Fatigue Usage Factor Research Articles

Mitigation of hanger pin failure in Pakistan railway carriage system by the application of COMSOL Multiphysics

The frequency of failures in hanger pins of Pakistan Railway carriages has risen to an alarming level. Such as hanger pins have become the reason for the highest number of cases regarding failures of Carriage and Wagons in Pakistan. The pins have been failing after only 3 months while the intended life of these pins was supposed to be 6 months at least. Previously we have been using rectangular cross-section cotter pins in the hanger brackets. Studies have shown that instead a circular cross-section cotter pin can make a major contribution to the lower the value of these fatigue stresses. In this study, we compute and perform the stress and fatigue analysis on the hanger pin assembly using Findley criterion. Findley criterion was used as it most closely resembled in the properties needed to carry out our desired simulation. COMSOL model is used to compute the stresses as well as do the fatigue analysis on the said model. Fatigue usage factor has been used in the COMSOL. The first part contains the analysis on the already in-effect hanger pins of rectangular cross-sectional area. While the second half contains analysis done by changing the cross-section to modified circular shaped hanger cotter pins. The new proposed material proved to have decreased the stresses induced in the components thus increasing its life.

3D numerical analysis of the structural behaviour of a carbon fibre reinforced polymer drive shaft

Due to their high strength and favourable mechanical behaviour, metals are used in a variety of applications within the automotive industry, including drive shafts. However, the use of metallic drive shafts in the automotive sector presents some disadvantages such as high inertial masses. This work investigates the mechanical benefits of using Carbon Fibre Reinforced Polymers (CFRP) for manufacturing drive shafts. A Formula Student car was used as a model for the present work design for the drive shaft. Drive shafts made of Steel AISI 4340, Aluminium, and CFRP are investigated when subjected to mechanical excitations. Simulation includes the use of Comsol Multiphysics software. The CFRP drive shaft was modelled using the layered material feature. Various stacking sequences are tested. Results show that [90°/0°/-45°/+45°] sequence presents the best mechanical behaviour. Analytical and numerical calculations for the natural frequencies are performed and compared. CFRP drive shaft is observed to give the highest fundamental natural frequency when compared to the metallic counterparts. Fatigue analysis are also studied and revealed that the drive shafts can sustain the applied load for its expected fatigue life, with the CFRP drive shaft having the highest fatigue usage factor. Critical buckling analysis showed that the drive shaft made of steel has the highest critical buckling torque. However, drive shafts made of carbon fibre reinforced polymer was found to be 40.7% lighter than the aluminium tube and 79.6% lighter than the steel tube.

Influence of fatigue on superconducting REBCO tapes under repeated cyclic tensile, bending and twisting loads: A simulation-based investigation

The effect of repeated cyclic loading on the superconducting REBCO tape under tensile, bending, and torsional loadings is investigated. The Fatigue Usage Factor (FUS) is calculated for each cyclic loading condition to identify degradation using the Matake criterion. The thicknesses of the tapes' constituent layers are also varied to identify the relative influence of each layer on overall fatigue performance. When the tape was subjected to fatigue-type loading, the thickness of the copper and Hastelloy layers was found to play a significant role. This holds true under tensile, bending, and twisting loading conditions. However, out of the three loading conditions, bending exhibits the greatest variation in FUS value with changes in Hastelloy and copper layer thickness. The maximum value of the fatigue usage factor is observed in the edges of the Hastelloy layer in all three loading cases. It has been found that the properties of the layer material, as well as the adjacent layer, play an important role in determining the fatigue strength of the tape.

Balanced bending fatigue life for helical gear drives to enhance the power transmission capacity through novel rack cutters

This article proposes an idea for balancing the bending fatigue life between the gear and pinion of a novel helical gear drive. In this study, the helical gear is developed through analytical equations based on a novel rack cutter tooth thickness factor, and the estimation of principal stress and strain at the critical root fillet of the helical gear teeth is carried out through finite element analysis. Further, the fatigue module in COMSOL- Multiphysics software is employed to determine the bending fatigue life through strain life approach based on Smith-Watson-Topper with Neuber’s rule and fatigue usage factor based on Findley criteria. The effect of major gear parameters such as helical angle, pressure angle, teeth number, gear ratio, addendum height and addendum modification factor (S+, S− and S0) on bending fatigue life are computed based on novel helical gear with different rack cutter tooth thickness factor of gear and pinion. Finally, the above parametric study shows an optimum rack cutter tooth thickness factor between the gear and pinion to achieve a balanced bending fatigue life and fatigue usage factor, which aids in improving the power transmission capacity of the helical gear drive.

A Thermo-Mechanical Stress Based Fatigue Life Evaluation of a Mine Hoist Drum Brake System Using COMSOL Multiphysics.

In this study, the fatigue usage factors for Findley and Matake stress-based criteria were determined in the case of an MK5×2 mine hoist drum brake system subjected to cyclic maneuver braking. The study was conducted for this type of brake system, because the majority of mine hoists in Romanian mines are equipped with this brake type, being in operation for several decades. A geometric model of the brake was built using SolidWorks and imported in COMSOL Multiphysics to perform thermo-mechanical simulations. Based on the deformations and von Mises stresses determined by the thermomechanical simulation and, considering the calculated endurance limits of the brake system materials, Matake and Findley fatigue life evaluation simulations from COMSOL’s fatigue module were conducted. The results show that the highest fatigue is expected on the drum lining surface towards the exit point from under the brake shoe in both cases, and the values of the usage factor of 0.307 (Findley) and 0.401 (Matake) are both under the critical value 1, meaning that the stress limit has not been exceeded for the brake system components and, thus, failure is not expected. Simulations were conducted considering an estimated 1.06 × 105 cycles during one year, more than both the usual service/replacement interval of the friction components of the brake, and the period of mandatory technical inspections imposed by regulations.

Modelling and simulation of the fatigue usage factor of γ-TiAl alloy fabricated through Laser Additive Manufacturing (LAM)

Recently, laser additive manufacturing (LAM) technologies are increasingly being applied for producing components with excellent physical and mechanical properties in the aerospace, automotive and energy industries. This work is aimed at modelling the fatigue usage factor of γ-TiAl alloy fabricated through LAM. The modelling and simulation were performed using the COMSOL Multiphysics 5.4 software by developing a y-TiAl alloy microstructure. This was modelled to generate the material properties (density, heat capacity at constant pressure and thermal conductivity) from the microstructure of a unit cell as a general representation of the alloy. The computed properties were used in modelling the LAM process to fabricate γ-TiAl alloy part with subsequent fatigue simulation to determine the usage factor (Ke). From the models, the maximum Von Mises stress and transient temperature were 2.88 x108 Nm-2 and 1510 K respectively, for the LAM fabrication process; while the fatigue usage factor model showed a maximum Von Mises stress of 2.91 x108 Nm-2 and a fatigue usage factor of 0.35.

Environmental Effect on Fatigue Crack Initiation under Equi-Biaxial Loading of an Austenitic Stainless Steel

The lifetime extension of nuclear power stations is considered an energy challenge worldwide. That is why the risk analysis and the study of various effects of different factors that could potentially prevent safe long-term operation are necessary. These structures, often of great dimensions, are subjected during their life to complex loading combining varying multiaxial mechanical loads with non-zero mean values associated with temperature fluctuations under a PWR (pressure water reactor) environment. Based on more recent fatigue data (including tests at 300 °C in air and a PWR environment, etc.), some international codes (RCC-M, ASME, and others) have proposed and suggested a modification of the austenitic stainless steels fatigue curve combined with a calculation of an environmental penalty factor, namely Fen, which has to be multiplied by the usual fatigue usage factor. The determination of the field of validation of the application of this penalty factor requires obtaining experimental data. The aim of this paper is to present a new device, “FABIME2e” developed in the LISN (Laboratory of Integrity of Structures and Normalization) in collaboration with EDF (Electricity of France) and Framatome. These new tests allow the effect of a PWR environment on a disk specimen to be quantified. This new device combines structural effects such as equibiaxiality and mean strain and the environmental penalty effect with the use of a PWR environment during fatigue tests.

A JSME Code Case on Piping Seismic Design Based on Inelastic Response Analysis and Strain-Based Fatigue Criteria

Abstract A Code Case in the framework of the Nuclear Codes and Standards of Japan Society of Mechanical Engineers (JSME) has been published to incorporate seismic design evaluation methodologies for piping systems by detailed inelastic response analysis and strain-based fatigue criteria as an alternative design rule to the current rule, in order to provide a more rational seismic design evaluation by taking directly the response reduction due to plasticity energy absorption into account. The Code Case provides two strain-based criteria: one is a limit to maximum amplitude of equivalent strain amplitude derived from detailed analysis and the other is a limit to the fatigue usage factor also based on the equivalent strain amplitude. Some discussions are provided on the adequacy of additional damping in the simplified inelastic analysis and the safety margin and reliability of fatigue evaluation by the detailed inelastic response analysis provided in the Code Case.

Large eddy simulation of thermal mixing with conjugate heat transfer at BWR operating conditions

Thermal fatigue occurs in most metals under cyclic heat loads and can threaten the structural integrity of metal parts. Detailed knowledge of these loads is of utter importance to prevent such issues. In this study, a large eddy simulation (LES) with wall-adapting local eddy viscosity (WALE) subgrid model is performed to better understand turbulent thermal mixing in an annulus with a pair of opposing cold inlets at a low axial level (z=0.15m) and with a pair of opposing hot inlets at a higher axial level (z=0.80m). Each inlet pair is 90° from each other in the azimuthal direction. Conjugate heat transfer between fluid and structure is accounted for. The geometry simplifies a control-rod guide tube (CRGT) in a boiling water reactor (BWR). LES results are compared with measurement data. This is one of the first times BWR conditions are met in both experiments and LES: pressure equals 7.2 MPa, while the temperature difference between hot and cold inlets reaches 216 K. LES temperatures at the fluid-structure interface are fairly correlated with their experimental equivalents, with regard to mean values, local variances, and dangerous oscillation modes in fatigue-prone areas (z=0.65-0.67m). An elastic analysis of the structure is performed to evaluate stress intensities there. From them, cumulative fatigue usage factors (CUFs) are estimated and used as screening criteria in the subsequent frequency analysis of temperature time series at the fluid-structure interface. The likelihood of initiating a fatigue crack is linked to the maximum CUF, which is 3.2 × 10−5 for a simulation time of ~10s.

Turbo-drill thrust ball bearing raceway fatigue analysis based on the Dang Van criterion

ABSTRACT Turbo-drill is subjected to harsh working condition where drilling fluid, impact loads and high speed can cause thrust ball bearing raceway surface to quickly fatigue failure. Based on the Dang Van multi-axis fatigue evaluation criteria, the finite element model for raceway surface fatigue analysis was established, the fatigue usage factor under periodic loading was obtained. The results demonstrated that when the hardened layer thickness was larger than 0.4 mm, the fatigue usage factor had a dramatic reduction, thicker hardened layer thickness can significantly reduce the risk of raceway surface fatigue failure. Under the normal working condition of turbo-drill, the larger axial load can lead to a significant increase in fatigue usage factor, the axial load and hardened layer thickness have no influence on the maximum equivalent plastic strain, but they can remarkably change the maximum Mises stress. Therefore, the reasonable axial load and hardened thickness can improve the fatigue life of thrust ball bearing.

PWR effect on crack initiation under equi-biaxial loading development of the experiment

The lifetime extension of the nuclear power stations is considered as an energy challenge worldwide. That is why, the risk analysis and the study of various effects of different factors that could potentially represent a hazard to a safe long term operation are necessary. The methodology for fatigue dimensions of the Pressurized Water Reactor components (PWR) is based on the use of design curves established from test carried out in air at 20 °C on smooth specimens by integrating safety coefficient that covers the dispersion of tests associated with the effects of structures. To formally integrate these effects, some international codes have already proposed and suggested a modification of the austenitic stainless steels fatigue curve combined with a calculation of an environmental penalty factor, namely Fen, which has to be multiplied by the usual fatigue usage factor. The aim of this paper is to present a new device “FABIME2E” developed in the CEA-LISN in collaboration with EDF and AREVA. These new tests allow quantifying accurately the effect of PWR environment on semi-structure specimen. This new device combines the structural effect like equi-biaxiality and mean strain and the environmental penalty effect with the use of PWR environment during the fatigue tests.

Visualization of Thermal Fatigue Damage Distribution With Simplified Stress Range Calculations

This paper proposes simplified methods to evaluate fatigue damage in a component subjected to cyclic thermal loads to visualize damage distribution by using typical computer-aided engineering systems. The objective is to perform the evaluations on a standard desktop PC within a reasonably short computation time. Three simplified methods for defining elastic stress ranges are proposed in place of the method in the ASME Subsection NH procedures. A thermal fatigue test that was previously performed using a type-304 stainless steel (304SS) cylinder is simulated to validate the proposed methods. Heat transfer and elastic analyses are conducted. Simultaneously with the analyses, fatigue usage factors are calculated using user subroutines formulated in this study, including the three simplified methods and the ASME NH-based method. The calculated values of the fatigue usage factor are visualized using a graphical user interface (GUI) incorporated into a commercial finite-element analysis (FEA) code. The fatigue usage factor distribution obtained using the simplified methods could be calculated without requiring large amounts of memory and long computation time. In addition, the distribution of the fatigue usage factor was consistent with the distribution of cracks observed in the test.

Design Optimization and Fatigue Analysis for Seal Joint of Control Rod Drive Mechanism

Two kinds of seal joint thickness of control rod drive mechanism seal house were analyzed on stress and fatigue by using finite element method, and it provides analytical basis for equipment optimization, design manufacturing and problem handing. In the fatigue computing, all the transients were grouped into several groups, so as to separate the transients not at the same stage obviously. Meanwhile, the transients can be respectively combined in every group to reduce the redundant conservatism of computation. The elastoplastic strain correction factor was modified by analyzing thermal and mechanical load separately referring the rules of RCC-M 2002.By comparing the stress of two thickness joints, the results are found that the fatigue results of the thinner thickness are safer, but this is contrary to the rule of other results. The fatigue usage factor can be reduced by using modified elastoplastic strain correction factor when the amplify of the primary and secondary stress is large produced by both thermal load and mechanical load.

PWR Effect On Crack Initiation Under Equi-biaxial Loading

The lifetime extension of the nuclear power stations is considered as an energy challenge worldwide. That is why, the risk analysis and the study of various effects of different factors that could potentially prevent safe long term operation are necessary. These structures, often of great dimensions, are subjected during their life to complex loading combining varying mechanical loads, multiaxial, with nonzero mean values associated with temperature fluctuations and also PWR environment. Based on more recent fatigue data (including tests at 300°C in air and PWR environment, etc…), some international codes (RCC-M, ASME and others) have proposed and suggested a modification of the austenitic stainless steels fatigue curve combined with a calculation of an environmental penalty factor, namely Fen, which has to be multiplied by the usual fatigue usage factor. The aim of this paper is to present a new device "FABIME2E" developed in the LISN in collaboration with EDF and AREVA. These new tests allow quantifying the effect of PWR environment on disk specimen. This new device combines the structural effect like equi-biaxiality and mean strain and the environmental penalty effect with the use of PWR environment during the fatigue tests.

Fatigue Life Estimation of a Layered Composite Plate

This paper presents the FEM approach of fatigue life estimation of a layered composite plate having a central elliptical cut-out subjected to time variation loads. Some properties and material data, such as data used for the S-N curve / Wöhler curve of the material, represented in cyclic stress versus number of cycles to failure coordinates, which is required for starting the fatigue analysis, were taken from the OPTIMAT database.The plate analysis was parameterized and modeled with the Shell281 element type. This type of element can be used in a triangular form more efficiently than other types of shell elements available in version 15 of ASYS APDL.Initially, the static analysis was performed to identify the node with the maximum principal stress (hot spots). This node was used for performing the fatigue analysis. The fatigue parameter to estimate fatigue life is cumulative fatigue usage factor. This factor is obtained by adding together all individual usage factors calculated for each variable load that is applied to the analyzed plate. The fatigue usage factor is used to estimate the percentage of life that is consumed after applying the fatigue loads. The value of the usage factor is in the range from 0 to 1.

Fatigue Strength Evaluation Of Pressurizer Wall Structure In Pressurized Water Reactor

<p>Fatigue strength evaluations have been performed to the pressurizer component in Pressurized Water Reactor. Fatigue is the main failure mechanism of material during system in operation. Therefore, this evaluation becomes important to be performed since the pressurizer has a very important function in the reactor’s system. Analysis was performed by using Nuclear Power Plant operation data from 40 years operation and base on Miner theory. This analysis covered all stress level experienced by the reactor during the service. To determine the value of fatigue usage factor a, fatigue curve of SA 533 material was applied. Analysis results show that the cumulative fatigue damage during 40 years in operation is 4,23×10<sup>-4</sup>. This value still far enough below failure criteria, which a value is 1. Therefore, the pressurizer design has already fulfilled the design qualification in term of fatigue aspect.</p>

弾塑性応答を考慮した配管系の耐震安全性評価

A Code Case in the framework of JSME Nuclear Codes and Standards is currently being developed to incorporate seismic design evaluation of piping by detailed elastic-plastic response analysis and strain-based fatigue criteria as an alternative design rule to the current rule, in order to provide a more rational seismic design evaluation. The Code Case provides two strain-based criteria; one is a limit to maximum amplitude of equivalent strain amplitude derived from detailed analysis and the other is a limit to the fatigue usage factor also based on the equivalent strain amplitude. The Code Case also provides an evaluation method by simplified inelastic analysis with an additional damping taking the response reduction due to plasticity into account. Some discussions are made on the adequacy of additional damping in the simplified inelastic analysis and the safety margin and reliability of fatigue evaluation by the detailed elastic-plastic response analysis provided in the Code Case.

New Approach for Fatigue Damage Monitoring Based on Actual Operating History of Nuclear Power Plants

Metal fatigue is a well-known phenomenon whereby material characteristics are deteriorated when even a small load is applied repeatedly. Therefore, an accurate fatigue evaluation is very important in terms of component integrity and reliability. In the design stage, the fatigue evaluation of nuclear class 1 components has to be performed in accordance with Sec. III of the ASME Boiler and Pressure Vessel Code. However, operating experience shows that the design transients are very conservative compared to the actual ones in terms of the heating/cooling rates and the number of transient occurrences. Considering that these two factors affect the thermal stress and thereafter the fatigue usage factor (FUF), the actual fatigue damage can differ from the design fatigue evaluation result. In order to evaluate and monitor the FUF exactly, therefore, various methods have been proposed and widely implemented. Among these, the cycle-based approach (CBA) utilizes the stresses for the design transients and reflects only the actual number of transient occurrences. For this reason, the CBA provides a conservative FUF, although it is very simple and easy to implement. Therefore, a simple and accurate fatigue monitoring method is still needed.The purpose of this paper is to develop a new approach for effective fatigue damage monitoring. To do this, a thorough review is conducted for the design transients and actual transients for the Westinghouse-type pressurized water reactors in Korea. In addition, a wide range of finite element analyses are carried out varying the heating/cooling rates and the pattern of the transients. Based on this result, a new CBA is proposed incorporating the simple correction factors for both the heating/cooling rates and the transient patterns. A case study is also carried out for the reactor pressure vessel outlet nozzle to verify the validity and applicability of the proposed method. The result indicates that the proposed method can provide a realistic FUF, and more importantly, it is very easy to implement. From these, it is anticipated that the new approach can be widely used in practical fatigue monitoring of nuclear components and piping.

Research on the Environment Assisted Fatigue Based on Flaw Tolerance Method

Shanghai Nuclear Engineering Research and Design Institute (SNERDI) have been involved in “Fatigue Evaluations Using Flaw Tolerance Methods to Consider Environmental Effects” task group (TG) under the WG Environmental Fatigue Evaluation Methods (WG EFEM) in 2012 founded by ASME section III committee which is intend to find alternative rules for fatigue assessments when considering primary loop water environment. EAF TG has researched a sample problem based on a heavy-walled primary loop stainless steel nozzle for light water reactor (LWR). The cumulative fatigue usage factor and Fen (Environmentally Assistant Fatigue Factor) value is determined by ASME Code Case N-792. Based on this, the fatigue crack growth is calculated according to the rules of ASME section XI non-mandatory appendix L. The crack depth at 1000 cycles and the cycles when the crack grow to 0.75 times of wall thickness is calculated for the axial and circumferential crack respectively. Moreover, the crack closure effect in the fatigue crack growth under PWR environment has been studied. The results of the two methods of Fen factor correction and flaw tolerance are compared and discussed.

Strain test and stress intensity assessment of a CPR1000 Nuclear Power Plant pressurizer during pre-delivery hydrostatic test

Strain gages are applied to get the strain and stress of a CPR1000 Nuclear Power Plant (NPP) pressurizer during the pre-delivery hydrostatic test. The measured strain curves are discussed to find the deformation features of the cylinder. The stresses of cylindrical base metal, longitudinal welds and girth welds are calculated and compared with the theoretical values. The stresses in girth welds and upper head nozzle welds show non-uniformity at these areas. The possible reasons are discussed for this phenomenon. The stress intensity is calculated and evaluated according to the allowable limit. The fatigue usage factor is evaluated by considering the effect of internal pressure rise-and-fall cycle to pressurizer’s total fatigue life. The evaluated results show that the hydrostatic test has little effect on the integrity or fatigue life of the pressurizer. This test provides the basic deformation data of the pressurizer, which plays an important role in the ageing assessment and management during operation.