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Fracture Mechanics Approach to Splitting in Low Spring Index Cold Coiling Process

Published

Author(s)

Y. Prawoto, S. Manville, T. Sakai, L. Lee, M. Tanaka, Thomas H. Gnaupel-Herold

Abstract

This paper is an attempt to understand the coil splitting phenomena by means of fracture mechanics. The methods used combines the residual stress measurement with neutron and finite element analysis. The support of the metallurgical evaluation is used as an evidence to justify the use of fracture mechanics concept. Comparing coil springs manufactured at two different manufacturing lines, namely N1 and N6, residual stress distributions in three main directions were measured using neutron diffraction. The results of the residual stress measurement were then converted to the stress intensity factor to enable the analysis in fracture mechanics. The mixed mode analysis of opening, Mode I, and in‐plane shearing, Mode II, is used to solve the splitting problem. The discrepancy between the coil made at N1 and N6 was identified and taken into account in terms of the profile difference. Based on this difference, an FEA simulation was conducted. The results support the experimental finding, which is that the shape of the coil manufactured influences the pattern of the residual stress, which leads to different splitting behavior. This simple analysis helps practitioners understand why, and how, some cold coiled products split after manufacturing. It is concluded that this very basic concept of fracture mechanics can be used to establish the limit of the cold coiling process by evaluation of the mixed mode stress intensity factor to the fracture toughness of the material.
Citation
Journal of Failure Analysis and Prevention
Volume
19
Issue
3

Keywords

spring, residual stress, fracture mechanics, neutron diffraction

Citation

Prawoto, Y. , Manville, S. , Sakai, T. , Lee, L. , Tanaka, M. and Gnaupel-Herold, T. (2019), Fracture Mechanics Approach to Splitting in Low Spring Index Cold Coiling Process, Journal of Failure Analysis and Prevention, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=927919 (Accessed September 25, 2021)
Created June 1, 2019, Updated February 26, 2020