Assessment of Thermal Shock Fatigue Tests in Rocks

Abstract

We assembled a thermal shock fatigue testing machine that repeats the cycles of rapid heating by furnace and rapid cooling by water bath. Using this test machine, we investigated the damages of thermal shock fatigue process, in four kinds of rocks, observing the extension of rocks by thermal shock fatigue and the change of strength and physical properties. From the experimental result, we examined the relationship between the strength and other physical properties of the rocks.
The results are;
1. The process of crack extension by thermal shock fatigue could be divided into three stages, that is crack initiation, crack coaleScence and fracturing of the rocks. Let T denote the testing temperature and N the number of repetition cycles of heating and cooling, and we could approximately express the relation as follows;
T=A_iN^-κ
where κ is the gradient and A_i is the stage of the crack initiation (A₁), the crack coaleacence (A₂) and the f raturing of the specimen (A₃).
By examining the constants in the above expression, we can deScribe the properties of the thermal shock fatigue of the rock.
2. As the repetition cycles of heating and cooling increase, the early part of the stress-strA_in curve began to show the non-linearity. This is caused by the initiation and the coaleScence of cracks.
3. Since the non-linear part of the stress-strA_in curve is considered to show the damages of thermal shoch fatigue, we examined the validity of √E′/ρ with the velocity of the primary wave, where E′ is the secant modulus at 100kgf/cm², which is correspond to the slope of early part of stress-strA_in curve. The results show that the degree of V_p or by examining the non-linear part of the stress-strA_in curves.
4. Contrasting the uni-axial compressive strength (S_c) agA_inst the 50% secant modulus (E₅₀) or the velocity of primary wave (V_p) shows that the increase or decrease, respectively, but the better correspondence is seen between S_c and E₅₀ than between S_c and V_p.