Welding characteristics and temperature increases of ultrasonic plastic welding parts over a frequency range from 27 to 94 kHz are studied. Using 27, 40, 67, and 94 kHz ultrasonic plastic welding systems, temperature increases at welding surfaces of lapped 1.0-, 2.0-, and 3.0-mm-thick polypropylene plates and polymethyl methacrylate plates are measured using 0.1-and 0.2-mm-diameter thermocouples inserted between plates, and temperature distributions at cross sections of lapped plate specimens are measured using a thermotracer. The 94 kHz vibration system used for ultrasonic plastic welding consists of a bolt-clamped Langevin-type longitudinal vibration source using four 30-mm-diameter piezoelectric ceramic (PZT) rings, a stepped horn (vibration velocity transform ratio N ¼ 3:0) and a catenoidal horn (N ¼ 3:13) with an 8-mm-diameter welding tip. The other vibration systems have similar configurations. In the case of using a higher-frequency system, increases in temperature measured at the welding parts are larger. Temperature rises are larger for lapped plate specimens than that for a one-piece specimen owing to the vibration loss of welding surfaces.

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A thermal-mechanical fatigue (TMF) testing system has been developed which is capable of studying the fatigue behaviors of gas turbine materials under simultaneous changes of temperatures and strains (or stresses). Furthermore, an advanced alternating current potential difference (ACPD) measurement technique has been developed successfully to perform on-line monitoring of fatigue crack initiation and growth in specimens tested under isothermal and TMF conditions. In this paper, the basic principles of the ACPD technique as well as all the relevant experimental procedures for performing ACPD measurements, including probe setup, choice of alternating currents (AC) and frequencies, noise rejection, data acquisition, and signal processing, are described. The linear relationship between ACPD signals and crack lengths, as well as the effects of thermal cycling on the ACPD signal, are presented and discussed. The capabilities of the TMF and ACPD systems are well illustrated by fatigue crack initiation and growth test results under isothermal and TMF conditions. These tests were performed on two titanium forgings, Ti-6Al-4V (Ti64) and Ti-6Al-2Sn-6Mo (Ti6246), respectively. Alloy Ti64 was TMF cycled between 150 and 400°C, while Ti6246 was cycled between 200 and 482°C. The resolution for detecting crack initiation at the root of notches was found to be 50 μm with 95% confidence while the resolution for crack growth was 2 μm per mV change of ACPD. An environmental assisted cracking model applied to TMF crack growth is proposed for rationalizing the data.

We construct a kink solution on a non-BPS D-brane using Berkovits' formulation of superstring field theory in the level truncation scheme. The tension of the kink reproduces 95% of the expected BPS D-brane tension. We also find a lump-like solution which is interpreted as a kink-antikink pair, and investigate some of its properties. These results may be considered as successful tests of Berkovits' superstring field theory combined with the modified level truncation scheme.

Welding characteristics and temperature increases of plastic welding parts over a frequency range of 27 kHz to 94 kHz are studied. Using 27 kHz, 40 kHz, 67 kHz and 94 kHz ultrasonic plastic welding systems, temperature increase at welded surfaces of 1.0-mm-thick polypropylene plates and polymethyl methacrylate plates is measured using thermocouples inserted between plates, and temperature distributions at cross-sections of lapped plate specimens are measured using a thermotracer. The 94 kHz vibration system used for ultrasonic plastic welding consists of a bolt-clamped Langevin type longitudinal vibration source using four 30-mm-diameter piezoelectric ceramic (PZT) rings, a stepped horn (vibration velocity transform ratio N ¼ 3:0) and a catenoidal horn (N ¼ 3:13) with an 8-mm-diameter welding tip. The other vibration systems have similar configurations. Using a higher frequency system, increases in temperature measured at the welding parts are higher. The maximum temperature increase measured using thermocouples and a thermotracer was over 330 C.KEYWORDS: ultrasonic plastic welding, high-frequency vibration system, frequency characteristics of plastic welding, 27 kHz to 94 kHz vibration system, temperature rise at welding part, temperature distribution at specimen cross section