Thesis-1974-Turner.pdf (6.88 MB)
The formability of aero-engine alloys
thesis
posted on 2018-08-22, 11:47 authored by Alan F. TurnerThe alloys used in aero-engine manufacture have widely differing
properties and are subject to a multitude of forming operations.
Unfortunately, there are many cases of failure occurring during forming,
even though a specification restricts the maximum thinning strain.
Recently, difficulties involved in the formability of mild steel
have resulted in the use of forming limit diagrams (FLD) to explain these anomalies. In this work
a similar technique was applied to aero engine alloys. The FLDs for
six commonly used aero engine alloys were determined by measuring
the maximum, principal strain increments on the surface of a sheet
metal blank. The blank was deformed to failure by fluid forming, using various dies to give different stress ratios. The maximum,
principal strain was then plotted against the strain perpendicular
to it, resulting in the FLD for that material. Further tests were
performed with solid punch tooling and these results showed how
various friction conditions can give rise to different stress ratios.
The instability strains were determined and were virtually
coincident with the maximum load condition. This allowed Swift's
treatment of instability strains to be applied, after determining
the work hardening characteristics of the material from uniaxial, tensile
tests. Unfortunately, the simple agreement was poor, but by fitting the Swift relationship incrementally, it was found that an approximately
constant work hardening exponent and anisotropy parameters could be
obtained. However, the 12% Cr–Mo steels showed a variation in the
anisotropy parameters consistent with the stress ratio, although the
work hardening exponent remained constant. This implies that a preferred
orientation develops at small strains in these materials.
Funding
Rolls–Royce Ltd. Science Research Council.
History
School
- Aeronautical, Automotive, Chemical and Materials Engineering
Department
- Materials
Publisher
© Alan Frederick TurnerPublisher statement
This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/Publication date
1974Notes
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy at Loughborough University.Language
- en