High-resolution optical microscopy for characterising microstructural deformation in microtensile testing.

Imaging surface deformation of a coupon specimen in microtensile testing with an optical microscope presents challenges due to the narrow depth of field (DoF) of optical microscopes. Materials being heterogeneous at microscopic length scale, the sample surface deforms into a complex 3D surface texture, evolving continuously as the loading increases. Because of the narrow DoF, the region that is in focus within the field of view (FoV) decreases substantially in size with the increasing out-of-plane heterogeneous deformation. To address this challenge, a method based on image blending and stabilisation of the captured image frames is proposed. Image blending combines the partial regions that are in focus from a set of successive image frames captured at different working distances from the object surface plane to construct a single image that has a large part of the FoV in focus. The blended images are then obtained at different levels of macroscopic strains, that is the global homogeneous strain, in order to characterise the evolution of the heterogeneous deformation. The image stabilisation removes any misalignments of the blended images by spatially realigning them choosing a common feature as a reference point. The validation of the proposed method with conventionally and additively manufactured stainless steel 316L (SS 316L) specimens demonstrates excellent improvement in image quality. Almost 100% of the FoV is maintained in focus regardless of the amount of out-of-plane heterogeneous deformation caused during tensile testing, which is quite remarkable for optical microscopy imaging. Consequently, the blended and stabilised images enhanced the accuracy of digital image correlation (DIC). Time-lapse videos of the deformation generated using these images captured the evolution of the slip bands and their transmission through twinning boundaries in the stainless steel microstructure. Overall, this study demonstrates the feasibility of using image-processing techniques to advance optical microscopy to image complex 3D surfaces evolving with time.

Variability in the management of hypertension and cost-effectiveness: methodology, community care results and potential cost reductions.

This study examined factors contributing to variability in the cost-effectiveness of managing hypertension using the Weinstein and Stason methodology. Empirical analysis was based on resource use and blood pressure data from 160 persons ages 25-64 in an urban community family practice center in 1976. The exploratory study presented results on blood pressure reduction, annual treatment costs, the importance of different cost factors, variability in management costs and potentials for increasing cost-effectiveness. For males cost-effectiveness estimates were similar to those of Weinstein and Stason , while the results for women were somewhat different due to less cost-effectiveness in hypertension management for older women. With small modifications in current Family Practice procedures the cost-effectiveness of managing hypertension appears to be able to be increased in many cases by as much as one-third.