An experimental and numerical study of forces and residual stresses in AISI 316L stainless steel joints due to conventional and pulse gas tungsten arc welding

This paper aims to present the results of a numerical and experimental study of the temperature field, internal forces and the residual stresses in 2 mm thick autogenous welds of AISI 316L stainless steel produced by continuous and pulse current gas tungsten arc welding. A special experimental device was used to measure the temperature and the internal forces due to the welding. The welds were qualified for internal and external weld imperfections according to ISO 15614-1. FEM software ANSYS® Multyphysics™ was applied in order to solve the thermal and mechanical problems. Normal residual stresses were measured by the hole-drilling strain gauge method in the continuous current weld. The peak value of the longitudinal stress was 80 % of the base metal yield stress. The magnitude of the numerically obtained residual stress values was found to be 16 % to 19 % above the measured one in the longitudinal and transverse direction, respectively. The experimental device used in this study allowed for a real time measurement of forces far from the weld seam. On the basis of the correspondence between the calculated and measured forces the numerical results were verified. Therefore, this device might open up new possibilities for determining thermo-mechanical material data

Assessment of the Topside Sounder Model Profiler performance

In this investigation we apply a model-assisted technique to construct the topside electron density profile.This technique is based on the Topside Sounder Model (TSM), which provides the plasma scale height (Ts), O+/H+ transition height (Th), and their ratio Rt=Ts/Th, derived from topside sounder data of Alouette and ISIS satellites. The Topside Sounder Model Profiler (TSMP) incorporates TSM and uses the model quantities as anchor points for the construction of topside density (Ne) profiles. In the present version, TSMP takes the F2 peak characteristics – foF2, hmF2, and the neutral scale height HmF2 at hmF2– from ground-based Digisonde measurements. Previous investigations have demonstrated that HmF2, used in the Digisondes to construct the topside profiles, is smaller than the topside scale height extracted from topside sounder profiles, at middle latitudes. Therefore the Digisonde scale heights have to be adjusted by a factor estimated for each Digisonde location. When the Digisonde scale height is corrected by this factor, the reconstructed topside profiles are close to those provided by TSM. The new TSMP/Digisonde assisted technique of topside profile construction can improve the topside profiles from the worldwide network of Digisonde sounders. Extensive comparison and verification with ground and satellite derived TEC assesses the performance of the proposed technique. A first indication from the comparison with CHAMP reconstructed profiles shows lower density of TSMP/Digisonde profiles between 400 km and 2000 km. Further comparisons with Vary-Chap profiles and RPI plasmagrams from the IMAGE satellite will lead to useful conclusions concerning the performance of the proposed method up to geosynchronous altitudes

A new method for reconstruction of the vertical electron density distribution in the upper ionosphere and plasmasphere

Ground-based ionosphere sounding measurements alone are incapable of reliably modeling the topside electron density distribution above the F layer peak density height. Such information can be derived from Global Positioning System (GPS)-based total electron content (TEC) measurements. A novel technique is presented for retrieving the electron density height profile from three types of measurements: ionosonde (foF2, foE, M3000F2, hmf2), TEC (GPS-based), and O+-H+ ion transition level. The method employs new formulae based on Chapman, sech-squared, and exponential ionosphere profilers to construct a system of equations, the solution of which system provides the unknown ion scale heights, sufficient to construct a unique electron density profile at the site of measurements. All formulae are based on the assumption of diffusive equilibrium with constant scale height for each ion species. The presented technique is most suitable for middle- and high-geomagnetic latitudes and possible applications include: development, evaluation, and improvement of theoretical and empirical ionospheric models, development of similar reconstruction methods utilizing low-earth-orbiting satellite measurements of TEC, operational reconstruction of the electron density on a real-time basis, etc