Abstract
In creep age forming (CAF), large integral panel components of high-strength aluminum alloy can be shaped and strengthened under external elastic loading at an elevated temperature through creep deformation and age hardening, simultaneously. However, the high ribbed structure on panel may induce stress concentration, inhomogeneous plastic deformation and even damage evolution on the bending rib, leading to the difficulty in controlling forming precision and material properties. Therefore, the generation and evolution of damage are necessary to be considered in the design of CAF. Taking 7050 aluminum alloy as the case material, the continuous and interrupted creep aging tests at 165 °C and three stress levels (300, 325, and 350 MPa) were conducted, and the corresponding material properties, precipitate, and damage microstructures were studied by mechanical properties tests, transmission electron microscope (TEM) and scanning electron microscope (SEM) characterizations. With the increase of stress level, the creep deformation occurs easier, the precipitates grow up faster, the creep damage occurs earlier, the growth rate and the size of microvoids increase, the mechanical properties decrease more rapidly, and the dominant mechanism of creep fracture changes from shear to microvoid coalescence. To simulate creep aging behavior with damage, a continuum damage mechanics (CDM) based model is calibrated and numerically implemented into ABAQUS solver via CREEP subroutine. The CAF of 7050 aluminum alloy panels with different height ribs were conducted by experiment and FE simulation. The forming process presents a typical stress relaxation phenomenon. The creep damage mainly occurs on the bending rib due to the severe stress concentration. With the increase of rib height, the creep strain and damage degree increase, but the springback decreases.
Highlights
Aim at the integrated manufacturing of shape forming and performance tailoring, creep age forming (CAF), as a novel and promising sheet metal forming technology, has been developed and applied to manufacturing the integral panel components in the aerospace field [1]
The high strength aluminum alloy panel is elastic loaded to fit the die for obtaining the target shape under the artificial aging temperature
Under this specific thermal-mechanical field of CAF, the elastic deformation is gradually changed into permanent deformation by creep, and in the meantime, the material can be strengthened by aging [2]
Summary
Aim at the integrated manufacturing of shape forming and performance tailoring, creep age forming (CAF), as a novel and promising sheet metal forming technology, has been developed and applied to manufacturing the integral panel components in the aerospace field [1]. Ho et al [15,16] established a set of physically-based unified creep constitutive equations to model aging hardening and creep deformation behaviors of 7010 aluminum alloy sheet in CAF, and obtained agreement well between the predicted and experimental results of yield strength and springback. These studies provide beneficial knowledge for the revelation of deformation mechanism, the optimization of technological parameters and the simulation of forming process. A CDM based creep aging model was calibrated and embedded into the commercial FE solver ABAQUS by CREEP subroutine to numerically investigate the CAF process of AA7050 ribbed panel, and the real CAF tests were carried out to verify the accuracy of the model
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