Dynamic Loading History Research Articles

Study on multibody contact load distribution characteristics of scraper conveying system of continuous miner

Understanding the interaction of the scraper chain–sprocket–tail drum–chain path is of great significance to improving the transportation efficiency and service life of the intermediate scraper conveying system of fully mechanized excavation equipment. The dynamic characteristics of the internal tension, running resistance, and multicontact interface load of the scraper chain are the theoretical basis of the research. Firstly, a method for obtaining periodic cyclic dynamic load history is proposed, and then the model of a single-chain scraper conveyor for a continuous shearer is constructed by using RecurDyn and simulation structures. Finally, the influence of parameters such as conveying inclination angle and running speed of the sleeve scraper chain on the reliable operation of the conveying system is determined. The results show that when the conveying angle is 12°, the scraper conveying system runs stably and the impact between multirigid bodies is small. As the chain speed increases from 0.85 to 2.4 m/s, the wear of the conveying system gradually increases, and the contact load distribution of upper chain plate 2, upper chain plate 3, and lower chain plate 3 is seriously worn.

The influence of operation variables on stress spectrum of high-speed train bogie frames

Dynamic load histories of vulnerable fatigue sites in structures are of paramount importance for safety design, and such load–time histories with long duration are usually lumped together to a load spectrum for safety assessment. In this paper, long-term field tests involving several operation variables, including track types, operation speeds, passenger lines, trains and their in-service time, were carried out to obtain stress–time histories of the bogie frame of high-speed trains. By comparing the stress spectra from different operation conditions, we identified the correlation between operation variables and the characteristics of stress spectra. It was found that both track type and operation speed play a prominent role in the magnitudes of stress spectra. Combined with the segmented Weibull model, we quantified the impact of operation variables on damage and confirmed that the inflection stress in the segmented Weibull model can be used as a measure of track status. The results revealed in this report could help obtain a systematic understanding of the fatigue performance of structures of complex dynamic systems like high-speed trains.

Multi-Objective Reliability-Based Optimization of Control Arm Using MCS and NSGA-II Coupled with Entropy Weighted GRA

Lightweight design is one of the important ways to reduce automobile fuel consumption and exhaust emissions. At the same time, the fatigue life of automobile parts also greatly affects vehicle safety. This paper proposes a multi-objective reliability optimization method by integrating Monte Carlo simulation (MCS) with the NSGA-II algorithm coupled with entropy weighted grey relational analysis (GRA) for lightweight design of the lower control arm of automobile Macpherson suspension. The dynamic load histories of the control arm were extracted through dynamic simulations of a rigid-flexible coupling vehicle model on virtual proving ground. Then, the nominal stress method was used to predict its fatigue life. Six design variables were defined to describe the geometric dimension of the control arm, while mass and fatigue life were taken as optimization objectives. The multi-objective optimization design of the control arm was carried out based on the Kriging surrogate model and NSGA-II algorithm. Aiming at the uncertainty of design variables, the reliability constraint was added to the multi-objective optimization to improve the reliability of the fatigue life of the control arm. The optimal design of the control arm was determined from Pareto solutions by entropy weighted grey relational analysis (GRA). The optimization results show that the mass of the control arm was reduced by 4.1% and the fatigue life was increased by 215.8% while its reliability increased by 7.8%. The proposed multi-objective reliability optimization method proved to be feasible and effective for lightweight design of a suspension control arm.

Dynamic crack propagation from a circular defect in a unidirectional carbon fiber reinforced plastic composite

A single-ply unidirectional IM7/8552 carbon fiber reinforced plastic composite with artificially introduced circular defects is subjected to dynamic tensile loading using a modified Kolsky tension bar. A high-speed X-ray phase contrast imaging method is integrated with the Kolsky bar setup to record the crack initiation from the defects and subsequent propagation in the material in real time during the tensile loading. The tensile loading was applied either in longitudinal (0° to fibers) or transverse (90° to fibers) direction of the specimens. Shear failure of the matrix and axial splitting along the loading/fiber direction were observed in longitudinal specimens to initiate from the edge of the artificial circular defects. Debonding of fiber and matrix was observed in transverse specimens, which initiated from the top and bottom edge of the hole. The dynamic tensile loading history during the crack propagation was recorded using a piezoelectric load cell and synchronized with the observed damage and failure processes.

Prognostic Health Monitoring Method for Fatigue Failure of Solder Joints on Printed Circuit Boards Based on a Canary Circuit

Devices mounted on printed circuit boards (PCBs) are subject to temperature variations resulting from power switching and ambient temperature changes, and may be subject to random dynamic load histories from sources such as vibration. Since solder material is mechanically the most ductile part, fatigue failure may occur in solder joints. Health monitoring for fatigue life under field conditions is a key issue for improving availability and serviceability for maintenance. We have developed a failure precursor detection technology and a fatigue life estimation method for ball grid array (BGA) solder joints, based on a canary circuit. This method estimates fatigue failure life of an actual circuit by detecting failure connections in a canary circuit (a dummy circuit of daisy-chained solder joints). The canary circuit is designed to fail before the actual circuit under the same failure mode by using accelerated reliability testing and inelastic stress simulation. A feasibility study of the failure probability estimation method is conducted by applying the method to a PCB on which a BGA component is mounted. It is confirmed that the fatigue life under a thermal cyclic load can be estimated from a canary circuit, that estimation of fatigue life under a random dynamic load is feasible, and that the estimation results are consistent with results from actual random vibration tests. The proposed method is found to be useful for prognostic health monitoring of solder joint fatigue failure.

Dynamic Transverse Debonding of a Single Fiber

By integrating a Kolsky tension bar along with a high-speed x-ray phase contrast imaging method and a high speed optical camera, high strain rate debonding processes of an opaque composite composed of a single S-2 fiber and SC-15 epoxy resin is recorded in real time and analyzed. Specifically, imaging of transverse debonding initiation and progression along with debonding loads are obtained and then compared to quasi-static debonding loads in this research. The dynamic loading direction was perpendicular to the fiber axial direction. The dynamic tensile loading history as the debonding initiated and propagated was recorded using a piezoelectric load cell. The initial debonding crack speed was also measured. Quasi-static experiments were also completed as a basis of comparison. It is shown that the debonding loads under dynamic and quasi-static loading conditions are similar. The fracture surfaces from the dynamically debonded samples were subsequently examined by scanning electron microscopy.

Test study on the influences of dynamic stress and load history to the dynamic properties of the remolded red clay

The dynamic properties of subgrade materials are critical factors affecting stability within the traffic engineering discipline. Remolded red clays are frequently used as subgrade filling materials, however, to date, a paucity of data exist on to the dynamic properties of this material. Accordingly, a large number of dynamic triaxial tests under cyclic loads were carried out to quantify the suitability of remolded red clay as subgrade filling. Several potentially influencing dynamic factors were considered, including dynamic stress, vibration frequency, consolidation confining pressure, consolidation ratio and compactness. Plastic strain and dynamic strength curves of remolded red clays under varying dynamic loads and load histories have been developed, in addition to the inclusion of those influencing factors. Test results show that within the range not exceeding the inherent strength of the test samples, increases soil compactness, confining pressure, and vibration frequency serves to enhance overall dynamic power in concurrence with retarding the development of accumulated plastic strain. Conversely, an improvement in the amplitude of the dynamic stress and consolidation ratio was shown to cause a decrease in dynamic strength and acceleration in the development of accumulated plastic strain. An empirical equation relating critical dynamic strength and load histories of remolded red clay has been developed for the provision of fundamental reference data for future studies. Pruebas sobre la influencia de la carga dinámica y la historia de carga en las propiedades dinámicas de arcilla roja reestructurada ResumenLas propiedades dinámicas de los materiales de base son factores cruciales que afectan la estabilidad en la ingeniería de tráfico. La arcilla roja reestructurada se utiliza frecuentemente como material de relleno de bases, sin embargo, hasta la fecha, existe una escasez de información sobre las propiedades dinámicas de este material. De acuerdo con esto, se realizó un gran número de pruebas triaxiales dinámicas bajo cargas cíclicas para cuantificar la pertinencia de la arcilla roja reestructurada como material de relleno en bases. Se consideraron varios factores dinámicos que podrían ser determinantes, como la fuerza dinámica, la frecuencia de vibración, la presión de confinamiento, el índice de consolidación y la compactibilidad. Se desarrollaron las curvas de fuerza plástica y dinámica de arcilla roja reestructurada con varias cargas dinámicas e historia de cargas, además de la inclusión de los factores determinantes. El resultado de las pruebas muestra que dentro del rango de la fuerza inherente a las muestras de estudio, el incremento de la compactibilidad del suelo, la presión de confinamiento y la frecuencia de vibración sirven para mejorar, en general, el poder dinámico al tiempo que retrasa el desarrollo de la fuerza plástica. Al contrario, el mejoramiento de la amplitud de la fuerza dinámica y el índice de consolidación muestra una reducción en la fuerza dinámica y una aceleración en el desarrollo de la fuerza plástica acumulada. Finalmente, se desarrolló una ecuación empírica que relaciona la fuerza dinámica crítica y las cargas históricas de arcilla roja reestructurada con el fin de proveer información de referencia para estudios futuros.

Residual drift analyses of realistic self-centering concrete wall systems

To realise the full benefits of a self-centering seismic resilient system, the designer must ensure that the entire structure does indeed re-center following an earthquake. The idealised flag-shaped hysteresis response that is often used to define the cyclic behaviour of self-centering concrete systems seldom exists and the residual drift of a building subjected to an earthquake is dependent on the realistic cyclic hysteresis response as well as the dynamic loading history. Current methods that are used to ensure that re-centering is achieved during the design of self-centering concrete systems are presented, and a series of cyclic analyses are used to demonstrate the flaws in these current procedures, even when idealised hysteresis models were used. Furthermore, results are presented for 350 time-history analyses that were performed to investigate the expected residual drift of an example self-centering concrete wall system during an earthquake. Based upon the results of these time-history analyses it was concluded that due to dynamic shake-down the residual drifts at the conclusion of the ground motion were significantly less than the maximum possible residual drifts that were observed from the cyclic hysteresis response, and were below acceptable residual drift performance limits established for seismic resilient structures. To estimate the effect of the dynamic shakedown, a residual drift ratio was defined that can be implemented during the design process to ensure that residual drift performance targets are achieved for self-centering concrete wall systems.

Dynamic loading history and collapse analysis of the pipe during deepwater S-lay operation

In the deepwater S-lay operations depending on the required stinger radius and rollers configuration, relatively large plastic deformation is induced when the pipe passes over the stinger, under the combined loadings of bending, axial tension, roller reaction force and the pipelay vessel motion. The resulting plastic deformation does not vanish after the pipe leaves the stinger. It accumulates until the pipe reaches the seabed. The inherited residual deformation might reduce the collapse capacity of the pipe under the external pressure loading. The present paper investigates the dynamic loading history of the pipe during the S-lay operation based on a test-verified finite element model, and then calculates the residual plastic deformation of the pipe cross-section after the pipe reaches the seabed. Finally, the nonlinear collapse analysis is implemented based on the modified RIKS method to evaluate the capacity of the installation-induced deformed pipe. The results confirm that the deepwater S-lay operation will lead to obvious plastic deformation of the pipe, which decreases the pipe collapse capacity to some extent.

Residual compressive and shear strengths of novel coconut-fibre-reinforced-concrete interlocking blocks

The results of an experimental study to evaluate the residual compressive and shear strengths of novel coconut-fibre-reinforced-concrete (CFRC) interlocking blocks are discussed in this paper. This work is part of a research project in which the development of mortar-free interlocking structures is intended for cheap and easy-to-built earthquake-resistant housing. Recently, mortar-free walls made of these blocks were tested under a series of harmonic and earthquake loadings. Only few blocks at the wall bottom were damaged, the other blocks (with no visual damage) had gone under numerous uplifts which might have affected the block strengths. In parallel, the blocks without any use over a period of time in tropical environment are also considered as coconut fibres are natural materials whose strengths might have decayed. These two cases represent two real scenarios in which (I) a structure stands without having an earthquake over a period and (II) a structure having a series of dynamic loading. In both cases, the residual strengths are of much interest to determine the remaining serviceable life of the structures. The results show that the impact of dynamic load histories on capacities of CFRC interlocking blocks was relatively more in comparison to the effect of age. The compressive and in-plane strengths were increased up to 3.2% and 5.7%, respectively, after undergoing a series of dynamic loading. This shows the advantage of earthquake loading on mortar-free structures.

Research on the dynamic performance of low-yield-strength shear panel damper for bridge application

This study seeks to develop a scientific understanding of the effects of dynamic loading history on the low-yield-strength shear panel damper (LYSPD) mechanical properties and fatigue performance. The LYSPD model is supposed as perfect elastic-plastic without strength deterioration. By adjusting the damper strength with the above supposition in the DYMO software, the serial earthquake response waves of the LYSPD under different soil conditions are obtained firstly. Subsequently, several waves, the most prone to damage at each soil condition, are selected as dynamic loading waves to verify the LYSPD dynamic performances experimentally. The test results suggest that the dynamic loading histories have no influence on the LYSPD strength or the supposed model while they affect the fatigue performance. The applicability and accuracy of three fatigue evaluation methods, cumulative plastic shear strain, cumulative energy absorption and Miner rule, are also compared according to the test results.

Influence of strain rates and loading histories on the compressive damage behaviour of concrete

Reported herein are the results of dynamic compressive tests of plain concrete specimens that were carried out with strain rates ranging from 10−5/s to 10−2/s. It is found that the compressive strength and the initial elastic modulus increase but the critical strain of concrete decreases with the increasing strain rate. The damage is defined as a reduction in the tangent modulus. The damage behaviours of concrete in the stress and strain space are investigated. Dynamic compressive load histories with different strain rates and different magnitudes are conducted on plain concrete specimens, and then the dynamic compressive damage tests of these specimens are also conducted. The effects of load histories on dynamic strain–strain curves, dynamic compressive strengths and the dynamic damage behaviour of concrete are studied.

Performance of Highway Bridge Girder Anchorages under Simulated Hurricane Wave Induced Loads

Many bridges along the Gulf Coast of the United States were damaged by hurricanes, especially in the 2004 and 2005 hurricane seasons. Many more bridges are susceptible to similar damage. This research examines the structural performance of three commonly used connection details for AASHTO Type III prestressed concrete girders: headed studs, through bolts, and clip bolts. Full-scale specimens were fabricated and tested under static and dynamic cyclic load histories using expected maximum loads from previously conducted hydraulic tests of a scale model of a highway bridge spanning a coastal embayment. The load effects considered included (1) vertical uplift force, (2) lateral force, (3) combined lateral and vertical forces, and (4) dynamically applied wave force time histories. Connection performance was evaluated by comparing initial concrete cracking, strand slip, and ultimate capacity. The experimental results showed that the insert clip-bolt connections had the lowest capacity and produced significant a...

A Study on the effect of dynamic behavior of external fuel tank horizontal fin on fatigue life

Fatigue crack propagation on aircraft external fuel tank horizontal fin is one of the common phenomenon of structural failure. In the past, it was reported that the primary factor of the fatigue crack is the oscillatory vertical load acting on the horizontal fin. Furthermore, the previous studies have revealed that the most of oscillatory vertical load on the horizontal fin was due to the influence of vortex air flow induced by opening the speed brake. The main goal of this study is to evaluate the behaviour of the horizontal fin of external fuel tank related to oscillatory vertical load generated by speed brake. To achieve this objective, structural analysis based on Finite Element Method has conducted by utilizing the dynamic load history of speed brake. Especially, this research examined the effect of dynamic behaviour on fatigue life with a fatigue analysis in both time and frequency domain.

Viscoelastic finite element analysis of the cervical intervertebral discs in conjunction with a multi-body dynamic model of the human head and neck

This article presents the effects of the frontal and rear-end impact loadings on the cervical spine components by using a multi-body dynamic model of the head and neck, and a viscoelastic finite element (FE) model of the six cervical intervertebral discs. A three-dimensional multi-body model of the human head and neck is used to simulate 15 g frontal and 8.5 g rear-end impacts. The load history at each intervertebral joint from the predictions of the multi-body model is used as dynamic loading boundary conditions for the FE model of the intervertebral discs. The results from the multi-body model simulations, such as the intervertebral disc loadings in the form of compressive, tensile, and shear forces and moments, and from the FE analysis such as the von Mises stresses in the intervertebral discs are analysed. This study shows that the proposed approach that uses dynamic loading conditions from the multi-body model as input to the FE model has the potential to investigate the kinetics and the kinematics of the cervical spine and its components together with the biomechanical response of the intervertebral discs under the complex dynamic loading history.

Finite Element Analysis on Fatigue Stress History of a Railway Bogie Bolster

An efficient finite element (FE) method, multivariate quadratic regression approach, is proposed for calculating the fatigue stress spectrum of engineering structures. The calculation starts from a dynamic load history. A regression function is established as a relation from the concurrent components of structural balance force systems into the structural stress. Parameters of the relation are measured by the stress data using an elastic-plastic FE method under selected groups of balance force systems. The selected systems should cover the possible load range with a similar service condition. After passing the fit effect check, the regression equation can transfer the structural load history into the stress history at the preferred position. Application on the determination of fatigue stress spectrum for the bolster of K6 type bogie has indicated availability of the present approach. Some deficiencies have been overcome from the much time cost by transient approach and the entire elastic material relation by quasi-static approach.

Fatigue Life Prediction of a Railway Bogie Frame

A fatigue life prediction method was introduced. The method was based on the combination of time domain and frequency domain method. Dynamic model of a complete railway locomotive system was established using SIMPACK software. The dynamic load histories acting on the bogie frame can be obtained by the Multi-Body System (MBS) analysis technique with time integration. FEM model of the bogie frame was established by applying ANSYS software. The natural frequencies and mode shapes of the frame were calculated and the dangerous nodes in the critical location were determined using the modal analysis technique. The stresses in dangerous nodes were calculated with the quasi-static stress/strain technology. PSD of the stresses was generated using the Fast Fourier Transformation (FFT). Fatigue life of the bogie frame was evaluated with the Dirlik’s formulation. Results showed that the calculated life of the analyzed bogie frame could meet the design requirement.

Safety Envelope for Load Tolerance and its Application to Fatigue Reliability Design

In this paper, a safety envelope concept for load tolerance is introduced. This shows the capacity of the current design as a future reference for design upgrade, maintenance, and control. The safety envelope is applied to estimate the load tolerance of a structural part with respect to the fatigue reliability. First, the dynamic load history is decomposed into the average value and amplitude, which are modeled as random variables. Second, through fatigue analysis and uncertainty propagation, the reliability is calculated. Last, based on the implicit function evaluation for the reliability, the boundary of the safety envelope is calculated numerically. The effect of different distribution types of random variables is then investigated to identify the conservative envelope. In order to improve the efficiency of searching the boundary, probabilistic sensitivity information is utilized. When the relationship between the safety of the system and the load tolerance is linear or mildly nonlinear, the linear estimation of the safety envelope turns out to be accurate and efficient. During the application of the algorithm, a stochastic response surface of logarithmic fatigue life with respect to the load capacity coefficient is constructed, and the Monte Carlo simulation is utilized to calculate the reliability and its sensitivities.

An internal state variable plasticity-based approach to determine dynamic loading history effects on material property in manufacturing processes

Worked materials in large deformation processes such as forming and machining experience a broad range of strain, strain rate, and temperatures, which in turn affect the flow stress. However, the flow stress also highly depends on many other factors such as strain path, strain rate and temperature history. Only a model that includes all of these pertinent factors is capable of predicting complex stress state in material deformation. In this paper, the commonly used phenomenological plasticity models (Johnson–Cook, Usui, etc.) to characterize material behavior in forming and machining were critically reviewed. Although these models are easy to apply and can describe the general response of material deformation, these models lack the mechanisms to reflect static and dynamic recovery and the effects of load path and strain rate history in large deformation processes. These effects are essential to understand process mechanisms, especially surface integrity (residual stress, microhardness, and microstructure) of the manufactured products. As such a dislocation-based internal state variable (ISV) plasticity model was used, in which the evolution equations enable the prediction of strain rate history and temperature history effects. These effects can be quite large and cannot be modeled by the equation-of-state models that assume that stress is a unique function of the total strain, strain rate, and temperature, independent of the loading path. The temperature dependence of the hardening and recovery functions results in the prediction of thermal softening during adiabatic temperatures rises, which are common in metal forming and machining. The dynamic mechanical behaviors of three different benchmark work materials, titanium Ti-6Al-4V, AISI 52100 steel (62 HRc), and aluminum 6061-T6, were modeled using the ISV approach. The material constants were obtained by using a nonlinear regression-fitting algorithm in which the stress–strain curves from the model were correlated to the experiments at different (extreme) temperatures. Then the capabilities of the determined material constants were examined by comparing the predicted material flow stress with the test data at different temperatures, strains, and strain rate history. The comparison demonstrates that the internal state variable plasticity model can successfully recover dynamic material behavior at various deformation states including the loading path effect. In addition, thermal softening due to adiabatic deformation was also captured by this approach.

Influence of a cyclic and dynamic loading history on dynamic properties of dry sand, part II: cyclic axial preloading

Initial fabric of a soil induced by its cyclic strain history is an important parameter among others like void ratio, state of stress and amplitude concerning the further accumulation of deformations under cyclic loading. It is of high importance to determine methods in order to estimate the initial fabric of the grain skeleton or the cyclic loading history of the soil. An attempt is made in this paper to correlate small strain stiffness of non-cohesive soil with its cyclic loading history. For this purpose several cyclic triaxial tests with specimens subjected to cyclic axial loading were performed and changes of small strain soil properties due to this cyclic loading were studied. All these tests showed only moderate changes of small strain stiffnesses independently of the different boundary conditions. Thus, a correlation between fabric or strain history and small strain stiffnesses seems not to be possible.