509 research outputs found
Sociocultural valuation of human impacts on marine ecosystems: The case of the NMPANS in Greece
No full textData and code files for replicating the results and findings from our published research paper "Sociocultural valuation of human impacts on marine ecosystems: The case of the National Marine Park of Alonissos in Greece" by Brodersen M., Tyllianakis E., Vassilopoulos A., Vassilopoulou V. published in the Journal of Environmental Economics and Polic
Sociocultural valuation of human impacts on marine ecosystems: The case of the NMPANS in Greece
No full textData and code files for replicating the results and findings from our published research paper "Sociocultural valuation of human impacts on marine ecosystems: The case of the National Marine Park of Alonissos in Greece" by Brodersen M., Tyllianakis E., Vassilopoulos A., Vassilopoulou V. published in the Journal of Environmental Economics and Polic
Welfare Effects of Food Miles Labels
No full textWe assessed the consumer welfare effects of two generic food miles labels: carbon dioxide (CO2) emission label and time and number of kilometres label. Using data from a choice experiment, our results generally suggest that a mandatory labeling policy for either type of label would have a positive welfare effect. However, a label informing consumers about the time and number of miles the food product has travelled provides greater positive welfare effects than a label informing consumers about the amount of CO2 emission
Welfare Effects of Food Miles Labels
No full textWe assessed the consumer welfare effects of two generic food miles labels: carbon dioxide (CO2) emission label and number of miles label. Using data from a choice experiment, our results generally suggest that a mandatory labeling policy for either type of label would have a positive welfare effect on both informed and uninformed consumers. However, a label informing consumers about the number of miles the food product has travelled provides greater positive welfare effects than a label informing consumers about the amount of CO2 emission
Gastrocnemius muscle specific force in boys and men
No full textThe aim of this study was to assess whether the in vivo specific force and architectural characteristics of the lateral gastrocnemius (GL) muscle of early pubescent boys (n = 11, age = 10.9 +/- 0.3 yr, Tanner stage 2) differed from those of adult men (n = 12, age = 25.3 +/- 4.4 yr). Plantarflexor torque was 55% lower in the boys (77.4 +/- 21.4 N x m) compared with the adults (175.6 +/- 31.7 N x m, P < 0.01). Physiological cross-sectional area (PCSA), determined in vivo using ultrasonography and MRI, was 52% smaller in the boys (P < 0.01). No difference was found in pennation angle, or in the ratio of fascicle length (L(f)) to muscle length between the boys and men. Moment arm length was 25% smaller in the boys (P < 0.01). Antagonist coactivation, assessed using surface EMG on the dorsiflexors, was not different between the boys and men (11.8 +/- 6.7% and 13.5 +/- 5.8%, respectively). Surprisingly, GL force normalized to PCSA (specific force) was significantly higher (21%) in the boys than in the men (13.1 +/- 2.0 vs. 15.9 +/- 2.7 N/cm(2), P < 0.05). This finding could not be explained by differences in moment arm length, muscle activation, or architecture, and other factors, such as tendinous characteristics and/or changes in moment arm length with contraction, may be held responsible. These observations warrant further investigation
INFLUENCE OF PRE-CURING STAGE IN ADDITIVE MANUFACTURING OF ADVANCED THERMOSETTING COMPOSITES
No full textThe arising of cure-related defects during manufacturing of thermosetting composites and their hardly predictable effect on mechanical performance is often cause for part rejection, which is detrimental for both cost and sustainability. Additive Manufacturing (AM) of continuous
fibre-reinforced thermosets is envisaged to bring significant benefits in terms of reducing temperature overshoot, and consequently residual stresses. The work investigates the influence of the introduction of a pre-curing phase upon the exothermic overshoot and the defects induced
during deposition of pre-cured tows (i.e. microbuckling). A Finite Element Analysis (FEA) addressing the cure simulation has been developed, and pre-cured specimens have been tested.
The findings point out that a pre-cure level between 20% and 30% reduces the temperature overshoot within the laminate by 90%, generating in-plane waviness with a severity that should not compromise its performance
Measurement of damage growth in ultrasonic spot welded joint
No full textUltrasonic spot welding is a joining technique for thermoplastic composites with great potential regarding processing speed and cost. To investigate the damage tolerance and possible inherent damage arresting behavior of multi-spot welded joints, a technique is necessary to measure damage growth in the joints under cyclic loading. Visual inspection is not possible because the damage is not located on the outside surface and conventional techniques such as C-scan are not practical during a fatigue test because the specimen would have to be removed from the setup. This paper details a methodology for quantifying damage growth rates in singlespot welded joints using surface strain measurements made by Digital Image Correlation. This represents the first step towards developing a methodology for quantifying damage progression behavior in complex multi-spot welded joints.Structural Integrity & CompositesAerospace Structures & Computational Mechanic
Identifying microstructural features in unidirectional composite tapes
No full textCarbon fibre-reinforced polymer composites (CFRPs) outperform most structural engineering materials in specific stiffness and/or specific strength, especially in their unidirectional configuration. Unidirectional composites can be found as individual structural elements in cables or pin-loaded straps; they are however most commonly found in the form of tapes, representing a semi-finished product for subsequent processing to laminates by tape laying, winding or press moulding. The outstanding properties of such composites are affected by its microstructure. It influences the structural performance and fatigue life when architected into thin ply composites [1]. The microstructure is also affected by processing conditions, respectively recursively affects processability as observed in the deconsolidation [2] or intimate contact formation [3] during laser assisted tape laying. This work presents a novel approach to identify microstructural features. This is achieved by Voronoi tessellation-based evaluation of the fibre volume content on cross-sectional micrographs, with consideration of the matrix boundary. The method [4] is shown to be robust and is suitable to be automated and has the potential to be expanded into 3d imaging techniques [5]. It further has the potential to discriminate specific microstructural features and to relate them to processing behaviour. The method is experimentally validated on tape samples with characteristic processing history.Aerospace Manufacturing TechnologiesAerospace Structures & Computational Mechanic
Stochastic Modelling of Randomly Oriented Tapes Thermoplastic Composites in Net-Shaped Specimens
No full textDiscontinuous tape composites have considerable attention due to their high formability and tailorable structures. Despite their advantages, this discontinuity leads to complex structures and makes it difficult to predict their mechanical properties. On the other hand, they have high orientational and dimensional sensitivity, which causes spatial variability and complexity in the structure to predict the mechanical properties. This spatial variability is also related to the mould cavity. A constitutive model was improved to explain the relationship between DT orientations and the mould cavity. According to the modelling technique, a random DT distribution was generated by Random Sequential Adsorption then, the Set Voronoi Tessellation was implemented to obtain DT layers. Afterwards, the Classical Laminate Theory and Finite Element Method were applied to compare the virtual net-shaped DT specimens. The results of both methods showed high stiffness at the edges of the specimens.Aerospace Manufacturing Technologie
Enhancement of mode I fracture toughness of adhesively bonded secondary joints using different layup patterning of CFRP
No full textDelamination growth in fibre reinforced polymer composites is generally evaluated with experiments that have been standardized for quasi-static load conditions. These tests characterize unidirectional delamination growth in mode I (DCB), mode II (ELS or ENF) of mixed mode conditions (MMB). However, little attention is paid in literature to the applicability of these tests to in-service delamination problems that are generally characterized by planar delamination growth. In this study, the relation between planar delamination growth, induced by transverse quasi-static indentation loading, and these unidirectional delamination tests was investigated. To that aim, prior planar delamination growth tests reported in literature, performed at EPFL, were analysed to identify up to what extent this planar growth could be correlated to the concepts of strain energy release and strain energy density. Once this appeared to successful, an experimental setup was designed to measure the delamination boundary during the transverse indentation loading of planar delamination specimens made of nontransparent carbon fibre reinforced polymer composites. With that set-up, quasi-static and fatigue planar delamination growth experiments were performed, and delamination contours could be successfully captured. While the quasi-static tests revealed limited growth, evaluation with numerical simulations revealed that the indentation force required to extend the delamination quasi-statically would cause damage to the specimen. This is attributed to the increasing length of the delamination contour when delaminations expand, which is not the case with standard unidirectional specimen. With the fatigue tests, however, delamination growth was achieved, but interestingly enough two phases were observed; first the delamination propagated in a planar fashion, while at some point in time work did not exceed an apparent threshold. Instead of no growth, however, the delamination still increased but then in a transverse manner. What makes this study of particular interest, is that the strain energy density as criterion could capture the strain energy offered (work) along the entire delamination contour, while the strain energy release rate described the resistance to delamination growth. This latter observation is in agreement with the original concept employed by Griffith when he formulated the basis of linear elastic fracture mechanics. This presentation present the experiments performed, the analysis of results, and will conclude with a proposal how to relate standard unidirectional tests to planar growth, considering that these standard tests contain little to no information on transverse phenomena with respect to strain energy density (work) and strain energy release (dissipation).Structural Integrity & Composite
- …
