内部开口 meaning in Chinese

internal opening

Nondestructive testing is a very important and difficult research lesson about the defect of concrete structures . this paper mainly measures the stress waves conveying in concrete structures and the depth of surface - opening cracks in concrete plates by using impact echo method after carefully reading a lot of articles about the state and the abroad of concrete nondestructive in the field and incorporating the special conditions on the laboratory
混凝土结构物的缺陷的无损检测是一个非常重要而又非常困难的研究课题，本论文在大量参阅了国内外关于混凝土结构物无损检测的研究资料后，结合本实验室的具体条件，应用冲击反射法集中对应力波在混凝土板块内传播速度和混凝土结构物内部开口裂纹深度的测量等一系列问题展开了研究。