方形岩石试件冲击载荷下的动力响应分析

Dynamic Response Analysis of Square Rock Specimen under Impact Load

采用ANSYS/LS-DYNA有限元分析软件模拟研究了方形岩石试件单轴冲击下的动力响应。研究了不同长径比方形试件的应力均匀性并以此确定试件的最佳长径比,分析了试件在不同冲击速度下的应力应变关系、应变率变化以及动态破坏模式等。结果表明,脉冲经"切削式圆-方"变截面杆传播后,平均衰减百分比为10.0%;采用定义的轴向应力不均匀系数和横向应力不均匀系数分析不同长径比方形试件的应力均匀性,确定最佳长径比为0.4;不同冲击速度下的反射波与应变率时程曲线均有一定的平台期,表明冲击试验可实现恒应变率加载,试件内应力能够均匀分布;应变率较低时,试件基本没有破坏,且表现出一定的弹性特性;应变率较高时,试件以拉伸劈裂破坏为主,且往往沿水平和垂直两对称轴碎裂,以4个角为核形成碎块;在试件未破坏或破坏前,有明显的弹性阶段和塑性阶段。随应变率增加,试件杨氏模量增大,动态强度增强,应变范围也明显扩大。

The dynamic response of square rock specimens to uniaxial impact was studied by using the finite element software ANSYS/LS-DYNA by simulation. The stress uniformity of square specimens with different aspect ratios was investigated for preliminarily determining the best aspect ratio. Then the impact tests were conducted for analyzing stress-strain relationship,strain rate variation,as well as dynamic failure modes of the specimens under different impact velocities.Results show that an attenuation percentage is 10.0% on average for pulse after spreading through the specimen bar with a variable cross-section from round to square. Stress uniformity of the specimens with different aspect ratios was analyzed by using the defined non-uniform coefficient of axial stress and radial stress,leading to the best aspect ratio set at 0.4.There＇s a plateau for both reflected waves and strain rate-time curves under different impact velocities,indicating the constant strain rate loading can be achieved and the stress within the specimen can be uniformly distributed. Specimens aren＇t destroyed at a lower strain rate,showing certain elastic properties. At a higher strain rate,specimens are predominantly destroyed by tensile fracturing,with fracture along the horizontal axis and vertical axis forming fragments in four corners as the core. There shows apparent elastic stage and plastic stage for undamaged specimens or before specimens are damaged. With an increase in strain rate,Young＇ s modulus,dynamic strength and strain range all increase.