The temperature field induced by the dynamic stresses of a transverse crack in periodically layered composites

The temperature field induced by the dynamic application of a far-field mechanical loading on a periodically layered material with an embedded transverse crack is investigated. To this end, the thermoelastically coupled elastodynamic and energy (heat) equations are solved by combining two approaches. In the first one, the dynamic representative cell method is employed for the construction of the time-dependent Green’s functions generated by the displacement jumps along the crack line. This is performed in conjunction with the application of the double finite discrete Fourier transform on the thermomechanically coupled equations. Thus the original problem for the cracked periodic composite is reduced to the problem of a domain with a single period in the transform space. The second approach is based on wave propagation analysis in composites where full thermomechanical coupling in the constituents exists. This analysis is based on the coupled elastodynamic-energy continuum equations where the transformed time-dependent displacement vector and temperature are expressed by second-order expansions, and the elastodynamic and energy equations and the various interfacial and boundary conditions are imposed in the average (integral) sense. The time-dependent thermomechanically coupled field at any observation point in the plane can be obtained by the application of the inverse transform. Results along the crack line as well as the full temperature field are given for cracks of various lengths for Mode I and Mode II deformations. In particular the temperature drops (cooling) at the vicinity of the crack’s tip and the heating zones at its surroundings are generated and discussed.     

Crack resistance in two-dimensional periodic materials of medium and low porosity

The plane problem of crack resistance in elastic materials with doubly periodic system of voids is investigated. The relatively high fractional density (medium and low porosity) of above 0.6 which is typical for the partially-sintered materials is addressed. The stress field in the voided plane with embedded Mode I crack of arbitrary length bridging the voids is evaluated. In the framework of stress criterion of fracture this field allows the determination of the fracture toughness of the considered material with periodic microstructure in terms of the solid (parent) material tensile strength.The mathematical modeling of this problem is complicated due to the fact that the “ligaments” between the voids are so thick that they cannot be treated as beams. As a result, theoretical methods used to evaluate the fracture toughness of low-density cellular materials are not applicable. Accordingly, the present problem is solved by means of a novel analysis which is based on the combined use of the representative cell method, based on the discrete Fourier transform, in conjunction with a higher-order theory and a micromechanical model. These combined three approaches allow the performance of an accurate continuum mechanics analysis of the highly non-uniform stress field in the voided material with a crack.The analysis of this field for different crack lengths has shown which length must be employed in the fracture toughness evaluation. The dependence of the fracture toughness upon the relative density is examined and found to vary linearly in the majority of the considered density range. This result agrees with the known experimental observations and other theoretical predictions.     

Angle-dependent light scattering in materials with controlled diffuse solar optical properties

Light scattering plays a prominent role in a wide range of energy-efficient materials and solar applications. Some examples are materials for daylighting, diffusely reflecting sunscreens, foils for radiative cooling and nanocrystalline solar cells. Measurements of the angular profile of light scattering are very useful for obtaining a detailed characterization of the light scattering mechanisms. We review recent theoretical results on the forward and backward light scattering profiles. Forward scattering is of major importance for novel pigmented polymeric daylighting materials. Measurements of scattering profiles are in good agreement with Mie theory. Backscattering profiles from highly diffusely reflecting paints containing titanium oxide-based pigments have also been measured. It seems that scattering from the paint surface dominates at low pigment volume fractions. Results for paints with high pigment volume fractions are interpreted in terms of coherent backscattering effects from the pigment particles.     

Large watershed management and restoration: dioxin sediment remediation case study

This paper reviews continuing, long-term remediation of river sediments containing dioxin and other chemical compounds in a large watershed of the Great Lakes Region. Chlorinated dibenzo-p-dioxins are a ‘family’ of chemically related compounds commonly known as chlorinated dioxins or simply, dioxins. The highest levels are usually found in sediments, soil and animal fats. The most toxic chemical in this group is 2,3,7,8-tetrachlorodibenzo-para-dioxin, the ‘standard’ to which other dioxins are compared and which has been shown to be very toxic in animal studies. The US Environmental Protection Agency (EPA) and Michigan Department of Environmental Quality (MDEQ) have made a lengthy effort to assess and remediate portions of the Saginaw Bay Watershed, including the Tittabawassee River. The paper reviews the EPA-proposed ‘phased approach’ to restoration and remediation of a short segment (Segment 1) of the Tittabawassee River sediments. Sediments are contaminated with a number of chemical pollutants other than dioxins, including arsenic, cholorbenzenes, cholorphenols, ethyl parathion, o-phenylphenol and polycyclic aromatic hydrocarbons. The paper evaluates three proposed ‘cleanup alternatives’, with final action method suggested based on effectiveness, feasibility for implementation and cost.     

Remote sensing of emissions from in-use small engine marine vessels

This paper reports the first use of a remote sensing device to measure emissions from in-use marine vessels. Emissions from 307 small marine vessels were measured as they passed through the Hiram M. Chittenden locks near Seattle, WA. Of these vessels, 89 were matched to state registration information to allow for further analysis of emissions vs model year, fuel type, and engine type. Emission factors are reported for CO, HC, and NOx in grams of pollutant per kilogram of fuel. The measured emission factors generally agreed with those derived from laboratory studies. HC emissions are disproportionately skewed across the fleet where 40% of the emissions come from just 10% of the fleet. These are most likely due to the remaining two-stroke engines in the fleet. CO and HC emissions show no improvement with newer vessels.     

Global source-receptor relationships for mercury deposition under present-day and 2050 emissions scenarios

Global policies regulating anthropogenic mercury require an understanding of the relationship between emitted and deposited mercury on intercontinental scales. Here, we examine source-receptor relationships for present-day conditions and four 2050 IPCC scenarios encompassing a range of economic development and environmental regulation projections. We use the GEOS-Chem global model to track mercury from its point of emission through rapid cycling in surface ocean and land reservoirs to its accumulation in longer lived ocean and soil pools. Deposited mercury has a local component (emitted Hg(II), lifetime of 3.7 days against deposition) and a global component (emitted Hg(0), lifetime of 6 months against deposition). Fast recycling of deposited mercury through photoreduction of Hg(II) and re-emission of Hg(0) from surface reservoirs (ice, land, surface ocean) increases the effective lifetime of anthropogenic mercury to 9 months against loss to legacy reservoirs (soil pools and the subsurface ocean). This lifetime is still sufficiently short that source-receptor relationships have a strong hemispheric signature. Asian emissions are the largest source of anthropogenic deposition to all ocean basins, though there is also regional source influence from upwind continents. Current anthropogenic emissions account for only about one-third of mercury deposition to the global ocean with the remainder from natural and legacy sources. However, controls on anthropogenic emissions would have the added benefit of reducing the legacy mercury re-emitted to the atmosphere. Better understanding is needed of the time scales for transfer of mercury from active pools to stable geochemical reservoirs.     

Mineral and trace element composition of the Lokpanta oil shales in the Lower Benue Trough, Nigeria

The concentrations of minerals and trace elements in the Lokpanta oil shale from the Lower Benue Trough, Nigeria have been determined by X-ray diffraction (XRD) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), respectively. X-ray diffraction data were evaluated using the SIROQUANT™ interactive data processing system based on Rietveld interpretation methods. A new method of trace element determination in oil shale, involving LA-ICP-MS analysis of glass beads prepared by fusing oil shale ash on an iridium strip heater was used, and the accuracy of the method was assessed by including a standard shale reference material (SGR-1b) in the analysis program.The minerals in the raw oil shales are mainly quartz, calcite and clay minerals, with the latter being represented by kaolinite and interstratified illite/smectite. Ashes of the oil shale samples prepared at 815 °C have quartz and (in some cases) illite as the dominant mineral phases, along with a significant proportion of amorphous materials. The Lokpanta oil shales are highly enriched in some potentially hazardous trace elements, including V, Cr and Ni, when compared with oil shales from other deposits around the world. The results obtained for the trace elements in the reference material show that the LA-ICP-MS method described in this study is very accurate and precise for the determination of a wide range of trace elements in oil shales.