Development of swinging part profilometer for optics

A new surface metrology instrument, the ‘Swinging Part Profilometer’ (SPP), has been developed for in-situ measurement of optics undergoing robot-processing in the ground (non-specular) state. In this paper, we present the hardware-design of the SPP, together with software for hardware-control, data-acquisition and surface-reconstruction. First results on a sample part are presented, compared with interferometric metrology, and error-contributions considered. Notably, during each individual scan of a measurement-cycle, the probe remains fixed. This lends itself to automated probe-deployment by the same robot as performs surface-processing, as probe stability is required on only the time-scale for a single scan

Precision determination of absolute neutron flux

A technique for establishing the total neutron rate of a highly-collimated monochromatic cold neutron beam was demonstrated using a method of an alpha-gamma counter. The method involves only the counting of measured rates and is independent of neutron cross sections, decay chain branching ratios, and neutron beam energy. For the measurement, a target of 10B-enriched boron carbide totally absorbed the neutrons in a monochromatic beam, and the rate of absorbed neutrons was determined by counting 478keV gamma rays from neutron capture on 10B with calibrated high-purity germanium detectors. A second measurement based on Bragg diffraction from a perfect silicon crystal was performed to determine the mean de Broglie wavelength of the beam to a precision of 0.024 %. With these measurements, the detection efficiency of a neutron monitor based on neutron absorption on 6Li was determined to an overall uncertainty of 0.058 %. We discuss the principle of the alpha-gamma method and present details of how the measurement was performed including the systematic effects. We also describe how this method may be used for applications in neutron dosimetry and metrology, fundamental neutron physics, and neutron cross section measurements.Comment: 44 page

Determination of Loading and Residual Stresses on Offshore Jacket Structures by X-ray Diffraction

As basements of offshore wind turbines (OWTs) in deep water (>50 m), jacket structures are an economic alternative to monopiles. For this reason, the structural durability of jackets has become more important. In such structures, welded tubular joints are weak points for fatigue design. The harmful effect of tensile residual stresses in welding joints is well known. For these reasons, the residual stresses and the loading stresses of offshore jacket structures were determined by X-ray diffraction (XRD) using a mobile diffractometer. This allows us to directly determine the load stress at the fatigue-critical locations, namely at the weld toe at the testing rig. High tensile residual stresses up to 250 MPa were determined in a welded (and unloaded) condition. At a loaded structure (10,000 load cycles), a lower residual stress level was determined. During loading, a local increase in the stress at the welded joint that is between 1.4 and 4 times higher than the applied nominal stress was determined. Furthermore, it is shown that additional treatment (grinding and clean blasting) influences the local stress state significantly

Sample Preparation Techniques for Grain Boundary Characterization of Annealed TRISO-Coated Particles

Crystallographic information about layers of silicon carbide (SiC) deposited by chemical vapor deposition is essential to understanding layer performance, especially when the the layers are in nonplanar geometries (e.g., spherical). Electron backscatter diffraction (EBSD) was used to analyze spherical SiC layers using a different sampling approach that applied focused ion beam (FIB) milling to avoid the negative impacts of traditional sample polishing and address the need for very small samples of irradiated materials for analysis. The mechanical and chemical grinding and polishing of sample surfaces can introduce lattice strain and result in the unequal removal of SiC and the surrounding layers of different materials due to the hardness differences among these materials. The nature of layer interfaces is thought to play a key role in the performance of SiC; therefore, the analysis of representative samples at these interfacial areas is crucial. In the work reported herein, a FIB was employed in a novel manner to prepare a more representative sample for EBSD analysis from tristructural-isotropic layers that are free of effects introduced by mechanical and chemical preparation methods. In addition, the difficulty of handling neutron-irradiated microscopic samples (such as those analyzed in this work) has been simplified using pretilted mounting stages. The results showed that while the average grain sizes of samples may be similar, the grain boundary characteristics can differ significantly. Furthermore, low-angle grain boundaries comprised 25% of all boundaries in the FIB-prepared sample compared to only 1% to 2% in the polished sample from the same particle. This study demonstrated that the characterization results from FIB-prepared samples provide more repeatable results due to the elimination of the effects of sample preparation