Search

A simple and effective method for generation and detection of a guided wave in a pipe was proposed using an iron hose-fixing belt as a reflector of the guided wave. The reflector is located (2n+1)λ/4 (n=1,2,3,,,) apart from a guided wave sensor in axial direction for the effective generation or detection in the magneto-strictive transduction. The reflector setting is determined under the consideration to the distance between the sensor and the reflector as well as phase inversion at the reflector. In above reflector setting, large amplitude is obtained because multiple-reflection between the reflector and the sensor occurs under phase matching conditions. In this paper, the principle of the method was first described. Experiments were carried out with the non-dispersive T(0,1) mode to verify the principle in comparison to a simple theory.

Ni-NiO composites with different NiO contents were fabricated by a conventional PM method. Nickel oxide particles, which were selected as dispersoids, were embedded in nickel matrix. Tensile tests were conducted on the composites containing up to 9 weight percent of NiO at room temperature. Typical tensile properties, such as yield strength, tensile strength and elongation, of the composites were evaluated. Yield stress of the composites monotonically increased with increase of the NiO content. In contrast, both tensile strength and elongation decreased with increasing NiO content. Variations in the tensile strength of the composites were explained on the basis of the nature and amount of dispersoids and their interaction with nickel matrix. The decrease in the tensile strength was related to its density change. In addition, the relationship between tensile strength and NiO content was well described by Eudier's equation. Decreases in both tensile strength and elongation were caused by propagation of grain boundary cracks initiated from decohesion of dispersoid/matrix interface.

This paper discusses the tensile properties and acoustic emission behavior of Ni-NiO alloys and Ni-Al2O3 alloys prepared by means of the PM method. The mechanical properties of these materials were changed by their manufacturing process conditions. In the case of Ni-NiO alloys, the sintering time of 3.6ks along with repressing and resintering processes may be effective. On the other hand, the best conditions for Ni-Al2O3 alloys are the sintering time of 10. 7ks with neither repressing nor resintering. The AE characteristics of Ni-NiO alloys became highly apparent. It appeared that the AE events generated in the region of 5-40% strain were related to the decohesion of the matrix / dispersoid interface. The AE events with high energy and high peak amplitude before fracture of the Ni-NiO specimen were produced by intergranular cracking. The AE activity of Ni-Al2O3 alloys was weaker than that of Ni-NiO alloys ; that is, the peak amplitude distribution of AE events generated in Ni-Al2O3 alloys became narrow and most AE events had low energy.

The relationship between ductility at creep rupture and the change in the creep fracture mechanism has been discussed. The Ni-NiO eutectic alloys have considerably greater elongation at failure than pure Ni. A creep rupture strain has been divided into three groups of strains; i. e., strain for primary creep regions, for steady-state creep regions and for tertiary creep regions. Both stress and temperature dependence of the amount of these three strains have been investigated. The strain corresponding to the tertiary creep region increases with increasing stress. Consequently, the rupture strain for both materials increases. The rupture strain for both materials linearly increases with the strain for the steady-state creep region. It is suggested that greater elongation in Ni-NiO alloys may be attributed to the high ductilitiy in the nickel matrix which is produced by the addition of nickel oxide. The change in the fracture mechanism from intergranular creep fracture to transgranular creep fracture results in the increase of strain corresponding to the tertiary creep regime.

In this paper the authors presented a computational method to de termine the original waveforms at source points where acoustic emission (AE) is generated. Using a fast electrical pulse as a standard input signal, it has become possible to obtain the reproducible transfer function of AE measuring system from the generation of AE to the detection of received signals. By introducing the numerical operations to minimize noise and distortion which are often contained in analyzed waveforms, Fourier synthesis has been made applicable to an inverse problem such as source wave analysis. Consequently the authors have been able to obtain reproducible source waves with higher accuracy in considerably short time of calculation. A few experiments to determine source waves were carried out and the results showed the validity of the method.