In this study, we report the development of a free-standing fiber -based mesh cathode made of electrospun composite microfibers containing 80 wt% lithium iron phosphate (LFP), as well as conductive microfibers containing carbon nano -fillers acting as the current collector (CC). Neither the electrode nor the current collector undergoes post -fabrication treatment or calcination. Scanning electron microscopy confirmed that the meshes are constructed of well -shaped microfibers and exhibit a high porosity, enabling efficient electrolyte penetration and improved electron and ion -transport channels. Two cathode architectures of the LFP/polymer-based CC meshes were explored: bilayered and interlayered. Both architectures are characterized by a high surface -to -volume ratio. The interlayered structure showed superior electrochemical performance due to enhanced LFP-CC fiber -to -fiber contacts and reduced resistance. Comparative analysis with electrospun LFP on aluminum foil revealed comparable specific capacity but higher polarization in the electrospun LFP/CC meshes, attributed to increased internal resistance and limited fiber -tofiber contacts. However, the electrospun interlayered LFP/CC mesh exhibited significantly higher gravimetric energy density (197 Wh/kg (LFP + CC) and 94 Wh/kg (LFP + Al), respectively), offering lightweight and higherenergy -density electrode materials, thus guiding the design of high-performance flexible lithium -ion batteries.

In Part I of this study, fracture toughness tests were carried out in modes I, II and mixed modes I/II on two laminate composites. Both composites contain carbon fibers in an epoxy matrix. One laminate is unidirectional and the second is composed of plies fabricated from a twill fabric. The tests were carried out using double cantilever beam, end-notched flexure and mixed mode bending specimens according to ASTM and ISO standards. This is an extensive and complete study of the in-plane, quasi-static fracture toughness (both initiation and resistance) of two material systems. In Part II of this study, micro-computerized tomography carried out on some of the specimens is reported. On the basis of these images, the experimental behavior was related to the micromechanical structure of the materials. In addition, load–displacement curves were simulated numerically by means of a cohesive zone model and the finite element method to gain better insight into the failure behavior observed.

In order to reduce medical facility overload due to the rise of the elderly population, modern lifestyle diseases, or pandemics, the medical industry is currently developing point-of-care and home medical device systems. Diabetes is an incurable and lifetime disease, accountable for a significant mortality and socio-economic public health burden. Thus, tight glucose control in diabetic patients, which can prevent the onset of its late complications, is of enormous importance. Despite recent advances, the current best achievable management of glucose control is still inadequate, due to several key limitations in the system components, mainly related to the reliability of sensing components, both temporally and chemically, and the integration of sensing and delivery components in a single wearable platform, which is yet to be achieved. Thus, advanced closed-loop artificial pancreas systems able to modulate insulin delivery according to the measured sensor glucose levels, independently of patient supervision, represent a key requirement of development efforts. Here, we demonstrate a minimally invasive, transdermal, multiplex, and versatile continuous metabolites monitoring system in the subcutaneous interstitial fluid space based on a chemically modified SiNW-FET nanosensor array on microneedle elements. Using this technology, ISF-borne metabolites require no extraction and are measured directly and continuously by the nanosensors. Due to their chemical sensing mechanism, the nanosensor response is only influenced by the specific metabolite of interest, and no response is observed in the presence of potential exogenous and endogenous interferents known to seriously affect the response of current electrochemical glucose detection approaches. The 2D architecture of this platform, using a single SOI substrate as a top-down multipurpose material, resulted in a standard fabricated chip with 3D functionality. After proving the ability of the system to act as a selective multimetabolites sensor, we have implemented our platform to reach our main goal for in vivo continuous glucose monitoring of healthy human subjects. Furthermore, minor adjustments to the fabrication technique allow the on-chip integration of microinjection needle elements, which can ideally be used as a drug delivery system. Preliminary experiments on a mice animal model successfully demonstrated the single-chip capability to both monitor glucose levels as well as deliver insulin. By that, we hope to provide in the future a cost-effective and reliable wearable personalized clinical tool for patients and a strong tool for research, which will be able to perform direct monitoring of clinical biomarkers in the ISF as well as synchronized transdermal drug delivery by this single-chip multifunctional platform.

Metal-organic frameworks (MOFs) exhibit an exceptional surface area-to-volume ratio, variable pore sizes, and selective binding, and hence, there is an ongoing effort to advance their processability for broadening their utilization in different applications. In this work, we demonstrate a general scheme for fabricating freestanding MOF-embedded polymeric fibers, in which the fibers themselves act as microreactors for the in situ growth of the MOF crystals. The MOF-embedded fibers are obtained via a two-step process, in which, initially, polymer solutions containing the MOF precursors are electrospun to obtain microfibers, and then, the growth of MOF crystals is initiated and performed via antisolvent-induced crystallization. Using this approach, we demonstrate the fabrication of composite microfibers containing two types of MOFs: copper (II) benzene-1,3,5-tricarboxylic acid (HKUST-1) and zinc (II) 2-methylimidazole (ZIF-8). The MOF crystals grow from the fiber's core toward its outer rims, leading to exposed MOF crystals that are well rooted within the polymer matrix. The MOF fibers obtained using this method can reach lengths of hundreds of meters and exhibit mechanical strength that allows arranging them into dense, flexible, and highly durable nonwoven meshes. We also examined the use of the MOF fiber meshes for the immobilization of the enzymes catalase and horse radish peroxidase (HRP), and the enzyme-MOF fabrics exhibit improved performance. The MOF-embedded fibers, demonstrated in this work, hold promise for different applications including separation of specific chemical species, selective catalysis, and sensing and pave the way to new MOF-containing performance fabrics and active membranes.

In this paper, a method is proposed for evaluating the delamination growth rate da/dN for any given R-ratio (load or displacement ratio) using data from a relatively small number of tests. To this end, double cantilever beam (DCB) specimens fabricated from a plain woven prepreg (G0814/913) arranged in a multi-directional (MD) layup were tested. First, quasi-static tests were carried out to obtain the resistance G(IR)-curve. Then, constant amplitude fatigue tests were preformed to determine the delamination growth rate da/dN. In both tests, displacement control was imposed. Four different cyclic displacement ratios R-d, namely 0.1, 0.33, 0.5 and 0.75, were used for the fatigue tests. When the delamination growth rate da/dN, calculated from the experimental data, was plotted with respect to gm,,c and Delta G(Ieff) = (root GImax - root GImin)(2), different behavior of the da/dN curves was observed. In addition, modification of the Hartman-Schijve representation was made. When the da/dN data was plotted with respect to the new modified representation which was denoted here as Delta K-1 all of the data obtained for different displacement ratios collapsed into one master curve. From this master curve, da/dN values may be calculated for any given R-ratio. (C) 2016 Elsevier Ltd. All rights reserved.

The main challenges in successfully using CNTs as a reinforcement phase in a composite are homogenous dispersion and distribution of the CNTs in the matrix, as well as improving the interfacial bond between them. Functionalization of CNTs has proved an effective method for overcoming these challenges.The goal of this study is to determine the mechanical properties of a composite material using experimental methods. The composite consists of a poly(methyl methacrylate), or PMMA, matrix enhanced by different weight fractions (wt%) of nanotubes functionalized by two methods. Carboxylated CNTs were further functionalized by the grafting from (GF) and the grafting to (GT) methods. The effect of these functionalization methods on the CNTs is evaluated through measurement of effective mechanical properties of a composite containing them, as well as, through a comparison to a previous investigation, in which non-functionalized (NF) CNTs were employed. Tensile tests were carried out on neat PMMA and PMMA containing functionalized CNTS; there were two GF batches containing 0.8 wt and 1.5 wt% of CNTs; and three GT batches containing 1.5 wt%, 3 wt% and 6 wt% of CNTs. (C) 2016 Elsevier Ltd. All rights reserved.

Double cantilever beam (DCB) specimens fabricated from 15 plies of a plain woven prepreg (G0814/913) arranged in a multidirectional (MD) layup were tested by means of constant amplitude fatigue cycles under displacement control. Four different displacement cyclic ratios were used, namely 0.1, 0.33, 0.5 and 0.75. The delamination propagation rate da/dN was calculated from the experimental data and plotted with respect to different functions of the mode I energy release rate GI. When one of those functions, denoted here as ΔKI was used, all of the data obtained for the different displacement ratios collapsed into one master curve.

Silica aerogels are ultralow density materials with nano-sized skeleton network of pores. Their high brittle nature presents a major challenge for mechanical testing and a need exists for novel testing methods. Two new mechanical setups and testing techniques are proposed for measuring the aerogel elastic mechanical properties. Both techniques employ full-field Digital Image Correlation (DIC) for surface deformation measurements. The first setup uses disk compression experiment, known as diametral compression test (Brazilian disk). However, the elastic properties of the material cannot be obtained directly. Instead, an inverse mechanics computational scheme, using both a finite element (FE) model and analytical solution, is proposed. The second direct testing setup is uniaxial compression of rectangular-shaped blocks. The Young's modulus and Poisson's ratio are extracted directly from the experimental stress–strain curves. Our results of tested samples show the relation between the density and the Young's modulus to coincide with previously published trends. The direct and iterative inverse-mechanics solution methods agree well with each other. The Poisson's ratio is found to be independent of the material apparent density. Comparisons between the two methods and recommendations for expanding the disk testing approach to fracture toughness are discussed.

Double cantilever beam (DCB) specimens fabricated from a graphite/epoxy (G0814/913) woven prepreg containing a straight through notch were tested by means of constant amplitude fatigue. The specimen was composed of 15 layers with fibers alternating between the weft and warp in the 0°/90° and the +45°/−45° directions. Eight fatigue tests were carried out to determine the delamination growth rate da/dN vs the nearly mode I cyclic energy release rate ΔGI. Comparison of the delamination growth rate was made to the crack propagation rate of an aluminum alloy. It was found that a crack in the aluminum will grow faster but will be less sensitive to uncertainties or changes in load level.

The aim of this investigation is to measure the interface fracture toughness of a woven composite. For this purpose, double cantilever beam (DCB) specimens are tested to measure the load as the delamination grows. The specimen is composed of 15 layers of a carbon–epoxy, balanced weave with alternate layers containing fibers in the \(0^{\circ }\!/90^{\circ }\) directions and the \(+45^{\circ }\!/\!\!-\!45^{\circ }\) directions. A thin piece of Teflon is placed between two layers of differing directions. The specimens are analyzed by means of the finite element method and an interaction energy or \(M\)-integral to determine the stress intensity factors, interface energy release rate and phase angles. The first term of the asymptotic solution for the stress and displacement fields obtained by means of the Stroh and Lekhnitskii formalisms is used to define auxiliary solutions for the \(M\)-integral. The critical interface energy release rate is found and exhibits a slowly increasing resistance curve. Comparisons are made to a simple expression from the literature.

This study focuses on the behavior of a crack in piezoelectric material in which the crack is parallel to the poling direction. Tests were carried out on four-point bend specimens made of PZT-5H (Morgan Electro Ceramics, Wrexham, UK). Cracks were introduced parallel to the poling direction. With an electric field induced perpendicular to the cracks, the load was increased until failure occurred. Using the load at fracture, the level of the electric field and the critical crack length, finite element analyses were carried out to determine the intensity factors. These included K I , K IV and a small K II component. The latter occurred because of the small asymmetry of the crack. The material within the crack (air) was modeled to be a dielectric material. A fracture criterion is implemented in which the test results show small scatter about the failure curve. These tests were carried out in order to improve on the scatter obtained from a previous set of tests presented in Motola et al. (Int J Fract 159:167–190, 2009a). The scatter from those results will be explored.

In this study, effective mechanical properties of Polymethyl-methacrylate (PMMA) reinforced with Carbon Nanotubes (CNTs) are determined by means of two approaches. First of all, tensile tests are carried out to obtain Young's modulus E, Poisson's ratio nu, the stress to failure sigma(f) and the strain to failure epsilon(f). In addition, by means of the High-Fidelity Generalized Method of Cells (HFGMC) micromechanical model, Young's modulus and Poisson's ratio are calculated. The tests and analyses are carried out for neat PMMA, as well as the composite with weight fractions of CNTs of 0.5%, 1% and 2%.

A methodology developed for measuring Young's modulus and the full stress-strain curve on micron-sized specimens was extended here to measure Poisson's ratio. A dog-bone type specimen was used within a small loading machine with a maximum load of 5 N. The specimen was fabricated from single crystal silicon (SC-Si) with the specimen gage and loading direction in the (0 01) orientation. A silicon on insulator (SOI) wafer was used with a deep reactive ion etching (DRIE) based process. Geometrical parameters of the initial cross-sectional area of the gage were measured by means of image processing on environmental scanning electron microscope (ESEM) images. The test setup also consists of an optical microscope with a monochromatic camera and a data acquisition system. The strains were obtained through the displacement field which was determined by means of digital image correlation (DIC). A speckle pattern was placed on the specimen gage. SC-Si was chosen to study since it is expected that on both the micro and macro-scales, Young's modulus and Poisson's ratio will have the same value. Hence, the accuracy of the method may be examined.The average value of Young's modulus E = 131.4 +/- 2.1 GPa was obtained with the micro-specimens and is consistent with values determined on the macro-scale (E = 130 GPa). The average value of Poisson's ratio on the micro-scale was found as v = 0.23 +/- 0.03 which is lower than the macro-scale value of v = 0.28. The failure stress was determined to be sigma(f) = 1.46 +/- 0.10 GPa. Results for Young's modulus reflect the reliability of the methodology which is suitable for characterization of a large variety of materials exploited in micro-devices for both sensing and actuation. The reasons for the low values measured for v were investigated through emulations of determining the strains. An improvement in the image acquisition system is suggested. (C) 2011 Elsevier B.V. All rights reserved.

In this investigation, quasi-static fracture tests double cantilever beam (DCB) woven composite specimens containing a straight through delamination are presented.The specimen is shown in Fig. 1.The fibers are carbon 300T which are transversely isotropic.The epoxy matrix is 913 and is isotropic.Each ply is a balanced plain weave of carbon fiber yarn in an epoxy matrix.The plies are laid up so that they alternate between a 0°/90° and a +45°/ -45° weave.There are 15 plies with the delamination located between the seventh and eighth plies.Thus the interface is between a 0°/90° weave and a +45°/ -45° weave.Each of these plies is anisotropic.Mechanical properties were calculated by means of the High Fidelity Generalized Method of Cells (HFGMC) [1].The specimens are based on the ASTM Standard D5528-01 [2] which is used for testing unidirectional composites.In order to obtain a relation between the interface energy release rate Gi, the mode mixity phase angles, the applied load and crack length, finite element analyses were carried out.The stress intensity factors were determined by means of an interaction energy integral.To this end, the Stroh formalism [3] was used to determine the first term of the asymptotic expressions for the stress and displacement fields in the neighborhood of the delamination front.Similar methods have been used for straight through delaminations in cross-plies [4,5].The experimental set-up consists of an Instron loading machine (no.8872) with a load cell of maximum load 250 N.This small load cell is required since the maximum load at fracture is approximately 60 N.The Instron measures the load as a function of time.Figure 1: Double cantilever beam woven composite specimen.

Fracture tests carried out on unpoled and poled PZT-5H four-point bend specimens are presented in this paper. The crack faces were parallel to the poling direction. Both mechanical loads and electric fields were applied to the poled specimens. The experimental results were analyzed by means of the finite element method and a conservative M-integral including the crack face boundary conditions. Fracture tests on four-point bend PIC-151 specimens with the crack faces perpendicular to the poling directions were also analyzed here; the experimental results were taken from the literature. A mixed mode fracture criterion is proposed for piezoelectric ceramics. This criterion is based upon the energy release rate and two phase angles. This criterion was implemented with experimental results from the literature and from this investigation. Excellent agrement was found between the fracture curve and the experimental results of the specimens with the crack faces perpendicular to the poling direction. With some scatter, reasonable agreement was observed between the fracture curve and the experimental results of the specimens with crack faces parallel to the poling direction.

Experiments are carried out to determine the delamination toughness for a crack along the interface between two transversely isotropic materials. The material chosen for study consists of carbon fibers embedded within an epoxy matrix. A crack is introduced between two layers of this material, with fibers in the upper layer along the  + 45°-direction and those in the lower layer along the  − 45°-direction both with respect to the crack plane. The Brazilian disk specimen is employed in the testing. To calibrate the specimens, stress intensity factors are obtained which result from the applied load, as well as residual curing stresses. It may be noted that all three modes are coupled, leading to a three-dimensional problem. The finite element method and a mechanical M-integral are employed to determine the stress intensity factors arising from the applied load. For the residual stresses, a three-dimensional conservative thermal M-integral is presented for stress intensity factor determination. The stress intensity factors found for the applied load and residual stresses are superposed to obtain a local energy release rate, together with two phase angles. From the load at fracture, the critical interface energy release rate or interface toughness \({{\mathcal G}_{ic}}\) as a function of phase angles ψ and ϕ is determined. Results are compared to a fracture criterion.