The segmental dynamics of amorphous poly(ethylene-vinyl acetate) copolymers (from PVAc to EVA50) were studied. In that sample set with similar backbone stiffness and different amount of dipoles, the ...dynamic glass transition was investigated by Modulated Temperature Differential Scanning Calorimetry and Broadband Dielectric Spectroscopy measurements. A decrease of the cooperativity length scale was obtained with the vinyl acetate (VAc) content decreasing. On the other hand, there was no modification of the temperature dependence of the relaxation time. Thus, the fragility value is quite constant whatever the VAc content. These results show that fragility and cooperativity have two different origins. An extrapolation to nonconstrained polyethylene amorphous phase was proposed and new glass transition temperature and fragility values were determined.
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•Amorphous phase mobility is studied for poly(ethylene-vinyl acetate) copolymers.•Fragility is constant from PVAc to EVA50 while cooperativity length decreases.•New extrapolated Tg and fragility values are proposed for PE.•Fragility and cooperativity are not governed by the same macromolecular properties.
In this paper a numerical analysis of the influence of strain rate in the response of carbon/epoxy woven composites is carried out. Unit cell models at two different length scales have been ...developed, in order to simulate the behaviour of such composites. An anisotropic plasticity with different hardening rules under different stress states is proposed for the carbon fibre yarns. Results show reasonable variations of the composite strengths under dynamic loads.
The effect of the open hole on the behaviour of carbon fibre reinforced polymer composites (CFRP) under compressive dynamic loading was investigated. To this end, two different set-ups (quasi-static ...and dynamic) for compression loading were developed. The un-notched plain woven CFRP (AS4 fibres and 8552 matrix) studied in this work was characterized in terms of apparent strength at different off-axis angles at compression loading. The maximum stress criterion was found to be the model which better represents the transverse-shear failure points of the woven composite. Later the effect of the open hole in similar samples were studied, concluding that the hole effect has more impact on the strength for samples with the fibre align with the load. A modification of the Lekhnitskii theory has been proposed in order to take into account the non-linearity of the material and to unveil its role in open hole specimens.
Microorganisms play a key role in the carbon (C) cycle through soil organic matter (SOM). The rate of SOM mineralization, the influence of abiotic factors on this rate and the potential behaviour of ...SOM are of particular interest in the northern Antarctic Peninsula and offshore islands. This is one of the most rapidly warming regions on Earth with numerous ice-free areas, some with abundant wildlife and with the greatest known soil organic carbon (SOC) storage in Antarctica. The latter implies extended Antarctic summer conditions promote increased terrestrial plant growth and soil microbial activity (SMA). SMA, determined by respirometry, is a measure of ecosystem function, and depends on microclimatic conditions and soil environmental properties. SMA and the effect of abiotic variables have been analysed in locations with different soil types, on Cierva Point (Antarctic Peninsula), Deception Island and Fildes Peninsula (King George Island). Soil microbial biomass carbon (SMBC) ranged from 5.66 to 196.6 mg SMBC kg−1and basal respiration (BR) from 2.86 to 160.67 mg CO2 kg−1 d−1. SMBC and BR values were higher in Cierva Point, followed by Fildes Peninsula and Deception Island, showing the same trend of SOM abundance. Except for Cierva Point, low nitrogen, phosphorus and C concentrations were observed. SMBC/total organic carbon (TOC) levels indicated that SOC was recalcitrant and SOM content was closely related to the extent of vegetation cover observed in situ. High metabolic quotient values obtained at Cierva Point and Deception Island (median values 7.27 and 6.53 mg C-CO2 g SMBC−1 h−1) and low SMBC/TOC in Cierva Point suggest a poor efficiency of the microbial populations in the consumption of the SOC. High SMBC/TOC values obtained in Deception Island indicates that SMBC may influence SOM stabilization. Mineralization rates were very low (negligible values to 1.44%) and sites with the lowest values had the highest SOM.
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•Antarctic Peninsula (AP) region is one of the most rapidly warming regions on Earth•Soil organic carbon in Maritime Antarctic ice-free areas is scarce or recalcitrant.•Soil microbial biomass carbon and basal respirometry values are low.•Due to nutrient scarcity and carbon source recalcitrance qCO2 values are high.•Greatest soil organic carbon storage in Antarctica is within the AP region
Sternal surgical wound infection (SSWI) in cardiac surgery is associated with increased morbidity. We investigated the incidence of SSWI, the main germs implicated and predictors of SSWI. Prospective ...study including patients undergoing full median sternotomy between January 2017 and December 2019. Patients were followed‐up for 3 months after hospital discharge. All sternal wound infections up to 90 days after discharge were considered SSWI. 1004 patients were included. During follow‐up, 68 (6.8%) patients presented SSWI. Patients with SSWI had a higher incidence of postoperative renal failure (29.4% vs 17.1%, P = .007), a higher incidence of early postoperative reoperation for non‐infectious causes (42.6% vs 9.1%, P < .001), longer ICU stay (3 2–9 days vs 2 2–4 days, P = .006), and longer hospital stay (24.5 14.8–38.3 days vs 10 7–18 days, P < .001). Gram‐positive germs were presented in 49% of the cultures, and gram‐negative bacteria in 35%. Early reoperation for non‐infectious causes (OR 4.90, 95% CI 1.03–23.7), and a longer ICU stay (OR 1.37 95% CI 1.10–1.72) were independent predictors of SSWI. SSWI is rare but leads to more postoperative complications. The need for early reoperation because of non‐infectious cause and a longer ICU stay were independently associated with SSWI.
Composite laminates are subjected to cryogenic temperatures in exposed aircraft structures during flight or in cryogenic tanks. The combination of cryogenic temperatures and high velocity impacts ...represents a threat to their integrity. This work investigates the behavior of carbon–epoxy laminates under high velocity impacts (from 70 to 500 m/s) at room and cryogenic (-150 °C) temperatures and under two different plate orientations with respect to the projectile direction. The damage pattern of impacted specimens at low temperature, revealed by C-scan and X-ray tomography, exhibits a higher density of fiber breaks and shear matrix cracks which do not translate to a larger projected damaged area. The experimental analysis through interlaminar shear strength tests and the calculation of ply thermal stresses exclude the association of this particular pattern to damage mechanisms induced during the temperature decrease.
Hydrodynamic Ram (HRAM) is a phenomenon that occurs when a high-kinetic energy object penetrates a fluid-filled container. The projectile transfers its momentum and kinetic energy through the fluid ...to the surrounding structure, increasing the risk of catastrophic failure and excessive structural damage. This is of particular concern in the design of wing fuel tanks for aircraft since it has been identified as one of the important factors in aircraft vulnerability. Usually the HRAM phenomenon is analyzed considering completely filled tanks, but its effect on partially filled containers should also be taken into account due to the fact that tanks use to be impacted under these conditions. In the present paper, the commercial finite element code LS-DYNA has been used to simulate an HRAM event created by a steel spherical projectile impacting a partially water-filled aluminium square tube. The ALE formulation is employed to reproduce the event. Experimental tests which indicate the pressure at different points of the fluid, displacement of the walls and cavity evolution for different impact velocities, are compared with the numerical results in order to assess the validity and accuracy of the ALE technique in reproducing such a complex phenomenon.
Carbon fiber reinforced epoxy laminates are widely used in the design and manufacturing of aeronautical structures. Among different manufacturing procedures, resin transfer moulding (RTM) has emerged ...as a cost-effective alternative to prepregs manufactured in an autoclave. However, the laminate obtained by RTM exhibits approximately 20% lower mechanical properties. To address this limitation, the addition of nanoparticles has been suggested as a solution. In this study, graphene particles were obtained by in-situ mechanical exfoliation in the resin and directly injected into the mould. The major achievement of this study is that the entire manufacturing process was performed at an industrial scale using the same tooling used to produce aircraft structures. Laminates with varying concentrations and dispersion times were manufactured using RTM and subjected to compression after impact tests, resulting in a 7.6% improvement. Furthermore, analysis through SEM techniques revealed the role of graphene in the bear capacity of the laminates. Finally, to demonstrate the feasibility of the proposed methodology in an industrial environment, a real aircraft structure was manufactured with graphene, without any modifications to the actual industrial process.
Differences in meat quality characteristics between the four Canada beef quality grades (Canada Prime, AAA, AA, and A) at days 4 and 18 post mortem were investigated using 48 (n = 12/grade) bovine M. ...longissimus thoracis (LT, rib eye). There was no difference in intramuscular fat content between Canada A and AA LT, and Canada AA LT had a higher mean Warner-Bratzler shear force (WBSF) than LT from all other grades (P = 0.0009) at day 18 post mortem. Canada Prime muscles were lighter and yellower than muscle from all other grades, and their increased lightness persisted with ageing. Mean cooking loss was lowest in Canada Prime LT and correlated with intramuscular fat content (r = −0.41 and − 0.29, days 4 and 18, respectively). Results confirmed differences in cooked product toughness can exist between the grades, with the potential for reduced tenderization in Canada AA LT.
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