煤应变型冲击破坏尺寸效应声发射特征试验研究

Experimental study on the size effect of acoustic emission characteristics of coal strainbursts

为探究煤冲击破坏过程中的尺寸效应现象,采用自主研发的煤岩冲击破坏试验装置对5种不同尺寸的方形试样开展单轴压缩试验,并重点监测其声发射特征。研究表明:煤的弹性模量随边长尺寸的增加而增加,抗压强度及峰值应变随尺寸的增加而减小,尺寸较大的试样,在整体冲击破坏发生前会有局部小型冲击破坏的发生;随着边长尺寸的增加,声发射总振铃计数增长速度加快,声发射信号大能量更多在临近破坏阶段,但尺寸增加到300mm时,声发射能量尺寸效应不明显。大尺寸试样的声发射b值会因为局部冲击而产生突降;声发射定位信号反映了试样破坏方式,随着边长尺寸的变大,声发射定位信号愈加分散,试样破坏方式由剪切破坏为主转为张拉破坏为主。

In order to investigate the phenomenon of scale effect in the bursting failure of coal measure,the bursting failure tests under uniaxial compression conditions were carried out on square coal samples with different sizes by using the house-developed test apparatus.The acoustic emission characteristics during the bursting failure of the coal samples were investigated.The study shows that as the sample size increases,the elastic modulus of coal increases and the compressive strength and peak strain decrease.For larger samples,ejections of small fragments from the skin of the sample trend to occur before the final catastrophic bursting failure.This phenomenon is unlikely to occur for small samples.As the sample size increases,the growth rate of acoustic emission events increases,and the number of AE events with large energy increases.This size effect trends to disappear when the sample size reaches 300 mm.The acoustic emission b-value of large size specimen produces sudden drop due to localized bursting failure.The distribution characteristics of the acoustic emission events reflects the damage mode of coal sample.The distribution of acoustic emission events trends to become more dispersed as the coal sample becomes larger,and the damage mode of specimen is changed from shear damage to tensile damage.