Dynamic Behaviors of Polyurea Elastomer: Experimental Characterization, Microscopic Mechanisms and Constitutive Modeling
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摘要:
聚脲弹性体在冲击防护领域有广阔的应用前景，然而，目前对于聚脲在高压冲击、层裂等情况下的变形失效物理机制仍不明晰，尚缺乏有效描述聚脲在多种应变率及应力状态下动态变形和失效的本构及损伤模型. 针对这些挑战性问题，该文结合实验表征、分子动力学仿真以及宏观力学建模，对聚脲弹性体在不同应变率、冲击压力及应力状态下的变形失效行为进行了系统研究. 通过建立聚脲全原子和两种粗粒化模型及微结构演化分析，揭示了聚脲在高应变率拉伸、高压冲击等载荷下的变形微观物理机制，以及高应力三轴度下的动态失效物理机制. 建立了考虑强冲击下应变率-温度-压力耦合效应的聚脲弹性体本构模型，以及包括孔洞形核准则、流动法则的多种变形模式统一描述的宏观损伤模型. 经验证，所建立的宏观力学模型能够正确描述聚脲在冲击载荷下的动态变形失效行为. 该工作可为后续聚脲弹性体的优化设计及冲击防护应用提供指导.
Abstract:The application of polyurea elastomer to impact protection has broad prospects. However, the physical mechanisms of dynamic deformation and failure of the polyurea under high-pressure impact, delamination, and other conditions are still unclear. Besides, effective constitutive and damage models to describe the dynamic behaviors of polyurea under various strain rates and stress states are still scarce. In response to these challenging issues, the dynamic behaviors of polyurea elastomers under different strain rates, impact pressures, and stress states were systematically studied through experimental characterization, molecular dynamics simulation, and macroscopic mechanical modeling. Full atomic and 2 coarse-grained models for polyurea were established, its microstructure evolution was analyzed, and the microscopic physical mechanisms of deformation and failure of polyurea under high-strain-rate tension, high-pressure impact and high stress triaxiality loading, were revealed. A constitutive model for polyurea elastomers was established in view of the coupling effects of strain rates, temperature and pressure under strong impact. A macroscopic damage model uniformly describing multiple deformation modes was built, including void nucleation criteria and void flow rules. Through verification, the established macroscopic mechanical models can accurately describe the dynamic behaviors of polyurea under impact loading. This work provides a guidance for the optimization design and impact protection application of polyurea elastomers in the future.
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Key words:
- polyurea elastomer /
- dynamic behavior /
- void damage /
- constitutive model /
- molecular dynamics
edited-byedited-by1) （我刊编委庄茁、柳占立来稿） -
图 2 聚脲合成实验装置与PUR1000聚脲样品
Figure 2. The experimental setup for polyurea synthesis and the samples of polyurea PUR1000
图 3 DMA测定的PUR1000与PUR650的动态模量
Figure 3. Dynamic moduli of PUR1000 and PUR650 measured by DMA
图 4 PUR1000不同大变形实验的应力-应变曲线
Figure 4. Stress-strain curves of PUR1000 obtained from different large-deformation experiments
图 7 MD模拟及AFM获得的PUR1000微相分离结构比较
Figure 7. Comparison of the microphase-separation structure of PUR1000 obtained by the MD modeling and AFM observation
图 10 全原子模型模拟PUR1000单轴拉伸时的各部分能量变化
Figure 10. Energy variations of PUR1000 under uniaxial tension simulated by the all atom model
图 11 CGMD1模型模拟PUR1000受单轴拉伸的快照
Figure 11. Snapshots of PUR1000 under uniaxial tension obtained by the CGMD1 modeling
图 12 不同冲击速度下PUR1000的分子键演化
Figure 12. Evolutions of molecular bonds of PUR1000 under different impact velocities
图 13 不同冲击速度下PUR1000 f或密度随时间演化
Figure 13. Evolutions of f or densities of PUR1000 over time under different impact velocities
图 14 层裂强度与局部温度关系分析
Figure 14. Analysis of the relationship between spallation strength and local temperature
图 15 $\dot{e}_x=10^8$等三轴拉下的PUR1000动态损伤过程及最大主应变分布
Figure 15. Dynamic damage process and maximum principal strain distribution of PUR1000 under $\dot{e}_x=10^8$ equal triaxial tension
图 16 $\dot{e}_x=10^8$等三轴拉下PUR1000软粒子体积分布
Figure 16. Volume distributions of soft particles of PUR1000 under $\dot{e}_x=10^8$ equal triaxial tension
图 17 单轴应变拉伸下整体应变ex=100%时的快照
Figure 17. The microscopic snapshot at the moment of ex=100% under uniaxial tension
图 18 聚脲的黏塑性本构模型示意图
Figure 18. Sketch of the viscoplastic constitutive model for polyurea
图 19 本构模型模拟结果与实验结果比较
Figure 19. Comparison of simulation results between constitutive models and experimental results
图 20 高压冲击下温度效应分析
Figure 20. Analysis of temperature effects under high-pressure impact
图 21 $\dot{e}_{x}=10^{8}$单轴应变拉伸下，$f, \theta_{\mathrm{m}}$和$\sigma_{x x}$随$e_{x}$的变化
Figure 21. Variations of $f, \theta_{\mathrm{m}}$ and $\sigma_{x x}$ with $e_{x}$ under uniaxial－strain tension with $\dot{e}_{x}=10^{8}$
图 22 考虑动态损伤失效的聚脲本构模型示意图
Figure 22. Sketch of the constitutive model for polyurea considering dynamic damage and failure
图 24 不同三轴度算例中不同应变数据的$\dot{\theta}_{v}-\bar{S}$图
Figure 24. The $\dot{\theta}_{v}-\bar{S}$ diagram of different strain states in the examples with different triaxiality
图 25 不同三轴度算例中的临界失效点$\dot{e}_{\max }-e_{\max }$图或$\dot{\theta}-\theta$图
Figure 25. The $\dot{e}_{\text {max }}-e_{\text {max }}$ or $\dot{\theta}-\theta$ diagram of critical failure points in the examples with different triaxiality
表 1 实验和MD模拟获得的PUR1000性能
Table 1. The physical parameters of PUR1000 obtained by experiments and the MD modeling
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表 2 各变形模式的载荷条件与应力三轴度
Table 2. Loading conditions and stress triaxiality for different deformation modes
deformation mode x y z xz triaxiality uniaxial stress $\dot{e}_x$ σyy=0 σzz=0 exz=0 0.333 plane stress $\dot{e}_x$ $\dot{e}_y=\dot{e}_x$ σzz=0 exz=0 0.667 tensile-shear $\dot{e}_x$ ey=0 ez=0 $\dot{e}_{x z}=a \dot{e}_x(a=2, 3, 4)$ ~1.6~2.3 uniaxial strain $\dot{e}_x$ ey =0 ez=0 exz=0 ~4.33 plane strain $\dot{e}_x$ $\dot{e}_y=\dot{e}_x$ ez=0 exz=0 ~8.76 equal triaxial tension $\dot{e}_x$ $\dot{e}_y=\dot{e}_x$ $\dot{e}_z=\dot{e}_x$ exz=0 ∞
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表 3 PUR1000失效模型材料参数
Table 3. Material parameters of the failure model the PUR1000
A/MPa C10/MPa m ξ0/s-1 Svoid/MPa λc 1 200 30 0.15 5×105 320 0.3
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