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

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 5-126 MPa 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 3600 s while stress relaxation tests for 1800 s. 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.