Simulations of delamination in CFRP laminates: Effect of microstructural randomness

Due to their high specific strength and stiffness, fibre-reinforced composite materials are being increasingly used in structural applications where a high level of performance is important (e.g. aerospace, automotive, offshore structures, etc.). Performance in service of these composites is affected by multi-mechanism damage evolution under loading and environmental conditions. For instance, carbon fibre-reinforced laminates demonstrate a wide spectrum of failure mechanisms such as matrix cracking and delamination. These damage mechanisms can result in significant deterioration of the residual stiffness and load-bearing capacity of composite components and should be thoroughly investigated. The delamination failure mechanism is studied in this paper for a double cantilever beam (DCB) loaded in mode I. Several sensitivity studies are performed to analyse the effects of mesh density and of parameters of the cohesive law on the character of damage propagation in laminates. The microstructural randomness of laminates that is responsible for non-uniform distributions of stresses in them even under uniform loading conditions is accounted for in the model. The random properties are introduced with the use of Weibull’s two-parameter probability density function. Several statistical realisations are carried out which show that the effect of microstructure could significantly affect the macroscopic response emphasizing the need to account for microstructural randomness for accurate predictions of load-carrying capacity of laminate composite structures.     

Inversion with regularization for the retrieval of tropospheric aerosol parameters from multiwavelength lidar sounding

We present an inversion algorithm for the retrieval of particle size distribution parameters, i.e., mean (effective) radius, number, surface area, and volume concentration, and complex refractive index from multiwavelength lidar data. In contrast to the classical Tikhonov method, which accepts only that solution for which the discrepancy reaches its global minimum, in our algorithm we perform the averaging of solutions in the vicinity of this minimum. This averaging stabilizes the underlying ill-posed inverse problem, particularly with respect to the retrieval of number concentration. Results show that, for typical tropospheric particles and 10% error in the optical data, the mean radius could be retrieved to better than 20% from a lidar on the basis of a Nd:YAG laser, which provides a combination of backscatter coefficients at 355, 532, and 1064 nm and extinction coefficients at 355 and 532 nm. The accuracy is improved if the lidar is also equipped with a hydrogen Raman shifter. In this case two additional backscatter coefficients at 416 and 683 nm are available. The combination of two extinction coefficients and five backscatter coefficients then allows one to retrieve not only averaged aerosol parameters but also the size distribution function. There was acceptable agreement between physical particle properties obtained from the evaluation of multiwavelength lidar data taken during the Lindenberg Aerosol Characterization Experiment in 1998 (LACE 98) and in situ data, which were taken aboard aircraft.     

Large deformation of thermally bonded random fibrous networks: microstructural changes and damage

A mechanical behaviour of random fibrous networks is predominantly governed by their microstructure. This study examines the effect of microstructure on macroscopic deformation and failure behaviour of random fibrous networks and its practical implication for optimisation of its structure by using finite-element simulations. A subroutine-based parametric modelling approach—a tool to develop and characterise random fibrous networks—is also presented. Here, a thermally bonded polypropylene nonwoven fabric is used as a model system. Its microstructure is incorporated into the model by explicit introduction of fibres according to their orientation distribution in the fabric. The model accounts for main deformation and damage mechanisms experimentally observed and provides the meso- and macro-level responses of the fabric. The suggested microstructure-based approach identifies and quantifies the spread of stresses and strains in fibres of the network as well as its structural evolution during deformation and damage. Its simulations also predict a continuous shift in the distribution of stresses due to structural evolution and progressive failure of fibres.     

Continuous physical activity recognition for intelligent labour monitoring

Multimedia Tools and Applications - The paper addresses the problem of human activity recognition based on the data from wearable sensors. Human activity recognition depends on a wide context of...     

Preferential Engagement and What Can We Learn from Online Chess?

Minds and Machines - An online game of chess against a human opponent appears to be indistinguishable from a game against a machine: both happen on the screen. Yet, people prefer to play chess...     

Effect of fluorination on preparation of Bi(Pb)SCCO 2 2 2 3 by the citrate precursor process

Citrate precursor technology was used to prepare fluorine substituted Bi(Pb)SCCO 2 2 2 3 superconducting phase. Samples with the nominal composition of up to three F atoms per formula were synthesized. A number of experimental methods have been used to characterize the samples and to trace the phase transformations during the preparation process: DTA/TGA, XRD, EPMA (WDS and EDS), atomic absorption, potentiometry with fluoride selective electrode, resistance and inductive measurements. Fluorine was shown to enhance considerably the formation of the 2 2 2 3 phase. Thermodynamic calculations of P-T-X equilibrium in the Bi-Pb-Sr-Ca-Cu-O-F-C-H-N system were made in a wide temperature range to determine the composition of the vapours coexisting with the solid phases at different stages of the preparation process.A part of the results was presented at the M²S-HTSC IV Conference in Grenoble, France, 1994.     

Influence of turbulent mixing on fast polymerization reactions

Investigations on development of a macrokinetics approach were generalized to the analysis of fast chemical reactions, mainly using cationic polymerization of isobutylene as an example, which is a new class of liquid‐phase processes. The removal of diffusional constraints on polymer synthesis, by intensification of turbulent mixing in the reaction zone, makes it possible to calculate the kinetic parameters of polymerization and polymer‐analogous reactions, to optimize the molecular characteristics of polymeric products obtained, and to control the character of the process as a whole. The laws pertaining to the progression of fast processes are considered for the synthesis of separate polymers, in particular stereoregular polydienes, ethylene–propylene copolymers, and chlorobutyl rubber. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 613–624, 2004     

Integration of Production Steps on a Single Equipment

The article describes a new method for integrated processing which combines high-energy heating by high frequency currents (HEH HFC) and abrasive grinding. Research clearly showed that implementation of integrated processing may lead to 2 … 2.5-fold increasing of the processing performance. It was established experimentally that the proposed integrated treatment results in increasing of the microhardness and the level of residual compressive stresses in the surface layer. This increases the contact–fatigue strength of steel parts up to 10% … 16%.