This article reports on the destructive and nondestructive evaluation of dry spots or patches in thick unidirectional glass/epoxy laminates. Dry spots in composites can act as weak regions potentially resulting in catastrophic failure if undetected. Composite samples with dry spots were fabricated and nondestructive evaluation was first carried out using non-contact air coupled ultrasonics. Two types of dryness were investigated: surface and mid-plane dryness. Both types were tested using two ultrasonic testing methods. The ultrasonic velocity was used to determine stiffness and dryness fraction maps. The results showed that the dryness could be detected and characterized using the ultrasonic nondestructive evaluation. To validate the results, a destructive analysis was carried out by cutting the sample into small pieces and burning them to obtain the weight of matrix and fibers. This was further used in micromechanics models to obtain void and dryness fractions. Both model and ultrasonic results show that dry spots result in spatial gradient of mechanical properties around the dry spot. Nondestructive characterization of dryness helps in deciding if the part must be scrapped or repaired based on the severity in terms of loss of stiffness.

本文报告了对厚单向玻璃/环氧树脂层压板中的干斑或斑点的破坏性和非破坏性评估。如果未检测到，复合材料中的干斑可能会充当薄弱区域，从而可能导致灾难性故障。制造具有干燥斑点的复合材料样品，首先使用非接触式空气耦合超声进行无损评估。研究了两种类型的干燥：表面干燥和中平面干燥。两种类型均使用两种超声测试方法进行了测试。超声速度用于确定刚度和干燥分数图。结果表明，使用超声波无损评估可以检测到干燥并进行表征。为了验证结果，通过将样品切成小块并将其燃烧以获得基体和纤维的重量进行破坏性分析。将其进一步用于微力学模型以获得空隙率和干燥率。模型和超声结果均表明，干燥点导致干燥点周围机械性能的空间梯度。干燥度的非破坏性表征有助于根据硬度损失的严重程度来决定是否必须报废或修理零件。