多尺度聚丙烯纤维混凝土力学性能试验和拉压损伤本构模型研究

发布时间：2018-08-27 19:15

【摘要】：多尺度聚丙烯纤维混凝土(Multi-scale polypropylene fiber concrete，简称MPFC)是指同种品质，几何形态不同的两种或两种以上的聚丙烯纤维混掺在混凝土中的新型复合建筑材料。聚丙烯细纤维对混凝土的早期塑性开裂有抑制作用，对后期硬化混凝土抗裂性改善较小。以往采用聚丙烯纤维与钢纤维混掺的方法阻止硬化混凝土的开裂，提高韧性。但钢纤维存在易锈蚀，价格高等缺点，而聚丙烯粗纤维是一种新型增强增韧材料，具有耐腐蚀性能好，价格低等优点。在环境较为恶劣的工程中可代替钢纤维使用。鉴于此，本研究采用室内试验、理论分析和数值模拟相结合的方法，对MPFC试件进行较为深入的力学性能研究，主要研究内容和成果如下： ①对MPFC进行抗裂性试验研究，结果表明聚丙烯细纤维在塑性态混凝土中的阻裂效应优于粗纤维，聚丙烯粗纤维在混凝土硬化阶段的抗裂效果优于细纤维；多尺度聚丙烯纤维在塑性态混凝土中的阻裂存在着正、负两种效应，在硬化阶段的抗裂效果与粗纤维相当。 ②通过单轴拉伸试验研究MPFC的抗拉性能，结果显示MPFC的抗拉峰值荷载较素混凝土有较小提高；MPFC在单向拉伸荷载作用下，应力-应变曲线下降段出现了低应力-应变硬化现象，MPFC抗拉韧性的改善幅度优于单掺聚丙烯纤维混凝土。 ③对MPFC进行单轴抗压试验研究，结果显示MPFC抗压峰值荷载有小幅提高；MPFC的抗压应力-应变曲线下降段比素混凝土平缓。MPFC峰值后的应力随应变的增加降低缓慢，应力一应变曲线下包面积较大，其峰值后的抗压韧性性能得到较好改善。 ④对MPFC进行四点弯曲试验研究，结果表明MPFC的抗弯强度有小幅提高；MPFC在弯曲荷载作用下，荷载-挠度曲线下降段出现非常明显的低荷载-变形硬化特性，曲线所包面积较大，峰值荷载后抗弯韧性的改善幅度远大于聚丙烯细纤维混凝土，同时也大于聚丙烯粗纤维混凝土。通过对比拉、弯性能指标建立MPFC拉弯对应关系，MPFC弯拉强度比值在2.15～2.80之间，抗弯韧性指数大于抗拉韧性指数，，但数据整体变化趋势相同，表明四点弯曲试验可以代替单轴拉伸试验，成为评价MPFC独特力学性能的简单实用试验方法。 ⑤根据试验结果，建立适合于描述MPFC抗拉、抗压特性的损伤本构模型，得到聚丙烯纤维混凝土损伤因子的曲线形状参数，为此类MPFC在工程中的应用提供理论基础。 ⑥基于有限差分理论，推导多尺度聚丙烯纤维混凝土拉压损伤本构模型的有限差分表达形式；结合FLAC3D软件良好的开发平台，利用VC++程序实现多尺度聚丙烯纤维混凝土损伤模型的二次开发，获得该模型的动态链接计算程序，并通过试验模拟和算例分析验证二次开发模型程序的正确性和合理性。 ⑦利用多尺度聚丙烯纤维混凝土损伤模型的二次开发计算程序，对多尺度聚丙烯纤维隧道衬砌进行数值分析。结果表明多尺度聚丙烯纤维改善了混凝土的抗变形能力，提高了混凝土的刚度。
[Abstract]:Multi scale polypropylene fiber concrete (MPFC) is a new type of composite building material mixed with two or more kinds of polypropylene fibers of the same quality and different geometry in concrete. In the past, polypropylene fiber was mixed with steel fiber to prevent the cracking of hardened concrete and improve its toughness. But steel fiber has the disadvantages of easy corrosion and high price, and polypropylene crude fiber is a new type of reinforced and toughened material with good corrosion resistance and low price. In view of this, the mechanical properties of MPFC specimens were studied by means of laboratory test, theoretical analysis and numerical simulation. The main research contents and results are as follows:
The results show that the crack resistance of PP fiber in plastic concrete is better than that of coarse fiber, and the crack resistance of PP fiber in hardening stage is better than that of fine fiber. The crack resistance is equivalent to that of coarse fiber.
(2) The tensile properties of MPFC were studied by uniaxial tensile test, and the results show that the peak tensile load of MPFC is slightly higher than that of plain concrete; the stress-strain curve of MPFC shows low stress-strain hardening phenomenon under uniaxial tensile load, and the improvement of MPFC tensile toughness is better than that of PP fiber reinforced concrete.
(3) The uniaxial compressive test of MPFC shows that the peak compressive load of MPFC increases slightly; the descending section of the compressive stress-strain curve of MPFC is gentler than that of plain concrete; the stress after the peak value of MPFC decreases slowly with the increase of strain, and the envelope area under the stress-strain curve is larger, and the compressive toughness after the peak value is better improved. Good.
Four-point bending test of MPFC shows that the bending strength of MPFC is improved slightly, and the load-deflection curve of MPFC shows obvious low-load-deformation hardening characteristics under bending load. The area covered by the curve is large, and the improvement of bending toughness after peak load is much greater than that after polypropylene fiber coagulation. The bending strength ratio of MPFC ranges from 2.15 to 2.80, and the flexural toughness index is greater than the tensile toughness index. But the overall change trend of the data is the same, indicating that the four-point bending test can replace the uniaxial tensile test and become the evaluation of MPFC. A simple and practical test method for unique mechanical properties.
_According to the test results, a damage constitutive model suitable for describing the tensile and compressive properties of MPFC is established, and the curve shape parameters of damage factors of polypropylene fiber reinforced concrete are obtained, which provides a theoretical basis for the application of MPFC in engineering.
_Based on the finite difference theory, the finite difference expression of the damage constitutive model of multi-scale polypropylene fiber reinforced concrete under tension and compression is deduced, and the secondary development of the damage model of multi-scale polypropylene fiber reinforced concrete is realized by using VC++ program on the good development platform of FLAC3D software, and the dynamic link calculation program of the model is obtained. Simulation and case analysis verify the correctness and rationality of the two development model program.
_Numerical analysis of multi-scale polypropylene fiber tunnel lining is carried out by using the secondary development calculation program of multi-scale polypropylene fiber concrete damage model. The results show that multi-scale polypropylene fiber improves the deformation resistance of concrete and the stiffness of concrete.
【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU528.572

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