Advances in Experimental Mechanics V

Paper Title Page

Authors: E.M. Anawa, Abdul Ghani Olabi
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.
Authors: Khaled Y. Benyounis, Abdul Ghani Olabi, J.H. Abboud
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.
Authors: Rhys Pullin, Karen M. Holford, S.L. Evans
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 cluster). 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.
Authors: Nuttaphon Sathon, Janice M. Dulieu-Barton
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.
Authors: M.A. Garcia-Romeu-Martinez, Vincent Rouillard, Michael A. Sek, V.A. Cloquell-Ballester
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.
Authors: C. Pinna, Yong Jun Lan
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 applied compression.
Authors: Masayuki Kamaya, Joao Quinta da Fonseca, L.M. Li, Michael Preuss
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.
Authors: Raphaël Moulart, René Rotinat, Fabrice Pierron, Gilles Lérondel
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.
Authors: Rafal M. Molak, M. Kartal, Zbigniew Pakiela, W. Manaj, Mark Turski, S. Hiller, S. Gungor, Lyndon Edwards, Krzysztof Jan Kurzydlowski
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.

Showing 21 to 30 of 45 Paper Titles