Interdiffusing core-shell nanofiber interleaved composites for excellent Mode I and Mode II delamination resistance

Electrospun nanofibre interleaving has a great potential for toughening of composite laminates as an effective, safe and industrially relevant method. Although many studies showcase large increases in delamination resistance, these are typically obtained under either Mode I or Mode II loading and for a wide variety of nanofibres. Here, we present a more general approach towards simultaneous excellent Mode I and Mode II delamination resistance using a single nanofibre system without the need for additional chemical modification steps or speciality polymers. It is illustrated based on the concept of interdiffusion of polycaprolactone nanofibres during the curing process into the epoxy matrix resin for improved adhesion. The results show that for a simultaneous increase in Mode I and Mode II delamination resistance, the adhesion and the fibre morphology of the nanofibres are crucial. The methodology is then expanded to allow for industrial relevant working windows by core-shell structured polyamide/polycaprolactone nanofibres. This approach results in a of 650 ± 50 J m-2 (+ca. 60% vs. virgin material) and a of 3160 ± 35 J m-2 (+ca. 60% vs. virgin material)

Detailed experimental validation and benchmarking of six models for longitudinal tensile failure of unidirectional composites

Longitudinal tensile failure of unidirectional fibre-reinforced composites remains difficult to predict accurately. The key underlying mechanism is the tensile failure of individual fibres. This paper objectively measured the relevant input data and performed a detailed experimental validation of blind predictions of six state-of-the-art models using high-resolution in-situ synchrotron radiation computed tomography (SRCT) measurements on two carbon fibre/epoxy composites. Models without major conservative assumptions regarding stress redistributions around fibre breaks significantly overpredicted failure strains and strengths, but predictions of models with at least one such assumption were in better agreement for those properties. Moreover, all models failed to predict fibre break (and cluster) development accurately, suggesting that it is vital to improve experimental methods to characterise accurately the in-situ strength distribution of fibres within the composites. As a result of detailed measurements of all required input parameters and advanced SRCT experiments, this paper establishes a benchmark for future research on longitudinal tensile failure

Fracture Simulation of Structural Glass by Element Deletion in Explicit FEM

In finite element simulation of glass cracking for practical engineering problems, the method of element deletion is often used despite its shortcomings. With this technique, an element is removed from the system upon reaching a certain failure criterion. Many different formulations for the failure behaviour of an element are possible, differentiated by the physical correctness of their representation and by their implications on the numerical stability of the calculation. In this paper, three failure models are characterised by use of a unit element model and evaluated for the drop weight impact on a monolithic glass plate. Several issues can be identified: (i) incorrect calculation of fracture energy for large-sized elements; (ii) shock wave propagation upon deletion of an element leading to spurious failure of other elements; (iii) unrealistic crack formation when the failure model does not account for crack directionality. A crack delay failure model for structural glass is proposed to avoid the aforementioned problems. This failure model uses only physical material properties as input and limits the damage rate during fracture

Seasonal variation of stable intrathyroidal iodine in nontoxic goiter disclosed by x-ray fluorescence

The intrathyroidal stable iodine (ITI) was determined in 776 patients chosen at random. Ninety % of these patients presented with nontoxic goiter. Curve-filtering analysis techniques showed a seasonal variation in ITI: an acrophase was found in April/May, a nadir in Semptember/October. The possible relationship of this seasonal variation with the intake of iodine or alimentary antithyroid substances are discussed, as well as a possible relationship with variation in chronic TSH stimulation related to ambient temperature. © 1982, Italian Society of Endocrinology (SIE). All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe