Advanced Materials Research Vols. 41-42

Abstract: The use of magnetic Barkhausen Noise Analysis (BNA) has been proven to be an effective tool for the non-destructive detection of microstructural anomalies in ferrous materials. Used as an in-process tool for the detection of grinding burn, heat treat defects and stresses, BNA is a quick comparative and quantitative alternative to traditional destructive methods. Applications of BNA as a quality control tool in gear production have existed for nearly two decades. This paper presents examples that demonstrate how BNA is used to evaluate changes in microstructural properties. Quantitative results correlate BNA test values to X-Ray diffraction values for the detection of changes in surface residual stress. Other quantitative analysis correlates BNA test values to surface hardness values for the detection of re-tempering burn. Qualitative results correlate BNA test values to acid etch patterns/colors for the detection of grinding burn defects. Robotically automated systems can test gear teeth and provide immediate feedback for process control and quality assurance.

Abstract: Boilers in power, refinery and chemical processing plants contain extensive range of tube bends. Tube bends are manufactured by bending a straight-section tube. As a result, the crosssection of a tube bend becomes oval. Using the finite element analysis (FEA) and artificial neural network (ANN), the paper presents the relationships between the plastic collapse pressures and tube bend dimensions with various degrees of ovality. It is found that as ovality increases the plastic collapse pressure decreases. Also, the reduction of plastic collapse pressure with ovality is small for a thick tube bend when compared with that for a thin tube bend.

Abstract: Hydrogen cracking in steel weldments can drastically reduce the toughness and ductility of welds in steel structures. Unfortunately, the development of the hydrogen economy will also see materials being increasingly exposed to hydrogen, in processes such as during hydrogen production and transportation. Thus, test methods are required which allow for a reproducible assessment of hydrogen embrittlement in weld material. In this article, rectangular test specimens made from weld bead on plate samples were subject to 4-point bend testing to investigate the relationship between applied stress, hydrogen content and embrittlement. This test concentrates the stresses in the weld bead, thus reducing the effects of premature HAZ cracking and enabling failure to develop in the weld metal, and showed good reproducibility. This test may form the basis for an industry test. Another test method is described using an un-machined weld bead on plate. A method of calculating the stresses and strains in this specimen in 4-point bending was developed.

Abstract: The aims of this study are to investigate the microstructure evolution of AZ31 Mg alloys with normal rolling and cross rolling as the large strain hot rolling affects microstructure, texture and mechanical properties of AZ31 Mg alloys. In the microstructures of as-rolled both samples, twins are clearly apparent, small and recrystallized grains are visible along some grain boundary and twinned regions. The Lankford values of large strain cross rolled sample obviously demonstrate the higher average r-value and lower planar anisotropy value. The press formability of cross rolled Mg alloy might be improved due to control of texture and grain size by severe deformation.

Abstract: The Australian Nuclear Science and Technology Organisation (ANSTO) has recently started commissioning the new Australian Research Reactor OPAL that has replaced the old HIFAR reactor in January 2007. At the first stage, the new reactor will provide neutrons to several neutron scattering instruments. Among them is the residual stress diffractometer Kowari that was designed to study engineering problems related to residual stresses as well as allow material science research using neutron diffraction. We give an update on the progress of the instrument’s installation and commissioning and present an example to illustrate how neutron diffraction can be used to obtain information about residual stresses in a flash butt welded plate.

Abstract: The postbuckling behavior and progressive failure of thin-walled box-shape composite beams (BSCBs) have been studied using a simplified composite panel model. It is shown that the carrying capacity of BSCBs under bending and torsion mainly depends on the postbuckling and progressive failure of panels. It is often necessary to identify and follow secondary buckling of tailored panels for correct estimation of carrying capacity. The failure process of stiffened composite panels is simulated in following path. The criterion of local failure in flange of stiffeners is applied to predict the ultimate failure of stiffened composite panels and thin-walled BSCBs. The comparison of the modeling and test shows that the prediction of BSCBs failure is satisfactory.

Abstract: This paper introduces a finite element solution for predicting the normal pressure on large diameter squat silo wall, with the application of contact element and nonlinear model. The finite element analysis (FEA) described in this paper is compared with the full-scale tests and Coulomb theory and the Chinese Code. The predicted results are in good agreement with Coulomb theory, when the top of the stored solid is horizontal; while the result of Coulomb theory is much larger than the other solutions, when the top of the stored solid is a conical surcharge pile. The results from the modified Rankine theory in Chinese Code are acceptable in both conditions. Finally, the effects on the normal pressure of Young′s Modulus are also discussed.

Abstract: The basic concept of an Aircraft Stuctural Integrity Program is to ensure that airframes are adequately managed to ensure safe operation without catastrophic failure, to maximise fleet availibilty and to minimise cost of ownership. In managing these three aspects, a number of conventional and advanced technologies are being adopted and applied within the RAAF. Composites and bonding technology has been developed and transitioned onto various RAAF aircraft over many years in the form of Bonded Patch Repairs to airframe structures (wing and fuselage). Based upon conventional heat treatment behaviour of aluminium alloys, Retrogressive Re-Ageing technology is being transitioned to minimise stress corrosion cracking. From structural mechanics and FEA technologies, Geometric Shape Optimisation methods have been applied to minimise peak stress thresholds within aged airframe structures. To manage structural degredation (fatigue and corrosion) a number sensor-based monitors are being developed and applied on RAAF aircraft. Finally, using the reliability methodology, a proactive management program to assess the extent of corrosion degradation within a whole aircraft is being instituted. This methodology is being articulated through a new paradigm known as “Environmental Degradation Management System – Tool Box” (EDMS-TB). Within RAAF it can be demonstrated that candidate technologies which are adopted have direct and in-direct positive influences within ASIPs to address the key structural integrity parameters of Safety, Availability and Cost of Ownership.

Abstract: In the car body stamping process, trim/blank die cutting edges are subjected to very high tribological loads that result in loss of tool material from both the punch and die cutting edges. According to Archard’s wear model, normal contact force and sliding distance directly affects the wear. Therefore, knowledge of the acting forces on local contact areas has a pivotal role towards the prediction of tool wear. This paper presents a finite element modelling approach to determining the contact pressure distribution on the tool cutting edges during a trimming/blanking process. Characteristic areas on sheared edge profile, variation of punch force and high contact pressures affected areas have also been analysed.

Abstract: In proton exchange membrane fuel cells (PEMFCs), the bipolar plates supply the reactant gases through the flow channels to the electrodes and serve the purpose of electrochemically connecting one cell to another in the electrochemical cell stack. Requirements of the bipolar plate material are: high values of electronic conductivity; high values of thermal conductivity; high mechanical strength; impermeability to reactant gases; resistance to corrosion; and low cost of automated production. Metallic materials meet many of these requirements but the challenge has been in obtaining the required corrosion resistance. In the paper, six metallic materials were investigated as potential bipolar plate materials. The results showed that the corrosion rates were too high even for the most corrosion resistant metals (SS316L and grade 2 Ti), and that coatings would be required.