NET TG1: Residual stress analysis on a single bead weld on a steel plate using neutron diffraction at the new engineering instrument ‘STRESS-SPEC’

Non-destructive analysis of phase specific residual stresses and textures is only possible by diffraction methods. The new neutron diffractometer STRESS-SPEC was installed at FRM-II in Munich, Germany, for this purpose. It is designed to be equally applied to texture and residual stress analyses by virtue of its flexible configuration. The results of measurements on a single bead on plate weld within the framework of the European Network on Neutron Techniques Standardisation for Structural Integrity (NET) are presented here, in order to demonstrate the reliability and accuracy of the instrument by comparing previous results from other neutron diffraction facilities by using a Bayesian statistical approach.     

Residual stresses measurement by neutron diffraction and theoretical estimation in a single weld bead

Welding residual stresses are important in pressure vessel and structural applications. However, residual stress remains the single largest unknown in industrial damage situations. They are difficult to measure or theoretically estimate and are often significant when compared with the in-service stresses on which they superimpose. High residual stresses lead to loss of performance in corrosion, fatigue and fracture.     

Residual stress due to welding and its effect on the assessment of cracks near the weld interface

An experimental/analytical hybrid-type investigation of the effects of residual stress on crack propagation due to welding has been performed. The residual stresses in the SAW welded A533B plates and electron beam welded plates that consist of HT80 and A533B steels were detected by an acoustoelastic technique. The measured residual stress was incorporated into a finite element procedure, which simulated stable crack growth in 1T compact specimens, where the effects on far-field crack parameters and on near-field crack parameters were examined. Also investigated was the effect on fatigue crack propagation with the hypothetical residual stress of the identical distribution to that in the electron beam weld. The significance of the residual stress distribution ahead and behind the crack tip in relation to the plastic zone size was identified.     

Ring tests on high density polyethylene: Full investigation assisted by finite element modeling

In order to characterize the mechanical behavior of HDPE pipes, the ASTM D 2290-04 standard recommends carrying out tensile tests on notched rings, cut out from the pipe. This very simple test is also utilized to investigate the aging effect of the pipe by determining the strain at failure. Comparison between full ring and notched ring mechanical responses are discussed. Constitutive modeling including strain rate effects was performed by finite element analysis. This allowed a better understanding of the stress state in the cross section perpendicular to the loading direction. Additionally, the influence of a thin layer of oxidized HDPE in the inner wall of the ring was studied in the light of the finite element results.     

Hydrogen storage in FeTi: Surface segregation and its catalytic effect on hydrogenation and structural studies by means of neutron diffraction

Surface studies by means of AES and XPS show that during the activation process of FeTi titanium diffuses to the surface and metallic iron clusters are formed. They catalyze the hydrogen absorption and are the reason for the irreversible change of the magnetic properties of FeTi upon hydrogenation. At room temperature the surface segregation is not effective enough to restore the catalytic active surface so that FeTi is deactivated easily in air.Structural studies of FeTi, FeTiD and FeTiD_1.74 were performed. The best agreement between observed and calculated intensities of FeTiD is obtained with space groups P222₁ (Pmc2₁) and P2/c. The lattice parameters of the orthorhombic unit cell are $\text{a = 2.966}\text{A}\text{?}\text{, b = 4.522}\text{A}\text{?}$ and $\text{c = 4.370}\text{A}\text{?}$.     

Computation of flow and heat transfer in rotating two-pass rectangular channels (AR = 1:1, 1:2, and 1:4) with smooth walls by a Reynolds stress turbulence model

Numerical predictions of three-dimensional flow and heat transfer are presented for rotating two-pass smooth channels with three aspect ratios (AR = 1:1; 1:2; 1:4). Detailed predictions of mean velocity, mean temperature and Nusselt number for two Reynolds numbers (Re = 10,000 and 100,000) were carried out. A total of fifteen calculations have been performed with various combinations of rotation number, Reynolds number, and coolant-to-wall density ratio. The rotation number and inlet coolant-to-wall density ratio varied from 0.0 to 0.28 and from 0.13 to 0.40, respectively. The focus of this study is to investigate the effect of the channel aspect ratio, the Reynolds number, and the coolant-to-wall density ratio on the nature of the flow and heat transfer. A multi-block Reynolds-averaged Navier–Stokes (RANS) method was employed in conjunction with a near-wall second-moment turbulence closure. In the present method, the convective transport equations for momentum, energy, and turbulence quantities are solved in curvilinear, body-fitted coordinates using the finite-analytic method.     

Proposal of reference stress for a surface flaw on a cylindrical component from a review-with-comparison of the local metal loss assessment rule between API 579-1 and the p-M diagram method

The Remaining Strength Factor (RSF) approach in Part 5 of API 579-1/ASME FFS-1 is an assessment method for a cylindrical component with a local metal loss based on surface correction factors. Also, reference stress solutions that are applied in the Failure Assessment Diagram (FAD) method for a cylindrical component with a crack-like flaw are provided in Annex D using surface correction factors. In the recently-developed p-M diagram method, the reference stress solution for local metal loss evaluation in a cylindrical component is derived using bulging factors, which are similar but not identical to the surface correction factors used in API 579-1/ASME FFS-1. This paper describes the results of a comparative study among the RSF approach, reference stress solutions for the FAD method, and the p-M diagram method, in terms of plastic collapse evaluation of a cylindrical component. These results were compared with the FEA and experimental results to confirm how these estimated stresses could be validated. This study also involves recommended reference stress solutions for a cylindrical component with a crack-like flaw or a local metal loss, which should be adopted as fitness-for-service rules, and a discussion on the influence of the design margin of the construction code on allowable flaw depth.     

Effect of CeO2 on oxidation and electrical behaviors of ferritic stainless steel interconnects with NiFe coatings

Ferritic stainless steels are promising materials for application in interconnects of solid oxide fuel cells (SOFC). The present problems to be solved urgently for using ferritic stainless steels as interconnects are their rapid increase in electrical resistance and the cathode poisoning caused by evaporation of chromia. In the present study, the NiFe and NiFeCeO₂ alloy coatings have been electro-deposited onto 430 stainless steels (430SS). During oxidation at 800 °C in air, an outer dense NiFe₂O₄ layer and an inner protective Cr₂O₃ layer have thermally grown on the coated samples. The NiFe₂O₄ layer retards the outward migration of chromium effectively. The addition of CeO₂ reduces the growth rate of Cr₂O₃ and decreases the number of pores near the oxide scale/alloy interface. Moreover, a higher electrical conductivity has been achieved by the addition of CeO₂.