•The main failure mechanism that appears in the composite panels is delamination.•Most of the panels exhibit no-delaminated or almost full delaminated area.•A dimensionless variable that describes ...the influence of parameters is presented.
This work analyses the behaviour of carbon/epoxy unidirectional laminates subjected to high velocity impacts of ice spheres. To this end, ice projectiles were launched against composite laminates in a wide range of velocities (50 − 250 m/s). Two different ice diameters (40 and 50 mm) and two laminate thicknesses (4 and 6 mm) were considered. The internal damage was measured using both destructive and non-destructive techniques, which allow an accurate quantification of the delaminated area. Finally the influence of the different parameters considered on the damage of the laminate is analysed by means of a dimensionless variable.
The mechanical performance of composite materials under impact phenomena is of interest for several industries. Although the effect of the strain rate on composites significantly affects the ...behaviour of these materials, most studies describe the mechanical behaviour of CFRP laminates neglecting the strain rate dependence. This work presents a new constitutive model to numerically implement the change of in-plane properties of an plain weave CFRP (AGP193) over a wide range of strain rates (up to 500 s−1). Open hole compression tests are used to validate the model under quasi-static and dynamic loading. The importance of implementing the influence of strain rate on mechanical properties is illustrated by the maximum strength plot and the stress–strain history, both of which would be underestimated without the inclusion of strain rate in the model. The strain rates at the edge of the hole greatly exceed the average values in the sample, leading to an underestimation of the apparent strength up to 100% if the strain rate effect is not taken into account.
Hydrodynamic ram (HRAM) is a phenomenon that occurs when a high-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. It 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. For the present work, water-filled aluminium square tubes (6063-T5) were subjected to impact by steel spherical projectiles (12.5
mm diameter) at impact velocities of 600–900
m/s. The aluminium tubes were filled at different volumes to study how an air layer inside the tank might influence the impact behaviour. The test boxes were instrumented with five strain gauges and two pressure transducers. The formation process of the cavity was recorded with a high-speed camera. This work presents the results of these tests.
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
In this work, the effect of high velocity impacts on carbon/epoxy tape quasi-isotropic laminates is studied. Experimental test were carried out at two different impact angles and in a wide range of ...velocities (from 80 to 490m/s). Both parameters, the residual velocity and the damaged area, are used to evaluate the effect of the kinetic energy of the projectile on the laminate response. In addition it has been proposed a simplified analytical model which allows to identify the different energy absorbtion mechanisms and predict the residual velocity of the projectile. Finally the energy absorbed by the laminate during the impact is studied.
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.
This research connects the mechanical and dielectric responses of three samples of hybrid polymer films composed of iron oxide nanoparticles and polyvinyl butyral (PVB) matrices with different ...average molecular weight. The mechanical responses were analyzed by dynamic mechanical analysis and the electrical responses by dynamic dielectric analysis, and they were interpreted by two fractional models, the Mechanical and the Dielectric Fractional Model. Correlation between mechanical and dielectric responses was determined for hybrid films. The comparison between fractional model parameters reveals that PVB matrix, with different average molecular weight, combined with the same nominal concentration of Fe-ions precursor, produces higher molecular mobility when average molecular weight is higher, and for the three samples, studied molecular mobility is higher for the dielectric manifestation of
α
-relaxation than the mechanic response. These results contribute in an important way to a better understanding of the molecular mobility of these materials where the possible applications require a certain compromise between the mechanical and electrical properties.
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.
In recent years, vulnerability against high-velocity impact loads has become an increasingly critical issue in the design of composite aerospace structures. The effects of Hydrodynamic Ram (HRAM), a ...phenomenon that occurs when a high-energy object penetrates a fluid-filled container, are of particular concern in the design of wing fuel tanks for aircraft because it has been identified as one of the important factors in aircraft vulnerability. 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. For the present work, water-filled CFRP square tubes were subjected to an impact of steel spherical projectiles (12.5
mm diameter) at impact velocities of 600–900
m/s. The CFRP tubes were filled to different volumes to examine how volume might influence the tank behavior. The composite test boxes were instrumented with six strain gauges and two pressure transducers, and the formation process of the cavity was recorded using a high-speed camera. The damage produced in the tubes was then analyzed, and differences were found according to the testing conditions. This work presents the results of these tests.
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