ALBERT

Notes: Abstract  Patch formation is common in grazed grasslands but the mechanisms involved in the formation and maintenance of patches are not clear. To increase our knowledge on this subject we examined possible reasons for patch formation and the influence of management on changes between patch states in three experiments in native pasture communities in the Crows Nest district, south-east Queensland. In these communities, small-scale patches (tall grassland (dominated by large and medium tussock grasses), short swards (dominated by short tussock grasses and sedges), and lawns (dominated by stoloniferous and/or rhizomatous grasses)) are readily apparent. We hypothesized that the formation of short sward and lawn patches in areas of tall grassland was due to combinations of grazing and soil fertility effects. This was tested in Experiment 1 by applying a factorial combination of defoliation, nutrient application and transplants of short tussock and stoloniferous species to a uniform area of tall grassland. Total species density declined during the experiment, was lower with high nutrient applications, but was not affected by defoliation. There were significant changes in abundance of species that provided support for our hypotheses. With light defoliation and low nutrients, the tall grassland remained dominated by large tussock grasses and contained considerable amounts of forbs. With heavy defoliation, the pastures were dominated by medium tussock grasses and there were significant decreases in forbs and increases in sedges (mainly with low nutrients) and stoloniferous grasses (mainly with high nutrients). Total germinable seed densities and those of most species groups were significantly lower in the heavy defoliation than the light defoliation plots. Total soil seed numbers were not affected by nutrient application but there were fewer seeds of the erect forbs and more sedge seeds in plots with high nutrients. The use of resting from grazing and fire to manage transitions between patches was tested. In Experiment 2, changes in species density and abundance were measured for 5 years in the three patch types with and without grazing. Experiment 3 examined the effects of fire, grazing and resting on short sward patches over 4 years. In Experiment 2, total species density was lower in lawn than short sward or tall grassland patches, and there were more species of erect forbs than other plant groups in all patch types. The lawn patches were originally dominated by Cynodon spp. This dominance continued with grazing but in ungrazed patches the abundance of Cynodon spp. declined and that of forbs increased. In the short sward patches, dominance of short tussock grasses continued with grazing but in ungrazed plots their abundance declined while that of large tussock grasses increased. The tall grassland patches remained dominated by large and medium tussock species. In Experiment 3, fire had no effect on species abundance. On the grazed plots the short tussock grasses remained dominant but where the plots were rested from grazing the small tussock grasses declined and the large tussock grasses increased in abundance. The slow and relatively small changes in these experiments over 4 or 5 years showed how stable the composition of these pastures is, and that rapid changes between patch types are unlikely.

Notes: Abstract The dependence of the mechanical properties such as strength, modulus and fracture toughness on the volume fraction of the reinforcing glass fibres and glass beads in polyoxymethylene (POM) matrix was studied. The majority of the measured quantities in tension or flexure tests, seemed to be linear functions of either the volume fraction of the glass fibres or the glass beads. The relationship between some individual mechanical properties seemed to be linear as well. Consequently, many of the mechanical properties of these POM composites (POM/GF and POM/GB) could be estimated from one measured property using the relationships presented. Also, the same property measured for the two composite systems was found to be linearly related. Consequently, the mechanical properties of one composite system, (i.e. POM/GB) could be used to determine that of the other system (i.e. POM/GF) at the same filler concentration.

Notes: Abstract The use of a conventionalJ analysis to describe the ductile tearing of thin low density polyethylene sheet is described. This is a measure of the total energy required to cause fracture. The use of the current energy release rate to determine the local dissipation rate is then given and it is shown that an initiation (plane strain) and reasonably constant propagation (plane stress) values are obtained.

Notes: Abstract The results of previous work, in which static fracture tests were applied to propylene-ethylene copolymers, suggest that under circumstances of high constraint the theory of fracture mechanics is useful in the description of the fracture behaviour of such tough materials. In this work similar experiments have been carried out on a series of polypropylene/EPR/HDPE blends in order to compare their behaviour with that of the copolymers. From the evidence it appears that these materials are very similar to the copolymers in terms of fracture behaviour and morphology. The examination of impact fracture behaviour of the blends showed that both instrumented and energy measuring pendulum machines yield similar results when loading times are similar. However, it has been shown that short loading times may lead to high fracture energies, which cause blunting of the crack tip. This behaviour has been modelled using previously developed theory. The effects described demonstrate the care required in impact data interpretation.

Notes: A method for the determination of residual stresses in plastic pipe by layer removal and subsequent slitting is described. Results are analyzed from deflections measured on a high density polyethylene pipe. The use of these data in the calculation of KI around a semi-elliptical flaw at the pipe wall is then discussed.