Relationship between constant-load creep, decreasing-load creep and stress relaxation of titanium alloy

Abstract

The mechanism of sheet metal parts hot sizing is considered as constant-strain stress relaxation due to creep. This creep deformation in stress relaxation is limited within the elastic strain range, unlike multi-step decreasing-load creep test in which the creep deformation is unlimited. In this paper, the short-term constant-load, decreasing-load creep and stress relaxation tests were performed on Ti6Al4V alloy specimens at 700°C. The initial stress in the range of 5–126MPa was applied in constant-load and decreasing-load creep, and initial strain of 0.002, 0.004, 0.0065 and 0.02 was loaded during stress relaxation. The two kinds of creep tests were performed for 3600s while stress relaxation tests for 1800s. The creep rate–stress, creep rate–time and creep strain–time relationships were studied respectively based on the test data. Constitutive creep models were developed according to constant-load creep and stress relaxation data, respectively. Application of the established models on simulation of constant-strain, constant-load and decreasing-load creep was introduced. Results show that the creep model from the SRT test is able to predict the stress relaxation behavior well while creep model from the constant-load creep tests is reliable in the simulation of constant-load and decreasing-load creep deformation.