Experimental and numerical study of inelastic behavior based on simulated cylinder head specimen under thermal cycling conditions

During the start-stop cycle of marine diesel engines, the cylinder head bears the cyclic thermal stress and produces irreversible deformation. Previous studies mainly predicted the thermomechanical fatigue life of cylinder heads based on the strain fatigue damage criterion, but the multi-factor damage mechanism and law of thermal cycle load on the structural integrity of cylinder heads are not clear. A transient thermal cycle analysis method of the viscoelastic plastic Chaboche model was developed to quantitatively account for the marine engine cylinder head's local deformation and leakage failure. The Chaboche model combines the temperature-dependent nonlinear kinematic hardening equation and Norton-Bailey creep equation. A thermal cycling test of simulated cylinder head specimen was designed to cautiously verify the inelastic cyclic behavior of the multiaxial thermal and structural coupling effect. The model and numerical method are verified by the deformation and fatigue test of the specimen. Then the permanent deformation and leakage of the cylinder head and water-cooled valve seat are analyzed. The results show that multiaxial thermal cycle simulation verified the deformation prediction with an error of no more than 14%. Inelastic deformation induced by temperature cycling leads to gradual leakage failure in the exhaust nose bridge area of the cylinder head. The irreversible deformation gradually reduces the contact sealing force, and the cyclic loading plasticity that dominates is 8.36 times that of the creep deformation.