43 research outputs found
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 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.Comment: 4 pages, 4 figures.eps, Revte
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 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 by 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 obtained was investigated in order to find the scaling law
dependence of the voltage and the current on the system size when the
disorder was changed. Our results show that the scaling laws are only verified
for the disordered regime.Comment: 4 pages, 8 figures.ep
Failure regime 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.Comment: 4 pages, 4 figures.eps, Revte
Bursts in a fiber bundle model with continuous damage
We study the constitutive behaviour, the damage process, and the properties
of bursts in the continuous damage fiber bundle model introduced recently.
Depending on its two parameters, the model provides various types of
constitutive behaviours including also macroscopic plasticity. Analytic results
are obtained to characterize the damage process along the plastic plateau under
strain controlled loading, furthermore, for stress controlled experiments we
develop a simulation technique and explore numerically the distribution of
bursts of fiber breaks assuming infinite range of interaction. Simulations
revealed that under certain conditions power law distribution of bursts arises
with an exponent significantly different from the mean field exponent 5/2. A
phase diagram of the model characterizing the possible burst distributions is
constructed.Comment: 9 pages, 11 figures, APS style, submitted for publicatio
Southern African Large Telescope Spectroscopy of BL Lacs for the CTA project
In the last two decades, very-high-energy gamma-ray astronomy has reached maturity: over 200 sources have been detected, both Galactic and extragalactic, by ground-based experiments. At present, Active Galactic Nuclei (AGN) make up about 40% of the more than 200 sources detected at very high energies with ground-based telescopes, the majority of which are blazars, i.e. their jets are closely aligned with the line of sight to Earth and three quarters of which are classified as high-frequency peaked BL Lac objects. One challenge to studies of the cosmological evolution of BL Lacs is the difficulty of obtaining redshifts from their nearly featureless, continuum-dominated spectra. It is expected that a significant fraction of the AGN to be detected with the future Cherenkov Telescope Array (CTA) observatory will have no spectroscopic redshifts, compromising the reliability of BL Lac population studies, particularly of their cosmic evolution. We started an effort in 2019 to measure the redshifts of a large fraction of the AGN that are likely to be detected with CTA, using the Southern African Large Telescope (SALT). In this contribution, we present two results from an on-going SALT program focused on the determination of BL Lac object redshifts that will be relevant for the CTA observatory
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