Self-activated healing of delamination damage in woven composites

A study of the healing of delamination damage in woven E-glass/epoxy composites is performed. With the ultimate goal of self-healing in mind, two types of healing processes are studied. In the first a catalyzed monomer is manually injected into the delamination. In the second a self-activated material is created by embedding the catalyst directly into the matrix of the composite, then manually injecting the monomer. Healing efficiencies relative to the virgin fracture toughness of up to 67% are obtained when the catalyzed monomer is injected and about 19% for the self-activated materials. Scanning electron microscopy is used to analyze the fracture surfaces and provide physical evidence of repair.     

Self-activated ‘green’ carbon nanoparticles for symmetric solid-state supercapacitors

Tuning of porosity and surface properties of nanoparticles especially on carbon-based nanomaterials, adopting a ‘greener’ or self-activation synthesis technique for electrical charge storage, is progressing. Herein, we report the self-activation of Teak wood sawdust in a nitrogen atmosphere at different activation temperatures to synthesize carbon nanoparticles. The activated carbon nanoparticles synthesized at 900 °C exhibits a maximum?~?360 m² g^?1 surface area with?~?2 nm average pore size diameter. Five electrolytes viz. KOH, KCl, Na₂SO₄, NaCl, and H₃PO₄ are used for studying the supercapacitance nature of the activated carbon nanoparticles in a 3-electrode configuration. A maximum specific capacitance of?~?208 F g^?1 @ 0.25 A g^?1 is obtained in 1 M KOH as the electrolyte. Two symmetric supercapacitors, aqueous (1 M KOH) and solid-state (PVA/KOH), are fabricated, and their performance difference is compiled. The solid-state symmetric supercapacitor performs in a wider voltage window (1.7 V) with a superior energy density of 27.1 Wh kg^?1 at a power density of 178 W kg^?1.

Graphical abstract

     

Damage in impact fragmentation

Using a simple and generic molecular dynamics model, we study damage in a disc of interacting particles as the disc fragments upon impact with a wall. The damage, defined as the ratio of the number of bonds broken by the impact to the initial number of bonds, is found to increase logarithmically with the energy deposited in the system. This result implies a linear growth with damage for the total number of fragments and for the power law exponent of the fragment size distribution.     

Stone fragmentation by ultrasound

The presence of kidney stone in the kidney causes discomfort to patients. Hence, removal of such stones is important which is commonly done these days, non-destructively, with lithotripters without surgery. Commercially, lithotripters like extra-corporeal shock wave lithotripters (ESWL) made by Siemens etc are in routine use. These methods are very cumbersome and expensive. Treatment of the patients also takes comparatively more time because of more number of sittings. Some delicate nerves and fibres in the surrounding areas of the stones present in the kidney are also damaged by high ultrasonic intensity used in such systems. In the present work, enhancement of the kidney stone fragmentation by using ultrasound is studied. The cavitation bubbles are found to implode faster, with more disintegration efficiency of the lithotripters, which give better treatment to the patients.     

Mechanics of fibre fragmentation

A fragmentation specimen consists of a single fibre embedded along the axis of a long narrow resin block. When the fibre is broken by a tensile load, either a lateral crack runs outwards into the resin, initiated by the break, or a debond (or equivalently a cylindrical crack in the resin) propagates along the fibre. Debonding always occurs with thin fibres. Strain energy release rates have now been calculated, analytically for long debonds and by FEA for short ones. The force to propagate a debond is found to increase as the debond grows, reaching a final value, termed pull-out force, that is higher for softer fibres. If this force exceeds the strength of the fibre, then the fibre breaks again. This is the proposed mechanism of fibre fragmentation. For weakly-bonded, stiff fibres, the inferred minimum distance between breaks, i.e. the critical fragment length, is deduced to be of the order of the geometric mean of the radii of fibre and resin block, about 0.1–0.5 mm for typical fragmentation specimens, and it increases as the ratio of fibre stiffness to resin block stiffness increases, in agreement with observation.     

Shielding and fragmentation studies

Radiation dosimetry for manned spaced missions depends on the ability to adequately describe the process of high-energy ion transport through many materials. Since the types of possible nuclear interactions are many and complex, transport models are used which depend upon a reliable source of experimental data. To expand the heavy ion database used in the models we have been measuring charge-changing cross sections and fragment production cross sections from heavy-ion interactions in various elementa targets. These include materials flown on space missions such as carbon and aluminium, as well as those important in radiation dosimetry such as hydrogen, nitrogen and water. Measuring heavy-ion fragmentation through these targets also gives us the ability to determine the effectiveness of new materials proposed for shielding such as graphite composites and polyethylene hybrids. Measurement without a target present gives an indication of the level of contamination of the primary beam, which is also important in radiobiology experiments.     

A comparison of fragmentation models

The key to conducting an accurate lethality assessment is the use of a robust assessment methodology. One of the critical components of a lethality assessment is the characterization of the debris cloud created by the initial high speed impact. Without a proper characterization, it is impossible to obtain an accurate prediction of the response of an interior target component to subsequent debris cloud impact loadings. The fast-running codes FATEPEN2, KAPP-II, and PEN4 contain fragmentation models that characterize the debris cloud fragment population resulting from a high speed impact. The objective of the work described in this paper as to compare the predictions of the fragmentation models within these three codes over the 1–16 km/s impact velocity regime. This objective was achieved through a parametric study of debris cloud material characterization using the fragmentation schemes in the FATEPEN2, KAPP-II, and PEN4 semi-empirical lethality assessment schemes for a variety of projectile and target materials and configurations.     

Electron-impact-induced fragmentation of proline molecule

The formation of ionized products upon single and dissociative ionization of proline (C₅H₉NO₂) molecule by electron impact at high (11.5 MeV) and low (below 150 eV) energies has been studied using mass-spectrometric techniques. The mass-spectra of proline molecule have been obtained and interpreted and the near-threshold fragment ion yields have been measured, from which the absolute values of ionization energies of the initial molecule and the appearance potentials of its main fragment ions are determined. Analysis of the influence of exposure to a high-energy beam of accelerated electrons on the resulting mass spectra of initial molecules showed that high-energy irradiation produces irreversible changes in the initial molecular structure.     

Size effects in single grain fragmentation

Size effects on the compressive strength of cylinders and spheres are considered using Weibull statistical flaw size distribution. It is shown that failure is almost surely initiated from the bulk of the particle for large sizes, rather than from the vicinity of the loading contact points. Experiments performed on plaster on cylinders support our theoretical prediction, for the scaling of the particle strength with its size, using the experimentally determined Weibull modulus.     

Analysis of the single-fiber fragmentation test

An analysis of the single-fiber fragmentation test was investigated.An approximate solution for the stress fields of a fiber embedded in a polymer matrix of different elastic moduli was obtained by the Eshelby method. The fiber was modeled as a prolate spheroid. The axial stress of the fiber increases with increasing aspect ratio and fiber-matrix shear modulus ratio and decreases with increasing matrix and fiber Poisson's ratios. Using this analysis, the fracture stress of a single-fiber fragmentation specimen was derived. The applied stress at fiber fracture decreases monotonically with increasing aspect ratio of the fragmented fiber and increases with increasing fiber and matrix Poisson's ratios. This model is in qualitative agreement with published experimental data.     

Study on the fragmentation of shells

Fragmentation can be observed in nature and in everyday life on a wide range of length scales and for all kinds of technical applications. Most studies on dynamic failure focus on the behaviour of bulk systems in one, two and three dimensions under impact and explosive loading, showing universal power law behaviour of fragment size distribution. However, hardly any studies have been devoted to fragmentation of shells. We present a detailed experimental and theoretical study on the fragmentation of closed thin shells of various materials, due to an excess load inside the system and impact with a hard wall. Characteristic fragmentation mechanisms are identified by means of a high speed camera and fragment shapes and mass distributions are evaluated. Theoretical rationalisation is given by means of stochastic break-up models and large-scale discrete element simulations with spherical shell systems under different extreme loading situations. By this we explain fragment shapes and distributions and prove a power law for the fragment mass distribution. Satisfactory agreement between experimental findings and numerical predictions of the exponents of the power laws for the fragment shapes is obtained     

Spurious interface fragmentation in multiphase SPH

We investigate the issue of sub‐kernel spurious interface fragmentation occurring in SPH applied for multiphase flows. It has appeared recently that current SPH formulations for multiphase flows involving an interface between immiscible phases can suffer from non‐physical particle mixing through the interface, especially for flows with high density ratios. This is an important issue, in particular for applications where physical phenomena take place at the interface itself, such as phase change or the evolution of two‐phase flow patterns. In this paper, various remedies proposed in the literature are discussed. The current assumption that spurious interface fragmentation occurs only when there is no surface tension at the interface is revisited. We show that this is a general problem of current SPH formulations that appears even when surface tension is present. A new proposition for an interface sharpness correction term is put forward. A series of simulations of two‐dimensional and three‐dimensional bubbles rising in a liquid allow a comprehensive study and demonstrate the dependence of the new correction term on the kernel smoothing length. On the other hand, the overall flow behavior, including the interface shape, is not affected. Copyright © 2015 John Wiley & Sons, Ltd.     

A statistical theory of fragmentation processes

The goal of the work reviewed here is a theory of material behavior accounting for the average deformation that results from the opening, shear, growth and coalescence of an ensemble of microcracks. A concomitant is the calculation of permeability from crack structure. The first part of this paper summarizes previous developments. In particular, the initial work on this problem made use of a linear Liouville equation to characterize the change in crack distribution resulting from crack growth and coalescence. Straightforward analytic solutions to this equation were possible because the mean free path of cracks was assumed constant. Though this assumption is useful for the early stages of crack growth, increasing crack size reduces the mean free path in the later stages of fragmentation. This problem is addressed in the second part of this paper. The governing (nonlinear) Liouville equation is derived therein, and it is shown that it can be reduced to an ordinary differential equation of third order involving only a single free parameter, denoted by β. This equation has now been solved numerically to determine the limiting value of the mean free parth as a function of β, and the results are presented in graphical form. In the third part of this paper prospects for further developments are briefly discussed.     

Dynamics and fragmentation of thick-shelled microbubbles

Localized delivery could decrease the systemic side effects of toxic chemotherapy drugs. The unique delivery agents we examine consist of microbubbles with an outer lipid coating, an oil layer, and a perfluorobutane gas core. These structures are 0.5-12 /spl mu/m in radius at rest. Oil layers of these acoustically active lipospheres (AALs) range from 0.3-1.5 /spl mu/m in thickness and thus the agents can carry a large payload compared to nano-scale drug delivery systems. We show that triacetin-based drug-delivery vehicles can be fragmented using ultrasound. Compared with a lipid-shelled contrast agent, the expansion of the drug-delivery vehicle within the first cycle is similar, and a subharmonic component is demonstrated at an equivalent radius, frequency, and driving pressure. For the experimental conditions explored here, the pulse length required for destruction of the drug-delivery vehicle is significantly greater, with at least five cycles required, compared with one cycle for the contrast agent. For the drug-delivery vehicle, the observed destruction mechanism varies with the initial radius, with microbubbles smaller than resonance size undergoing a symmetric collapse and producing a set of small, equal-sized fragments. Between resonance size and twice resonance size, surface waves become visible, and the oscillations become asymmetrical. For agents larger than twice the resonance radius, the destruction mechanism changes to a pinch-off, with one fragment containing a large fraction of the original volume.     

Charge-remote fragmentation of odd-electron peptide ions

Comparison between the gas-phase fragmentation of odd-electron M+*, [M + H]2+*, and [M - 2H]-* ions of model peptides suggests that charge-remote radical-driven fragmentation pathways play an important role in the dissociation of odd-electron peptide ions. We have found that charge-remote processes are responsible for a variety of side-chain losses from the precursor ion and some backbone fragmentation. These fragmentation pathways most likely involve hydrogen abstraction by the radical site that initiates subsequent cleavages. These findings are generally relevant to our understanding of the fragmentation patterns of odd-electron peptide ions produced through various approaches including the capture of low-energy electrons, electron detachment, and electron transfer.     

PAFRAG modeling of explosive fragmentation munitions performance

A technique for predicting performance of explosive fragmentation munitions presented in this work is based on integrating three-dimensional axisymmetric hydrocode analyses with analyses from a newly developed fragmentation computer code PAFRAG. The validation of the PAFRAG code fragmentation model was accomplished using the existing munition arena test data. After having established the crucial parameters of the model, a new explosive fragmentation munition was designed and optimized. Upon fabrication of the developed munition, the performance of the new charge was tested in a series of small-scale experiments including the flash radiography, the high-speed photography, and the sawdust fragment recovery. Considering relative simplicity of the model, the accuracy of the PAFRAG code predictions is rather remarkable.     

Impact breach and fragmentation of glass plate

The present paper describes a first-order analytic model of the breach of monolithic glass plate subject to impact by chunky projectiles. The purpose of the model is to provide a theoretical framework for examining the consequences of the impact breach experiments of Sun et al. [Sun X, Khaleel MA, Davies RW. Modeling of stone-impact resistance of monolithic glass ply using continuum damage mechanics. Int J Damage Mech 2005;14:165-78]. A failure criterion of the Tuler-Butcher form [Tuler FR, Butcher BM. A criterion for the time dependence of fracture. Int J Fracture Mech 1968;4:431-7] is used with the model. The experimental impact breach experiments joined with the analytic model demonstrate time-dependent failure and lack of replica scaling for the present data. Methods are explored for the assessment of fragmentation resulting from the impact breach of brittle materials.