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5 混凝土内部缺陷的超声检测 在混凝土结构物的施工及使用过程中,往往会形成一些缺陷和损伤,例如孔洞、裂缝、不密实区、蜂窝及保护不足、钢筋外露以及层状疏松等。这些缺陷和损伤严重影响结构物的承载力和耐久性。混凝土超声检测时所需测量的物理量是声时、衰减、接收波形以及频谱等。其判别缺陷的基本依据是: (1)超声波在混凝土中遇到缺陷时存在反射和绕射,按声时或声速变化来判别及计算缺陷的大小。 (2)超声波在缺陷处产生散射、吸收,因此接收波能量显著减小,可判断缺陷存在及大小。 (3)超声波遇到缺陷时,接收频率明显降低,可判别内部缺陷。 (4)超声波在缺陷处,波型会转换和不同相位叠加,接收波会畸变,可判别缺陷。
5 Ultrasonic testing of concrete internal defects Ultrasonic testing of concrete structures tends to create defects and damages during the construction and use of concrete structures such as holes, cracks, unfit areas, lack of honeycomb and protection, exposure of steel bars and lamellar porosity. These defects and damage seriously affect the bearing capacity and durability of the structure. The physical quantities required for concrete ultrasonic testing are acoustic, attenuation, received waveform and spectrum. The basic criteria for the determination of defects are: (1) ultrasonic reflection and diffraction in the presence of defects in the concrete, according to sound or sound velocity changes to determine and calculate the size of defects. (2) Ultrasound produces scattering and absorption at the defect, so the energy of the received wave is significantly reduced, and the existence and size of the defect can be judged. (3) Ultrasound encountered a defect, the receiving frequency was significantly reduced, can determine the internal defects. (4) ultrasonic at the defect, the wave will be converted and superimposed on different phases, the receiving wave will be distorted, can identify defects.