On strain-rate and inertia effects of concrete samples under impact
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摘要: 结合混凝土试件的真三轴静载冲击实验结果,分别运用考虑应变率效应的Holmquist-Johnson-Cook (HJC)模型和考虑静水压效应的Drucker-Prager (DP)模型进行数值分析,以探讨研究混凝土试样应变率效应和惯性效应的方法。在探究混凝土的应变率效应和横向惯性效应的关系时,使用HJC模型的数值模拟结果来拟合DP准则的各个参数。结果表明:随着应变率的升高,混凝土的强度会提高,并且这种强度的提高,也有一部分原因是第一应力不变量I1的增大所导致的。因此,混凝土试件的应变率效应和横向惯性约束具有较强的耦合作用。理论和数值分析了冲击下试样内部的横向应力分布特征与应变率、静水压和试样尺寸的关系,结果发现:试样内部横向应力的幅值随着应变率、静水压的升高而增大,但随着试样尺寸的增大而减小。为了探讨横向惯性带来的强度提升效果,提出了一个有关冲击方向最大应力σx和等效应力σe的参数ξ,且ξ=(σx−σe)/σx。此参数具有尺寸效应、应变率效应和静水压效应,但是此参数与应力三轴度的关系表现出应变率无关特性,可为应变率效应的研究提供新的思路。Abstract: Based on the dynamic experimental results of concrete specimens under true triaxial confinement, the Holmquist-Johnson-Cook (HJC) model considering the strain rate effect and the Drucker-Prager (DP) model considering the hydrostatic pressure effect were employed for numerical analysis to explore the methods for studying the strain rate effects and inertia effects. In order to explore the relationship between the strain rate effect and the lateral inertia effect of concrete, the numerical simulation results of the HJC model were used to fit the parameters of the DP criterion, and the values of the parameters α and k at four strain rates were obtained. The relationship between the DP criterion parameters and the strain rate and hydrostatic pressure was comprehensively analyzed. The results of numerical analysis show that with the increase of strain rate, the strength of concrete increases, and this strength increase is partly due to the increase of the first stress invariant I1. It can be concluded that the strain rate and lateral inertia constraint of concrete specimens have a strong coupling effect. The relationship between the distribution characteristics of the transverse stress and the strain rate, hydrostatic pressure and specimen size under impact are analyzed theoretically and numerically. The results show that the amplitude of the transverse stress increases with the strain rate and hydrostatic pressure, but decreases with the sample size. In order to investigate the effect of lateral inertia on the strength improvement, a parameter ξ related to the maximum stress σx and the equivalent stress σe in the impact direction, defined as ξ=(σx−σe)/σx, was proposed. The relationship between the strain rate, hydrostatic pressure, specimen size and the parameter ξ was analyzed by the HJC model. It is found that this parameter has evident size effect, strain rate effect and hydrostatic pressure effect. However, the relationship between the parameter ξ and the stress triaxiality shows a strain rate independent characteristic. It can provide a new way for the investigation of strain rate effect.
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Key words:
- impact dynamics /
- concrete /
- strain rate effect /
- inertia effect /
- stress triaxiality
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ρ0/(kg·m−3) G/GPa A B C N $ f' $/MPa 2 440 14.875 0.69 1.50 0.007 0.61 48 T/MPa $ {\dot \varepsilon _0}/{{\text{s}}^{ - 1}} $ εf,min Smax pc/MPa μc pl/MPa 4 1 0.01 7 594.3 0.03 800 μl D1 D2 K1 K2 K3 0.1 0.04 1 85 −171 208 表 2 混凝土DP模型参数
Table 2. Parameters of the DP model for cement mortar
ρ0/(kg·m−3) E/GPa νcon ϕ/(o) k′ ψ/(o) 2440 35.7 0.3 30 0.78 30 -
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