节理充填物厚度对运动裂纹扩展的影响

Effects of joint filling thickness on crack propagation behaviors

为研究冲击载荷作用下节理充填物厚度对裂纹扩展行为的影响,以石膏为有机玻璃预制裂纹充填物,利用新型数字激光动态焦散线实验系统,对3种不同节理充填物厚度的有机玻璃进行三点弯冲击实验。实验结果表明,相同冲击载荷作用下,竖向预制裂纹均竖直向上扩展,是典型的Ⅰ型裂纹,充填物越厚,竖向裂纹越容易起裂。竖直裂纹扩展至水平预制裂纹后,充填物厚度为1、3、5 mm的试件的水平预制裂纹汇聚能量的时间分别为433、2200、2580μs,起裂时的应力强度因子分别为635.2、742.4、906.8 kN/m3/2,表明充填物越厚,水平裂纹越难起裂。水平预制裂纹扩展过程中共发生2次曲裂,是典型的Ⅰ-Ⅱ复合型裂纹,节理充填物越厚,其扩展轨迹越弯曲;当裂纹扩展至距离试件上边界3 mm时,扩展方向偏离第1次裂纹曲裂切线而朝向试件上边界扩展,试件最终断裂,测量发现充填物厚度为1、3、5 mm的试件的断裂点与冲击载荷作用点的距离分别为16.5、11.0、6.0 mm。

To explore the effects of the thickness of joint-filling material on the dynamic fracture properties of cracks under impact load,the gypsum was used as the material filled into the prefabricated cracks in polymethyl methacrylate(PMMA)specimens,three-point bending impact tests were conducted on the PMMA specimens with different joint filling thicknesses by using a novel digital laser dynamic caustics experimental system.The experimental results show that the vertical prefabricated cracks propagate vertically upward toward the free surface under the same impact load,which is a tytical mode-Ⅰcrack,and the thicker the filling,the easier the vertical crack initiation.When the vertical crack propagates to the horizontal prefabricated crack,the energy gathering times of the horizontal prefabricated cracks in the specimens with a filling thickness of 1,3 and 5 mm are 433,2200 and 2580μs,respectively.And the stress intensity factors of crack initiation are 635.2,742.4 and 906.8 kN/m3/2,respectively.It indicates that the thicker the filling,the more difficult the horizontal crack initiation.The horizontal prefabricated crack is a typicalⅠ-Ⅱcomposite crack.The thicker the joint filler,the more curved the propagation path of the horizontal prefabricated crack.When the distance between the crack and the upper boundary of the specimen is 3 mm,the horizontal crack propagates towards the upper boundary of the specimen,and the specimen finally breaks.It is found that the distances between the fracture points and the impact load points of the specimens with the filling thicknesses of 1,3 and 5 mm are 16.5,11.0 and 6.0 mm,respectively.