In this study, static and dynamic tensile tests were carried out to study rock fracture mechanism. Brazilian test was adopted as the static tensile test with changing strain rates. while modified pipe test based on Hoppkins' effect was adopted as dynamic test. Vertical pipe test was modified to have inclination. By this modification, variable was reduced to friction force only. As a result of all these tests, the characteristics of rook including static &dynamic tensile strengths etc have been obtained. &a general relationship between tensile strength &strain rate is suggested by a formula.
Dynamic testing as discussed in the literature covers various types of test such as creep, fatigue, impact and extends over a wide range of strain rates. Therefore, it is important to establish or define the load or strain rate associated with the type of dynamic test being conducted. In this paper the discussion will be concerned with dynamic tensile strength of Tae-Jeon granite in the strain-rate range of 5.67 × 10¹ - 3.6 × 106 /sec by tensile test. Static and dynamic tensile strength and fracture mechanism was studied. Brazilian test was adopted as the static tensile test with changing strain rates, while modified pipe test based on Hoppkins' effect was adopted as dynamic test. Vertical pipe test was modified to have inclination. By this modification, variable was reduced to friction force only. A simple dynamic tensile fracture experiment was designed to measure the dynamic tensile strength of a rock and its dynamic fracture energy. For Homogeneous rock material, the experiment can also measure the dynamic tensile strength.
The strain energy associated with a stress wave is the internal energy contained in the material in the form of elastic deformation energy. It is the product of stress and strain (divided by the material's initial density. if one wants to have the strain energy per unit mass rather than per unit volume). For a simple compressive or tensile wave. However, in the process of fracturing, only half of the impactor's kinetic energy can be used for deformation work at the fracture surfaces. The other half is transmitted back into the two separating parts in the form of elastic tensile waves.
Static and dynamic tensile strength tests were conducted on the Tae-Jeon granite of Korea. Strengths obtained from both test on 54 mm-diameter specimens.
Brazilian test was adopted as a static tensile strength test. Experimental results have suggested that the static tensile strengths or granite increasing loading rate, as shown in Table I.
Fig. 2 shows a schematic picture of the overall experimental setup, Fig 3 shows the idealized wave velocity in the hammer and rock specimen at different times after impact. If hammer length is three times of rock specimen length, peak tensile wave force is generated at 100p sec or 120p sec. Table 2 shows results of pipe test, Table 3 shows dynamic tensile strength in high strain rate.