Interpretation of Fracture Toughness and R-Curve Behavior by Direct Observation of Microfracture Process in Ti-Based Dendrite-Containing Amorphous Alloys

Fracture properties of Ti-based amorphous alloys containing ductile beta dendrites were explained by directly observing microfracture processes. Three Ti-based amorphous alloys were fabricated by adding Ti, Zr, V, Ni, Al, and Be into a Ti-6Al-4V alloy by a vacuum arc melting method. The effective sizes of dendrites varied from 63 to 104 mu m, while their volume fractions were almost constant within the range from 74 to 76 pct. The observation of the microfracture of the alloy containing coarse dendrites revealed that a microcrack initiated at the amorphous matrix of the notch tip and propagated along the amorphous matrix. In the alloy containing fine dendrites, the crack propagation was frequently blocked by dendrites, and many deformation bands were formed near or in front of the propagating crack, thereby resulting in a zig-zag fracture path. Crack initiation toughness was almost the same at 35 to 36 MPaaem within error ranges in the three alloys because it was heavily affected by the stress applied to the specimen at the time of crack initiation at the crack tip as well as strength levels of the alloys. According to the R-curve behavior, however, the best overall fracture properties in the alloy containing fine dendrites were explained by mechanisms of blocking of the crack growth and crack blunting and deformation band formation at dendrites. (C) The Minerals, Metals & Materials Society and ASM International 2015ope

Increased yield and persistence of several annual medic species and Medicago sativa by inoculation with selected strains of Sinorhizobium meliloti and S. medicae

A broad range of genotypes of Medicago sativa, and annual medics including M. polymorpha, M. tornata and M. littoralis were inoculated with strains of Sinorhizobium meliloti or S. medicae of differing effectiveness for symbiotic N2 fixation then sown at 4 field locations. Dry matter production over 2 seasons was strongly related to plant density, which in turn was related to symbiotic effectiveness. Eighteen months after sowing at Esperance, Western Australia, lucerne inoculated with strain WSM922 showed 79% higher plant density and 43% more production than control strain CC169. At Broomehill, no significant differences existed in dry matter production between lucerne cultivars inoculated with strains WSM922, WSM826 and U45. Across all lucerne genotypes, inoculation with WSM922 outyielded those inoculated with CC169 by 99%. At Jerramungup, the difference in yield between these 2 inoculant strains was 44%. Results were consistent with those previously obtained under controlled conditions and emphasised the necessity to remain aware of the symbiotic requirements of newly produced cultivars. An analysis of nodule occupancy at 1 site using PCR-RAPDs revealed the dominance of a particular rhizobial strain (WSM922) in uninoculated plots which had become colonised over 3 seasons. The necessity for separate inoculant species of Sinorhizobium in Australia to satisfy the symbiotic requirements of the acid and alkaline groups of medics was reaffirmed

Estimation of host-strain compatibility for symbiotic N-fixation between Rhizobium meliloti, several annual species of Medicago and Medicago sativa

Standard methods for estimating host-strain compatibility for N-fixation in vitro proved inadequate for examination of the symbiosis between Rhizobium meliloti and Medicago sativa, M. littoralis, M. tornataas well as for hybrids between M. littoralisand M. truncatula. When screening procedures in soil free of background R. melilotiwere adopted, nitrogen fixation appeared to be unrestricted by the screening environment. During the experiments it became clear that the single commercial inoculant strain available in Australia (CC169) was poorly effective at N-fixation with many of the lucerne and annual medic cultivars examined. Interspecific hybridisation between M. truncatulaand M. littoralis also produced genotypes that were particularly difficult to satisfy in a symbiotic sense. Despite the existence of substantial host-strain genotype interactions between the symbiotic partners, several alternative strains of R. meliloti proved to be broadly effective at N-fixation. One of these, WSM826, has since become commercially available in Australia

A second generation of annual pasture legumes and their potential for inclusion in Mediterranean-type farming systems

A second generation of annual pasture legumes and their root-nodule bacteria has been released to agriculture in Mediterranean-type environments. These new species emanate from selection activity focussed upon ‘alternative legumes’. In 1992, in response to changing constraints upon production, a program was initiated which sought species with different ideotypic traits to the traditional annual medics and clovers used in agriculture in southern Australia. Traits sought in the new species were deeper root systems, improved persistence from higher hardseed levels, acid tolerant symbioses, tolerance to pests and diseases and ease of harvesting with conventional cereal harvesters. Several cultivars of species new to Australian agriculture such as biserrula (Biserrula pelecinus), French serradella (Ornithopus sativus), gland clover (Trifolium glanduliferum) and improved varieties of arrowleaf clover (Trifolium vesiculosum) and yellow serradella (Ornithopus compressus) were developed and have had rapid adoption and impact in southern Australian ley- and phase-farming systems. This paper reviews the importance of ley farming for Australian agriculture, the shortcomings of the traditional medics and clovers and the imperatives for a second generation of annual pasture legume species to be developed. In addition to enhancing ley farming, the commercial availability of a second generation of annual pasture legume species has provided a much needed impetus for the development of more flexible and sustainable farming systems

The breeding system of Ornithopus sativus Brot. subsp. sativus

Genetic traits within Ornithopus sativus Brot. make it suitable for breeding as a forage legume in agriculture. The breeding system of O. sativus must be understood to stabilize valuable traits once developed. Hybridization between white‐flowered and pink‐flowered genotypes of O. sativus revealed the white flower colour to be inherited recessively to pink, while early flowering showed genetic dominance over late flowering (d = 0.5). The pink flower colour was always associated with red pigmentation on seedling hypocotyls, which provided a pragmatic aid in the selection process. Pollination of O. sativus is largely autogamous, but examination of hypocotyl colour of seedlings from white‐flowered trap plants placed among pink‐flowered plants in a sward indicated a xenogamic cross‐pollination rate of 25% is possible. This significant level of cross‐pollination revealed opportunities for breeding desirable traits within the species, while providing a warning that shifts in population structure could occur in response to selection pressure

Long‐term storage of forage legumes greatly alters the hard seed breakdown pattern in situ

Knowledge of the hard seed content of annual legumes, and its pattern of breakdown, is critical to the understanding of their ecology and management within farming and natural ecosystems. For logistical reasons, seed that has been stored for varying lengths of time is often used for pasture establishment and agronomy experiments. However, the implications of storage on hard seed physiology are unknown. The aim of this study was to explore the impact of seed storage on its subsequent pattern of hard seed breakdown when exposed to field conditions. Experiments examined seed from six different annual legume genotypes that had been either produced the prior year or stored under ambient conditions for 11–22 years. Comparisons were then made between the two seed sources on hard seed breakdown patterns in situ. Although initial hard seed levels were mostly unaffected by storage (seed of five genotypes remained over 93% hard after more than 11 years of storage), the patterns of release from dormancy during exposure to hard seed breakdown conditions of stored seed differed greatly (p 90% to 90% hard during the same period. Given this large and consistent impact, it is recommended that studies of the patterns of hard seed breakdown in legumes compare seed stored under consistent and well‐defined conditions

Preliminary assessment of bladder clover (Trifolium spumosum L.) as an annual legume for ley farming systems in southern Australia

Trifolium spumosum L. (bladder clover) is an aerial seeding annual legume that is adapted to fine-textured soils throughout the Mediterranean Basin. This article is the first of two papers that describe the process of domestication of T. spumosum as a new species to commercial agriculture. This paper describes a broad range of investigations into the ecology, agronomy and rhizobiology of this new species. Through a series of five experiments, we have tested the general hypothesis that T. spumosum accessions demonstrate a range of sought-after agronomic traits and offer an alternative to annual Medicago spp. for ley farming systems in the medium to low rainfall areas of the mixed crop/livestock zone of southern Australia. T. spumosum presents seeds at the top of the canopy in heads that do not readily shatter, so seed can be harvested using conventional cereal harvesters instead of the specialist suction equipment required for harvest of seed from annual T. subterraneum and Medicago spp. T. spumosum was found to be relatively fecund and had high levels of biomass production in comparison to the other annual legumes that were tested. The species also demonstrated high levels of within-season hardseededness (remaining hard in summer and softening in autumn) so seedbanks would be protected from summer rainfall events. In addition, T. spumosum showed high levels of between-season dormancy, which allows the species to carry a seedbank through a cropping phase or series of poor seasons. A herbicide experiment showed that clover species varied in tolerances, with T. spumosum the least sensitive of all of the legumes tested to Flumetsulam. A cross-inoculation experiment to measure symbiotic effectiveness revealed that WSM1325 (current clover strain) surpasses WSM409 (previous strain) in its relationship with the annual clovers of contemporary interest, while being highly effective at nitrogen fixation with T. spumosum. The results of this study and an associated investigation into feeding value indicate that T. spumosum offers a productive alternative to annual Medicago spp. on fine-textured soils. Of the T. spumosum accessions tested, the most promising has been released under the cultivar name of AGWEST Bartolo