Numerical simulation of the tensile strain hardening and multiple cracking behavior of ECC based on beam theory
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摘要: 基于描述超高延性水泥基复合材料(Engineered cementitious composites, ECC)中单根纤维拔出行为的等效弹性地基梁模型,通过纤维-基体系统切面的平面应变有限元分析,提出了等效连续梁弹簧约束刚度的显式计算方法,建立了改进的等效弹性地基梁模型,并将模型应用于ECC单轴拉伸应变硬化与多缝开裂行为的数值模拟分析。分别基于摩擦滑轮模型和等效弹性地基梁模型计算ECC应力-应变关系曲线,并与试验结果进行对比。结果表明:对于聚乙烯(PE)/ECC,大部分情况下基于等效地基梁模型的计算结果与试验结果相比于聚乙烯醇(PVA)/ECC更加吻合。表明本文提出的改进的等效地基梁模型能够很好地描述抗弯刚度无法忽略的纤维的拔出行为,对于此类ECC材料和结构的受力机理和设计理论具有一定的参考价值。Abstract: Based on the equivalent elastic foundation beam model describing the single fiber pullout behavior in engineered cementitious composites (ECC), an improved model was established by plane strain finite element analysis of the fiber-matrix system section, proposing an explicit calculation method for the spring restrained stiffness of the equivalent continuous beams. The model was applied to the numerical simulation analysis of uniaxial tensile strain hardening and multi-joint cracking behavior of ECC. The stress-strain relationship curves of ECC were calculated based on the frictional pulley model and the equivalent elastic foundation beam model, respectively, and compared with the experimental results. The results show that for polyethylene fiber (PE)-ECC, the calculation results based on the equivalent foundation beam model are in better agreement with the experimental results. It indicates that the improved equivalent foundation beam model proposed in this paper can well describe the pull-out behavior of fibers whose flexural stiffness cannot be neglected, and is of reference value for the force mechanism and design theory of such ECC materials and structures.
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图 5 弹性地基平面应变模型
Figure 5. Plane strain model of elastic foundation
X—Location from the fracture plane; h(x): distance from the fiber bottom to the fracture plane at x; γ—Inclination angle; H—Distance from the fiber center to the top edge; r—Radius of the fiber; B—Distance from the fiber center to the side edge
表 1 摩擦滑轮模型和等效弹性地基梁模型主要参数的选取
Table 1. Selection of the main parameters in the frictional pulley model and equivalent foundation beam model
Fiber radius
r/μmFiber elastic modulus
Ef/GPaMatrix elastic modulus
Em/GPaFrictional stress
τ/MPaFiber Poisson's ratio
νfMatrix Poisson's ratio
νmFiber embedded length
Le/mm10 9.75 19.5 1.0 0.25 0.25 1.5 20 39 1.5 3 30 108 2.0 6 表 2 ECC单轴拉伸数值模拟平均结果
Table 2. average results of numerical simulation of ECC uniaxial tension
Fiber
typeModel type Initial cracking
stress/MPaInitial cracking
strain/%Ultimate tensile
strength/MPaUltimate tensile
strain/%Number of
cracksPVA/ECC Frictional pulley model 3.10 0.08 4.64 3.59 36 Equivalent foundation
beam model3.05 0.09 5.61 7.44 46 PE/ECC Frictional pulley model 5.25 0.03 8.96 2.91 45 Equivalent foundation
beam model5.30 0.03 9.62 5.49 46 -
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