bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stepwise S‐N curve and fish‐eye failure in gigacycle fatigue
Authors: Nishijima  , Kanazawa  
Published: March 2003

Fatigue failure is normally initiated at the surface of a material. For some materials, failure can be initiated both at the surface and the interior. This twofold materials behaviour in fatigue is represented by a stepwise shape in the S–N curve. An internal failure mode is especially important for fatigue life in the gigacycle range, as this mode is predominant at low stress ranges.Materials with a hardened surface fail from the surface only at high stresses, and at low stresses from the inside, forming a fish‐eye facet on the fracture surface. Exactly the same behaviour can be observed for materials without a hard surface, even at elevated temperatures. This paper displays some of the results obtained at NRIM and discusses possible interpretations.
Interior fatigue fracture of gear teeth
Authors: Mackaldener  , Olsson  
Published: March 2003

A new type of gear tooth fatigue failure is presented and analysed. It is initiated in the interior of the tooth and is given the self‐explanatory name tooth interior fatigue fracture (TIFF).A fractographic examination of TIFF is presented. The fracture surface of TIFF has characteristic features that distinguish it from other gear failures.A hypothesis for TIFF initiation is presented. The crack‐initiating stresses in the interior of the gear tooth are: (i) a residual tensile stress due to case hardening; and (ii) alternating stresses due to idler usage of the gear.A finite element analysis is used to compute the stress state history of engaging gear teeth throughout the load cycle. The critical plane fatigue criterion of McDiarmid is employed. The analysis shows that the risk of fatigue initiation is high in the root of the tooth and in a large region in the interior of the tooth. These findings agree with test results where both modes of failure occurred.
On the mechanism of fatigue failure in the superlong life regime (N>107 cycles). Part II: influence of hydrogen trapped by inclusions
Authors: Murakami Y. , Nomoto T. , Ueda T. , Murakami Y. 
Published: March 2003

High cycle fatigue fracture surfaces of specimens in which failure was initiated at a subsurface inclusion were investigated by atomic force microscopy and by scanning electron microscopy. The surface roughness Ra increased with radial distance from the fracture origin (inclusion) under constant amplitude tension–compression fatigue, and the approximate relationship: Ra ≅ CΔK 2I holds. At the border of a fish‐eye there is a stretched zone. Dimple patterns and intergranular fracture morphologies are present outside the border of the fish‐eye. The height of the stretch zone is approximately a constant value around the periphery of the fish‐eye. If we assume that a fatigue crack grows cycle‐by‐cycle from the edge of the optically dark area (ODA) outside the inclusion at the fracture origin to the border of the fish‐eye, we can correlate the crack growth rate da/dN, stress intensity factor range ΔKI and Ra for SCM435 steel by the equation and by da/dN proportional to the parameter Ra .Integrating the crack growth rate equation, the crack propagation period Np2 consumed from the edge of the ODA to the border of the fish‐eye can be estimated for the specimens which failed at Nf > 107. Values of Np2 were estimated to be ∼1.0 × 106 for the specimens which failed at Nf ≅ 5 × 108. It follows that the fatigue life in the regime of Nf >107 is mostly spent in crack initiation and discrete crack growth inside the ODA.
Fatigue crack propagation behaviour derived from S–N data in very high cycle regime
Authors: TANAKA K , AKINIWA Y 
Published: March 2003

ABSTRACT The crack propagation law was derived from the S–N data in the very high cycle fatigue of a bearing steel. The propagation rate, da/dN (m/cycle), of surface cracks was estimated to be a power function of the stress intensity range, ΔK (MPa√m) with the coefficient Cs = 5.87 × 10−13 and the exponent ms = 4.78. The threshold stress intensity range was 2.6 MPa√m. The crack propagation from internal inclusions was divided into Stages I and II. For Stage I, the coefficient of the power law was C0 = 3.44 × 10−21 and the exponent m0 = 14.2. The transition from Stage I to II took place at ΔK = 4.0 MPa√m. For Stage II, the coefficient was Ci = 2.08 × 10−14 and the exponent mi = 4.78. The specimen size and loading mode did not influence the surface fatigue life, while the internal fatigue life was shortened in larger specimens and under tension–compression loading. For ground specimens, the surface fatigue life was raised by the compressive residual stress, while reduced by the surface roughness introduced by grinding. For shot‐peened specimens, fatigue fracture did not take place from the surface because of a high surface compressive residual stress. The internal fatigue life was reduced by the tensile residual stress existing in the interior of the specimens.
Very high‐cycle fatigue behaviour of shot‐peened high‐carbon–chromium bearing steel
Authors: SHIOZAWA K. , LU L. 
Published: March 2003

ABSTRACTEffect of shot‐peening on fatigue behaviour in the gigacycle regime was investigated in order to clarify the duplex S–N curve characteristics. Cantilever‐type rotary bending fatigue tests were performed in laboratory air at room temperature by using hourglass‐shaped specimens of high‐carbon–chromium bearing steel, JIS SUJ2. Fatigue crack initiation site changed from the surface of untreated specimen to the subsurface of the specimen because of hardening and compressive residual stress with shot‐peening in the region of high‐stress amplitude. On the other hand, no difference in fatigue life controlled by the subsurface crack initiation between untreated specimen and shot‐peening one was observed in high‐cycle region. It was suggested that the S–N curve corresponding to the internal fracture mode is inherent in the material, as compared with the S–N curve of surface fracture mode, which is affected by surface conditions, environmental conditions and so on. Subsurface crack initiation and propagation behaviour were discussed under the detailed measurement of crack initiation area and shape of the fish‐eye fracture surface.
Modelling of fatigue damage progression and life of CFRP laminates
Authors: PAPANIKOS P. , TSERPES K. I. , PANTELAKIS SP. 
Published: March 2003

ABSTRACTA progressive fatigue damage model has been developed for predicting damage accumulation and life of carbon fibre‐reinforced plastics (CFRP) laminates with arbitrary geometry and stacking sequence subjected to constant amplitude cyclic loading. The model comprises the components of stress analysis, fatigue failure analysis and fatigue material property degradation. Stress analysis of the composite laminate was performed by creating a three‐dimensional finite element model in the ANSYS FE code. Fatigue failure analysis was performed by using a set of Hashin‐type failure criteria and the Ye‐delamination criterion. Two types of material property degradations on the basis of element stiffness and strength were applied: a sudden degradation because of sudden failure detected by the fatigue failure criteria and a gradual degradation because of the nature of cyclic loading, which is driven by the increased number of cycles. The gradual degradation of the composite material was modelled by using functions relating the residual stiffness and residual strength of the laminate to the number of cycles. All model components have been programmed in the ANSYS FE code in order to create a user‐friendly macro‐routine. The model has been applied in two different quasi‐isotropic CFRP laminates subjected to tension–compression (T–C) fatigue and the predictions of fatigue life and damage accumulation as a function of the number of cycles were compared with experimental data available in the literature. A very good agreement was obtained.
Prediction of the energy dissipation rate in ductile crack propagation
Authors: ATKINS A. G. , CHEN Z. , COTTERELL B. 
Published: March 2003

ABSTRACTIn this paper, energy dissipation rate D vs. Δa curves in ductile fracture are predicted using a ‘conversion’ between loads, load‐point displacements and crack lengths predicted by NLEFM and those found in real ELPL propagation. The NLEFM/ELPL link was recently discovered for the DCB testpiece, and we believe it applies to other cracked geometries. The predictions for D agree with experimental results. The model permits a crack tip toughness R(Δa) which rises from Jc and saturates out when (if) steady state propagation is reached after a transient stage in which all tunnelling, crack tip necking and shear lip formation is established. JR is always greater than the crack tip R(Δa) and continues to rise even after R(Δa) levels off.The analysis is capable of predicting the usual D vs. Δa curves in the literature which have high initial values and fall monotonically to a plateau at large Δa. It also predicts that D curves for CCT testpieces should be higher than those for SENB/CT, as found in practice. The possibility that D curves at some intermediate Δa may dip to a minimum below the levelled‐off value at large Δa is predicted and confirmed by experiment. Recently reported D curves that have smaller initial D than the D‐values after extensive propagation can also be predicted. The testpiece geometry and crack tip R(Δa) conditions required to produce these different‐shaped D vs. Δa curves are established and confirmed by comparison with experiment.The energy dissipation rate D vs. Δa is not a transferable property as it depends on geometry. The material characteristic R(Δa) may be the ‘transferable property’ for scaling problems in ELPL fracture. How it can be deduced from D vs. Δa curves (and by implication, JR vs. Δa curves) is established.
Equivalent initial flaw size testing and analysis of transport aircraft skin splices
Authors: FAWAZ S. A. 
Published: March 2003

ABSTRACTThe equivalent initial flaw size (EIFS) concept was developed nearly 30 years ago in an attempt to account for the initial quality, both manufacturing and material properties, of a structural detail prone to fatigue cracking. Widespread use of this concept has been limited due to the large amount of test data required to develop a reliable EIFS distribution. In this effort, an EIFS distribution was determined for four types of flat, production like transport aircraft fuselage skin joints loaded by remote tension. Two crack growth prediction codes, AFGROW and FASTRAN, were used to not only develop the EIFS but also to compare the crack growth algorithms in each code. The EIFS calculations are prone to compounding errors in the crack growth analysis due to the changing stress intensity factor solutions and stress fields as the crack gets longer. Thus, only including EIFS calculations for mechanically small cracks, crack lengths less than 1.27 mm, results in a mean EIFS of 18.0 μm with a standard deviation of 3.78 μm.
Mechanisms of plant species impacts on ecosystem nitrogen cycling
Authors: Knops J. M. H. , Bradley K. L. , Wedin D. A. 
Published: March 2003

AbstractPlant species are hypothesized to impact ecosystem nitrogen cycling in two distinctly different ways. First, differences in nitrogen use efficiency can lead to positive feedbacks on the rate of nitrogen cycling. Alternatively, plant species can also control the inputs and losses of nitrogen from ecosystems.Our current understanding of litter decomposition shows that most nitrogen present within litter is not released during decomposition but incorporated into soil organic matter. This nitrogen retention is caused by an increase in the relative nitrogen content in decomposing litter and a much lower carbon‐to‐nitrogen ratio of soil organic matter. The long time lag between plant litter formation and the actual release of nitrogen from the litter results in a bottleneck, which prevents feedbacks of plant quality differences on nitrogen cycling. Instead, rates of gross nitrogen mineralization, which are often an order of magnitude higher than net mineralization, indicate that nitrogen cycling within ecosystems is dominated by a microbial nitrogen loop. Nitrogen is released from the soil organic matter and incorporated into microbial biomass. Upon their death, the nitrogen is again incorporated into the soil organic matter. However, this microbial nitrogen loop is driven by plant‐supplied carbon and provides a strong negative feedback through nitrogen cycling on plant productivity. Evidence supporting this hypothesis is strong for temperate grassland ecosystems. For other terrestrial ecosystems, such as forests, tropical and boreal regions, the data are much more limited. Thus, current evidence does not support the view that differences in the efficiency of plant nitrogen use lead to positive feedbacks.In contrast, soil microbes are the dominant factor structuring ecosystem nitrogen cycling. Soil microbes derive nitrogen from the decomposition of soil organic matter, but this microbial activity is driven by recent plant carbon inputs. Changes in plant carbon inputs, resulting from plant species shifts, lead to a negative feedback through microbial nitrogen immobilization. In contrast, there is abundant evidence that plant species impact nitrogen inputs and losses, such as: atmospheric deposition, fire‐induced losses, nitrogen leaching, and nitrogen fixation, which is driven by carbon supply from plants to nitrogen fixers. Additionally, plants can influence the activity and composition of soil microbial communities, which has the potential to lead to differences in nitrification, denitrification and trace nitrogen gas losses. Plant species also impact herbivore behaviour and thereby have the potential to lead to animal‐facilitated movement of nitrogen between ecosystems.Thus, current evidence supports the view that plant species can have large impacts on ecosystem nitrogen cycling. However, species impacts are not caused by differences in plant quantity and quality, but by plant species impacts on nitrogen inputs and losses.
Functional diversity (FD), species richness and community composition
Authors: Petchey Owen L. , Gaston Kevin J. 
Published: March 2003

AbstractFunctional diversity is an important component of biodiversity, yet in comparison to taxonomic diversity, methods of quantifying functional diversity are less well developed. Here, we propose a means for quantifying functional diversity that may be particularly useful for determining how functional diversity is related to ecosystem functioning. This measure of functional diversity “FD” is defined as the total branch length of a functional dendrogram. Various characteristics of FD make it preferable to other measures of functional diversity, such as the number of functional groups in a community. Simulating species' trait values illustrates how the relative importance of richness and composition for FD depends on the effective dimensionality of the trait space in which species separate. Fewer dimensions increase the importance of community composition and functional redundancy. More dimensions increase the importance of species richness and decreases functional redundancy. Clumping of species in trait space increases the relative importance of community composition. Five natural communities show remarkably similar relationships between FD and species richness.
The ecology of tool‐use in the woodpecker finch (Cactospiza pallida)
Authors: Tebbich Sabine , Taborsky Michael , Fessl Birgit , Dvorak Michael 
Published: March 2003

AbstractInsects, mammals and birds are known to use tools, but empirical evidence of the ecological importance of tool‐use is scarce. Here, we present the first ecological study of tool‐use by a bird species. Woodpecker finches use twigs or cactus spines to pry arthropods out of tree‐holes. We compared tool‐use during wet and dry seasons in two different vegetation zones: the Arid Zone and the humid Scalesia Zone. In the Scalesia Zone, where food was abundant and easily accessible, woodpecker finches rarely used tools. In contrast, in the Arid Zone, where food was limited and hard to access, they obtained half of their prey using tools during the dry season. Tool‐use enabled the birds to reach particularly large and otherwise inaccessible prey hidden in tree‐holes. Our data suggest that tool‐use in the woodpecker finch has evolved in response to the dry and unpredictable conditions in the coastal zone of the Galápagos Islands.
Top‐down and bottom‐up diversity cascades in detrital vs. living food webs
Authors: Dyer Lee A. , Letourneau Deborah 
Published: March 2003

AbstractApex predators and plant resources are both critical for maintaining diversity in biotic communities, but the indirect (‘cascading’) effects of top‐down and bottom‐up forces on diversity at different trophic levels are not well resolved in terrestrial systems. Manipulations of predators or resources can cause direct changes of diversity at one trophic level, which in turn can affect diversity at other trophic levels. The indirect diversity effects of resource and consumer variation should be strongest in aquatic systems, moderate in terrestrial systems, and weakest in decomposer food webs. We measured effects of top predators and plant resources on the diversity of endophytic animals in an understorey shrubPiper cenocladum(Piperaceae). Predators and resource availability had significant direct and indirect effects on the diversity of the endophytic animal community, but the effects were not interactive, nor were they consistent between living vs. detrital food webs. The addition of fourth trophic level beetle predators increased diversity of consumers supported by living plant tissue, whereas balanced plant resources (light and nutrients) increased the diversity of primary through tertiary consumers in the detrital resources food web. These results support the hypotheses that top‐down and bottom‐up diversity cascades occur in terrestrial systems, and that diversity is affected by different factors in living vs. detrital food webs.
Phoenix clones: recovery after long‐term defoliation‐induced dormancy
Authors: Morrow Patrice A. , Olfelt Joel P. 
Published: March 2003

AbstractMany long‐lived plants are known to prolong dormancy in response to abiotic stresses such as drought. We are unaware, however, of any reports of plants prolonging dormancy in response to biotic stresses such as herbivory. We monitored 140 putative Solidago missouriensis clones (hereafter ‘clones’) ≥ 13 years before, during and after intense defoliation by the specialist herbivore Trirhabda canadensis. Eight of the clones produced no above‐ground growth in the season following defoliation. Though apparently killed, these clones reappeared 1–10 years after they disappeared, with six of them robustly recovering in a single season. We used 38 RAPD markers to test the hypotheses (denoted by H and numbered with subscripts) that territories were recovered by (H1) seedling establishment or (H2) rhizomes. We compared pre‐defoliation and post‐recovery genotypes in two clones using the same 38 markers. Our data document the existence of very large clones (60–350 m2 with c. 700–20 000 ramets), and support the hypothesis that recovery is from rhizomes. Within‐clone diversity is low, and the pre‐defoliation and post‐recovery genotypes match. We consider mechanisms that could enable plants entering dormancy with depleted resources to robustly recover, and the implications of dormancy for avoiding biotic stress such as that induced by T. canadensis.
Measuring mass transfer processes of octane with the help of an alkSalkB::gfp‐tagged Escherichia coli
Authors: Jaspers Marco C. M. , Meier Christoph , Zehnder Alexander J. B. , Harms Hauke , Van Der Meer Jan Roelof 
Published: March 2003

Diffusion of octane from oily droplets in different microscale settings was measured using Escherichia coli expressing the stable green fluorescent protein (GFP) from the alkB promoter of Pseudomonas oleovorans. GFP fluorescence intensities were determined quantitatively at the single‐cell level after 1.0 or 2.5 h incubation and compared with different calibration series using known concentrations of octane. By immobilizing the E. coli sensor cells on the bottom glass plate of a microscope flow chamber, it was possible to monitor the diffusion process for octane in aqueous solution as a function of time and distance from non‐aqueous phase droplets of octane alone or oily octane mixtures. When a gas phase was included in the flow chambers, octane transport could be demonstrated from the oily mixtures to the cells through both gas and liquid phase. Assays of non‐immobilized sensor cells in microdroplets in the presence or absence of soil particles incubated with octane through the vapour phase revealed a slight reduction in the total amount of induced E. coli cells in the presence of soil. Our results indicate the power of using GFP‐marked single‐cell biosensors in determining microscale bioavailability of organic pollutants.
Isolation and phylogenetic characterization of acidophilic microorganisms indigenous to acidic drainage waters at an abandoned Norwegian copper mine
Authors: Johnson D. Barrie , Rolfe Stewart , Hallberg Kevin B. , Iversen Eigil 
Published: March 2003

SummaryThe biodiversity of culturable acidophilic microbes in three acidic (pH 2.7–3.7), metal‐rich waters at an abandoned subarctic copper mine in central Norway was assessed. Acidophilic bacteria were isolated by plating on selective solid media, and dominant isolates were identified from their physiological characteristics and 16S rRNA gene sequences. The dominant iron‐oxidizing acidophile in all three waters was an Acidithiobacillus ferrooxidans‐like eubacterium, which shared 98% 16S rDNA identity with the type strain. A strain of Leptospirillum ferrooxidans was obtained from one of the waters after enrichment in pyrite medium, but this iron oxidizer was below detectable levels in the acidic waters themselves. In two sites, there were up to six distinct heterotrophic acidophiles, present at 103 ml−1. These included Acidiphilium‐like isolates (one closely related to Acidiphilium rubrum, a second to Acidiphilium cryptum and a third apparently novel isolate), an Acidocella‐like isolate (96% 16S rDNA identity to Acidocella facilis) and a bacterium that shared 94.5% 16S rDNA identity to Acidisphaera rubrifaciens. The other numerically significant heterotrophic isolate was not apparently related to any known acidophile, with the closest match (96% 16S rDNA sequence identity) to an acetogen, Frateuria aurantia. The results indicated that the biodiversity of acidophilic bacteria, especially heterotrophs, in acidic mine waters may be much greater than previously recognized.
Population dynamics of type I and II methanotrophic bacteria in rice soils
Authors: Macalady Jennifer L. , McMillan Andrew M. S. , Dickens Angela F. , Tyler Stanley C. , Scow Kate M. 
Published: March 2003

SummaryMethane‐oxidizing bacteria (methanotrophs) consume a significant but variable fraction of greenhouse‐active methane gas produced in wetlands and rice paddies before it can be emitted to the atmosphere. Temporal and spatial dynamics of methanotroph populations in California rice paddies were quantified using phospholipid biomarker analyses in order to evaluate the relative importance of type I and type II methanotrophs with depth and in relation to rice roots. Methanotroph population fluctuations occurred primarily within the top 0–2 cm of soil, where methanotroph cells increased by a factor of 3–5 over the flooded rice‐growing season. The results indicate that rice roots and rhizospheres were less important than the soil–water interface in supporting methanotroph growth. Both type I and type II methanotrophs were abundant throughout the year. However, only type II populations were strongly correlated with soil porewater methane concentrations and rice growth.