Fatigue Load Spectrum Research Articles

Dynamic reliability approach of chip scale package assembly under vibration environment

Purpose – The purpose of this paper is to perform experimental tests on fatigue characteristics of chip scale package (CSP) assembly under vibration. Some suggestions for design to prolong fatigue life of CSP assembly are provided. Design/methodology/approach – The CSP assembly which contains different package structure modes and chip positions was manufactured. The fatigue characteristics of CSP assembly under vibration were tested. The fatigue load spectrum of CSP assembly was developed under different excitation. The fatigue life of chips can be estimated by using the high-cycle fatigue life formula based on different stress conditions. The signal–noise curve shows the relationship between fatigue life and key factors. The design strategy for improving the fatigue life of CSP assembly was discussed. Findings – The CSP chip has longer fatigue life than the ball grid array chip under high cyclic strain. The closer to fixed point the CSP chip, the longer fatigue life chips will have. The chip at the edge of the printed circuit board (PCB) has longer fatigue life than the one in the middle of the PCB. The greater the excitation imposed on the assembly, the shorter the fatigue life of chip. Research limitations/implications – It is very difficult to set up a numerical approach to illustrate the validity of the testing approach because of the complex loading modes and the complex structure of CSP assembly. The research on an accurate mathematical model of the CSP assembly prototype is a future work. Practical implications – It builds a basis for high reliability design of high-density CSP assembly for engineering application. In addition, vibration fatigue life prediction method of chip-corner solder balls is deduced based on three-band technology and cumulative damage theory under random vibration so as to verify the accuracy of experimental data. Originality/value – This paper fulfils useful information about the dynamic reliability of CSP assembly with different structural characteristics and material parameters.

Dynamic Reliability Analysis of Gear Transmission System of Wind Turbine in Consideration of Randomness of Loadings and Parameters

A dynamic model of gear transmission system of wind turbine is built with consideration of randomness of loads and parameters. The dynamic response of the system is obtained using the theory of random sampling and the Runge-Kutta method. According to rain flow counting principle, the dynamic meshing forces are converted into a series of luffing fatigue load spectra. The amplitude and frequency of the equivalent stress are obtained using equivalent method of Geber quadratic curve. Moreover, the dynamic reliability model of components and system is built according to the theory of probability of cumulative fatigue damage. The system reliability with the random variation of parameters is calculated and the influence of random parameters on dynamic reliability of components is analyzed. In the end, the results of the proposed method are compared with that of Monte Carlo method. This paper can be instrumental in the design of wind turbine gear transmission system with more advantageous dynamic reliability.

Fatigue Analysis of MW Wind Turbine Top Flange

On the basis of the finite element analysis model of the wind turbine flange, this paper studies the fatigue damage of the MW wind turbine flange, analyzing the fatigue stress of the wind turbine flange with MSC.Marc/Mentat software, realizing load simulation of flange fatigue case with Bladed software, and calculating the fatigue loading spectrum of the flange with the method of rain flow circulation count. The fatigue damage calculation method which combines the rain flow circulation count method with Palmgren-Miner linear cumulative damage law, is proposed to modify the S-N curve of the flange material according to GL standard. The result shows the method feasible and reliable which provides one more accurate analysis idea for the fatigue life of the wind turbine generator system top flange.

착륙장치 피로 시험평가

항공기 착륙장치의 피로설계에는 안전수명 방법이 적용된다. 즉, 균열이나 유해한 변형과 같은 구조적 결함이 항공기 운용수명 기간을 모사하는 피로 하중 스펙트럼 조건에서 발생하지 않아야 한다. 일반적으로 항공기 착륙장치는 고주기 피로 환경에 노출되므로, 설계 단계에서 착륙장치의 피로 수명은 응력 기반의 해석을 통해 예측한다. 이를 위해 재료의 분산(Scatter) 및 표면처리 특성 등을 고려한 설계 S-N 선도를 구성하여 해석에 사용한다. 시험평가 단계에서는 실물 착륙장치에 대한 피로시험을 통해 피로설계 요구조건 충족 여부를 최종 검증한다. 본 논문에서는 항공기 착륙장치의 피로수명 해석 및 시험절차를 실제 적용 사례를 통해 제시하였다.<BR>

Research on the Fatigue Design Load of Orthotropic Steel Box Girder for Long Span Suspension Bridge

Traffic composition and the vehicle load were statistically analyzed and a fatigue vehicle load model was established according to the law of equivalent fatigue damage. Based on the MATLAB programming language and the Statistics Toolbox, vehicle fatigue load spectrum was simulated for accurately assessing actual fatigue stress of existing bridge under traffic loading. And the fatigue load could be used in the design for suspension bridge steel box girder.

Determination of Fatigue Load for Light Rail Support of Caiyuanba Yangtze Bridge in Chongqing

In this paper, in combination with the specific conditions of light rail traffic volume, fatigue load spectrum parameters of light rail support are to be determined by background project light rail line 3 of Chongqing Caiyuanba Yangtze Bridge, through which the internal force history is then calculated. Three million constant amplitude fatigue loads that the test needs are finally determined through linear fatigue damage cumulative theory.

Determination of Fatigue Load for Light Rail Support of Caiyuanba Yangtze Bridge in Chongqing

In this paper, in combination with the specific conditions of light rail traffic volume, fatigue load spectrum parameters of light rail support are to be determined by background project light rail line 3 of Chongqing Caiyuanba Yangtze Bridge, through which the internal force history is then calculated. Three million constant amplitude fatigue loads that the test needs are finally determined through linear fatigue damage cumulative theory.

The Compiling of the Motorcycle Frame Load Spectrum Based on Dynamic Characteristic Analysis

The load spectrum of a frame, which is a key component of a motorcycle, can be used to frame loading experiment and life prediction of a motorcycle. Through the dynamic characteristics analysis of the motorcycle frame, we can get the dynamic model of the weak parts in line with the actual conditions, as well as the preparation of the load course make it to become the program load spectrum for experimental load. Taking a 125-type motorcycle for example, establish the finite element model of the frame for modal analysis and transient analysis. Establish the fatigue load spectrum of the hazardous locations by analysis. Provide a realistic experimental methodology of program load spectrum.

Study on Fatigue Characteristic of Double Block Ballastless Track under Coupling Loads

Regarding double block ballastless track as research subject, three mechanical models were established, which include steel bar and concrete interaction mechanical model, spatial finite element static model of double block ballastless track, train-double block ballastless track vertical coupling dynamics model. According to concrete and steel bar stress time-dependant curves under axial even temperature and shrinkage load, temperature grads load and train load, fatigue load spectrum under coupling loads was obtained by using rain-flow counting method. Based on steel bar and concrete S-N curve, and Palmgren-Miner linear fatigue damage accumulation rule, track concrete layer fatigue life predicting model of double block ballastless track was established. Taking Changsha climatic condition for an example, the fatigue life of double block ballastless track is predicted, and the effects of design parameters to fatigue life are analyzed.

Fatigue damage modelling of adhesively bonded joints under variable amplitude loading using a cohesive zone model

In this paper, the fatigue response of adhesively bonded joints under variable amplitude (VA) cyclic loading was predicted using a numerical model. The adhesive layer was modelled using the cohesive zone model with a bi-linear traction-separation response. A damage model, incorporating fatigue load ratio effects, was utilised in conjunction with the cohesive zone model to simulate the detrimental influence of VA fatigue loading. This model was validated against published experimental results obtained from fatigue tests of adhesively bonded single lap joints subjected to various types of VA fatigue loading spectra. This model successfully predicted the damaging effect of VA fatigue loading on the adhesively bonded joints and was generally found to be a significant improvement on the other damage models considered.

Realization and Analysis of Bending Fatigue Strength Test for Gears under Random Loading

For the bending fatigue under the random load condition, the Miner cumulative fatigue theory was analyzed qualitatively. Random amplitude fatigue load spectrum for experiments was compiled according to that gears work under the load with Gaussian distribution load spectrum. Gear bending fatigue was carried out by the method of group test under the conditions of random load on the electro-hydraulic servo testing machine. Then the P-S-N curve of bend fatigue was got under Gaussian distribution load spectrum with particular coefficient of variation. Experiments prove that fatigue life from the result of random luffing amplitude fatigue experiments is lower than that from constant amplitude fatigue experiments, in which the upper limit of fatigue loads is the mean of load spectrum. It will be not reliable to estimate the bending fatigue life of gears that in the actual service.

Fatigue system reliability analysis of riveted railway bridge connections

A system-based model for fatigue assessment of riveted railway bridge connections, comprising a number of basic components, is presented in this article. Probabilistic fatigue load spectra are developed through Monte Carlo simulation of train passages over a finite element model of a typical, short-span bridge. Uncertainties arising from loading, resistance and modelling sources are taken into account. The riveted connection is treated through a set of generic sub-systems that capture potential damage in identifiable hot-spots, such as rivets, holes and angle fillets. The fatigue reliability over time is evaluated through system reliability methods by treating these hot-spots as the elements of a structural system. The results show that the probability of failure of the connection depends significantly on the form of the system adopted for the analysis and the rivet clamping force. Damage scenarios accounting for the potential loss of rivet clamping force are investigated, and it is shown that, in some cases, they can affect connection reliability considerably.

Traffic load modelling based on structural health monitoring data

Live and fatigue load models are foundations for the life-cycle design of highway bridges. Many highway bridges are now equipped with structural health monitoring (SHM) systems, which provide valuable data to establish load models. In this paper, traffic load models of the Binzhou Yellow River Highway Bridge are developed based on the field measurement of vehicles by an existing SHM system. The probabilistic distribution model and extreme value distribution of gross vehicle weight are statistically analysed using the monitoring data. The results indicate that they follow the bimodal lognormal and Gumbel distributions, respectively. The fatigue load spectrum is also studied. The logistic model is employed to predict the long-term traffic volume, and its parameters of the logistic model are updated using the monitored traffic volume. The combination of the fatigue load spectrum and the traffic volume forecast using the updated logistic model provides a load model for estimation of fatigue damage evolution of bridges.

Stochastic Characterization and Update of Fatigue Loading for Mechanical Damage Prognosis

Accurate characterization and prediction of loading, while properly accounting for uncertainty, are essential for probabilistic fatigue damage prognosis. Three different techniques, including rainflow counting, the Markov chain method, and autoregressive moving average (ARMA) method, are reviewed for stochastic characterization and reconstruction of the fatigue load spectrum for prognosis. The ARMA method is extended by introducing random coefficients and probabilistic weights, to account for the uncertainty in the selection of models, inherent variability of loading, and uncertainty due to sparse data. A continuous model updating framework based on usage monitoring data is developed and applied to all the three techniques mentioned above. The relation between prediction accuracy and updating period is evaluated quantitatively. A quantitative model validation metric is proposed for assessing the accuracy of load prediction.*

Comparison of Tensile Fatigue Resistance and Constant Life Diagrams for Several Potential Wind Turbine Blade Laminates

New fatigue test results are presented for four multidirectional laminates of current and potential interest for wind turbine blades, representing three types of fibers: E-glass, WindStrand™ glass, and carbon, all with epoxy resins. A broad range of loading conditions is included for two of the laminates, with the results represented as mean and 95∕95 confidence level constant life diagrams. The constant life diagrams are then used to predict the performance under spectrum fatigue loading relative to an earlier material. Comparisons of the materials show significant improvements under tensile fatigue loading for carbon, WindStrand, and one of the E-glass fabrics relative to many E-glass laminates in the 0.5–0.6 fiber volume fraction range. The carbon fiber dominated laminate shows superior fatigue and static strengths, as well as stiffness, for all loading conditions.

A two-parameter model for crack growth simulation by combined FEM–DBEM approach

This paper describes the application of a two-parameters crack growth model, based on the usage of two threshold material parameters (Δ K th and K max,th) and on the allowance for residual stresses, introduced at the crack tip by a fatigue load spectrum or by material plastic deformations. The coupled usage of finite element method (FEM) and dual boundary element method (DBEM) is proposed in order to take advantage of the main capabilities of the two methods. The procedure is validated by comparison with available experimental results, in order to assess its capability to predict the retardation phenomena, introduced by a variable load spectrum or by a plastic deformation introduced with a tool on the panel (indentation). In particular two different tests are made: the first test involve a CT specimen undergoing a load spectrum and the second one involve a dented panel undergoing a constant amplitude fatigue load. In both cases a satisfactory numerical–experimental correlation will be proved. The main advantages of the aforementioned procedure are: the simplicity of the crack growth law calibration (few constant amplitude tests are sufficient without the need for any non-physical calibration parameters), and the possibility to simulate residual stress effects on crack propagation with a simplified approach, based on linear elastic fracture mechanics.

틸트 로터형 항공기의 플랩퍼론 연결부에 대한 크리깅 기반 피로해석

피로해석은 반복하중 하에서의 항공우주 구조물에 대한 구조적 파괴를 예방하기 위해 수행된다. 본 논문에서는 틸트로터형 무인 항공기에 대하여 피로수명에 대한 평가를 하였다. 먼저 틸트로터형 무인항공기의 기동에 맞는 하중 스펙트럼을 생성해 내었으며, F.C.L. 부품중 하나인 플랩퍼론 연결부위에 대하여 피로해석을 수행 하였다. 틸트로터형 무인항공기는 크게 두 가지 기동 형태로 나눌 수 있는데, 이 착륙시의 헬리콥터 형태와 순항시의 고정익 형태가 되겠다. 전체적인 피로하중 스펙트럼을 만들기 위해서 헬리콥터 형태에는 FELIX를, 고정익 형태에서는 TWIST를 사용하였다. 한편으로는, S-N 실험점이 해석에 사용될 때 재료수명의 전 영역에 대한 S-N 회귀식을 얻기 위하여 크리깅 메타 모델이 사용되었다. 그리고 최소 자승법을 이용한 이차 회귀식에 대한 S-N 커브 역시 생성하였다. 더욱이 이 커브들이 갖고 있는 정확도를 측정하기 위하여 결정 계수법을 사용하였다. 마지막으로는 플랩퍼론 연결 부위에 대한 피로수명 결과를 MSC. Fatigue와 비교하였다. The fatigue analysis is performed to avoid structural failure in aerospace structures under repeated loads. In this paper, the fatigue life is estimated for the design of tilt rotor UAV. First of all, the fatigue load spectrum for tilt rotor UAV is generated. Fatigue analysis is done for the flaperon joint which may have FCL(fracture critical location). Tilt rotor UAV operates at two modes: helicopter mode such as taking off and landing; fixed wing mode like cruising. To make overall fatigue load spectrum, FELIX is used for helicopter mode and TWIST is used for fixed wing mode. The other hand, the Kriging meta model is used to get S-N regression curve for whole range of material life when S-N test data are analyzed. And then, the second order of S-N curve is accomplished by the least square method. In addition, the coefficient of determination method is used to ensure how accuracy it has. Finally, the fatigue life of flaperon joint is compared with that obtained by MSC. Fatigue.

Low Δ K faceted crack growth in titanium alloys

This communication describes the results of spectrum fatigue loading experiments conducted on cast and hot isostatically pressed Ti–6Al–4V. The purpose of the experiments is to elucidate the nature of faceted crack growth that occurs at low values of Δ K in titanium alloys during cyclic loading. The results clearly show that multiple load cycles are required for the crack to traverse one grain and produce a single facet. The confusing terminology related to low Δ K fatigue fracture topography is reviewed and the term “low Δ K faceted growth” is proposed as a preferred descriptor.

New method for automobile reliability test correlated with customers

In order to research the fatigue reliability of the load carrying structures on a heavy duty vehicle, a new reliability test technique correlated customer usage is proposed based on automotive proving ground, and the technique can combine the real customer field usage to the vehicle with the enhancement test on proving ground, and avoid the test blindness. Aiming at the data that are tested on the typical road surfaces of the customer and enhancement roads of proving ground, the rain-flow counting method is used to obtain the load distribution matrixes, according to the correlation equation, the cumulative fatigue damage and loading spectrum covering the 90% customer and proving ground are optimized and calculated. Through the correlation analysis of the test data, the road surface enhancement coefficient and the customer data reliability test specifications of proving ground are obtained. The test results indicate that the new specifications can predict the potential failures of the load carrying structures quickly, shorten the test cycles, and reduce the test cost and new product development expense, compared with the existing test method.

The development of a fatigue loading spectrum for small wind turbine blades

This paper details a formulation to create a fatigue loading procedure for the blade of a small wind turbine using a combination of detailed short-term aeroelastic and wind measurements and averaged long-term wind data from the Australian Bureau of Meteorology. Detailed aeroelastic measurements from the blade of an operating small wind turbine were acquired simultaneously with wind speed measurements and show that the blade does not respond instantaneously to all changes in wind speed. A methodology has been developed to create a fatigue loading procedure using the blade stress cycles determined from the detailed measurements in conjunction with long-term wind data. The proposed method overcomes the necessity to acquire long-term detailed operational data before developing a blade fatigue loading procedure without compromising on accuracy.