Cyclic plasticity of hardened oil well cement paste: A nonlinear kinematic hardening perspective

Abstract

The present work focuses on the deformation of oil well cement subjected to cyclic loading. Different from the conventional models based on damage theory, the strain accumulation in this study is characterized in the framework of nonlinear kinematic hardening plasticity. The main feature of the proposed model is that a recall (nonlinear) term is introduced in the hardening rule so that the back stress hardens nonlinearly with plastic deformation. Accordingly, the back stress varies differently across the unloading and reloading paths, leading to a no-closed hysteresis loop and a ratcheting strain. The proposed model is validated through several experiments conducted on oil well cements cured at different curing temperatures and curing ages. The model results for the ratcheting straining of oil well cement under both uniaxial and triaxial compression agree well with experimental results. In particular, the proposed model well reproduces a much more pronounced residual strain during the first cycle, and a minor as well as constant accumulation rate for the subsequent cycles. For a comparison, such greater residual strain and the following smaller constant residual strain can not be characterized by the conventional damage-based models, which produces an increasing accumulation rates with the cycle numbers.