Impulse-Frequency Response and EIS Based NDE for Characterizing Bond Integrity of Adhesive Joints Subjected to Environmental Degradation

Single-Lap Joint (SLJ) and three-point end-notched flexure (ENF) joint configurations were used to bond 1” × 1/8″ (25.4mm × 3.175mm) aluminum 2024 T-4 adherends using a range of 3M™ high performance pressure sensitive adhesives (Adhesives 69, 73 and 85) and VHB™ acrylic foam tapes (Foam 41, 50, 52). Batches of bonded specimens were subjected to two types of aggressive environments simulating extreme service conditions: freeze-thaw cycling from 10°F to 50°F at 6 cycles per day (ASTM C666 Procedure A) for 21 days with samples immersed in water; heat-cool cycling (with 90% of maximum recommended temperature by the manufacturer of both acrylic foam and adhesive transfer tapes attained at 70% relative humidity) and 3 cycles per day for 21 days. Electrochemical Impedance Spectroscopy (EIS) and Fast Fourier Transform (FFT) based impulse frequency response vibration Non-Destructive Evaluation (NDE) techniques were used to monitor overall bond integrity.