Global ETD Search

11	Fatigue Life Calculation By Rainflow Cycle Counting Method Ariduru, Secil 01 December 2004 (has links) (PDF) In this thesis, fatigue life of a cantilever aluminum plate with a side notch under certain loading conditions is analyzed. Results of experimental stress analysis of the cantilever aluminum plate by using a uniaxial strain gage are presented. The strain gage is glued on a critical point at the specimen where stress concentration exists. Strain measurement is performed on the base-excited cantilever beam under random vibration test in order to examine the life profile simulation. The fatigue analysis of the test specimen is carried out in both time and frequency domains. Rainflow cycle counting in time domain is examined by taking the time history of load as an input. Number of cycles is determined from the time history. In frequency domain analysis, power spectral density function estimates of normal stress are obtained from the acquired strain data sampled at 1000 Hz. The moments of the power spectral density estimates are used to find the probability density function estimate from Dirlik&rsquo / s empirical expression. After the total number of cycles in both time and frequency domain approaches are found, Palmgren-Miner rule, cumulative damage theory, is used to estimate the fatigue life. Results of fatigue life estimation study in both domains are comparatively evaluated. Frequency domain approach is found to provide a marginally safer prediction tool in this study. TJ Mechanical Engineering. 1-1570
12	Verificação do projeto estrutural de uma máquina de ensaio de fadiga de cadeira de rodas. / Verification of the structural design of a wheelchairs fatigue testing machine. Moraes Junior, Ronaldo de Souza 28 July 2008 (has links) Para realizar ensaios de fadiga, é preciso que a máquina ou equipamento de testes tenha uma durabilidade muito maior que as estruturas ou componentes a serem ensaiados. O presente trabalho propõe-se a investigar a estrutura de uma máquina de ensaio de fadiga de cadeira de rodas, com o objetivo de determinar sua vida em fadiga. Para isto, uma análise da interação entre cadeira de rodas e máquina de ensaio é feita, do ponto de vista dinâmico, através de dados experimentais e modelagem em elementos finitos. A máquina de ensaio é constituída por uma estrutura com dois tambores rotativos, que possuem ressaltos, e suportam as rodas da cadeira de rodas. Estimada a força no tempo que a cadeira exerce sobre os tambores, calculam-se as tensões na estrutura, identificam-se as regiões de maiores tensões e estima-se a vida em fadiga da estrutura. / Fatigue analysis of full-scale structures and components is possible by using appropriated devices and machines which has to be much more durable than the structures or components being tested. The present work is proposed to investigate the structure of a wheelchair fatigue testing machine and predict its fatigue life. To reach this goal a dynamic analysis based on experimental data combined with the finite element method of the testing machine and wheelchair interaction is done. The machine is made of a structure and two turning drums that have slats and support the wheelchairs. With the timedependent force that wheelchair applies to the drums, the stresses are calculated to the whole structure, the sites with higher stresses are identified and the fatigue life of the structure is predicted. Cadeiras de rodas Dynamic response Ensaios de fadiga Fatigue life Finite elements Método dos elementos finitos Rainflow S-N Curve Stress history
13	Verificação do projeto estrutural de uma máquina de ensaio de fadiga de cadeira de rodas. / Verification of the structural design of a wheelchairs fatigue testing machine. Ronaldo de Souza Moraes Junior 28 July 2008 (has links) Para realizar ensaios de fadiga, é preciso que a máquina ou equipamento de testes tenha uma durabilidade muito maior que as estruturas ou componentes a serem ensaiados. O presente trabalho propõe-se a investigar a estrutura de uma máquina de ensaio de fadiga de cadeira de rodas, com o objetivo de determinar sua vida em fadiga. Para isto, uma análise da interação entre cadeira de rodas e máquina de ensaio é feita, do ponto de vista dinâmico, através de dados experimentais e modelagem em elementos finitos. A máquina de ensaio é constituída por uma estrutura com dois tambores rotativos, que possuem ressaltos, e suportam as rodas da cadeira de rodas. Estimada a força no tempo que a cadeira exerce sobre os tambores, calculam-se as tensões na estrutura, identificam-se as regiões de maiores tensões e estima-se a vida em fadiga da estrutura. / Fatigue analysis of full-scale structures and components is possible by using appropriated devices and machines which has to be much more durable than the structures or components being tested. The present work is proposed to investigate the structure of a wheelchair fatigue testing machine and predict its fatigue life. To reach this goal a dynamic analysis based on experimental data combined with the finite element method of the testing machine and wheelchair interaction is done. The machine is made of a structure and two turning drums that have slats and support the wheelchairs. With the timedependent force that wheelchair applies to the drums, the stresses are calculated to the whole structure, the sites with higher stresses are identified and the fatigue life of the structure is predicted. Cadeiras de rodas Ensaios de fadiga Método dos elementos finitos Dynamic response Fatigue life Finite elements Rainflow S-N Curve Stress history
14	Gewinnung sicherer Lastannahmen aus Simulation und Messung zur Festigkeitsauslegung von Straßen- und Stadtbahnen Zechel, Gero 21 February 2017 (has links) (PDF) Die Nutzung historisch solider Lastannahmen, wie sie zum Beispiel die VDV Richtlinie 152 in der Fassung von 1992 festlegt, ist für die Festigkeitsauslegung neuartiger Straßen- und Stadtbahnfahrzeuge unzureichend, da die Annahmen und Methoden der Komplexität und insbesondere der Nichtlinearität moderner Fahrzeugkonzepte keine Rechnung tragen. Diese Arbeit zeigt auf, wie sich entstandene Lücken in den Lastannahmen durch Simulation und Messung von Fahrzeug und Gleis analysieren, verstehen und schließen lassen. Den Kern bildet dabei der Einsatz detaillierterer Simulationsmodelle von Fahrzeug und Gleis, deren Eingangsdaten mit Hilfe von Messungen gewonnen und deren Ausgangsdaten mit ihnen verifiziert und ergänzt werden müssen. Hierfür werden Methoden und Werkzeuge entwickelt, die ein ein vielseitiges Baukastensystem für die Fahrzeuganalyse, Modellvalidierung und Datenbewertung bilden, und zu sicheren Lastannahmen für die Fahrzeugauslegung führen. Lastannahmen Schienenfahrzeugtechnik Straßenbahn Stadtbahn Tram Strukturmechanik Finite Elemente Methode FEM Mehrkörpersimulation MKS Fahrzeugmessung Gleismessung Langzeitmessung Synchronisierung Ortung Zustandsautomat Korrelation Schnittlasten Elastische Strukturen Simulationsszenarien Lastfallsynthese Betriebsfestigkeit Rainflow-Zählverfahren Rainflowtabelle Lastspiele Beanspruchungskollektiv Äquivalentamplitude Auslastungsgrad load assumptions light rail vehicles LRV tram structure mechanics finite element analysis FEA multi-body simulation MBS vehicle measurement track measurement long-term measurement synchronisation positioning finite state machine correlation interface loads elastic bodies simulation scenarios load case synthesises endurance fatigue rainflow counting rainflow table load cycles ddc:620 rvk:ZO 5230
15	Advancing reliability information for Wave Energy Converters Thies, Philipp Rudolf January 2012 (has links) Marine renewable energy promises to provide a significant contribution to the future electricity supply. It is estimated that 17% of today's UK electricity demand could be generated from wave and tidal sources. The ambition to harvest this resource is in the public interest, as it eases the pressures on energy security, holds the potential to reduce carbon emissions and has the prospect to create a new UK industry sector worth £15 billion. From an engineering perspective, marine energy is one of the least developed renewable energy technologies and has to be regarded as unproven. The reliability of components and devices in the harsh marine environment is one of the main engineering challenges. Reliability assessments and the assurance of acceptable reliability levels are dependant on the adequacy of failure information, which is scantily available for marine energy. This thesis shows that large failure rate uncertainties impede the reliability assessment for wave energy converters and how a suite of experimental, numerical and statistical methods can be applied to improve scarcely available reliability information. The analysis of component load conditions identifies fatigue as failure mode of concern and the fatigue life of mooring lines and marine power cables is quantified in a floating wave energy application. A Bayesian statistical approach and dedicated service-simulation component testing is proposed, and implemented to improve the quality of reliability estimates and to provide relevant data and assurance. The methods presented, along with the results, will assist reliability assessment and design during early development stages, and will inform the prediction of maintenance requirements during operation. Reliable marine energy systems will be the technical enabler for the successful transition of prototype devices to a commercially viable marine energy industry. 621.312134
16	Continuous Time Fatigue Modelling for Non-proportional Loading Gundmi Satish, Sajjan January 2019 (has links) Fatigue analysis is a critical stage in the design of any structural component. Typically fatigue is analysed during post-processing, but as the size of the analysed component increases, the amount of data stored for the analysis increases simultaneously. This increases the computational and memory requirements of the system, intensifying the work load on the engineer. A continuum mechanics approach namely ’Continuous time fatigue model’, for fatigue analysis is available in a prior study which reduces the computational requirements by simultaneously computing fatigue along with the stress. This model implements a moving endurance surface in the stress space along with the damage evolution equation to compute high-cycle fatigue. In this thesis the continuous time fatigue model is compared with conventional model (ie.Cycle counting) to study its feasibility. The thesis also aims to investigate the continuous time fatigue model and an evolved version of the model is developed for non-proportional load cases to identify its limitations and benefits. Multiaxial Fatigue Loading Fatigue Analysis Continuous Time fatigue model Endurance Surface Rainflow Counting Cyclic loading Cycle Counting Damage Evolution High-cycle fatigue Non-proportional loading Aerospace Engineering Rymd- och flygteknik
17	Gewinnung sicherer Lastannahmen aus Simulation und Messung zur Festigkeitsauslegung von Straßen- und Stadtbahnen Zechel, Gero 12 July 2016 (has links) Die Nutzung historisch solider Lastannahmen, wie sie zum Beispiel die VDV Richtlinie 152 in der Fassung von 1992 festlegt, ist für die Festigkeitsauslegung neuartiger Straßen- und Stadtbahnfahrzeuge unzureichend, da die Annahmen und Methoden der Komplexität und insbesondere der Nichtlinearität moderner Fahrzeugkonzepte keine Rechnung tragen. Diese Arbeit zeigt auf, wie sich entstandene Lücken in den Lastannahmen durch Simulation und Messung von Fahrzeug und Gleis analysieren, verstehen und schließen lassen. Den Kern bildet dabei der Einsatz detaillierterer Simulationsmodelle von Fahrzeug und Gleis, deren Eingangsdaten mit Hilfe von Messungen gewonnen und deren Ausgangsdaten mit ihnen verifiziert und ergänzt werden müssen. Hierfür werden Methoden und Werkzeuge entwickelt, die ein ein vielseitiges Baukastensystem für die Fahrzeuganalyse, Modellvalidierung und Datenbewertung bilden, und zu sicheren Lastannahmen für die Fahrzeugauslegung führen. info:eu-repo/classification/ddc/620 ddc:620
18	FATIGUE CHARACTERIZATION OF RISERS AND PIPELINES UNDER REALISTIC VARIABLE AMPLITUDE LOADING AND THE INFLUENCE OF COMPRESSIVE STRESS CYCLES Iranpour, Mohammad 11 January 2013 (has links) One of the most prominent factors affecting the performance and longevity of risers is vortex induced vibration (VIV), which can cause severe fatigue damage, especially in risers used in deep waters. The available approaches for analyzing VIV induced fatigue in risers mainly focus on the VIV aspect of the problem; indeed less attention has been paid on the effect of VIV on a riser’s fatigue life and in prediction of fatigue life using various models. This dissertation first demonstrates how one can characterize fatigue of pipes and risers using an equivalent plate specimen as opposed to using a pipe specimen, thereby simplifying the task, yet obtaining good accuracy. Actual variable amplitude loadings (VAL) are used to study the fatigue crack growth in risers’ material with a focus on the various influencing parameters. Extensive experimental investigations are performed, followed by analytical and computational nonlinear finite element analyses. It is shown that the higher harmonics do cause significant fatigue damage, thus their influence should not be ignored. The influence of load interaction effects is also investigated, focusing on the fatigue crack growth retardation effects due to tension overloads, as well as the acceleration effects due to compression underloads. The crack closure concept is then used to explore into both the fatigue retardation and acceleration effects within a VAL scenario. An effective method for calculation of the stress intensity factor is proposed, which considers only the tensile portion of the stress range, while proposing another effective approach for accounting for the influence of compressive stress cycles. Moreover, a two-parameter approach is used in this dissertation, relating the fatigue crack growth rate (FCGR) to the crack tip opening displacement (CTOD). It is shown that the CTOD provides adequate information for calculating the FCGR under VAL, and it can be effectively used to account for the influence of the compressive stress cycles. The experimental investigation also considers the retardation effect resulting from the applied peak tensile overload cycles (TOLC) and the influence of various so-called “clipping” levels, demonstrating the significant influence of the TOLC on crack growth retardation in VAL.

Search results