用应变片法确定混凝土动态起裂时间的研究

在混凝土等准脆性材料的动态起裂韧度K_(1d)测试中,准确确定试件裂尖的起裂时间是测试工作的关键。采用分离式霍普金森压杆系统,对圆孔裂纹平台巴西圆盘混凝土试件进行动态径向冲击试验,通过在裂尖粘贴应变片的方法来确定起裂时间。讨论了应变片在裂纹尖端的粘贴位置、粘贴方向等因素对起裂时间测试值的影响,结果表明裂尖应变片的最佳粘贴方式是:在裂纹延长线上或在裂尖并与裂纹垂直的线上,都距离裂尖3 mm左右,且粘贴方向与裂纹延长线垂直。给出了考虑贴片位置和试件厚度的起裂时间计算公式。

Determining dynamic fracture initiation time for concrete with strain gauge method

In testing dynamic fracture initiation toughness K_(Id) of quasi-brittle materials, such as, concrete, it was crucial to determine fracture initiation time of crack tip accurately.Dynamic experiment was performed using a holed-cracked flattened Brazilian disc of concrete, which was diametrically impacted by split Hopkinson pressure bar (SHPB), the fracture initiation time was determined by using the strain gauge method.Different sticking location of a strain gauge, different direction of a strain gauge and other factors to affect determining fracture initiation time were discussed.Based on the experiment results, the best approach was that, the strain gauge should be stuck along the crack extension line or the vertical line to the crack at the crack tip, the distance was about 3 mm from the crack tip to the center of the strain gauge, and the sticking direction of the strain gauge was vertical to the crack.A formula to determine the fracture initiation time was given considering the sticking location of the strain gauge and thickness of the specimen.