Study of propagation and pulsation of slip band using dynamic digital speckle pattern interferometry

摘要

The phenomena of Portevin-Le Chatelier (PLC) band propagation and its pulsation accompanying the serration of load curve in a tensile test (constant load strain rate: 10~(-5)/s) of aluminum alloy were directly observed by using dynamic digital speckle pattern interferometry (DSPI) method. In the plastic deformation stage, a slip band is formed and propagates repeatedly along the tensile direction with a certain speed (the beginning speed is several mm/s) and a certain bandwidth (several mm). The propagation speed decreases gradually with the increasing of plastic deformation, and finally the specimen cracks at the position where the band stops. The same slip fringe patterns observed from the front surface and rear surface of the specimen simultaneously show that the slip plane goes through the thickness of specimen. Pulsation of fringe density in the inside of the slip band accompanying with the serrations of load curve was observed. The pulsation period corresponds with the width of the serration. When the load falls in the serrations, the slip deformation happens just like an avalanche, and the time of the avalanchine slip is less than 0.03 seconds. Corresponding to the happening of the avalanchine slip, dense shrinkage fringes appear on the outside of the slip band. The specimen takes a shrinkage deformation in the outside of the slip band to compensate the elongation deformation in slip band at the moment of avalanchine slip, even for a tensile test. The elongation value in the inside of the slip band causing by the avalanchine slip is in the order of 10 μm by calculating with observed results.