Study of Adhesive Bonds by Mechanical Tests, Ultrasounds and Electromechanical Impedance Method

Abstract

The paper deals with adhesive bonding of CFRP plates. Adhesive bonding of composites is considered as good alternative to riveting, provided that good tools are available to assess the bond quality after manufacturing and during the lifetime of structures. The performance of an adhesive bond depends on the physico-chemical properties of the adherent surfaces. A weak bond can be caused by improper surface preparation before bonding. In the research reported herein, modifications of one of the surfaces to be bonded were considered. These modifications are realized using chemical contamination or thermal treatment. The influence of surface modification on bond performance was investigated by electromechanical impedance (EMI) method, ultrasounds and mechanical tests. In the EMI method, a piezoelectric transducer was mounted at the middle of each sample surface. Using an impedance analyzer the electrical parameters were measured for wide frequency band. Due to piezoelectric effect the electrical response of a piezoelectric transducer is related to mechanical response of the sample to which the transducers is attached. The ultrasonic testing (UT) was focused on C-scan analysis taking into consideration the amplitude and time of flight of the signals. A probe with 10 MHz central frequency was used, to highlight different effects on the responses. Mode-I and Mode-II fracture toughness tests were conducted aiming to gain knowledge on the influence of surface modification on the bond strength. The performed investigation showed that bond quality is influenced by the bond modifications.