Failure Analysis of Motor Tire Bead Wires During Torsion Test
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CASE HISTORY—PEER-REVIEWED
Failure Analysis of Motor Tire Bead Wires During Torsion Test Souvik Das • Prashant Koli • Jitendra Mathur • Arthita Dey Tanmay Bhattacharyya • Sandip Bhattacharyya
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Submitted: 30 January 2013 / Published online: 10 October 2013 ASM International 2013
Abstract Torsion testing is used to determine the quality of steel wire used for motor tire beads in pneumatic tires. These steel wires must have good-tensile strength so that the tire bead can support the finished tire safely, and yet retain adequate ductility to deform easily around the forming wheel. The present paper highlights premature failure of bead wire which failed during torsion test. Torsion property is one of the important parameters of tire bead as it monitors both the metallurgical soundness and surface quality of a drawn wire. From the analysis, it has been concluded that probable reason for premature failure is due to strain aging (dynamic and static) caused by interstitial atoms which bounds the mobile dislocations resulting in increases yield strength and decreases bead formability. Moreover, the microstructural study indicates that failed specimen has misaligned and broken lamella of pearlite with globular cementite which creates the array of voids. These voids hinder the rotation of pearlite during torsion test thus leading to brittle fracture. Keywords Motor tire bead Torsion Interstitial atoms Globular cementite
Introduction High carbon steel wires are vital material for variety of applications such as bead wire, spring, and steel cord for reinforcing pneumatic tires. The bead is that part of the tire
S. Das (&) P. Koli J. Mathur A. Dey T. Bhattacharyya S. Bhattacharyya Metallurgical Laboratories, R&D and Scientific Services, Tata Steel Limited, Jamshedpur 831001, India e-mail: [email protected]; [email protected]
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that contacts the rim on the wheel. Wires used for tire bead applications are drawn from patented wire to achieve specific properties required for critical applications. The bead seats tightly against the two rims on the wheel to ensure that a tubeless tire holds air without leakage. These steel wires must have good-tensile strength so that the tire bead can support the finished tire safely, and yet retain adequate ductility to deform easily around the forming wheel. Bead wire ductility, i.e., the ability of a high strength steel wire to deform plastically without fracturing, is determined by torsion value. Torsion and bend both are important as these two aspects determined the material quality and surely safety of the passengers in a running car. Torsion property monitors both the metallurgical and surface quality of a wire used for critical applications. The performance of tire on road improves with the higher torsion values offering improved passenger safety. It has been reported earlier that the torsion property of high carbon steel wire depends on optimum combination of strength and ductility. A comprehensive work on torsion failure of carbon steel wire was reported
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