数字梯度敏感方法及其在航空透明件断裂力学中的应用

Digital Gradient Sensing(DGS)Method and its Application in Fracture Mechanics of Transparent Parts Used in Aviation

本文将数字梯度敏感方法用于航空透明件断裂力学问题研究。首先,基于透明材料的弹性-光学效应,建立了透明件应力状态与光线穿过透明件后的偏转角之间的关系。在平面应力假设下,利用最小二乘拟合建立了I型裂纹尖端应力强度因子与光学偏转角的关系。其次,通过数字梯度敏感方法搭建非接触光学测试平台,开展了带单边裂纹的航空有机玻璃试件三点弯曲实验,应用数字梯度敏感方法提取了I型裂纹尖端应力强度因子。最后,通过选择不同计算子区域和步长大小,分析了数字梯度敏感方法中的子区域和步长选择对计算结果的影响。研究结果表明,数字梯度敏感方法实验所得应力强度因子与经验公式计算所得结果偏差小于10%,通过增加最小二乘拟合项数以及合理的子区域和步长选择可以减小数字梯度敏感方法计算应力强度因子误差。

Fracture mechanics of transparent parts used in aviation was studied by using digital gradient sensing method. First, relation between the stress state of transparent material and the deflection angle of light passing through transparent material was established based on elasto-optic effect of transparent materials. In the plane stress assumption, relation between the type I crack-tip stress intensity factor and the optical deflection angle was also established by using least squares fitting. Then, a non-contact optical test platform was constructed through digital gradient sensitive method, and three point bending test was carried out for PMMA specimen with unilateral crack. The stress intensity factor of type I crack-tip was extracted using digital gradient sensing method. Finally, by selecting different calculation sub-region and step size, the effect of sub-region and step size in digital gradient sensing method on the calculated stress intensity factor was analyzed. Results show that the error between the type I stress intensity factor obtained from digital gradient sensing experiment and the calculated results using empirical formula is less than 10 %. The accuracy of digital gradient sensing experimental results can be further improved by increasing the terms of least square fitting and selecting reasonable sub-region and step size.