Experimental characterisation of rate-dependent compression behaviour of fibre reinforced composites

Fibre reinforced polymers (FRP) materials are being increasingly used for aerospace and automotive structural applications. One of the critical loading conditions for such applications is impact, consequently, understanding of the composite behavior under such loads becomes critical for structural design. The analysis and design process for achieving impact-resistant composite structures requires rate-dependent constitutive models, which, in turn, requires material properties of the composite over a range of strain rates. It is, therefore, the objective of the research to investigate the strain rate-dependent behavior of fiber reinforced composites under compressive loads for a wide range of fiber orientations. Quasi-static (≈ 1e-3 s-1) and high loading (≈ 200 s-1) rates are considered for the experimental study. Accordingly, two different test setups are utilized, a screw-driven universal testing machine for quasi-static tests and a Split Hopkinson Pressure Bar (SHPB) system for dynamic tests. The stress-strain response of the composite is reported for the different fiber orientations and the strain rates, revealing the rate-dependent characteristics of the carbon fiber reinforced composite. From the test results, it is observed that, the dependency of the fracture strength on the loading rate is significant. The results are summarised in terms of the failure envelope in the transverse compression-in-plane shear σ22-σ12 plane for the two strain rates

A Wedge-DCB Test Methodology to Characterise High Rate Mode-I Interlaminar Fracture Properties of Fibre Composites

A combined numerical-experimental methodology is presented to measure dynamic Mode-I fracture properties of fiber reinforced composites. A modified wedge-DCB test using a Split-Hopkinson Bar technique along with cohesive zone modelling is utilised for this purpose. Three different comparison metrics, namely, strain-displacement response, crack propagation history and crack opening history are employed in order to extract unique values for the cohesive fracture properties of the delaminating interface. More importantly, the complexity of dealing with the frictional effects between the wedge and the DCB specimen is effectively circumvented by utilising right acquisition techniques combined with an inverse numerical modelling procedure. The proposed methodology is applied to extract the high rate interlaminar fracture properties of carbon fiber reinforced epoxy composites and it is further shown that a high level of confidence in the calibrated data can be established by adopting the proposed methodology

On the Rate-dependent Plasticity Modelling of Unidirectional Fibre-reinforced Polymeric Matrix Composites

Three different approaches to plasticity are investigated to model the experimentally-observed non-linear behaviour of unidirectional fibre-reinforced polymeric matrix materials. The first and simplest approach consists on assuming independent one-dimensional rate-dependent plasticity on in-plane (12) and through-thickness longitudinal (13) shear components of the Cauchy stress tensor. The second, employs a 3D extension of the plane stress Hill'48 anisotropic plastic surface. The third and the last is formulated as a quadratic yield function inspired by Puck's fracture initiation criterion. It searches for a plastic localisation plane in which a certain combination of normal and shear stresses is maximum. Numerical simulations are conducted to analyse the off-axis compression behaviour of carbon fibre reinforced epoxy composite under varying loading rates. The afore-mentioned three different approaches are explored with an aim to predict the experimentally-observed non-linear response of such composites. The model parameters are determined using a deterministic inverse modelling strategy employing an iterative domain reduction optimisation technique. As far as the experiments are concerned, the quasi-static and medium rate tests were carried out in universal testing machines, while the experiments at high rate were conducted in a Split Hopkinson Pressure Bar system. The effectiveness in terms of accuracy and robustness of the three approaches are discussed

Predictions of the mechanical properties of unidirectional fibre composites by supervised machine learning

We present an application of data analytics and supervised machine learning to allow accurate predictions of the macroscopic stiffness and yield strength of a unidirectional composite loaded in the transverse plane. Predictions are obtained from the analysis of an image of the material microstructure, as well as knowledge of the constitutive models for fibres and matrix, without performing physically-based calculations. The computational framework is based on evaluating the 2-point correlation function of the images of 1800 microstructures, followed by dimensionality reduction via principal component analysis. Finite element (FE) simulations are performed on 1800 corresponding statistical volume elements (SVEs) representing cylindrical fibres in a continuous matrix, loaded in the transverse plane. A supervised machine learning (ML) exercise is performed, employing a gradient-boosted tree regression model with 10-fold cross-validation strategy. The model obtained is able to accurately predict the homogenized properties of arbitrary microstructures

pH of soil of Majalgaon command area (Jayakwadi project stage-III), India

Present paper deals with the study of pH of soil of Majalgoan command area, India. pH varied from 7.55 to 8.98 in different soil types and showed increased trend with depth in most of the profiles

A general existence principle for fixed point theorems in D

We establish two general principles for fixed point theorems in D-metric spaces, and then show that several theorems in D-metric spaces follow as corollaries of these general principles

Characterizations of the diurnal shapes of OI 630.0 nm dayglow intensity variations: inferences

International audienceMeasurements of OI 630.0 nm thermospheric dayglow emission by means of the Dayglow Photometer (DGP) at Mt. Abu (24.6° N, 73.7° E, dip lat 19.09° N), a station under the crest of Equatorial Ionization Anomaly (EIA), reveal day-to-day changes in the shapes of the diurnal profiles of dayglow intensity variations. These shapes have been characterized using the magnetometer data from equatorial and low-latitude stations. Substantial changes have been noticed in the shapes of the dayglow intensity variations between 10:00?15:00 IST (Indian Standard Time) during the days when normal and counter electrojet events are present over the equator. It is found that the width (the time span corresponding to 0.8 times the maximum dayglow intensity) of the diurnal profile has a linear relationship with the integrated electrojet strength. Occasional deviation from this linear relationship is attributed to the presence of substantial mean meridional wind

Pyridine clubbed coumarin analogues: Their synthesis and biological studies as antimicrobials and antioxidants

1713-1720The major aim of this study is to develop the new class of coumarin candidate clubbed with dihydropyridine-3-carbonitrile with an improved potency as an antimicrobial and antioxidant agent. The key intermediate 6-nitro-4-methyl coumarin-yl chloro acetate 5 have been linked to the 6-(4-fluorophenyl)-2-oxo-4-phenyl-1,2-dihydro pyridine-3-carbonitrile IIa-j derivative to afford 4-methyl-6-nitro-2-oxo-2H-chromen-7-yl-2-(3-cyano-6-(4-fluoro phenyl)-4-(substituted-phenyl) pyridin-2-yl-oxy) acetates 7a-j via efficient organic transformations. All the new derivatives have been characterized by spectral studies (IR, 1H and 13C NMR and mass spectroscopy). In vitro antimicrobial activity have been carried out using the broth microdilution method and antioxidant potency using DPPH bioassays. Bioassay results reveal that compound 7e are equipotent against E. coli with MIC value 50 µg/ mL compared to standard drug ciprofoloxacin. A final analogue 7c with 4-chlorophenyl substituent indicated better antifungal potency against C. albicans with MIC value 100 µg/ mL compared to standard drug griseofulvin. In addition, newly synthesized analogues have been found to be significant scavengers of DPPH radical with IC50 values of 32.11 μg/mL. It has been observed that the potent antibacterial candidate has proved to possess significant antioxidant activity. The presence of chlorine and hydroxy group on phenyl ring plays an important role for the potency in above mentioned biological assay