Abstract In-flight ice accretion on fixed-wing aircraft and rotorcraft can be catastrophic if not mitigated. Most modern ice protection systems are active systems, which require electrical or mechanical power to remove accreted ice, thereby increasing weight, cost, and complexity. Scientists and engineers now seek passive, erosion-resistant materials and coatings with low ice adhesion strength. Ideally, such materials, when applied to vulnerable components of an aircraft, would cause any ice to shed off the surface under normal aerodynamic loading. To aid in the development of low-ice-adhesion-strength materials, the growth and structural behavior of impact ice in a wide range of atmospheric conditions must be characterized. The structural behavior of ice has been examined under pure shear, tension, compression, and mixed-mode loading. However, one important loading consideration that has not been widely investigated on atmospheric ice is strain rate. Knowledge of the relationship between impact ice adhesion strength and strain rate is important because it can be used to design future ice protection systems, and it may dictate the appropriate course of action for a pilot flying through icing conditions—for instance, whether a helicopter pilot should increase the rotor speed rapidly or slowly to induce shedding of the ice. NASA Glenn Research Center funded the design and construction of a new centrifuge-style ice adhesion test rig (“AJ2”) by the Penn State AERTS lab. The ice is accreted dynamically by spinning flat metal test coupons at high speed inside a simulated icing cloud environment. The design and analysis of the AJ2 rig is described in detail in this paper. Experiments were performed using AJ2 to investigate how the adhesion strength of impact ice related to the strain rate applied to it. Stainless steel test coupons of known surface roughness were tested in a range of environmental temperatures. The strain rates applied to the ice ranged between 5E−8 and 5E-5 s−1. It was discovered that a similar power function exists between strain rate and adhesion strength as found in the freezer-ice studies described in the literature. Despite scatter in the data, regression analysis determined the relationship between strain rate, temperature, and adhesion strength to be statistically significant. The power “1/n” for a coupon roughness of 64 nm (Sa) was greater than that of the 80-nm coupon; this was the case for both tested temperatures. However, for the relatively smooth surfaces tested, regression analysis suggested that the surface roughness had negligible effect on adhesion strength. Lower temperatures caused a higher power “1/n” and coefficient “c” in the power function. The variation of the coefficient with temperature is consistent with Glen's power law for the creep of glacier ice in compression. However, Glen did not observe a variation of the power with temperature. The value of “n” in the current study ranged from 2.6 for the smoothest sample at the coldest temperature, to 8.8 for the roughest sample at the warmest temperature. In most cases of the current study, “n” was within the range of previously-reported values in literature (1.5 to 6).

中文翻译：

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应变率变化对冲击冰剪切粘附强度的影响

摘要 如果不加以缓解，固定翼飞机和旋翼飞机上的飞行积冰可能是灾难性的。大多数现代防冰系统都是主动系统，需要电力或机械动力来去除积冰，从而增加了重量、成本和复杂性。科学家和工程师现在正在寻找具有低冰附着强度的被动、抗侵蚀材料和涂层。理想情况下，这种材料在应用于飞机的易损部件时会导致任何冰在正常空气动力载荷下从表面脱落。为了帮助开发低冰粘附强度材料，必须表征撞击冰在各种大气条件下的生长和结构行为。冰的结构行为已经在纯剪切、拉伸、压缩和混合模式载荷下进行了检查。然而，在大气冰上尚未广泛研究的一项重要载荷考虑因素是应变率。了解撞击冰附着强度和应变率之间的关系很重要，因为它可用于设计未来的防冰系统，并且它可能决定飞行员在结冰条件下飞行的适当行动方案——例如，直升机飞行员是否应快速或缓慢增加转子速度以引起冰脱落。美国宇航局格伦研究中心资助了宾夕法尼亚州立大学 AERTS 实验室设计和建造的新型离心式冰附着试验台（“AJ2”）。通过在模拟的结冰云环境中高速旋转扁平金属测试试样，冰会动态地积聚。本文详细介绍了 AJ2 钻机的设计和分析。使用 AJ2 进行实验以研究冲击冰的粘附强度与施加到它的应变率之间的关系。已知表面粗糙度的不锈钢试样在一系列环境温度下进行测试。应用于冰的应变率介于 5E-8 和 5E-5 s-1 之间。发现在应变率和粘附强度之间存在类似的幂函数，如文献中描述的冷冻-冰研究中发现的那样。尽管数据分散，回归分析确定应变率、温度和粘附强度之间的关系在统计上是显着的。64 nm (Sa) 试样粗糙度的功率“1/n”大于 80 nm 试样的功率“1/n”；两种测试温度都是这种情况。然而，对于测试的相对光滑的表面，回归分析表明表面粗糙度对粘附强度的影响可以忽略不计。较低的温度会导致功率函数中的功率“1/n”和系数“c”更高。系数随温度的变化与冰川冰压缩蠕变的格伦幂律一致。然而，格伦没有观察到功率随温度的变化。当前研究中的“n”值范围从最冷温度下最光滑样品的 2.6 到最热温度下最粗糙样品的 8.8。在当前研究的大多数情况下，“n”在文献中先前报告的值范围内（1.5 到 6）。系数随温度的变化与冰川冰压缩蠕变的格伦幂律一致。然而，格伦没有观察到功率随温度的变化。当前研究中的“n”值范围从最冷温度下最光滑样品的 2.6 到最热温度下最粗糙样品的 8.8。在当前研究的大多数情况下，“n”在文献中先前报告的值范围内（1.5 到 6）。系数随温度的变化与冰川冰压缩蠕变的格伦幂律一致。然而，格伦没有观察到功率随温度的变化。当前研究中的“n”值范围从最冷温度下最光滑样品的 2.6 到最热温度下最粗糙样品的 8.8。在当前研究的大多数情况下，“n”在文献中先前报告的值范围内（1.5 到 6）。