Benoît Blaysat

Assessing the Metrological Performance of DIC Applied on RGB Images

Thanks to the rise of digital reflex cameras, RGB CMOS sensors present nowadays interesting features, at relatively low prices. For instance, the Canon 5DSR sensor displays 50 million pixels. Nevertheless, such cameras being dedicated to photography and not to measurement, their high pixel density makes the associated sensor noise to be relatively high compared to the sensor noise of measurement cameras. Moreover, a Bayer filter mosaic is added in front of the pixels of such sensors in order to produce RGB images by interpolation. Embedded camera processors demosaice these data to elaborate full RGB pictures. Additional post-processing steps, including white balance and gamma correction, are also used in order to prevent any color shift and to give a pleasing-to-the-eye output.

Speckle Image Rendering for DIC Performance Assessment

Assessing the metrological performance of the methods available for displacement field measurement is of primary importance in experimental mechanics. It often relies on synthetically rendered images of a specimen before and after deformation. In this context, the only varying quantity should be the displacement field in order to prevent any other phenomenon to bias the estimation of the metrological performance. Concerning digital image correlation (DIC), images of a random speckle pattern are needed. We propose a new algorithm to render such images with a classic model of stochastic geometry, namely the Boolean model.

Towards standardized mechanical characterization of microbial biofilms: analysis and critical review

Developing reliable anti-biofilm strategies or efficient biofilm-based bioprocesses strongly depends on having a clear understanding of the mechanisms underlying biofilm development, and knowledge of the relevant mechanical parameters describing microbial biofilm behavior. Many varied mechanical testing methods are available to assess these parameters. The mechanical properties thus identified can then be used to compare protocols such as antibiotic screening. However, the lack of standardization in both mechanical testing and the associated identification methods for a given microbiological goal remains a blind spot in the biofilm community. The pursuit of standardization is problematic, as biofilms are living structures, i.e., both complex and dynamic. Here, we review the main available methods for characterizing the mechanical properties of biofilms through the lens of the relationship linking experimental testing to the identification of mechanical parameters. We propose guidelines for characterizing biofilms according to microbiological objectives that will help the reader choose an appropriate test and a relevant identification method for measuring any given mechanical parameter. The use of a common methodology for the mechanical characterization of biofilms will enable reliable analysis and comparison of microbiological protocols needed for improvement of engineering process and screening.

Studying with a Full-Field Measurement Technique the Local Response of Asphalt Specimens Subjected to Freeze-Thaw Cycles

Asphalt is a strongly heterogeneous material, whose global thermo-mechanical behavior is generally studied at a large spatial scale. Observing the local strain fields which occur between aggregates and mastic (i.e., asphalt binder + filler) is however crucial to understand the phenomena that influence the global response of such materials, and then better design them. In this study, full-field measurements were used to investigate the difference in behavior between various types of asphalt containing Recycled Asphalt Pavement (RAP). We focused here on their response when they were subjected to freeze-thaw cycles. The local contraction/expansion of the specimens subjected to various cooling/heating phases was observed with the grid method. The strain distribution has been found to be very heterogeneous because of the difference in coefficient of thermal expansion between aggregates and mastic. The influence of the percentage of RAP on the global response of the specimen is observed and discussed.

DIC in Machining Environment, Constraints and Benefits

The manufacturing of structural aluminum alloy parts used in aeronautics requires several steps of both forming processes and heat treatments before final machining. Some of the process steps will generate residual stresses and some will reduce residual stresses. For highly alloyed thick aluminum plates and closed-die forging parts, the material removal during the machining of complex geometries will release residual stresses and it can lead to part distortion.