Failure Analysis of a Fractured Steel Track-type Chain Caused by High-cycle Fatigue of the Clamp Holder
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TECHNICAL ARTICLE—PEER-REVIEWED
Failure Analysis of a Fractured Steel Track-type Chain Caused by High-cycle Fatigue of the Clamp Holder Marianna Katsivarda . Sofia Papadopoulou . Athanasios Vazdirvanidis . George Pantazopoulos
Submitted: 19 September 2020 / Accepted: 24 September 2020 ASM International 2020
Abstract The potential root causes of the premature fracture of an in-service caterpillar-type chain component (shoe block and the respective clamp holder) were investigated. The clamp holder’s fracture surface and a cross section of the microstructure were examined by means of stereo- and optical microscopy. Hardness measurements were also taken. The clamp holder microstructure consisted of lower bainite. Fractographic examination revealed that fatigue (reversed bending mode under low applied stress) was the dominant mechanism resulting in the failure of the clamp holder. Crack initiation occurred at the outer surface of the holder which possessed deep surface defects. The final holder fracture subsequently caused unbalanced stress conditions overloading the shoe block (which is a secondary fracture phenomenon). Keywords Fractography Fatigue Steel clamp holder Steel shoe block
Introduction and Background Information The present failure analysis case study investigates the root cause of fracture of a chain link (shoe block) alongside its respective clamp holder of a roller unit used for copper tube drawing machine. Both failed samples were examined to determine the cause of failure and its origin. Since multiple steel fragments and components were received,
M. Katsivarda S. Papadopoulou A. Vazdirvanidis G. Pantazopoulos (&) ELKEME Hellenic Research Centre for Metals S.A., 61st km Athens – Lamia National Road, 32011 Oinofyta, Viotias, Greece e-mail: [email protected]
the failure scene was reconstructed to promote the features that caused the final failure. A clamp holder is a cylindrical metallic bar which is usually in a forged condition. Common reasons that may result to its failure relate to the manifestation of an inappropriate microstructure during its production process (e.g., containing inclusions), mechanical defects and loading conditions exceeding the materials mechanical properties [1]. More than 80% of the operating equipment failures are caused by fatigue, as a result of complex and irregular stress cycles during their operation [2, 3]. This cyclic loading leads to fatigue fracture which produces a surface appearing brittle on a macroscopic scale. Characteristic morphologies of the final fatigue stage showing an overload-related brittle fracture mode (cleavage fracture) are presented in Ref. [4], while a quasi-cleavage fracture is observed in a tool steel gripper in Ref. [5]. This final failure mode is caused by the incremental propagation of cracks leading to the reduction in the cross section of the component to the point where it can no longer support the maximum applied load; initiating a rapid fracture process [6]. Three distinct stages are observed in a typical fatigu
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