Three types of Portevin–Le Chatelier effects: Experiment and modelling

An experimental and numerical investigation of the behaviour of AA5083 aluminium alloy in presence of the Portevin–Le Chatelier effect

On the propagation and pulsation of Portevin-Le Chatelier deformation bands: An experimental study with digital speckle pattern metrology

The digital image correlation (DIC) method obtains comparable results with strain gauges and its reliability and accuracy are commonly accepted in the measurement of affine deformations. However, in engineering measurements, there are always substantial local deformations with high strain gradients, such as the Portevin-Le Chatelier (PLC) shear bands, deformations near gaps, and crack tips. In these situations, strain gauges are restricted because the results within the contact areas are smoothed. Although the DIC method can be employed to measure these local deformations, the calculation parameters (e.g., the order of the shape functions, and template size) seriously impact the results. By analyzing PLC shear bands with different gradients in tensile tests and simulated bands, the deep mechanism on how shape functions and templates impact on the accuracy of DIC results is established. This study also demonstrates that second-order shape functions are more suitable than first-order shape functions to describe local deformations. The theory that the results of second-order shape functions are reliable and accurate when the relative error between first- and second-order shape functions is less than 10 %, is proposed. In addition, improving the spatial resolution and the acquisition frequency is proposed, and proved to achieve reliable results.

Effects of Various Shape Functions and Subset Size in Local Deformation Measurements Using DIC

Time-resolved deformation measurements of the Portevin–Le Chatelier bands

Time-division digital speckle pattern interferometry to observe temporal variation of in-plane deformation fields of a whole process of plastic deformation until fracture was proposed. Experiment of tensile test of an aluminum plate exhibited dynamic movements of successive fringe patterns which were very complicated. They suggest that plastic deformation propagates nonlinearly in the specimen by repetition of energy relaxation processes and concentration processes.

Time-Division Observation of Plastic Deformation Process Using Digital Speckle Pattern Interferometry

Nondestructive evaluations of iron-based material (A533B) have been investigated on the leakage flux from the surface by using Hall elements, on magnetic noises, on sub-micron deformations by Ar-laser speckle interferometry and on residual stresses by X-ray diffraction. A high resolution and high sensitivity for spatial inhomogeneity observation were attained as small as 200μm for residual strains less than 0.5 %.

Nondestructive Cross Evaluations of Iron-based Material by Magnetic Sensors and by Laser Speckle Interferometry

Whole deformation processes and slipboard propagation of aluminum alloy in tensile experiments are directly observed on whole field in real time by dynamic speckle interferometry. In plastic deformation, an inclined white band appears. It sweeps the specimen surface repeatedly in a certain sped and band width along the tensile direction. Sometimes the inclined angle of the white band transfers symmetrically. With plastic deformation increasing, the band speed decreases gradually, and the specimen cracks finally at the position where the band stops. Transient process of the white band formation is captured with a high speed CCD camera. It is revealed that the white band is a sharp slip deforming region consisted of concentrated inclined fringes. An interesting phenomenon that the strain value at a point of the specimen surface changes like a stair shape is accounted by the sweeping movement of the slipboard. The moving picture encoding technique is introduced to encode all of the sequential fringe patterns as one MPEG2 file. By watching the moving picture, the analysis of a huge volume of fringe patterns becomes easy, and subtle changes of fringe patterns can be observed clearly.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Slipband propagation in aluminum alloy with dynamic speckle interferometry

Whole deformation processes and slipband propagation of aluminum alloy in tensile experiments are directly observed on whole field in real time(1 frame/s) by dynamic speckle interferometry. In plastic deformation, an inclined white band appears. It sweeps the specimen surface repeatedly in a certain speed and band width along the tensile direction. Sometimes the inclined angle of the white band transfers symmetrically. With plastic deformation increasing, the band speed decreases gradually, and the specimen cracks finally at the position where the band stops. Transient process of the white band formation is captured with a high speed CCD camera. It is revealed that the white band is a sharp slip deforming region consisted of concentrated inclined fringes. An interesting phenomenon that the strain value at a point of the specimen surface changes like a stair shape is accounted by the sweeping movement of the slipband. The moving picture encoding technique (MPEG2) is introduced to encode all of the sequential fringe patterns as one MPEG2 file. By watching the moving picture, the analysis of a huge volume of fringe patterns becomes easy, and subtle changes of fringe patterns can be observed clearly.

Investigation of slipband propagation in aluminum alloy with dynamic speckle interferometry

Degradation processes of stressed solid materials was investigated by newly developed speckle interferometry. Sequence of speckle correlation fringes were obtained by subtracting couples of interfering speckle patterns successively acquired. The behavior of plastic deformation and fracture were observed on a video monitor as moving fringe patterns of in-plane deformation components. In experiments of a specimen of carbon steel S45C, we observed a characteristic white band which can be interpreted as a Luder's band sweeping over the specimen in the yielding state of the loading test. In experiments of an aluminum alloy specimen, complicated movement of a white and was found corresponding to load serration.

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Papers

Time-Division Observation of Plastic Deformation Process Using Digital Speckle Pattern Interferometry

Nondestructive Cross Evaluations of Iron-based Material by Magnetic Sensors and by Laser Speckle Interferometry

Slipband propagation in aluminum alloy with dynamic speckle interferometry

Investigation of slipband propagation in aluminum alloy with dynamic speckle interferometry

Speckle interferometry to investigate degradation processes of stressed solid materials