated by accelerated stress tests (ASTs), cycling the cell voltage under H2/N2 (anode/cathode). Here we examine the degradation of membrane electrode assemblies with Vulcan carbon supported Pt catalysts over extended square-wave voltage cycles between 0.6-1.0 VRHE at 80 °C and 30%-100% RH under either H2/N2 or H2/Air; for the latter case, differential reactant flows were used, and the lower potential limit is controlled to correspond to the high-frequency resistance corrected cell voltage, assuring comparable aging conditions. Over the course of the ASTs, changes of the ECSA, the hydrogen crossover current, the proton conduction resistance and the oxygen transport resistance of the cathode electrode, as well as the differential-flow H2/O2 and H2/Air performance at 80 °C/100% RH were monitored. While the ECSA loss decreases with decreasing RH, it is independent of the gas feeds. Furthermore, the H2/Air performance loss only depends on the ECSA loss. ASTs under H2/N2 versus H2/Air only differ with regards to the chemical/mechanical degradation of the membrane.

Mechanical response of sandstone exposed to monotonic and multilevel fatigue loading: Insights from deformation, energy and acoustic emission characteristics

Rock masses containing intermittent discontinues under dynamic loading have rarely been investigated, although step-path failure frequently occurs in field engineering. This work aims to explore the action mechanism of dynamic cyclic loading and discontinuities on step-path failure. Four treatments including the control (Intact sandstone), pre-flawed samples with assemblage of two 30° dip fissures (type-I), assemblage of 10° and 65° dip fissures (type-II) and assemblage of two 65° dip fissures (type-III) were replicated. Laboratory experiments consisted of conventional uniaxial compression tests (UCT) and multilevel constant-amplitude fatigue tests (MLFT). Real-time acoustic emission (AE) monitoring was conducted along with scanning electron microscopy (SEM) observation on the fractured surfaces. Results indicated that the mechanical properties, energy evolution, AE characteristics and microscopic features of sandstones were significantly influenced by pre-existing fissures. The weakened rates of peak strength ranged from 2.80% to 85.63%, and regardless of loading methods, always followed the sequence of type-I > type-II > type-III. We contribute the weakening effect to the reduction in the effective bearing area and the increase in the dip angle of the rock bridge. With the same pre-fissure morphology, the sandstone under MLFT has enhanced its deformation resistance compared to under UCT. In addition, the maximum AE count/energy during the whole cyclic stage were always significantly lower than those during the monotonic rising process. SEM images revealed that long-term fatigue loading lead to numerous micro pores and transgranular cracks. Ultimately, a simple constitutive model was proposed based on the statistical damage mechanics and geometric damage theory.

Features of application in critical structures of products made by fused deposition using 3D printing technology

The technology of hot-melt 3D printing has prospects for military equipment and other special applications, provided that necessary requirements for the quality, strength and durability of plastic components are met. However, there is a problem of insufficient accuracy and unexplored patterns of change in technological parameters during 3D printing, which makes it necessary to manufacture critical structures using plasma deposition technology. The main purpose of the article is to study and evaluate the features of using the fused deposition method in 3D printing technology for the manufacture of products that are critical special-purpose structures and require increased strength and durability. To achieve this purpose, the technology and means of 3D printing by fused deposition method (filament feed control system with a circular encoder) have been improved. It has been established that the use of the filament feed control system can reduce the number of visually detected defects on the surface of printed products by an average of 71.7%, but increase the amount of wire consumed by 13% and the average printing time by 15-17%, which is due to the lack of supporting structures for the resulting surfaces. The research conducted in this paper has shown an increase in delamination strength of elements of critical structures, such as brackets for mounting a laser rangefinder to the body of an unmanned aerial vehicle. With the help of the filament feed control system, the strength of these elements has increased from 27.4 (tensile) and 32.1 (compressive) to 38 (tensile) and 44.3 MPa (compressive). There is also a more than 2.7-fold increase in the number of dynamic load cycles during endurance tests. This study indicates greater dynamic stability and less fatigue of the elements manufactured by fused 3D printing using a filament feed control system. The results will have practical applications in various fields, including military applications

Failure and acoustic behavior of combinational flaws sandstone subjected to dynamic compression loads

This paper described work initiated with two objectives in mind. First was to explore the influence of strain rate effects on the strength law and deformation characteristics of plate sandstone with combined flaws. Second objective was to analyze the breaking response law and acoustic behavior of flawed sandstone under the influence of disturbance frequency and prefabricated dip angle. Thus, a self-developed physical simulation test system combined with the real-time AE monitoring system, were conducted a series of dynamic cyclic loading tests on the flawed plate sandstone. The results indicated that the dynamic frequencies and dip angles had significant effects on the deformation, strength and failure mode of specimens. Additionally, the degree of specimen failure decreased with the increase of disturbance frequency under the same inclination angle; along with, the most severe failure occurred when the inclination angle was 45 ° under the same disturbance frequency. The main failure mode of specimens was shear failure from the distribution of AF-RA. Meanwhile, for specimens with small angles (30 °, 45 °) and low frequencies (0.1, 0.3 Hz), the failure types were more complex (tensile-shear mixed failure). On the other hand, the AE characteristics mainly included three stages: I-initial cycle, II-stable development, and III-damage & failure. The CNT and ENE were greatly influenced by the disturbance frequency and inclination angle. In addition, the b-value decreased and fluctuates violently, and the strength of the samples was reduced as the loading frequency decreased. The specimens with smaller inclination angles had larger internal activity scales and more frequent damage activities with smaller b-value. Furthermore, Correlation dimension Dm was positively correlated with the change of disturbance frequency, and it was smaller when the inclination angle was 45 °.

Role of confinement in coseismic pulverization: Testing the rock record of rupture directivity on the San Jacinto fault, Southern California

The San Jacinto fault juxtaposes Pleistocene Bautista Formation sediments against Cretaceous tonalite near Anza, California. While the tonalites show typical features of pulverized fault zone rocks on the NE side of the fault, the weakly consolidated Bautista Formation shows evidence of pulverization at a depth of 120 m, yet only background level deformation at 70 m, consistent with the expectation that a minimum confining pressure is required to initiate pulverization in poorly consolidated sediments. We test this hypothesis by simulating pulverization using a modified Split Hopkinson Pressure Bar apparatus, in which dry and wet sediments are subjected to up to three repeated dynamic triaxial compressive load cycles. We suggest unconsolidated sediments require a minimum confining pressure under axial compression to initiate pulverization and multiple seismic cycles to reach the observed fracture densities. Companion experiments conducted on Ottawa sand suggest sub-grain scale inelastic deformation in the bulk (i.e., not localized in deformation bands) occurs preferentially at high strain rates. Furthermore, the compressive origin of sediment pulverization, along with evidence of tensile fragmentation in cross-fault tonalite, supports a preferred northwest rupture direction along the southern section of the San Jacinto fault.

Transient model of unsteady creep of sliding zone soil under cyclic dynamic load based on fractional derivative

The shear mechanical behavior of soils in the slip zone under cyclic loading is of great importance for the stability analysis of landslides. In this paper, an experimental device is developed to study the nonlinear deformation mechanism of soil in sliding zone under cyclic load. Based on field tests and model tests, the change of shear strength parameters of the soil in the slip zone with cyclic loading parameters was investigated. Based on the deformation characteristics of slip zone soils under cyclic dynamic loading, the unsteady creep transient model based on fractional derivative is established, and three deformation types of sliding zone soil are described: stable, critical and destructive. The Levenberg-Marquardt (LM) algorithm is used to fit the nonlinear curves, and the applicability of the model is also verified. This research method provides a test apparatus and a method for studying the deformation characteristics of slip zone soils under cumulative loading.

Seismic Damage Analysis of Pile Foundation on Liquefiable Sandy Soil Foundation

Under the action of cyclic dynamic loads caused by earthquakes, the sandy soil foundation will liquefy, which may easily lead to damage to the pile foundation. For example, the soil liquefaction will cause pile foundation subsidence, the failure of the connection between pile cap and cap, and the beam drop caused by pile foundation moving sideways with soil. There are many influencing factors of foundation liquefaction, and the influence of many factors on foundation liquefaction is highly nonlinear. The author analyzes the liquefaction principle of sandy soil foundation and combines the seismic damage data of pile foundation with the experimental data of large-scale shaking table. Then this paper describes the damage and failure characteristics of pile foundation on liquefied sandy soil foundation.