A test device for damage characterisation of composites based on in situ computed tomography

For engineering design of composites, suitable damage models are required which have to predict the onset of damage, the successive failure and the subsequent reduction of the mechanical properties. To verify existing modelling approaches, the clear experimental identification of the particular damage entities is an essential condition. However, due to the complexity of the failure mechanisms of novel materials like heterogeneous textile composites, a comprehensive damage analysis is still a challenging problem. Recent progress in the field of computed tomography enables in situ measurements to detect damage phenomena in composites under loading. The article describes such a novel test device that combines an integrated testing machine with a high precision computer tomograph. The in situ method was used to study the damage evolution in carbon fibre reinforced plastics (CFRPs) made of weft knitted and woven preforms. A special focus was set to damage processes under loading in thickness direction. For this purpose, cylindrical tensile specimens according to ASTM D 7291 were manufactured and tested. Compression specimens with different aspect ratios have been used to study the compressive failure of CFRP woven composites. The experimental results are discussed with respect to the possibilities and limitations of the in situ based test method.     

Investigation of smoke gases and temperatures during car fire – large‐scale and small‐scale tests and numerical investigations

The hazards for passengers during vehicle fires result from the increasing temperature and the emitted smoke gases. A fire was set on a car to investigate the development of temperature and of gaseous fire products in the passenger compartment. The study was based on a full‐scale test with a reconstructed scene of a serious car fire. The aim of this work was to identify the conditions for self‐rescuing of passengers during a car fire. A dummy, equipped with several thermocouples, was placed on the driver's seat. Also, the smoke gases were continuously collected through a removable probe sensor corresponding to the nose of the dummy in the passenger compartment and analyzed using Fourier transform infrared spectroscopy. Additionally, several car components were investigated in the smoke density chamber (smoke emission and smoke gas composition). It was found that the toxic gases already reached hazardous levels by 5 min, while the temperatures at the dummy were at that time less than 80 °C. The toxicity of smoke gases was assessed using the fractional effective dose concept. The various experimentally parameters (temperature and smoke gas composition) were implemented into numerical simulations with fire dynamics simulator. Both the experimental data and the numerical simulations are presented and discussed. Copyright © 2015 John Wiley & Sons, Ltd.     

Desalination using solar energy: Towards sustainability

This paper describes the theoretical rationale for a new low temperature phase-change desalination process, and six examples of applications to illustrate how this process can be engineered for sustainable desalination. In this process, brackish water is evaporated at near-ambient temperatures under near-vacuum pressures created by the barometric head without any mechanical energy input. Thermodynamic advantages and benefits of low temperature phase-change desalination are discussed and results from simulation studies and a prototype test system are presented. Three of the examples illustrate how the proposed process can be driven by solar energy: a) utilizing direct solar energy; b) inclusion of an external reflector; c) utilizing photovoltaic energy during non-sunlight hours. The other examples illustrate how the proposed process can be driven by waste heat: i) waste heat rejected by an absorption refrigeration unit driven by grid power; ii) waste heat rejected by an absorption refrigeration unit driven by solar collectors; and iii) waste heat rejected by an absorption refrigeration unit supported by a photovoltaic array. Merits of utilizing solar energy and process waste heat in reducing energy consumption and greenhouse gas emissions are discussed in detail.     

A novel approach to prepare etoposide‐loaded poly(N‐vinyl caprolactam‐co‐methylmethacrylate) copolymeric nanoparticles and their controlled release studies

A series of copolymeric nanoparticles of methyl methacrylate and N‐vinylcaprolactam were synthesized from microemulsions containing sodium dodecyl sulfate. Etoposide as a model drug was loaded in nanoparticles during in situ polymerization. Stable nanolatex were produced and characterized for size and shape by dynamic light scattering (DLS) and transmission electron microscopy. Particles were found to be spherical in nature with size less than 50 nm. Structural characterization of copolymers was done by infrared and nuclear magnetic resonance spectroscopy. Differential scanning calorimetery (DSC) and X‐ray diffractometry (XRD) techniques were used to evaluate molecular level interaction of etoposide with nanoparticles. Drug encapsulation efficiency was determined by ultraviolet (UV) spectrometry and found to be 35–67%. DSC, XRD, and UV data suggested the molecular level dispersion of drug in the nanoparticles. In vitro release studies and in vitro cytotoxicity showed prolonged and controlled release of etoposide from nanoparticles along with IC₅₀ values of nanoparticles in the range of 0.01–0.1 mg/mL. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2013     

Extending the concept of IIR filtering to array processing using approximate spatial IIR structure

Various array processing techniques applied to uniform linear arrays are involuntarily realized using structures that are analogous to finite impulse response filters. This observation leads to the following question: “can we extend infinite impulse response (IIR) filtering to array processing?”. In this paper, we introduce the concept of IIR array in spatial domain. Note that IIR array here does not mean time-domain IIR filtering for array beamforming which is commonly understood. This paper is dedicated to the study of an alternate approach for array signal processing which defines IIR structure in spatial domain. To illustrate the applicability of the concept of IIR array, we propose a new direction-of-arrival estimation technique as well as a beamformer with the spatial domain IIR array implementation. The performance of the proposed methods are comparable to the existing techniques. These illustrations are intended to introduce a new approach which potentially can offer more degrees of freedom to control the performance of the array and reduce the complexity of the system for a desired performance.     

Extracorporeal circulation in pregnancy: report of a case. Update and review of the literature

OBJECTIVE: To investigate the role of platelet activating factor (PAF) in the hypoxic pulmonary hypertension. MATERIAL AND METHODS: Fifteen of 30 male Wistar rats were exposed to hypoxia for 3 weeks, and another 15 rats served as controls. The pulmonary arterial pressure was examined by catheterization. The sections of rat lung were treated by the avidin-biotin-peroxidase complex method to expose the location of PAF. RESULTS: The rats developed pulmonary hypertension and right ventricular hypertrophy after hypoxic exposure. Under the light microscope, PAF is distributed on the vascular and alveolar walls of normal lung, and the content of PAF in the lung of rats with hypoxic pulmonary hypertension are remarkably higher than those of normoxic controls. CONCLUSIONS: PAF plays not only a physiological role in the rat lung, but also a pathophysiologic role in hypoxic pulmonary hypertension.     

Experimental and numerical studies on the braiding of carbon fibres over structured end-fittings for the design and manufacture of high performance hybrid shafts

Braiding is an attractive manufacturing method for tubular elements such as hollow shafts and struts. One of the main challenges however is the integration of suitably performing end-fittings. Recent advances in additive layer manufacture have enabled the fabrication of end-fittings which can be ‘co-impregnated’ or ‘co-cured’ with the fibre preform in a single step, i.e. without the need for secondary adhesive bonding. This requires the introduction of protrusions onto the surface of the end-fitting to promote mechanical interlocking with the fibres. However, the lack of accurate modelling tools for the simulation of this manufacturing process means that much empiricism is currently used in the design of such structures. A novel numerical framework is presented here for the full-scale simulation of the braiding process over structured end-fittings. Nonlinear finite element analysis is applied at the meso-scale, with strands of beam elements representing individual yarns and meshed surfaces modelling the mandrel and tooling. Penalty-based contact formulations are then used to simulate all inter-yarn and yarn-metal interactions, enabling detailed predictions of fibre paths around surface protrusions. In order to verify and validate this numerical framework, a series of full-scale braiding experiments was conducted using additively-manufactured thermoplastic mandrels. Final braid patterns as well as the occurrence of braid imperfections were investigated and compared to model predictions. It is shown that the proposed modelling strategy reproduces well the trends observed experimentally in terms of final braid quality. A parametric study was then conducted on the effects of initial end-fitting alignment with respect to oncoming yarns, suggesting that better control over this parameter could reduce considerably the occurrence of braid imperfections.     

Trismus and pain after removal of impacted lower third molars

PURPOSE: This study evaluated trismus and pain after removal of impacted lower third molars and investigated whether these responses were related to difficulty of surgery. PATIENTS AND METHODS: A consecutive series of 104 patients, all of whom underwent removal of an impacted lower third molar under local surgery, was studied. Difficulty of surgery was evaluated on a modified version of the Parant scale: I, extraction with forceps only; II, extraction by ostectomy; III, extraction by ostectomy and coronal section; IV, complex procedures. Trismus was evaluated in terms of maximum interincisal distance (MID) 1 and 5 days after surgery. Pain was evaluated on the basis of reported analgesic use 1 and 5 days after surgery. RESULTS: Among group I subjects, mean day 1 MID did not differ significantly (P > .05) from mean presurgery MID, whereas mean day 1 MID in groups II, III, and IV was significantly lower than before surgery. In groups II, III, and IV, mean day 5 MID remained lower than before surgery. The proportion of group I patients using analgesics was significantly lower on both days 1 and 5 than the proportion of patients using analgesics in groups II, III, and IV. In all groups, the proportion of patients using analgesics dropped significantly between days 1 and 5. CONCLUSION: Trismus is less severe after simple (forceps-only, grade I) extractions than after surgical extractions (grades II to IV). However, trismus severity after surgical extraction does not depend on difficulty of surgery. Pain, as revealed by reported analgesic use, is likewise less severe after simple extractions. Regardless of extraction type, pain declines between days 1 and 5 postsurgery.     

Effect of convection on boundary layer structures in finite thermoelasticity

Abstract

Till now, all of the research on boundary layer structures in thermoelasticity has focused on conduction as the primary mode of heat transfer. In this article, we investigate the additional effect of convection on the deformation field boundary layer structures formed within a thin infinite slab made of a neo-Hookean material. We find that additionally introducing convection in finite thermos-elasticity shifts the boundary layer vertically, while retaining its shape.