PBO纤维增强环氧树脂复合材料层间Ⅰ型断裂韧性的DIC技术测量

Ⅰ型双悬臂梁(DCB)试验通常用于单向复合材料的层间抗拉性能研究，目标是测量Ⅰ型层间断裂韧性，其可作为复合材料分层扩展及失效机制研究的重要输入参数。在DCB试验中必须经常暂停试验以实现多次测量裂纹长度，这不仅会对裂纹传播产生潜在影响，造成测量误差且多次反复试验的时效性较差。数字图像相关(DIC)测试技术应用于裂纹扩展长度测量具有实时跟踪、精确定位的优点，可有效提高Ⅰ型断裂韧性试验的测量效率，但应用于非连续变形行为仍存在局限性，且易受到图像噪声的干扰，产生测量误差。本文发展了一种基于DIC测试技术的实时获取裂纹长度的检测方法，通过图像匹配算法获取试件的非连续变形位移场，并提出一种根据全局横向位移离散程度的辨别方法，实现了裂纹尖端的实时捕捉。再通过DCB试验，与传统测量方式对比，裂纹长度的测量误差平均不超过2.76%，验证了该方法的准确性和高效性，同时也克服了聚对苯撑苯并双噁唑(PBO)/环氧树脂复合材料侧表面毛糙、散斑质量较差及纤维桥接对测量结果的干扰，最终获取了有效的Ⅰ型层间断裂韧性初始值及稳态扩展值。

Mode I interlaminar fracture toughness measurement of PBO fiber reinforced epoxy composites by DIC technology

The mode I double cantilever beam (DCB) test was commonly applied to investigate the material resistance to crack propagation in unidirectional composites, aiming at obtaining the interlaminar fracture toughness in mode I, which was an important input parameter for the study of delamination propagation and failure mechanism of composite materials. The DCB test must be suspended frequently for the multiple measurements of the crack length, which will not only have a potential effect on the propagation of crack and even lead to the measurement error, but also can be a time and effort consuming process. Digital image correlation (DIC) technology applied to crack propagation length measurement has the advantages of real-time tracking and precise positioning, effectively improving the measurement efficiency of the mode I fracture toughness, but it still has limitation when applied to discontinuous deformation behavior, and it is susceptible to interference from image noise, resulting in measurement error. This paper developed a real-time crack length detection method based on DIC and obtained the discontinuous deformation displacement field of the specimen through an image matching algorithm, and then proposed an identification method based on the degree of dispersion of the global lateral displacement, which realized the crack tip real-time capture. Then, compared with the traditional measurement method in the DCB test, the measurement error of the crack length does not exceed 2.76% on average, which verifies the accuracy and efficiency of the method, meanwhile, overcomes the measurement interference caused by roughness of the side surface, the poor speckle quality and the fiber bridging of the poly p-phenylene-2,6-benzoxazole (PBO)/epoxy composites. Finally, the effective initial value and steady-state propagation value of the mode I interlaminar fracture toughness.