Heterogeneous deformation during electromagnetic ring expansion test

High speed forming methods become attractive in manufacturing and it significantl reduces the cost and energy requirements. Conventional manufacturing processes such as forging, forming, stamping and cutting of metals typically involve a strain rate of 10 2 – 10 4 s-1 which includes high energy rate fabrication (HERF) methods [1]. During advanced manufacturing methods such as high speed forming and high speed welding processes, certain local regions (e.g. interfaces) of materials could also experience significantly high strain rate (> 10 4 s-1). In order to understand the physical behaviours of materials and to design/control/optimise, such manufacturing processes that require an appropriate technique to capture the material’s viscoplastic property under the high strain rate deformation. Therein, the electromagnetic ring expansion test becomes a promising method to characterize the material behaviours under the high strain rate deformation. The ring expansion is caused by Lorentz force that is generated due to the magnetic induction on the ring. However, the realistic nature of the electromagnetic ring expansion test is quite complex because of the coupling physics between electromagnetic-thermal-mechanical components. Therefore, in this study we evaluate certain controlling parameters which govern the fundamental behaviour of the electromagnetic ring expansion test. Particularly the rotation and inhomogeneous deformation of the ring are noticeably observed and these phenomena require extra attention

Interface evolution during magnetic pulse welding under extremely high strain rate collision: mechanisms, thermomechanical kinetics and consequences

Magnetic pulse welding enables to produce perplexing interfacial morphologies due to the complex material response during the high strain rate collision. Thus, a thermomechanical model is used in this study to investigate the formation mechanism of the wake, vortex, swirling and mesoscale cavities with the increase of the impact intensity at the interface. The formation of these interfacial features are difficult to characterize by insitu methods, thus the origin of phenomena still remain a subject of open discussion. Our studies identify the governing mechanisms and the associated thermomechanical kinetics, which are responsible for the formation mechanism of interfacial features. Numerical predictions of wake and vortex resulted from the re-entrant jetting in-conjunction with the complex interfacial mixing concur with the experimental observations. The computational analysis reveals multiple heating stages of the interface due to the contact of ejecta particulates, adiabatic shearing during the onset of the collision, and the swirling motion of the materials at the interface zone. This repeated heating of the materials and the advent of rapid solidification produce the vortex zones. The high-speed kinematics of the vortex in conjunction with the local heating at the vicinity of the interface leads to the formation of swirling structure and mesoscale cavities in the center of the swirls, which are in good agreement with experimental observations. Thus, the simulation provides a non-destructive approach to identify the interfacial structures in an impact welded joint

Effect of the nanopores in the Al-Cu intermetallic phase on nanoindentation instabilities at the Al/Cu interface of a magnetic pulse impact weld

This paper investigates the features of an AlxCuy intermetallic phase produced by the high strain rate collision at an Al/Cu interface during magnetic pulse impact welding. A SEM observation coupled with a EDX analysis reveals a nanoporous Al2Cu phase. A mechanical characterization using a high resolution nanoindentation shows a P-h curve with a pop-in phenomenon which is attributed to the nanoporosity of the Al2Cu phase. As the nanoporosity fraction increases from ~1 % to ~6 %, the hardness decreases twofold with a linear tendency. The total cumulative length of pop-ins increases with the nanopores fraction, with a linear tendency also. The critical force of pop-ins is lowered by the porosity content. The curve of highest porosity fraction exhibits the lowest values of critical force. These observations correlate the nanopores to the pop-ins. Compared to the parent metals, the Al2Cu intermetallic phase exhibits a higher hardness in between 4 and 10 GPa

Heterogeneous deformation during electromagnetic ring expansion test

High speed forming methods become attractive in manufacturing and it significantl reduces the cost and energy requirements. Conventional manufacturing processes such as forging, forming, stamping and cutting of metals typically involve a strain rate of 10 2 – 10 4 s-1 which includes high energy rate fabrication (HERF) methods [1]. During advanced manufacturing methods such as high speed forming and high speed welding processes, certain local regions (e.g. interfaces) of materials could also experience significantly high strain rate (> 10 4 s-1). In order to understand the physical behaviours of materials and to design/control/optimise, such manufacturing processes that require an appropriate technique to capture the material’s viscoplastic property under the high strain rate deformation. Therein, the electromagnetic ring expansion test becomes a promising method to characterize the material behaviours under the high strain rate deformation. The ring expansion is caused by Lorentz force that is generated due to the magnetic induction on the ring. However, the realistic nature of the electromagnetic ring expansion test is quite complex because of the coupling physics between electromagnetic-thermal-mechanical components. Therefore, in this study we evaluate certain controlling parameters which govern the fundamental behaviour of the electromagnetic ring expansion test. Particularly the rotation and inhomogeneous deformation of the ring are noticeably observed and these phenomena require extra attention