Analysis of cracks generated in the spinning-mandrel teeth

A new paper in « Case study in Engineering Failure Analysis » published on  ScienceDirect.com. The spinning process, using a splined mandrel, is always prone to premature failure of the splined mandrels. Such a failure is thought to be related to the magnitude of the forming forces exerted on the mandrel by the forming rollers during the spinning process. In the present paper, the characteristic of corner cracks in the mandrel teeth (made of S7 tool steel) of a spinning process has been investigated. Fractography analyses using scanning electron microscopy (SEM) clearly confirm “fatigue” as being the main reason for the failure.

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Biomechanical evaluation of bending strength of spinal pedicle screws

A new article in « Engineering Failure Analysis » of septembre 2014. Pedicle screws are used for treating several types of spinal injuries. Although several commercial versions are presently available, they are mostly either fully cylindrical or fully conical. In this study, the bending strengths of seven types of commercial pedicle screws and a newly designed double dual core screw were evaluated by finite element analyses and biomechanical tests. The finite element analysis further revealed that the point of maximum tensile stress in the screw model was comparable to the point at which fracture occurred during the fatigue test.

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Failure analysis of an MVR mechanical vapor recompressor Impeller

This article, published in  » Engeeniring Failure Analysis » of september 2010, describes the root cause failure analysis of a mechanical vapor recompressor (MVR) impeller used in a dairy processing plant. A detailed investigation was commissioned to determine the source of the oscillatory stresses that must have been present to cause fatigue. A vibration analysis indicated large torsional oscillatory stresses, leading to fatigue, were induced by excitation of the 1st and 2nd torsional vibration modes of the MVR impeller and motor system. The excitation was induced by the control system for the motor variable speed drive (VSD).

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Review on Interface Fracture and Delamination of Composites

In this review paper, a methodology for measuring the interface fracture toughness of a crack between two isotropic, homogeneous materials and a delamination between two laminae of unidirectional composite materials of differing directions is presented. Four cases are considered.  For the laminates described here, they were determined by the Stroh and Lekhnittski formalisms. A failure criterion determined from first principles is presented.

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Failure Analysis of a Bearing in a Helicopter Turbine Engine

This article documents the metallurgical evaluation of a rolling element bearing that failed due to electrical discharge damage. This rolling element bearing was used in a helicopter turbine engine that failed in-flight, resulting in a hard landing of the helicopter. Optical and electron microscopy as well as energy dispersive spectroscopy were used to evaluate the bearing. Pitting and material transfer on the external bearing races bearing and mating surfaces revealed that the electrical discharge damage occurred while the engine’s components were not rotating.

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Failure Analysis of Air Cooled Condenser Gearbox

A new article in « Case Studies in Engineering Failure Analysis » published on Sciencedirect.com.

Gears are very reliable components and normally work 5 to 6 years without failure. This article is a case study of failure analysis of a gearbox which was failed in three months after its installation. The problem was identified by maintenance engineers through vibration monitoring of gearbox. Hardness measurement of case and core revealed that the core was harder than case and the applied load was sufficiently high for failure of gear. Recommendations were given to improve the fatigue life of gearbox.

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Comportement en fatigue des matériaux métalliques. Fatigue des assemblages soudés

Cet ouvrage 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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Fracture of a dental prosthesis from an inner thermal crack

A new paper about « Case study in Engineering Failure Analysis » published on ScienceDirect.com.

This paper describes the fractographic analysis of a veneer-ZrO2 single-unit dental prosthesis that fractured in a shell-like manner. Analysis of the retrieved fragment revealed that the crack originated in the bulk of the veneer from a thermal flaw located between two layers of the veneering material. Using the measured flaw plane it showed that the conditions of loading at fracture were complex and probably involved important tangential components.

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Failure analysis of a burner ring made of 20Cr32Ni1Nb alloy in gas turbine combustion chamber

A new paper in « Case study in Engineering Failure Analysis » published on ScienceDirect.com.

The failure analysis of an insert ring of a burner in a 156 MW gas turbine, made of 20Cr32Ni1Nb alloy is presented. Normally, the useful service life of these parts under ideal conditions is about 30000 hours. However, more likely fracture and failure could be observed in5000-hour inspections, which resulted in the early and premature replacement of these parts. This paper brings out the detail of investigation carried out.

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Failure analysis of cracked Brass turrets used in electronic circuits

A new paper in « Case study in Engineering Failure Analysis » published on ScienceDirect.com.

This paper describes cracking of turret terminals made of free cutting brass during swaging operation. The crack propagation tendency during cold working of brass turret terminals made from different compositions is studied through optical and scanning electron microscopy. Finally, composition for obtaining crack free terminals during swaging is suggested for applications involving cold swaging.

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