A simple and accurate four-node quadrilateral element using stabilized nodal integration for laminated plates

This paper reports the development of a simple but efficient and accurate four-node quadrilateral element for models of laminated, anisotropic plate behaviour within the framework of the first-order shear deformation theory. The approach incorporates the strain smoothing method for mesh-free conforming nodal integration into the conventional finite element techniques. The membrane-bending part of the element stiffness matrix is calculated by the line integral on the boundaries of the smoothing elements while the shear part is performed using an independent interpolation field in the natural co-ordinate system. Numerical results show that the element offered here is locking-free for extremely thin laminates, reliable and accurate, and easy to implement. Its convergence properties are insensitive to mesh distortion, thickness-span ratios, lay-up sequence and degree of anisotropy.     

Simulation of stretch forming with intermediate heat treatments of aircraft skins

In the aerospace industry stretch forming is often used to produce skin parts. During stretch forming a sheet is clamped at two sides and stretched over a die, such that the sheet gets the shape of the die. However for complex shapes it is necessary to use expensive intermediate heat-treatments in between, in order to avoid Lüders lines and still achieve large deformations. To optimize this process FEM simulations are performed. The accuracy of finite element analysis depends largely on the material models that describe the work hardening during stretching and residual stresses and work hardening reduction during heat treatments due to recovery and particle coarsening. In this paper, a physically based material modeling approach used to simulate the stretch forming with intermediate heat treatments and its predictive capabilities is verified. The work hardening effect during stretching is calculated using the dislocation density based Nes model and the particle coarsening and static recovery effects are modeled with simple expressions based on physical observations. For comparison the simulations are also performed with a phenomenological approach of work hardening using a power law. The Vegter yield function is used to account for the anisotropic and biaxial behavior of the aluminum sheet. A leading edge skin part, made of AA 2024 has been chosen for the study. The strains in the part have been measured and are used for validation of the simulations. From the used FEM model and the experimental results, satisfactory results are obtained for the simulation of stretching of aircraft skins with intermediate heat treatments and it is concluded that the physics based material modeling gives better results.     

Numerical study of stream-function formulation governing flows in multiply-connected domains by integrated RBFs and Cartesian grids

This paper describes a new numerical procedure, based on point collocation, integrated multiquadric functions and Cartesian grids, for the discretisation of the stream-function formulation for flows of a Newtonian fluid in multiply-connected domains. Three particular issues, namely (i) the derivation of the stream-function values on separate boundaries, (ii) the implementation of cross derivatives in irregular regions, and (iii) the treatment of double boundary conditions, are studied in the context of Cartesian grids and approximants based on integrated multiquadric functions in one dimension. Several test problems, i.e. steady flows between a rotating circular cylinder and a fixed square cylinder and also between eccentric cylinders maintained at different temperatures, are investigated. Results obtained are compared well with numerical data available in the literature.     

Pyroresistivity in conductive polymer composites: a perspective on recent advances and new applications

Conductive polymer composites (CPCs) with pyroresistive behaviour are of interest for a wide variety of applications such as safe batteries, resettable fuses, temperature sensors and self‐regulating heating devices. Due to their ease of processing, low density, tunable electrical properties, good oxidation resistance, and good flexibility and toughness, CPCs have become the preferred choice of pyroresistive materials in a number of applications. The pyroresistive behaviour of CPCs can be tuned to satisfy the specific requirements of different applications. In this perspective paper, recent progress in the use of pyroresistive CPCs is reviewed. In particular, various factors influencing their performance are discussed and compared, in connection with the associated application, with a special focus on reproducibility and positive temperature coefficient intensity levels. Some of the remaining challenges are identified, together with future prospects in this evolving field. © 2018 Society of Chemical Industry     

Discovery of New Classes of Compounds that Reactivate Acetylcholinesterase Inhibited by Organophosphates

Acetylcholinesterase (AChE) that has been covalently inhibited by organophosphate compounds (OPCs), such as nerve agents and pesticides, has traditionally been reactivated by using nucleophilic oximes. There is, however, a clearly recognized need for new classes of compounds with the ability to reactivate inhibited AChE with improved in vivo efficacy. Here we describe our discovery of new functional groups—Mannich phenols and general bases—that are capable of reactivating OPC‐inhibited AChE more efficiently than standard oximes and we describe the cooperative mechanism by which these functionalities are delivered to the active site. These discoveries, supported by preliminary in vivo results and crystallographic data, significantly broaden the available approaches for reactivation of AChE.     

Characterization of rigid polyurethane foams containing microencapsulated Rubitherm<Superscript>®</Superscript> RT27: catalyst effect. Part II

Catalyst Tegoamin 33 has been used for the synthesis of rigid polyurethane (RPU) foams containing microencapsulated Rubitherm^® RT27 and having a high mechanical resistance. These materials could be employed in buildings for thermal insulation and thermal energy storage (TES). The fillers content influence on the foaming process and also the foam properties was evaluated. It was observed that a foam containing up to a 18 wt% of microcapsules can be manufactured, improving the TES capacity while maintaining the mechanical properties of the neat foam. Besides, it was observed that the mechanical resistance of foams synthesized using catalyst Tegoamin 33 are higher than those obtained when catalyst Tegoamin BDE was employed, with the mechanical resistance of the foam containing 21 wt% being higher than those of foams synthesized with catalyst BDE containing only 11 wt% of fillers while maintaining the advantages of an improvement in TES capacity. A general model of reaction curve of n tank-in-series of a same time constant was used to fit the rising curves. This model allowed to predict the final volume of the synthesized foam. Finally, TES capacities and mechanical properties of the synthesized foams were in the range of those reported in literature. Moreover, foam densities satisfied the restriction established by the Spanish regulation for building applications.