SETTING OF THE ANGLE OF INCIDENCE FOR GENERATING LAMB WAVES BY NON-CONTACT METHODEFFECT OF FRICTION ON THE MICROMECHANICAL PROPERTIES OF AISI 316L AUSTENITIC STEEL

The article examined the problem of the experimental setting of incidence angles for the generation of Lamb waves in plate-type parts by the non-contact ultrasonic control method. This type of control is mainly done by the use of two types of waves: Rayleigh, which detects invisible defects on the surface of parts, and Lamb waves mode A0 and S0. Mostly used is the mode A0 due to the propagation over distances of interest in the tested materials. One of the primary aim during the testing process is to position the ultrasonic transducers (transmitter and receiver) at oblique angles of incidence on a surface. The transducers should be positioned on an access face of the plate, as is common in industrial practice, at a fixed distance from the measured plate, and leaving an air gap between transducers and the tested plate. The ultrasonic transducers are moved simultaneously linearly or in zigzag on the surface of the plate-type part to measure the hidden defects (cracks, pores, inclusions) that appear in the composite materials during the manufacturing process or during the operation. The presented work brings new insights into the setting of the angle of incidence for generating lamb waves by non-contact method.

Rat Ultrasonic Vocalizations as Social Reinforcers—Implications for a Multilevel Model of the Cognitive Representation of Action and Rats’ Social World

Rats are social animals. For example, rats exhibit mutual-reward preferences, preferring choice alternatives that yield a reward to themselves as well as to a conspecific, over alternatives that yield a reward only to themselves. We have recently hypothesized that such mutual-reward preferences might be the result of reinforcing properties of ultrasonic vocalizations (USVs) emitted by the conspecifics. USVs in rats serve as situation-dependent socio-affective signals with important communicative functions. To test this possibility, here, we trained rats to enter one of two compartments in a T-maze setting. Entering either compartment yielded identical food rewards as well as playback of pre-recorded USVs either in the 50-kHz range, which we expected to be appetitive or therefore a potential positive reinforcer, or in the 22-kHz range predicted to be aversive and therefore a potential negative reinforcer. In three separate experimental conditions, rats chose between compartments yielding either 50-kHz USVs versus a non-ultrasonic control stimulus (condition 1), 22-kHz USVs versus a non-ultrasonic control stimulus (condition 2), or 50-kHz versus 22-kHz USVs (condition 3). Results show that rats exhibit a transient preference for the 50-kHz USV playback over non-ultrasonic control stimuli, as well as an initial avoidance of 22-kHz USV relative to non-ultrasonic control stimuli on trend-level. As rats progressed within session through trials, and across sessions, these preferences diminished, in line with previous findings. These results support our hypothesis that USVs have transiently motivating reinforcing properties, putatively acquired through association processes, but also highlight that these motivating properties are context-dependent and modulatory, and might not act as primary reinforcers when presented in isolation. We conclude this article with a second part on a multilevel cognitive theory of rats’ action and action learning. The “cascade” approach assumes that rats’ cognitive representations of action may be multilevel. A basic physical level of action may be invested with higher levels of action that integrate emotional, motivational, and social significance. Learning in an experiment consists in the cognitive formation of multilevel action representations. Social action and interaction in particular are proposed to be cognitively modeled as multilevel. Our results have implications for understanding the structure of social cognition, and social learning, in animals and humans.

Influence of carbon fiber on tribotechnical characteristics of polyetheretherketone

Superstructural thermoplastic polymers, including polyetheretherketone, are now widely used in many industries. However, its rather high coefficient of friction and insufficient wear resistance limits its use in friction units of machines and mechanisms. This article covers the influence of T700 Toray carbon fiber on the tribotechnical characteristics of Victrex150G aromatic polyetheretherketone. As a result of the researches it has been found out that the developed carbon plastics exceed the base polymer in friction coefficient and wear 1.2-1.54 and 1.7-8.8 times, respectively, due to the formation of a stable "transfer film" on the steel counterbody (so-called antifriction layer): finely dispersed particles of the polymer matrix and crushed products of wear of carbon fiber penetrate into the microcavities of the counterbody. This is confirmed by the fact that the roughness of carbon plastics has decreased by 50 % in cpomparison with the base polymer. The greatest improvement in tribological properties is observed at 10 mass%, of carbon fiber content, then the properties get worse. That can be explained by the increase in defects of the material due to the dominant loosening at the "polymer-fiber" boundary that confirms the results of microhardness and ultrasonic control. The obtained results show that the composite with an effective carbon fiber content (10 mass%) can be recommended for the manufacture of parts of movable joints of machines and mechanisms operating under friction without lubrication in various industries: agricultural, automotive and textile. etc.

Features of ultrasonic control of butt welded joints of polyethylene pipes

The reliability of ultrasonic testing (UT) of the quality of welded joints of polyethylene pipelines, made end-to-end with a heated tool, is considered in comparison with mechanical tests and radiography. The greatest detection of solid defects is provided by ultrasonic inspection with the use of chord tipe probes (not less than 90 %). When detecting defects translucent for ultrasound (lack of penetration, lack of fusion, etc.), the reliability decreases to 70÷80 %. Keywords: welding, polyethylene pipeline, quality control, ultrasonic testing, chord tipe probe. [email protected]

ABOUT SOME FEATURES OF APPLICATION OF A TANDEM TECHNIQUE IN THE ULTRASONIC TESTING

On the basis of received before the formula of an acoustic сhannel for the circuit of the ultrasonic control the tandem technique and a reflector as a side drilled hole carries out calculations echo signals for various base distances, depths of reflector and angles of probes. Influence on amplitude of a registered signal of a choice of position of a point of reflection on depth of the control is shown. It is established, that mutual replacement of positions of transmitting and receiving probes with identical parameters in a tandem technique practically has not an effect for amplitude of a registered signal. Influence on amplitude of a signal of distinction of angles of transmitting and receiving probes is shown. Comparison of the signals received at use of the circuit of the control on a tandem technique with reflection of a shear wave from a bottom surface and at use of the circuit of a path for separate angle probes with reflection of a wave only from a surface of defect has shown, that a choice of base distance between probess for the point of reflection which are taking place on small distance from a bottom surface, provides also an opportunity of detection of volumetric defects on significant distance from this surface.