Abstract: Dissimilar metal welds between Ferritic steel and Austenitic steel (F/A)are commonly used
in power plants, food industry, pharmaceutical industry and many other applications. There are
many issues/problems associated with the joining of dissimilar materials, depending on the
materials being joined and the process selected. During the laser welding process, residual stresses
are introduced by a rise in temperature during the melting or heating process followed by a very
quick cooling of the weld and the surrounding material.
In this study, CO2 continuous laser welding has been successfully applied for joining 316
stainless steel with AISI 1009 low carbon steel F/A. Design of Experiment techniques (DOE) has
been used for some of the selected welding parameters (laser power, welding speed, and focus
position) to model the dissimilar F/A joints in terms of its residual stresses. The Hole-Drilling
Method technique was use for measuring the residual stress of dissimilar welded components.
Taguchi approach for selected welding parameters was applied and the output response was
the residual stresses. The results were analysed using analysis of variance (ANOVA) and signal-tonoise
(S/N) ratios for the effective parameters combination.
Abstract: Establishing the relationship between process parameters and the magnitude of residual
stresses is essential to determine the life of welded components. It is the aim of this paper to
develop mathematical models to assess residual stresses in the heat-affected zone of dissimilar butt
jointed welds of AISI304 and AISI1016. These models determine the effect of process parameters
on maximum residual stress. Laser power, travel speed and focal position are the process input
parameters. Plates of 3 mm thick of both materials were laser welded using a 1.5 kW CW CO2
Rofin laser as a welding source. Hole-drilling method was used to compute the maximum principal
stress in and around the HAZ of both sides of the joint.
The experiment was designed based on a three factors five levels full central composite design
(CCD). Twenty different welding runs were performed in a random order, 6 of them were centre
point replicates and the maximum residual stresses were calculated for each sample. Design-expert
software was used to fit the experiential data to a second order polynomial. Sequential F test and
other adequacy measures were used to check the model’s performance. The results show that the
developed models explain the residual stress successfully. Using the developed models, the main
and interaction effect of the process input variables on the residual stresses at either side of the weld
were investigated. It is found that all the investigated laser parameters are affecting the performance
of the residual stress significantly.
Abstract: This paper reports on a practical investigation into methodology confidence of detection
(COD) in acoustic emission (AE) testing. The developed technique relies on a commercially
available software technique called “source cluster analysis” that examines the number of detected
signals over a specific area. Two factors that control cluster analysis are cluster size (the area that
signals are detected within) and cluster threshold (the number of detected events required to trigger
A confidence of detection matrix was developed based on altering cluster size and cluster threshold
which was then applied to a practical investigation of a four-point bend test monitored using AE.
Fracture length in the specimen was monitored using a foil crack gauge. The varying sizes and
thresholds of the confidence matrix were used in a cluster analysis of the recorded AE data, as the
initial cluster formed in the fracture region a crack length could be identified (based on the foil
crack gauge). Results showed that it was possible to detect a crack length of 0.55 mm with a very
high level of confidence.
Abstract: Thermoelastic stress analysis (TSA) is a well established technique for stress analysis.
Recent studies have revealed that the technique can be used to detect sub-surface defect effectively.
In this study, the technique has been used to examine the thermoelastic response to sub-surface
damage in simple bar specimens. The non-adiabatic thermoelastic response from areas close to the
damage has been studied. The study shows that the phase of the response along with the thermal
diffusion can provide a parameter that will help reveal subsurface stresses.
Abstract: During the transportation phase of the distribution cycle, packaging systems are subjected
to random dynamic compressive loads that arise from vibrations generated by the vehicle. The level
and severity of these dynamic compressive loads are generally a function of the vibration levels, the
stack configuration and stack weight. The container’s ability to withstand these compressive loads
for sufficiently long periods depends on the material’s characteristics as well as the container
design. The research presented herein tests the hypothesis that cumulative damage in the material
under random dynamic compression will result in a reduction in the overall stiffness as well as an
increase in the overall damping of the element. These are expected to be manifested, respectively,
as a shift in the fundamental resonant frequency as well as an increase in the bandwidth of the
frequency response function of the material at resonance when configured as a single degree of
freedom system. The paper presents the results of preliminary experiments in which a number of
corrugated paperboard samples were subjected to dynamic compressive loads by means of broadband
random base excitation with a vibration table coupled with a guided dead-weight arrangement.
The level of cumulative damage in the sample was continuously evaluated by monitoring the
stiffness and overall damping of the sample which were extracted from the Frequency Response
Function (FRF) of the system. This was obtained from continuous acceleration measurements of the
vibration table and the guided dead weight.
Abstract: The deformation of metals at high homologous temperatures typical of industrial forming
processes such as hot rolling is investigated using an electron micro-lithography technique enabling
strain measurements at the scale of the microstructure of these metals. Grids with a typical 5 μm
pitch have been laid on the surface of an aluminium alloy and a stainless steel deformed by plane
strain compression at 400oC and 850oC respectively. In-plane strain values can be computed from
the displacements of the intersections of the grids. Strain maps can then be plotted over
representative areas of the microstructures together with strain distributions within each phase of
the microstructure. Results obtained for a commercial high-purity aluminium alloy with 5%
magnesium show a strong localisation of deformation at triple points with a local equivalent strain
value of 1.7 for a 0.22 applied strain at 400oC. As for the two-phase stainless steel deformed to a
strain of 0.3, results show a high heterogeneity of deformation within each phase with a localisation
of deformation into bands in the ferrite phase and local values reaching more than two times the
Abstract: Work has been carried out recently, which demonstrates misorientation measurements
recorded by using electron backscatter diffraction (EBSD) enables one to undertake local post
mortem plastic strain quantification once the degree of misorientation is calibrated against plastic
strain. The present paper builds on this work and investigates the possibility of determining strain in
individual grains. Due to the anisotropy of crystalline grains, polycrystalline material deform
inhomogeneously on a microstructural level. In this study, the local strain induced in a pure copper
specimen during tensile loading measured using EBSD was compared to in-situ strain
measurements using optical microscopy imaging in conjunction with image correlation technique.
By applying an averaging procedure for improving the accuracy of the measured EBSD data, the
distribution of the misorientation within grains was quantified, and, as one would expect, it tended
to be highest near the grain boundaries.
Abstract: This work deals with the development of a full-field extensometric method at a micrometric
scale in order to precisely identify the local features of a metallic alloy at the scale of the grains.
The full-field method that has been chosen is the grid method that applies a spatial phase-shifting
algorithm to a periodic pattern. To mark the sample, direct interferometric photolithography was used.
The paper presents the basic features of the technique and first mechanical test results are commented.
Abstract: The aim of this collaborative study was to measure mechanical properties of 14MoV67-3
steel taken from small sections of material machined in-situ from an operating high pressure
collector pipe after different operating lifetimes (from 0h to 186 000h) at elevated temperatures
(540°C). Conventional methods of measuring mechanical properties of materials, such as the
uniaxial tensile test require relatively large test samples. This can create difficulties when the
amount of material available for testing is limited. One way of measuring mechanical properties
from small quantities of material is using micro tensile test samples. In this work, micro-samples
with a total length of 7.22mm were used. Digital Image Correlation method (DIC) was employed
for the strain measurements in a uniaxial tensile test. This paper shows that there is measurable
difference in the yield, ultimate tensile strength and elongation to failure as a function of the plant
operating conditions. This work demonstrates, therefore, a ‘semi-invasive’ method of determining
uniaxial stress-strain behaviour from plant components.