直升机结冰强度设计标准研究

介绍了影响直升机结冰特性的主要因素。针对国内直升机防/除冰系统设计标准中关于结冰强度划分没有明确界定的问题,通过引用适航规章要求并借鉴国外直升机结冰条件的设计标准,对直升机的结冰强度设计标准进行了分析和阐述,并提出了国内标准划分的建议以及在民用直升机防/除冰系统设计中的应用问题。

涂层弹性模量对结冰附着强度的影响

通过对铝合金及聚甲基丙烯酸甲酯(PMMA)基底涂覆不同弹性涂层进行表面改性,研究了涂层弹性对基底结冰附着强度的作用。用单组份室温硫化硅橡胶WH-705与BOPP进行对比。采用水杯制冰结冰强度测试试验法,以结冰切向附着力为指标,测量铝合金和PMMA两种材料(典型金属和非金属材料)基底表面未涂覆和涂覆弹性涂层后的结冰附着强度。试验结果表明,相对于标准基底,涂覆弹性涂层后基底表面结冰强度有显著变化。其中,涂覆硫化硅橡胶的铝表面结冰强度降低73.27%,PMMA表面降低14.85%。分析表明,涂层的弹性系数、分布规律等对结冰附着强度的影响显著。本文研究可为弹性涂层在防除冰方面的实际应用提供依据。

极地环境下船舶表面动态结冰黏附强度的实验研究

本文基于结冰风洞模拟极地环境,利用切向结冰黏附强度测试系统,通过拉伸实验研究了极地温度环境条件下冻结时间、结冰接触面积等因素对结冰黏附强度特性的影响规律。结果表明,动态结冰的切向结冰黏附强度随冻结时间延长而增强,相较于静态结冰,动态结冰可在更短时间内在界面处产生黏附强度;动态结冰的切向结冰黏附强度随环境温度降低而增强,但在到达临界区间后逐渐减弱;动态结冰的切向结冰黏附强度随结冰接触面积增加呈线性下降趋势。

Design of an Experimental Set‑up Concerning Interfacial Stress to Promote Measurement Accuracy of Adhesive Shear Strength Between Ice and Substrate

Accumulation of ice on airfoils and engines seriously endangers the safety of the fight.The accurate measurement of adhesion strength at the ice-substrate interface plays a vital role in the design of anti/de-icing systems.In this pursuit,the present study envisages the evaluation of the stress at the icesubstrate interface to guide the design of experimental set-ups and improve the measurement accuracy of shear strength using the finite element analysis(FEA)method.By considering such factors as the peeling stress,maximum von-mises stress and uniformity of stress,the height and radius of ice and the loading height are investigated.Based on the simulation results,appropriate parameters are selected for the experimental validation.Simulation results show that the peeling stress is decreased by reducing the loading height and increasing the height of ice.Higher ice,increasing loading height and smaller ice radius are found to be beneficial for the uniformity of stress.To avoid cracks or ice-breaking,it is imperative that the ice should be of a small radius and greater height.Parameters including the ice height of 25 mm,radius of 20 mm,and loading height of 9 mm are adopted in the experiment.The results of FEA and the experimental validation can significantly enhance the measurement accuracy of shear strength.

冻结过程冰黏附界面应力特性规律与分析

根据水/冰和铝合金的热膨胀系数差异及水结冰相变膨胀特性,观察水在铝合金表面的冻结过程,并利用应变测试方法间接获取结冰界面应力变化规律。结合水滴在铝合金表面冻结过程中的形态特征,分析了结冰过程冻结界面切向黏附力的形成规律及产生特点。试验发现,在冻结过程中,随着环境温度的降低,水与铝合金间的界面应变先逐渐降低;当铝合金表面附着水发生相变时,结冰黏附界面应变迅速增加;待铝合金表面附着水完全冻结后,黏附界面应变趋于稳定。分析表明,低温环境里铝合金表面附着水进入过冷状态,水及铝合金基底收缩,界面应变降低;当水开始相变,与基底表面接触区域附着水相变冻结,伴随冰黏附现象的产生,咬合并黏附于界面,相变膨胀力克服铝合金基底的收缩应力,界面应变迅速增加;待附着水完全冻结结冰及环境温度稳定时,冰与铝合金间形成稳定的黏附界面,结冰黏附界面应力趋于稳定。研究结冰黏附界面应力特性有助于阐释结冰黏附及其强度的形成规律,为工程领域开发或优化过程干预式防除冰技术提供理论支撑。