C75混凝土动态劈裂行为试验与数值模拟分析

Experimental and numerical analysis of dynamic splitting behavior of C75 concrete

摘要:

为研究C75混凝土动态抗拉强度特性和应变率效应,采用大直径霍普金森压杆,对其开展动态劈裂试验,并对试样中应力平衡进行检验,同时,基于ANSYS/LS-DYNA软件数值模拟混凝土的动态劈裂破坏过程.采用MATLAB将劈裂强度公式中的圆盘内部应力等值线进行可视化,基于修正的Griffith准则对巴西圆盘中心起裂现象进行理论分析.结果表明:在10⁰~10¹/s应变率范围内,混凝土劈裂强度与应变率对数基本呈现线性增长关系；在较低弹速下试件表现为沿径向对称破裂,随着弹速的增加,试样两端出现明显的三角形破碎区域,且靠近入射端破碎较严重；二维受力状态下,巴西圆盘试样的最大与最小主应力之比(σ₁/σ₃)等值线近似呈封闭的菱形,其比值在圆盘的中心处达到最大值-3.0；考虑应变率效应的Cowper-Symonds黏塑性本构能够较好地表征C75混凝土的动力学行为,其模拟的试样破坏过程与采用高速摄影技术观测到的结果吻合度较高；C75混凝土的抗拉特性明显优于同样水灰比下的C35混凝土,但其应变率敏感性要比C30土工聚合物混凝土低.

Abstract:

Based on the assumptions of uniformity and one-dimensional stress wave theory, the splitting tests of C75 concrete were conducted using a large-diameter Hopkinson pressure bar to study its dynamic tensile strength property and strain-rate effect, and the dynamic stress equilibrium was carefully checked. At the same time, the stress contours were visualized with MATLAB, and the theoretical basis for the center cracking of Brazil disc was provided based on the modified Griffith theory. The failure processes of specimens in the dynamic splitting were simulated using LS-DYNA software. The results show that the dynamic tensile strength and the logarithmic strain rate were almost linearly dependent when the strain rate ranged from 10⁰ to 10¹/s. The specimen broke diametrically at low projectile velocity. Triangular crushed zones appeared at the two ends of the specimen with the increase of projectile velocity, and they became more serious in incident end. Under the 2D condition, the contours of the ratio of the maximum to minimum principal stress of the Brazil disc specimen (σ₁/σ₃) resembled a closed diamond, and the ratio of compressive strength to tensile strength at the center of the disc specimen had a maximum value of -3.0. The dynamic behaviors of the C75 concrete can be well described using the viscoplastic Cowper-Symonds constitutive mode considering strain rate effect. The simulation of the fracture process showed good agreement with the results observed by using the high-speed photography. The tensile strength of the C75 concrete is much better than that of the C35 concrete with the same water-cement ratio, but its strain rate sensitivity is lower than that of the C30 geopolymer concrete.