Determination of plasticity following deformation and welding of austenitic stainless steel

Intergranular strain has been associated with high-temperature cracking of welded pipework in 316H austenitic stainless steel material used in nuclear power plant heat exchangers. In this study, neutron diffraction has been used to study the development of intergranular strains in plastically-deformed and welded 316H stainless steel. Measurements have been made of the intergranular strain evolution with increasing plastic strain in base material, and correlated with further measurements made in samples extracted from welded pipes, where the pipes were welded following plastic deformation to different levels of plastic strain. Strong tensile strain evolution was seen on the compliant 200 grain family. The results were correlated with various proxy measures of plastic strain, including hardness and diffraction peak width, and excellent agreement was obtained

Tropical cyclone motion and recurvature in TCM-90

September 1992.Also issued as author's thesis (M.S.) -- Colorado State University, 1992.Includes bibliographical references.Rawinsonde and satellite data collected during tie Tropical Cyclone Motion (TCM- 90) experiment, which was conducted during the summer of 1990 in the Western North Pacific, is used to examine tropical cyclone steering motion and recurvature. TCM-90 composite results a.re compared with those found in a previous composite study using twenty-one years (1957-77) of Western North Pacific rawinsonde data during the same August- September period and also for August-September months during this same 21- year period. Both data sets indicate that the composite deep-layer-mean (850-300 mb) winds 5-7° from the cyclone center provide an important component of the steering flow for tropical cyclones. However, despite the rawinsonde data enhancements of the TCM-90 experiment, data limitations prevented an accurate observation of steering flow conditions at individual time periods or for the average of only 5-10 time periods when composited together. Examination of environmental wind fields surrounding a recurving cyclone (Typhoon Flo, Sept. 1990), and those for non-recurving TCM-90 storms verify significant differences in the upper tropospheric zonal wind fields north and -northwest of the tropical cyclone one to two days prior to the beginning of the initial right turn of recurvature. Typhoon Flo actually began to recurve when 200 mb positive zonal winds had penetrated to within 6 degrees radius of the cyclones' center from the northwest. Tropical cyclones which did not recurve had negative zonal winds at this radius and azimuth. This special area to the north and northwest of the cyclone has been termed the "window of forecast opportunity". Basic statistical analyses of the typical spread of individual wind values at specific octants and 2 degree radial belts were ma.de for all TCM-90 rawinsonde and satellite wind data composites. The typical standard deviation about the mean of composited zonal and meridional winds in individual octants and radial belts was 5-6 m/s at lower levels and 6-7 m/s at upper levels. Zonal wind differences in excess of this threshold would be required for confidence in distinguishing between i1 dividual cases of recurvature and non-recurvature.Sponsored by DOD-NAVY-ONR N00014-91-J-1092

Development and application of the contour method to determine the residual stresses in thin laser-peened aluminium alloy plates

The contour method was applied to obtain residual stress fields in a laser-peened 2.0-mm-thick Al2024-T351 sample. In order to remove the effects of near-surface wire electro-discharge machining (EDM) cutting artefacts on the measured residual stresses, sacrificial blocks were attached to both surfaces of the thin sample with a polymer-based glue doped with silver particles. A data analysis routine based on bivariate spline smoothing was conducted to obtain a 2D residual stress map. The results were compared with incremental hole drilling, and X-ray diffraction and layer removal techniques. The results are in good agreement in terms of the magnitudes and the location of the peak stresses, with the exception of the contour method results. Owing to the low thickness of the samples, the data analysis is very sensitive to the parameters used in the spline fitting, leading to fluctuation in the results. It is concluded that the contour method can be applied to thin samples, however, extra attention is required. Since the uncertainty is higher compared to the conventional contour method results, it is good practice to compare the results with at least one other experimental method

Evolution of stress fields and phase content in corroded zirconium cladding materials

In this study, the evolution of stress fields and structural phase composition have been studied using Raman spectroscopy pre- and post-transition in the oxide layer of re-crystallised ZIRLO and recrystallised zircaloy-4 (Zr-4) after corrosion exposure in a static autoclave. The structural phase composition analysis showed that the proportion of the tetragonal zirconia phase on the surface decreased with increasing corrosion time. High compressive stresses were found in the thin oxide, increasing with corrosion time, reaching a maximum in the transition period and decreasing slightly after that. The results show the relationship between the crystallographic phase and the residual stresses developed in the oxide

Spontaneous Fruit Fly Optimisation for truss weight minimisation:Performance evaluation based on the no free lunch theorem

Over the past decade, several researchers have presented various optimisation algorithms for use in truss design. The no free lunch theorem implies that no optimisation algorithm fits all problems; therefore, the interest is not only in the accuracy and convergence rate of the algorithm but also the tuning effort and population size required for achieving the optimal result. The latter is particularly crucial for computationally intensive or high-dimensional problems. Contrast-based Fruit-fly Optimisation Algorithm (c-FOA) proposed by Kanarachos et al. in 2017 is based on the efficiency of fruit flies in food foraging by olfaction and visual contrast. The proposed Spontaneous Fruit Fly Optimisation (s-FOA) enhances c-FOA and addresses the difficulty in solving nonlinear optimisation algorithms by presenting standard parameters and lean population size for use on all optimisation problems. Six benchmark problems were studied to assess the performance of s-FOA. A comparison of the results obtained from documented literature and other investigated techniques demonstrates the competence and robustness of the algorithm in truss optimisation.Comment: Presented at the International conference for sustainable materials, energy and technologies, 201

Germanium diffusion in aluminium: connection between point defect parameters with bulk properties

The understanding of dopant diffusion and its temperature dependance is technologically important in metals. As a model system we consider germanium diffusion in aluminium. This is an appropriate system as germanium does not form intermetallic compounds in aluminium and therefore it simplifies the investigation of its diffusion behavior. Here we use experimental elastic and expansivity data to derive the germanium diffusion coefficient in aluminium in the framework of the so-called cBΩ model, between 673 and 883 K. This model is a powerful way to study point defect parameters in metals as it connects them to bulk properties, which are more easily accessible. The calculated diffusivities are in excellent agreement with the experimental data

Residual stresses in aerospace structures reinforced with bonded crack retarders

Bonded crack retarder technology is an innovative concept to improve the fatigue performance of aircraft structures. Stiffening ‘straps’ are adhesively bonded to areas where potential fatigue cracking may occur. The straps retard the growth of fatigue cracks, by a combination of the local stiffening effect that reduces the crack driving force, and bridging in the wake of the crack. However, bonded crack retarder results in thermal residual stresses that may adversely affect the performance of the reinforced structure due to extensive fatigue loads in service. This is the first study where we have looked at the application of GLARE6/5 fibre-metal laminate as a bonded crack retarder onto a structural butt joint and simulated manhole mock-up assemblies containing cold-worked holes. Neutron diffraction was used for residual stress measurements. Results indicate that the strap-bonding process has no discernible effect on the magnitude of the compressive cold-working stresses. The use of bonded crack retarders should not, therefore, impair the benefits of cold working of fastener joints in aircraft structures