Ultrasonic monitoring on glass fiber reinforced cement (GRC) bending test

Abstract

Glass fiber reinforced cement (GRC) is a composite material based on Portland cement and alkali resistant glass fibers. This composite has good mechanical properties including toughness and flexural strength. The characterization of this material is carried out by four points bending test. During this test, elastic and plastic behaviour are identified from load vs. deflection curves. The scope of the research is to monitor this bending test by means on ultrasonic pulses in order to detect changes on the material and to correlate them with mechanical behaviour. In this sense, pulse velocity, energy, attenuation and non-linearities of the ultrasonic received signals have been analysed. First changes in energy, attenuation and nonlinearities were detected during the change from elastic to plastic step and the first pulse velocity change were observed during the plastic step.

Ultrasonic broadband signals monitoring of glass-fiber reinforced cement (GRC) bending tests

“…Figure 5a shows the evolution of α mat (t, f ) as the bending test progresses. In the first instance and for a fixed value of t, the attenuation parameter rises with the increase of the analysed frequency, as suggested in most of the literature and in previous papers [6,15,20]. For each frequency, this means, for a fixed frequency f , the parameter of attenuation also rises along the experiment.…”

“…In order to follow the same scheme as in previous papers [15], this parameter has also been analysed for a fixed working frequency, thus obtaining an index that depends only on the time. In the present paper, the chosen fixed frequency is 363 kHz since the third harmonic appears in the center of the transducer band (≈ 1 MHz), being more sensitive to its location in the spectrum.…”

“…The first approach was recently published by the authors, in which the monitoring of GRC plates under a four point bending test using an ultrasonic pulse with a fixed frequency was carried out. Thus, the P-wave velocity, attenuation, energy and non-linear parameters were obtained [15]. Monitoring mechanical tests with nondestructive techniques provides a wealth of information about the material under study, allowing the prediction of its behaviour.…”