Application Of Cyclic Loading Research Articles

Shaking table tests to investigate the influence of grain shape on tnb he excess pore water pressure

Liquefaction that occurred in the Palu city in 2018 is the most devastating natural phenomena. The liquefaction phenomenon is a condition in which a saturated soil loses its strength due to an earthquake. This study aims to determine the increase in excess pore water pressure in solid particles and void particles after they are subjected to earthquake loading. Testing is done by shaking the table. Earthquake loads are modeled with cyclic loads, which are sine waves with acceleration amplitudes of 0.35g and 0.38g. The results showed that liquefaction conditions had not yet occurred in cyclic load applications with an acceleration amplitude of 0.35g and a time duration of 7s. At an acceleration amplitude of 0.38g with a time duration of 60 s, the sand model underwent liquefaction at 7s after the test began. Analysis of the results of transducer records installed at a distance of 0.10 m from the surface of the test model shows that the addition of pumice by 10%, 30%, and 50% can reduce pore pressures by 15%, 62%, and 85%, respectively.

Crystal Plasticity Modeling of Laser Peening Effects on Tensile and High Cycle Fatigue Properties of 2024-T351 Aluminum Alloy

Abstract This study aims to model the effects of multiple laser peening (LP) on the mechanical properties of AA2024-T351 by including the material microstructure and residual stresses using the crystal plasticity finite element method (CPFEM). In this approach, the LP-induced compressive residual stress distribution is modeled through the insertion of the Eigenstrains as a function of depth, which is calibrated by the X-ray measured residual stresses. The simulated enhancement in the tensile properties after LP, caused by the formation of a near-surface work-hardened layer, fits the experimentally obtained tensile curves. The model calculated fatigue indicator parameters (FIPs) under the following cyclic loading application show a decrease in the near-surface driving forces for the crystal slip deformation after the insertion of the Eigenstrains. This leads to a higher high cycle fatigue (HCF) resistance and the possible transformation of sensitive locations for fatigue failure further to the depth after LP. Experimental observations on the enhancement in the HCF life, along with the relocation of fatigue crack nucleation sites further to the depth, reveal the improvement in the HCF properties due to the LP process and validate the numerical approach.

Shape Memory Behavior of Rapidly Quenched High-copper TiNiCu Alloys

Rapidly quenched quasibinary TiNi–TiCu system alloys with high copper contents (above 20 at.%) exhibit excellent shape memory effect and have considerably narrower hysteresis as compared with the TiNi binary alloy, this advantage being of special importance for cyclic load applications, e.g. for microelectromechanics (MEMS). The aim of this work is to study the effect of annealing parameters and copper content on the shape memory effect in TiNiCu alloys. Thin amorphous ribbons of TiNi-TiCu alloys with copper contents of 25 to 40 at.% were produced by planar flow casting at a melt cooling rate of about 106 K/s. The alloys were crystallized by isothermal annealing with variable duration and by exposing specimens to a short (10 ms) electric pulse. Increasing the copper content to above 30 at.% considerably reduces the plasticity and shape memory effect of the alloys. However, significant reduction of annealing duration greatly improves the shape memory performance due to prevention of the formation of brittle Ti-Cu phases in the alloys structure.

Investigating the fatigue and mechanical behaviour of 3D printed woven and nonwoven continuous carbon fibre reinforced polymer (CFRP) composites

This paper evaluates the mechanical properties of woven continuous carbon fibre composites printed by additive manufacturing (AM). Comparison mechanical test studies (tensile, flexural and fatigue) were carried out with two nonwoven AM printed composites (unidirectional and multidirectional fibres), along with those of both a woven composite, as well as a composite reinforced using chopped carbon fibres. Compared with the 17 MPa tensile strength obtained for the chopped fibre composite, the average strength of unidirectional (nonwoven), multidirectional (nonwoven) and woven fibre composites were 39, 13 and 19-fold higher, respectively. The tensile strength of the woven composites was 52% lower than that attained by the unidirectional (nonwoven) fibre composites; and 38% higher than the multidirectional (nonwoven) fibre composites. A comparison was also made between the flexural and fatigue performance of the unidirectional (nonwoven) and woven fibre composites. The flexural strength of the latter was approximately 39% lower than the nonwoven composites, however, the load bearing capacity of woven fibre was superior. This performance difference was supported by the fatigue testing results. At 70% of maximum tensile load capacity after 2 × 105 cycles, the nonwoven composites failed, while the woven composites continued to perform until a level of 85% of maximum load capacity was reached. The superior fatigue strength of the AM fabricated woven carbon fibre composites, demonstrates their potential for use in high cyclic load applications.

Effect of confining pressure and loading frequency on dynamic characteristics of Batu Pahat marine clay

This paper presents the laboratory study on the dynamic characteristics of marine clay subject to cyclic load over a long period of time. Remoulded marine clay samples were used to conduct the experiments using a dynamic triaxial machine. Confining pressure and loading frequency were varied while pore pressure development, resilient strains and plastic strain resulting from the application of cyclic loading were observed. The results acquired from this study revealed that as soon as the cyclic loading was introduced, it induced pore pressure that triggered the rapid accumulation of permanent strain and gradual increase in resilient strain. However, after the strain reached a stable value, the rate of accumulation of the permanent deformation started decreasing. The results also showed that an increase in confining pressure improved the marine clay resistance to cyclic loading. Similarly, when the loading frequency increased, it caused a decrease in strain generation and vice versa.

A new design of a multifunctional abutment to morse taper implant connection: Experimental mechanical analysis

The objective of this study was to evaluate a new design of multifunctional abutment for Morse taper implant connections, relative to the retentive stability after the application of cyclic loads in cemented and screwed crowns. Multifunctional abutments with two different angulations in the seating portion of the crown were tested, forming 2 groups (n = 30 samples per group): Group Abut11, where Smart abutments with an angle of 11.42° were used; Group Abut5, where Ideale abutments with an angle of 5° were used. Fifteen samples from each group received cemented crowns (CC) and another fifteen screwed crowns (SC). All crown samples were subjected to the mechanical cycling test at 360,000 cycles at a frequency of 4 Hz and 150 N of the load. The samples with CC were subjected to the tensile test to remove the crowns, while in the samples with SC, the detorque value of the fastening crown screws was measured. The mean tensile strength value of CC in the Abut11 group was 131.9 ± 13.5 N and, in the Abut5 group was 230.9 ± 11.3 N; while the detorque mean value in samples with SC 5.8 ± 1.8 N for the Abut11 group and, 7.6 ± 1.1 N for Abut5 group. Significant statistical differences were found between the two groups in both situations tested (p < 0.05). The multifunctional abutments, presenting a lesser angulation of the crown-seating portion, showed higher values of retention of the CC and a lesser screw loosening of torque of the fixing screws in the SC after the application of cyclic loads when compared to the abutments with more angulation in the crown-seating portion.

Long-Term Drained and Post-liquefaction Cyclic Behaviour of Offshore Wind Turbine in Silty Sand Using Element Tests

Offshore wind turbine (OWT) structure foundations and soil are subjected to long-term cyclic loading from wind and waves. Loads due to earthquake also act on the OWT system in seismically active areas. The long-term dynamic behaviour of the OWT is challenging due to the complex nature of dynamic loads. The soil stiffness changes due to the application of cyclic loading, which leads to a change in the natural frequency and response of the OWT system. Therefore, the assessment of long-term dynamic behaviour soil surrounding the foundation of the OWT structure is essential due to the operational condition and seismic event. In this study, element tests are conducted utilizing cyclic triaxial test apparatus to examine the long-term drained and post-liquefaction long-term cyclic behaviour of silty sand. Secant shear modulus and damping ratio are estimated under drained condition due to 10,000 load cycles. Silty sand behaviour at liquefied phase and post-liquefaction long-term cyclic behaviour phases are investigated at different effective confining pressure, relative density, and shear strain rate. Based on the element tests, a numerical model is proposed predicting the long-term fundamental frequency of OWT to avoid resonance.

Impact of repeated loads on saline soils of earth roadbed

The constant development of the road network in Uzbekistan, especially in widespread saline soils, necessitates increased attention to road structure strength. Since vehicles differ in weight and speed, it is obvious that the saline soil under the pavement is subjected to successive impacts of a load of different power and application force. Experimental studies to identify the patterns of changes in saline soils' physical and mechanical properties under repeated and short-term loads were conducted on a device specially designed by the authors of this study. The experiments were conducted on samples of sulfate and chloride-sulfate medium-saline heavy silty sandy loam, compacted at optimal moisture content to maximum density. When conducting the experiment, the impact duration of vertical load Рver = 0.15 MPa on the sample was tload = 0.2 sec, and the interval between the loads was 0.5 sec, the frequency of application was f = 1.2 Hz. The number of short-term load applications was recorded using an electric meter installed on the device. After a certain number of short-term cyclic load applications on the sample, its physical and mechanical properties were determined following the requirements of state standards (GOST). The results of the study show that with an increase in the number of cyclic and short-term load impacts on the sample, the following values increase: residual strain, density, and modulus of setting, relative swelling, swelling pressure, ultrasonic transmission rate, coefficient of filtration; while the porosity, coefficient of porosity, soaking, ultimate strength in uniaxial compression, the coefficient of dynamic viscosity, adherence, the angle of internal friction and the modulus of elasticity of soil decrease. It was determined that under the repeated impact of short-term loads in compacted saline soil, residual strains and short-term redistribution of stresses in the contact of soil and salt particles occur, which leads to a change in the physical and mechanical properties of soil.

Identification of Chaboche\u2013Lemaitre combined isotropic\u2013kinematic hardening model parameters assisted by the fuzzy logic analysis

A very good knowledge of material properties is required in the analysis of severe plastic deformation problems in which the classical material processing methods are accelerated by the application of the additional cyclic load. A general fuzzy logic-based approach is proposed for the analysis of experimental and numerical data in this paper. As an application of the fuzzy analysis, the calibration of Chaboche–Lemaitre model hardening parameters of PA6 aluminum is considered here. The experimental data obtained in a symmetrical strain-controlled cyclic tension–compression test were used to estimate the material’s hardening parameters. The numerically generated curves were compared to the experimental ones. For better fitting of numerical and experimental results, the optimization approach using the least-square method was applied. Unfortunately, commonly accepted calibration methods can provide various sets of hardening parameters. In order to choose the most reliable set, the fuzzy analysis was used. Primarily selected values of hardening parameters were assumed to be fuzzy input parameters. The error of the hysteresis loop approximation for each set was used to compute its membership function. The discrete value of this error was obtained in the defuzzification step. The correct selections of hardening parameters were verified in ratcheting and mean stress relaxation tests. The application of the fuzzy analysis has improved the convergence between experimental and numerical stress–strain curves. The fuzzy logic allows analyzing the variation of elastic–plastic material response when some imprecisions or uncertainties of input parameters are taken into consideration.

Cyclic response of monopile-supported offshore wind turbines under wind and wave loading in sand

Monopiles are popular solutions as the foundation to support offshore wind turbines (OWTs), which suffer from various amplitudes of continuous lateral cyclic wind and wave loading. The accumulation of tilt and change of the natural frequency of OWTs under cyclic loading have become crucial issues for OWT design. Hence the monopile-tower-soil system was established at the small-scale level based on similarity laws with a suit of constant-amplitude and multi-amplitude tests in dense sand. Two sets of gear-driving assembly were successfully set up to achieve the application of cyclic loading to the model OWT. The amplitude and symmetry of cyclic loading were specified as three indicative regions according to those of real wind farms. On the basis of test results, the two-way loading was found to be the most hazardous situation and the preloading condition led to a high accumulation of tilt. The change of natural frequency was controlled by the load magnitude and tended to increase during cyclic loads, while a sharp decrease was observed when sand subsidence was generated. The post-cyclic lateral capacity seemed to be a slight increase compared with the static capacity. The relevant analyses based on test results can provide practical recommendations for OWT design.

Experimental study of the influence of sand base reinforcement on the development of deformations under static and cyclic loading

The results of plate tests conducted in the laboratory of “soil Mechanics” of TSTU are presented. The cases of application of static and cyclic loads on reinforced and unreinforced sand base are considered. In these tests, the density of the sand base, the depth of the reinforcement element, and the initial load stage from which cycling was performed were changed. Three series of experiments were performed in a tank with rigid side walls. As the base, a fine, low-moisture, homogeneous sand was used. In the first series of experiments a stepwise increasing load was transferred to the plate at different densities. In the second series, a cyclic load was transferred to the base, with a value equal to half of the previously found ultimate load. In the third series of experiments, a reinforcing element was placed in the base at various distances from the sole of the foundation model and the load was applied both stepwise increasing static and cyclic. It is shown that the settlement during introduction of cyclic loading is from 20 to 50% of the total value. Reinforcement of the base allows you to reduce the settlement of cycling load. At the same time, there is a significant increase in the bearing capacity of the foundation and a decrease in the values of total deformations.

Simulation of the asphalt concrete stiffness degradation using simplified viscoelastic continuum damage model

A procedure based on the simplified viscoelastic continuum damage model is developed to simulate asphalt concrete stiffness degradation caused by the application of cyclic loads. Several tests are performed to characterize the linear viscoelastic and fatigue damage properties of four asphalt mixtures. It was found that the piecewise approach proposed to simulate the stiffness evolution successfully describes the damage growth under loads applications. It was also found that the exponential model used to fit the characteristic curves best describes the stiffness evolution for the entire load history. Finally, stiffness evolution simulations showed higher fatigue resistance for polymer-modified mixtures.

Hysteresis Model for Soft Cohesive Soils under Combinations of Static and Cyclic Shear Loads

Abstract The application of large-amplitude cyclic shear loads on soft soils results in large strains after a certain number of cycles. These strains are highly dependent on static shear load and c...

A micromechanical model for loading and unloading behavior of fiber reinforced plastics under cyclic loading

AbstractThe high fatigue resistance and low weight features make the unidirectional‐carbon fiber reinforced plastics (UD‐CFRP) attractive for cyclic loading applications. However, the complex damage mechanisms within the composite hinder the understanding of its fatigue response. An energy‐based fatigue model has been proposed for the fatigue behavior of epoxy polymers. However, this kind of approaches dependent on the accurate description of the material's behavior. Our work aims to build a representative volume element model (RVE) for the simulation of the cyclic shear loading behavior of UD‐CFRP, which could support the later extension of an energy‐based fatigue model. To precisely reproduce the micromechanical stress‐strain distribution within the matrix, a nonlinear viscoelastic model has been implemented and validated against experimental data. As a result, the simulated UD‐CFRP hysteresis, as well as the stiffness and strain energy density were accurately reproduced for two load ratios (R = 0.1 and R = − 1). Additionally, the cyclic strain accumulation observed in the UD‐CFRP can be accurately described by the proposed model.

Evaluation of Equivalent Flexural Strength for Complete Removable Dentures Made of Zirconia-Impregnated PMMA Nanocomposites.

High-impact (HI) polymethyl methacrylate (PMMA), obtained from modification of conventional PMMA, is commonly used in prosthodontics as a denture base material for improved impact resistance. However, it suffers from poor flexural strength properties. The aim of this study was to investigate the flexural strength of complete removable dentures made of HI heat-polymerised PMMA resin reinforced with zirconia nanoparticles at two different concentrations. The effect of fatigue loading on the flexural strength behaviour of the dentures was also investigated. A total of 30 denture specimens were fabricated from PMMA with different concentrations of zirconia nanoparticles: 0 (control), 3, and 5 wt.%. Ten specimens in each group were divided into two subgroups, with five specimens in each, to conduct both flexural strength and fatigue loading test of each of the subgroups. Fatigue loading was applied on the dentures using a mastication simulator and equivalent flexural strength was calculated with data from bending tests with and without fatigue cyclic loading. One-way analysis of variance (ANOVA) of the test data was conducted with the Bonferroni significant difference post-hoc test at a preset alpha value of 0.05. Paired t-test was employed to identify any difference between the specimens with and without the application of fatigue loading. The fractured surface of the denture specimens was examined with a scanning electron microscope (SEM). The bending tests demonstrated that the mean equivalent flexural strength of reinforced HI PMMA denture specimens with 5 wt.% zirconia nanoparticles increased significantly (134.9 ± 13.9 MPa) compared to the control group (0 wt.%) (106.3 ± 21.3 MPa) without any fatigue loading. The mean strength of the dentures with PMMA +3 wt.% zirconia also increased, but not significantly. Although the mean strength of all specimen groups subjected to fatigue loading slightly decreased compared to that of the specimen groups without any fatigue cyclic loading, this was not statistically significant. Denture specimens made of HI heat-polymerised PMMA reinforced with 5 wt.% zirconia nanoparticles had significantly improved equivalent flexural strength compared to that made of pure PMMA when the specimens were not subjected to any prior fatigue cyclic loading. In addition, the application of fatigue cyclic loading did not significantly improve the equivalent flexural strengths of all denture specimen groups. Within the limitations of this study, it can be concluded that the use of zirconia-impregnated PMMA in the manufacture of dentures does not result in any significant improvement for clinical application.

Flexible electrospun PVDF-BaTiO3 hybrid structure pressure sensor with enhanced efficiency.

Ceramic doped-polymer structures as organic and inorganic hybrid structures constitute a new area of advanced materials for flexible and stretchable sensors and actuators. Here, uniform ceramic-polymer composites of tetragonal BaTiO3 and polyvinylidene fluoride (PVDF) were prepared using solution casting to improve the pressure sensitivity. By introducing Ba–TiO3 nanoparticles to PVDF nanofibers, piezoelectricity and pressure sensitivity of hybrid nanofiber mats were significantly improved. In addition, we proposed a novel flexible and stretchable multilayered pressure sensor composed of electrospun nanocomposite fibers with high electrical sensitivity up to 6 mV N−1 compared to 1.88 mV N−1 for the pure PVDF sensors upon the application of cyclic loads at 2.5 Hz frequency and a constant load of 0.5 N. Indeed, this work provides a composition-dependent approach for the fabrication of nanostructures for pressure sensors in a wide variety of wearable devices and technologies.

Finite Element Modeling of a Thin Circular Disc Manufactured by Forming Process used in Cyclic Loading and Unloading Applications

Abstract The presented work focuses on numerical modelling and analysis of the forming process of a thin circular disc of negligible thickness, that is later subjected to vibration-induced loading and unloading cycles (fatigue) during application. During the forming process, the material of the pre-form (Mild-Carbon Steel, AISI-1075) is shaped into the required profile of the disc, using a fast moving punch that impacts on a die underneath. The profile consists of a hole at the center of the disc and predefined surface gradations along the periphery. This punching process is followed by heat treatment to relax the residual stresses developed. This paper discusses the development of a detailed thermo-mechanical coupled model using the finite element method, to simulate the different stages of the forming process; namely, the punching process, the instantaneous punch release and structural creep, and the subsequent heat treatment to induce stress relaxation. The numerical model is intended to predict the amount of residual stress and equivalent plastic strain that are developed in the disc at the end of each stage of the forming process. The stress concentration in the disc has serious implications on the subsequent cyclic loading and unloading application. The results obtained from standard tests indicate initiation and propagation of cracks in the disc during application. The intensity and occurrence of crack initiation have a direct connection to the maximum residual stress developed in the disc during the forming process. In addition, the heat treatment model is also intended to investigate the temperature distribution in the disc, during the heating and the subsequent cooling operations. The results of the finite element model are then validated with experimental measurements for each of the stages of the forming process. The finite element packages, Abaqus/Explicit and Abaqus/Standard, are used in conjunction for the aforesaid modeling

Cyclic and post-cycling anchor response in geocell-reinforced sand

Plate anchors are commonly used to resist static, cyclic, and monotonic post-cyclic uplift loads. Under cyclic loading, progressive sudden failure may occur, characterized by accumulated displacement — even under loads significantly less than the static capacity. Despite extensive usage of geocell materials for increasing cyclic resilience, the influence of geocell reinforcements on cyclic uplift capacity is not well understood. In this study, a series of near-full-scale experimental tests, with and without geocell, are presented. Results show that the unreinforced system fails cyclically under a load that is almost 70% of its ultimate uplift capacity (Pu), but use of geocell enables stable cyclic resistance of over 100% Pu. For the given soil and configurations, a cyclic displacement rate that reaches less than 0.05 mm/cycle tends to highlight a likely stable response. Evaluation of the soil’s response to cyclic loading demonstrates that, with increasing loading cycles, the loading is increasingly transmitted through the soil close to the anchor in the unreinforced case, but that the reinforced case is less prone to this phenomenon. The monotonic post-cycling capacity of both reinforced and unreinforced anchors decreases after application of cyclic loading; however, the unreinforced scenario demonstrates larger decreases in capacity, particularly in the residual capacity.

Use of acoustic techniques to analyse interlayer shear-torque fatigue test in asphalt mixtures

Shear-torque tests were used for the first time to assess the fatigue behaviour of double-layered asphalt specimens. During the test, an acoustic emission (AE) technique was used to evaluate the damage process leading to failure. Results showed that the application of cyclic loading led to the decrease of the complex shear modulus, until the physical separation of the two layers. AE analysis showed that damage mostly occurred in the interlayer zone. The comparison between mechanical and AE results suggested that the damage evolution phase occurred when approaching the end of the test when the stiffness decrease was about 70%.

Response of pavement foundations incorporating both geocells and expanded polystyrene (EPS) geofoam

The suitability of geocell reinforcement in reducing rut depth, surface settlements and/or pavement cracks during service life of the pavements supported on expanded polystyrene (EPS) geofoam blocks is studied using a series of large-scale cyclic plate load tests plus a number of simplified numerical simulations. It was found that the improvement due to provision of geocell constantly increases as the load cycles increase. The rut depths at the pavement surface significantly decrease due to the increased lateral resistance provided by the geocell in the overlying soil layer, and this compensates the lower competency of the underlying EPS geofoam blocks. The efficiency of geocell reinforcement depends on the amplitude of applied pressure: increasing the amplitude of cyclic pressure increasingly exploits the benefits of the geocell reinforcement. During cyclic loading application, geocells can reduce settlement of the pavement surface by up to 41% compared to an unreinforced case – with even greater reduction as the load cycles increase. Employment of geocell reinforcement substantially decreases the rate of increase in the surface settlement during load repetitions. When very low density EPS geofoam (EPS 10) is used, even though accompanied with overlying reinforced soil of 600 mm thickness, the pavement is incapable of tolerating large cyclic pressures (e.g. 550 kPa). In comparison with the unreinforced case, the resilient modulus is increased by geocell reinforcement by 25%, 34% and 53% for overlying soil thicknesses of 600, 500 and 400 mm, respectively. The improvement due to geocell reinforcement was most pronounced when thinner soil layer was used. The verified three-dimensional numerical modelings assisted in further insight regarding the mechanisms involved. The improvement factors obtained in this study allow a designer to choose appropriate values for a geocell reinforced pavement foundation on EPS geofoam.