Archives du mot-clef analyse de défaillances

Comportement en fatigue des matériaux métalliques. Fatigue des assemblages soudés – Soudage à l’arc

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2017-01-19_09h12_33L’édition de la collection Fatigue est issue de la révision de l’ouvrage de référence « Données technologiques sur la fatigue » publié au début des années 1980 par le Cetim. L’objectif de cette collection, composée à terme de plusieurs fascicules, est de délivrer à tout un chacun un état de l’art dans le domaine de la fatigue, appliqué à tous les domaines et de se placer dans un contexte de capitalisation des connaissances. Cet ouvrage (9Q249) de la collection Performances du Cetim « Comportement en fatigue des matériaux métalliques – Fatigue des assemblages soudés – Soudage à l’arc » est le deuxième fascicule de la collection.  Dédié spécifiquement à la fatigue des assemblages soudés, il traite notamment de la conception de ces assemblages, de leur optimisation et des moyens pour calculer leur résistance. Les bonnes pratiques de conception des assemblages soudés, le choix de l’acier et un classement de ces assemblages en fonction de leurs contraintes admissibles sont données en annexe.

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Metallurgical investigation of cracked aluminium alloy valve

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1-s2-0-s2213290213000096-gr1A case study published in « Case Studies in Engineering Failure Analysis« , July 2013.

The high strength aluminium alloy Al–5.5Zn–2.5Mg–1.5Cu (AA7075) is being widely used in realisation of aerospace components. A component ‘fill and vent valve’ used in liquid propulsion system was fabricated from AA 7075 forgings in T7352 temper condition, and subsequently undergone various functional tests, four years back. Recently, during dye penetrant test after proof pressure test at 525 bar, a valve indicated presence of a crack. Detailed metallurgical investigation indicated that failure was caused by stress corrosion cracking.

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A study of the preload force in metal-elastomer torsion springs

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neidhart-springsNeidhart type suspension units composed of metal-elastomer torsion springs can be a good alternative to steel helical springs in applications such as vibration absorbers or vehicle suspension systems. Assembling this type of spring requires initial preload of the elastomeric working elements, which determines their operating properties.The results of experimental tests and numerical simulations concerning the preload of elastomeric working elements in Neidhart type suspension units are presented in the paper. The performed research made it possible to propose a new calculation model for determining the preload force value acting on the elastomeric cylindrical elements applied in this type of suspension unit. The results obtained using the proposed model exhibit good convergence with FEM simulation results within the range of the tested geometrical and material properties.

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Fatigue Failure Analysis of Rim

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thikf9m1kxA new article published in the « International Research Journal of Engineering and Technology« , Aug-2016.

A Finite Element Method methodology is proposed for fatigue life and failure prediction of automotive steel wheel by the simulations of dynamic radial fatigue test (RFT). A short review of theoretical models, numerical simulation models were described in conjunction with bilinear elasto-plastic finite element stress analysis under wheel rotating loading.

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Failure of high-chromium iron roll in compact strip production MILL

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2016-12-08_11h16_13A case study published in « Case Studies in Engineering Failure Analysis« , july 2013.

A high chromium (HiCr) iron work roll broke in three pieces in finishing stand 4 in a compact strip production (CSP) mill of a steel company. The paper describes the causes of the roll failure manufactured from high chrome grade steel along with the precautionary measure.

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Investigation of turbine blade failure in a thermal power plant

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1-s2-0-s2213290213000333-gr2A paper published in « Case Studies in Engineering Failure Analysis« , july 2013

The present work reports an investigation of a failure in a blade in the LP stage of a thermal power plant of 310 MW. After opening the turbine casing, one blade in the LP region was found fractured. The main damage occurred in the blade row 36 which is the L-3 row of the flow in the turbine side. The key objective of this paper was to identify the root of the failure.

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An investigation on the corrosion of flue gas sensor in boiler stack

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2016-12-08_11h01_42A  paper published in « Case Studies in Engineering Failure Analysis« , July 2013

A commercial gas velocity sensor used for flue gases monitoring was subject to severe corrosion failure. An investigation was conducted based on visual inspection, microstructural study and SEM observation coupled to EDX analysis. A combination of mechanisms was proposed including a dominating severe dew point corrosion for both transducer and its covering, galvanic attack and an eventual hydrogen attack for the transducer side part. Recommendations were proposed to avoid a future severe damage to such type of sensor including an insulation between transducer and covering metals and an up-grade of the titanium alloy used.

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Vintage-La rupture en service des assemblages vissés

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Vintage assemblages vissesLes experts en analyse de défaillances du Cetim ont réalisé courant 1988 une étude statistique de 139 cas de ruptures d’assemblages vissés. Les résultats ont montré que pour les deux tiers des cas traités, 53 % des cas de rupture est dû à un phénomène de fissuration progressive et 47 % correspond à des ruptures brutales. Pour le tiers restant, plusieurs causes  conjuguées étaient à l’origine des défaillances.

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An investigation of cracking causes in an outlet RTJ flange in ISOMAX unit

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2016-11-16_18h55_18A paper published in « Case Studies in Engineering Failure Analysis« , available on sciencedirect.com.

Corrosion has always been a problem in the petroleum refining and the petrochemical operations. The equipment of ISOMAX unit, such as reactors, furnace tubes, valves, and pipelines are frequently performed at high temperatures and high pressure condition. This working conditions, accelerates the failures due to corrosion. Therefore, heat- and corrosion-resistant alloys, e.g., austenitic stainless steels, have been widely used in this unit because of their excellent corrosion resistance, mechanical strength and toughness.

This paper describes failure analysis procedure of a cracked high pressure 321 SS RTJ flange in ISOMAX unit. In order to get conclusions related to crack propagation mechanisms of the flange, some investigations were done on the cracked flange that is mentioned in the body of the paper.

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Failure analysis of titanium alloy fasteners for aerospace applications

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2016-11-16_18h46_14A paper published in « Case Studies in Engineering Failure Analysis« , available on sciencedirect.com.

As a qualification of bolt for flight assembly, the bolt assembly has undergone proof pressure test at 2.4 MPa, Vibration test at frequency range of 20–100 Hz, ±3 db/oct for 120 s in both lateral and longitudinal directions and flight acceptance test. During routine visual inspection before electrical check, it was observed in one of the three fasteners that the head of the bolt had got sheared off from the shank portion of bolt. Further, a failure analysis was carried out on the failed bolt.

The objective of the study is metallurgical analysis of the failed bolt, fractography study to find out the root cause of the failure, and optimization of processing parameters for fastener manufacturing.

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