Vibration and Fatigue Analysis

At present, the linear fatigue accumulation theory proposed by Miner is used to calculate the fatigue problem of random vibration. In this process, the loading order of the loads is ignored, so that the results obtained are riskier. The nonlinear fatigue cumulative damage theory takes into account the effects of the load loading sequence, but the calculation becomes more complicated. Many scholars have shown that the fatigue calculation of alternating loads is not strictly linear, and the high and low order will affect the damage index. This phenomenon will be more obvious in the random vibration process. In this paper, the effects of loading sequence on the calculation of non-Gaussian random vibration fatigue damage are studied by virtual experiments. Through the phase selection method, 7 sets of excitations with different kurtosis were loaded onto the notched specimen. Through the calculation results of fatigue damage in the notch sensitive area, it was confirmed that the damage calculated by linear and nonlinear cumulative damage formula was improved with the increase of kurtosis. The results can make a significant difference.

A major obstacle to obtaining cost-effective experimental data on the fatigue life of sandwich panels is the prohibitive amount of time and cost required to carry out millions of cycles. On the other hand, vibration techniques applied to sandwich geometries fail to match the stress patterns that are obtained from standard flexural fatigue tests. To overcome such limitations, a vibration-based fatigue technique is proposed, which entails the use of sandwich specimens whose geometries are optimized to reproduce the stress distribution observed during three point bend loading while vibrating at the first resonant frequency. The proposed vibration technique was experimentally validated. The results, compared with the average number of cycles to failure at different stress ratios obtained via the Three-Point Bending test, showed high levels of accuracy. The proposed method is robust and time effective and indicates the possibility of attaining fatigue lifetime prediction of a wide class ...

A major obstacle to obtaining cost-effective experimental data on the fatigue life of sandwich panels is the prohibitive amount of time and cost required to carry out millions of cycles. On the other hand, vibration techniques applied to sandwich geometries fail to match the stress patterns that are obtained from standard flexural fatigue tests. To overcome such limitations, a vibration-based fatigue technique is proposed, which entails the use of sandwich specimens whose geometries are optimized to reproduce the stress distribution observed during three point bend loading while vibrating at the first resonant frequency. The proposed vibration technique was experimentally validated. The results, compared with the average number of cycles to failure at different stress ratios obtained via the Three-Point Bending test, showed high levels of accuracy. The proposed method is robust and time effective and indicates the possibility of attaining fatigue lifetime prediction of a wide class ...

Welding is a commonly applied joining method in many applications in arctic and marine conditions, e.g., in ship and offshore structures, and energy production equipment. Such applications are usually subjected to fluctuating load conditions, and during a decades-long service, they may experience millions of load cycles. Consequently, fatigue strength design and acceptable flaw sizes in the welded details of these structures are among the most important design criteria. Multiple fatigue strength assessment approaches exist for assessing the fatigue strength of a welded detail. The present study introduces a numerical and analytical fatigue strength assessment, conducted on a non-load-carrying X-joint, which is a representative joint type used in many steel constructions. Fatigue analyses are carried out following the DNVGL-RP-C203 and BS7910:2013 fatigue design guidelines for offshore steel structures. The stress intensity factors (SIFs) for linear elastic fracture mechanics (LEFM) analyses were obtained using three different methods: the weight function approach, the analytical equations provided in the IIW Recommendations, and by conducting numerical crack propagation analysis using the Franc2D software. All three methods had a good agreement particularly for short crack depths, indicating the applicability of the analytical approaches for the fatigue analyses. The results showed that the consideration of degree of bending at the welded detail is crucial due to the distinguishing notch stress factors of membrane and bending loading, and different stress distributions in the through-thickness direction. In addition, it was found that the LEFM-based fatigue life assessments are significantly more conservative than the life predictions obtained using the structural hot-spot and effective notch stress approaches.

Due to the high level of fatigue loads as well as a large number of load cycles caused by wind and wave loads together, fatigue performance of welded connections is a design driving criterion for offshore wind turbine support structures. In this paper prediction of fatigue reliability of welded multi-planar tubular joints of the support structure of a fixed jacket offshore wind turbine designed for a northern North Sea site in a water depth of 70 m is performed. Dynamic response of the jacket support structure due to wind and wave loads is calculated by using a decoupled procedure with good accuracy. Hot-spot stresses at failure-critical location of the relative reference brace of the selected tubular joint are derived by summation of the single stress components from axial, in-plane and out-of-plane action, the effects of planar and non-planar braces are also considered. A two-parameter Weibull function is used to fit the long-term statistical distribution of hot-spot stress ranges by combination of time domain simulation for representative environmental conditions (wind/sea states) in operational condition. The main uncertainties associated with the whole procedure of reliability analysis are identified and quantified. The load histories are normalized to ensure that fatigue design criteria based on the SN-Miner-Palmgren approach is satisfied. Hence the reliability estimates obtained refer to fatigue design of tubular joints that satisfy design criteria. The reliability analysis is based on fracture mechanics (FM) analysis of crack growth. The corrosion-induced increased crack growth rate is taken into account by considering the increased hot-spot stress range due to changes of nominal stress and stress concentration factors (SCFs) produced by the thickness thinning (wastage) effects of all braces and chord of the selected tubular joint with a general uniform corrosion model. The geometry function effect and the material degradation effect due to corrosion on the reliability analysis are also investigated. The effects of inspection and repair with and without consideration of corrosion are quantified based on the quality of inspection in terms of probability of crack detection curves. The sensitivity of the reliability index on important random variables is estimated.

The connecting rod is the intermediate member between the piston and the Crankshaft. Its primary function is to transmit the push and pull from the piston pin to the crank pin, thus converting the reciprocating motion of the piston into rotary motion of the crank. Existing connecting rod is manufactured by using Carbon steel. The axial stresses are produced due to cylinder gas pressure (compressive only) and the inertia force arising in account of reciprocating action (both tensile as well as compressive), where as bending stresses are caused due to the centrifugal effects. The result of which is, the maximum stresses are developed at the fillet section of the big and the small end. Hence, the project deals with the stress analysis of connecting rod by Finite Element Method ANSYS WORKBENCH 16.0 Software. The main objective in this paper to review on design evaluation and optimization of connecting rod parameters by using finite element method is to achieve suitable design for connec...

Purpose: Different kinds of alloys used in industry for structures and engine components are subjected to very high cycle fatigue (gigacycle regime) damage under the service conditions. In this study, fatigue damage evolution of some metallic-industrial alloys was investigated on very high cycle fatigue regime and calculation of the stress intensity factor (SIF) using finite element method (FEM) was realized under the ultrasonic vibration conditions. A formula of SIF vs. Cracks size and position of the crack has been developed. In fact, calculation of the SIF under ultrasonic vibrating fatigue has to be a function of amplitude instead of nominal stress as frequently used in traditional fatigue from Woehler.Design/methodology/approach: The specimens are tested at ultrasonic fatigue frequency of 20 kHz with a stress ratio of R=-1 (tension-compression) under load control. In order to control the displacement amplitude at the end of the amplifier was calibrated by optical sensor before ...

The coupling of vibration and fatigue crack growth in a simply supported uniform Euler–Bernoulli beam containing a single-edge crack is analyzed. The fatigue crack length is treated as a generalized coordinate in a model for the mechanical system. This coupled model accounts for the interaction between the beam oscillations and the crack propagation dynamics. Nonlinear characteristics of the beam motion are introduced as loading parameters to the fatigue model to match experimentally observed failure dynamics. The method of averaging is utilized both as an analytical and numerical tool to: (1) show that, for cyclic loading, our fatigue model reduces to the Paris' law and (2) compare the predicted fatigue damage accumulation with the experimental data for chaotic and random loadings. A utility of the fatigue model is demonstrated in estimating fatigue life under irregular loadings.

The aim of this paper is to propose a lifetime prediction method for threaded connections. The example discussed here is a drillstring connection used in the oil and gas industry. The method is based on a mechanical analysis performed either with finite elements or a closedform solution described in a companion paper, and a fatigue analysis using the Dang Van criterion which has been extended to finite life domain. The mechanical analysis provides the stabilized stress path and the fatigue analysis provides the fatigue life. Fatigue tests have been performed on small scale threaded connections in order to validate the methodology. The comparisons with the predictions show the difficulties to estimate the fatigue life on structures presenting high stress gradient due to scale effects.

Fatigue-life curves are used in order to estimate crack-initiation, and also to prevent water leakage on Pressure Water Reactor pipes. Such curves are built exclusively from push-pull tests performed under constant and uniaxial strain or stress-amplitude. However, thermal fatigue corresponds to a nearly perfect biaxial stress state and severe loading fluctuations are observed in operating conditions. In this frame, these two aspects have been successively investigated in this paper: In order to investigate on potential difference between thermal fatigue and mechanical fatigue, tests have been carried out at CEA using thermal fatigue devices. They show that for an identical level of strain-amplitude, the number of cycles required to achieve crack-initiation is significantly lower under thermal fatigue. This enhanced damage results probably from a perfect biaxial state under thermal fatigue. In this frame, application of the multiaxial In order to investigate on cumulative damage effect in fatigue, multi-level strain controlled fatigue tests have been performed. e linear damage rule ("DLDR") improves significantly predictions of fatigue-life.

Ïðåäñòàâëåíà ñèñòåìàòèçèðîâàííàÿ ìåòîäèêà òåîðåòè÷åñêîé îöåíêè ðàáî÷èõ õàðàêòåðèñòèê ãàçîâîãî äâèãàòåëÿ âíóòðåííåãî ñãîðàíèÿ è ïàðàìåòðîâ óñòàëîñòíîãî ðàçðóøåíèÿ åãî ïîðøíåé è âûïîëíåíà åå ýêñïåðèìåíòàëüíàÿ âåðèôèêàöèÿ ïóòåì íàòóðíûõ èñïûòàíèé äâèãàòåëÿ. Ìåòîäèêà âêëþ÷àåò â ñåáÿ ìîäåëèðîâàíèå ïðîöåññîâ âíóòðåííåãî ñãîðàíèÿ è òåïëîïåðåäà÷è, êèíåìàòè÷åñêèé è äèíàìè÷åñêèé àíàëèçû äâèaeóùèõñÿ ÷àñòåé äâèãàòåëÿ, àíàëèç ïåðåõîäíîãî òåðìîóïðóãîãî ïðîöåññà è óñòàëîñòíîãî ðàçðóøåíèÿ ïðè êîìïëåêñíîì òåðìîìåõàíè÷åñêîì íàãðóaeåíèè. Ðàñ÷åòíûå çíà÷åíèÿ äàâëåíèÿ è òåìïåðàòóðû äëÿ ðàçëè÷íûõ óãëîâ ïîâîðîòà êðèâîøèïíî-øàòóííîãî ìåõàíèçìà õîðîøî ñîãëàñóþòñÿ ñ ýêñïåðèìåíòàëüíûìè äàííûìè. Ðåçóëüòàòû ðàñ÷åòà õàðàêòåðèñòèê òåïëîïåðåäà÷è ïîäòâåðaeäàþòñÿ äàííûìè ýêñïåðèìåíòàëüíûõ èçìåðåíèé ñ ïîìîùüþ òåðìîäàò÷èêîâ Templugs. Äâèaeóùàÿñÿ ñèñòåìà ñ÷èòàåòñÿ íå äèñêðåòíîé, à íåïðåðûâíîé ñ òî÷íî ìîäåëèðóåìûìè íåëèíåéíûìè ìíîãîòî÷å÷íûìè êîíòàêòíûìè ðåàêöèÿìè. Ïðè ðàñ÷åòàõ óñòàëîñòíîé äîëãîâå÷íîñòè èñïîëüçóþòñÿ ìîäèôèöèðîâàííûå êðèòåðèè Ìàê-Äèàðìèäà è Ôèíäëè äëÿ ìíîãîöèêëîâîé óñòàëîñòè, ïðåäëîaeåííûå îäíèì èç àâòîðîâ ýòîé ðàáîòû. Âûïîëíåíà èõ âåðèôèêàöèÿ ñ ïîìîùüþ ýêñïåðèìåíòàëüíûõ äàííûõ. Ìåòîäèêà ìîaeåò èñïîëüçîâàòüñÿ äëÿ îöåíêè öåëåñîîáðàçíîñòè ïðåîáðàçîâàíèÿ áåíçèíîâîãî äâèãàòåëÿ â ãàçîâûé. Ðàñ÷åòíûå äàííûå î ðàçëè÷íûõ óñòàëîñòíûõ õàðàêòåðèñòèêàõ, ïîëó÷åííûå ïðè òåðìîìåõàíè÷åñêîì íàãðóaeåíèè, ïîäòâåðaeäàþò òî÷íîñòü ïðåäëîaeåííûõ êðèòåðèåâ óñòàëîñòè è ïîêàçûâàþò, ÷òî ñðîê ñëóaeáû ïîðøíÿ äâèãàòåëÿ âíóòðåííåãî ñãîðàíèÿ ñóùåñòâåííî óìåíüøàåòñÿ, åñëè âìåñòî áåíçèíà èñïîëüçóåòñÿ ïðèðîäíûé ãàç. Êëþ÷åâûå ñëîâà: ìîäåëèðîâàíèå âíóòðåííåãî ñãîðàíèÿ, äèíàìè÷åñêèé àíàëèç, äâèãàòåëü, ïîðøåíü, óñòàëîñòíîå ðàçðóøåíèå, ýêñïåðèìåíò. Introduction. Due to fuel and pollution crises encountered in the two past decades and serious worries about the future of the petroleum resources, remarkable researches recently have been performed to replace the gasoline by more reliable or more economic fuels. In some countries, researchers have proposed using the natural gas, e.g., in the form of compressed natural gas (CNG), as an alternative

In engineering, the study of the dynamic response of structures subjected to nondeterministically variable loads is particularly important, especially when considering the damage that such loads can cause due to fatigue phenomena. This is the case, for example, of the vibrations that a satellite must withstand during the launch phase. In the preliminary design phases, it is very useful to have semi-analytical calculation methodologies that are sufficiently reliable but, at the same time, simple. In the technical literature, there are numerous publications that deal with the study of the random dynamic response of beam models. In general, the presented studies are rather complex, and the dynamic solutions are often obtained in the time domain. The case of a linear elastic uniform cantilever beam model is considered here, for which the analytical expressions of the transfer functions for acceleration, displacement, bending moment, and bending stress are calculated, taking as input the acceleration assigned to the root section or an external lateral load. Knowing the spectral density of the input loads, the spectral densities of all the above-mentioned variables are calculated along the beam axis, assuming stationary and ergodic random processes. Using the spectral density of each output variable, the effective value (RMS) is obtained via integration, which allows for a preliminary estimate of the severity of the working conditions of the beam. The spectral density of the responses also allows us to quickly highlight the contribution of each natural vibration mode as the spectrum of the load varies. The results were obtained using simple spreadsheets available to the reader.

Ship hull vibration is a major contributor to fatigue crack growth and main engine excitation is identified as an important vibration source. A general method to solve any vibration problem arising onboard a ship does not exist, which encourages the use of a reliability-based framework for assessing ship vibration and its consequences. A stochastic model of vibration response is developed for the probabilistic formulation of the failure probability of the occurrence of crack propagation of a secondary structural hull component. The secondary structural component considered is a pipe stack support. The pipe stack support connects a cargo pump pipe stack to the wall inside the cargo tank, and the support is welded directly onto this wall. First, a generic cargo hold model is analysed with engine speed and the relative distance between the engine and the structural component under consideration as stochastic variables. Then, submodels are used to investigate the local vibration of the ...

This paper presents the about fatigue life prediction based on finite element analysia and variable amplitude loading (VAL). Parabolic spring is one of the vital component in a vehicle suspension system, and it is commonly used in trucks. It needs to have an excellent fatigue life, and recently, manufacturers rely on constant loading fatigue data. This study objective is to simulating the variable amplitude loading for the fatigue life analysis. Service loading of parabolic spring has been collected using data acquisition system. Finite element analysis (FEA) was performed on the spring model so stress and damage distribution can be observed. Experimental works was done in order to validate the FEA result. The main finding can be obtained when VAL as the input, and it was then combines with the FE model. Fatigue life simulation was performed and analyzed. From the results, the fatigue damage using VAL was predicted and the result was correlated with FEA.

This study presents fatigue strength assessment of the trimaran platform by the spectral approach. Spectral fatigue calculations are based on complex stress transfer functions established through direct wave load analysis combined with stress response analysis. In this study, ANSYS software with 3 dimensional linear seakeeping code AQWA is used to compute frequency response functions of the vessel at zero forward speed. Finite element analysis of global trimaran structure is performed in ANSYS software utilizing hydrodynamic wave loads. Hot spot stress approach is used to compute stress transfer functions of the selected critical details. A MATLAB program, based on direct calculation procedure of spectral fatigue is developed to calculate total fatigue damage using wave scatter data of North Atlantic. Damage incurred during individual heading direction is also calculated and presented by means of polar diagrams to study its contribution towards cumulative fatigue damage.

Frequent fatigue failure of heavy mining equipment has created the need for fatigue life prediction of its cracked components. As the first step, field monitoring of a cable shovel boom that had a history of chronic fatigue cracking was conducted. A set of load spectra for the boom was constructed from the collected field data. A finite element model of the boom was prepared and calibrated against the test data to predict the stress and strain histories. Eight crack growth rate coupon tests were carried out to obtain the fatigue properties of the material used. Constant amplitude equivalent stress ranges were calculated based on Palmgren-Miner's cumulative damage rule and crack growth rate tests results.

Slender marine structures such as mooring lines and risers are susceptible to failures due to stress variations coming from environmental actions. Wave, wind and current are random phenomena, and consequently the most adequate methodology to estimate the fatigue damage accumulation on these structures is the probabilistic fatigue analysis. In practice, the estimation of fatigue life requires the numerical simulation of a huge number of loading cases to compute the multi-dimensional integral of the total fatigue damage. This paper presents an efficient approach to compute the long-term fatigue damage of marine structures. The proposed method needs only a few number of numerical simulations to estimate the structure fatigue life. It uses a parametric interpolation procedure to evaluate the fatigue damage for any individual short-term condition (sea state) required in the calculation of the multi-dimensional integral. In this way, the total number of short-term structural analyzes is considerably reduced. The effectiveness and accuracy of the proposed method is compared to the full direct integration by means of two comprehensive examples. The first studied case is an idealized theoretical model of a single-degree-offreedom (SDOF) system under wave loading, and the second one is a Steel Catenary Riser (SCR) connected to a FPSO (Floating, Production, Storage and Offloading floating unit). Due to their nonlinear structural behavior, the numerical simulations of slender marine structures, such as risers and mooring lines connected to floating units, are performed in time domain using very detailed finite element-based models requiring a huge computer time (for instance, a single nonlinear stochastic time domain simulation of a metallic riser in deep water can easily take more than two hours in

The paper presents a method for effective stress characteristics defining while the evaluation of fatigue toughness is practiced. Correlation between fatigue lifetime, function of spectral density and the exponent of S-N curve is given. The method could be applied in various forms of spectral densities. The analysis of interdependences between dynamic loads, toughness characteristics and the railway structure fatigue life-time is shown on the example of an electric powered train.

The paper presents a method for effective stress characteristics defining while the evaluation of fatigue toughness is practiced. Correlation between fatigue lifetime, function of spectral density and the exponent of S-N curve is given. The method could be applied in various forms of spectral densities. The analysis of interdependences between dynamic loads, toughness characteristics and the railway structure fatigue life-time is shown on the example of an electric powered train

A neural network for the prediction of oscillatory loads used for on-line health monitoring of flight critical components in an AH-64A helicopter is described. The neural network is used to demonstrate the potential for estimating loads in the rotor system from fixed-system information. Estimates of the range of the pitch link load are determined by the neural network from roll, pitch, and yaw rates, airspeed, and other fixed-system information measured by the flight control computer on the helicopter. The predicted load range is then used to estimate fatigue damage to the pitch link. Actual flight loads data from an AH-64A helicopter are used to demonstrate the process. The predicted load ranges agree well with measured values for both training and test data. A linear model is also used to predict the load ranges, and its accuracy is noticeably worse than that of the neural network, especially at higher load values that cause fatigue damage. This demonstrates the necessity of the non-linear modelling capabilities of the neural network for this problem.

This study paper looks into the structural integrity and failure mechanisms of washing machine top frames, with the goal of improving household appliance durability and reliability. Critical regions prone to fatigue failure were identified using SolidWorks software. Stress analysis and deformation analysis revealed the failure prone areas but upon assessing the costs associated with designing new molds for modified design and performing the breakeven calculation, we decided to go with an approach of using an alternate material which will not cause any change in existing mold. Polycarbonate (PC) with 50% long glass fiber reinforcement, were investigated to improve fatigue resistance. A new top frame of this material was made along with existing material ABS. Testing on a door simulator machine demonstrated a considerable improvement in durability, with the PC-based top frame demonstrating a 1128% increase in cycle endurance over the ABS counterpart. Top frame made up of ABS broke after 297 cycles and PC with 50% long glass fiber top frame broke after 3697 cycles. These findings highlight the significance of systematic design optimization and material selection for assuring long-term performance and safety in washing machine top frames.

The Composite plate is taken as a fuselage of Boeing 787 passenger aircraft. The fuselage of any passenger aircraft is considered as a shell with a large radius of curvature and having multiple openings like doors and windows. The presence of such cut-outs in the shell structure causes perturbations in the original stress system, resulting in an increase in the local stress levels. Almost all the major failures during the service of an aircraft occur due to initiation of cracks in the region of maximum stress. Thus, Study and evaluation of maximum stress concentration is vital. Various methods are presented in the literature to find Stress Concentrations around various geometries, but for Rectangular cut outs with Circular radius in an Anisotropic Plate. The report deals with the stresses and stress concentration phenomenon around the doors and windows of Boeing 787TM aircraft. As the diameter of fuselage is very large compared to the dimensions of doors and windows, the problem have been modelled as an Infinite Plane with Multiple Openings under Biaxial Loading. The Analytical solution of the stress concentrations is found by Finite Element Analysis using ANSYS.

Cyclic wave loads can cause fatigue of the joints in the Jacket Platform structure, which is made of steel material and is prone to vibration resonance. This study compares the fatigue life of the Yetagun North Field (YET-D) jacket platform analyzed using the spectral and deterministic fatigue methods using the API RP-2A WSD standard and adding the Weld Improvement Technique 3D visual model and the analysis is processed using the Structure Analysis Computer System (SACS) Connect Edition v11.3 software. Fatigue analysis of Spectral Method without Weld Improvement Technique has exceeded the service life of 20 years, while some joints are less than the service life using the Deterministic Method, but after the Weld Improvement Technique using the S-N curve WJ3 the joint life increases to exceed its service life. The most critical joint 2043, has a fatigue life of 2.79 years for deterministic fatigue and 64.04 years for spectral fatigue. When WJ3 was applied, the fatigue life increased to 21.3 years and 514.8. Analysis of the fatigue life of Spectral and Deterministic Fatigue Method couplings based on the location of the elevation Joints with the same type of fatigue life will increase when approaching 0 m elevation from the seabed, but the Deterministic Method has a smaller life ratio than the Spectral.

The stress response to random vibrations is an important factor to be taken into account in designing embedded electronic devices. Several test specifications and qualifications use the random vibrations to increase the reliability of electronic products. Fatigue damage estimation of embedded electronic solder joints has not been addressed, especially under random vibration loading. In this paper numerical random vibration analysis with finite element method of an embedded electronic device is used to estimate the stresses Power Spectral Density (PSD). These PSD of stresses are then used in different probabilistic fatigue damage approaches to estimate the reliability of the solder joints regarding the vibration fatigue damage. Two different probabilistic approaches of random fatigue are employed; the time-domain approach based on Rainflow and Monte Carlo simulations and the frequency domain approach based on spectral techniques and statistical data. However, the fatigue damage estimation depends mainly on the accurate results of the stresses PSD. Thus, this work proposes to develop the sub-modelling technique to the random vibration analysis in order to provide accurate results of the stresses PSD. Moreover, this paper discusses the advantages of the approaches listed above to estimate the fatigue damage in solder joints of an electronic component and shows the effectiveness of sub-modelling techniques in the random vibration analysis.

The work performs a prospective study on probabilistic approach of thermal fatigue in mixing tees (Civaux 1 damage case) by means of the limit state function and Monte Carlo simulation. It is based on previous work where a deterministic assessment for thermal fatigue crack growth in high-cycle loadings, under the large nonlinear gradient stress profiles through wall-thickness due to sinusoidal thermal loading, has been done. The probabilistic approach considers variability in initial crack depth and Paris law C scaling parameter by means of specific probability density distributions. The crude Monte Carlo Simulations are performed using specific routines implemented in MATLAB software with Statistics Toolbox, and probabilities of failure are derived using the failure function which is defined based on a limit state given by the critical crack depth. The results were checked against predictions from empirical cumulative distribution and a good agreement was found. An important task w...

Engine turbine blades are subjected to cyclic thermal stress during engine start-up, shutdown and various operating conditions. These thermal loads may generate temperature gradients and tensions inside the blades, which may cause structural fatigue damage and failure, and in severe cases may directly lead to flight accidents. In order to ensure the integrity and reliability of the engine blade structure, the fatigue analysis of the engine blade structure considering thermal stress is of great significance for the safety of aircraft. In this paper, the fatigue life of the engine blade structure is simulated and analysed considering the thermal load. Firstly, the research background and current research status are briefly introduced, and then the relevant theories for fatigue analysis of blade structures are elaborated. Then, a three-dimensional engine blade structure model is built in CATIA software, and it is imported into ANSYS software for thermal stress analysis. On this basis, ...

Fatigue life estimation is of high importance during the design stage of a machine or component. Basic fatigue calculations are made based on the use of an S-N curve. As far as constant amplitude loads are applied, this approach works well. However, most part of components in service are subjected to a variable amplitude load spectrum. In this case, linear approaches for fatigue life estimation can lead to over conservative results, which in other words means a heavier and more expensive machine. To further investigate the effect of (complex) service spectra (measured or statistically calculated), simpler load variations must be studied. This paper aims to show the general trend of these events and suggest the underlying physical phenomena behind load and interaction effects. As it will be highlighted, overloads are frequent in a spectrum and they are believed to be responsible for retardation effects. The plasticity induced crack closure mechanism is the most profound explanation f...

A recent work conducted by the authors [Maktouf, W., Saï, K., 2015. An investigation of premature fatigue failures of gas turbine blade. Engineering Failure Analysis, 47, 89-101.] demonstrated that the root cause of the premature blade failure was caused by high-cycle fatigue (HCF) mechanism initiated at a localized carbon-rich area inducing grain boundary brittleness. The blade was subject to multiaxial cyclic loadings during its service life and any attempt to assess component fatigue strength leads to the question of choosing an appropriate fatigue design criterion. In this paper several multiaxial fatigue models are applied as post-processing step of the Finite Element Analysis (FEA) output results and the estimated fatigue lifetimes were assessed under different loading conditions. The material fatigue parameters, required as an input to the selected fatigue models were determined through a series of bending and torsion tests on specimens made of aged Inconel 718. A numerical post-processing algorithm was developed for Fatemi-Socie fatigue criterion and included as additional post-computation model in the used computer aided fatigue damage evaluation tool. The authors point out that the majority of the multiaxial fatigue studies available in the literature are conducted mainly for correlating the experimental laboratory results on specimens while they have been used in the frame of this study to investigate their application to an industrial case.

ABSTRACTThis study entails the fatigue analysis of a complex plate‐like structure subjected to random loading. The stress and fatigue life assessment is performed by means of experimental strain gauge measurements, finite element analysis and a quasi‐static fatigue assessment procedure known as the fatigue equivalent static load (FESL) methodology. Firstly, the integrity of shell elements for accurately capturing the stiffness properties and stress distribution in the vicinity of welds is investigated. Furthermore, the stress response of the structure to random dynamic loading is investigated and validated in terms of its suitability for assessment by the FESL methodology. Nominal stress and hot‐spot stress fatigue life predictions are made, based on measurements as well as the FESL procedure. The viability and integrity of the FESL methodology is critically assessed after which the actual fatigue life of the structure under particular loading conditions is determined for comparison.

For basic observations or for industrial applications it is of interest to use flat specimens at very high frequency in the gigacycle regime. In this work, thin flat sheet, with 1.2 mm thickness of a complex phase ferrite-martensitic steels were considered for carrying out fatigue tests at high frequency (20 kHz) up to the gigacycle regime (>10 9 cycles). The crack initiation tests were carried out with water cooling, while the crack growth test were carried out in laboratory air at room temperature. All the tests were carried out under loading ratio R=-1. To do that, special designs of specimens were made and computed using FEM for defining the stress amplitude for endurance tests. Special attachments for specimens to the ultrasonic system's horn were enhanced. A particular FEM computing of the stress intensity range on crack growth specimens was carried out for determining the specimen dimensions and an equation that defines the stress intensity range as a function of the harmonic displacement amplitude, dynamic Young's modulus, material density and crack length. Detailed procedures and fatigue results are presented in this paper.

A simple methodology to predict crack initiation life is described in the fatigue damage assessment of metallic structures typically used in ground vehicle industry. A phenomenological constitutive model is integrated with a notch stress-strain analysis method and local loads under general multiaxial fatigue loads are modeled with linear elastic FE analyses. The computed stressstrain response is used to predict the fatigue crack initiation life using effective strain range parameters and two critical plane parameters. The proposed methodology is employed in the fatigue test cycle prediction of the biaxial cornering tests of light-alloy wheels. Numerical simulations indicate that estimates using critical plane models provide better correlations between the cornering test cycles and predicted cycles. Also, comparisons in terms test failure locations and estimated crack initiation sites are given.

This paper deals with the fatigue damage of the welded cantilever under a high-speed train subjected to wind-induced loading using a field test campaign and a CFD (Computational Fluid Dynamic) simulation. The results show that significant airflow pressure on the cantilever frames and the structural resonance are the main cause of the fatigue damage of welded joints. During long-term operation, the free end of the cantilever tends to vibrate undesirably, which affects the service life of the structure. Firstly, a finite element model with constant amplitude of wind pressure is created based on the current design specifications to assess the static and fatigue strength of the cantilever. The simulation results show that the structural strength meets the standard design requirements. However, the results of the field test show that the acceleration at the free end of the cantilever is 32.0 m/s2, which far exceeds the relevant requirements. Meanwhile, there is a significant difference in aerodynamic pressure on the frame surfaces between the leading and trailing cars. An aerodynamic model is created for two full-size cars with the CFD method. The results show that FIV (flow-induced vibration) is the main cause of the continuous vibration of the elastic cantilever frame as long as the wake shedding occurs at a frequency close to the natural frequency of the frame. This study provides a reference for the aerodynamic fatigue design of the equipment mounted high-speed trains, especially for structures with low stiffness affected by open airflow.

This research paper focuses on the fatigue analysis of load-carrying cruciform joints made up of thick plates, which are crucial components in ship structures. The study investigates the fatigue life of fillet welded cruciform joints using both 2D and 3D geometries. Various loading conditions and boundary conditions are considered, and an elastic-plastic finite element analysis is conducted using ABAQUS 2021. The number of cycles to failure is estimated using Fe-Safe and the strain-based Brown Miller Morrow model. The results, presented through contour plots, Log Life repeats, and Load Range vs. Number of Cycles graphs, reveal the fatigue behavior and failure locations. Additionally, the methodology is validated against experimental data from literature, demonstrating its applicability. The findings provide insights into the fatigue characteristics of load-carrying cruciform joints in thick plates, contributing to enhanced design and reliability in the shipbuilding industry.

Shipbuilding industry is a valuable and profit earning industry which plays a vital role in country’s economic development. Ships have crucial impact on country’s trade due to necessary support for maritime transportation. Moreover, ships can be utilized for protecting coastal area. Steel chiefly utilized for ships construction due to its good strength and durability. This study emphasizes on residual stress analysis of AH-36 shipbuilding steel. Abaqus software is utilized for finite element analysis to evaluate residual stresses. Mitigation of these residual stresses is very essential; hence preheating technique is discussed in this study. Preheating was conducted at three temperatures i.e., 100 C,150 C and 200 C. Results indicate that Von Mises stresses were decreased effectively due to preheating. 12.6%, 21% and 45.6% reduction were observed at preheating temperatures 100 C, 150 C and 200 C respectively. Further evaluation of stresses revealed that due to preheating of base plate, longitudinal stresses reduced to 21.3%, 44% and 52.4% by increasing preheating temperature from 100 C,150 C and 200 C, respectively. Mitigation of thermal gradient between weld zone and base plate resulted in reduction in overall stresses of base plate.

A new type of suspension component with dry friction damping has been developed. It consist of an Ωshaped spring wire which ends can slip in their mountings. By positioning these components under 90 o around the suspended object, the suspension functions in all six degrees of freedom. The suspension component will be modelled as a series connection of a spring with a coulomb damper, which in turn is in parallel with a second spring. This model will be analysed using Hamilton's equations of motion to deal with the non-linear phenomena. An experimental setup has been realized whereupon the suspension components are validated using hammer impulses. The observed response is an efficiently damped sinusoidal motion which turns into an undamped sinusoid with small amplitude. In the spectrum, the resonance has been limited in magnitude to 10 dB and the isolation characteristic remaines -40 dB/decade equivalent to the undamped spring.

airplane oil pressure reservoirs are major fuel supplying parts of airplanes to have flight maneuvers. Since they are always working under alternating loadings, they are prone to produce fatigue fractures. Therefore, they will undergo vibration endurance tests in general. And the fixed-frequency vibration endurance test is commonly used in engineering. This paper has established a finite element model for the vibration test system, taken into consideration the influence of liquid fuel and introduced the fluid-solid coupling method to conduct harmonic response analysis on different excitation conditions with MSC.Nastran, thus obtaining the stress distribution under different loading conditions. Moreover, the results have been compared with the test results to verify correctness of the method, thus providing references for the improvement in structural design.

Several standard fatigue testing methods are used to determine the fatigue stress-life prediction model (S-N curve) and the endurance limit of Reinforced Concrete (RC) beams, including the application of constant cyclic tension-tension loads at different stress or strain ranges. The standard fatigue testing methods are time-consuming and expensive to perform, as a large number of specimens is needed to obtain valid results. The purpose of this paper is to examine a fatigue stress-life predication model of RC beams that are developed with an accelerated fatigue approach. This approach is based on the hypothesis of linear accumulative damage of the Palmgren–Miner rule, whereby the applied cyclic load range is linearly increased with respect to the number of cycles until the specimen fails. A three-dimensional RC beam was modeled and validated using ANSYS software. Numerical simulations were performed for the RC beam under linearly increased cyclic loading with different initial loadin...

Objectives: This study was focused on the finite element techniques to investigate the effect of surface treatment on the fatigue life of the vibrating cylinder block for new two-stroke free piston engine using random loading conditions. Motivation: An understanding of the effects related to the random loading is necessary to improve the ability of designers to accurately predict the fatigue behavior of the components in service. An internal combustion engine cylinder block is a high volume production component subjected to random loading. Problem statement: Proper optimization of this component that is critical to the engine fuel efficiency and more robustly pursued by the automotive industry in recent years. A detailed understanding of the applied loads and resulting stresses under inservice conditions is demanded. Approach: The finite element modeling and analysis were performed utilizing the computer aided design and finite element analysis codes respectively. In addition, the fatigue life prediction was carried out using finite element based fatigue analysis code. Aluminum alloys were considered as typical materials in this study. Results: The frequency response approach was applied to predict the fatigue life of cylinder block using different load histories. Based on the finite element results, it was observed that the fatigue life was significantly influenced for the nitriding treatment. The obtained results were indicated that the nitrided treatment produces longest life for all loading conditions. Conclusion: The nitriding process is one of the promising surface treatments to increase the fatigue life for aluminum alloys linear engine cylinder block.

Vibration fatigue tests and analysis for flip chip solder joint reliability assessments were investigated. Dynamic characterizations of flip chip on board (FCOB) assemblies were evaluated using accelerometer and high speed camera measurements during vibration tests. A vibration fatigue test and analysis methodology for flip chip solder joint fatigue life prediction have been developed. Out-of-plane vibration fatigue tests were investigated for constant G-level tests at 3'3, 5G and 10G respectively. A sinusoidal sweep test within a narrow band near the fundamental resonant frequency was used. Solder joint failure detection was made by daisy chained resistance monitoring during the test. A plot of G-level versus mean time to failure (MTTF) was developed, A varying G-level vibration test with 3G, 5G and 1OG blocks arranged in ascending sequence was conducted for cumulative fatigue damage assessment study. The linear cumulative damage analysis method (Miner's rule) predicted non-conservative results for vibration fatigue failures in the flip chip solder joints. Finite element analysis (FEA) using a global-local beam modeling method was used to compute the fundamental natural frequency result compared to experimental data. A quasi-static analysis method was developed to model the effect of flip chip location on solder joint fatigue life. plate because the increase in stiffness of PWB due to the mounting of the components is approximately offset by the increase in total mass the populated PWB [3]. But this approximation can lead to different errors for different packages, such as BGA, FCOB, and QFP etc. When the surface mount component is small, such as a FCOB, the approximation can yield accurate results. In this study, modal analyses using different models were performed. Two-level global-local modeling approach, which has been used by many researchers [4-6] can lead to accurate results compared to test results. The analyses by Basaran [7, 81, Chandaroy [9] and Zhao et al [IO] show that solder joints respond elastically mainly at room temperature vibration loading. The quasi-static analysis was conducted for FCOB assembly to calculate the stress strain for flip chip solder joints. 2. Vibration Test Test vehicle and setup: Flip chip is suitable interconnect technology for high W O and performance microelectronics devices. Flip chip packaging can cater to the increasing demands on miniaturization, high density of W O channels, high performance, high reliability. So in this study, flip chip on board (FCOB) assembly was selected for vibration test to analyze the dynamic response of the FCOB to sinusoidal vibration. The specimen and chip number is shown in Fig. 1.

Vibration fatigue test and analysis methodology for flip chip solder joint fatigue life assessment have been developed by performing vibration tests with constant G-level and varying G-level input excitation. The linear cumulative damage analysis method (Miner's rule) predicts non-conservative result for vibration fatigue life of flip chip solder joint. Finite element analysis (FEA) using a global-local-beam modeling method was used to calculate the natural frequency and were compared to experimental data. A quasistatic finite element analysis method was developed to investigate solder joint stress strain behavior for solder joint vibration fatigue life prediction. Harmonic finite element analysis was also carried out to predict solder joint fatigue life. Results from quasi-static analysis and harmonic analysis were compared. Based on Miner's rule and stress amplitude results from FEA results, different assumed cumulative damage index (CDI) factors were investigated in fatigue life prediction.

ABSTRACTIn the present paper a non‐local stress approach for fatigue assessment based on weakest‐link theory and statistics of extremes is presented. It is a non‐local stress approach in the sense that it takes the complete stress field into account rather than just the highest local stress. The statistical distribution of fatigue strength data from smooth standard specimens serves as a starting point for the computation of the probability of fatigue failure of a mechanical component under cyclic loading. The probability of fatigue failure can be obtained by post‐processing results from a standard finite element stress analysis. It is shown that the non‐local stress approach can be linked to the probability of finding the fatigue critical defect in the most highly stressed volume of the component. A numerical procedure is presented that is fully compatible with the results from a standard finite element stress analysis. It is further shown how the fatigue strength distribution can b...

In vibration fatigue the frequency contents of dynamic loading and structure's dynamic response overlap, resulting in amplified stress loads of the structure. Time domain fatigue approach does not give a good insight into the underlying mechanics of failure and therefore recently vibration fatigue in frequency domain is getting a lot of scientific attention. Gaussianity and stationarity assumptions are applied in frequency-domain methods for obtaining dynamic structure's response and frequency-domain methods for calculating damage accumulation rate. However, in application, the structures are excited with non-Gaussian and non-stationary loads and this study addresses the effects of such dynamic excitation to experimental time-to-failure of a structure. The influence of non-Gaussian, but stationary excitation, is experimentally studied via excitation signals with equal power density spectrum and different values of kurtosis. The non-Gaussianity was found not to significantly change the structure's time-to-failure and therefore, the study focuses on the non-stationary excitation signals that are also inherently non-Gaussian. The non-stationarity of excitation was achieved by amplitude modulation and significantly shorter times-to-failure were observed when compared to experiments with stationary non-Gaussian excitation. Additionally, the structure's time-to-failure varied with the rate of the amplitude modulation. To oversee this phenomenon the presented study proposes a non-stationarity index which can be obtained from the excitation time history. The nonstationarity index was experimentally confirmed as a reliable estimator for severity of non-stationary excitation. The nonstationarity index is used to determine if the frequency-domain methods can safely be applied for time-to-failure calculation.

Even if in fatigue application it is common to assume stationary and Gaussian excitation, the impact of non-Gaussian and non-stationary loadings on the service life of a mechanical component is known. Non-Gaussian and non-stationary excitations are generally observed in several industrial applications (i.e. automotive, aeronautical, etc.) and for this, the assessment of the effect of such loads results necessary. From this assumption, the activity herein presented starts from experimental results, previously obtained, that analysed the influence of non-Gaussianity (generally evaluated by kurtosis) and of non-stationarity of inputs on the fatigue life of an Y-shaped specimen. In the present paper the finite element model of the sample and its full validation obtained by numerical/experimental comparison is presented. Moreover, due to the relevant effect of the system's dynamics on the stress/strain response previously observed, a wider assessment of non-Gaussianity and non-stationarity influence on the fatigue life has been numerically analysed together with the influence of the multi modal behaviour of the component by adopting an excitation frequency range that excites two modes of the model.

The Composite plate is taken as a fuselage of Boeing 787 passenger aircraft. The fuselage of any passenger aircraft is considered as a shell with a large radius of curvature and having multiple openings like doors and windows. The presence of such cutouts in the shell structure causes perturbations in the original stress system, resulting in an increase in the local stress levels. Almost all the major failures during the service of an aircraft occur due to initiation of cracks in the region of maximum stress. Thus, Study and evaluation of maximum stress concentration is vital. Various methods are presented in the literature to find Stress Concentrations around various geometries, but for Rectangular cut outs with Circular radius in an Anisotropic Plate. The report deals with the stresses and stress concentration phenomenon around the doors and windows of Boeing 787TM aircraft. As the diameter of fuselage is very large compared to the dimensions of doors and windows, the problem have been modelled as an Infinite Plane with Multiple Openings under Biaxial Loading. The Analytical solution of the stress concentrations is found by Finite Element Analysis using ANSYS.

This paper presents a sequential approach used in fatigue life prediction of a low pressure steam turbine blade during resonance conditions encountered during a turbine start-up by incorporating probabilistic principles. Material fatigue properties are determined through experimental testing of used blade material X22CrMoV12-1 along with statistical modelling using regression analysis to interpret the stress-life diagram. A finite element model of a freestanding LP blade is developed using the principle of sub-structuring which enables the vibration characteristics and transient stress response of the blade to be determined for variations in blade damping. Random curve fitting routines are performed on the fatigue and FEM stress data to ensure that the selection of the random variables used in fatigue life calculations is stochastic in nature. The random vectors are selected from a multivariate normal distribution. The use of confidence intervals in the probabilistic fatigue life model works effectively in being able to account for uncertainty in the material fatigue strength parameters and varying stress in the blade root. The predicted fatigue life of the blade is shown to be in good agreement with discrete life modelling results.

The electronic equipment are used in several fields like, automotive, aerospace, consumer goods where they are subjected to vibration loads leading to failure of solder joints used in these equipment. This paper presents a methodology to predict the fatigue life of Pb-free surface mounted BGA packages subjected to random vibrations. The dynamic characteristics of the PCB, such as the natural frequencies, mode shapes and damping ratios were determined. Spectrum analysis was used to determine the stress response of the critical solder joint and the cumulative fatigue damage accumulated by the solder joint for a specific duration was determined.

The fatigue limit of materials, due to the improvement of fatigue life of structures and mechanical components should be extended from the traditional 10 6-10 7 cycles up to 10 9 and more, but with traditional testing hardware this is a difficult technical task due to the length of time needed for the completion of tests. Ultrasonic fatigue testing machines seem to be adequate for very high cycle fatigue (VHCF) tests. We propose here to evaluate the behavior of the hysteretic damping in an attempt to associate that with damage parameter. The approach here presented is based on the fact that the fatigue issue can be understood in terms of the energy available for irreversible process triggering. This nonconservative energy will be involved in micro-structural changes in the material before being dissipated as thermal energy. In fact, the balance between the energy supplied to and returned by the material is positive and the hysteretic damping factor represents the inelastic fraction of energy in each cycle. Aiming at building a model to correlate the hysteretic cycle parameters and the fatigue process, both energy loss and material response of the specimens are measured during the fatigue test. The fatigue tests are carried out with an ultrasonic machine test, operated at 20 kHz with amplitude or temperature control, under HCF and VHCF for copper specimens. The results show the behavior of hysteretic damping parameter during fatigue life, the equivalent dissipated energy per cycle and a good correlation between the hysteretic damping factor parameter and the fatigue process S-N curve, suggesting that factor as a promising fatigue life parameter useful for some cases of fatigue life prediction.

Deck is a super structural element of a bridge and is considered as the most susceptible element of a bridge. The main problem in the highway system is its Bridge deck deterioration. The Use of advanced material for bridge deck system is a long-term solution for the deterioration problem for decks made up of concrete. Here a bridge deck with polyurethane core is considered.