“…FE model established in ABAQUS is demonstrated in Figure 3. The Johnson-Cook constitutive model usually utilized in medium or high strain rate conditions [43][44][45] was considered to describe the dynamic response of the specimens. The Johnson-Cook model is given as follows:…”
This study aims to explore the upper limit of expansion size in dynamic cold expansion (DCE) and discuss the fatigue life enhancement mechanisms of this process. To achieve this, fatigue tests were conducted and the fractured surfaces were analyzed. Residual stress was measured both experimentally and numerically, and micromorphology was investigated. The stress distributions were also used to predict the fatigue life, with corresponding investigations of static cold expansion (SCE) conducted for comparison. The results indicate that the DCE process can achieve a larger upper limit expansion size than the SCE, leading to an extension of higher fatigue life. Additionally, the DCE induces larger compressive residual stress, especially at the mandrel entrance layer, and more significant grain refinement than the SCE. These factors are considered as the main mechanisms responsible for the fatigue life enhancement in the DCE process. The predicted results were in good agreement with the experimental data.
“…FE model established in ABAQUS is demonstrated in Figure 3. The Johnson-Cook constitutive model usually utilized in medium or high strain rate conditions [43][44][45] was considered to describe the dynamic response of the specimens. The Johnson-Cook model is given as follows:…”
This study aims to explore the upper limit of expansion size in dynamic cold expansion (DCE) and discuss the fatigue life enhancement mechanisms of this process. To achieve this, fatigue tests were conducted and the fractured surfaces were analyzed. Residual stress was measured both experimentally and numerically, and micromorphology was investigated. The stress distributions were also used to predict the fatigue life, with corresponding investigations of static cold expansion (SCE) conducted for comparison. The results indicate that the DCE process can achieve a larger upper limit expansion size than the SCE, leading to an extension of higher fatigue life. Additionally, the DCE induces larger compressive residual stress, especially at the mandrel entrance layer, and more significant grain refinement than the SCE. These factors are considered as the main mechanisms responsible for the fatigue life enhancement in the DCE process. The predicted results were in good agreement with the experimental data.
“…In DCE process, the strain rate can reach a medium strain rate (10 0 −10 2 s −1 ). Hence, Johnson-Cook constitutive model which was usually utilized for material response under medium or high strain rate such as electromagnetic riveting, 58 shot peening, 59 electromagnetic forming 60 was used to describe the dynamic response of the plate during DCE because of the similarity of these processes. The Johnson–Cook model is given as follows:Where σ− is the equivalent flow stress, ε− is the plastic equivalent strain, ε−.…”
In this study, residual stress distributions and fatigue performances of electromagnetic driving dynamic cold expansion (DCE) open-holed sheets were investigated. Fatigue behaviors were tested, and residual stress fields were obtained experimentally and numerically. Furthermore, a fatigue life prediction method based on three-dimensional stress distribution was proposed. Results showed that DCE method extended higher fatigue life and produced more uniform residual stress along hole axial direction than static cold expansion (SCE) method. The stress distribution differences led to different fatigue crack initiation and propagation modes of DCE and SCE specimens. Uniform stress distributions along axial direction in DCE specimens contributed to random initiations and horizontal propagations of fatigue cracks, while the fatigue cracks in SCE specimens usually initiated at the mandrel entrance layer and propagated to the mandrel exit layer. Moreover, the predicted fatigue life results agreed well with experimental data.
“…Tubular WP flow stress approximated by Johnson–Cook material model is as given by equation (16). The temperature effect is ignored here as any small rise in temperature has little influence on electrical and mechanical properties of WP material 15–17 Figure 6.Flowchart of sequential coupled simulation.Figure 7.The 2D axis symmetric arrangement and meshing.…”
The frequency of capacitor discharge current is an important parameter in the electromagnetic forming process. In the present work, simulation and experimental study of electromagnetic expansion is carried out on aluminium tubes (Al 5052). The aim is to obtain the optimum frequency of discharge current that gives maximum tube expansion at constant discharge energy. A two-dimensional axisymmetric numerical simulation model is developed that couples electromagnetic and structural phenomenon sequentially. After validating experimental tube expansion results with numerical results, the simulation model is used to analyse the effect of variation in current frequency on the tube expansion. It is observed that maximum tube expansion and higher process efficiency occurred at 5 kHz, which is considered as the optimum frequency for the used experimental set-up. In contrast to sheet forming case observed in the literature, results of tube expansion show that maximum forming is obtained at a frequency where the ratio of skin depth to tube thickness is less than 1. It is also noticed that the optimum frequency depends on the inductance and resistance of the system.
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