水泥基体中仿生钢纤维的拔出试验

Pullout Test of Bio-inspired Steel Fiber from Cementitious Matrix

从仿生学的角度制备端部具有不同锥角(0°,2°,5°,7°)的异形钢纤维,根据纤维表面是否处理分为有化学黏结与无化学黏结2种,并使用MTS万能试验机测试了仿生异形钢纤维从水泥砂浆基体中以不同速率(2.5 mm/min,25 mm/min,250 mm/min)拔出的力和位移,并计算得到最大拔出力和拔出功.结果表明,当钢纤维端部锥角从0°增加到5°时,最大拔出力有明显的增加,但7°时稍有减小;对于5°及7°锥角的钢纤维,随着加载速率从2.5mm/min增大到250mm/min,钢纤维的最大拔出力分别增大20.2%和13.4%;而0°及2°锥角钢纤维在加载速率增加到250 mm/min时,最大拔出力相对于加载速率为25 mm/min时的最大拔出力分别减小25.9%和8.2%;0°,2°和5°有黏结钢纤维的最大拔出力与相同锥角无黏结钢纤维的最大拔出力相比,分别增加64.1%,22.2%和6.7%,而7°锥角有黏结钢纤维的最大拔出力比无黏结钢纤维的最大拔出力减小6.2%;3种加载速率下,2°锥角钢纤维拔出力所做的功最大,纤维表面是否处理对拔出功无明显影响;本文设计的异形钢纤维能有效增强钢纤维与水泥砂浆基体的等效黏结强度.

In this study, tapered steel fibers with various angles （0°, 2°, 5°, and 7°） were designed in the point view of biomimetic. The surfaces of the fibers were classified into chemical bonding and no chemical bonding based on whether their surfaces were treated or not. The fibers were pulled out from cementitious matrix under various loading speeds （2.5 mm/min, 25 mm/min, and 250 mm/min） using a MTS load frame. Pullout force and displacement of the fiber were recorded for further calculation of maximum pullout force and work of pullout. The experimental results show that the maximum pullout force increases significantly when the taper angle increases from 0° to 5°, but decreases slightly when the angle is 7°. The maximum pullout force increases by 20.2% and 13.4% with the pullout speed increasing from 2.Smm/min to 250mm/min for 5° and 7° fibers,respectively. The maximum pullout force decreases by 25.9% and 8.2% for 0° and 2° fiber when pullout speed increases from 25 mm/min to 250 mm/min, respectively. The maximum pullout force for untreated fibers are 64.1 %, 22.2 % and 6.7% higher than that for treated fiber when the taper angles are 0°,2° and 5°, respectively. However, for the fibers with 7° taper angle, the maximum pullout force of untreated fiber is 6.2° lower than the treated ones. The work of pullout for 2° fiber is the largest under three various speeds. There is no obvious effect on the work of pullout whether the fiber is treated or not. The tapered fibers designed in this work can effectively enhance equivalent adhesive strength between the fiber and cement mortar matrix.