APPLICATION OF INCLINED LONGITUDINAL ULTRASONIC WAVES TO IMPROVE THE EFFICIENCY OF RAIL FLAW DETECTION

The article is devoted to the question of rail ultrasonic testing confidence. At present there is a range of flaw orientation angles in within which the testing is absent and, therefore such flaws can be lost. To except this drawback the current sound testing scheme in flaw detector railcars is to be supplemented with inclined probes exciting longitudinal wave. Experimental checks using echomethod showed the good results on an October railway section with flaw models and on a loaded Zabaycalskaya railway section. The next step was idea of mirror-shadow method using as well as echomethod by turning of probes towards each other. Envelope analysis of bottom signals allows receiving additional information about flaws: location depth of its center and form. But using of pair of probes was not enough for unambiguous definition of other geometric flaws characteristics. That is why the bottom signal envelope of straight probe was to be analyzed additionally. A mobile (as well removable) searching system of rail checking means has such probe as a rule. In the process of writing the article previously obtained formulas to calculate depth, inclination angle and plane size of revealed flaw were modified. Values changing during testing process are absent now. Algorithm of flaws identification on the basis of bottom signals envelope is given. The approach is confirmed by mathematical modeling in CIVA-UT.

A New Method of Predicting the Structural and Mechanical Change of Materials during Extrusion by the Method of Multiple Plastic Deformations

The formulation of the Hall–Petch relationship in the early 1950s has raised immense interest in studying the influence of the grain size of solid materials on their properties. Grain refinement can be achieved through extreme deformation. In the presented study, Equal-Channel Angular Pressing (ECAP) was successfully applied to produce an ultrafine-grained microstructure in a pure commercial Cu of 99.9 wt%. Samples were processed by ECAP at 21 °C for six passes via route A. A new equation of equilibrium that allows the exact determination of the number of extrusions and other technological parameters required to achieve the desired final grain size has been developed. The presented research also deals, in a relatively detailed and comparative way, with the use of ultrasound. In this context, a very close correlation between the process functions of extrusion and the speed of longitudinal ultrasonic waves was confirmed.

Investigating Ultrasound-Induced Acoustic Softening of Aluminum 6061

Blaha and Langenecker are the first to document the phenomena known as “acoustic softening”: a significant reduction of static stress in tensile tests when applying longitudinal ultrasonic waves to various metals. Based on experimental observations, they hypothesized that acoustic heating due to internal friction and energy activation at dislocations was responsible for this temporary weakening of the material. Later research studies investigating the acoustic softening process used different experimental setups leading to alternative theories of the softening process such as superposition of static and dynamic stress. The variation in the design of the experiments leads to significant differences in observations, causing differing interpretations of the results and the formation of competing theories. We reviewed previous experimental studies and found that the optimum setup is similar to Blaha’s and Langenecker’s. Their setup minimizes noise factors such as friction at the oscillator specimen interface, which could contribute to heating and stress reduction. Therefore, we present our experimental setup composed of an MTS tensile test machine and a Branson ultrasonic welder to study the softening of aluminum 6061 and discuss our own results and how they compare with those in the literature. Additionally, we investigate the applicability of competing theories of softening based on our experimental data.