Relationship between microstructure and deformation behaviour during dynamic compression in Ti-3Al-5Mo-5V alloy

The relationship between microstructure and deformation and damage behaviour during dynamic compression in Ti-3Al-5Mo-5V alloy has been studied using several experimental techniques, including optical microscopy, scanning electron microscopy and microhardness measurements. It was found that the deformation behaviour during dynamic compression was closely related to deformation parameters. After dynamic deformation, the deformation shear band that formed in the titanium alloy had microhardness similar to that of the matrix. However, the microhardness of the white shear band was much higher than the matrix microhardness. The effects of deformation parameters, including deformation rate and deformation degree, on deformation localisation were investigated. Based on the results from the present work, the microstructure and deformation processing parameters can be optimised. In addition, treatment methods after dynamic compression were explored to restore alloy properties. Using post-deformation heat treatment, the microstructure and property inhomogeneity caused by shear bands could be largely removed.

Effect of post-weld-annealing on the tensile deformation characteristics of laser-welded NiTi thin foil

Laser welding is an important process for fabricating complex components involving NiTi shape memory
alloy. As welding is a thermal process, the amount of heat input and the rate of cooling have significant
impact on the microstructure and hence the resultant characteristics of NiTi. In this study, the effect of
laser welding and post-weld-annealing from 573 K to 1173 K on the thermal phase transformation behaviors,
tensile deformation and micro-hardness characteristics of the laser-welded NiTi thin foils were investigated.
It was found that the as-welded sample exhibited inferior super-elasticity compared to the base
material, and the super-elasticity could be partially restored by annealing at 573 K. On the other hand,
annealing of the weldment above the recrystallization temperature would lower the super-elasticity.

Coupled Temperature-Displacement Modelling of Injection Stretch Blow Moulding of PET bottles using Buckley Model

This study presents a fully coupled temperature–displacement finite element modelling of the injection stretch-blow moulding (ISBM) process of polyethylene terephthalate (PET) bottles using ABAQUS with a view to optimising the process conditions. A physically-based material model (Buckley model) was used to predict the mechanical behaviour of PET at temperatures slightly above its glass transition temperature. A model incorporating heat transfer between the stretch rod, the preform and the mould was built using axisymmetric solid elements. Extensive finite element analyses were carried out to predict the deformation, the distribution and history of strain and temperature during ISBM of a 20 g–330 ml bottle, which was made in an in situ test on a Sidel SB06 machine. Comparisons of numerical results with the measurements demonstrate that the model can satisfactorily model the sidewall thickness and material distributions. It is also shown that significant non-linear differentials exist in temperature and strain in both bottle thickness and length directions during the process. This justifies the employment of a volume approach to accurately predict the final mechanical properties of the bottles governed by the orientation and crystallinity which are highly temperature and strain dependent.

Modelling the correlation between processing parameters and properties of maraging steels using artificial neural network

An artificial neural network (ANN) model is developed for the analysis and simulation of the correlation between the properties of maraging steels and composition, processing and working conditions. The input parameters of the model consist of alloy composition, processing parameters (including cold deformation degree, ageing temperature, and ageing time), and working temperature. The outputs of the ANN model include property parameters namely: ultimate tensile strength, yield strength, elongation, reduction in area, hardness, notched tensile strength, Charpy impact energy, fracture toughness, and martensitic transformation start temperature. Good performance of the ANN model is achieved. The model can be used to calculate properties of maraging steels as functions of alloy composition, processing parameters, and working condition. The combined influence of Co and Mo on the properties of maraging steels is simulated using the model. The results are in agreement with experimental data. Explanation of the calculated results from the metallurgical point of view is attempted. The model can be used as a guide for further alloy development.

On visco-elastic modelling of polyethylene terephthalate behaviour during multiaxial elongations slightly over the glass transition temperature

The mechanical response of Polyethylene Terephthalate (PET) in elongation is strongly dependent on temperature, strain and strain rate. Near the glass transition temperature Tg, the stress-strain curve presents a strain softening effect vs strain rate but a strain hardening effect vs strain under conditions of large deformations. The main goal of this work is to propose a viscoelastic model to predict the PET behaviour when subjected to large deformations and to determine the material properties from the experimental data. To represent the non–linear effects, an elastic part depending on the elastic equivalent strain and a non-Newtonian viscous part depending on both viscous equivalent strain rate and cumulated viscous strain are tested. The model parameters can then be accurately obtained trough a comparison with the experimental uniaxial and biaxial tests. The in?uence of the temperature on the viscous part is also modelled and an evaluation of the adiabatic self heating of the specimen is compared to experimental results.

Element-Free Galerkin modelling of composite damage

Delamination and matrix cracking are routine damage mechanisms, observed by post-mortem analysis of laminated structures containing geometrical features such as notches or bolts. Current finite element tools cannot explicitly model an intralaminar matrix microcrack, except if the location of the damage is specified a priori. In this work, a meshless technique, the Element-Free Galerkin (EFG) method, is utilized for the first time to simulate delamination (interlaminar) and intralaminar matrix microcracking in composite laminates.

nero- a post-maximum supernova radiation transport code

The interpretation of supernova (SN) spectra is essential for deriving SN ejecta properties such as density and composition, which in turn can tell us about their progenitors and the explosion mechanism. A very large number of atomic processes are important for spectrum formation. Several tools for calculating SN spectra exist, but they mainly focus on the very early or late epochs. The intermediate phase, which requires a non-local thermodynamic equilibrium (NLTE) treatment of radiation transport has rarely been studied. In this paper, we present a new SN radiation transport code, nero, which can look at those epochs. All the atomic processes are treated in full NLTE, under a steady-state assumption. This is a valid approach between roughly 50 and 500days after the explosion depending on SN type. This covers the post-maximum photospheric and the early and the intermediate nebular phase. As a test, we compare nero to the radiation transport code of Jerkstrand, Fransson & Kozma and to the nebular code of Mazzali et al. All three codes have been developed independently and a comparison provides a valuable opportunity to investigate their reliability. Currently, nero is one-dimensional and can be used for predicting spectra of synthetic explosion models or for deriving SN properties by spectral modelling. To demonstrate this, we study the spectra of the 'normal' Type Ia supernova (SN Ia) 2005cf between 50 and 350 days after the explosion and identify most of the common SN Ia line features at post-maximum epochs. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Effect of postweld heat treatment on the microstructure and cyclic deformation behavior of laser-welded NiTi-shape memory wires

NiTi wires of 0.5 mm diameter were laser welded using a CW 100-W fiber laser in an argon shielding environment with or without postweld heat-treatment (PWHT). The microstructure and the phases present were studied by scanning-electron microscopy (SEM), transmission-electron microscopy (TEM), and X-ray diffractometry (XRD). The phase transformation behavior and the cyclic stress–strain behavior of the NiTi weldments were studied using differential scanning calorimetry (DSC) and cyclic tensile testing. TEM and XRD analyses reveal the presence of Ni4Ti3 particles after PWHT at or above 623 K (350 °C). In the cyclic tensile test, PWHT at 623 K (350 °C) improves the cyclic deformation behavior of the weldment by reducing the accumulated residual strain, whereas PWHT at 723 K (450 °C) provides no benefit to the cyclic deformation behavior. Welding also reduces the tensile strength and fracture elongation of NiTi wires, but the deterioration could be alleviated by PWHT.

Multibody modelling of gabion beams for impact applications

Gabions are stone-filled wire containers which are frequently used as retaining walls. However, due to their high mass, relatively low cost and visual appeal, a row of single gabion blocks, joined at the ends, has the potential to be used as a roadside impact absorption device where traditional steel or concrete devices may not be suitable. To evaluate such application, the shear and bending deformation of gabions under vehicle impact need to be investigated. In this paper, the shear response of a single gabion block is analytically modelled and a gabion beam multibody model is developed using a discretisation method to capture the deformability of the gabion structure. The material properties of the gabion beam are adopted from experimental values available in the literature and the modelling is statically validated over a three-point bending test and a distributed loading test. The results show that the discretised multibody modelling can be effectively used to describe the static deformation behaviour of gabion blocks.

Modelling and characterization of ultrasonic consolidation process of Aluminium alloys

Ultrasonic consolidation process is a rapid manufacturing process used to join thin layers of metal at low temperatures and low energy consumption. In this work, finite element method has been used to simulate the ultrasonic consolidation of Aluminium alloys 6061 (AA-6061) and 3003 (AA-3003). A thermomechanical material model has been developed in the framework of continuum cyclic plasticity theory which takes into account both volume (acoustic softening) and surface (thermal softening due to friction) effects. A friction model based on experimental studies has been developed, which takes into account the dependence of coefficient of friction upon contact pressure, amount of slip, temperature and number of cycles. Using the developed material and friction model ultrasonic consolidation (UC) process has been simulated for various combinations of process parameters involved. Experimental observations are explained on the basis of the results obtained in the present study. The current research provides the opportunity to explain the differences of the behaviour of AA-6061 and AA-3003 during the ultrasonic consolidation process. Finally, trends of the experimentally measured fracture energies of the bonded specimen are compared to the predicted friction work at the weld interface resulted from the simulation at similar process condition. Similarity of the trends indicates the validity of the developed model in its predictive capability of the process. © 2008 Materials Research Society.

Evaluation of Cyclic Deformation Behavior of Laser-welded Shape Memory NiTi Alloys at Different Working Temperatures

Post-weld heat-treatment (PWHT) has been established as one of the cost-effective ways to improve the functional properties, namely shape memory and super-elastic effects (SME and SE), of laser-welded NiTi alloys. However, the functional performance of the laser-welded joint at different working temperatures has not been explored yet. The purpose of this study is to investigate the effect of different working temperatures on the functional properties of the laser-welded NiTi alloys before and after PWHT by applying cyclic deformation tests. Two laser-welded samples: as-welded and heat-treated sample (after PWHT at 350 oC or 623 K) were tested in this work at room temperature, 50 oC (or 323 K) and 75 oC (or 348 K) respectively. The samples were cyclically loaded and unloaded for 10 cycles up to 4 % strain. The critical stress to induce the martensitic transformation and the residual strain after the cyclic tests were recorded. The results indicate that the heat-treated sample exhibited better functional properties than the as-welded sample at room temperature and 50 oC (or 323 K). However, both the as-welded and heat-treated samples failed in the cyclic tests at 75 oC (or 348 K). These findings are important to determine the feasible working temperature range for the laser-welded NiTi components to exhibit desirable functional properties in engineering applications involving cyclic loading.