Alstom (Belgium)

The welding of dissimilar metallic assemblies produced by high-velocity impact occurs at high strain rates ( i.e. , impact velocities) and various dynamic collapsing angles. However, the quality of the resulting weld surface depends on several parameters, one of which is the jet formation and particle cloud formation upon impact. This phenomenon arises from intense heat and pressure upon impact, playing a decisive role in determining the resulting weld quality. Here, the jet formation of such welds is described, providing new insights into the understanding of cold-welding methods. Jet formation plays a key role in generating the necessary conditions required to weld two dissimilar metal surfaces. Copper (Cu) and aluminum (Al) samples were subjected to high strain-rate loading using the single-stage gas gun available at ID19 beamline (ESRF, France) coupled with ultra-fast synchrotron X-ray radiography in order to investigate, in situ , the production, propagation, and evolution of jets upon impact of dissimilar metals. Several impact conditions (impact angle and material configuration) were investigated at an approximate impact velocity of 500 m/s. The results reveal that the jet size, speed, and morphology evolve differently as a function of the initial impact conditions. These results demonstrate, for the first time, a direct in situ investigation of jet dynamics and weld quality in impact welding of dissimilar metallic materials. • Synchrotron X-ray imaging reveals jet dynamics in dissimilar metal impacts. • Impact angle strongly influences jet morphology and propagation behavior. • Flyer–target material configuration controls jet angle and jet velocity. • Jet growth shows a linear relationship between jet length and time.

We report on an industrial ultrafast laser system for internal marking and engraving of transparent materials. Current engraving techniques, using nanosecond infrared or UV laser, are either limited to surface marking, or create thermal stress which can lead to fracture of material. Using an infrared ultrafast laser, we describe an industrial equipment able to non-aggressively mark alphanumeric or datamatrices at a high speed, with a high readability. Anti-counterfeiting and normative applications will be presented, as well as integration on a production line.

The determination of ferroresonant oscillations in circuits with voltage transformers is a highly nonlinear problem due to the possible core saturation. It is achieved with an algorithm based upon the harmonic balance method in the frequency domain. Advantages over a time domain description are discussed. Branches of solutions in relevant parameter planes can be continued beyond bifurcation points and lead to a better understanding of the stability domains of the periodic ferroresonant oscillations. The method has been extended to the study of quasi-periodic oscillations by approximation models. The theoretical principles are validated on a full scale three-phase 15 kV configuration with ungrounded neutral, in which fundamental, subharmonic and quasi-periodic oscillations are initiated by controlled current pulse injections. Experimental stability limits have been determined and yielded good agreement with the theoretical ones. The limit value of the damping resistor in the delta-connected tertiary windings of the transformers is determined by the presented method.