Delamination-Debond Behaviour of Composite T- Joints in Wind Turbine Blades

image T-jointA pubication in « Journal of Physics »: Conference Series, 2014. Wind turbine industry utilizes composite materials in turbine blade structural designs because of their high strength/stiffness to weight ratio. T-joint is one of the design configurations of composite wind turbine blades. T-joints are prone to delaminations between skin/stiffener plies and debonds between skin-stiffener-filler interfaces. In this study, delamination/debond behavior of a co-bonded composite T-joint is investigated under 0° pull load condition by 2D finite element method. The failure sequence consists of debonding of filler/stringer interface during one load drop followed by a second drop in which the 2nd filler/stringer debonds, filler/skin debonding and skin delamination leading to total loss of load carrying capacity. This type of failure initiation has been observed widely in the literature. Failure initiation and propagation behavior, initial and max failure loads and stress fields are affected by the property change. In all cases mixed-mode crack tip loading is observed in the failure initiation and propagation stages. In this paper, the detailed delamination/debonding history in T-joints is predicted with cohesive elements for the first time.

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Reduction in diversion due to coil break

A new case study, in « Case Studies, in Engeeniring Failure Analysis », Volume 2, Issue 2, October 2014, Pages 76–83.

Diversion due to coil break in cold rolled non oriented (CRNO) grades of coils showed an increasing trend during Jan–May’12 at Silicon Steel Mill (SSM), Rourkela Steel Plant (RSP). Coil break increased from a level of less than 1% during to a level of 30% in May’12. Further studies were carried out in the processing lines and material flow was tracked from steel making to final product. The probable reasons were identified and corrective measures were taken leading to reduction in diversion due to coil break less than 2%.

 Acceder article

Crack of a first stage blade in a steam turbine

A new Case Study in « Case Studies in Engineering Failure Analysis », Volume 2, Issue 2, October 2014, Pages 54–60

The failure of the first stage blade in a steam turbine of 55 MW was investigated. The blade was made of 17-4 PH stainless steel and has been used for 12 years before failure. The current work aims to find out the main cause of the first stage blade failure. The result showed that the crack at the blade root tang was due to corrosion fatigue and the crack occurred at the blade root fillet owing to stress corrosion cracking.

Acceder article


A detailed review and Prediction of Ductile Fracture

A publication in « IJRAME« , april 2014.

Earlier researchers were studied the failure analysis through various Failure Mode and Effective Analysis (FMEA) technique and tried to predict the fracture before failure occurs. This work attempts to predict the ductile fracture criterion for the sheet metal to avoid the failure by means of considering various controllable and uncontrollable parameters. With the Design of Experiments and the Artificial Neural Network techniques a ductile fracture initiation criteria modeled and the model will be validated through Finite element simulation for the verification of the quality. If comparison results are within the limit condition, the model can be utilized for the prediction of ductile fracture before it happens in the real application.

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An interesting  publication in “Engineering Failure Analysis” available online 24 April 2014.

A nearly authentic translation of Adolf Martenś investigation report on the failure of numerous hydrogen storage cylinders is provided.

  • Explosion of the iron containers caused immense destruction on the air field Berlin-Tempelhof in 1894.
  • The translation reveals very detailed experimental procedures and at that time quite modern materials testing technologies.
  • The importance of Adolf Martens as a pioneer in conducting failure investigations becomes obvious.

Acceder article

An investigation into failure analysis of interfering part of a steam turbine journal bearing

A new Case Studies in Engineering Failure Analysis. Journal bearings as so sensitive parts of steam turbines are very susceptible to failure through different mechanisms of wear, fatigue and crush during service conditions. Failure occurring through these mechanisms lead to turbine completely shut down as a result of interfering in working conditions of bearing different parts. In this research, failed interfered part of a journal bearing related to a 320,000 kW steam turbine was examined. The studies were revealed that the bearing part loosing and inappropriate clearance can produce relative displacements under cyclic gradient loading. This condition was detrimental for the service life of turbine journal bearing via failure through fretting fatigue mechanism.

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Caractérisation d’assemblages par collage

Vous avez besoin de caractériser la tenue mécanique de votre assemblage collé pour valider le choix de votre colle et du process de fabrication associé et vérifier la conformité de produit au cahier des charges,   optimiser ou sécuriser vos cycles de production.Les multiples compétences des experts du Cetim en collage, fatigue mécanique et calcul du Cetim vous font bénéficier de leur expérience du milieu industriel pour vous aider à innover et fiabiliser votre produit.

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La thermographie infrarouge active s’impose

La thermographie infrarouge active consiste à soumettre l’élément à contrôler à une excitation extérieure maîtrisée et à y analyser la propagation de la chaleur : les perturbations visualisées révèlent alors les éventuels défauts surfaciques ou subsurfaciques tels que fissures, délaminages, corrosion, inclusions d’eau ou d’éléments étrangers, etc. La formation du Cetim, sur deux jours, débute par la présentation des principes physiques de la méthode, les matériels utilisés, les types d’excitation, les logiciels de traitement d’image, les paramètres d’influence, etc.

La société Otecmi, a souhaité se former à la thermographie infrarouge active. Une technique bien adaptée à la détection des défauts dans les composites…

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