Nondestructive evaluation of residual stress in low-carbon steel

The effects of the preferred orientation on the temperature dependence of ultrasonic velocity in low carbon steels are investigated. The sensitivity of the acousto-elastic constant to changes in microstructure is assessed as well as the possibility of determining some mechanical properties of a material by measuring the acousto-elastic constant

Nondestructive ultrasonic characterization of engineering materials

The development of an ultrasonic method for the nondestructive characterization of mechanical properties of engineering material is described. The method utilizes the nonlinearity parameter measurement which describes the anharmonic behavior of the solid through measurements of amplitudes of the fundamental and of the generated second harmonic ultrasonic waves. The nonlinearity parameter is also directly related to the acoustoelastic constant of the solid which can be determined by measuring the linear dependence of ultrasonic velocity on stress. A major advantage of measurements of the nonlinearity parameter over that of the acoustoelastic constant is that it may be determined without the application of stress on the material, which makes it more applicable for in-service nondestructive characterization. The relationships between the nonlinearity parameter of second-harmonic generation and the percentage of solid solution phase in engineering materials such as heat treatable aluminum alloys was established. The acoustoelastic constants are measured on these alloys for comparison and confirmation. A linear relationship between the nonlinearity parameter and the volume fraction of second phase precipitates in the alloys is indicated

Does Community and Environmental Responsibility Affect Firm Risk? Evidence from UK Panel Data 1994-2006

The question of how an individual firm’s environmental performance impacts its firm risk has not been examined in any empirical UK research. Does a company that strives to attain good environmental performance decreases its market risk or is environmental performance just a disadvantageous cost that increases such risk levels for these firms? Answers to this question have important implications for the management of companies and the investment decisions of individuals and institutions. The purpose of this paper is to examine the relationship between corporate environmental performance and firm risk in the British context. Using the largest dataset so far assembled, with Community and Environmental Responsibility (CER) rankings for all rated UK companies between 1994 and 2006, we show that a company’s environmental performance is inversely related to its systematic financial risk. However, an increase of 1.0 in the CER score is associated with only a 0.02 reduction in firm’s risk and cost of capital

The Determination of Tensile Stresses Using the Temperature Dependence of Ultrasonic Velocity

The effects of applied tensile stresses on the temperature dependence of 10 MHz ultrasonic longitudinal velocity have been studied in three types of commercial aluminum alloys, 6064-T4, 2024-T351, and 3003-T251. In all measurements, it is found that the velocity decreases linearly with temperature, and the slope of the linear relationshi\u27p changes considerably as a function of applied tensile stresses within the elastic limit of the specimen used. Furthermore, the results indicate that the relative changes in the temperature dependence of the velocity due to stress is insensitive to composition and texture, and the data obtained on the different types of aluminum alloys can be represented by a single relationship. The sensitivity of the temperature dependence of the ultrasonic velocity to applied elastic stress is estimated to be ±8 MN/m2 which compares favorably with those obtained by other techniques

Thermoelastic analysis of solar cell arrays and their material properties

Announced report discusses experimental test program in which five different solar cell array designs were evaluated by subjecting them to 60 thermal cycles from minus 190 deg to 0.0 deg. Results indicate that solder-coated cells combined with Kovar n-interconnectors and p-interconnectors are more durable under thermal loading than other configurations

On the elastic approximation to the vacancy formation energy in metals

Isotropic elastic continuum model application to calculate energy and entropy of vacancy formation in metal crystal

The Use of the Temperature Dependence of Ultrasonic Velocity to Measure Residual Stress

The behavior of the temperature dependence of longitudinal ultrasonic velocity in type A533B steel in the presence of external as well as residual stresses has been investigated. In all measurements, the ultrasonic velocity in the vicinity of room temperature is found to vary linearly with temperature, and the slope of the linear relationship increases or decreases according to whether the stress is applied in tension or in compression respectively. The results also indicate that the temperature dependence of the velocity is a linear function of applied stress, and the slope of this linear relationship is the same for all specimens tested, and for both tensile and compressive stresses. These results are then used to obtain a relationship between the temperature dependence and residual stress in type A533B steel

Nondestructive Evaluation of Bulk Stresses in Aluminum and Copper

The effect of applied stress on the temperature dependence of the longitudinal ultrasonic velocity has been investigated in commercial aluminum and copper. Velocities of 10 MHz longitudinal waves as a function of temperature were measured on ten specimens of these metals while they were subjected to external compressive stresses. In all measurements, the velocity increased linearly as the temperature was lowered in the temperature range between 280 and 200 K. Furthermore, the slope of this linear relationship was found to decrease linearly as the amount of applied compressive stress was increased within the elastic limit of the specimen under investigation. The maximum decrease in the temperature dependence of aluminum and copper were respectively 23% which occurred at a stress of 96 MPa, and 6% which occurred at 180 MPa. The linear relationship between the temperature dependence of the ultrasonic velocity and the applied stress was then used to determine the change as a function of distance of the tangential compon.ent of the stresses developed when an aluminum rod was shrunk fit into a slightly smaller hole drilled in an aluminum disc. Excellent agreement was obtained between the computed stress distribution, and that measured using the temperature dependence method