Uniqueness of rate-dependency, creep and stress relaxation behaviors for soft clays

This work focuses on the uniqueness of rate-dependency, creep and stress relaxation behaviors for soft clays under one-dimensional condition. An elasto-viscoplastic model is briefly introduced based on the rate-dependency of preconsolidation pressure. By comparing the rate-dependency formulation with the creep based formulation, the relationship between rate-dependency and creep behaviors is firstly described. The rate-dependency based formulation is then extended to derive an analytical solution for the stress relaxation behavior with defining a stress relaxation coefficient. Based on this, the relationship between the rate-dependency coefficient and the stress relaxation coefficient is derived. Therefore, the uniqueness between behaviors of rate-dependency, creep and stress relaxation with their key parameters is obtained. The uniqueness is finally validated by comparing the simulated rate-dependency of preconsolidation pressure, the estimated values of secondary compression coefficient and simulations of stress relaxation tests with test results on both reconstituted Illite and Berthierville clay.

Static recovery of A5083 aluminum alloy after a small deformation through various measuring approaches

Static recovery was confirmed to be the dominant softening mechanism during annealing for the studied A5083 aluminum alloy.The kinetics of static recovery,described based on the activation parameters(activation energy and volume of static recovery)and the static softening fraction,were mainly studied through two thermomechanical tests,namely,double-pass compression and stress relaxation tests.A new approach was proposed to measure the static softening fraction in the stress relaxation test.In general,a higher temperature or strain rate accelerates static recovery,while interestingly,the effect of pre-strain on static recovery is opposite in cases with and without external stress,owing to the enhanced static recovery by external stress during annealing.In addition,microhardness tests and electron backscatter diffraction(EBSD)characterization were also conducted to verify the accuracy of the results.The grain average misorientation approach based on EBSD characterization was confirmed to be effective in distinguishing and quantifying static recovery.It is noteworthy that the special stress hardening phenomenon occurring at 400℃and 0.1/s is caused by strain aging,showing the complexity of the material behaviors after deformation of the studied aluminum alloy.