Electrospinning core‐shell nanofibers for interfacial toughening and self‐healing of carbon‐fiber/epoxy composites

This article reports a novel hybrid multiscale carbon‐fiber/epoxy composite reinforced with self‐healing core‐shell nanofibers at interfaces. The ultrathin self‐healing fibers were fabricated by means of coelectrospinning, in which liquid dicyclopentadiene (DCPD) as the healing agent was enwrapped into polyacrylonitrile (PAN) to form core‐shell DCPD/PAN nanofibers. These core‐shell nanofibers were incorporated at interfaces of neighboring carbon‐fiber fabrics prior to resin infusion and formed into ultrathin self‐healing interlayers after resin infusion and curing. The core‐shell DCPD/PAN fibers are expected to function to self‐repair the interfacial damages in composite laminates, e.g., delamination. Wet layup, followed by vacuum‐assisted resin transfer molding (VARTM) technique, was used to process the proof‐of‐concept hybrid multiscale self‐healing composite. Three‐point bending test was utilized to evaluate the self‐healing effect of the core‐shell nanofibers on the flexural stiffness of the composite laminate after predamage failure. Experimental results indicate that the flexural stiffness of such novel self‐healing composite after predamage failure can be completely recovered by the self‐healing nanofiber interlayers. Scanning electron microscope (SEM) was utilized for fractographical analysis of the failed samples. SEM micrographs clearly evidenced the release of healing agent at laminate interfaces and the toughening and self‐healing mechanisms of the core‐shell nanofibers. This study expects a family of novel high‐strength, lightweight structural polymer composites with self‐healing function for potential use in aerospace and aeronautical structures, sports utilities, etc. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Penetration of a rigid projectile into an elastic-plastic target of finite thickness

This paper considers the problem of non-steady penetration of a rigid projectile into an elastic-plastic target of finite thickness. A specific blunt projectile shape in the form of an ovoid of Rankine is used because it corresponds to a reasonably simple velocity field which exactly satisfies the continuity equation and the condition of impenetrability of the projectile. The target region is subdivided into an elastic region ahead of the projectile where the strains are assumed to be small, and a rigid-plastic region near the projectile where the strains can be arbitrarily large. Using the above mentioned velocity field, the momentum equation is solved exactly in both the elastic and the rigid-plastic regions to find expressions for the pressure and stress fields. The effects of the free front and rear surfaces of the target (which is presumed not to be too thin) and the separation of the target material from the projectile are modeled approximately, and the force applied to the projectile is calculated analytically. An equation for projectile motion is obtained which is solved numerically. Also, a useful simple analytical solution for the depth of penetration or the residual velocity is developed by making additional engineering approximations. Moreover, the solution procedure presented in this paper permits a straight forward approximate generalization to accommodate a projectile with arbitrary shaped tip. Theoretical predictions are compared with numerous experimental data on normal penetration in metal targets, and the agreement of the theory with experiments is good even though no empirical parameters are used. Also, simulations for conical and hemispherical tip shapes indicate that the exact shape of the projectile tip does not significantly influence the prediction of integral quantities like penetration depth and residual velocity.     

Transverse stability of a liquid jet in a counterflowing air stream

The development of small perturbations which bend a liquid jet in a counterflowing air stream is analyzed here. It is demonstrated that the most dangerous perturbations of the jet axis have a spatial distribution, and the increment of perturbation buildup is calculated.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 38, No. 5, pp. 806–812, May, 1980.     

Meltblowing: Multiple polymer jets and fiber-size distribution and lay-down patterns

In this work a comprehensive model of three-dimensional configurations of polymer jets in meltblowing from die exit to deposition screen is developed. In addition, multiple jets were modeled simultaneously, as well as deposition on a screen moving normally to the principal jet direction was accounted for. All important properties of polymer melts are used in the simulations, namely density, zero-shear viscosity and the viscoelastic relaxation time. In addition, the material parameters responsible for the temperature-dependent variation of the material properties are used. All the other parameters are the operational parameters characterizing gas flow. The results include prediction of the fiber deposition patterns and fiber-size distributions in the resulting nonwovens. The angular distributions in lay-down nonwovens are also predicted. Comparisons with the experimental data suggest that the model captures main trends rather accurately.     

Computation of a laminar non-self-similar semibounded fluid jet

The numerical solution of dynamic and heat problems of a laminar plane incompressible fluid jet being propagated along a solid surface is performed within the framework of boundary-layer theory.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 32, No. 4, pp. 666–673, April, 1977.