Influence of short steel fiber on mechanical properties of carbon textile reinforced concrete under low-cycle fatigue loading
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摘要: 为了研究低次数疲劳加载下短切钢纤维对碳纤维织物增强混凝土(C-TRC)力学性能的影响，通过万能试验机对不同短切钢纤维掺量(0vol%、0.5vol%、1.0vol%)的试件进行低次数疲劳加载实验和疲劳加载前后的准静态拉伸试验，并结合数字图像相关分析得到拉伸状态下裂纹与应变分布。结果表明：添加短切钢纤维能够增大C-TRC的拉伸强度、杨氏模量和韧性，降低试件的能量耗散及剩余累积应变，增加裂纹条数和裂纹宽度。疲劳荷载能够降低C-TRC的刚度、极限强度、峰值应变及韧性，加快C-TRC的破坏。添加短切纤维能够降低疲劳加载造成的性能损耗，且0.5vol%掺量的增强效果最佳。基于现有的剩余强度-剩余刚度关联模型和实验数据，改进了强度退化模型，对实验数据进行拟合并与现有模型进行对比，其结果与实验数据吻合更好。该成果对于织物增强混凝土(TRC)疲劳性能的评价具有指导意义。Abstract: In order to study the influence of the short steel fiber on the mechanical properties of carbon textile reinforced concrete (C-TRC) under low-cycle fatigue loading, low-cycle fatigue loading test and quasi-static tensile tests before and after fatigue loading were conducted on specimens with various contents of short steel fiber (0vol%, 0.5vol% and 1.0vol%) by a universal testing machine, and distributions of crack and strain were obtained by digital image correlation (DIC) method. The results show that the addition of short steel fiber can increase the tensile strength, the Young’s modulus and toughness of C-TRC, reduce the energy dissipation and residual accumulated strain and increase the crack number and crack width. Fatigue load can reduce the rigidity, tensile strength, peak strain, and toughness, and accelerate the destruction of C-TRC. The addition of short steel fiber can reduce the property degradation caused by fatigue loading, and the 0.5vol% addition has the best enhancement effect. The strength degradation model was modified based on the existing residual strength-residual stiffness coupled model and experimental data, The modified model is used to fit the experimental data and be compared with the existing model. The results show that the modified model is more consistent with the experimental data. These findings will be available for the fatigue performance evaluation of textile reinforced concrete (TRC).
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Key words:
- carbon textile /
- short steel fiber /
- tensile test /
- fatigue loading /
- TRC
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图 3 碳纤维织物混凝土(C-TRC)拉伸试件
Figure 3. Tensile specimen of carbon textile reinforced concrete (C-TRC)
图 5 疲劳荷载谱
Smax and Smin—Maximum and minimun fatigue stress; σmax—Determined failure stress from the monotonous tensile tests; Sm—Average fatigue stress; Sa—Stress amplitude; T—Cycle period
Figure 5. Fatigue load spectrum
图 6 低次数疲劳加载作用下C-TRC拉伸应力-应变曲线
N—Cycle index; E+ and E−—Upward Young's modulus and downward Young's modulus; σsmin and σsmax—Minimum and maximum stress in a single cycle; εsmin—Minimum strain in a single cycle; Bi—Minimum stress point in the ith cycle; Ai and Ai+1—Maximum stress point in the ith and (i+1)th cycle; εsmax_1 and εsmax_2—Maximum strain in the ith and (i+1)th cycle
Figure 6. Tensile stress-strain curves of C-TRC subjected to low-cycle fatigue loading
图 7 低次数疲劳加载作用下C-TRC疲劳力学性能变化
Ediss—Dissipated energy
Figure 7. Variations in fatigue mechanical properties of C-TRC subjected to low-cycle fatigue loading
图 8 低次数疲劳加载作用下C-TRC主裂纹宽度变化
Figure 8. Variations in width of the major crack of C-TRC subjected to low-cycle fatigue loading
图 9 短切钢纤维掺量对C-TRC裂纹宽度影响(第100次循环)
Figure 9. Influence of short steel fiber contents on crack width of C-TRC (100th cycle)
图 10 C-TRC裂纹宽度对比(第100次循环)
Figure 10. Comparison of the crack width of C-TRC (100th cycle)
图 11 低次数疲劳加载作用下C-TRC裂纹宽度的Mann-Kendall检验对比
ZMK—Test statistic of Mann-Kendall' test; Zα/2(α=0.025)—Test statistic at the significance level of 0.5
Figure 11. Comparison of the Mann-Kendall' test results of the crack width of C-TRC subjected to low-cycle fatigue loading
图 12 短切钢纤维掺量对C-TRC疲劳性能的影响(第100次循环)
Figure 12. Influence of short steel fiber contents on fatigue properties of C-TRC (100th cycle)
图 13 C-TRC拉伸应力-应变曲线
σT and σu—Cracking stress and peak stress; εT and εu—Cracking strain and peak strain; E—Elastic modulus
Figure 13. Tensile stress-strain curves of C-TRC
图 14 疲劳加载前后C-TRC的拉伸力学性能对比
Figure 14. Comparison of the tensile mechanical properties of C-TRC before and after fatigue loading
图 15 C-TRC剩余强度和剩余刚度的理论与试验结果对比
Sr and Er—Residual strength and residual rigidity; S0 and E0—Initial strength and initial rigidity
Figure 15. Comparison of theoretical and experimental results of the residual strength and residual rigidity of C-TRC
图 16 不同短切钢纤维掺量的C-TRC裂纹和应变分布
Figure 16. Crack and strain distribution of C-TRC with various contents of short steel fiber
图 18 不同短切钢纤维掺量的C-TRC疲劳加载前后的裂纹数量和平均裂纹间距
Figure 18. Crack number and average crack spacing of C-TRC with various contents of short steel fiber before and after fatigue loading
表 1 基体配合比设计
Table 1. Mix design of the matrix
kg/m3 Cement
(P·O 42.5)Fly ash Silica fume Sand (0-0.6 mm) Sand (0.6-1.2 mm) Superplasticizer Water Defoamer 712 303 65 450 901 4.4 330 2.6 
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表 3 短切钢纤维的物理和力学性能参数
Table 3. Physical and mechanical parameters of short steel fiber
Diameter/mm Length/
mmTensile strength
/MPaYoung's modulus
/GPaDensity
/
(g·cm−3)0.20 6-8 3015 200 7.8
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表 2 碳纤维织物的物理和力学性能参数
Table 2. Physical and mechanical parameters of carbon textile
Model Textile
size/mm2Tex/
(g·(1000 m)−1)Grammage/
(g·cm−2)Coating Section area of
single yarn/mm2Tensile strength of
single yarn/MPaYoung's modulus of
single yarn/GPaWarp Weft Warp Weft Warp Weft TC33-3 K 5×5 270-320 1.8 Epoxy resin 0.18 0.16 3450 3100 238 216
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表 4 C-TRC拉伸实验设计
Table 4. Experimental design for tensile tests of C-TRC
Specimen Textile Layers of textile ${V_{\text{f}}}$/vol% Q0%CT/C Carbon 2 0 Q0.5%CT/C Carbon 2 0.5 Q1.0%CT/C Carbon 2 1 Notes: Q—Quasi-static tensile tests; 0%, 0.5%, 1.0%—Contents of short steel fiber are 0vol%, 0.5vol% and 1.0vol%; CT—Carbon textile; C—Concrete; ${V_{\text{f}}}$—Volume fraction of carbon textile.
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表 5 C-TRC低次数疲劳加载试验设计
Table 5. Experimental design for low-cycle fatigue loading tests of C-TRC
Specimen Textile Layers of textile Vf/vol% Cycle Stress level/% L0%CT/C Carbon 2 0 100 5-60 L0.5%CT/C Carbon 2 0.5 100 5-60 L1.0%CT/C Carbon 2 1 100 5-60 Note: L—Low-cycle fatigue loading test.
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表 6 不同短切钢纤维掺量的C-TRC的疲劳性能参数(第100次循环)
Table 6. Fatigue properties parameters of C-TRC with various contents of short steel fiber (100th cycle)
Specimen $ {E}_{+} $
/GPa
E–/GPa$ {E}_{\mathrm{d}\mathrm{i}\mathrm{s}\mathrm{s}} $
/10–4 J
Bi/%L0%CT/C 2.04 2.04 590 0.533 L0.5%CT/C 2.18 2.18 453 0.493 L1.0%CT/C 2.10 2.11 475 0.513
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表 7 不同短切钢纤维掺量的C-TRC主裂纹出现时间和出现位置
Table 7. Occurrence time and location of major crack of C-TRC with various contents of short steel fiber
Specimen NO.1 NO.2 NO.3 Occurrence time Location
/mmOccurrence time Location
/mmOccurrence time Location
/mmL0%CT/C Before fatigue loading 43 Before fatigue loading 36 Before fatigue loading 42 L0.5%CT/C Before fatigue loading 43 8th cycle 44 Before fatigue loading 44 L1.0%CT/C Before fatigue loading 36 Before fatigue loading 15 16th cycle 18
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表 8 疲劳加载前后的C-TRC拉伸力学性能试验结果
Table 8. Test results of the tensile mechanical properties of C-TRC before and after fatigue loading
Specimen Rigidity/
GPaReduction rate/% Tensile strength/MPa Tensile load/
kNReduction rate/% Ultimate strain/% Reduction rate/% Toughness/
(kJ·m−3)Reduction rate/% Q0%CT/C 24.40 — 11.20 5.04 — 1.23 — 87.78 — Q0.5%CT/C 24.60 — 12.90 5.81 — 1.40 — 106.89 — Q1.0%CT/C 22.30 — 14.20 6.39 — 1.37 — 110.67 — L0%CT/C 1.07 95.6 9.15 4.12 18.2 0.84 32.0 38.00 56.8 L0.5%CT/C 1.75 92.9 11.40 5.13 11.8 1.13 19.3 66.67 37.7 L1.0%CT/C 1.14 94.9 11.30 5.09 20.5 0.99 28.0 51.56 53.4
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表 9 未添加短切钢纤维时C-TRC的剩余刚度-剩余强度关联模型参数与拟合结果
Table 9. Parameters of the residual strength-residual stiffness coupled model of C-TRC without short steel fiber and fitted results
Cycle Eq. (8) R2 Eq. (9) R2 $ q $ $ w $ $ r $ $ a $ $ H $ 100 0.0012 12.4 0.93 0.61 0.04 0.68 0.94 200 0.0014 14.1 0.95 0.74 0.07 0.54 0.93 Average value 0.0013 13.3 0.68 0.06 0.61 Notes: q and w—Unknown parameters in Eq.(8); r, a, and H—Unknown parameters in Eq.(9); R2—Goodness of fit.
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表 10 不同加载次数下的C-TRC的剩余强度和剩余刚度
Table 10. Residual strength and residual rigidity of C-TRC subjected to various loading cycles
Stress level/
%Cycle NO.1 NO.2 NO.3 Sr/S0
/%Er/E0
/%Sr/S0
/%Er/E0
/%Sr/S0
/%Er/E0
/%5-60 100 82.4 3.1 86.6 4.1 85.3 4.1 200 81.7 4.7 88.4 4.1 79.6 4.4 300 82.3 5.4 79.4 4.5 81.7 4.9 500 79.4 4.2 77.6 3.6 78.3 4.2 Notes: Sr and S0—Residual strength and initial strength; Er and E0—Residual stiffness and initial stiffness.
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