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In this paper, fracture mechanics concepts are reviewed and their relevance to examine the toughness of highly deformable materials such as high-density polyethylene (HDPE) pipe materials is discussed. Using two different specimen configurations (single edge notched bending and compact tension), it was found that the $$J-R$$ approach is unable to give pertinent indications on fracture toughness of HDPE. Alternatively, applying the essential work of fracture approach to double edge notched tension specimen, seems a more appropriate way to measure the fracture strength of HDPE and therefore to analyze the fracture process of such materials. Nevertheless, the severe necking occurring at the crack tip and in the plastic zone makes difficult the crack growth measurement, which clearly depends on the strain state and on the stress triaxiality level. [ABSTRACT FROM AUTHOR]

In this work the impact of ultra-violet (UV) irradiation on the mechanical behaviour of amorphous biodegradable poly (lactic acid) (PM) films is analysed PLA films were submitted to UV irradiation for increasing exposure time. Two kinds of experiments were conducted, chemical and mechanical. The chemical degradation was measured by gel permeation chromatography technique. The PM films were mechanically investigated by stretching experiments before and after UV exposure. Their mechanical properties were obtained by a video- controlled system. Our purpose is to establish the relationship between macroscopic mechanical response and molecular parameters such as the molecular weight, and external solicitations such as temperature, strain rate and UV irradiation. The interactions between photo degradation and changes in polymer properties are discussed. [ABSTRACT FROM AUTHOR]

The article reports on the plastic flow of a polymer during the equal channel angular extrusion (ECAE) process. The ECAE modifies microstructure through high plastic deformation while maintaining the samples geometry. A model of this process is made in order to research certain behaviors of the polypropylene with finite element analysis and the Gurson-Tvergaard damage potential are used. Also, the model is used in order to predict what the extrusion loads, strains, stress fields, and void volume fraction distributions are.

Roots of nine of the 12 vascular plant species present on sub-Antarctic Heard Is land were examined for mycorrhizae. All species examined had some type of mycorrhization with most possessing associations with vesicular-arbuscular mycorrhizae or dark septate mycorrhizae. The degree of mycorrhization varied considerably across sites. Sampled plants were growing on either morainic or beach substrates with some areas exposed only in the last century. As mycorrhizae are known to play an important role in the nutrient uptake by host-plants, these results support the idea that mycorrhizae can influence the capacities of plants to colonize in cold and low-nutrient environments such as sub-Antarctic glacier forelands. Comparisons with data from other sub-Antarctic islands are made. [ABSTRACT FROM AUTHOR]

Primary succession was studied on recently deglaciated areas in front of the Amore Glacier, Kerguelen Islands (490 30'S, 690 30'E). Vegetation, colonization processes and soil development were investigated on seven sites on the outwash plain over a distance of 5 km and representing a > 200-yr old chronosequence. Seven species are involved in the succession, showing four patterns of change: (1) 'pioneer' (Poa kerguelensis, Poa annua, Colobanthus kerguelensis and Cerastium fontanum); (2) 'intermediate' (Festuca contracta); (3) 'late colonizer' (Azorella selago); and (4) 'fluctuating' (Agrostis magellanica). Two of the pioneers are introduced species (Poa annua and Cerastium). The total plant cover increases significantly with the age of the sites butnever exceeds 4.2%. The plant succession pattern observed in this study appears to be related to soil development. Root architecture and fine particle dynamics in the soil may explain the behaviour of the different species along the chronosequence. The pioneer species have avery shallow root system whereas the intermediate and late colonizers are deeper and longer rooted. The dominance of Azorella selago (Apiaceae) in the oldest community may be attributed to its unique root system in relation to the vertical distribution of silt cappings in the soil. [ABSTRACT FROM AUTHOR]

The aim of this study was to estimate the influence of biotic and abiotic factors on Suaeda maritima reproduction on a salt marsh. Individuals of Suaeda maritima were submitted in natural conditions to four series of densities (100, 1,000, 4,000 and 8,000 plants/m2). When density increases, individuals tend to be less or non-branched, while individual biomass decreases. Consequently, individual seed production decreases as density increases. Despite morphological modifications, Suaeda maritima present density-dependent mortality. For a unit area, total biomass and seed production are higher at intermediate density (1,000 plants/m2). Environmental factors could interfere with self-thinning. They seem to limit the effect of competition on mortality and to have an influence on individual and total seed production. This experiment stressed the importance of a biotic factor such as intra-specific competition, which occurs at the same time as abiotic factors, in Suaeda maritima dynamics in the field.