Experimental investigation of interfacial crack arrest in sandwich beams subjected to fatigue loading using a novel crack arresting device

A recently proposed face-sheet–core interface crack arresting device is implemented in sandwich beams and tested using the Sandwich Tear Test configuration. Fatigue loading conditions are applied to propagate the crack and determine the effect of the crack stopper on the fatigue growth rate and arrest of the crack. Digital image correlation is used through the duration of the fatigue experiment to track the strain evolution as the crack tip advances. The measured strains are related to crack tip propagation, arrest, and re-initiation of the crack. A finite element model is used to calculate the energy release rate, mode mixity and to simulate crack propagation and arrest of the crack. Finally, the effectiveness of the crack arresting device is demonstrated on composite sandwich beams subjected to fatigue loading conditions

Fatigue damage evolution in GFRP laminates with constrained off-axis plies

The characterisation of fatigue damage evolution in constrained glass fibre reinforced plastic off-axis laminates is presented. A newly developed imaging technique known as Automatic Crack Counting (ACC) is used to quantify the off-axis crack state in constant amplitude (CA) and variable amplitude (VA) block loading tension-tension fatigue tests and constant amplitude compression-tension tests. The quantified crack states are analysed by combining the newly developed ACC method with a data mining approach and applying these to large data sets obtained during fatigue tests. It is shown that for a constant stress level, the stochastic nature of off-axis crack initiation and crack growth is accurately modelled by the Weibull distribution, with the distribution parameters being efficiently derived using the developed approach. The data-rich characterisation provides new insight in the crack density evolution process for VA and C-T loading, as well as derived Weibull distribution parameters in combination with the classical S-N curves and Paris? Law relationship. Hence, providing an improved approach that includes the stochastic and deterministic information for physically based modelling of crack density evolution for fatigue loading

Meta-analysis of exome array data identifies six novel genetic loci for lung function

Background: Over 90 regions of the genome have been associated with lung function to date, many of which have also been implicated in chronic obstructive pulmonary disease. Methods: We carried out meta-analyses of exome array data and three lung function measures: forced expiratory volume in one second (FEV1), forced vital capacity (FVC) and the ratio of FEV1 to FVC (FEV1/FVC). These analyses by the SpiroMeta and CHARGE consortia included 60,749 individuals of European ancestry from 23 studies, and 7,721 individuals of African Ancestry from 5 studies in the discovery stage, with follow-up in up to 111,556 independent individuals. Results: We identified significant (P<2·8x10-7) associations with six SNPs: a nonsynonymous variant in RPAP1, which is predicted to be damaging, three intronic SNPs (SEC24C, CASC17 and UQCC1) and two intergenic SNPs near to LY86 and FGF10. Expression quantitative trait loci analyses found evidence for regulation of gene expression at three signals and implicated several genes, including TYRO3 and PLAU. Conclusions: Further interrogation of these loci could provide greater understanding of the determinants of lung function and pulmonary disease

Thermomechanical interaction effects in composite sandwich structures – initial experimental analysis and derivation of mechanical properties

An experimental study of the effect of increasing temperature on the tensile modulus of PVC foam is presented. The focus is on obtaining reliable measurements of specimen deformation using optical techniques based on digital image correlation (DIC). A FE model that accounts for the 3D strain distribution in the specimen was used to inform the test specimen design. A new testing methodology and test rig design is devised and described in the paper. Firstly, tests are conducted at room temperature using DIC to obtain the strain on two opposite surfaces of the specimen simultaneously, to assess the effect of any specimen misalignment and devise a correction approach referred to as a ‘misalignment ratio’. In the elevated temperature test only one face was optically accessible through an optical window in a thermal chamber. Therefore the experiments are performed over a temperature range of 30°C to 90°C using only a single camera and the misalignment ratio applied. It is shown that the proposed methodology provides precise measurements and the thermal degradation of the tensile modulus can be obtained

The effect of temperature on the failure modes of polymer foam cored sandwich structures

The influence of elevated temperature on the stability of sandwich structures is investigated. A new analytical solution is proposed that enables the calculation of the critical wrinkling stress in sandwich beams subjected to load and elevated temperatures. The effect of a through thickness temperature gradient is accounted for by imposing different stiffnesses of the core for the different temperatures. The sandwich beam studied in the paper is loaded in a simply supported four-point bending configuration, where one of the face sheets is heated. The experimental approach utilises high-speed imaging where the strains are calculated from measured displacements obtained from digital image correlation (DIC). A shift of the failure mode from face sheet yielding to face sheet wrinkling is observed with increasing temperatures. The results from the new analytical method agree well with corresponding experimental results. Finite element analysis is also conducted, which shows excellent correspondence with the theory and the experimental data. The work clearly demonstrates that under certain conditions the load response of the sandwich beam can become nonlinear and unstable, and hence will fail well below face sheet yielding load because of the loss of stiffness of the core material