Calibration of ultrasound tester delay time by cutting a wooden beam

Obtaining precise and reliable test results requires specific tools on one hand, and at the same time, reliability of the results should not be questioned. One of the necessary steps to achieve this goal is the calibration of the measuring device before the test. This article describes an experiment involving calibration of the device by an independent method called cutting beam calibration carried out on the ultrasonic material tester UMT 01. The standard calibration of this device is carried out by using a dedicated metal disc as a template. Calibration of the tester consisted of determining the time delay of the measured signal. The obtained results were used to prepare charts and to determine of signal time delay, called correction, which also allowed determining the velocity of ultrasonic wave in the tested material in three ways. The experiment was conducted on samples of three species of wood: Norway spruce, Scots pine and sycamore. The velocity of ultrasonic wave from research was compared with literature data.

Finite element analysis of double resonance bender disk low frequency transducer

A bender disk transducer can generate low-frequency sound in a small size and light weight. But traditional bender disk transducer only works at single frequency by using first order bending mode and emits moderate levels of power. In this work, a double resonance bander disk low frequency transducer is investigated by using finite element model. The double resonance bender disk transducer consists of two segmented 3-3 mode piezoelectric ceramic disk on the both side of hollow metal disc, which could generate larger displacement in order to increase power radiation. A simple elastic mass system placed inside the hollow metal disc is introduced in the system to produce other lower resonance modes. Through the FEM calculations, it is found that the transmitting voltage response (TVR) of bender disk transducer could enhance 4dB in the first order bending mode resonance frequency, which is compared with traditional bender disk transducer with the same size. The TVR of lower resonance mode which is produced by additional central simple support elastic mass system in segmented bender disk transducer is more than 130dB. Through the optimization of finite element simulation, a double resonance bender disk transducer is designed, and its resonance frequency is 600Hz and 1kHz, respectively. The value of TVR is 130dB and 134dB corresponding to two resonance frequency. The double resonance bender disk transducer is compact dimension, low weight and it is a high performance low frequency transducer.

New method for dynamic tribological test of engineering polymers

In this article, tribological tests of Polyamide 6 (PA 6), Ultra High Molecular Weight Polyethylene (UHMW PE) and Polyoxymethylene copolymer (POM C) by a new testing method is introduced. The tribometer used in the test is capable for pin-on-disc measuring within all possible layout known in tribology practice, otherwise can be modified into special model of fatigue sliding test. The pin was a specimen made from examined materials, always in contact with a rotating metal disc under a normal load, which is usually static. However, since vibration exists in every practical scene as an important phenomenon, for instance in turning process, we added vibration load into the test. The supplement load is generated by a special-designed vibrating machine. Then properties of examined materials can be studied more profoundly under vibration load. As a result, different value of friction coefficient in static and vibration load have been discovered and taken into comparison.