Residual Stress Distribution in Deformed Aluminum Bars

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Title
Author
Tutor

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Abstract
The purpose of this study was to evaluate the distribution of residual stresses along
deformed aluminum bars. First, the experimental samples comprise of 6061-T6 and
7075-T6 aluminum alloys. The bars underwent machining prior to their deformation
in a four point bending apparatus. Other samples were collected from the materials
and were used in tensile tests to investigate their particular material properties. The
residual strains in the deformed sections were measured, with the aid of a neutron
diffractometer. After this, the diffraction data will be utilized to determine the
distribution of residual stresses along the y-axis of the aluminum bars. Finally, data
analysis will be performed to establish the pattern of distribution of residual
stresses along the y-axis of the samples.

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Contents
Title............................................................................................................................ 1
Author........................................................................................................................ 1
Tutor........................................................................................................................... 1
Abstract...................................................................................................................... 2
Introduction................................................................................................................ 4
Experiment details..................................................................................................... 6
Sample preparation.................................................................................................... 6
Material properties and Mechanical testing................................................................7
Data analysis.............................................................................................................. 7
Discussion................................................................................................................ 11
Conclusion................................................................................................................ 11
Bibliography............................................................................................................. 13
Introduction

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Residual stresses occur in machine components due to various machine processes
and heat treating procedures. According to Simon Abis and others, the
measurement of these stresses is very essential because diminish the durability of
equipment parts by lowering the fatigue and tensile strength of metallic materials.1
Moreover, they often precipitate crack elongation thus leading to machine failure.
Consequently, Simon Abis and others emphasize that engineering professionals
should not only concentrate on controlling surface stresses, but also consider the
harmful effects of residual stresses.2
Currently, many manufacturers, especially car manufacturers, have made the
reduction of machine dimensions one of their sole objectives. Therefore, it has
become very important to measure intrinsic residual stresses that emerge from the
adoption of thinner parts, so that various machine components do not lose their
strength. Even though it is possible to quantify surface residual stresses with the aid
of x-ray diffraction and strain gauges, such strategies are ineffective if one wishes
to measure the deep lying residual stresses. Hence, Michael T Hutchins3 states that
the use of neutron diffraction is more effective in such applications.
Neutron beams are capable of penetrating inner regions unlike x-ray radiation. This
makes neutron diffraction a very efficient method of gauging the three dimensional
residual stresses, within larger components in a non-destructive fashion. We can
define diffraction as the outcome of waves interacting with geometrical bodies.
Furthermore, it is a phenomenon characterized by the continuous alternation of
destructive ad constructive interference among waves, which emerge from two
distinct sources. Additionally, a basic tenet of the discipline of quantum mechanics
stipulates that all sub-atomic structures including protons, neutrons and electrons
possess characteristics that are both wave and particle like in nature. Per Michael T
Hutchins3, a particle has a de Broglie wavelength, which depends on its momentum,
p, through the Planck constant, h.
λ= h
p
The wave-like qualities of these particles implies that diffraction will always occur
whenever radiation impinges on solid crystalline bodies. Additionally, as the
interaction between atoms and particles proceeds in a crystalline lattice, each atom
is inevitably converted into a radiation producing body according to the principles of
1 Simon Abis, Robert Caciuffo and Roger Coppola, 'Neutron Diffraction Study of Deformation
Textures In 7012 Aluminum Alloy Extruded Bars' (2016) 6 Materials Letters, 22-50.
2 John S. Robinson, Damon J. Hughes and Charles .E. Truman, 'Confirmation of Principal
Residual Stress Directions in Rectilinear Components by Neutron Diffraction' (2010) 47
Strain, 35-67.
3 Michael T Hutchings,
Introduction to the Characterization of Residual Stress by Neutron
Diffraction (13th edn, Taylor & Francis 2014), 5.