•Design of a particular specimen: hybrid composite/metal assembled by bonding.•Calculation of the compliance and energy release rates of this specimen.•Analytical solution (of compliance and energy ...release rate GI) by changing Kanninen’s theory (elastic beam foundation).•Fatigue law calculation using the compliance for the crack measurement for this type of specimen.
Composite structures assembled by bonding are widely found in different areas of high performance applications such as aeronautics. The energy release rate (G) is mainly used to predict fracture. However, in some special cases, this parameter serves to investigate the propagation, the rate or the stability of a crack. The main issue resides in the calculation of this energy release rate because it strongly depends on the crack geometry and the loading mode. An energetic criterion based on the compliance method was chosen, assuming that the release of potential energy is transformed in surface energy due to the creation of wider cracks (new surfaces). To investigate the properties of an asymmetrical composite/metal bonded structure, modified Double Cantilever Beam (DCB) specimens were tested in mode I. The fracture toughness and the fatigue behavior were evaluated by experimental means, finite elements modeling (FEM) and linear elastic fracture mechanics (LEFM) theories. Timoshenko and Kanninen theories, experimental and FEM results were compared on an R-curve. A modified Kanninen theory was then proposed, to take into account the specific assembly design. As a result, the Paris’ law was built for that situation. The objective of this work was to adapt and validate a non-standard fatigue compliance methodology which calculates the energy release rates in mode I, for asymmetrical bonded structures.
In aeronautics the weight of a structure is important and its strength is crucial. Composite structures are more and more used for their lightness and their high performance in fatigue solicitations. ...Nevertheless, metallic materials remain essential for some functions, which sometimes lead to the creation of hybrid structures, achievable with the use of bonding techniques. The bonding of metallic materials over composite, requires accurate knowledge of bonding properties in static and fatigue, including the capability to perform a residual strength assessment in case of local damage such as a discrete disbond. In order to test the fracture mechanics properties of the adhesive, modified specimens such as the Double Cantilever Beam (DCB) were used. Because of the materials' stiffness difference, they were specially designed to produce a pure mode I in the crack plane. The strain energy release rate, G, was chosen as the governing fracture parameter. The classic way to test specimens in fatigue is controlling the displacement (or the force) of the actuator. The new approach proposed in this paper, consists in controlling the variation of energy (ΔG) during the fatigue tests, thus a user-specified constant value of ΔG will be applied on the specimens. The purpose of this work is to compare the classical Paris’ law, obtained by using a controlled force feedback, and the fatigue law obtained with an energy control. The advantages of the new approach will be described.
This article concerns the modelling of post-impact damage propagation in thin carbon/epoxy and glass/epoxy hybrid woven composite laminates loaded in fatigue tension. The modelling is based on the ...semi-continuous approach implemented into the explicit finite element code RADIOSS. The bundles are modelled with rod elements and the resin is modeled with a specific damageable shell element, used to stabilize the bundles. This approach is extended to post-impact fatigue tensile loadings. Resin damaging is implemented for the shell elements through two fatigue laws Yxy-Nresina and Yxy-Nresinb based on thermodynamical forces and identified through the experimental results obtained in Part I. Fiber breakage is introduced for rod elements through Basquin curves based on tensile and compressive strains. The damage accumulation is taken into account by a Miner’s rule. For several impact energies and amplitude of fatigue loading, the modelling well correlates the experimental results in terms of damage propagation scenario, path and speed.
This article concerns the experimental study of post-impact damage propagation in two thin carbon/epoxy and glass/epoxy hybrid woven composite laminates loaded in fatigue tension. Low velocity normal ...drop weight impact tests are first performed. Post-impact fatigue tensile tests are then carried out. They are controlled in displacement. The damage propagation is monitored by RX Tomography and Digital Image Correlation. The influence of the impact energy and the displacement level variation on the post-impact damage propagation is studied. Post-impact fatigue tests are also conducted on thin carbon/epoxy and glass/epoxy mono-material woven composite laminates in order to understand the phenomenons which occur in the hybrid laminates. Two different behaviours depending on the hybrid configuration are obtained. The post-impact damage propagation in fatigue is mainly influenced by the carbon plies orientations. Levels of loading and impact energies have an influence on the initiation of the damage propagation and on the speed. They have also an influence of the damage propagation scenario when delamination occurs. The influence of the stacking sequence is also studied. The change of the carbon plies position in the hybrid laminate leads to a change of the post-impact fatigue behaviour.
A role for melanocortin signaling in the regulation of body weight in humans has been clearly established. Haploinsufficiency of the type 4 melanocortin receptor is associated with early-onset ...obesity, implying that this receptor provides an important tonic inhibition of weight gain. Agouti-related peptide (AGRP) is an endogenous antagonist of melanocortin signaling. Therefore, loss of AGRP function could lead to the expression of a lean phenotype. We investigated the potential role of AGRP in human weight regulation by examining the association between the Ala67Thr AGRP polymorphism and indices of body composition. Significant associations were found between homozygosity for this mutation (n = 8) and body composition phenotype in 874 subjects of the Quebec family study (QFS). By PCR-RFLP analysis, we have identified eight individuals who are homozygous for the 67Thr variant allele within the QFS population, where none were observed in SAFHS. The eight QFS homozygote individuals have lower weight (-16%; P = 0.02), body mass index (-17%; P = 0.01), fat free mass (-9%; P = 0.002), fat mass (FM) (-20%; P = 0.04), and leptin (-20%; P = 0.02) when compared to those carrying at least one 67Ala allele. Individuals homozygous for the 67Thr allele had a BMI that was either at or slightly below an ideal range for their age. Thus, the Ala67Thr AGRP polymorphism is associated with lower body weight in humans, with the largest effect being observed on body FM. We did not observe any difference in the stability or cellular distribution of the mutant protein in a heterologous expression system, thus the mechanism of this effect requires further investigation.
The melanocortin system includes five receptors (MC1R to MC5R), and mouse and human MC4R has been shown to be involved in the regulation of feeding, and mouse MC3R in body composition. To verify a ...possible similar effect of MC3R in humans, we analyzed one insertion and one single nucleotide polymorphism by restriction fragment length polymorphisms (RFLP), and a microsatellite (D20S32e) in relation to body composition and glucose metabolism.
Eight hundred twelve subjects of the Québec Family Study (QFS) cohort were analyzed for body composition, food intake, and energy metabolism phenotypes. Southern Blot with the complete MC3R cDNA was used to detect a new +2138InsCAGACC variant by Pst1 restriction. PCR-RFLP with BsaJ1 was used to type amino acid polymorphism V81I arising from a G241A nucleotide change. PCR and automatic DNA sequencers were used for the analysis of the TG dinucleotide repeat D20S32e located between -1933/-1892 of MC3R. In a covariance analysis among genotypes, phenotypes were adjusted for age and sex as covariates. Food intake and energy metabolism phenotypes were also adjusted for body mass index (BMI), and leptin and abdominal fat, as assessed by a computed tomography scan, for fatness using six skinfold thicknesses.
An association between the +2138InsCAGACC MC3R polymorphism was observed with fat mass (FM), percent body fat (%FAT), and total abdominal fat (ATF). Homozygote subjects for the +2138 insertion variant allele in normal weight (BMI < 25 kg/m(2)) and overweight (25 < or = BMI < 30 kg/m(2)) subjects showed a similar level of fatness despite the overall difference in BMI. In normal weight, homozygotes for the insertion allele showed higher mean values than heterozygotes and homozygotes for wild-type allele without insertion (%FAT: 24.0 +/- 1.1 versus 19.3 +/- 0.9 and 20.5 +/- 0.8, p = 0.0005; FM: 15.7 +/- 0.9 kg versus 11.7 +/- 0.7 kg and 12.6 +/- 0.6 kg, p = 0.0003). In contrast, overweight subjects homozygote for the variant allele showed lower mean values (%FAT: 27.0 +/- 1.2 versus 31.4 +/- 0.8 and 30.9 +/- 0.7, p = 0.002; FM: 18.3 +/- 1.0 kg versus 22.8 +/- 0.8 kg and 22.0 +/- 0.6 kg, p = 0.0001). This resulted in a similar level of body fat between both BMI groups for subjects homozygote for the insertion allele versus wild-type allele carriers (%FAT: +/-2-3% versus +/-10-12%; FM: +/-2 kg versus +/-9-11 kg). In obese subjects (BMI > or = 30 kg/m(2) ), a lower level of ATF was seen (-15%, p = 0.002). Other polymorphisms and phenotypes tested showed no association.
A new 12138InsCAGACC MC3R polymorphism is associated with the level of adiposity and with body fat partitioning in interaction with corpulence in humans.
This article concerns the study of post-impact damage propagation in two thin hybrid woven composite laminates loaded in tension. Low velocity normal drop weight impact tests are first performed. ...Post-impact quasi-static tensile tests are then carried out and monitored by Digital Image Correlation. The influence of the impact energy variation on the fracture surfaces and the residual strength is studied. In order o have a better understanding of the mechanisms involved into the hybrid laminates, four monomaterial sample configurations are also tested. When the damage after impact is barely visible, the sample behaves as a non-impacted sample. When the damage is visible, it propagates whatever the impact energy. The damage grows in the direction perpendicular to the loading for all the monomaterial laminates while two different damage scenarios are observed for the hybrid laminates. The residual strength evolves in three steps depending on the impact energy: first a very low decrease, then an important drop and finally a plateau.
UCP3 is a mitochondrial membrane transporter that is postulated to uncouple oxidative phosphorylation from ATP synthesis producing heat instead of ATP. Human UCP3 is mainly expressed in skeletal ...muscle, which plays an important role in energy homeostasis and substrate oxidation. Therefore, UCP3 is a good candidate gene for obesity.
We analyzed, among 734 subjects from the Québec Family Study, a new GA repeat microsatellite located in intervening sequence (IVS) 6 (GAIVS6) in UCP3 gene, and two already described restriction fragment length polymorphisms (RFLP) Y210Y(C-->T) and V102I(G-->A). Covariance analysis across genotypes for different adiposity, resting energy expenditure, and glucose metabolism variables was undertaken with age and sex, plus body fat and body mass for nonadiposity phenotypes, as covariates.
We found strong associations between GAIVS6 and body mass index (p = 0.0001), fat mass (p = 0.0005), percentage body fat (p = 0.0004), the sum of six skinfold thickness (p = 0.0001), and leptin level (p = 0.0001). Homozygote for the GAIVS6 240 bp alleles (15% frequency in QFS) showed higher adiposity than subjects with the GAIVS6 238 bp allele (70% in QFS). The exons, the 5' untranslated region (UTR), and the exon-intron junctions of UCP3 gene from subjects homozygote for either GAIVS6 238 bp or 240 bp alleles were sequenced in search for mutations. Variants 5'UTR-55C-->T and Y210Y(C-->T) were detected, whereas IVS4-36C-->T was uncovered, but no new exonic or splice junction mutation was observed. RFLP Y210Y(C-->T) was not associated to adiposity in QFS; V1021(G-->A) showed no variation.
Our results suggest that some alleles of UCP3 are involved in the etiology of human obesity.
This article concerns the modelling of post-impact damage propagation in thin woven composite laminates. Simulations of low velocity impacts and post-impact quasi-static tension are performed on ...single-material and hybrid laminates. The modelling is based on the semi-continuous approach implemented into the explicit finite element code RADIOSS. The bundles are modelled with rod elements and a specific damageable shell element is used to stabilize this truss structure. Improvements are brought with the introduction of a compressive failure criterion for the rod elements and the development of a pseudo-plastic law with damaging for in in-plane shear. The results provided by the modelling well correlates the experimental observations in terms of damage propagation and load-displacement curves for all the configurations studied.
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