The microscopic defects that distributed randomly in metals are not only hard to detect, but also may inevitably cause catastrophic failure. Thus, autonomic probing and healing for damage inside metals continue to be a challenging. Here we show a novel approach for self-healing using electropulsing as a stimulus to trigger repairing of damaged metals. This is achieved via a process that through expelling absolutely currents, the microcrack causes them to be redistributed to form a concentrated and a diluted region around it, thereby inducing an extremely high temperature gradient and a large compressive stress, which drive material flow to close microcracks. Simultaneously, a large enough heat for bonding atoms was produced. That is, the microcrack as an empty cavity can be regarded as a special micro-device to shape a localized microscopic energy field, which in turn activates a healing process. The microstructure and mechanical property verified the extrinsic self-healing of a titanium alloy. The process is performed on a short timescale, is enable to detect automatically and act directly on the internal defects in metals, and to heal damage without any healing agent, long time heating as well as applied high pressure, offering unique advantages over conventional healing approaches.

The viscous pressure bulge (VPB) testes of the aluminum Al1060 sheet were carried out with stainless steel overlapped outside without lubricant. The influence of the compressive normal stress on the failure behavior of aluminum sheet was investigated by scanning electron microscope observations. The results indicate that the forming limit of overlapped aluminum sheet is increased significantly compared with the single aluminum sheet. Fractography shows that the void growth and conjunction in the thickness direction is restrained by normal pressure and the fracture mode of overlapped sheet transits from the dimple fracture to shear fracture due to the reduction of stress triaxiality.

Electronic speckle pattern interferometry (ESPI) was applied to hydraulic bulging to analyze the entire deformation process, especially the instability evolution of Al 1060 sheet. Speckle patterns of the specimens were captured continuously to record the deformation fields. The development of full-field strain rate during bulging was represented by the fringe patterns real-timely. The emergence of the defect and its subsequent transformation into groove and crack were revealed clearly by the aberration region in the fringe patterns. The onset of diffuse necking and localized necking were determined by the strain rate distribution curves calculated based on the fringe patterns. Results indicate that ESPI is a satisfying method to analyze the instability and fracture of sheet metals even in three dimension deformation. The growth of micro-crack caused a banded weak region. Diffuse necking occurred in the weak region due to strain localization. A groove generated in the banded weak region and then extended along the length direction. The remarkable strain localization in the groove indicated the onset of localized necking. The thickness of the groove decreased quickly and finally caused fracture. The accurately and quickly determined necking strains would lead to a safer FLD.

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Viscous pressure forming (VPF) is a new developed sheet soft-punch forming process in 1900s. The basic principle and characteristics of VPF are described. The applications of VPF technologies of nickel-based super-alloy corrugated thin-walled part, asymmetrical thin-wall part with variable diameter, super-alloy thin-walled part with variable diameters, corrugated thin-walled part with larger diameter and small section are presented. The results show that VPF is suitable for the forming of parts with high strength, low plasticity, super thin-wall and complex shaped.