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一、前言声发射是指在材料中由于能量快速释放而产生的瞬态弹性波。它既可用于研究各种现象如材料的破坏过程,又可用于检测材料中存在的各种缺陷。和 X 射线探伤、超声探伤一样是广为采用的无损检测技术。一般用压电换能器将声发射产生的应力波转变为低电平(十几微伏到数毫伏)高阻抗(数十到数百微微法)的电信号,然后经前置放大器放大、高通宽频滤波器滤波、最后经增益放大器放大。聚偏氟乙烯是最重要的压电聚合物,具有压电陶瓷(如锆酸钛酸铅 PZT)所不具备的许多特点,它的压电性能虽比不上压电陶瓷,但聚偏氟乙烯柔软,易于加工成形状复杂的制品;在较宽的频率范围(10kHz～5MHz)内有平坦的响应;它的内耗较高、密度较小,对试样的机械响应影响很小;它的声阻抗(材料的密度和声速之积)和玻璃纤维增强聚合物复合材料的声阻抗相近,因此,即使不用粘接剂,在界面上的能量反射很少,而 PZT 的阻抗比聚偏氟乙烯高一个数量级;最后聚偏氟乙烯成本较低。因此,在复合材料的声发射测试中,用聚偏氟乙烯代替 PZT 具有十分重要的意义。
First, the preface Acoustic emission refers to the transient elastic wave generated in the material due to the rapid release of energy. It can be used to study various phenomena such as material destruction process, but also can be used to detect various defects existing in the material. And X-ray flaw detection, ultrasonic flaw detection is widely used non-destructive testing technology. Piezoelectric transducers are generally used to convert acoustic waves generated by acoustic emission into low-level (tens of microvolts to a few millivolts) high-impedance (tens to hundreds of picofarads) electrical signals and amplified by preamplifiers , Qualcomm broadband filter, and finally amplified by the gain amplifier. Polyvinylidene fluoride is the most important piezoelectric polymer, with the piezoelectric ceramic (such as lead zirconate titanate PZT) does not have many of the characteristics of its piezoelectric performance, although smaller than the piezoelectric ceramic, but polyvinylidene fluoride Ethylene is soft and easy to process into complex shaped products. It has a flat response over a wide frequency range (10kHz ~ 5MHz). It has high internal friction and low density, which has little effect on the mechanical response of the sample. The acoustic impedance (the product of the density and the velocity of sound) is similar to the acoustic impedance of glass fiber reinforced polymer composites, so that even with no adhesive, there is little energy reflection at the interface and the impedance of PZT is lower than that of polyvinylidene fluoride An order of magnitude higher; and finally the cost of polyvinylidene fluoride is lower. Therefore, in the composite acoustic emission test, the use of polyvinylidene fluoride instead of PZT is of great significance.