DCIF (Directional Cooling-Induced Fracturing) Westerly Granite AE Borehole Damage Effect Test (Task 3-0)

Directional Cooling-Induced Fracturing (DCIF) experiments were conducted on three rectangular Westerly granite blocks (width=depth=4.0", height=2.0") which were preheated to 200, 400, and 600 degree C to induce damage (microcracks) with varying degrees. Liquid nitrogen was poured in a small, 1"-diameter copper cup attached to the top of the sample, and the resulting acoustic emissions (AEs) and temperature changes on the surface of the sample were monitored. The experiments were conducted under one selected biaxial stress (5.8MPa). The obtained AEs were used to determine the microcracking source locations and amplitude, and the associated moment tensors. The onset time of the AEs was correlated with the cooling temperature, which was used to show that the temperature at the onset of microcracking is not affected significantly by the preexisting damage, compared to the impact of the stress in the sample. Included in this submission are the animations of the AE locations and graphics displaying the measured temperature-AE activity changes for samples with different degrees of microcrack damage.

在三个矩形西里尔花岗岩块（宽度=深度=4.0英寸，高度=2.0英寸）上进行了方向冷却诱导裂缝（DCIF）实验，这些花岗岩块预先加热至200、400和600摄氏度以诱导不同程度的损伤（微裂纹）。在样品顶部连接的一个直径为1英寸的铜杯中注入液氮，并监测由此产生的声发射（AEs）和样品表面的温度变化。实验在单轴应力（5.8MPa）下进行。通过获得的AEs确定微裂纹源的位置和幅度，以及相关的矩张量。AEs的起始时间与冷却温度相关联，以此表明微裂纹起始时的温度不受预先存在的损伤的显著影响，相较于样品中的应力影响。本提交中包含AEs位置的动画以及显示不同微裂纹损伤程度样品测量的温度-AE活动变化的图形。