Stress Time History Research Articles

Analyze the influence of explosion stress wave on the dynamic fracture of PMMA plates with different curvature radius defects

Defects in brittle solid materials affect the transmission of stress waves, thereby influencing the fracture process of the material. In this paper, the effect of defect curvature radius on the propagation of explosion stress wave and crack propagation is studied. Polymethyl methacrylate (PMMA) is used as the experimental material. The explosive loading and transmission caustics systems are combined to observe and record the explosive fracture process of a PMMA plate with different curvature radius defects. First, the interaction process between the explosion stress wave and defects with different radii of curvature is analyzed via caustics. Then the propagation process of prefabricated defects under the action of the explosion stress wave is studied. Moreover, crack tip propagation speed and the change of the stress intensity factor are simultaneously calculated. Numerical simulation is used to restore the full-field stress change under the action of the explosion stress wave and the defect. Lastly, stress time history curve of the point in the proximity of the defect is analyzed.

Coupled thermoelasticity of FG-GPLRC multi-curved composite panel under thermal shock loading

This study is dedicated to explore the transient coupled thermoelasticity solution of the FG-GPLRC multi-curved composite panel subjected to thermal shock for the first time. Time dependent equations of motion within the context of theory of elasticity are formulated and analytically solved by means of Navier approach. The temperature gradient is acquaried by employing the energy balance equation for the composite cylindrical panel subjected to thermal shock at its outer surface and thermally isolated at its inner surface. The time history of deflections, stresses and temperature are acquired by applying modified format of Dubner’s and Abate’s technique to inverse the Laplace transform. The effective thermoelastic properties of the composite are calculated according to correlations presented by modified form of Halpin-Tsai micromechanics. The numerical results of this study are compared with those recorded in the associated high-quality sources to verify their accuracy. The thorough parametric exploration is executed to analyze the role of various items like mid-radius to thickness ratio, distribution patterns and weight fraction of GPL in the transient coupled thermoelasticity response of FG-GPLRC multi-curved composite panel.

Evaluation of bearing capacity and energy absorption of high- rise steel frames reinforced by viscous dampers

Development and improvement of the process of design and implementation of high-rise structures with special attention to reducing seismic damage is one of the most important issues studied by researchers. In this regard, steel structures along with viscous dampers are among the structural systems that have attracted the attention of many researchers today. Also in the field of passive control of structures, one of the most powerful tools are viscous dampers that are used to absorb earthquake energy and its loss to reduce the response of the structure. Therefore, the purpose of this study is to investigate the effect of this structural system on the response of 12, 22 and 32 story high-rise structures against seismic loads. To investigate this issue, in this study, a numerical model of viscous damper was first created using Abaqus software and validation of finite element response was performed accordingly. Then, the effect of acceleration of Bam and Tabas earthquakes on the behavior of this structural system was modeled separately and the results including hysteresis diagrams, time history of energy absorption and structural stress were discussed. The results, on average for the three structures in question, showed a 22% increase in energy absorption and a 13% increase in bearing capacity of high-rise steel structures after the application of viscous dampers..‎

Fatigue Assessment of Monopile Supported Offshore Wind Turbine under Non-Gaussian Wind Field

The vibration of offshore wind turbines caused by external loads is significant, which will cause fatigue damage to offshore wind turbines. Wind load is the main load during the operation period of the wind turbine, and available studies have shown that the external wind field often exhibits certain non-Gaussian characteristics. This article aims to obtain the fatigue assessment of the monopile foundation of the wind turbine under the non-Gaussian wind fields. A 5 MW wind turbine is selected in this article, and OpenFAST is applied to simulate the wind load. By comparing the Mises stress time histories of the pile foundation at a different depth, the fatigue analysis of the critical spots of the pile foundation is obtained. In the analysis of fatigue damage, the rain flow counting method is adopted, and the two-segment S-N curve is selected to analyze the fatigue life of the critical spots. The results show that, by taking the non-Gaussian characteristic of the wind field into account, the fatigue life of the monopile foundation decreases. Therefore, attention should be paid to the influence of non-Gaussian characteristics of wind fields on the fatigue life of monopile-supported wind turbines.

A New Approach to the Modeling of Magnetorheological Dampers and Application to Resonance Control

Abstract A predetermined flow pattern in a magnetorheological damper providing continuously variable resistance to flow is required for efficient damping of a given load. The required predetermined flow pattern rests on the a priori determination of the constitutive properties of the magnetorheological (MR) fluid determined to generate variable resistance to flow. The inverse problem of constructing the predetermined response of the damper with a specific displacement pattern of the piston in the damper for efficient damping of a given load is solved. The MR fluid in the damper is modeled as a Bingham phase change material with time-dependent yield stress offering continuously variable resistance to the flow in the piston to achieve the required specific displacement pattern. The governing equations are solved for any time history of the dimensionless yield stress of the fluid which in turn is determined from the imposed response of the damper. Analytical tools developed can be used in optimizing damper performance. The application of the method to resonance mitigation is illustrated.

Fatigue damage prognosis of steel bridges under traffic loading using a time-based crack growth method

Traditionally, the fatigue damage assessment of steel bridges is conducted using cycle-based methods. Cycle-based methods require stress time history be transformed to cycle history first before fatigue analysis can be performed. However, well-defined cycle history does not exist for the traffic-induced stress time history of bridges as it contains numerous large and small cycles with random stress ranges embedded together. To address this inherent difficulty, a time-based fatigue crack growth (FCG) model is proposed for fatigue damage prognosis of steel bridges under traffic loading. The time-based FCG method describes the crack growth in the time domain through a crack growth kinetics function derived based on the physical mechanism of fatigue crack propagation. To demonstrate the proposed method, numerical simulations are first performed using full-scale coupled vehicle-bridge interaction framework to generate stress time histories of a typical steel bridge under traffic loading. Then, FCG analysis is performed using the time-based method and the effects of road surface roughness and vehicle weight on the FCG are studied. Finally, a case study on the I-10 Twin Span Bridge is presented to demonstrate the time-based FCG method for fatigue damage prognosis using in situ monitoring data. The results show that the proposed method can be used to directly predict the FCG of steel bridges in the time domain using stress time histories obtained either from stress analysis or in situ monitoring.

Damage mechanisms and energy absorption of aluminosilicate glass under compression/tensile loading

The transparent laminated structures having annealed and tempered glass layer with adjoining interlayer are used increasingly in aircrafts, high-speed trains, and important installations. In a pursuit to realize the fracture initiation, propagation, speed, path, and catastrophic failure to dynamic impact event in brittle materials like (annealed and tempered) silicate glass are experimentally analyzed in this research article undergoing tensile and compression loading. The Kolsky bar system linked with high-speed framing camera is applied to record the deformation images of glass samples for compression/tensile dynamic loading. The captured images are studied to identify the damage development and final rupture of silicate glass specimens. The stress-time history curves were related with recorded high-speed stills to enlighten the load-bearing capacity and damage accumulation in glass specimens. The stress–strain relations from two types of loading were used to envisage the energy absorption capability of annealed and tempered glass. The collected debris after test suggested that both glass types are loading-rate sensitive and the tempered glass dices in fine particles than annealed glass. In compression, and tensile loading mode the maximum energy was absorbed in by tempered glass which supports the use of this type of glass in impact resistant transparent laminated structures. The microscopic and scan electron microscope (SEM) pictures of collected fragments were also analyze to observe the failure mechanism and fracture surfaces in two types of glasses.

Statistical distribution modelling and parameter identification of the dynamic stress spectrum of a tractor front driven axle

The reliability data from the front driven axle of a four-wheel drive tractor exhibits a multi-peak distribution because of the complex field environment. The aim of this study was to establish an accurate statistical model for the dynamic stress spectrum with mixed distributions. Using rain-flow counting, the stress-time history of the tractor was transformed into the rain-flow matrix with two parameters. The mean and range of the stress data in the rain-flow domain was modelled with the mixed Gaussian and Weibull distributions, respectively. The identification of unknown parameters is an important and here a novel parameter identification method that adopts a genetic algorithm (GA) for rapid searching was proposed with the generalised reduced gradient (GRG) method was applied for accurate identification. The results of finite element analysis (FEA) provide reference for the selection of the measured points. To obtain the dynamic strain signal, a real-time test system was built and a field experiment was carried out. The calculation and evaluation results confirmed that this approach precisely estimated parameters and established a highly accurate mixed model. For the mixed Gaussian and Weibull distributions, the determination coefficients R 2 exceed 0.98 and the maximum KS test values were not more than 0.2. Furthermore, this study provided accurate model parameters to determine the stress spectrum for the full-life cycle for use in future research. • Statistical modelling of axle data by mixed Gaussian and Weibull distributions. • Unknown model parameters estimated by combining intelligent algorithm. • Goodness of fit test can be adopted to evaluate parameter identification results. • Accurate statistical model for study of agricultural machinery fatigue reliability.

Structural response and fatigue assessment of a small vertical axis wind turbine under stationary and non-stationary excitation

The paper discusses the response and fatigue damage of the supporting tower of a small vertical axis wind turbine subject to stationary and non-stationary excitation due to wind, turbine rotation, emergency stop and start. Using in-field measurements and the Hot Spot Stress Approach, the study analyses a number of aspects that are usually disregarded in design verifications. The results highlight the importance of the detail modeling, the fundamental role played by the non-stationary conditions and the errors committed when using conventional models of the load. The emphasis of this paper is put on two main aspects: the use of full scale data and the detection of isolated events of non-stationary vibrations, the effects of which can be disregarded when using stress time-histories of 10 min - 1 h.

Cyclic behavior of sand under non-uniform shear stress waves

During an earthquake, soil deposits are often subjected to complex stress/strain time histories that are quite different from the simplified ones used in laboratory tests for evaluation of the stress-strain-strength of these soils. To mimic the stress/strain time histories experienced at different depths of a mildly sloping soil deposit, a series of direct simple shear tests were conducted on Ottawa F65 sand specimens. The trends observed in these experiments were then used to estimate the lateral spreading of mildly sloping saturated deposits of the same sand subjected to various base motion time histories measured in the centrifuge tests conducted as part of an international research project (Liquefaction Experiment and Analysis Project, LEAP-2015 and LEAP-2017).In each CDSS test, after imposing the initial stress state, the specimen was subjected to non-uniform stress waves that resembled the shear stress time histories likely to develop in the LEAP-2015 and LEAP-2017 centrifuge specimens. A total of 17 CDSS tests were performed on specimens with relative densities of approximately 66%. Initial vertical and shear stresses were imposed on each soil specimen to correspond to the state of stress in a mildly sloping soil layer at two depths of about 4 m and 3 m. A ramped sinusoidal shear stress wave similar to the ramped sinusoidal base motion used in the LEAP centrifuge experiments was employed. The test results displayed a consistent trend between the peak cyclic stress ratio and the permanent shear strain that developed in the soil. The effects of overburden stress on the magnitude of permanent deformations were observed. Smaller initial vertical stress resulted in a more dilative response and smaller permanent shear strain. The observed permanent shear strain vs. peak cyclic stress ratio curves were then used to predict the lateral spreading of mildly sloping deposits tested in the LEAP-2015 and LEAP-2017 centrifuge experiments. Reasonably close correlation between the predicted and measured displacements were obtained. The developed dataset, made publicly available on DesignSafe-CI, can be used for calibration, evaluation, and further development of constitutive models for liquefiable soils.

Fatigue performance evaluation for composite OSD using UHPC under dynamic vehicle loading

A novel composite orthotropic steel deck (OSD) using ultra-high performance concrete (UHPC) is comprised of an OSD and a thin UHPC layer that are connected through shear connectors. The innovative composite OSD system has been increasingly applied to long-span bridges in China to overcome the defect of conventional OSD that frequently suffers from fatigue cracking. However, the fatigue performance of the composite OSD system is usually evaluated with the deterministic analysis in previous studies, which may lead to inaccurate evaluation as many uncertainties, including the statistical properties of dynamic vehicle loadings and fatigue-prone details, have not been considered rationally. In this paper, the fatigue performance of the composite OSD using UHPC was investigated using the reliability-based fatigue analysis and compared with the fatigue performance of conventional OSD system. A three-dimensional vehicle-bridge coupled system was adopted to obtain the stress time histories of fatigue-prone details in the bridge decks under the action of dynamic vehicle loading. The vehicle model was determined based on the fatigue load pattern adopted in the AASHTO standard specifications and finite element models (FEMs) of both the conventional OSD and the composite OSD using UHPC were built based on a girder segment adopted from the HuMen Bridge in China. Four key influence factors, namely, the road surface condition (RSC), length of bridge deck FEM, vehicle speed, and overloading, were taken into consideration. The fatigue life of six typical fatigue-prone details in these two deck systems was evaluated and compared. The results show that the composite OSD using UHPC can effectively extend the fatigue life of OSD by at least 60% and even eliminate the risk of fatigue cracking for most fatigue-prone details. Compared to the reliability method, the fatigue life of OSD determined based on the deterministic method would be overestimated by 65–110% if the very poor RSC is considered. Besides, the composite OSD using UHPC exhibits a better fatigue performance than the conventional OSD system under the action of overloaded trucks. The results from the study can provide a reference for the design and maintenance of the composite OSD using UHPC.

Wind-induced vibration response analysis of Chinese solar greenhouses

Chinese solar greenhouses (CSG) are widely used in agricultural and horticultural industries in China. With the characteristics of lightweight, small stiffness and high flexibility, CSG are sensitive to wind loads. In this study, based on Davenport wind spectrum, the fluctuating wind speed time histories were simulated by harmony superposition method. The wind-induced vibration response of a 12 m span CSG was investigated by using ANSYS in time domain. The time histories of stress and displacement were obtained. The results show that both the stress and displacement under instantaneous wind loads are obviously larger than those under the corresponding mean wind loads. The most dangerous section appears near the front foot of the CSG structure. The critical wind speeds for dynamic and static instability are 38.7 and 58.5 m/s, respectively. Finally, a recommended nodal displacement wind vibration coefficient is given for practical structures. The analytical results can provide a reference for dynamic analysis and wind resistance design of CSG structures in the future.

Experimental research on the development of residual strain in seasonal frozen soil under freezing-thawing and impact type traffic loads

Vehicle load is among the main factors affecting the deformation of subgrade soil. In this research study, the concept of impact type traffic load is introduced to investigate the effects of vehicle load based on the dynamic stress and displacement time histories acquired from seasonal frozen subgrade soils. Using freezing-thawing and dynamic triaxial tests and considering the amplitude and loading sequence of impact type traffic load, the residual deformation characteristics of subgrade soil under impact type traffic loads and freezing-thawing cycles is studied. It was found that under impact type traffic load, the residual deformation of soils increased sharply as the amplitude of impact type traffic load increased. It was also found that the increase in the amplitude of impact type traffic load led to the increase of residual deformation in a scale of power and exponential function. The amplitudes of impact type traffic load affect the development stress-strain path of the residual strain. After the soil experienced the proper amount of pre-vibration of the light load, residual deformation decreased by 15%. After freezing-thawing, the residual strain of soil increased as the amplitude of the impact type traffic loads increased. Also, when the amplification effect of freezing-thawing on the residual strain was basically stable, the residual deformation increased by about 10%. The peak impact type traffic load had a large effect on soil deformation after the freezing-thawing process, leading to the observation that of the earlier the peaks, the stronger the effect of freezing-thawing. After the soil was subjected to preloading with a small load, the influence of the freezing-thawing cycles gradually stabilized. The results may be useful in preventing and controlling the risk of subgrade soil failure when construction takes place spring thaw periods.

Pump Operating Effects on The Transient Fluid Flow (Dept.M)

A water hammer phenomenon due to sudden closure of a valve, with centrifugal pump at upstream, was studied both experimentally and numerically. Taking into consideration the fluid-structure interaction, it produced a four equations model (fluid continuity, fluid momentum, and pipe wall momentum and stress strain equations). The four equations model was analytically solved using the method of characteristics to clarify, the centrifugal pump effect on the hammering waves. A FORTRAN program was developed to solve the model. The theoretical and experimental results indicated the pressure-time history at different positions along the pipe for different valve closing times. Also, predictions for stress-time history, fluid velocity-time history and structure velocity-time history were obtained at different positions along the pipe at different valve closing times. The obtained predictions are useful in pipeline design.

Impact Characteristics and Fatigue Life Analysis of Multi-Wire Recoil Spring for Guns

Recoil spring is a key part in automatic or semi-automatic weapons re-entry mechanism. Because the stranded wire helical spring (SWHS) has longer fatigue life than an ordinary single-wire cylindrically helical spring, it is often used as a recoil spring in various weapons. Due to the lack of in-depth research on the dynamic characteristics of the current multi-wire recoil spring in recoil and re-entry processes, the fatigue life analysis of the current multi-wire recoil spring usually only considers uniform loading and does not consider dynamic impact loads, which cannot meet modern design requirements. Therefore, this paper proposes a research method for fatigue life prediction analysis of multi-wire recoil spring. Firstly, based on the secondary development of UG, a three-wire recoil spring parameterized model for a gun is established. Secondly, ABAQUS is used to carry out a finite element analysis of its dynamic response characteristics under impact, and experimental verification is performed. Then, based on the stress-time history curve of the dangerous position obtained by finite element analysis, the rain flow counting method is used to obtain the fatigue stress spectrum of recoil spring. Finally, according to the Miner fatigue cumulative damage theory, the fatigue life prediction of the recoil spring based on the S-N curve of the material is compared with experimental results. The research results show that the recoil spring has obvious transient characteristics during the impact of the bolt carrier. The impact velocity is far greater than the propagation speed of the stress wave in the recoil spring, which easily causes the spring coils to squeeze each other. The maximum stress occurs at the fixed end of the spring. And the mean fatigue curve (50% survival rate) is used to predict the life of the recoil spring. The calculation result is 8.6% different from the experiment value, which proves that the method has certain reliability.

Fatigue Life Estimation of Elevator Car Frame with Double Floor by Stress Time History Simulation

The elevator car is an important load-carrying unit of the elevator, so any damage to the car parts can cause unsafety for the user, especially for passenger elevator. To eliminate the risks of insufficient strength, each elevator is inspected and tested with load equal to 125% of its nominal load before being put into service. However, load testing in-situ can only detect damage related to the static strength, fatigue hazards are difficult to be detected because fatigue accumulation occurs very slowly and depending on the stress time history. In practice, elevator structural elements are usually calculated in terms of its static strength, with a factor of safety taken higher than those of other structures without regard to fatigue strength. This paper presents the research results related to the calculation of fatigue life of elevator car frame through simulated stress time history by numerical method. By this way, the fatigue life of elevator car frame can be forecasted even at design stage.

RETRACTED: Fatigue reliability assessment for hangers of a special-shaped CFST arch bridge

Abstract The main bridge of the Yingzhou Bridge is a special -shaped concrete-filled steel tubular (CFST) arch bridge. As a key load-carrying member, the safety of a hanger affects the service life of arch bridges. This paper presents a comprehensive frame work for fatigue reliability analysis of hangers in CFST arch bridges. A simplified finite element (FE) model is established to satisfy the fatigue analysis accuracy. The mathematical model for traffic flow of the Yingzhou Bridge is simulated using the Monte Carlo method. Then the stress time history of the hanger is calculated. The rain flow counting method is used to obtain the stress range values and the number of cycles. Based on the Miner cumulative damage rule, considering the effect of mean stress, the fatigue reliability for hangers with and without corrosion is calculated using the Monte Carlo Importance Sampling method. It is found that the reliability index of inclined hangers is lower than that of vertical hangers. Inclined hangers have a higher probability of failure earlier. The reliability index of the inclined hanger X3 in the position where the stiffness changes is the lowest, which should be paid greater attention to in daily maintenance. The reliability index of hangers with corrosion is significantly lower than that of hangers without corrosion, and the decline rate of the reliability index is increased with time.

Reducing uncertainty in time domain fatigue analysis of offshore structures using control variates

This study is concerned with time domain fatigue analysis of offshore structures subjected to random waves. The fatigue damage calculated from a single realization of the stress time history is random, thus the mean damage is typically estimated via Monte Carlo simulation (MCS), by averaging over multiple realizations. This approach is time-consuming, because each realization involves a time domain dynamic analysis, and MCS has a slow convergence rate. Variance reduction techniques can improve the efficiency of MCS, but successful implementation necessitate prior information on the system behavior, which is difficult to acquire for this high-dimensional problem. Herein, a method is developed for reducing the variance of the MCS estimator of the damage, based on a new technique known as auto control variates. The control function is constructed via artificial neural network trained from existing MCS data, thus avoiding the need for prior information or additional simulations. The proposed method has several advantages; it is unbiased, and an error estimate is available. Besides, variance reduction is implemented at the post-processing stage; allowing multiple stress locations to be evaluated from the same dynamic simulation results. The case studies include a nonlinear single-degree-of-freedom system under different scenarios, and a full nonlinear model of a floating system. The proposed method enhances the MCS efficiency for all cases, with speedups ranging from one to two orders of magnitude.

Field Test and Numerical Analysis of Dynamic Stress of High-Speed Railway Tunnel Invert in Mudstone

In order to obtain the dynamic stress of invert and its filling in the high-speed railway tunnel under the vibration load of the train, this paper uses the field measurement method to arrange the resistance strain gauge inside the invert of the Lanzhou–Urumqi high-speed railway Fuchuan tunnel. The dynamic stress of the invert and its filling was measured, and the measurement results were verified by numerical analysis, the results obtained by the two were consistent. The results show that under the action of CRH5 electric multiple units, the dynamic stress time history curve of the invert and its filling has 16 peaks, with V-shape on both sides and W-shape in the middle. When the train load speed is constant, the dynamic stress in the tunnel invert and invert filling decreases with the increase of the depth. The dynamic stress at 0.5 m below the track bed is attenuated by about 23.1% compared to 0.2 m, the dynamic stress at 2.0 m below the track bed is attenuated by 67.5% compared to 0.2 m. Tunnel invert and its filling are the main carriers of train vibration load. The dynamic stress attenuation law of the invert and its filling conforms to the exponential function distribution. Through the data fitting, the calculation formula of the dynamic stress in different depths is given. The research results provide a new method for obtaining the dynamic stress of the invert and its filling in high-speed railway tunnel.

Simulation of vertical dynamic vehicle–track interaction using a three-dimensional slab track model

When improving track design, a better understanding of the track’s damage modes is needed, and the railway industry is then dependent on the availability of accurate simulations of the dynamic vehicle–track interaction. In the present study, the vertical dynamic interaction between a travelling railway vehicle and a slab track is simulated in the time domain by using an extended state-space vector approach. A three-dimensional slab track model is launched where the rails are modelled using Rayleigh–Timoshenko beam elements and the concrete panel and roadbed are represented by using either shell or solid finite elements. From the parameterised track model, which is developed in Abaqus using Python scripts, the system matrices are exported to Matlab where the simulation of the dynamic vehicle–track interaction is performed. A complex-valued modal superposition technique is employed, which reduces the computational cost of the simulation. In a post-processing step, calculated wheel–rail contact forces from the dynamic analysis are used as input to the Abaqus track model where various track responses are evaluated. In particular, the time history of principal stresses is determined at critical locations in the concrete panel. Also the influence of the speed of the vehicle on the wheel–rail contact forces, and the influence of a transverse culvert below the track (modelled as a local increase of the foundation bedding modulus) on the track stiffness variation at the rail level, are investigated. A mesh convergence study for a range of track responses has been conducted including investigations of when to use linear or quadratic elements and shell or solid elements. Finally, the presented three-dimensional models have been compared to an alternative two-dimensional model to determine in what situations a two-dimensional model is sufficient.