Measurement of Collision Conditions in Magnetic Pulse Welding Processes

MPW （magnetic pulse welding） is a solid state joining technology that allows for the generation of strong metallic bonds, even between dissimilar metals. Due to the absence of external heat, critical intermetallic phases can largely be avoided. In this process, Lorentz forces are utilized for the rapid acceleration of at least one of the two metallic joining partners leading to the controlled high velocity impact between them. The measurement of the collision conditions and their targeted manipulation are the key factors of a successful process development. Optical measuring techniques are preferred, since they are not influenced by the prevalent strong magnetic field in the vicinity of the working coil. In this paper, the characteristic high velocity impact flash during MPW was monitored and evaluated using phototransistors in order to measure the time of the impact. The results are in good accordance with the established PDV （photon Doppler velocimetry） and show a good repeatability. Furthermore, the collision front velocity was investigated using adapted part geometries within a series of tests. This velocity component is one of the key parameters in MPW; its value decreases along the weld zone. With the help of this newly introduced measurement tool, the magnetic pressure distribution or the joining geometry can be adjusted more effectively.

Adakitic Rocks Resulting from Partial Melting of Metabasite at High-Pressure Granulite-Facies Condition during Continental Collision

Objective Previous studies on adakitic rocks with high Sr/Y and La/Yb ratios have established that such rocks may form in a variety of tectonic settings through different petrogenetic processes including： （1） partial melting of subducted young （〈25 Ma）, hot and hydrated oceanic slab; （2） partial melting of thickened lower crust; （3） assimilation and fractional crystallization processes involving basaltic magma; （4） partial melting of delaminated lower crust; and （5） partial melting of hydrous garnet peridotite. The various origins for adakites provide important constraints on crustal growth and evolution throughout the Earth＇s history.

Multi-Object Tracking Based on Segmentation and Collision Avoidance

An approach to track multiple objects in crowded scenes with long-term partial occlusions is proposed. Tracking-by-detection is a successful strategy to address the task of tracking multiple objects in unconstrained scenarios,but an obvious shortcoming of this method is that most information available in image sequences is simply ignored due to thresholding weak detection responses and applying non-maximum suppression. This paper proposes a multi-label conditional random field（ CRF） model which integrates the superpixel information and detection responses into a unified energy optimization framework to handle the task of tracking multiple targets. A key characteristic of the model is that the pairwise potential is constructed to enforce collision avoidance between objects,which can offer the advantage to improve the tracking performance in crowded scenes. Experiments on standard benchmark databases demonstrate that the proposed algorithm significantly outperforms the state-of-the-art tracking-by-detection methods.

Measurement and analysis technologies for magnetic pulse welding： established methods and new strategies

Magnetic pulse welding （MPW） is a fast and clean joining technique that offers the possibility to weld dissimilar metals, e.g., aluminum and steel. The high-speed collision of the joining partners is used to generate strong atomic bonded areas. Critical brittle intermetallic phases can be avoided due to the absence of external heat. These features attract the notice of industries performing large scale productions of dissimilar metal joints, like automo- tive and plant engineering. The most important issue is to guarantee a proper weld quality. Numerical simulations are often used to predict the welding result a priori. Nevertheless, experiments and the measurement of process parameters are needed for the validation of these data. Sensors nearby the joining zone are exposed to high pressures and intense magnetic fields which hinder the evaluation of the electrical output signals. In this paper, existing analysis tools for process development and quality assurance in MPW are reviewed. New methods for the process monitoring and weld characterization during and after MPW are introduced, which help to overcome the mentioned drawbacks of established technologies. These methods are based on optical and mechanical measuring technologies taking advantage of the hypervelocity impact flash, the impact pressure and the deformation necessary for the weld formation.