Texture homogeneity and stability in severely warm-rolled and annealed ultrafine pearlite

The evolution of microstructure and texture was investigated in a severely warm-rolled ultrafine pearlitic steel. The steel was 95% warm-rolled at 600°C and annealed at 700°C for different time intervals. The spheroidisation of cementite initiated after 30% reduction and completed beyond 70% reduction. The 95% warm-rolled steel showed elongated as well as ultrafine equiaxed ferrite grains. Texture inhomogeneities were evidenced by the presence of Goss component ({011} <100>) on the surface originating due to surface shear and diffuse texture at the interior. Formation of equiaxed microstructure after annealing through continuous recrystallisation resulted in the retention of the surface Goss component. However, the Goss component was destroyed beyond annealing for 180?minutes due to the abnormal growth of other grains.     

Stitched Acousto-Optic Modulator Stroboscopic Interferometry for characterizing larger microstructures

Large field of view with higher resolution has become a strong requirement for the present measurement technology. Currently used sub-aperture stitching methods are suffering from the inaccuracies of computer controlled stages. In this work three different simplified stitching methods are presented. The stitching process proposed here is based on Acousto-Optic Modulator Stroboscopic Interferometry (AOMSI) of fixed field of view (FOV) and it does not require any computer controlled stage. A large microcantilever was tested in two stages, one from the root and the other from the tip portions separately, and the complete profile of the cantilever was extracted using the proposed stitching methods. The same cantilever also was tested using a commercial profilometer with a full field of view. There was a good agreement between the results from the proposed methods and a commercial profilometer. Obtaining extremely low amount of variation using the presented stitching methods validates the proposed stitching methods for large microstructures.     

Analytical optical solution of the extension of the depth of field using cubic-phase wavefront coding. Part II. Design and optimization of the cubic phase

In this paper we use our derived approximate representation of the modulation transfer function to analytically solve the problem of the extension of the depth of field for two cases of interest: uniform quality imaging and task-based imaging. We derive the optimal result for each case as a function of the problem specifications. We also compare the two different imaging cases and discuss the advantages of using our optimization approach for each case. We also show how the analytical solutions given in this paper can be used as a convenient design tool as opposed to previous lengthy numerical optimizations.     

FEM of residual stress and surface displacement of a single shot in high repetition laser shock peening on biodegradable magnesium implant

Laser shock peening (LSP) is one of the prominent surface processing techniques to improve the mechanical characteristics by inducing compressive residual stress on the specimen surface. Generally, LSP is performed using high energy, low repetition pulsed laser. Recently, High repetition laser shock peening (HRLSP) on biodegradable magnesium alloys has been reported. Increased speed and reduced operating costs are the key highlights of HRLSP. This work is aimed towards understanding of the residual stress profile beneath the specimen surface, where a Finite element method (FEM) has been proposed to show the ability of a tightly focussed nanosecond laser pulse for peening magnesium. The depth of maximum compressive residual stress of 48 MPa at 28 mm beneath surface was the result of the simulation. Also the Von Misses stress was analytically found to be 31.5 MPa, which is similar to the value from FEM at 30 MPa. Furthermore, the plastic displacement of FEM at 4.02 µm compares reasonably well with the experimental result at 3.698 µm, thereby validating the Finite element model. If increase in CRS can be created by single shot of laser pulse, it can be concluded that the same can be done beneath the entire magnesium surface using appropriate scanning protocols.

     

Optoelectronic region of interest detection: an application in automated cytology

Diagnostic cytology, which is used to screen for cervical cancer, involves characterizing cellular features such as shape, size, and texture. Automated screening of cervical smear slides is desirable but computationally challenging since each slide requires processing 2 x 10(9) pixels at a resolution of 0.8 mum per pixel. We demonstrate that the throughput of optical processors can be exploited in automated cervical smear-screening systems. In particular, we identify a morphological shape detector to perform the initial region of interest (ROI) detection and to demonstrate experimentally its optoelectronic implementation. The ROI detector is tested on 200 images, and its performance is characterized as a receiver operating characteristic (ROC). The area under the ROC curve is as high as 96.4% of the total area. The simulation and the experimental results are found comparable, and the discrepancy between the two results is determined to be a function of the number of bits represented in the filter plane device.     

Signal-to-noise analysis of task-based imaging systems with defocus

We analyze the signal-to-noise ratio (SNR) of arbitrary imaging systems in the presence of defocus. The modulation transfer function (MTF) and the mean SNR are combined to calculate the spatial-frequency spectrum of the SNR (the spectral SNR). Computational imaging methods are used for extending the depth of field (DOF) of the system. The DOF of a task-specific imaging system is defined as the range of defocus that causes the spectral SNR to drop below a minimum value within a band of spatial frequencies of interest. We introduce the polar-SNR plot as a tool for visualizing the spectral SNR of defocused imaging systems with asymmetric pupil functions. As an example, we perform the analysis of an imaging system used for biometric iris recognition.     

Extending the imaging volume for biometric iris recognition

The use of the human iris as a biometric has recently attracted significant interest in the area of security applications. The need to capture an iris without active user cooperation places demands on the optical system. Unlike a traditional optical design, in which a large imaging volume is traded off for diminished imaging resolution and capacity for collecting light, Wavefront Coded imaging is a computational imaging technology capable of expanding the imaging volume while maintaining an accurate and robust iris identification capability. We apply Wavefront Coded imaging to extend the imaging volume of the iris recognition application.     

Static characterization of microstructures using AOMSI and temporal phase-shifting (TPS) methods

Temporal phase shifting interferometry is the most common method for characterization of surface, profile and displacement properties of micro devices. Common methods of phase shifting require piezoelectric material based devices that have inherent errors due to non-linearity. To avoid these errors during phase shifting, a new phase shifting technique is presented in this work. This technique utilizes the advantage of stroboscopic interferometry to create phase shifted images without requiring any additional component for phase shifting. The proposed method was used for surface profiling and static characterization of the microstructures. Static characterization was performed to identify the tip deflection and profile variation of the microcantilever in response to various DC voltages. A capacitor-based cantilever was tested under varied electrostatic loads and the deflection of the cantilever was extracted using the proposed method. The deflection of the cantilever was predicted using energy method. Static characterization results from the proposed technique were found to be in good agreement with the predicted results.     

Annealing-Mediated Microduplex Structure and Texture Evolution in Severely Cold-Rolled Nanolamellar Pearlite: A Perspective on the Effect of Starting Inter-lamellar Spacing

Metallurgical and Materials Transactions A - The effect of inter-lamellar (IL) spacing on the microstructure and texture of severely cold-rolled and annealed pearlite was studied. For this purpose,...