In this paper, we report the use of the feedback signal of an ultrasonic fatigue system to dynamically deduce fatigue damage accumulation via changes in the nonlinear ultrasonic parameter. The applicability of this parameter in comparison to the resonant frequency for assessment of fatigue damage accumulation in a wrought aluminum alloy has been demonstrated, without the need for coupling fluids or independent generation of incident ultrasonic waves. The ultrasonic nonlinearity increased and the resonant frequency of the system decreased with initiation and propagation of the major crack. The nonlinear ultrasonic parameter shows greater sensitivity to damage accumulation than the resonant frequency. The number of cycles for crack propagation, estimated based on the changes in the nonlinear ultrasonic parameter, is in very good agreement with calculated crack growth rates based on the fractography studies.

No abstract

No abstract

Modified 9Cr-1Mo ferritic steel (T91/P91) has been subjected to a series of heat treatments consisting of soaking for 5 minutes at the selected temperatures, starting from the ␣ -phase region (1073 K) to the ␥ ϩ ␦-phase region (1623 K), followed by oil quenching. Hardness measurements, microstructural features, and grain-size measurements by the linear-intercept method have been used for correlating them with the ultrasonic parameters. Ultrasonic velocity and attenuation measurements, and spectral analysis of the first backwall echo have been used for characterization of the microstructures obtained by various heat treatments. As the soaking temperature increased above Ac 1 , the ultrasonic velocity decreased because of the increase in the volume fraction of martensite in the structure. There were sharp changes in the ultrasonic velocities corresponding to the two critical temperatures, Ac 1 and Ac 3 . Ultrasonic longitudinal-and shear-wave velocities were found to be useful in identifying the Ac 1 and Ac 3 temperatures and for the determination of hardness in the intercritical region. However, ultrasonic attenuation and spectral analysis of the first backwall echo were found to be useful to characterize the variation in the prior-austenitic grain size and formation of ␦ ferrite above the Ac 4 temperature. The scattering coefficients have been experimentally determined for various microstructures and compared with the theoretically calculated value of the scattering coefficients for iron reported in literature.

This study explores the effects of hybridization of glass fiber on low velocity impact behavior and damage tolerance capability of woven jute fabric composite. Laminates were fabricated by the hand lay—up technique using a mold and cured under light pressure at room temperature. Low velocity impact tests were conducted on jute and hybrid samples (150 × 150 mm) using an instrumented drop weight impact tower. All the samples were impacted at four different energy levels by changing the drop height, and load—energy—time plots were recorded using data acquisition software. Some of the samples were subjected to the non-destructive test (C-scan) to study the nature and extent of damage and to measure the delamination area. Post-impact tension tests were conducted to assess the damage tolerance capability of the composites. The results of the study indicated that jute laminates have better impact energy absorption capacity than jute—glass hybrid laminates; however their damage tolerance capability is less than jute—glass hybrid laminates.