聚脲是一种由异氰酸酯组分和氨基组分反应生成的新型弹性体高聚物。由于聚脲具有断裂伸长率高、应变率强化、高耗能等一系列优异的力学性能，其在工程领域尤其是防爆抗冲击领域显示出广阔的应用前景。然而，聚脲优异的力学性能伴随着复杂的力学行为，且其服役环境往往涉及到高应变率、大变形、高压等极端条件；另一方面，聚脲微观上存在从分子链网络到微相分离等复杂的多级结构，而且聚脲的微观结构随原料组分、合成方法以及固化条件等的不同而多变。因此，聚脲材料的复杂性一方面赋予了其更多的潜在应用价值，但同时也为认识和预测聚脲变形行为带来了巨大挑战。防爆抗冲击目前是聚脲材料最具应用价值的领域，虽然研究者们已经提出了多种聚脲抗冲击机理，但还未形成定论。因此，本文对典型聚脲材料开展了一系列静动态力学性能实验研究和微相分离结构实验研究，建立了聚脲非线性粘弹性本构模型，并通过有限元模拟探究了聚脲微观不均匀性对其抗冲击性能的影响。本论文开展的主要研究内容和结果如下：

（1）通过动态力学分析和静动态单轴压缩实验系统研究了聚脲材料小变形线性粘弹性力学性能和大变形非线性粘弹性力学性能。实验结果表明聚脲小变形线性粘弹性范围内具有温度、频率敏感性，且满足时温等效原理，通过时温叠加可以将动态模量频率范围从10⁰~10¹ Hz扩展到10⁰~10¹¹ Hz，相应的时温转换因子满足WLF方程；聚脲大变形非线性粘弹性具有温度、应变率敏感性，随温度降低或应变率增大，材料初始模量、流动应力增大，且温度敏感性随温度降低而增强。

（2）借助小角X射线散射实验，对聚脲微相分离结构进行了观测，结果表明聚脲为稠密准两相体系，硬畴长周期为7~8 nm，硬畴与软基间存在界面相，且厚度参数为0.41 nm；进一步对比不同加载情况的聚脲试样表明，压缩加载能增大聚脲硬畴长周期，且具有率相关性，但对中间相厚度几乎无影响；对热处理试样的观察发现热处理显著增大了聚脲硬畴长周期，且会减小界面厚度；最后，对比了不同热处理时间聚脲试样的力学性能，结果表明随热处理时间加长，聚脲硬畴长大粗化，增大了硬畴长周期，降低整体交联密度，导致聚脲橡胶平台储能模量减小，静动态压缩应力-应变曲线也出现了应力水平降低的情况，但减小幅度相当。

（3）针对聚脲应力-应变响应非线性、温度和应变率敏感的特点，从聚脲微观多级运动的角度出发，借助自由体积概念建立了聚脲非线性粘弹性本构模型。考虑聚脲应力响应由粘弹性、熵弹性和能弹性组成，分别对应聚脲微观上的链段运动、分子链拉伸和共价键拉伸。提出了剪切变形诱导自由体积的新机理，并给出了相应的自由体积分数演化方程，修正了经典自由体积非线性粘弹性本构模型无法描述剪切变形主导的非线性粘弹性行为。模型预测与静动态实验数据和文献中的数据均具有很好的吻合度。

（4）借助有限元模拟，从松弛时间分布不均匀性和自由体积分布不均匀性两个角度，分别通过Taylor冲击和代表体积元单轴压缩研究了聚脲微观不均匀性对其抗冲击变形耗能的影响。模拟结果表明，随松弛时间离散度增大，聚脲冲击耗能比先增后减；随自由体积分数离散度增大，聚脲平均应力单调增大，小应变加卸载过程耗能比先增后减，大应变加卸载过程耗能比单调增大；当自由体积分数离散度较小时，应力和耗能比均与自由体积具体分布形式无关，而自由体积分数离散度较大时，自由体积均匀分布情况下的应力和耗能比均高于高斯分布情况。

Polyurea is a new type of elastomeric polymer, which is formed through the reaction of isocyanate components with amine components. Due to its excellent mechanical property, such as high elongation, high strain rate strengthening and high dissipation, polyurea shows a broad application prospect in the engineering fields, especially the blast mitigation and anti-impact field. However, the excellent mechanical properties are accompanied by complex mechanical behavior. Besides, the service environment of polyurea usually involves extreme conditions, such as high strain rate, large deformation, high pressure and so on. From the perspective of microstructure, polyurea has a complex multi-scale structure ranging from molecular chain network to microphase-segregated structure. In addition, the microstructure of polyurea varies with the composition, synthesis method and curing condition. Thus, the complexity of polyurea not only gives it more potential application value, but also brings great challenges to understanding and predicting the deformation behavior of polyurea. Currently, shock mitigation and anti-impact are the most valuable application field of polyurea. Although researchers have proposed a variety of shock mitigation and anti-impact mechanisms of polyurea, no consistent conclusion has been reached. Therefore, a series of experimental studies on the static and dynamic mechanical properties and microphase-segregated structure were carried out on a typical polyurea material in this dissertation. A nonlinear viscoelastic constitutive model of polyurea was established. In addition, the influence of micro-heterogeneity on anti-impact property of polyurea was investigated by finite element simulation. The main contents and results are as follows:

(1) The linear viscoelastic mechanical properties under small deformation and nonlinear viscoelastic mechanical properties under large deformation of polyurea were studied through Dynamic Mechanical Analysis, quasi-static and dynamic uniaxial compression experiments respectively. The experimental results show that polyurea is temperature- and frequency- sensitive in the linear viscoelastic regime under small deformation, and the time-temperature equivalent principle applies to polyurea. The frequency range of dynamic modulus is extended from 10⁰~10¹ Hz to 10⁰~10¹¹ Hz by time-temperature superposition, and the corresponding shift factor satisfies the WLF equation. In the nonlinear viscoelastic regime under large deformation, polyurea is sensitive to temperature and strain rate. With the decrease of temperature or the increase of strain rate, the initial modulus and flow stress of polyurea increase. In addition, the temperature sensitivity increases with the decrease of temperature.

(2) The microphase-segregated structure of polyurea was observed through Small Angle X-ray Scattering experiments. The results show that polyurea is a quasi-two-phase system with high density of hard domain. The mean interdomain spacing of polyurea is about 7~8 nm and there is an interphase between the hard domain and the soft matrix with the thickness parameter being 0.41 nm. The comparison of polyurea samples under different loading conditions shows that compressive loading can increase the mean interdomain spacing of polyurea, which is rate dependent, but has little effect on the thickness of interphase. It is found that annealing increases the mean interdomain spacing of polyurea dramatically and decreases the thickness of the interphase. Finally, the mechanical properties of polyurea samples with different annealing times were compared. The results show that with the increase of annealing time, the hard domain of polyurea grow coarser, which increases the mean interdomain spacing and reduces the overall crosslinking density. As a result, the rubbery plateau of storage modulus of the polyurea decreases. The quasi-static and dynamic compressive stress-strain curves also show a decrease in stress level, but with nearly the same amplitude.

(3) To describe the nonlinear stress-strain response of polyurea and its sensitivity to temperature and strain rate, a free volume based nonlinear viscoelastic constitutive model of polyurea was established from the perspective of multi-scale micro-process of polymer. The stress response of polyurea is considered to be composed of viscoelasticity, entropic elasticity and energetic elasticity, which correspond to the interaction of chain segments, molecular chain stretching and covalent bond stretching of polyurea. A new mechanism of shear-induced increase of free volume is proposed, and the corresponding evolution equation of fractional free volume is given, which makes the model be able to describe the nonlinear viscoelastic behavior under shear-dominated loading case. The model prediction is in excellent agreement with the quasi-static and dynamic experimental data and the data in the literatures.

(4) With the help of finite element simulation, the influence of micro-heterogeneity on anti-impact performance of polyurea was studied through Taylor impact simulation and uniaxial compression of the representative volume element respectively from the perspectives of relaxation time distribution heterogeneity and free volume distribution heterogeneity. The simulation results show that the energy dissipation ratio of polyurea increases first and then decreases with the increase of relaxation time dispersion. As the fractional free volume dispersion increases, the average stress of polyurea monotonically increases, the energy dissipation ratio under small strain first increases and then decreases, and the energy dissipation ratio under large strain monotonically increases. As long as the fractional free volume dispersion is small, the stress and energy dissipation ratio are independent of the specific distribution form of free volume. Whereas the stress and energy dissipation ratio in the case of uniform distribution of free volume are higher than those in the case of Gaussian distribution when the fractional free volume dispersion is large enough.