PSI - Issue 6

A.M. Bragov et al. / Procedia Structural Integrity 6 (2017) 161–167 Author name / Structural Integrity Procedia 00 (2017) 000–000

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The length/diameter ratio of the specimens was in the recommended limits of 0.3 – 1.0; the ends of the measuring bars were oiled before testing to decrease the effect of friction forces. The synchronized strain pulses of the measuring bars for the case when the specimen maintained its integrity are shown in Fig. 1а, and for the case of its total disintegration in Fig. 1б. It can be noted that, when the specimen maintained its integrity, drop of the amplitude of the transmitted pulse takes place after the effects of the incident pulse, and the reflected pulse has a ‘negative trail’, which brings down deformation and creates an unloading branch on the deformation diagram of the material. In the case when the specimen disintegrated in the first loading cycle, the transmitted pulse amplitude drops abruptly; at the same time, the reflected pulse amplitude increases almost up to the level of the amplitude of the incident wave, which is still effective. The character of deformation and failure under pulsed loading is qualitatively similar for all the tested brittle materials. Fig. 2 exemplifies the deformation diagrams of ceramic brick in the axes of stress-time and stress-strain for different strain-rate regimes. The dotted lines correspond to the strain rate history in the experiments.

Fig. 2.Deformation diagrams of ceramic brick for different strain rates in the axes of stress-time and stress-strain

To obtain material properties under dynamic tension, a modification of the present method, a splitting test, or ‘Brazilian test’, was used. Tensile strain as a function of time is determined based on the strain pulse registered at the cross-section of the supporting measuring bar according to the following formulas:

• For cylindrical specimens

L D EA

T ε

( ) 2 t =

( ) t

σ

⋅

tension

π

0 0

• For specimens in the form of rectangular parallelepiped

EA

T ε

( ) 0.5187 0 0 B H t =

( ) t

σ

⋅

tension

In these formulas Е , А , are elastic modulus and cross-section area of the measuring bars, respectively; L 0 , D 0 are height and diameter of a cylindrical specimen, respectively; H 0 , B 0 are height and side of the cross-section of a specimen in the form of a rectangular parallelepiped, respectively; ε Т ( t ) is strain pulse of the supporting measuring bar transmitted through the specimen. The adequacy of this methodology was analyzed in Rodriguez et al. (1994), where it is noted that the ‘Brazilian test’ can be applied for determining tensile strength of brittle materials, exhibiting elastic behavior and the equilibrium loading state of the specimen, and it fails along the diametric plane. Fig. 3 depicts profiles of