Exploiting Slow Dynamics Effects for Damage Detection in Concrete

Nonlinear ultrasonic techniques have been developed over the last decades to detect the presence of damage in materials of interest in the field of civil engineering, such as concrete or mortar. The dependence on the strain amplitude of measurable quantities, such as wave velocity, damping factor, resonance frequency, etc. is normally considered a qualitative indicator of the presence of defects at the microstructural level. The experimental approaches proposed have the advantage of being sensitive to small variations in the sample microstructure and are therefore more adapted to detect the presence of small cracks or damaged areas with respect to traditional linear ultrasonic techniques. However, nonlinear methods are difficult to implement, since they usually require a calibrated experimental set-up which also behaves linearly at high amplitudes of excitation. The slow dynamics features, typical of the hysteresis generated by damage, have been given much less attention as a tool for damage detection even though their quantification is often less demanding in terms of an experimental set-up. Here, we provide the first evidence of how recovery, which is part of the slow dynamics process, is sensitive to the presence of damage in concrete samples and thus could be considered as an easy-to-measure nonlinear indicator for Structural Health Monitoring purposes

"Experimental evidence of correlations between conditioning and relaxation in hysteretic elastic media"

Consolidated granular materials and materials with damage at the microstructural level exhibit anomalous elastic behavior even when excited by low-amplitude elastic waves. Their response is given by a combination of slow- and fast-dynamics effects which, as their definition implies, act on very different time scales. In particular, conditioning (a transition to an elastic state dependent on the strain amplitude) and relaxation (full recovery of the elastic properties when the strain is removed) have been observed in different materials and under different dynamic excitations. An experimental parametric analysis of the phenomenon, aiming to establish correlations between the effects on different elastic physical properties (wave velocity and attenuation coefficient) and between the evolution of conditioning and relaxation is proposed here, with the goal of better characterizing slow dynamics and allowing one to go beyond the phenomenological description of elastic hysteresis currently available. At the same time, by studying different materials, we wish to highlight the possibility of using slow dynamics as an additional tool for materials characterization

Short Digital Signatures and ID-KEMs via Truncation Collision Resistance

Truncation collision resistance is a simple non-interactive complexity assumption that seems very plausible for standard cryptographic hash functions like SHA-3. We describe how this assumption can be leveraged to obtain standard-model constructions of public-key cryptosystems that previously seemed to require a programmable random oracle. This includes the first constructions of identity-based key encapsulation mechanisms (ID-KEMs) and digital signatures over bilinear groups with full adaptive security and without random oracles, where a ciphertext or signature consists of only a single element of a prime-order group. We also describe a generic construction of ID-KEMs with full adaptive security from a scheme with very weak security ( selective and non-adaptive chosen-ID security ), and a similar generic construction for digital signatures

Enhancement of the total focusing method imaging for immersion testing of anisotropic carbon fiber composite structures

Conference of 43rd Annual Review of Progress in Quantitative Nondestructive Evaluation, QNDE 2016 ; Conference Date: 17 July 2016 Through 22 July 2016; Conference Code:126650International audienceThe use of composite structures has importantly increased because of their reduced weight, assembly simplification and excellent specific strength and stiffness. The multiple possibilities of their manufacturing allow today to integrate within a single structure multiple functions: design, mechanical strength, multi-material...These structures, by their geometric and structural complexity (anisotropy, attenuation and scattering noise), do not always allow the application of conventional ultrasound real-time methods. In this communication, the problem related to anisotropy is treated in a first part with an analysis of the influence of materials properties on the conventional array imaging methods. In the second part, anisotropy is taken into account in the Total Focusing Method (TFM) to improve the image quality in carbon fiber composite plates

Restoration image degraded by a blurred variable in the field

Various methods of deconvolution have been developed for several decades, notably in astronomy and microscopy. The extension of these techniques to the case of a spatially varied blur is currently an open problem. In this work, we consider a zone-invariant point spread function model to take into account blur variation in the image. Thus an algorithm has been used where the minimization of the criterion is performed in parallel on different areas of the image, while taking into account the estimates in the neighboring areas of the sub-images under consideration, so that the final solution is the minimum of the criterion where the blur is spatially varied