Obtaining strain-rate dependent traction-separation law parameters of epoxy adhesive joints and predicting fracture for dissimilar bonding adherends

This study investigated the mode I fracture behavior of double cantilever beam (DCB) epoxy adhesive joints with similar adherends on the both sides (i.e., aluminum-aluminum or copper-copper) at different strain rates; i.e., quasi-static (∼10 ⁻³ s ⁻¹), low (∼7 s ⁻¹) and intermediate (∼14 s ⁻¹ ) rates. The fracture energy of the DCB joint in Al-adhesive-Al specimens decreased (i.e., by ∼62%, p = 0.0013) with an increase in the applied strain rate from quasi-static to low values, while it remained almost unchanged with further increase of stain rate to intermediate range (p > 0.05). For Cu-adhesive-Cu cases, however, the fracture energy was found to be almost insensitive to the applied strain rate over the range tested (p > 0.05). A cohesive zone model (CZM) was built and strain-rate dependent parameters of traction-separation (TS) law were obtained. These parameters were then used to predict the fracture of epoxy adhesive joints bonded with dissimilar substrates (i.e., copper-aluminum). Predicted fracture loads of the Cu-adhesive-Al cases obtained from the stain-rate dependent model were in reasonable agreement with measured forces (i.e., from ∼0 to 24%) at a given strain rate. Therefore, once TS law parameters for Al-adhesive and Cu-adhesive interfaces were determined, the CZM could predict the fracture of the joint bonded with Al and Cu on its sides.