Palavesamuthu Manikandan

Mach stem formation in explosion systems, which include high modulus elastic elements

Results of experimental and numerical research of the Mach stem formation in explosion systems, which include high modulus elastic elements, are presented. The experimental data are discussed, and the analysis using ANSYS AUTODYN 11.0 is provided. It is shown that the phenomenon is reproduced for various high explosives. The Mach stem formation is observed in the conditions close to critical conditions of detonation transfer from an active to a passive HE charge. The best conditions for the Mach stem formation have been observed for TG-40/60 (Russian analog of Composition B) with silicon carbide insert heights of 16.5 mm, 18 mm, and 19.5 mm. The physical reason of the phenomenon is the propagation of a convergent detonation wave into highly compressed HE. The phenomenon is reproduced in numerical simulation with ANSYS AUTODYN 11.0. Calculated maximum value of pressure on the symmetry axis of passive HE charge was up to 1.25 Mbar. Results of metallographic analysis of steel identification specimen on the r...

Effect of Mechanical Alloying Parameters on the Formation of Ni?Cu Solid Solution Coating on the Ni Balls

Mechanical alloying is a viable technique to produce coatings of limited thickness on a solid substrate. Elemental copper powder was mechanically alloyed with nickel balls in a planetary ball mill under various milling times and rotation speeds. The mutual diffusion of the elements during milling which led to the formation of a Ni–Cu solid solution and the creation of Ni–Cu coating on the surface of Ni balls was studied. The maximum hardness of the coating increased to threefold (HV0.01594) that of the substrate. Micro-structural characterization of the coating surface using optical microscope, scanning electron microscope (SEM), and electron probe micro-analyzer (EPMA) indicates that, by using appropriate processing conditions, a thick, fully-dense coating can be metallurgically bonded to the nickel balls. X-ray diffraction (XRD) results revealed the formation of nanocrystalline solid solutions.

Cladding of Titanium and Magnesium Alloy by Explosive Welding Using Underwater Shockwave Technique and Effect on Interface

The wide use of clad joints in practical application has been inhibited due to the difficulty in welding certain combinations such as tungsten/-copper, molybdenum/-copper and magnesium with aluminum, titanium and stainless steel. These material combinations are generally classified as difficult to weld by conventional material joining techniques due to the vast difference in material properties and the degradation of mechanical properties of the joints. Explosive welding is here a viable alternative technique. Explosive welding is a solid-phase welding process that uses the energy of a detonating explosive to create a strong metallurgical bond. This technique has achieved impressive success in the joining of metallurgically incompatible combinations that are otherwise impossible to join by conventional welding techniques. Though the technique is suitable for joining only thin plates, it is efficient in joining some difficult to join combinations like magnesium with aluminum, titanium and stainless steel. In this paper, the result of welding titanium and magnesium was reported.

Transition joints of aluminum and magnesium alloy made by underwater explosive welding technique

In this study, aluminum alloy A5052 and magnesium alloy AZ31 were joined by conventional parallel setup of explosive welding and underwater explosive welding. Microstructural characterization of conventional welded joints revealed a characteristic wave formation with vortices and contact surface melting layer containing intermetallics. In order to reduce the vortices and melting layer, underwater explosive welding was used. The welding parameters are regulated to reduce the kinetic energy loss during collision. The low kinetic energy loss in underwater explosive welding resulted in the formation of small waves with less vortices and no melting layer.

Explosive Welding of Molybdenum/Copper Using Underwater Shock Wave

In this research, surface modification of copper with molybdenum was made using explosive welding technique. The underwater shock waves derived from the detonation of explosives was used to bond thin films of molybdenum on copper. Visual observation shows a sound joining of Mo/Cu. Microstructural characterization reveals the bonding interface with a clear wave formation between the participant metals. A clear wavy interface is formed when the weldable conditions lie in the weldability window. When the weldable conditions lie near the right limit or lower limit, a jet trapped region was formed.

Structural evolution of the Cu-Ni solid solution formed by Ball Mechanical Alloying Treatment (BMAT)

A nanostructured powder with uniform distribution of Ni and Cu powders was produced by means of the Ball Mechanical Alloying Treatment (BMAT). Mutual diffusion of Ni and Cu in the nanostructured layer and the microstructure of the cross section of the remaining powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Electron Probe Microanalyzer (EPMA). X-ray diffraction patterns revealed that increasing the milling time gives rise to decreasing crystallite size and lattice parameter during the MA process. Furthermore, scanning electron microscopy (SEM) was utilized not only for evaluating the morphology and microstructure of the remaining powder particles but also for proving this claim that during MA process, the mutual diffusion of Ni and Cu has occurred. Elemental mappings also show that the alloying process occurred in samples but obtaining the uniform shape, size and microstructure of the powder requires increase in the milling time.

Phenomenon of energy focusing in explosion systems which include high modulus elastic elements

The results of experimental studies of physical reasons and conditions of the phenomenon of energy focusing in explosion systems including high modulus elastic elements are presented. Experiments were conducted to study the conditions of this phenomenon for TG‐40/60, SEP and Composition B. For each HE a number of experiments has been conducted for various heights of silicon carbide inserts. Presence or absence of a hole in the steel specimen was determined. Also a number of frame‐by‐frame recordings of the process with record step of 1 μs have been performed. It is shown that the energy focusing phenomenon is reproduced for various high explosives. The phenomenon is observed in the conditions close to critical conditions of detonation transfer from an active to a passive HE charge. The best conditions for the phenomenon were observed for TG‐40/60 for ceramic insert heights of 16.5 mm, 18 mm and 19.5‐mm. Physical reason of focusing process is the propagation of a concave detonation wave into highly compres...

Some Trials on Underwater Explosive Welding of Thin W Plate onto Copper Substrate

The possibility of the use of underwater shock wave to weld a thin plate onto a base plate is demonstrated in the present investigation. The composite materials of tungsten and copper have been used for many applications such as high heat flux components, welding electrodes, electrical contacts at high voltage and heat sink. In this work, thin tungsten plate was tried to weld on a copper base plate using underwater explosive welding technique which has been developed by one of the authors’ group. This technique enables to accelerate a thin plate to several hundreds m/s to satisfy the condition of explosive welding. Such an order of the velocity is adequate to form welding at the interface. In the case of the use of underwater shock wave derived from the detonation of an explosive in water, the kinetic energy required for the welding is appropriate and it makes possible to suppress the effect of heating which may induce excessive melting and/or form brittle intermetallics at the interface. The welding interface showed wavy structure typically found in explosively welded materials and the bonding strength is expected to be high as the clads explosively welded by conventional method. The effect of experimental parameters on the interfacial microstructure is discussed.

Observation of High Velocity Oblique Collision of Titanium and Stainless Steel Plates by Using Gas Gun

The jet formed from the high velocity collision of metal plates have proven both scientifically unique and of potential interest, although the underlying deformation mechanism remains less firmly established. In this study, oblique collision of titanium and stainless steel observed by high-speed camera is discussed. The nature of jet, its velocity and its existence at low velocity are all discussed and theoretical developments are connected. Microstructural studies are done on the sample welded using gas gun and a comparison with explosive welded sample is made.