Blister-detection specimen

A configuration frequently used in cyclic stress testing is the reduced area adhesive bond (RAAB) specimen. This is similar to the blister detection specimen, but is 1/2 inch wide and a 1/4-inch hole is drilled through the center of the overlap region this provides more environmental exposure of the bondline. Potter has reported using RAAB specimens to compare the durabilities of several modified epoxy adhesives.Specimens subjected to cyclic stressing failed in fewer hours than specimens held at a constant stress, even when cycled at a lower stress level. He also found that a slow cyclic rate was more damaging than a fast cyclic rate. 

Blister Detection Large area metal-to-metal bonding to ascertain adhesive flow characteristics during bonding. Conventional lap shear specimens are machined from the bonded sheet and are tested. The specimens are examined for evidence of air entrapment ( blistering ). 

It can be seen that for severely degraded specimens, both the harmonic analysis and Impedance techniques are capable of detecting the presence of gross corrosion. The harmonics method provides a reasonable estimation of the corrosion rate when the Impedance data exhibits Warburg type behaviour. For less severely degraded specimens, especially those exhibiting blister attack, the Impedance method Is not as successful as the harmonic analysis technique. 

Because of its surface sensitivity, AES has been a valuable tool for identification of contaminants at Interfaces where delamlnatlon has occurred. Sometimes no contaminants are detected at Interfaces where delamlnatlon has occurred. Lack of evidence for contaminants can indicate mechanical reasons for the delamlnatlon. Specimens can be prepared by using adhesive tape to separate films or using a sharp point to peel back blister like features. Whenever possible both sides of the failed Interface should be analyzed. 

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