Subcritical crack growth in fibrous materials

We present experiments on the slow growth of a single crack in a fax paper sheet submitted to a constant force $F$. We find that statistically averaged crack growth curves can be described by only two parameters : the mean rupture time $\tau$ and a characteristic growth length $\zeta$. We propose a model based on a thermally activated rupture process that takes into account the microstructure of cellulose fibers. The model is able to reproduce the shape of the growth curve, the dependence of $\zeta$ on $F$ as well as the effect of temperature on the rupture time $\tau$. We find that the length scale at which rupture occurs in this model is consistently close to the diameter of cellulose microfibrils

Beyond the personal–anonymous divide: agency relations in powers of attorney in France in the eighteenth and nineteenth centuries

Powers of attorney are often interpreted as evidence of trust among the parties involved. We build a novel dataset of notarized powers of attorney, capturing a wide variety of agency relationships in four large French commercial cities in the eighteenth and nineteenth centuries, to test hypotheses on the relational basis of economic relationships. We find little support for the idea of a radical shift from personal to anonymous relationships during our period. Our results point to more nuanced transformations. The preference for proxies in the same occupation as the principal somewhat declined, while professional proxies emerged and principals used relational chains, especially involving notaries, to find proxies.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151849/1/ehr12784_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151849/2/ehr12784.pd

Acoustic emission potentialities for characterization of Mullins effect in natural rubber materials filled with carbon black

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Tensile Deformation and Cracking Sequence of Foamed AlSi10 with Skin

5th Biennial International Conference on Porous Metals and Metallic Foams (MetFoam 2007), Montreal, CANADA, SEP 05-07, 2007International audience28 mm thick panels of cellular AlSi10 were produced by powder compact foaming. Tensile specimens machined from these panels are tested with the original skin on both sides of the samples. The density distribution determined by medical X-ray tomography is transformed into domains of constant densities. The tensile straining of that multiphase continuum is simulated using the finite difference method. The input data for the stiffness and strain hardening are scaled to the domains' densities for the skin and the core of the panel. The stiffness increases slightly with initial straining. Crack initiation is recorded by acoustic emission, while strain hardening continues until complete fracture of a skin. The sequence of crack growth is predicted by the simulation

A Multi-Channel Setup to Study Fractures in Scintillators

International audienceTo investigate fractoluminescence in scintillating crystals used for particle detection, we have developed a multi-channel setup built around samples of double-cleavage drilled compression (DCDC) geometry in a controllable atmosphere. The setup allows the continuous digitization over hours of various parameters, including the applied load, and the compressive strain of the sample, as well as the acoustic emission. Emitted visible light is recorded with nanosecond resolution, and crack propagation is monitored using infrared lighting and camera. An example of application to $\text{B}{{\text{i}}_{4}}\text{G}{{\text{e}}_{3}}{{\text{O}}_{12}}$ (BGO) is provided