Vibration and Fatigue Analysis

In an IC engine, the most heavily stressed part is connecting rod. Its functionality is connecting crankshaft and piston, which transfer energy from piston to crankshaft and converts linear piston reciprocating motion into crankshaft rotational motion. Under the engine cyclic process, the connecting rod is subjected to tensile and compressive loading. The main forces occurred on the connecting rod are forces due to maximum gas pressure and the inertia of connecting rod plus reciprocating masses. The connecting rod must have maximum stiffness at the minimal weight. This research work is focused on modeling and analysis of connecting rod stress, deformation, fatigue strength, and life prediction for Toyota Hilux diesel engine made by four candidate materials (aluminum alloy 7068T6, aluminum alloy 7050 T765, carbon steel C-40 and forged steel 4340). The connecting rod model was done by CATIA V5R20 and Numerical prediction of the desired parameters has been evaluated by considering the ...

Hydraulic Structures are subject to varying loads of more or less cyclic character. These loads are primarily generated by differential water heads on, e.g., navigation lock gates, but also by waves, drive system forces and other actions. As a result, the designers must take account of an additional failure mode of these structures – the failure by fatigue.
The author was an initiator of a PIANC international Working Group in this field that recently published its report. To introduce this report to the engineering community, the ICE and British Section of PIANC organised a Seminar that also included the author's presentation. This document contains a PDF of that presentation.

Epoxy resin composites are frequently applied in moulds manufactured with rapid tooling technologies, because of their low shrinkage and easy mouldability. Various percentages of Aluminum particles added with Epoxy resin by weight are formed to dog-bone shaped specimens according to ASTM standards to determine fatigue strength and cylindrical shaped specimens to determine thermal conductivity. Micro-structural analysis is carried out to investigate the distribution of Aluminum particles in the composite. Mechanical properties are characterized in terms of Rockwell hardness and Fatigue test. Thermal conductivity, a critical parameter is determined for good service performance and durability of mould. Proportion of Aluminum and Epoxy resin for which the hardness, fatigue life, thermal conductivity of the composite holds well is determined for better mouldability. A Finite Element analysis is also performed to study the Fatigue behaviour.

Este artículo describe el análisis de falla realizado en dos muestras de cables de acero que sufrieron falla súbita bajo condiciones de carga de trabajo normales. La falla fue causada por una carga menor a la capacidad nominal. Luego de inspección óptica se evidenció que la falla fue ocasionada por fatiga del material de uno de los cables.

MSC: 81.70.Bt

The existing motorcycle helmets are thermally uncomfortable as there is no provision for air flow inside the helmet. A new design of helmet, with grooves in the liner foam and slot in the outer shell and liner foam to improve the ventilation, is proposed. Computational fluid dynamics studies show considerable improvement in air velocities inside the helmet in the presence of grooves and slot. Impact dynamics and biomechanics studies on various motorcycle helmets with deformable and rigid head show that the proposed design meets the requirements of the standards in the drop test. The optimum size of the groove and number of grooves for a motorcycle helmet are decided on the basis of the above studies.

This project deals with the fatigue analysis of aircraft composite fuselage,it will be designed to have optimal structural weight with the required safety margins. The structural stress, deflection, strain, and margins of safety distributions are to be visualized and the design is to be improved. The elasticity, stiffness, strength and stress distribution is more in the nodes of the structure. Where the fuselage frame is semimonocoque in construction holding former and skin.In the semi-monocoque structures where the skin carries the external loads, the internal fuselage pressurization and is strengthen using frames and stringers. When coming to the material section, the  Aluminum  alloy material are mostly used, but as metal designs have reached a high degree of perfection, extraordinary weight and cost savings are unlikely in the future. The carbon fiber composites have high strength to weight ratio when compared to aluminum alloy.  The fuselage structure of aircraft is modeled using CATIA software. The original model is imported to ANSYS and the fatigue analysis is carried out. The applicability of the proposed procedure was demonstrated. Based on finite element analyses.  The main objective analysis is importing composites in fuselage is merely considered applied and compared with aluminum. These comparison asses the weight reduction and fatigue life obtained with the use of composite materials for designing.

This paper "Fatigue Analysis and Design of Different Compressor Rotor Blade of an Orpheus Engine" is carried out in blade shop department, Engine Division, Compressor rotor blades are made up of aluminium and titanium based super alloys, is mounted on the rotor disc of compressor assembly unit. The purpose of compressor rotor is to raise the pressure of incoming air to have an efficient combustion in the combustion chamber to generate enough power to propel the aircraft. Moreover the Orpheus engine speed between 5000 to 7000 rpm is the critical rpm which is due to the 2 nd and 3 rd stage of rotors. It is therefore becomes mandatory to carry out fatigue testing on every production batch of indigenously developed forging of rotor-2 and rotor-3 blade before fitment on to the engine. Presently the rate of rejection during fatigue testing is up to 70%. The proposed paper is an attempt to reduce the rejection rate of compressor rotor blades stage-2 and 3 comparing the results through structural analysis procedures may help us to provide suggestions for increasing the fatigue life of the rotor blades. As a result this paper comes up with recommendations to improve the fatigue life of blades by improving the surface finish of blade by introduction of manual

This paper presents the life estimation of the diffuser structure. Literature shows that the welds are the source of failure in case of welded structure; hence the estimation of its life is very critical. There are two kinds of methods for life estimation stress life approach and strain life approach which have been validated for simple problems. Stress life approach was identified as appropriate for life estimation of the variable diffuser. There are papers indicating the methodology for life estimation using commercial software for life prediction. Here, Optistruct-Hyper-Works for pre-processing and solver and Hyper-View-Hyper-Works for post processing has been used for the indeterminate structure, complex loading and boundary condition. The mathematical model subjected to the variable pressure contours for a particular Mach No., with the gimbal joint boundary condition at the test section end and the roller support at the other end. In this paper stress and fatigue analysis of the variable diffuser has been carried out and life of the variable diffuser has been estimated. Keywords —fatigue analysis; finite element method; fatigue life. I. INTRODUCTION Fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. Mechanical components and structures used in day today life contain notches and geometrical discontinuities in them. For example, shafts have keyways in them and pressure vessels contain openings for the operational requirements. These notches, holes, keyways produce stress concentrations in the structure. Notches and keyways can be the region where crack initiation takes place which leads to crack propagation and finally failure of the structure when the stresses higher than the nominal value. Therefore predicting fatigue strength of the component is relevant considering design and safety of the component. Hence fatigue crack initiation life can be estimated based on local stress-strain approach. Wind tunnel is used for aerodynamic flow simulation around the scaled models for force and moment measurements. Wind tunnel testing is indispensible in the design phase of any vehicle flying (subsonic to supersonic) for its aerodynamic characterisation. There are two types of wind tunnels open circuit and closed circuit wind tunnels. In open circuit tunnels the high pressure air stored in the reservoir is forced on to the model through a nozzle to get the required Mach no and then is let out to the atmosphere with the aid of a diffuser. Whereas in case of close circuit tunnel the high pressure compressed air is recalculated in a close circuit. Variable diffuser is one of the components in the wind tunnel circuit. The CSIR-NAL trisonic wind tunnel is more than 50 years old. The diffuser of the wind tunnel needs to be analyzed for fatigue life. The literature reviews show that the linear static analysis has to be carried out for the given loads and then wind tunnel runs are to be used for cyclic loading case for fatigue.

Crack in component if undetected may lead to catastrophic failure of the component. The
cracked rotor problem received the first attention in 1970 and after that the interest among the
researchers started. The vibration behavior of cracked structures, in particular cracked rotors, is
important to study as the introduction of the crack alters the vibration characteristics of the structure.
The problem of damage and crack detection in structural components has acquired important role in past
few years. However, cracked rotor studies are mainly deals with single crack. For multiple cracked
structures the problem of crack sizing and location becomes more complex. Only few authors have
pointed out the multiple crack assessment in the rotor. The proposed work is on vibration analysis of
multiple cracked shaft beam. An Euler Bernoulli beam fixed at one end with two transverse cracks is
considered. The vibration characteristics of the shaft are studied using Experimental Modal Analysis and
Finite Element Analysis. The mode shapes and natural frequencies of the beams are studied and their
variation with change in position and depth of the crack is also studied. The study shows good agreement
of the results obtained using Finite Element Analysis and Experimental Modal Analysis.

Fatigue is an important design consideration for tall steel structures. Accurate prediction of fatigue endurance is essential to design the elements subjected to wind and earthquake induced fatigue. The design guidelines given in codes of practices are applicable only to simple shapes and laboratory experimental verification is costly. Therefore, simulation using finite element software is becoming popular. An attempt is made to couple Abaqus finite element analysis software and fe-safe software to estimate the fatigue life of a structure. First, the accuracy of the techniques and idealizations used in simulations validated by simulating experiments available in the literature. Standard Uni-Axialfatigue experiments which were conducted at several strain amplitudes showed a closer relationship to simulation results. Moreoversensitivity of fatigue life to surface finish and stress strain dataset importing method in fe-safe software were evaluated. It was found that the surface finish is a highly sensitive parameter and it should be estimated accurately. Elastic plastic block method gave good results while elastic block method with Neuter’s rule gave poor results. This indicates the importance of using elastic plastic block method for low cycle fatigue especially when stress redistribution is high. Simulation result of multi-axial fatigue experiment showed similar results to the results obtained from the physical experiments. The verified technique was then applied to estimate the fatigue life of a 64m tall steel mast with an opening located at the top of a 285m tall concrete tower. The sensitivity of the plate thickness and shape of the opening of the mast were studied. It was found that a small increase in plate thickness rapidly increases the fatigue endurance. This shows the importance of using stiffeners in fatigue prone areas. Comparison of the shape of the opening showed that square shape would have higher endurance thana circular shape* of the same opening area. However only monolithic sections were studied here and effects on welds and bolted connections are beyond the scope of this research. *Follow-up note: further research with finer FE mesh found that circular shapes have higher endurance than rectangular shapes. See Kariyawasam K. and Mallikarachchi C. Estimation of fatigue lives of steel masts using Finite Element Modelling. Int. Conf. Struct. Eng., SSESL; 2015, doi:10.13140/RG.2.1.2992.5208

Setting an optimal inspection plan for fatigue critical offshore piping relies on accurately estimating its remnant fatigue life (RFL). Several modeling approaches, such as knowledge-based, model-based, data-driven, fusion techniques etc., have been used to build RFL models in the past. The aim of this paper is to review these approaches and thereby recommend the most favorable approach for building a probabilistic RFL model for offshore piping. Firstly, a brief discussion about the aforementioned approaches is presented. Thereafter, a comparison is made between these approaches. For instance, there is uncertainty in model-based approaches, due to the assumptions of the underlying physical model, which poses substantial limitations on this approach. Conversely, a data-driven approach exploits the monitored operational data associated with the condition of the piping system. Fusion technique combines the features of the former two approaches and is recommended to build a model for estimating the RFL of offshore piping.

Thick walled components such as high pressure (HP) steam turbine casings operating under high parameter conditions are subjected to a complex stress state. As a result of that stress state, some parts of HP turbine casing undergo to the creep fatigue caused by the combination of thermal fatigue resulted from repeated start/stop operation and the creep which occurs during long-term operation at high temperature and high-pressure. It is well known that domestic thermal power plants have been in use over 100000 h which means that significant cost is required not only for maintenance, but often for renewal of equipment. Based on comprehensive investigation, the results of residual life assessment of one high pressure steam turbine casing, which belongs to the older turbine generation, taking into account simultaneous action of thermal fatigue and creep, are presented in this paper. Also, the critical flaw crack size of HP turbine casing is determined because this parameter has a strong influence on casing integrity and residual life. The results of residual life assessment provide not only a basis for further maintenance, but also estimated time for reparation or renewal.

Two-wheeler has a provision for a sounding a horn to be used while commuting so as to warn the passerby of the approaching vehicle as well as a signal for maintaining a safe distance or to communicate for any other reasons for safety. The horn is crucial as it is directly related to safety and the malfunction may evoke secondary claims and may affect the good-will of the customer. In most malfunction problems of two wheeler horns is due to fatigue failure of spring in warranty period so it is important to calculate the fatigue life and reduce fatigue failure in its intended working period (i.e. before 3,00,000 cycles). A typical helical compression spring configuration of two wheeler horn is chosen for study. Life analysis determines fatigue life of spring by the safe stress and corresponding pay load of the helical compression spring. This work describes fatigue analysis of the helical compression spring is performed using NASTRAN solver and compared with analytical results. The pre processing of the spring model is done by using HYPERMESH software. The present work attempts to analyze the life using MSC fatigue software and also verified by experimentation. Life of spring found to be infinity using software analysis as well as experimentally. To extend life in place of present spring co-axial (series) spring is analyzed. Also factors affecting fatigue life of this compression spring are stated.

Crack in component if undetected may lead to catastrophic failure of the component. The cracked rotor problem received the first attention in 1970 and after that the interest among the researchers started. The vibration behavior of cracked structures, in particular cracked rotors, is important to study as the introduction of the crack alters the vibration characteristics of the structure. The problem of damage and crack detection in structural components has acquired important role in past few years. However, cracked rotor studies are mainly deals with single crack. For multiple cracked structures the problem of crack sizing and location becomes more complex. Only few authors have pointed out the multiple crack assessment in the rotor. The proposed work is on vibration analysis of multiple cracked shaft beam. An Euler Bernoulli beam fixed at one end with two transverse cracks is considered. The vibration characteristics of the shaft are studied using Experimental Modal Analysis and ...

A methodology is proposed for estimating damage accumulation due to fatigue in the entire body of a metallic structure using output-only vibration measurements from a sensor network installed at a limited number of structural locations. Available frequency domain stochastic fatigue methods based on Palmgren-Miner damage rule, S-N fatigue curves on simple specimens subjected to constant amplitude loads, and Dirlik’s probability distribution of the stress range are used to predict the expected fatigue damage accumulation of the structure in terms of the power spectral density (PSD) of the stress processes. The PSD of stresses at unmeasured locations are estimated from the response time history measurements available at the limited measured locations using Kalman filter and a dynamic model of the structure. The effectiveness and accuracy of the proposed formulation is demonstrated using a multidegree-of-freedom spring-mass chain model and a two-dimensional truss model arising from structures that consist of members with uniaxial stress states.

Abstract:
Centrifugal fans are high speed rotating turbo machines vulnerable to vibrations resulting in the failure of
the system eventually. During every start-up and shutdown of centrifugal fan, the fan blades are subjected
to centrifugal, bending and vibratory loads. This repeated start-up and shutdown can reduce the life of fan
blades. A fatigue and modal analysis of the fan is, therefore, very important in the design and development
of fans, to prevent premature failure. In this paper the finite element analysis of a centrifugal fan impeller,
for a high tuned design is carried out using ANSYS. The Finite Element Analysis is to be done on the
following platform, “Fatigue and modal analysis at 705 rpm at 110°F” to determine the various
performance parameters. Analysis is linear static structural and the model used is Gerber stress theory.
From fatigue analysis we can determine whether the fan is safe to run in the operating conditions and
further the design can be improved. Modal analysis of the fan is very important in the design and
development of fan, to prevent premature failure. In modal analysis the first ten natural frequencies were
compared to the frequency generated from fan operating speed. This is done to avoid resonance
phenomenon which causes the vibration failure. So that fan can run safely in the operating conditions.

;-project deals with the fatigue analysis of aircraft composite fuselage,it will be designed to have optimal structural weight with the required safety margins. The structural stress, deflection, strain, and margins of safety distributions are to be visualized and the design is to be improved. The elasticity, stiffness, strength and stress distribution is more in the nodes of the structure. Where the fuselage frame is semimonocoque in construction holding former and skin.In the semi-monocoque structures where the skin carries the external loads, the internal fuselage pressurization and is strengthen using frames and stringers. When coming to the material section, the Aluminum alloy material are mostly used, but as metal designs have reached a high degree of perfection, extraordinary weight and cost savings are unlikely in the future. The carbon fiber composites have high strength to weight ratio when compared to aluminum alloy. The fuselage structure of aircraft is modeled using CATIA software. The original model is imported to ANSYS and the fatigue analysis is carried out. The applicability of the proposed procedure was demonstrated. Based on finite element analyses. The main objective analysis is importing composites in fuselage is merely considered applied and compared with aluminum. These comparison asses the weight reduction and fatigue life obtained with the use of composite materials for designing.

Crack in component if undetected may lead to catastrophic failure of the component. The cracked rotor problem received the first attention in 1970 and after that the interest among the researchers started. The vibration behavior of cracked structures, in particular cracked rotors, is important to study as the introduction of the crack alters the vibration characteristics of the structure. The problem of damage and crack detection in structural components has acquired important role in past few years. However, cracked rotor studies are mainly deals with single crack. For multiple cracked structures the problem of crack sizing and location becomes more complex. Only few authors have pointed out the multiple crack assessment in the rotor. The proposed work is on vibration analysis of multiple cracked shaft beam. An Euler Bernoulli beam fixed at one end with two transverse cracks is considered. The vibration characteristics of the shaft are studied using Experimental Modal Analysis and ...

This paper presents the life estimation of the diffuser structure. Literature shows that the welds are the source of failure in case of welded structure; hence the estimation of its life is very critical. There are two kinds of methods for life estimation stress life approach and strain life approach which have been validated for simple problems. Stress life approach was identified as appropriate for life estimation of the variable diffuser. There are papers indicating the methodology for life estimation using commercial software for life prediction. Here, OptistructHyper-Works for pre-processing and solver and Hyper-ViewHyper-Works for post processing has been used for the indeterminate structure, complex loading and boundary condition. The mathematical model subjected to the variable pressure contours for a particular Mach No., with the gimbal joint boundary condition at the test section end and the roller support at the other end. In this paper stress and fatigue analysis of the ...

The polyoxymethylene commercially known by acetal is unstable polymer that because of its chain end is not stable. Therefore the commercial resin usually contain certain amount if additives, which they are responsible of stabilizing the chains end (end cap) and preventing the chains from oxidization and degradation. Different amount of stabilizer may have an influence on the material resin characteristic and on its microstructure and morphology. Therefore the effects of the amount of stabilizer on the long trim performance of the acetal-copolymer commercially known by M25 were examined. The effects of time and temperature on the resistance of the acetal-copolymer to the fatigue crack propagation were investigated along with different amount of stabilizing additives. In general the results show that by increasing the amount of stabilizing additives to the acetal-copolymer the resistance to fatigue crack propagation (FCP) were found to be improved. The polymer resin becomes more stable with increasing the stabilizer level on FCP at different temperature and also more stable against the aging process, which mains improve its resistance to the degradation with the time. However it was found that a small change in the amount of stabilizing additives from a critical amount has large influence on FCP resistance of the acetal copolymer.

A methodology is proposed for estimating damage accumulation due to fatigue in the entire body of a metallic structure using output-only vibration measurements from a sensor network installed at a limited number of structural locations. Available frequency domain stochastic fatigue methods based on Palmgren-Miner damage rule, S-N fatigue curves on simple specimens subjected to constant amplitude loads, and Dirlik's probability

Variation of the modal reactive power distribution of a damaged composite plate is modeled and analyzed both analytically and numerically. Large variation of local reactive power flow in or around the damage region of a plate under resonant vibration is related to the change of strain and kinetic energies in the damage region. Feasibility of damage identification based on the detection of this local variation of modal reactive power flow in a structure is studied. Compared with the damage identification techniques based on the determination of the active power flow in a damaged plate, the proposed method only requires data of a vibration mode shape of the structure and it is easier to apply in practice. Modal power flow of an orthotropic plate with a region of reduced stiffness in the plate is analyzed. Numerical tests show that the proposed method is effective for detection of the damage and the modal power flow is more sensitive to the change of plate stiffness than the strain mode shape in the test case.

A methodology is proposed for estimating damage accumulation due to fatigue in the entire body of a metallic structure using output-only vibration measurements from a sensor network installed at a limited number of structural locations. Available frequency domain stochastic fatigue methods based on Palmgren-Miner damage rule, S-N fatigue curves on simple specimens subjected to constant amplitude loads, and Dirlik's probability distribution of the stress range are used to predict the expected fatigue damage accumulation of the structure in terms of the power spectral density (PSD) of the stress processes. The PSD of stresses at unmeasured locations are estimated from the response time history measurements available at the limited measured locations using Kalman filter and a dynamic model of the structure. The effectiveness and accuracy of the proposed formulation is demonstrated using a multidegree-of-freedom spring-mass chain model and a two-dimensional truss model arising from structures that consist of members with uniaxial stress states.

The fatigue problem of structures under concurrent thermal and vibration loading has not been thoroughly studied even though it is common in applications of aero-engine combustor liners. Here we attempt to explore such a problem using a simplified combustor liner model that is implemented by the commercial finite element software ANSYS Workbench. The modal parameters at various temperatures are calculated and the fatigue behavior under stochastic base excitation and thermal environment are analyzed. The results show that thermal loading not only has an effect on dynamic characteristics but also reduces the vibration fatigue life of the structure.

The work reported in this paper compared the fatigue damage accumulated under uni-axial loading (a procedure promoted by the vibration testing standards) to that induced by multi-axial loading. The comparison was performed for a helicopter structural element (the flare ...

Crack in component if undetected may lead to catastrophic failure of the component. The cracked rotor problem received the first attention in 1970 and after that the interest among the researchers started. The vibration behavior of cracked structures, in particular cracked rotors, is important to study as the introduction of the crack alters the vibration characteristics of the structure. The problem of damage and crack detection in structural components has acquired important role in past few years. However, cracked rotor studies are mainly deals with single crack. For multiple cracked structures the problem of crack sizing and location becomes more complex. Only few authors have pointed out the multiple crack assessment in the rotor. The proposed work is on vibration analysis of multiple cracked shaft beam. An Euler Bernoulli beam fixed at one end with two transverse cracks is considered. The vibration characteristics of the shaft are studied using Experimental Modal Analysis and ...

A methodology is proposed for estimating damage accumulation due to fatigue in the entire body of a metallic structure using output-only vibration measurements from a sensor network installed at a limited number of structural locations. This method can also be seen as a tool  for a life-time prognosis within SHM concepts. Available frequency domain stochastic fatigue methods based on Miner’s damage rule, S-N fatigue cycle curves and Dirlik’s probability dis-tribution of the stress range are used to predict the expected fatigue accumulation of the struc-ture in terms of the power spectral density of the stress processes. In predicting the damage and fatigue lifetime, it is assumed that the unmeasured excitations can be modeled by stationary sto-chastic processes. The power spectral densities of stresses at unmeasured locations are estimat-ed from the response time history measurements available at the limited measured locations using Kalman filter and a model of the structure. The proposed formulation is demonstrated using a MDOF spring-mass chain model arising from structures that consist of members with uni-axial stress states.

É objectivo deste pequeno “relatório” mostrar quais são as capacidades e limitações do uso da plataforma de desenvolvimento Arduino, num caso concreto, o cálculo da FFT para diferentes frequências do sinal de entrada. Para tal vão ser efectuadas algumas medições de carácter prático utilizando o modelo Arduino Duemilinove, disponível actualmente na Escola Naval (EN).
Como segundo objectivo, e não menos importante, espera-se fazer uma comparação entre os microcontroladores utilizados nos modelos Arduino Mega com ATmega1280, Arduino Duemilinove com ATmega168 e Arduino Duemilinove com ATmega328. Tentando assim dar uma perspectiva das capacidades existentes no mercado, vendo quais serão as melhores opções a tomar.