Stress Time History Research Articles

Dynamic response of functionally gradient austenitic-ferritic steel composite panels under thermo-mechanical loadings

In this paper, the dynamic response of functionally gradient steel (FGS) composite cylindrical panels in steady-state thermal environments subjected to impulsive loads is investigated for the first time. FGSs composed of graded ferritic and austenitic regions together with bainite and martensite intermediate layers are analyzed. Thermo-mechanical material properties of FGS composites are predicted according to the microhardness profile of FGS composites and approximated with appropriate functions. Based on the three-dimensional theory of thermo-elasticity, the governing equations of motionare derived in spatial and time domains. These equations are solved using the hybrid Fourier series expansion-Galerkin finite element method-Newmark approach for simply supported boundary conditions. The present solution is then applied to the thermo-elastic dynamic analysis of cylindrical panels with three different arrangements of material compositions of FGSs including αβγMγ, αβγβα and γβαβγ composites. Benchmark results on the displacement and stress time-histories of FGS cylindrical panels in thermal environments under various pulse loads are presented and discussed in detail. Due to the absence of similar results in the specialized literature, this paper is likely to fill a gap in the state of the art of this problem, and provide pertinent results that are instrumental in the design of FGS structures under time-dependent mechanical loadings.

Numerical Simulation of Creep Damage and Life Prediction of Superalloy Turbine Blade

Creep caused failure is an important failure mode of the turbine blade. A numerical approach of life assessment of the superalloy turbine blade is proposed in the present paper based on the Lemaitre-Chaboche creep damage model. Material damage is introduced into each element based on the ANSYS APDL function, and the creep damage effect is considered through the modification of Young’s modulus. At last, the strength life and stiffness life of the blade can be obtained through the maximum damage and maximum creep strain criterion, respectively. The present method can not only consider the effect of creep damage, but also give the time histories of the element stresses, damage, and creep strain. The above life prediction results based on the proposed method are compared with theθprojection method, and the results suggest that the present life prediction method of turbine blade is feasible and turbine blade’s life in the present study is determined by creep fracture rather than creep deformation.

ホイッピングを考慮した疲労強度評価に関する研究

Hull girder stresses caused by the whipping vibration increases as ship size becomes bigger, and it is therefore concerned that design fatigue life of such large ship might be unconservative. In this study, in order to clarify effects of superposed elastic vibrations on linear wave loads in the fatigue life estimation. Using created time history of stress, numerical simulations for fatigue strength of a post-panamax container ship has been conducted. Random stress time history is created using a storm-model, and a high frequency stress model is proposed to estimate effects of the whipping vibration. Two kinds of evaluation methods are adopted. One is fatigue crack propagation analysis using fracture mechanics taking account of the nonlinear retardation phenomena. The other is fatigue damage factor based on Miner's Law. Results of the fatigue strength analysis in a period of the maximum storm condition for a ship's life in the North Atlantic show that the fatigue crack length obtained by the fatigue crack propagation analysis has a similar trend as the damage factor by Miner’s Law. With regard to the effect on the fatigue strength of the whipping, different treatments of high frequency stress to extract low frequency time history give different results. If the low frequency time-history (LF) is adopted, the difference is remarkable, the fatigue damage of RAW become approximately 50%-100% greater than LF. If the envelope time-history (ENV) is adopted, the difference is relatively small, e.g. 0.1-2.0%.

Bridge Crane Random Stress Spectrum Processed and Fatigue Life Analysis

This paper estimates the fatigue residual life of bridge crane with probability distribution model of stress spectrum, which influences the main parameters of the stress characteristics of the fatigue accounting point.Random sample of load spectrum parameters are produced by Latin hypercube.We can use the dynamic simulation model to calculate the stress-time history during the entire simulation at the accounting point of fatigue,and then with rainflow counting to obtain the double parameters stress spectrum. The result is that the bridge crane has 22630 lifting cycles and 37566 stress cycles in two years of an inspection cycle, and stress spectrum includes 10 stress amplitude and mean stress.

Cyclic Resistance of a Loose Sand Subjected to Rotation of Principal Stresses

An experimental study aimed at providing insights into the effects of the inclination of principal stress directions with respect to the bedding plane and the role of principal stress rotation on the cyclic resistance of sands is presented. A new hollow cylinder torsional shear device commissioned at Carleton University was used to conduct the experiments in water-deposited Fraser River sand. Specimens at identical initial states were subjected to a constant amplitude cyclic shear stress along loading paths that impose different levels of stress rotation. Cyclic resistance decreased significantly as the maximum orientation of the major principal stress increased to approximately 45°–60°, but it increased with further rotation. This is contrary to the conventional idea according to which the weakest response is expected when the loading causes larger principal stress rotation and/or when the major principal stress is aligned with the bedding planes. The alignment of the plane of maximum shear stress toward and stronger time history of shear stress on the horizontal bedding planes lead to increased liquefaction susceptibility. The nature of shear stress on the bedding planes appears more critical than the alignment of the major principal stress along the bedding planes during cyclic loading. Test results also suggest that cyclic simple shear tests on the basis of stress rotation would represent a lower bound or closer to lower bound resistance. Thus, cyclic simple shear tests provide a convenient means of determining the cyclic resistance and the obtained resistance can be considered a conservative measure if field loading conditions deviate from that in simple shear.

A computational investigation for propagation of elasto-viscoplastic zones in the shock loaded circular plates

Purpose– The purpose of this paper is to introduce a computational time dependent modeling to investigate propagation of elastic-viscoplastic zones in the shock wave loaded circular plates.Design/methodology/approach– Constitutive equations are implemented incrementally by the Von-Kármán finite deflection system which is coupled with a mixed strain hardening rule and physical-base viscoplastic models. Time integrations of the equations are done by the return mapping technique through the cutting-plane algorithm. An integrated solution is established by pseudo-spectral collocation methodology. The Chebyshev basis functions are utilized to evaluate the coefficients of displacement fields. Temporal terms are discretized by the Houbolt marching method. Spatial linearizations are accomplished by the quadratic extrapolation technique.Findings– Results of the center point deflections, effective plastic strain and stress (dynamic flow stress) and temperature rise are compared for three features of the Von-Kármán system. Identifying time history of resultant stresses, propagations of the viscoplastic plastic zones are illustrated for two circumstances; with considering strain rate and hardening effects, and without them. Some of modeling and computation aspects are discussed, carefully. When the results are compared with experimental data of shock wave loadings and finite element simulations, good agreements between them are observed.Originality/value– This computational approach makes coupling the structural equations with the physical descriptions of the high rate deformation through step-by-step spectral solution of the constitutive equations.

Random fatigue. A new frequency domain criterion for the damage evaluation of mechanical components

The evaluation of the fatigue behavior of mechanical systems and components subjected to random loads is increasingly being addressed to the frequency domain environment both in terms of dynamic analysis and in terms of results post-processing.The procedure set out in the paper (bands method) is formulated without assumptions about the shape of the Power Spectral Density (PSD) function to be analyzed, in order to obtain a criterion that can be applied to any typology of the related random process. The basic idea of the proposed approach is that each PSD function can be divided into frequency bands, for each of them a Rayleigh distribution could be associated and that the aforementioned distributions could be opportunely combined to obtain the actual damage. The method is theoretically developed and numerically validated on a particular subset of PSD functions by comparing the results obtained with those carried out by the time domain damage evaluation reference method and a frequency domain direct approach (Dirlik’s method).With regard to the time domain reference criterion the stress time histories are generated by the indirect method (a previously defined authors’ method), the cycles spectra are obtained by Rain Flow Counting, (RFC) and the damage is evaluated by Palmgren–Miner’s rule.

Nonlinear Transient Thermal Stress Analysis of Temperature-Dependent Hollow Cylinders Using a Finite Element Model

In this paper, the nonlinear transient thermal stress analysis is conducted for temperature-dependent hollow cylinders subjected to a decaying-with-time thermal field. By the finite element method, the highly nonlinear governing equations are solved. The time histories of temperature, displacement, and stress due to the decaying-with-time thermal load are computed. A sensitivity analysis includes the effects of exponent of the decayed heat flux and temperature-dependency of density and material properties is carried out. Numerical results show some interesting characteristics of the thermoelastic behaviors of the hollow cylinders studied. In particular, the effect of temperature-dependency of the material properties on the thermoelastic parameters was demonstrated to be significant.

Dynamic Behavior of Thermal Stress in a Functionally Graded Material Thin Film Subjected to Thermal Shock

In the present article, a one-dimensional dynamic thermoelastic problem in a functionally graded material (FGM) thin film subjected to a thermal shock loading is analyzed. An exact analytical solution is obtained by employing techniques of the space-variable transformation and Laplace transform, in the case where variations in material properties of the FGM thin film are expressed as exponential functions of the space-variable. Numerical calculations for time histories of thermal stresses have been carried out. Obtained numerical results reveal that the thermal stress oscillation is unsteady when the mechanical impedance depends on the space-variable, whereas it is monotonic and periodic when the impedance is independent of the space-variable. The factor which causes the different behavior of the thermal stress oscillations is also investigated based on the analytical and numerical results.

On the effects of hull-girder vibration upon fatigue strength of a Post-Panamax container ship disaggregated by short-term sea state

The effects of hull-girder vibration on the fatigue strength of a Post-Panamax container ship are discussed in the present paper. Firstly, the short-term sea states are categorized according to the occurrence probability of each sea state. Time histories of hull-girder stress in short-term sea states are calculated by means of a nonlinear simulation code of ship response assuming that the hull-girder is rigid and flexible. Then, the calculated stress peaks are processed by the rainflow counting method, where two different counting procedures are used based on the considerations of crack propagation behaviors. Finally, the fatigue damage in life time of the ship in each categorized short-term sea state is estimated by means of Miner’s rule. Based on the calculated results, the effects of hull-girder vibrations on the fatigue damage are clarified by disaggregated damage from short-term sea state.

Vertical vibrations of composite bridge/track structure/high-speed train systems. Part 3: Deterministic and random vibrations of exemplary system

Abstract Based on the one-dimensional quasi-exact physical and mathematical modelling of a composite (steel-concrete) bridge/track structure/high-speed train system (BTT), developed in Part 2, advanced computer algorithms for the BTT numerical modelling and simulation as well as a computer programme to simulate vertical vibrations of BTT systems are developed. The exemplary bridge under numerical quasi-static and dynamic analysis, designed according to Polish standards, has a 15.00 m span length and belongs to the SCB series-of-types developed in Part 1. The bridge is loaded by a German ICE-3 high-speed train moving at the resonant and maximum operating speeds. A continuously welded ballasted track structure adapted to high operating velocities is applied. The output quantities include: time-histories of the vertical deflection of the main beams at the midspan, time-histories of the longitudinal normal stress in the bottom fibres of the main beams at the midspan, time-histories of the vertical acceleration of the bridge deck at the midspan, time-histories of the vertical accelerations of the suspension pivots in car-bodies, time-histories of the dynamic pressures of the wheel sets of moving rail-vehicles. The design quantities, understood as the extreme values of the output quantities, are used to verify the design conditions. The basic random factor, i.e. vertical track irregularities of the track, is taken into consideration. Basic statistics of the design quantities treated as random variables are calculated and taken into account in the design conditions.

Investigation on the Fatigue Characteristic in Support Structure of HL-2M Tokamak

In order to obtain enhanced plasma parameters a complete new tokamak HL-2M is now under construction in Southwestern Institute of Physics. To assure the structural safety of the device for the entire operation cycle, one of the most important issues is the lifetime-limiting effects due to the pulsed operation mode. Fatigue is one of the major failure modes to be considered in mechanical design, and pulsed operation imposes stress with significant alternating components on the support structure (SS). Therefore, the reliability of the whole device is strongly affected by the stress and fatigue characteristic of the SS as the interface structure. This article introduces the SS design and details the fatigue life calculation methods based on the different characteristics of the sub-structures. The fatigue life in hazardous areas of the toroidal field coils anti-torque structure (TFCs-ATs) has been determined by non-linear analysis results. And with the stress-time history data of the vacuum vessel & poloidal field coils support structure (VV&PFCs SS), the fatigue analysis of the hot spots has been completed based on rain-flow counting method and linear cumulative damage method. The calculated minimum fatigue life on TFCs-ATs and VV&PFCs SS is 4.743E+05 and 1.805E+06 cycles, respectively. And the calculated fatigue life on sub-structures can meet the required life for HL-2M tokamak: 1.0E+05 cycles.

Analytical and computational investigation into the influence of the compressive stress cycles on crack growth under variable amplitude loading using CTOD

ABSTRACTFatigue crack growth rate of 6061 T651 aluminum alloy centre‐cracked plates, subject to a variable amplitude loading (VAL), is established using a coupled analytical/computational approach. The method utilises the generalised Willenborg retardation model in conjunction with the Walker model, with several of the models parameters obtained through nonlinear finite element analyses. A two‐parameter approach is also used in this study to explore the influence of compressive stress cycles in a VAL scenario on the crack tip opening displacement, and in turn, on the resulting fatigue crack growth rate of the material. The work includes the evaluation of the crack tip opening displacement and residual stresses in the vicinity of a crack by nonlinear finite element analysis, and application of the Generalised Willenborg model to evaluate the fatigue crack growth; particularly, under the influence of the compressive stress cycles, tensile overloads and underloads have been investigated. The finite element analysis results are compared with the experimental results reported in earlier studies by the authors.The results further demonstrate two important phenomena, that is, (i) the influence of FCG retardation effects due to the tensile overloads and (ii) the acceleration effect due to the applied compressive underloads of a VAL stress–time history.

Prediction of the Fatigue Life for Large Wind Turbine Gearbox

Wind turbine gearbox is the key component. Because of alternating loads caused by gear engagement, variations of wind speed and fluctuation of load, it is prone to get fatigue damage, which lead to the high failure rate and low life. In this paper, obtaining the stress time histories through multi-body dynamics simulation, then base on the simulation data, statistical processing load time histories by used rain flow counting method, the last is that estimating fatigue life of components, combined with P-S-N curves of parts material and linear cumulative damage law. The fatigue life prediction of each component in gearbox would be implemented by matlab programming. Through the fatigue analysis of a megawatt-class wind turbine gearbox transmission chain, the design was verified feasibility, but not economic, and it show that this method has certain reference value and potential for improvement.

Influence of Small Stress Cycles on the Fatigue Damage of C70E Car Body

Dynamic stress tests are carried out on the line of Beijing to Chengdu, with the test car unit composed of one C70E general open wagon and one NX70 general flat wagon equipped by the test devices. The stress-time histories of different critical locations are gained for the C70E gondola car body. To research the car body fatigue strength of the C70E gondola with high accuracy, different fatigue threshold values are chosen to compile the stress spectra. The signals are transferred from time domain to frequency domain by the rain flow counting method, to establish spectra. Under the Miner linear accumulative damage law, fatigue damage accumulations are calculated from different spectra gained by different fatigue threshold values and the results show that small stress cycles contribute to the fatigue damage. Considering both the amount of work required and the influence level of the small stress cycles, it is reasonable to choose 5% of the stress range(the difference of the maximum amplitude and the minimum amplitude) as the threshold value for compiling stress spectra. By comparing the fatigue damage for different critical locations, it is observed that the relatively weak parts of the car body are located in the welded joint with bolster cover plate and center sill and the welded joint with large cross beam and side beam near an end side. The fatigue life of C70E open wagon is assessed, which satisfies the design and operational requirements.

A reliability-based methodology for considering corrosion effects on fatigue deterioration in steel bridges - Part II: Case study of Neka Bridge -

The methodology presented in Part I is examined on Neka Bridge, a railway, truss bridge in northern Iran. The study includes: considerations of climate and air pollution, extraction of the stress-time histories from the FE model, prediction of future traffic volumes in a probabilistic manner and assessment of the effects of MR&R actions on the deterioration profile. PDF of D is determined using Monte Carlo simulations, and the reliability profile is calculated from the performance function. The study shows that for a target reliability of 2.0, the fatigue life of the bridge is reduced by either 29% or 31% if dose-response function or qualitative-based y-t function is used, respectively.

A model-based observer for state and stress estimation in structural and mechanical systems: Experimental validation

In this paper we present the results from a validation study of a recently proposed model-based state observer for structural and mechanical systems. The observer uses a finite element model of the structure and noise contaminated measurements to estimate the state and stress time histories at arbitrary locations in the structure of interest. The initial conditions and unknown excitations are described by random vectors and random processes with known covariance and power spectral density. A laboratory model consisting of an aluminum cantilever beam was used to perform the experiment. Two types of loading conditions were tested: an impact hammer test and a band limited excitation delivered through a shaker. The results obtained with the proposed observer are compared to the measured stress at the locations of interest, and to estimates obtained using well-established estimation methods such as Luenberger observers and the Kalman filter. The main finding is that for all experiments conducted the proposed model-based observer yielded estimates with higher or comparable accuracy to all other methods considered, with the advantage of requiring significantly less computational effort and with a more direct and transparent implementation.

Investigating the importance of sediment resuspension in Alexandrium fundyense cyst population dynamics in the Gulf of Maine

Cysts of Alexandrium fundyense, a dinoflagellate that causes toxic algal blooms in the Gulf of Maine, spend the winter as dormant cells in the upper layer of bottom sediment or the bottom nepheloid layer and germinate in spring to initiate new blooms. Erosion measurements were made on sediment cores collected at seven stations in the Gulf of Maine in the autumn of 2011 to explore if resuspension (by waves and currents) could change the distribution of over-wintering cysts from patterns observed in the previous autumn; or if resuspension could contribute cysts to the water column during spring when cysts are viable. The mass of sediment eroded from the core surface at 0.4Pa ranged from 0.05kgm−2 near Grand Manan Island, to 0.35kgm−2 in northern Wilkinson Basin. The depth of sediment eroded ranged from about 0.05mm at a station with sandy sediment at 70m water depth on the western Maine shelf, to about 1.2mm in clayey–silt sediment at 250m water depth in northern Wilkinson Basin. The sediment erodibility measurements were used in a sediment-transport model forced with modeled waves and currents for the period October 1, 2010 to May 31, 2011 to predict resuspension and bed erosion. The simulated spatial distribution and variation of bottom shear stress was controlled by the strength of the semi-diurnal tidal currents, which decrease from east to west along the Maine coast, and oscillatory wave-induced currents, which are strongest in shallow water. Simulations showed occasional sediment resuspension along the central and western Maine coast associated with storms, steady resuspension on the eastern Maine shelf and in the Bay of Fundy associated with tidal currents, no resuspension in northern Wilkinson Basin, and very small resuspension in western Jordan Basin. The sediment response in the model depended primarily on the profile of sediment erodibility, strength and time history of bottom stress, consolidation time scale, and the current in the water column. Based on analysis of wave data from offshore buoys from 1996 to 2012, the number of wave events inducing a bottom shear stress large enough to resuspend sediment at 80m ranged from 0 to 2 in spring (April and May) and 0 to 10 in winter (October through March). Wave-induced resuspension is unlikely in water greater than about 100m deep. The observations and model results suggest that a millimeter or so of sediment and associated cysts may be mobilized in both winter and spring, and that the frequency of resuspension will vary interannually. Depending on cyst concentration in the sediment and the vertical distribution in the water column, these events could result in a concentration in the water column of at least 104cystsm−3. In some years, resuspension events could episodically introduce cysts into the water column in spring, where germination is likely to be facilitated at the time of bloom formation. An assessment of the quantitative effects of cyst resuspension on bloom dynamics in any particular year requires more detailed investigation.

Loader Boom Reliability Analysis with Artificial Neural Network Method

The artificial neural network is used to solve the reliability analysis of the engineering structure. When the limit state function of structure is highly complex or with nonlinearity, it is time-consuming or cumbersome to carry out reliability analysis with traditional methods. The artificial neural network response surface method is adopted to analyze the fatigue reliability of loader boom, the working process of loader machine is analyzed with FEM software and analytical method, the stress-time history and strain-time history of loader boom are schematized with rain-flow algorithm, consequently the fatigue life analysis on the structure can be carried out with local stress-strain method. The artificial neural network method is used to fit the performance function as well as its derivatives, so as to calculate the reliability of the structure. The numerical example results show that the proposed method has capability of solving industrial-scale reliability problems.

Analysis of complicated one‐dimensional stress oscillation behaviour in a functionally graded material plate

A one‐dimensional elastodynamic problem in a functionally graded material (FGM) plate subjected to an impact pressure is analyzed in this paper. Applying techniques of the space‐variable transformation and Laplace transform, exact analytical solutions are derived for two cases of variations in material properties when nonhomogeneous material properties are expressed as exponential functions of the space‐variable. Numerical calculations for time histories of stresses have been carried out. Analytical and numerical results reveal that the stress oscillation obtained from one analytical solution is complicated and quasi‐periodic when the mechanical impedance depends on the space‐variable, whereas it derived from the other analytical solution is monotonic and periodic when the impedance is independent of the space‐variable. The factor which causes the different behaviours is also investigated based on the analytical and numerical results. This effect could be a key to controlling a complicated stress oscillation in an FGM plate.