质子交换膜在湿-热耦合作用下的双轴拉伸力学性能研究

Proton exchange membrane (PEM) fuel cell has been widely used in the field of electrochemistry and energy, owing to its advantages of high energy conversion efficiency, high power density, low temperature start-up and zero emission. As the core component of PEM fuel cell, PEM is exposed to hydrothermal environment and subjected to biaxial tensile loads during normal operation. In this proposal, the mechanical response of PEM, including biaxial tensile property, biaxial stress-relaxation property, biaxial creep-recovery property and biaxial stress-cycling property, will be investigated under coupled hydrothermal and mechanical loads using an in-plane biaxial tensile testing system, and the mechanism of interaction between the hydrothermal and mechanical factors will be revealed. Then a visco-elastic-plastic constitutive model will be established to describe the mechanical behavior of PEM under coupled hydrothermal and mechanical loads by incorporating the hydrothermal and mechanical factors. Investigation of the mechanical properties of PEM under biaxial tensile loading in hydrothermal environment helps to understand the mechanical failure mechanism of PEM under real operating conditions, thus providing theoretic basis for its durability assessment.

质子交换膜燃料电池具有高能量转换效率、高功率密度、低温启动以及零排放等优点，在电化学和能源领域得到广泛的应用。作为质子交换膜燃料电池的核心部件，质子交换膜在实际运行工况下处于湿热环境中，并受到双轴拉伸作用。本项目将利用面内双轴拉伸试验系统，研究质子交换膜在湿-热-力耦合作用下的力学响应，包括双轴拉伸性能、双轴应力松弛性能、双轴蠕变-恢复性能和双轴应力循环性能，阐述湿-热-力各因素间相互作用机理，进而建立考虑湿-热-力各因素在内的黏弹塑性本构模型，描述质子交换膜在各因素耦合作用下的力学行为。对质子交换膜在湿热环境中双轴拉伸作用下力学性能的研究将有助于更好的理解其实际操作工况下的机械失效机理，从而为其耐久性评估提供理论依据。

作为质子交换膜燃料电池的核心部件，质子交换膜在实际运行工况下处于湿热环境中，并受到双轴拉伸作用。因此，本项目研究了质子交换膜在湿-热-力耦合作用下的面内双轴力学响应，包括双轴蠕变、双轴应力循环和双轴疲劳裂纹扩展性能性能等，并在此基础上建立起黏弹塑性本构模型。结果发现，双轴应力状态抑制循环应变的累积，且等双轴应力状态带来的约束作用最强。此外，该约束作用在更高湿度环境下表现的更为明显。对于蠕变行为，一点双轴应力将会显著降低蠕变应变。通过构建蠕变柔量主曲线，发现尽管双轴应力使得蠕变达到平衡的时间显著增加，但所需的激活能却没发生改变，表明有相同的变形机制。裂纹在双轴应力下发生弯曲和分叉现象，与燃料电池应力加速试验中观测到的现象一致，表明双轴应力是膜材料破坏的一个驱动力。基于上述现象，提出了基于Schapery模型和OW模型的循环粘弹塑性本构模型，能够很好地描述材料棘轮应变随循环圈数的累积情况。对质子交换膜在湿热环境中双轴拉伸作用下力学性能的研究有助于更好的理解其实际操作工况下的机械失效机理，从而为其耐久性评估提供理论依据。