Spontaneous imbibition experiment in newspaper sheets.

We study the behavior of an ink-paper interface in a spontaneous imbibition experiment as a function of time and paper orientation. To characterize the interface roughness the growth beta and Hurst H exponents (calculated using the root mean square interface width W) and the H{q} scaling exponent (calculated using the qth order height-height correlation function) are used. Our results indicate that the values of H and H{q} depend on the orientation of the paper sheets, while beta does not, and that the interface exhibits a multiaffine character during all its evolution.

Experimental realization of the fuse model of crack formation.

In this work, we present an experimental investigation of the fuse model. Our main goal was to study the influence of the disorder on the fracture process. The experimental apparatus used consisted of an L x L square lattice with fuses placed on each bond of the lattice. Two types of materials were used as fuses: copper and steel wool wires. The lattice composed only of copper wires varied from a weakly disordered system to a strongly disordered one. The lattice formed only by steel wool wires corresponded to a strongly disordered one. The experimental procedure consisted of applying a potential difference V to the lattice and measuring the respective current I. The characteristic function I(V) obtained was investigated in order to find the scaling law dependence of the voltage and the current on the system size L when the disorder was changed. Our results show that the scaling laws are only verified for the disordered regime.

Anisotropy in rupture lines of paper sheets.

We have experimentally investigated the fracture process in paper samples submitted to a uniaxial force. Five types of paper sheets (newsprint, towel, sulfite, silk, and couche papers) were fractured along two orthogonal orientations. In order to characterize the rupture lines of the paper sheets we utilized the Hurst exponent. Our results indicate a dependence of the Hurst exponent on the orientation of the paper sheets for samples of newsprint and, probably, towel and silk papers. For the other types of paper the Hurst exponent does not depend on the direction of crack propagation.

Roughness of CdTe thin films grown on glass by hot wall epitaxy.

Cadmium telluride films were grown on glass substrates using the hot wall epitaxy (HWE) technique. The samples were polycrystalline with a preferential (111) orientation. Scanning electron micrographs reveal a grain size between 0.1 and 0.5 µm. The surface morphology of the samples was studied by measuring the roughness profile using a stylus profiler. The roughness as a function of growth time and scale size were investigated to determine the growth and roughness exponents, ß and α, respectively. From the results we can conclude that the growth surface has a self-affine character with a roughness exponent α equal to 0.69 ± 0.03 and almost independent of growth time. The growth exponent ß was equal to 0.38 ± 0.06. These values agree with that determined previously for CdTe(111) films grown on GaAs(100).

Fracture toughness in fibrous materials.

In the present paper, a fiber bundle model in (1+1) dimensions that simulates the rupture process of a fibrous material pulled by an uniaxial force F is analyzed. In this model the load of a broken fiber is shifted in equal portions onto the nearest unbroken fibers. The force-displacement diagram is obtained for several traction velocities v and temperatures t. Also, it is shown how the fracture toughness K(c) changes with the traction velocity v and with the temperature t. In this paper it is shown that the rupture process is strongly dependent on temperature t and on velocity v.

Failure regimes in (1+1) dimensions in fibrous materials.

In this paper, we introduce a model for fracture in fibrous materials that takes into account the rupture height of the fibers, in contrast with previous models. Thus, we obtain the profile of the fracture and calculate its roughness, defined as the variance around the mean height. We investigate the relationship between the fracture roughness and the fracture toughness.