冲击荷载下含裂纹缺口三点弯动态断裂实验

Dynamic Fracture Experiment Study of a Three-point-bend Beam with Crack Notched under Impact Load

为研究缺口大小对含裂纹缺口构件动态断裂的影响,采用动态光弹性实验方法,对含裂纹缺口试件进行了冲击实验。基于冲击断裂过程中试件的等差条纹变化图片和动态应变仪采集的应变数据,分析了冲击荷载下裂纹尖端的动态应力强度因子、裂纹扩展速度和锤头应变的变化规律。结果表明:不同缺口角度试件受到冲击荷载后,应力强度因子的变化随时间变化的趋势基本一致,应力强度因子的峰值随角度增大而增大,应力强度因子的峰值在缺口角度大于90°后增大更显著;锤头应变都表现出先压缩后拉伸然后逐渐震荡趋于平缓的变化规律,当缺口角度大于90°时,锤头的最大压应变增长趋势显著增加;不同缺口角度试件的裂纹扩展速度随时间变化规律基本一致,但当缺口角度大于90°之后,试件的起裂时间显著延长。由此得出结论:当缺口角度对含裂纹缺口构件的动态断裂有一定影响,当缺口角度小于90°时影响不显著,当缺口角度大于90°时起裂难度显著增加。

In order to study the influence of the size of the notch on the dynamic fracture of the cracked notch component,an impact test on the cracked notch specimen was conducted by the dynamic photoelastic experiment method.Through the image of the uniform fringe change of specimen during impact fracture and the strain data collected from dynamic strain gauge,the variation law of dynamic stress intensity factor,crack propagation velocity and hammer strain in the crack tip under impact load were analyzed.The results show that when specimens with different notch angles are subjected to impact load,the variation trend of stress intensity factor with time remain the same basically.The peak value of stress intensity factor increases with the increase of angle,and the peak value of stress intensity factor increases significantly when the notch angle is greater than 90°.The strain of hammer head exhibits the change rule of first compression,then stretching,and gradually shaking to a gentle level.When the notch angle is greater than 90°,the maximum compressive strain of hammer head increases dramatically.The rate of growth on crack specimens with different notched angles varies with time.But when the notched angle is greater than 90°,the initiation time of the specimen is significantly prolonged.It is concluded that the notch angle has a certain effect on the dynamic fracture of the cracked notched component,but the effect is not significant when the notch angle is less than 90°,and the difficulty of cracking initiation is significantly increased when the notch angle is greater than 90°.