PSI - Issue 5

Igor Shardakov et al. / Procedia Structural Integrity 5 (2017) 210–216 Igor Shardakov / Structural Integrity Procedia 00 (2017) 000 – 000

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Table 1. Physical-mechanical properties of materials. Material

Elastic modulus (GPa)

Poisson ratio

Density (kg/m 3 )

Concrete

34.3 200

0.2 0.3

2500 7800 1500

Reinforcement

Epoxy resin

3.8

0.36

Figure 5 presents the graphs corresponding to the results of numerical experiments and illustrating time variations in accelerations normal to the beam surface at the points of location of the accelerometers D1 (solid line) and D2 (dashed line) at different states of the crack (I, II, III, IV). The wave front amplitudes (maximum in absolute magnitude), are denoted by a cross. These values are used to determine the values of the criterion K for 4 states of the crack K I = 1.065; K II = 0.409; K III = 0.828; K IV = 1.040. It follows from these data that the greatest distortion of the front of the wave passing through the area of the crack is observed for the crack with maximum opening (state II). The proposed criterion K responds fairly well to the partial length-wise filling of the crack (state III). Upon the complete filling of the crack (state IV), the value of the criterion K gets closer to its initial value.

Fig.5. Changes in normal accelerations at the points of location of the accelerometers D1 (solid line) and D2 (dashed line)

Of considerable interest is the question of how strong the impact load should be to generate a shock wave most sensitive to the presence of a crack. To this end, a great number of numerical experiments were performed to study the dependence of the criterion K on the duration of impact T (Fig.2) and the distance L between the point of impact and the place of location of the accelerometer D1. Figure 6 gives the graphs showing how the criterion K changes in relation to the distance L for three values of pulse duration: T = {0.27, 0.10, 0.05} msec. The solid line corresponds to state I (no crack), and the dashed line – to state III (the crack is filled over its total surface to a depth of 5-10mm).