88 research outputs found
Creep behaviour and tensile response of adhesively bonded polyethylene joints: Single-Lap and Double-Strap
The static and time-dependent behaviours of adhesively bonded polyethylene
Double-Strap (DS) joints were investigated to assess the viability of this
joint configuration relative to the Single-Lap (SL) joints. Both experiments
and finite element simulations are conducted. First, we individually
characterise the tensile and creep behaviour of the adhesive and adherent
materials; an epoxy-based adhesive and polyethylene, respectively. This
information is used to develop suitable constitutive models that are then
implemented in the commercial finite element package ABAQUS by means of user
material subroutines, UMATs. The numerical models are used to design the creep
tests on the adhesive joints. Afterwards, an extensive experimental campaign is
conducted where we characterise the static and creep behaviour of two joint
configurations, SL and DS joints, and three selected values of the overlap
length. In regard to the static case, results reveal an increase in the failure
load with increasing overlap length, of up to 10% for an overlap length of 39
mm. Also, slightly better performance is observed for the SL joint
configuration. For the creep experiments, we show that the DS adhesive joint
configuration leads to much shorter elongations, relative to the SL joints.
These differences diminish with increasing overlap length but remain
substantial in all cases. In both joint configurations, the elongation
increases with decreasing overlap length. For instance, increasing the overlap
length to 39 mm led to a 50% and a 30% reduction in elongation for SL and DS
joints, respectively. Moreover, the numerical predictions show a good agreement
with the experiments. The stress redistribution is investigated and it is found
that the shear stress is highly sensitive to the testing time, with differences
being more noticeable for the DS joint system
Mode II fracture energy in the adhesive bonding of dissimilar substrates: carbon fibre composite to aluminium joints
The end-notched flexure (ENF) test calculates the value of mode II fracture energy in adhesive
bonding between the substrates of same nature. Traditional methods of calculating
fracture energy in the ENF test are not suitable in cases where the thickness of the adhesive
is non-negligible compared with adherent thicknesses. To address this issue, a specific
methodology for calculating mode II fracture energy has been proposed in this paper. To
illustrate the applicability of the proposed method, the fracture energy was calculated by
the ENF test for adhesive bonds between aluminium and a composite material, which considered
two different types of adhesive (epoxy and polyurethane) and various surface treatments.
The proposed calculation model provides higher values of fracture energy than
those obtained from the simplified models that consider the adhesive thickness to be zero,
supporting the conclusion that the calculation of mode II fracture energy for adhesives with
non-negligible thickness relative to their adherents should be based on mathematical models,
such as the method proposed in this paper, that incorporate the influence of this thickness
Primary resistance of HIV to antiretrovirals among individuals recently diagnosed at voluntary counselling and testing centres in the metropolitan region of Recife, Pernambuco
Determining the prevalence and type of antiretroviral (ARV) resistance among ARV-naïve individuals is important to assess the potential responses of these individuals to first-line regimens. The prevalence of primary resistance and the occurrence of recent infections among individuals with human immunodeficiency virus (HIV)/acquired immune deficiency syndrome (AIDS) were identified among recently diagnosed patients at five sexually transmitted disease/AIDS testing and counselling centres in the metropolitan region of Recife (RMR), Pernambuco, Brazil, between 2007-2009. One-hundred and eight samples were analysed using the Calypte® BED assay. Males predominated (56%), as did patients aged 31-50 years. Twenty-three percent presented evidence of a recent HIV infection. The median CD4+ T lymphocyte count was 408 cells/mm³ and the median viral load was 3.683 copies/mL. The prevalence of primary resistance was 4.6% (confidence interval 95% = 1-8.2%) based on criteria that excluded common polymorphisms in accordance with the surveillance drug resistance mutation criteria. The prevalence of resistance to non-nucleoside reverse transcriptase, nucleoside/nucleotide reverse transcriptase and protease inhibitors were 3.8%, 1.5% and 0.8%, respectively. Fifty-seven percent of strains were from clade B, 37.7% were clade F and 3.1% were clade C; there were no statistically significant differences with respect to resistance between clades. Recent infection tended to be more common in men (p = 0.06) and in municipalities in the south of the RMR (Jaboatão dos Guararapes and Cabo de Santo Agostinho) (p = 0.046). The high prevalence of recent infection and the high prevalence of non-B strains in this poor Brazilian region merit further attention.Laboratório Central de Saúde Pública de Pernambuco Setor de VirologiaUniversidade Federal de Pernambuco Programa de Pós-Graduação em Medicina TropicalFiocruz Centro de Pesquisa Aggeu MagalhãesCentro de Testagem e Aconselhamento Herbert de SouzaUniversidade Federal de São Paulo (UNIFESP) Laboratório de RetrovirologiaUNIFESP, Laboratório de RetrovirologiaSciEL
Biased-corrected richness estimates for the Amazonian tree flora
Amazonian forests are extraordinarily diverse, but the estimated species richness is very much debated. Here, we apply an ensemble of parametric estimators and a novel technique that includes conspecific spatial aggregation to an extended database of forest plots with up-to-date taxonomy. We show that the species abundance distribution of Amazonia is best approximated by a logseries with aggregated individuals, where aggregation increases with rarity. By averaging several methods to estimate total richness, we confirm that over 15,000 tree species are expected to occur in Amazonia. We also show that using ten times the number of plots would result in an increase to just ~50% of those 15,000 estimated species. To get a more complete sample of all tree species, rigorous field campaigns may be needed but the number of trees in Amazonia will remain an estimate for years to come
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