Strength prediction for bi-axial braided composites by a multi-scale modelling approach

The final publication is available at Springer via http://dx.doi.org/10.1007/s10853-016-9901-z.Braided textile-reinforced composites have become increasingly attractive as protection materials thanks to their unique inter-weaving structures and excellent energy-absorption capacity. However, development of adequate models for simulation of failure processes in them remains a challenge. In this study, tensile strength and progressive damage behaviour of braided textile composites are predicted by a multi-scale modelling approach. First, a micro-scale model with hexagonal arrays of fibres was built to compute effective elastic constants and yarn strength under different loading conditions. Instead of using cited values, the input data for this micro-scale model were obtained experimentally. Subsequently, the results generated by this model were used as input for a meso-scale model. At meso-scale, Hashin’s 3D with Stassi’s failure criteria and a modified Murakami-type stiffness-degradation scheme was employed in a user-defined subroutine developed in the general-purpose finite-element software Abaqus/Standard. An overall stress–strain curve of a meso-scale representative unit cell was verified with the experimental data. Numerical studies show that bias yarns suffer continuous damage during an axial tension test. The magnitudes of ultimate strengths and Young’s moduli of the studied braided composites decreased with an increase in the braiding angle

Development of a new foetal growth curve from a large sample of italian population.

OBJECTIVE: Intrauterine growth curves are considered an essential instrument in prenatal medicine for an appropriate auxological classification of foetuses and they have a great importance in clinical practice. Nowadays, in Italy a national curve published in 1975, is the most used. It's based on birth weights of 8458 newborns from physiological pregnancies. The aim of the present study is to develop a modern foetal growth curve based on accurately selection of 35 240 physiological singleton Italian pregnancies with sure gestational age confirmed by ultrasound. METHODS: This is a retrospective analysis of 35 240 pregnancies from "A. Gemelli" University Hospital in Rome and "S. Anna" University Hospital in Turin from January 2001 to December 2006. Non-resident pregnant women or coming from other countries, women with diabetes, hypertensive disorders of pregnancy, multiple pregnancies, foetuses with major malformations and /or chromosomal disorders and stillborn foetuses were excluded. RESULTS: An increasing trend of median neonatal weight, in comparison that with the previous Italian National Curve drawn up in 1975, was found. CONCLUSIONS: Combining data from two centres, a new foetal growth curve, in which the 10th and the 90th percentiles are clinically reliable, was performed, in order to have a better tool to evaluate the Italian foetal population. A trend towards an increase of birth weight was observed if compared to previous growth curve drawn up more than 30 years ago