聚丙烯纤维增强混凝土断裂韧度及软化本构曲线确定
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摘要
对粗、细聚丙烯(Polypropylene, PP)纤维不同混掺情况下的混凝土切口梁试件进行三点弯曲试验,基于双K断裂理论探讨了不同尺寸PP纤维混掺方式对试件断裂韧度的影响及其破坏机理,并通过起裂、失稳、黏聚韧度3者之间的定量关系得到实测黏聚韧度、起裂韧度增量和桥接韧度。借鉴3种普通混凝土的双线性软化本构曲线计算得到理论黏聚韧度,并将其与实测黏聚韧度对比,确定适合于不同纤维掺入情况下PP纤维增强混凝土(Polypropylene fiber reinforced concrete, PFRC)的双线性软化本构曲线。研究结果表明,PFRC相对素混凝土有较高的起裂韧度、失稳韧度和断裂能;2或3种尺寸PP纤维混掺时,其桥接应力对桥接韧度的增强效果非常显著;3种尺寸PP纤维在裂缝扩展的不同阶段发挥桥接作用,体现了良好的混掺增强、增韧效应;徐世烺和Reinhardt改进的双线性软化本构曲线,取校正系数λ为6时,可较好地适用于PFRC。
The three‐point bending test was carried out on concrete notched beams with different amount of coarse and fine polypropylene(PP) fibers. Based on the double‐K fracture theory, the influence of mixing method of PP fibers with different sizes on the fracture toughness and failure mechanism were discussed.The real cohesive toughness, the increment of initiation toughness and the bridge connection toughness were gained by the quantitative relationship between the initiation toughness, the unstable toughness and the cohesive toughness. In addition, The theoretical cohesive toughness was calculated from three kinds of ordinary concrete bilinear softening constitutive curves, which was compared with the real cohesive toughness to determine the bilinear softening traction-separation law of PFRC, which was suitable for different PP fiber incorporation conditions. The results show that PFRC has higher initiation toughness,unstable toughness and fracture energy compared with plain concrete. The enhancement effect of bridge connection toughness from bridging stress is very significant when 2 or 3 sizes of PP fibers are mixed. The 3 sizes of PP fibers play the role of bridging at different stages of crack propagation, and it serves a well function of toughening and strengthening. The bilinear softening traction-separation law proposed by Xu and Reinhardt is well applicable for PFRC when the correction coefficient is 6.
The three‐point bending test was carried out on concrete notched beams with different amount of coarse and fine polypropylene(PP) fibers. Based on the double‐K fracture theory, the influence of mixing method of PP fibers with different sizes on the fracture toughness and failure mechanism were discussed.The real cohesive toughness, the increment of initiation toughness and the bridge connection toughness were gained by the quantitative relationship between the initiation toughness, the unstable toughness and the cohesive toughness. In addition, The theoretical cohesive toughness was calculated from three kinds of ordinary concrete bilinear softening constitutive curves, which was compared with the real cohesive toughness to determine the bilinear softening traction-separation law of PFRC, which was suitable for different PP fiber incorporation conditions. The results show that PFRC has higher initiation toughness,unstable toughness and fracture energy compared with plain concrete. The enhancement effect of bridge connection toughness from bridging stress is very significant when 2 or 3 sizes of PP fibers are mixed. The 3 sizes of PP fibers play the role of bridging at different stages of crack propagation, and it serves a well function of toughening and strengthening. The bilinear softening traction-separation law proposed by Xu and Reinhardt is well applicable for PFRC when the correction coefficient is 6.
引文
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[20]赵艳华,聂玉强,徐世烺.混凝土断裂能的边界效应确定法[J].工程力学,2007,24(1):5661.Zhao Yanhua,Nie Yuqiang,Xu Shilang.Determination of boundary effect on fracture of concrete[J].Engineering Mechanics,2007,24(1):5661.
[2]Liang N,Dai J,Liu X.Study on tensile damage constitutive model for multiscale polypropylene fiber concrete[J].Advances in Materials Science and Engineering,2016,9168984.
[3]邓宗才.混杂纤维增强超高性能混凝土弯曲韧性与评价方法[J].复合材料学报,2016,33(6):12741280.Deng Zongcai.Flexural toughness and characterization method of hybrid fibers reinforced ultrahigh performance concrete[J].Acta Materiae Compositae Sinica,2016,33(6):12741280.
[4]夏冬桃,刘向坤,夏广政,等.混杂纤维增强高性能混凝土弯曲韧性研究[J].华中科技大学学报:自然科学版,2013,41(6):108112.Xia Dongtao,Liu Xiangkun,Xia Guangzheng,et al.Flexural toughness of highperformance hybrid fiber reinforced concrete[J].Journal of Huazhong University of Science and Technology(Natural Science Edition),2013,41(6):108112.
[5]Caggiano A,Gambarelli S,Martinelli E,et al.Experimental characterization of the postcracking response in hybrid steel/polypropylene fiberreinforced concrete[J].Construction&Building Materials,2016,125:10351043.
[6]陆洲导,俞可权.高温后混凝土断裂韧度及软化本构曲线确定[J].同济大学学报:自然科学版,2012,40(9):13061311.Lu Zhoudao,Yu Kequan.Determination of residual fracture toughness and softening tractionseparation law of postfire concrete[J].Journal of Tongji University(Nature Science),2012,40(9):13061311.
[7]Xu S L.Determination of parameters in the bilinear,Reinhardt's and exponentially nonlinear softening curves and their physical meaning[C]∥Werkstoffe und Werkstoffprüfung im Bauwesen,Hamburg,Libri BOD,1999:410424.
[8]徐世烺,熊松波,李贺东,等.混凝土断裂参数厚度尺寸效应的定量表征与机理分析[J].土木工程学报,2017,50(5):5771.Xu Shilang,Xiong Songbo,Li Hedong,et al.Quantitative characterization and mechanism analysis on thicknessdependent size effect of concrete fracture[J].China Civil Engineering Journal,2017,50(5):5771.
[9]Amin A,Foster S J,Muttoni A.Derivation of theσw relationship for SFRC from prism bending tests[J].Structural Concrete,2015,16(1):93105.
[10]Li D S,Hai C,Ou J.Fracture behavior and damage evaluation of polyvinyl alcohol fiber concrete using acoustic emission technique[J].Materials&Design,2012,40:205211.
[11]Almusallam T,Ibrahim S M,AlSalloum Y,et al.Analytical and experimental investigations on the fracture behavior of hybrid fiber reinforced concrete[J].Cement&Concrete Composites,2016,74:201217.
[12]Dong W,Wu Z,Zhou X,et al.A comparative study on two stress intensity factorbased criteria for prediction of modeI crack propagation in concrete[J].Engineering Fracture Mechanics,2016,158:3958.
[13]Kazemi M T,Golsorkhtabar H,Beygi M H A,et al.Fracture properties of steel fiber reinforced high strength concrete using work of fracture and size effect methods[J].Construction&Building Materials,2017,142:482489.
[14]Tada H,Paris P C,Irwin G R.The Stress Analysis of Cracks Handbook[M].New York:Wiley,2000.
[15]陈江义,刘保元.纤维断裂损伤对复合材料板中导波频散特性的影响[J].吉林大学学报:工学版,2017,47(1):180184.Chen Jiangyi,Liu Baoyuan.Influence of fiber fracture damage on dispersion characteristic of guided wave in composite plate[J].Journal of Jilin University(Engineering and Technology Edition),2017,47(1):180184.
[16]Peterson P E.Crack Growth and Development of Fracture Zone in Plane Concrete and Similar Materials[M].Lund:Division of Building Materials,1981.
[17]CEB.CEBFIP model code 1990,Bulletin D information,No,213/214[S].
[18]Reinhardt H W,Xu S.Crack extension resistance based on the cohesive force in concrete[J].Engin eering Fracture Mechanics,1999,64(5):563587.
[19]Awinda K,Chen J,Barnett S J.Investigating geometrical size effect on the flexural strength of the ultra high performance fiber reinforced concrete using the cohesive crack model[J].Construction&Building Materials,2016,105:123131.
[20]赵艳华,聂玉强,徐世烺.混凝土断裂能的边界效应确定法[J].工程力学,2007,24(1):5661.Zhao Yanhua,Nie Yuqiang,Xu Shilang.Determination of boundary effect on fracture of concrete[J].Engineering Mechanics,2007,24(1):5661.