Vibration and Fatigue Analysis

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.

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 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.

The present work concerns solving Noise, Vibration and Harshness (NVH) and fatigue based on Power Spectrum Density (PSD) analysis of a landing gear's leg for an Un-Manned Aerial Vehicle (UAV). This analysis includes random vibration and high-cycle fatigue analysis in a random vibration environment. In this analysis, the cumulative damage ratio is computed using material S-N (Stress-Number of cycles) fatigue curve. Dirlik method is used for the analysis of lifetime as it is proven to provide accurate results for large number of applications, both in automotive and aerospace industry. It is also compared to other methods that have been developed in LS-DYNA ® as well. The input acceleration PSD data are provided through measurements. The obtained analysis results shows that although the landing gear design is safe according to dynamic and static load, its service life is about 3037 hours due to random vibration effect.

Vibration fatigue characteristics are critical for rotating machinery components such as turbine rotor blades. Lattice structures are gaining popularity in engineering applications due to their unique ability to reduce weight and improve the mechanical properties. This study is an experimental investigation of octet-truss lattice structure utilization in turbine rotor blades for weight reduction and to improve vibration fatigue characteristics. One completely solid and three lattice infilled blades with variable strut thickness were manufactured via additive manufacturing. Both free and forced experimental vibration analyses were performed on the blades to investigate their modal and vibration fatigue characteristics. The blades were subjected to random vibration using a vibration shaker. The response was measured using a triaxial accelerometer in terms of vibration acceleration time histories in the X, Y, and Z directions. Results indicate a weight reduction of up to 24.91% and enh...

Connecting rod act as an intermediate link between piston and crank. The push and pull from the piston pin to crank pin is carried out by connecting rod which results in the change of motion of the reciprocating piston to rotary motion of the crank. The work focus on experimental investigation of connecting rod for Pulsar 220 with development in existing design. In this work the attempt is to modify the existing design of connecting rod by satisfying the desired design and application constraint. The parameter of existing connecting rod like von misses stress, shear stress, total deformation is obtained from ANSYS software. In addition this work aims to carry out the test on UTM to find deflection and stress by satisfying the desired constraint. The hardness is determined along with the chemical composition of different elements. Modification of existing connecting rod is carried out. Different geometries are verified & optimum geometry is selected which is tested experimentally & c...

Additive manufactured structures are replacing the corresponding ones realized with classical manufacturing technique. As for metallic structures, 3D printed components are generally subjected to dynamic loading conditions which can lead to fatigue failure. In this context, it is useful, and sometimes mandatory, to determine the fatigue life of such components through numerical simulation. The methods currently available in literature for the estimation of fatigue life were originally developed for metallic structures and, therefore, it is now necessary to verify their applicability also for components fabricated with different materials. To this end, in the current activity three of the most used spectral methods for the estimation of fatigue life were used to determine the fatigue life of a 3D printed Y-shaped specimen realized in polylactic acid subjected to random loads with the aim of determining their adaptability also for this kind of materials. To certify the accuracy of the...

Fatigue assessment based on the critical plane approach is generally accepted to be more accurate for multiaxial non-proportional loading. Among different critical plane fatigue criteria, the modified Carpinteri-Spagnoli (C-S) criterion is rather a simple approach in which the critical plane orientation can be determined a priori. The aim of this paper is to investigate the applicability and reliability of the critical plane approach-based C-S criterion that can be employed to calculate the fatigue damage of bridge connections under railway traffic loading. A typical half through steel bridge subjected to railway traffic is analysed using Finite Element Modelling in ANSYS 17.2. The averaged principal stress directions determined through appropriate weight functions are used to predict the critical plane orientation. Then, the multiaxial fatigue damage is assessed through an equivalent stress expressed by a nonlinear combination of the normal and the shear stress components acting on the critical plane. Applicability of the C-S criterion is investigated by estimating the fatigue damage of critical welded connections and is compared with the fatigue damage computed according to Eurocode EN1993-1-9 under both constant and variable amplitude loading.

When we look at the fatigue reliability of a structure, its dynamic response will be closely related to the sensitivity to material properties both in terms of crack propagation and limit state. In this paper, we have identified 2 types of response spectra for hydroelectric turbines. The type 1 spectrum is simpler and was the first encountered. The type 2 spectrum is more complex and contains more Low Cycle Fatigue (LCF) stress cycles compare to type 1. Hence, reliability decreases faster for similar parameters values. For each spectrum, 3 scenarios have been identified. In this paper, we first present the simple typical response spectra expected, the reliability model and its relation to life expectancy with regards for High Cycle Fatigue (HCF). Next, we propose families of response spectra based on the observed data from in situ measurements. This is followed by a discussion on the sensitivity to material properties. Finally, we suggest specific guidelines and recommendations. We believe that a better knowledge of the structure response spectra with respect to fatigue reliability will help turbine operators and manufacturers to maximize the overall reliability of their equipment.

This paper present the result of whole-body vibration (WBV) of the Malaysian drivers driving a car through different road conditions; straight, winding, uphill, and downhill) at constant speed (80km/h). The objective of this study is to study the effect of the WBV towards the driving fatigue. Besides, the regression modeling of WBV for drivers' fatigue was developed. There were ten healthy and experienced drivers served as the subjects of this study. The WBV measurement was taken and evaluated using the tri-axial seat pad accelerometer and 4-channel VI-400PRO Human Vibration Meter (HVM). Design Expert 8.0.6 software was used for the development of regression model. This study is expected to analyze the WBV, and develop the regression model of the WBV by using regression analysis. The result of this study indicates that the subjects recorded the vibration values that show they feel fairly uncomfortable as it in the caution zone. The vibration exposure can cause the changes in body chemistry and metabolism, which can lead to fatigue effects. Besides, the regression model was successfully developed and validated, which the validation runs were within the 90% prediction interval of the developed model and the residual errors compared to the predicted values were less than 10%. Through this study, the significant parameters that influenced the WBV were also identified. WBV was influenced by the time exposure, type of road, gender, the interaction between time exposure and type of road, and interaction between time exposure and gender. Thus, the author believes there is a new contribution to the body of knowledge throughout this study.

A mechanical system's modal parameters change when fatigue loading is applied to the system. In order to perform an accelerated vibration-based fatigue test these changes must be taken into account in order to maintain constant-stress loading. This paper presents an improved accelerated fatigue-testing methodology based on the dynamic response of the test specimen to the harmonic excitation in the near-resonant area with simultaneous monitoring of the modal parameters. The measurements of the phase angle and the stress amplitude in the fatigue zone are used for the real-time adjustment of the excitation signal according to the changes in the specimen's modal parameters. The presented methodology ensures a constant load level throughout the fatigue process until the final failure occurs. With the proposed testing methodology it is possible to obtain a S-N point of the Woehler curve relatively quickly and to simultaneously monitor the changes

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.

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.

A mechanical system's modal parameters change when fatigue loading is applied to the system. In order to perform an accelerated vibration-based fatigue test these changes must be taken into account in order to maintain constant-stress loading. This paper presents an improved accelerated fatigue-testing methodology based on the dynamic response of the test specimen to the harmonic excitation in the near-resonant area with simultaneous monitoring of the modal parameters. The measurements of the phase angle and the stress amplitude in the fatigue zone are used for the real-time adjustment of the excitation signal according to the changes in the specimen's modal parameters. The presented methodology ensures a constant load level throughout the fatigue process until the final failure occurs. With the proposed testing methodology it is possible to obtain a S-N point of the Woehler curve relatively quickly and to simultaneously monitor the changes

A stress-state dependent traction-separation law is combined with an irreversible damage parameter to formulate a cohesive model relevant for life assessment under complex stress-states. Evolution of damage is based on continuum damage laws requiring two cohesive fatigue parameters. For two representative metals, model is able to reproduce typical stress-life response, mean stress effects and sequencing effects under variable amplitude loads. Control of cohesive fatigue parameters on characteristics of the stress-life curve is established, followed by predictions for proportional, cyclic stress-states. With increasing constraint, initiation and growth of damage is more rapid such that higher constraint results in lower life expectancy.

This research aims to investigate the effects of vibration amplitude in vibratory stress relief (VSR) on the fatigue strength of structures with residual stress. Experiments are carried out on specimens with residual stress generated by local heating. Flat specimens made of A36 steel are prepared to be suitable for setting up fatigue bending tests on a vibrating table. Several groups of samples are subjected to VSR at resonant frequencies with different acceleration amplitudes. The results show that VSR has an important influence on the residual stress and fatigue limit of steel specimens. The maximum residual stress in the samples is reduced about 73% when the amplitude of vibration acceleration is 57 m/s 2. The VSR method can also improve the fatigue limit by up to 14% for steel samples with residual stress.

The connecting rod is the intermediary member between the piston and the crankshaft. Its prime purpose is to transmit the reciprocating motion from the piston pin into rotary motion of the crankshaft. This paper exemplifies designing and Analysis of connecting rod of a marine engine using titanium alloy (grade 5). Presently existing connecting rod is manufactured by using Cast iron. Finite element analysis of connecting rod is done by considering the same material. The finest blend of analytical parameters like Stress and strain in each direction, Deformation and Factor of safety for marine diesel engine are done in ANSYS software. Also inertial forces at various angles and time are analyzed using the same software. Titanium alloy (grade 5) has more hardness and tensile strength. Due to low density it is lighter than cast iron. Because of less thermal conductivity it is less harmful to the crankshaft. Titanium alloy is corrosion resistant and it is better for marine use. A parametri...

The drag which exists due to interaction of wing-fuselage section is called as Interference drag. High interference drag may lead to Fatigue which is progressive a failure mechanism and material degradation. The degradation or damage accumulation progresses until a finite crack is nucleated. The objective is to design a Fail-Safe Structural component and do the stress analysis and introducing carbon nano tubes in the structure for the self-healing process which is the modern technique to detect and heal the cracks. We have designed a Wing-Bracket attachment and done the analysis of wing-fuselage interaction using Ansys. We have represented Goodman diagram for Maraging steel and explained the methodology of Selfhealing technique .The flow over the wing is accelerated such that aerodynamic interference between the wing and fuselage is critical in transonic flight regime, which may leads to structural failure

In this work, a computational framework is proposed for fatigue damage estimation in structural systems by integrating operational experimental measurements in a high-fidelity, large-scale finite element model. The proposed method is applied in a linear steel substructure of a lignite grinder assembly at a Public Power Corporation power plant. A finite element model of the steel base is developed and updated to match the dynamic characteristics measured in real operating conditions. This is achieved through coupled use of numerical and experimental methods for identifying, updating, and optimizing a high-fidelity finite element model. The full stress time histories of the complex mechanical assembly are estimated, at critical locations, by imposing operational vibration measurements from a limited number of sensors in the updated finite element model. Fatigue damage and remaining lifetime is subsequently estimated via commonly adopted engineering approaches, such as Palmgren-Miner damage rule, S-N curves, and rainflow cycle counting. Incorporation of a numerical model of the structure in the response estimation procedure permits stress estimation at unmeasured locations, thereby enabling the drawing of a complete and substantially dense fatigue map consistent with the vibration measurements. Fatigue predictions via the proposed framework are highly correlated to experimental fatigue results, proving the efficiency and applicability of the framework.

Classical fatigue limit prediction models and material-dependent characteristic length parameters for notched components are critically reviewed before a modified stress gradient based approach is proposed to integrate the non-propagation behavior of microstructurally small crack. Assuming fatigue limit (strength) as a general function of root surface stress and stress gradient defined over a characteristic length, an effective stress parameter is derived to characterize the resistance of a notch to fatigue limit (high cycle fatigue) loading. The model is validated by comparing with reviewed models through a large amount of test data. Physical interpretation and perspectives on the model are also discussed.

Many structures are subjected to random vibrations and those vibrations can cause a fatigue damage. So, to estimate the live time of the structure, we need to applied the fatigue multiaxial criteria at each point. Many studies demonstrate that the Sines criterion seems to give the best evaluation of the fatigue damage. But the application of this criterion need a high computing time if it's evaluated in the time domain. In this paper, we present a new methodology of calculation of the Local multiaxial fatigue damage, based on the formulation of the Sines criterion developed in the frequency domain. Each parameter of the Sines criterion will be calculated from the Power Spectral Densities of the stresses at each point of the structure. A finite element example is then used, at the end of this paper, to illustrate the application of the proposed strategy of calculation of the fatigue damage.

This study aims to assess the mechanical and thermal characteristics of epoxy/aluminum and unsaturated polyester/aluminum composite systems, using the formulations (1-x) EP + (x) Al microparticles and (1-x) UP + (x) Al microparticles, where x equals 0.00, 0.01, 0.03, and 0.05 wt%. Test specimens were created using an open mold-type die, and their impact strength, hardness, and thermal conductivity were experimentally examined. According to the results, epoxy/aluminum composites achieved their highest impact strength (15.63 KJ/m2) at 0.05 wt%, while the unsaturated polyester/aluminum composites achieved their highest impact strength (8.03 KJ/m2) at the same weight percentage. Moreover, the epoxy/aluminum composites exhibited superior impact strength compared to the unsaturated polyester/aluminum composites at the 0.05 wt% ratio.In terms of hardness, the epoxy/aluminum composites reached the highest Shore D value (78.6 H.NO.) at 0.05 wt%. On the other hand, the unsaturated polyester/aluminum composites displayed higher Shore D values (88.03 H.NO.) in the laboratory, with the 88.03 value being the highest for this type of composite, compared to 78.6 for the epoxy variant. La stly, the thermal conductivity (K) value increased in both epoxy/aluminum and unsaturated polyester/aluminum composites as the proportion of added aluminum powder grew.

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...

Fatigue damage is a type of damage usually occurring to repeatedly loaded elements of structures in various engineering fields. Accumulation of fatigue damage may cause failure of structural elements. Identification of incipient fatigue damage is essential to ensure safety of structures. Fatigue crack under repeated loads commonly behaves in a nonlinear dynamic manner, typically manifested by both occurrence of higher harmonic components and interaction of harmonic components. Interrogation of nonlinear dynamic manner provides a promising way to characterize structural fatigue damage. This study aims at developing a new method to interrogate nonlinear dynamic manner for fatigue damage identification. This method is based on bispectral analysis of structural vibrational responses. This method portrays fatigue damage by inspecting the presence of higher harmonic components and quantifying the interaction of these harmonic components. The method can precisely locate and quantify a smal...

Filament Wound structures are a kind of FRP composites that are being extensively used in many engineering fields because of their inherent advantages. This work involves the manufacturing technology viz. the filament winding technique to fabricate composite tubes. A step by step procedure of the fabrication process of tube is explained. The effectiveness of the FRP cylinders is evaluated by filling the E-Glass fibres in different orientation angle. The experimental results show that the cylinders having angle closer to the axial direction of the cylinder carrying more load capacity in comparison to normal FRP tubes. The Filament wound structures are able to effectively confine the fibres, thereby increasing their strength. To validate the results obtained from the experiments a 3-D finite element model of the filament wound tube was developed using NASTRAN in Unigraphics software. The nonlinear behaviour of the materials used in the experiments was incorporated into the FEA model by considering the appropriate stress-strain relationships. The behaviour of the confined composite cylinder was modelled using a Von-Mises stress criterion.are already defined on the style sheet, as illustrated by the portions given in this document.

A study of the Young's modulus as a function of the volumetric filler content in an epoxy matrix was carried out. To this aim, composites were prepared adding to the resin matrix particles of aluminum, copper and quartz with typical sizes of about 100 m. To measure values of the Young's modulus, an experimental setup based on the impulse excitation technique was developed. The results obtained are discussed in terms of two well-known micromechanical models: one based on the Hashin-Shtrikman relationships and in the other one the Kerner equation was used. The analysis of the information obtained for the three different types of filler used allow concluding that the Kerner equation describes correctly the Young's modulus behaviour as a function of filler content. From the fitting procedure of the experimental data, additional information regarding the Young's modulus was obtained.

Fatigue experiments are very important for the study of structural fatigue damage. As we all know, fatigue experiments usually consume a lot of resources and time, slowing down the research progress. The Locati method, which is applied to the frequency domain analysis method of random vibration fatigue, replaces the traditional up-down method and accelerates the progress of the fatigue experiment. This method can effectively improve efficiency and reduce test time and test piece consumption under the premise of ensuring accuracy. It is based on the material S-N curve, after one step-load fatigue test, combined with the FEM, the cumulative damage of the structure under random vibration load is quickly determined, and the life analysis is completed. The specimen was made by AISI304 and designed to make the fatigue damage of the second-order bending mode more significant. The random vibration acceleration defined by the Power Spectral Density method is used as a load and applied on the specimens through the shaker. In this process, the material properties of the structure will be optimally fitted according to the experimental results, so that the finite element model is as close as possible to the real structure for fatigue calculation. Finally, an experiment will be used to verify the accuracy of this method. The method has now been validated under Gaussian distributed signals.

This note reviews means for fatigue damage rates estimation using scaled Laplace distributed loads. The model is suitable for description of stresses containing transients of random amplitudes and locations. Moment method to estimate model parameters is given. Explicit formulas to compute rainflow damage rate as a function of excess kurtosis is presented. Laplace model is used to describe variability of forces measured at some location on a cultivator frame is presented. Validation of the model and uncertainty analysis in fatigue damage predictions is given.

A novel framework is proposed for estimating damage accumulation due to fatigue in the entire body of a metallic structure using vibration measurements from a limited number of sensors. Fatigue is estimated using Palmgren-Miner damage rule, S-N curves, rainflow cycle counting of the variable amplitude time histories of the stress components, or frequency domain stochastic fatigue methods based on PSD of the stress components. These methods can be applied to any point in the structure and construct the complete fatigue map of the entire structure, provided that the stress response characteristics (time histories or PSDs) at all desirable points are available. These stress response characteristics are predicted from limited number of vibration sensors using a high fidelity finite element model and different prediction methods, including Kalman filter type techniques, kriging approximations and modal expansion methods. The effectiveness of the proposed methods is demonstrated using simulated data from a chain-like spring-mass model and a small-scale model of a vehicle structure. The proposed framework can be used to construct fatigue damage accumulation and lifetime prediction maps consistent with the actual operational conditions provided by a monitoring system. These maps are useful for designing optimal fatigue-based maintenance strategies for metallic structures taking into account all uncertainties in modeling and fatigue predictions.

A study is undertaken to develop a methodology for determining the suitability of various high-cycle fatigue models for metallic structures subjected to combined thermal-acoustic loadings. Two features of this problem differentiate it from the fatigue of structures subject to acoustic loading alone. Potentially large mean stresses associated with the thermally preand post-buckled states require models capable of handling those conditions. Snap-through motion between multiple post-buckled equilibrium positions introduces very high alternating stress. The thermal-acoustic time history response of a clamped aluminum beam structure with geometric and material nonlinearities is determined via numerical simulation. A cumulative damage model is employed using a rainflow cycle counting scheme and fatigue estimates are made for 2024-T3 aluminum using various non-zero mean fatigue models, including Walker, Morrow, Morrow with true fracture strength, and MMPDS. A baseline zero-mean model is additionally considered. It is shown that for this material, the Walker model produces the most conservative fatigue estimates when the stress response has a tensile mean introduced by geometric nonlinearity, but remains in the linear elastic range. However, when the loading level is sufficiently high to produce plasticity, the response becomes more fully reversed and the baseline, Morrow, and Morrow with true fracture strength models produce the most conservative fatigue estimates.

Random fatigue analysis techniques have concentrated on linear structures that exhibit symmetric stress range probability density functions (PDF). In narrowband response and broadband random response it is assumed that the bending stress range PDF is symmetric and has zero mean stress. Structures that can exhibit geometrical nonlinearity, under large deflections, typically introduce membrane effects, which are additional positive tensile stresses that tend to skew the stress range PDF. This paper investigates fatigue analysis approaches that include mean stress effects and show how they can be applied to nonlinear random vibration problems.

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.