基于数字图像相关方法微裂纹萌生试验研究

Experimental Investigation of Micro Crack InitiationBased on Digital Image Correlation Method

关键词:  数字图像相关方法  原位系统  散斑制备  微裂纹  裂纹萌生

Key words:  Digital image correlation method  In-situ system  Speckle preparation  Micro crack  Crack initiation

摘要:

为了进一步研究疲劳裂纹在萌生阶段的特点，本文结合数字图像相关方法（Digital Image Correlation Method，DIC）设计并组建了配合液压疲劳试验机加载的原位观测系统。同时针对DIC测量方法中的关键技术进行研究，分别提出了一种可应用于视场宽度2mm 下DIC计算的微小散斑制备方法，以及空间调节方法以提高试验可靠性。最后应用该系统开展针对航空发动机火焰筒材料GH536的微裂纹自然萌生试验。通过采取两种不同的DIC分析策略，分别获得疲劳过程中的总应变幅以及最大累积塑性应变的演化规律。结果表明总应变幅演化可确定自然萌生裂纹位置，最小可识别50μm裂纹；最大累积塑性应变分析可得萌生寿命占比约85%，并在裂纹出现后塑性应变急剧增加。

Abstract:

To further study the behavior of crack in initiation stage, an in-situ observation system based on digital image correlation (DIC) method and the hydraulic fatigue test machine loading system was proposed. Meanwhile, the key techniques in DIC measurement were studied and a micro speckle preparation technique suitable for 2mm-width-vision field DIC calculation and spatial adjustment technique were proposed respectively to improve the experiment reliability. Finally, this system was applied for the micro crack natural initiation test for the GH536 which was applied in flame tube of combustion chamber of aero-engine. By adapting two different analysis strategies, the evolution of total strain amplitude and the maximum accumulated plasticity strain can be obtained respectively. The results indicate that the total strain amplitude can locate the natural crack initiation and identify minimum 50 micro meter crack while the maximum accumulated plasticity strain analysis suggests that initiation life accounts for 85% and the accumulated plasticity strain increases significantly once the crack appears.