The direct metal deposition (DMD) laser process is a novel technique, well adapted for aeronautical applications, that allows the building of complex 3D geometries through the interaction between a powder nozzle system and a continuous laser beam. A three-step analytical and numerical approach was carried out to predict the shapes of manufactured structures and thermal loadings induced by the DMD process. First, powder temperature was calculated using a recent analytical model, then the geometry of walls was predicted by a combined numerical + analytical modelling using a discretization of the physical interaction domain, and finally, a finite element calculation was carried out on COMSOL 3.3 Multiphysics software to describe thermal behaviour during DMD of a titanium alloy.Our thermal model takes into account the moving interface during metal deposition with a specific function κ (t, x, y, z) allowing the conductivity front to move simultaneously with the moving laser source (with an appropriate spatial energy distribution), thus representing rather precisely the DMD process. This allowed us to provide an adequate representation of temperatures near the melt-pool, and to reproduce with a good accuracy thermal cycles and melt-pool dimensions during the construction of up to 25-layer walls. This was confirmed by comparisons with experimental thermocouple data T = f(t), and fast camera melt-pool recording.

We report that 316L austenitic stainless steel fabricated by direct laser deposition (DLD), an additive manufacturing (AM) process, have a higher yield strength than that of conventional 316L while keeping high ductility. More interestingly, no clear anisotropy in tensile properties was observed between the building and the scanning direction of the 3D printed steel. Metallographic examination of the as-built parts shows a heterogeneous solidification cellular microstructure. Transmission electron microscopy observations coupled with Energy Dispersive X-ray Spectrometry (EDS) reveal the presence of chemical micro-segregation correlated with high dislocation density at cell boundaries as well as the in-situ formation of well-dispersed oxides and transition-metal-rich precipitates. The hierarchical heterogeneous microstructure in the AM parts induces excellent strength of the 316L stainless steel while the low staking fault energy of the as-built 316L promotes the occurrence of abundant deformation twinning, in the origin of the high ductility of the AM steel. Without additional post-process treatments, the AM 316L proves that it can be used as a structural material or component for repair in mechanical construction.

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A Ti-47Al-2Cr-2Nb (at.%) material was fabricated using two laser-based methods, “Selective Laser Melting” (SLM) and “Direct Metal Deposition” (DMD), for potential uses in aircraft jet engines. Experiments were conducted under controlled atmosphere by changing the processing parameters. Optimal parameters were searched for this relatively low ductility material to prevent cracking due to built-up residual stresses during fast cooling. It was observed that these non-equilibrium cooling conditions were fast enough to generate ultra fine and metastable structures exhibiting high microhardness values. Post heat-treatments were successfully used to restore homogeneous lamellar or duplex microstructures and to relieve the residual stresses. A comparison of these two methods is provided in terms of powder requirements and of process parameters to achieve noncracked structures and fully dense materials.

This paper describes a concept of the circulating codes covering the whole class of the space-time codes. The circulating codes do not narrow the radiated pattern of the antenna array, thus providing a wide angular coverage, possibly tunable. In turn, the beam-forming on transmit is achievable by means of the signal processing in one (or each) receiver channel. The modelling results demonstrate the efficiency of the circulating codes based on their multidimensional ambiguity functions.

A global signal processing chain for detection and localisation of moving human targets using a multistatic ultrawideband radar system with widely separated receiving antennas is proposed. The design options for the system are presented and justified, and the required signal processing steps are summarised. Special attention is then devoted to the critical issue of target association. A slow-time feature, video time density function, is proposed to associate target responses in different receiver channels. Video time density function is extracted from range-Doppler video sequences for each target. It indicates the slow-time evolution characteristic of the moving human targets, and thus is invariant to radar observation angles (provided that the target can be detected). Auction algorithm-based global nearest neighbour approach is extended to the measurement-to-measurement association between receivers. The decentralised tracking approach proposed is experimentally verified on measured data.

This study presents a simple yet ingenious transmit diversity technique (so-called hybrid codes) for phased array radar. Its main property is the capability of digital beamforming on transmit just like with a set of orthogonal signals employed by coherent multiple-input-multiple-output radar and simplicity (only one waveform has to be generated in time). The performance of the hybrid codes is examined by analysing the transmit ambiguity functions containing beampatterns and range profile for all angular directions of interest.

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