Mixed-mode crack growth in ductile thin-sheet materials under combined in-plane and out-of-plane loading

Ductile thin-sheet structures, such as fuselage skin or automobile panels, are widely used in engineering applications. These structures often-times are subjected to mixed mode (I/II/III) loading, with stable crack growth observed prior to final fracture. To characterize specific specimen deformations during stable tearing, a series of mixed-mode I/III stable tearing experiments with highly ductile thin-sheet aluminum alloy and steel specimens have been measured by using three-dimensional digital image correlation (3D-DIC). Measurements include (a) specimen’s deformed shape and 3D full-field surface displacement fields, (b) load-crack extension response and (c) crack path during stable tearing, (d) angular and radial distributions of strains and (e) the mixed mode crack-opening displacement (COD, measured at 1-mm from crack tip along crack surface) variation as a function of crack extension. Results indicate that for both aluminum alloy and steel at all mixed-mode I/III loading conditions (Φ = 30°, 60° and 90°), the crack tip fields have almost identical angular and radial polar strain distributions. The mixed mode I/III fields were different from those observed for the nominal Mode I loading case (Φ = 0°). The effect of the Mode III loading component is that it lowers the magnitude of the dominant strain component ε _θθ ahead of the growing crack tip and increases the singularity of the strain as compared with that in the mode I case. In addition, measurements indicate that the average mixed mode I/III stable COD for AL6061-T6 (GM6208 steel) is 4×(3×) greater than the average Mode I stable COD.     

Elution Patterns from Capillary GC for Methyl-Branched Alkanes

A common and confusing problem in analyses of insect hydrocarbons is in making sense of complicated gas chromatograms and interpreting mass spectra since branched chain compounds differing by one or two carbons in backbone or chain length may elute from the column at nearly the same time. To address this confusing situation, relative gas chromatography (GC) retention times are presented for typical mono-, di-, tri-, and tetramethylalkanes comprising most of the commonly appearing series of homologous methyl-branched alkanes up to 53 carbons that are found in insect cuticular hydrocarbons. Typical insect-derived methylalkanes with backbones of 33 carbons were characterized by Kovats indices (KI); monomethyl alkanes elute between KI 3328 and 3374, dimethylalkanes elute between KI 3340 and 3410, trimethylalkanes elute between KI 3378 and 3437, and tetramethylalkanes elute between KI 3409 and 3459, depending upon the positions of substituents. A protocol is described for identification of methyl-branched hydrocarbons eluted from nonpolar polysiloxane DB-1 capillary GC columns. In this protocol, retention indices (KI values) are assigned to peaks, then the patterns in GC peaks that probably contain homologs are marked to assist subsequent GC-mass spectrometric (GC-MS) interpretation. Use of the KI allows assignment of likely structures and the elimination of others, with demonstrative consistency, as there are no known exceptions. Interpretation of electron ionization mass spectra can then proceed within narrowed structural possibilities without the necessity of chemical ionization GC-MS analysis. Also included are specific examples of insect hydrocarbons that were assembled from 30 years of the literature, and these are intended to help with confirmation of confusing or contradictory structures.     

Morphology and electrical conductivity in polyaniline/polyolefinblends

The effects of processing and molecular composition on the morphology and electrical conductivity of melt pressed polyaniline (PANI)/polyolefin blends have been investigated. In all systems, the morphology was found to consist of two distinct phases, a conducting network of PANI embedded within the thermoplastic host. Low field conductivities ranging from 10^-14 to 10^-4 S/cm could be accessed, through a suitable choice of PANI content and processing conditions. To 200 V/mm, the conductivity of the material was found to increase exponentially with applied field, thereafter remaining close to constant until the onset of breakdown. On further analysis, the applied field E dependence of conduction current i prior to breakdown was found to obey a relationship of the form i=A sinh(bE), as reported in the literature for insulators in the so-called low-field regime. Despite the dramatic variations in electrical properties that result from incorporation of the conducting polymer, the low strain mechanical properties were not degraded to any great degree     

Correction to: Heat Treatment of Alloy 718 Made by Additive Manufacturing for Oil and Gas Applications

JOM - In the last paragraph of the section “SOLIDIFICATION AND THERMODYNAMIC SIMULATIONS”, the authors would like to change the sentence “Although the solvus temperature for...     

Poly(D,L‐lactide‐co‐glycolide)/poly(ethylenimine) blend matrix system for pH sensitive drug delivery

Poly(D ,L ‐lactide‐co‐glycolide) (PLGA) and poly(ethylenimine) (PEI) were blended and found to form a homogeneous pH sensitive matrix for drug release. Differential scanning calorimetry (DSC) studies of the PLGA/PEI blends showed a single glass transition temperature at all compositions. Fourier transform infrared spectroscopy (FTIR) demonstrated that the PLGA carbonyl peak at 1760 cm^?1 shifted to 1666 cm^?1 as a result of amide bond formation between the two polymers. This was confirmed by ¹³C nuclear magnetic resonance studies. A PLGA/PEI matrix of 90/10 weight ratio was chosen for evaluation for controlled drug release. Both hydrophobic β‐lapachone and hydrophilic rhodamine B showed pH dependent release profiles with faster release kinetics at lower pH values. The observed pH sensitive drug release was mainly attributed to two factors, pH dependent swelling and protonation of the PEI‐PLGA matrix. These results demonstrate utility of a PLGA/PEI matrix and its potential application in pH responsive drug delivery. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 89–96, 2006     

A regional pH-alkalinity relationship

An explicit equation relating the pH and alkalinity of natural waters is derived as an inverse hyperbolic sine function. For the range of pH generally encountered in lake and stream acidification studies, the parameters of the equation are related to the dissolved CO₂ saturation relative to atmospheric CO₂ and the concentration of weak acid anions, though the relationship is approximate. The functional form allows for statistical parameter estimation given a regional or temporal pH-alkalinity data-set. The relationship simplifies pH estimation in regional aquatic acidification models where alkalinity is computed as the master variable.     

Critical learning themes in project management education: Implications for blended learning

This research examines the underlying reasons why students taking project management courses emphasise skills that are transferable and the utilisation of e-learning environments as critical to their learning experiences. Students' opinions are expressed through a series of focus groups. We found that the underlying reasons for students' emphasis on these two factors as crucial to learning and teaching project management could be classed under five higher-order themes. The implications of our findings are that in order to develop desired human, conceptual and technical skills, a teaching approach based on a blend of learning that resides at the intersection of the ‘transferable skills’ and ‘e-learning environments’ construct is required for the effective teaching of project management. For effectiveness, this blended form of andragogy (learning focused on adults) must be flexible enough to cater for the vast variations in the profiles of students, and their individual learning preferences.     

On the nature of virtuous change in cultural landscapes: Exploring sustainability through qualitative models

Cultural landscapes are internationally valued resources, yet face endemic threats. Often the ‘drivers for change’ result in a loss of valued qualities, and are associated with ‘vicious circles’ of landscape deterioration. The way in which landscape may represent an integrative framework for research and policy is noted. It is argued that a key objective of research and policy should be to promote ‘virtuous circles’ in which social capital and economic entrepreneurship valorize distinctive landscape characteristics, leading to a situation of mutual reinforcement between human activity and environmental capital. Particular attention is given to qualitative models of virtuosity in the landscape. Positive feedback loops in the landscape are illustrated by reference to current examples of integrated rural projects. The further development of formal models as a basis for reinstating virtuous circles is advocated as a basis for the future planning and understanding of cultural landscapes.