Piezoresistive response of carbon fibric reinforced cementitious matrix during pull-out test and the establishment of equivalent delamination failure model
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摘要: 碳纤维织物增强水泥基复合材料(CFRCM)被广泛研究并应用于混凝土结构加固和性能自监测,但目前碳纤维的力阻响应机制尚不明确。本文通过CFRCM纤维束的拉拔试验发现其荷载-位移曲线符合典型的粘结滑移三阶段特征,拉拔过程中的电阻变化也呈现出波动缓慢上升-快速增长-缓慢增长的三阶段特征,碳纤维束脱粘阶段的电阻增长率与极限拉拔力呈现中高度的正相关性。进一步基于拉拔过程碳纤维束的力阻响应建立了纤维等效分层破坏模型及计算方法,为电阻信息与受荷状态的相互转化提供了新思路。Abstract: Carbon fibric reinforced cementitious matrix (CFRCM) is often used in the reinforcement of concrete structures and self-sensing structures. However, the mechanism of piezoresistive response is still unclear. In this paper, through the pull-out test of CFRCM, it is found that the load-displacement curves present typical three-stage characteristics of bond-slip model, and the change of resistance during the pull-out test also presents three-stage characteristics, which contains random fluctuation rising, rapid growth and slow growth stages. Further analysis shows that the growth rate of resistance in the debonding stage of carbon fiber bundles has a medium-high positive correlation with the ultimate pull-out force. An equivalent delamination failure model and calculation method of carbon fiber were established based on the piezoresistive response of carbon fiber bundles in the pull-out progress, which realized the mutual conversion between the resistance information and the charged state.
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表 1 砂浆配合比
Table 1. Mass proportion of the ingredients in the cementitious matrix
Mortar type Cement
(P·O 42.5)/gWater/g Medium sand
(0.5-1 mm)/gFine sand
(0-0.5 mm)/gRedispersible
latex powder/gPlasticizer/g Low strength mortar 100 45 133 67 1.5 0.15 表 2 试件编号
Table 2. Specimen number
Specimen number Le/mm Parallel specimen Specimen number Le/mm Parallel specimen P-60-1 60 1 P-120-1 120 1 P-60-2 2 P-120-2 2 P-60-3 3 P-120-3 3 P-60-4 4 P-120-4 4 P-60-5 5 P-120-5 5 Notes: P—Pull-out test; Le—Embedded length in mortar. 表 3 CFRCM束拉拔试件的极限拉拔力及脱粘阶段电阻变化幅度
Table 3. Ultimate pull-out force and resistance change in debonding stage of CFRCM specimens
Specimen Ultimate pull-out force/N ∆RII /R0/% Specimen Ultimate pull-out force/N ∆RII/R0/% P-60-1 268.63 3.49 P-120-1 578.21 4.43 P-60-2 537.62 11.23 P-120-2 398.36 3.64 P-60-3 621.21 10.63 P-120-3 532.24 18.48 P-60-4 347.44 3.00 P-120-4 655.07 5.73 P-60-5 752.26 15.25 P-120-5 705.69 11.82 Note: ΔRII—Resistance change of the debonding phase. 表 4 CFRCM束拉拔等效分层破坏模型计算过程关键参数
Table 4. Key parameters in the calculation of the equivalent delamination failure model of CFRCM specimens
Specimen Ncore η λs(0) λs(u0) Specimen Ncore η λs(0) λs(u0) P-60-1 7140 0.47 0.010 0.430 P-120-1 7064 0.18 0.010 0.750 P-60-2 4748 0.37 0.100 0.520 P-120-2 7157 0.12 0.010 0.780 P-60-3 5967 0.28 0.035 0.550 P-120-3 5965 0.20 0.037 0.510 P-60-4 7075 0.43 0.010 0.500 P-120-4 7374 0.09 0.010 0.750 P-60-5 2148 0.35 0.190 0.580 P-120-5 3070 0.22 0.160 0.680 Notes: Ncore—Number of core filaments; η—Initial fracture rate; λs(0), λs(u0)—Equivalent lap rate of fracture fibers when the displacement equal to 0 and u0, where u0 represents the beginning of the friction phase. -
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