Multiscale characterisation of the mechanical properties of austenitic stainless steel joints

A multiscale investigation was pursued in order to obtain the strain distribution and evolution during tensile testing both at the macro- and micro-scale for a diffusion bonded 316L stainless steel. The samples were designed for the purpose to demonstrate that the bond line properties were equal or better than the parent material in a sample geometry that was extracted from a larger component. The macroscopic stress-strain curves were coupled to the strain distributions using a camera-based 2D – Digital Image Correlation system. Results showed significant amount of plastic deformation predominantly concentrated in shear bands which were extended over a large region, crossing through the joint area. Yet it was not possible to be certain whether the joint has shown significant plastic deformation. In order to obtain the joints’ mechanical response in more detail, in situ micromechanical testing was conducted in the SEM chamber that allowed areas of 1x1 mm2 and 50x50 mm2 to be investigated. The size of the welded region was rather small to be accurately captured from the camera based DIC system. Therefore a microscale investigation was pursued where the samples were tested within an SEM chamber. Low magnification SEM imaging was utilised in order to cover a viewing area of 1 mm×1 mm while high magnification SEM imaging was employed to provide evidence of the occurrence of plastic deformation within the joint, at an area of just 50 μm×50 μm. The strain evolution over the microstructural level, within the joint and at the base material was obtained. The local strains were highly non-homogeneous through the whole test. Final failure occurred approximately 0.2 mm away from the joint. Large local strains were measured within the joint region, while SEM imaging showed that plastic deformation occurs via the formation of strong slip bands, followed by the activation of additional slip systems upon further plastic deformation which end up in additional slip bands to form on the surface. Plastic deformation occurred by slip and twinning mechanisms. Upon necking, significant out of plane deformations and slip deformation mechanisms were observed which suggested that plastic deformation was also happening at the last stages of damage evolution for the specific alloy. This was also evident from the large difference between the 600 MPa UTS stress value and the low stress values before final failure (which in many cases was below 30 MPa)

Optoelectronic THz mixer based on iron-doped InGaAs in a plasmonic microcavity

International audienceWe present an optoelectronic THz mixer based on irondoped InGaAs integrated into a plasmonic microcavity. The measured conversion loss is as low as ∼30 dB at 300 GHz, which constitutes a 30 dB improvement in comparison to state-of-the-art photoconductors without a plasmonic microcavity. In particular for application as receivers in high-data rate wireless telecom the presented design is very promising

Calcium oxide as a promising heterogeneous catalyst for biodiesel production: Current state and perspectives

The present paper is an overview of the recent progress in the development of various CaO-based catalysts suitable for biodiesel production. The mechanism, kinetics and optimization of transesterification reaction over these catalysts are first considered. Then, the practical application of CaO-based catalysts is discussed with a special stress on leaching and reusability of these catalysts. Also, various continuous reactor systems currently in use for biodiesel production are appraised. In addition to it, purification of crude biodiesel and the ecological aspects of using CaO-based catalysts are considered. Finally, the potentials of CaO-based catalysts for heterogeneous catalysis for biodiesel production are emphasized to assess the future perspectives of their use. This review might help in selecting suitable CaO-based catalysts and the optimum reaction conditions for biodiesel production

Photonic THz mixers based on iron-doped InGaAs embedded in a plasmonic microcavity

We present an optoelectronic mixer for the terahertz (THz) frequency-domain based on an iron-doped InGaAs layer integrated in a plasmonic microcavity. We show that this structure, under 1550-nm-wavelength illumination, allows for more than 70% absorption efficiency in a 220 nm-thin InGaAs absorber and very high Roff/Ron >1000. It leads to THz mixers driven by 1550-nm lasers showing conversion loss as low as ∼30 dB at 300 GHz. Therefore, this design is very promising for application as receivers in high-data-rate wireless telecom, in cw-THz spectrometers, or in photonics-enabled THz spectrum analyzers