Experimental Non-destructive Testing Research Articles

Improvement of reliability of dozers through taking into account hydrodynamic phenomena in fluid power systems

Improvement of reliability of mining machines and equipment is a complex challenge. It is required to take into account many specific operating conditions, as well as physical processes and phenomena running in such machines. Such phenomena include dynamic and hydrodynamic events. One of the factors to affect reliability of fluid power drives of mining machines is the hydrodynamic phenomena and processes in these systems. This article describes theoretically one of the hydrodynamic events, namely, a surge of pressure (overpressure) which appears in fluid power systems of mining machines in case of stop of the fluid flow while the pump keeps working and the emergency valve acts tardily, which is governed by settlement of resinous substances and power fluid decomposition products on the surface of parts of hydraulic equipment. The experimental studies into the time dependences of vibrational accelerations of the force main walls enable correlating these vibrations with pressure surges because of retar ded actuation of the emergency valve in the fluid power system of a dozer. The total level of vibrations of the force main walls in the dozers is measured by the parameter of the emergency valve series PIK during blade lifting, which agrees with the time dependences of the vibrational accelerations of the force main walls. The technical consequences of the pressure surges are described. The authors propose a diagnostic sign to judge about the behavior of emergency valves. The experimental nondestructive testing used a commercial vibration analyzer with a piezoelectric sensor.

Laser vibrometer measures surface acoustic waves for nondestructive testing

In assessing the safety of a structure, a nondestructive testing (NDT) technique should be able to detect the position of any defects and calculate their size. Most NDT techniques are thus necessarily complex, require qualified staff, and are unsuited to automation. In this article, we describe an experimental NDT methodology for crack detection using surface acoustic waves (SAWs) and optical laser Doppler vibrometer measurements. We evaluate whether ultrasonic laser measurements appropriately detect damage and imperfections in structural components. SAWs are elastic waves that are confined to the surface of a material. They travel along, penetrating about one wavelength into the surface (where the depth of penetration is defined by the depth at which 95% of the wave energy is transmitted). 4 We chose an ultrasonic optical technique instead of other currentlyavailable methods (e.g., ultrasonic scanning, magnetic particle inspection, x-ray imaging, and imaging techniques in general5) for two reasons. First, using the laser as a receiving ultrasound transducer enables remote access to the structure being tested. Second, laser scanning a region of interest makes it possible to obtain many measurements regarding the incident, transmitted, and reflected waves. These measurements, in turn, elucidate the behavior of the SAWs and of the crack itself. In the presence of surface discontinuities such as surface roughness and cracks, part of an incident wave is reflected. The rest is transmitted. Hence, gauging SAWs in the vicinity of a discontinuity allows one to infer information about the state of the surface. The material we tested was the slat track of an Airbus A320. This part of the plane is the movable support structure connecting the wing with the leading-edge slats (see Figure 1). A hydraulic test rig was used to induce in the structure the kind Figure 1. Shown is an Airbus A320 and the slat track used for testing.