Residual Stress Measurements in Extreme Environments for Hazardous, Layered Specimens

Background In nuclear fuel plates of low-enriched U-10Mo (LEU) clad with aluminum by hot isostatic pressing (HIP), post-irradiation stresses arising during reactor shutdown are a major concern for safe reactor operations. Measurement of those residual stresses has not previously been possible because the high radioactivity of the plates requires handling only by remote manipulation in a hot cell. Objective The incremental slitting method for measuring through-thickness stress profiles was modified, and a system for automated, remote operation was built and tested. Methods Experimental modifications consisted of replacing electric-discharge machining (EDM) with a small end mill and strain-gauge measurements with cantilever displacement measurements. The inverse method used to calculate stresses was the pulse-regularization method modified to allow discontinuities across material interfaces. The new system was validated by comparing with conventional slitting on a depleted U-10Mo (DU) fuel plate. Results The new system was applied to two measurements each on six as-fabricated (pre-irradiation) LEU miniature fuel plates. Variations between the measurements at two locations in the same plate were strongly correlated with measured geometrical heterogeneity in the plate—a tilt in the fuel foil. Compressive stresses in the U-10Mo were shown to increase from 20 to 250 MPa as the ratio of aluminum thickness to U-10Mo thickness increased causing increased constraint during cooling. Faster cooling rates during processing also increased stress magnitudes. Conclusions The measurements trends agreed with data in the literature from similar plates made with DU, which further validates the method. Because other methods are impractical in a hot cell, the modified slitting method is now poised for the first measurements of post-irradiation stresses.

VIRTUAL HULL MONITORING: CONTINUOUS FATIGUE ASSESSMENT WITHOUT ADDITIONAL INSTRUMENTATION

A novel technique to monitor hull stresses using data currently collected on most ships is explored. This technique, referred to herein as virtual hull monitoring, uses global position signals, measured or numerically-modelled wave data, and a database of calculated stress transfer functions. This enables monitoring of short-term stress states and corresponding fatigue damage accumulation for many structural locations, either onboard or at a central location, for an entire fleet. The components, benefits, and limitations of this proposed technique are discussed. Wave buoy and strain gauge measurements from a full-scale naval vessel trial are used in comparisons with hindcast wave data and the calculated stress spectra for one structural location. Close agreement between the wave data sources and corresponding stress spectra warrants further examination of virtual hull monitoring. 

A biomechanical invesitgation of the surface stress of a synthetic femur using infrated thermography validated by strain gauge measurements

As the North American population ages, there will be a massive increase in musculoskeletal impairments because these problems are most common in the elderly. A very common condition is osteoporosis, which can result in fractures. Therefore, the need for improved orthopaedic fracture repair implants is vital. Currently, the two main approaches in studying orthopaedic implants are strain gauge measurements and finite element modelling. This study introduces and validates a relatively new, non-destructive approach in analysing stress patterns in a biomechanics application. Lock-in infrared (IR) thermography calibrated with strain gauges was used to investigate the stress and strain patterns of a synthetic femur under dynamic loading. The femur was instrumented with strain gauges and tested using axial average forces of 1500N, 1800N, and 2100N at an adduction angle of 7 degrees to simulate the single-legged stance phase of walking. Three dimensional surface stress maps were obtained using an IR thermography versus strain gauge data with a Pearson correlation of R² = 0.99 and a slope ranging from 0.99 to 1.08, based on thermoelastic coefficient (Km) ranging from 1.067 x 10⁻⁵/MPa to 1.16 x 10⁻⁵/MPa, for the line of best fit. IR thermography detected bone peak stresses on the superior-posterior side of the femoral neck of 91.2MPa (at 1500 N), 96.0Mpa (at 1800 N), and 103.5MPa (at 2100 N). There was strong correlation between IR measured stresses and force along the anterior (R² = 0.87 to 0.99), posterior (R² = 0.81 to 0.99) and lateral (R² = 0.89 to 0.99) surface. This is the first study to provide an experimentally validated three dimensional stress map of a synthetic femur using IR thermography.

A biomechanical invesitgation of the surface stress of a synthetic femur using infrated thermography validated by strain gauge measurements

As the North American population ages, there will be a massive increase in musculoskeletal impairments because these problems are most common in the elderly. A very common condition is osteoporosis, which can result in fractures. Therefore, the need for improved orthopaedic fracture repair implants is vital. Currently, the two main approaches in studying orthopaedic implants are strain gauge measurements and finite element modelling. This study introduces and validates a relatively new, non-destructive approach in analysing stress patterns in a biomechanics application. Lock-in infrared (IR) thermography calibrated with strain gauges was used to investigate the stress and strain patterns of a synthetic femur under dynamic loading. The femur was instrumented with strain gauges and tested using axial average forces of 1500N, 1800N, and 2100N at an adduction angle of 7 degrees to simulate the single-legged stance phase of walking. Three dimensional surface stress maps were obtained using an IR thermography versus strain gauge data with a Pearson correlation of R² = 0.99 and a slope ranging from 0.99 to 1.08, based on thermoelastic coefficient (Km) ranging from 1.067 x 10⁻⁵/MPa to 1.16 x 10⁻⁵/MPa, for the line of best fit. IR thermography detected bone peak stresses on the superior-posterior side of the femoral neck of 91.2MPa (at 1500 N), 96.0Mpa (at 1800 N), and 103.5MPa (at 2100 N). There was strong correlation between IR measured stresses and force along the anterior (R² = 0.87 to 0.99), posterior (R² = 0.81 to 0.99) and lateral (R² = 0.89 to 0.99) surface. This is the first study to provide an experimentally validated three dimensional stress map of a synthetic femur using IR thermography.

Determination of Optimal Flat-End Head Geometries for Pressure Vessels Based on Numerical and Experimental Approaches

The experimental and numerical analyses of the pressure vessels with different flat ends are presented and discussed in the paper. The main aim of the study is to propose the optimal flat head end geometry. The analyses are focused on the comparison of standardized geometries and with the proposed elliptical cut-out. The experimental tests with the application of strain-gauge measurements and numerical modeling of the pressure vessel are conducted. The behavior under low and high pressures and the influence of the residual welding stresses, material properties, and geometrical tolerances on the level of the plastic deformation in the flat end is discussed. It is presented that the rules given in the recent standard are not sufficient for optimal selection of the optimal geometry. It is observed that in certain geometries the deviations of the pipe thickness may lead to a significant increase of the equivalent stresses. The residual welding stresses have a significant influence on the stress and strain level—particularly in the stress relief groove (SRG). The performed study and comparison of the different geometries allow for the proposal of the optimal shape of the flat end. It appeared that the pressure vessels with SRG are the most optimal choice, particularly when elliptic shapes are in use. In some cases (i.e., pipe with wall-thickness equal to 40 mm and the flat end with circular SRG), the optimal configuration is reached for dimensions beyond the admissible by code range.

The Impact of Excitation and Mode Shape on Non-Linear Blade Vibrations

Recently, reliable non-linear dynamic solvers for the analysis of frictionally coupled turbine blades have been developed which are based on either Higher Harmonic Balance Method or Non-linear Modal Analysis. One of these tools is OrAgL which was developed by Institute of Dynamics of Vibrations (Leibniz University of Hannover) and Institute of Aircraft Propulsion Systems (University of Stuttgart). In [1], the rig and engine validation results of with OrAgL performed forced response analyses have been published: The main aim of this paper was the comparison of non-linear numerical predictions (amplitude, frequencies) with the blade-to-blade averaged values of optical measurement results obtained using MTU’s non-contact vibration measurement system for shrouded turbine blades (BSSM-T). Detailed analyses and validations performed over the last two years showed several novel aspects of validation such as the comparison with strain gauge measurements. Moreover, a better understanding of the impact of excitation (magnitude and load distribution over the airfoil) as well as of the impact of the mode shape on the formation of saturation regimes is now possible. The results obtained from the analyses of real turbine blades are presented in this work.