Crack propagation in brittle heterogeneous solids: Material disorder and crack dynamics

Crack propagation in a linear elastic material with weakly inhomogeneous failure properties is analyzed. An equation of motion for the crack is derived in the limit of slow velocity. Predictions of this equation on both the average crack growth velocity and its fluctuations are compared with recent experimental results performed on brittle heterogeneous materials (Ponson in Phys Rev Lett, 103, 055501; Måløy et al. in Phys Rev Lett, 96, 045501). They are found to reproduce quantitatively the main features of crack propagation in disordered systems. This theoretical framework provides new tools to predict life time and fracture energy of materials from their properties at the micro-scale.     

Timed verification of the generic architecture of a memory circuit using parametric timed automata

Using a variant of Clariso-Cortadella’s parametric method for verifying asynchronous circuits, we analyse some crucial timing behaviors of the architecture of SPSMALL memory, a commercial product of STMicroelectronics. Using the model of parametric timed automata and model checker HYTECH, we formally derive a set of linear constraints that ensure the correctness of the response times of the memory. We are also able to infer the constraints characterizing the optimal setup timings of input signals. We have checked, for two different implementations of this architecture, that the values given by our model match remarkably with the values obtained by the designer through electrical simulation. Partially supported by project MEDEA+ Blueberries. A preliminary version appeared in the Proceedings of 4th International Conference on Formal Modelling and Analysis of Timed Systems (FORMATS’06), Sept. 2006.     

An orthotropic variant of the equilibrium gap method applied to the analysis of a biaxial test on a composite material

In this paper, it is proposed to apply the equilibrium gap method to orthotropic composite materials to retrieve damage laws from measured displacement fields. A finite difference implementation method is first proposed. A linear system is formed, for which the unknowns are piecewise constant orthotropic rigidities, while the measured displacements are input (known) data. In this example, a cruciform specimen is considered for biaxial test. It is shown that, by referring to FE computed displacement fields a prescribed contrast map can be identified. Corrupted artificial displacement fields obtained through non-linear simulations are also used. When considering shear damage, a procedure using estimated contrast maps to identify a damage law is validated. An experimental biaxial test on a 2.5 C/C composite is finally analysed following the proposed approach. For each unloading step, a contrast map for all moduli is obtained from full-field measurements. By assuming that the shear moduli contrasts result from a damage mechanism, one subsequently obtains damage maps, and therefore, a growth law. The results are first validated by comparing measured and FE reconstructed displacement fields, and by comparing the identified damage fields with post-processed ones.     

Mechanical behavior of entangled fibers and entangled cross-linked fibers during compression

Entangled fibrous materials have been manufactured from different fibers: metallic fibers, glass fibers, and carbon fibers. Specimens have been produced with and without cross-links between fibers. Cross-links have been achieved using epoxy spraying. The scope of this article is to analyze the mechanical behavior of these materials and to compare it with available models. The first part of this article deals with entangled fibrous materials without cross-link between fibers. Compression tests are detailed and test reproducibility is checked. In the second part, compression tests were performed on materials manufactured with cross-linked fibers. The specific mechanical behavior obtained is discussed.     

Effectiveness of rotatable sensor to improve image accuracy of ECT system

This paper presents a new design of rotatable sensor for ECT systems that can be mounted on a multi-phase flow installation. In order to attest how the performance of the sensor is affected by the rotatable frame, the effectiveness of the rotatable sensor is analyzed in terms of SNR (Signal-to-Noise Ratio) and image accuracy, which is dependent on the number of independent measurements, the image reconstruction strategy and the size of the mesh. The results confirm that with a sensor equipped with 16 electrodes, the optimum number of rotation steps is 3 in order to get the best compromise in terms of image accuracy and image reconstruction time. Results also show that this configuration achieves results similar to a classical sensor equipped with 32 electrodes.     

Carbon footprint as environmental performance indicator for the manufacturing industry

With the current focus on our climate change impacts, the embodied CO₂ emission or “Carbon footprint” is often used as an environmental performance indicator for our products or production activities. The ability of carbon footprint to represent other types of impact like human toxicity, and hence the overall environmental impact is investigated based on life cycle assessments of several materials of major relevance to manufacturing industries. The dependence of the carbon footprint on the assumed scenarios for generation of thermal and electrical energy in the life cycle of the materials is analyzed, and the appropriateness of carbon footprint as an overall indicator of the environmental performance is discussed.     

Uptake of Tritiated Liquids by Individual Breakfast Cereal Flakes

ABSTRACT: Surface liquid adhesion (SLA) and liquid absorption (LA) of tritiated liquids, including water and skim, low-fat, whole, and fat-enriched milks, by cornflakes (CF) and frosted flakes (FF) were determined by scintillation counting using water-[³H] at 0.5 μCi/mL. SLA or the liquid adhering to individual flakes after a short immersion period was the same for CF and FF in the case of water (approximately 0.011 μL mm⁻² of flake) but were always higher for CF than for FF and increased as the fat content in milks augmented. LA of individual flakes, followed for 300 s of soaking, increased with time and was always higher for CF than for FF (for the same liquid), however, data did not follow a regular pattern. Flakes showed quite compact outer surfaces and an internal porous matrix composed of air cells of various sizes separated by dense walls of different thicknesses. This heterogeneous microstructure of individual flakes may be the cause of the lack of a simple kinetics during the soaking process. Previous results obtained by soaking a mass of flakes overestimated the uptake of fluid by individual because they included the liquid occluded between the flakes.     

A dynamical framework to understand performance trade-offs and interference in dual tasks.

This study demonstrated that the dynamic pattern approach may reconcile resource and outcome conflict theories to explain performance in dual tasks. Participants performed a bimanual coordination task and a reaction time task with different conditions of attentional priority. Results showed a trade-off between pattern variability and reaction time when priority was given to the coordination task. Such a trade-off was indicative of resource allocation. An analysis of perturbation in the bimanual coordination revealed interference, a reputed sign of outcome conflict. Moreover, interference diminished substantially when priority was given to the bimanual task. The coexistence of performance trade-off and outcome conflict suggests that these two phenomena are not mutually exclusive. Rather, both may follow from modifying the coupling between the limbs through attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ultrafast compound imaging for 2-D motion vector estimation: application to transient elastography

This paper describes a new technique for two-dimensional (2-D) imaging of the motion vector at a very high frame rate with ultrasound. Its potential is experimentally demonstrated for transient elastography. But, beyond this application, it also could be promising for color flow and reflectivity imaging. To date, only axial displacements induced in human tissues by low-frequency vibrators were measured during transient elastography. The proposed technique allows us to follow both axial and lateral displacements during the shear wave propagation and thus should improve Young's modulus image reconstruction. The process is a combination of several ideas well-known in ultrasonic imaging: ultra-fast imaging, multisynthetic aperture beamforming, 1-D speckle tracking, and compound imaging. Classical beamforming in the transmit mode is replaced here by a single plane wave insonification increasing the frame rate by at least a factor of 128. The beamforming is achieved only in the receive mode on two independent subapertures. Comparison of successive frames by a classical 1-D speckle tracking algorithm allows estimation of displacements along two different directions linked to the subapertures beams. The variance of the estimates is finally improved by tilting the emitting plane wave at each insonification, thus allowing reception of successive decorrelated speckle patterns.