The subject of my PhD was the measurement and prediction of the strain in a
rolling process at different length-scales. It
involved both experimental work with rolling and plane strain
compression tests and numerical work with finite element
simulations of rolling and compression tests. I also dealt
with Finite Element
(FE) simulations of the behaviour of
ferrite under thermo-mechanical loading (micro-modelling).
University of Sheffield
I gained a reputation as a competent FE modeller and I
collaborated with other research groups building a range of
different models (bolted beams subject to fire load, contact analysis of bolted plates,
bending test, etc). As part of my academic work I often gave
presentations to sponsors and academic staff and I was involved in
laboratory demonstrating and tutoring in the department of
A scheme of my PhD work is shown in figure 1.
Fig.1 - Scheme of my research activities
The physical conditions of the rolling process
are so extreme (high temperature, large deformation, high speed)
that none of the traditional methods can be used to measure the
strain. Looking at the left-hand side of figure 1, the strain can
be measured both in compression and rolling tests using gridded
Fig. 2 - Aluminium
specimen before and after the compression test.
Compression tests are normally used to simulate the
material behaviour in a rolling process.
The strain is measured by comparing the grid before and after
deformation. This can also be done in a rolling experiment using
the specimen shown in figure 3.
Fig. 3 - Rolling specimen and gridded insert (x rolling
After measuring the strain, both compression and
rolling FE models are created using
in order to reproduce the experimental conditions (fig. 4)
including experimental problems such as tools misalignment (fig.
Fig. 4 - 2D model of
a compression test (50% reduction, 400 °C)
Fig. 5 - Insert after deformation with highly misaligned
tools and corresponding FE model. Comparison of FE and
experimental temperature during compression
Finally the measured temperature and strain are compared with the
numerical results. The results of these comparisons were very good and
a series of journal
have been published.
The right-hand side of the scheme in figure 1 shows another aspect
of my research work. It is the
measurement of the strain at a much smaller scale. Using a special
technique a microgrid can be laid on a specimen before
compression. This microgrid can have a pitch of up to 5 micron and it
allows the measurement of the deformation within a single grain or
Fig. 6 - Microgrid
on a duplex stainless steel (detail) and FE model.
A microgrid can be created on a stainless steel insert (figure 6).
The microgrid is visible on the two phases austenite and ferrite
before deformation (1).
The picture of the
model material before deformation
(1) is used to build a
Finite Element (FE) model of the microstructure
(2). This model
material (1) was cast, rolled and heat treated by myself. Different
material properties are assigned to ferrite and austenite in the
FE model. The stress-strain curves used to define the material
behaviour in the FE model were obtained through axisymmetric tests
of pure ferrite and pure austenite in a range of strain, strain
rates and temperatures. The area covered by the microgrid is 0.7×0.7
mm and the pitch of the microgrid shown
is 5 micron. The FE model covers
the whole area of the microgrid with over 40,000 nodes.
After the test, the
deformed microstructure (3) is analysed and the components of the
strain can be measured by using the deformed microgrid. Using this
data, contour plots of the measured strain components can be
obtained (5) and can be compared with the FE results
This technique can help
the development and the validation of those mathematical models
that deal with the relationship between strain at different length
scales (scale transition models).
My academic skills
Finite Element modelling of various non linear problems
Programming and linking commercial codes with user-developed
Experience in casting stainless steel with different volume
fractions of austenite and ferrite
Rolling and heat treatments to obtain suitable grain/phase size
Surface treatments on aluminium and stainless steel (etching,
Experience in compression and rolling tests
Use of optical microscope, SEM and EBSD techniques
Writing of articles, reports and Power Point presentations
Oral presentations to sponsors and academia
Assisting final year students in their project: teaching ABAQUS, ANSYS, Hypermesh, experimental set-up
Teaching and demonstrating: Matlab, Charpy test, tensile test, technical
drawing, wind tunnel
Marking assignments and reports
Organization of social events within the research group