Viscoelastic contract, work of adhesion and the JKR technique

The extension of the Johnson-Kendall-Roberts (JKR) theory of elastic contac t to a linear viscoelastic material is addressed with particular emphasis o n the debonding phase of a JKR test, We show that the contact stress at the moving edge of the contact zone is tensile and is characterized by a stres s intensity factor, K-J (t). In contrast to the elastic JKR theory, K-I (t) is no longer determined by the current contact area and applied load, but depends on the entire history of loading. Furthermore, K-I (t) no longer un iquely determines the energy flow (G) to the material at the moving edge of the contact zone since G is coupled to the local separation or bonding pro cess. This means that one cannot obtain the work of adhesion (W) directly f rom experimental data. Since the mechanics of viscoelastic deformation is i nvariably coupled to the separation or bonding process, the adhesion of vis coelastic bodies can no longer be completely characterized by a single para meter (i.e. W) approach. The theory presented here suggests that a better w ay to characterize the adhesion of viscoelastic materials is to relate the rate; of banding or debonding of surfaces to the K-I (t). Procedures for ob taining K-I (t) from experimental data are given for the bonding and debond ing phases of both force and displacement controlled tests.