Purpose: of this paper is to predict the hardness of cold rolled exhausts valve spindle
fabricated of Nimonic 80A via axisymmetric finite element analysis, compression testing,
and hardness inspection.
Design/methodology/approach: The stress-strain relationship of Nimonic 80A was
obtained via compression testing with deformation ratios of 10%, 20%, and 30%. Hardness
changes caused by the strain hardening effect were measured in cut specimens in both the
axial and circumferential directions following compression testing. The effective strain at the
measurement position was calculated via finite element analysis. The regression equation
for hardness changes caused by work hardening was derived from analysed strain and
inspected hardness. The cold-rolling deformation of an exhaust valve spindle was analysed
using axisymmetric finite element analysis.
Findings: The stress-strain relationship calculated from compression testing was well
expressed using the Holloman equation and the strain-hardness relationship by strain
hardening was successfully regressed using the shifted power law model for Nimonic 80A,
Nickel-Chromium based super alloy.
Research limitations/implications: This research focused hardness prediction of
spindle after ring rolling operation for generating beneficial compressive surface residual
stresses for enhancing fatigue life. Further research to quantify compressive residual stress
after rolling shall be followed to increase fatigue life.
Practical implications: The cold rolling process is a typical incremental forming method
and should be analysed under three-dimensional conditions. However, it takes lots of
time to solve incremental forming analysis. To predict hardness distribution after rolling in
the manufacturing field, FE analysis was performed under two-dimensional axisymmetric
conditions based on the assumption of no friction generated by the rolling tool. The deformed
shapes and hardness distribution from the inspection quality standard and two-dimensional
FE analysis showed very similar results. Simplified finite element analysis method for ring
rolling process for local area could be very effective method in the industrial field.
Originality/value: The stress-strain relationship and the hardness and strain relationship
were derived by compression test and hardness measurement for compressed specimen
for Nimonic 80A, Nickel-Chromium based super alloy. And simplified finite element analysis
method was suggested to predict deformed shape and hardness distribution of locally cold rolled region and achieved similar result between FE analysis result and Quality standard.
Suggested method would be very effective method to engine spindle manufacture to predict
hardness of different size of product.
Anisotropic Stress-Strain Relationship of Clay and its Application to Finite Element Analysis
