基于NSCB石灰岩试样的加载速率和尺寸效应对其断裂韧度的影响研究

Research on the loading rate and size effect of limestone fracture toughness based on NSCB specimens

为研究试样不同尺寸和加载速率对岩石Ⅰ型断裂韧度试验值的影响,采用石灰岩制作圆盘直径30,50,75,100,150 mm 5种几何相似的中心直裂纹半圆盘试样(notched semi-circular bend,NSCB),在RMT-150B岩石力学试验系统上对NSCB试样进行5种加载速率(0.002,0.02,0.2,2,10 kN/s)作用下的三点弯曲试验。结果表明:在试样尺寸一定条件下,试样的断裂韧度试验值随着加载速率的增加基本呈对数增大,在加载速率一定条件下,存在一个临界尺寸(圆盘直径50 mm),小于这个临界尺寸时,断裂韧度试验值增加幅度较大,大于这个临界尺寸时,试验值增加幅度较小,且基本呈线性增加。探讨了产生加载率和尺寸效应的原因,对于深入分析岩石断裂特性和准确确定岩石断裂韧度有一定意义。

In order to investigate the influence of different size of specimen and loading rate on the test value of rock mode I fracture toughness,five sizes of geometrically similar central straight crack half disk specimens of diameter 30,50,75,100,150 mm were made by limestone(notched semi-circular bend,NSCB).The three-point bending test of the NSCB specimens under five levels of loading rates(0.002,0.02,0.2,2,10 kN/s)were carried out on the RMT-150B rock mechanics test system.The results showed that as the sample sizes were certain,the test values of the fracture toughness of the specimen increased logarithmically with the increase of the loading rate.As the loading rate was certain,there was a critical size,which disk diameter was 50 mm.When it was less than this critical size,the fracture toughness test value increases greatly.However,when it greater than this critical size,the test value increased by a small amount and basically increased linearly.The reasons causing the loading rate and size effect were discussed,which was helpful to deeply analyze the fracture characteristics of rock and to determine the fracture toughness accurately.