bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development and characterization of interspecific hybrids of Trifolium alexandrinum×T. apertum using embryo rescue
Authors: Malaviya D. R. , Roy A. K. , Kaushal P. , Kumar B. , Tiwari A. , Lorenzoni C. 
Published: January 2005

AbstractThis is the first report on the development of interspecific hybrids between Trifolium alexandrinum and T. apertum using embryo rescue and characterization of F1 plants. T. apertum was used as the male parent and T. alexandrinum as the female parent. Development of interspecific hybrids under natural conditions is not successful and so embryo rescue was attempted. Of the several combinations tried, pollination 2 days after emasculation and embryos rescued 11 days after pollination was found to be the best. For embryo culture, EC3 medium consisting of MS basal supplemented with 2.3 μM kinetin and 3% sucrose was used. Germinated embryos were transferred to LSP3 medium 25 days after inoculation wherein most of the cultures showed multiple shoots that were split and subcultured on RL1 medium for rooting. After hardening, about 75% of hybrids were successfully transferred to the field. The hybrids, in general, showed morphological traits intermediate between the two parents; however, a few hybrids showed better growth than either parent. Some F1 plants were almost 3 weeks later in flowering than the female parent. Pollen fertility among these plants ranged from 78 to approximately 100%. Chromosomal associations at diakinesis and isozyme banding patterns for acid phosphatase (ACP), superoxide dismutase (SOD) and peroxidase also confirmed the hybrid nature of the plants.
Mechanism of crack path morphology and branching from small fatigue cracks under mixed loading
Authors: MURAKAMI Y. , TAKAHASHI K. , TOYAMA K. 
Published: January 2005

ABSTRACTIn order to investigate the crack path in materials containing a small crack under mixed mode loading, reversed torsion and combined push–pull/torsion fatigue tests were carried out on 0.47% carbon steel specimens containing an initial small crack. The initial small cracks were introduced by a preliminary push–pull fatigue test using a specimen that contained an artificial small hole of 40 μm diameter/depth. Push–pull fatigue tests followed by reversed torsion, and reversed torsion followed by push–pull were carried out. Fatigue tests of combined push–pull/torsion followed by push–pull were also carried out to examine the effect of crack geometry, such as branching and kinking, on cumulative fatigue damage. Different crack growth behaviours due to different loading modes and sequences complicatedly influenced the fatigue crack path and eventually the cumulative fatigue damage. Thus, existing fatigue damage theories cannot be applied to the cases presented in this study. A single factory roof morphology was formed on the fracture surface of the specimen having an initial semielliptical surface crack under cyclic torsion. Taking the result into consideration, torsional fatigue tests of circumferentially cracked specimens were carried out to investigate the Mode III crack growth threshold and the formation mechanism of the factory roof. It was found that the factory‐roof pattern was formed by Mode I crack branching from small semielliptical cracks nucleated ahead of the circumferential crack tip. Thus, stress intensity factors at the semielliptical crack tip ahead of the circumferential crack tip were analysed to make the mechanism of crack branching from the semielliptical crack clear. The analysis shows that the Mode III stress intensity factor, KIII, at the deepest point of the semielliptical crack decreases with increase in the depth of semielliptical crack. It follows that as the shear crack growth becomes difficult at the semielliptical crack tip, crack branching starts at the major axis ends in the direction for Mode I growth, forming factory roof, due to ΔKIth < ΔKIIIth.
The relationship between process mechanisms and crack paths in friction stir welded 5083‐H321 and 5383‐H321 aluminium alloys
Authors: JAMES M. N. , BRADLEY G. R. , LOMBARD H. , HATTINGH D. G. 
Published: January 2005

ABSTRACTFriction stir (FS) welding is a relatively new solid‐state welding process that offers high levels of joint performance with minimal preparation and little post‐weld dressing. The high levels of plastic work induced in the weld zone produce a very fine grain size in the stirred region of the weld (e.g. the nugget), while the low heat input limits residual stresses to a low fraction of the proof strength of the weld metal. These effects are generally beneficial to weld dynamic performance. The peculiar thermomechanical history in the FS weld region leads, however, to particular defects with some unusual effects on crack path, whose occurrence depends partly on crack speed, or growth rate. This paper presents observations regarding specific influences of the FS welding process on crack paths and dynamic performance for 5083‐H321 and 5383‐H321 aluminium alloys, and proposes an explanation for the observations in terms of the weld microstructures and thermomechanical history. The insights presented in this paper can be used to inform optimisation of the weld process parameters, through on‐line feedback and control of tool geometry, force footprint, torque and temperature.
Stress distributions in notched structural components under pure bending and combined traction and bending
Authors: ATZORI B. , FILIPPI S. , LAZZARIN P. , BERTO F. 
Published: January 2005

ABSTRACTThe availability of analytical expressions is often desirable in the analyses of fatigue crack initiation and early propagation. This paper presents approximate analytical expressions capable of describing the overall distribution of the maximum principal stress in finite size notched bodies subjected to bending and combined traction and bending. The formulae reported here represent an extension of an analytical complex function approach already presented in the literature, suitable for describing highly stressed zones surrounding the notch tip. Such an extension, derived by simply imposing global equilibrium conditions, enables us to increase the range of validity of the principal stress expression from the notch tip to the entire ligament width. The accuracy of the proposed expressions is tested against data from finite element analyses carried out on plates and bars weakened by semicircular, V‐ and U‐shaped notches. The agreement seems to be good.
Environmental and frequency effects on fatigue crack growth rate and paths in aluminium alloy
Authors: MICHEL S. A. , KIESELBACH R. , FIGLIOLINO M. 
Published: January 2005

ABSTRACTThe environmental and frequency effects on fatigue crack growth in aluminium alloys are studied theoretically and experimentally. 2024‐T351 and 7075‐T651 tested in corrosive environments (humid air or technically purified nitrogen) show a constant crack growth rate (da/dN) at low values of the effective stress intensity range (ΔKeff). Typical well‐known fits of this curve (da/dN vs ΔKeff) do not reflect the plateau‐like region. A new model of crack growth is presented, which physically attributes this region to the formation and subsequent fracture of a crack tip oxide layer. The thickness of this layer is measured with X‐ray photon electron spectroscopy. At higher loads, other mechanisms are understood to be active. The model parameters are determined from constant amplitude tests, and are valid for a given material and environment. In 7075‐T651 tested in nitrogen, with R= 0.1 and 83 Hz, unexpected macroscopical crack branching is observed when ΔKeff reaches approximately 3.0 MPa √m.
Review of the subsurface strain path approach to fatigue life assessment of components
Authors: SHATIL G. 
Published: January 2005

ABSTRACTFatigue lives obtained from complex testing and monitoring of different components often involve some degree of discrepancy in results due to geometrical variations, even when they are tested under controlled conditions and have a similar surface cyclic strain range at the critical location. Recently, several fatigue models have been developed to improve the correlation of specimen lives using a critical ‘process zone’ that surrounds the damaged material. A review of such an approach is presented. The approach is based on critical subsurface strains and consists of a fatigue damage summation procedure in the affected area. The fatigue life‐prediction model is applied to two structural materials using three geometries subjected to biaxial cyclic stresses. These include notched bars, rhombic plates and car components. The subsurface strains are evaluated by using a detailed elastic–plastic finite element analysis, and by considering critical subsurface fatigue strain paths. It is shown that in the several cases investigated, the subsurface approach appears to improve life predictions.
A predictor–corrector scheme for the optimization of 3D crack front shapes
Authors: KOLK K. , KUHN G. 
Published: January 2005

ABSTRACTA predictor–corrector scheme is presented to improve the shape of 3D crack fronts within the 3D simulation of fatigue crack growth. This concept is fully functional for mode‐I, and an extension for mixed‐mode problems is presented. The whole procedure is embedded in an automatic incremental crack growth algorithm for arbitrary 3D problems with linear elastic material behaviour. The numerical simulation is based on the 3D dual boundary element method (Dual BEM) and on an optimized evaluation of very accurate stress intensity factors (SIFs) and T‐stresses. As part of the proposed predictor–corrector scheme, 3D singularities along the crack front especially in the vicinity of the intersection of the crack front and the boundary are considered. The knowledge of these singularities allows the specification of crack front shapes with bounded energy release rate. Numerical examples with complex cross‐sections are presented to show the efficiency of the proposed crack growth algorithm. The obtained results are in good agreement with recent experimental results.
Near‐threshold fatigue crack path in Al–Zn–Mg alloys
Authors: PETIT J. 
Published: January 2005

ABSTRACTThis paper reviews the role of microstructure and environment on the path of fatigue cracks in a high purity Al‐4.5% wt Zn‐1.25% wt Mg alloy in the form of single crystals, bicrystals and polycrystals, and a commercial Al–Zn–Mg alloy type 7075 in three ageing conditions. Crack propagation rates were measured in air and in high vacuum, possible interactions of crack closure being uncoupled by considering data provided by tests performed with closure correction or in conditions without closure. The analysis of the experimental results is particularly focused on the role of the atmospheric environment on the crack path. The relation between the crack paths and the crack growth mechanisms is discussed on the basis of micrographic and micro‐fractographic observations and of mechanisms previously identified for the three basic crack propagation stages (stage I, stage I like and stage II) and for intergranular fatigue crack propagation.
Fatigue fracture planes and expected principal stress directions under biaxial variable amplitude loading
Authors: KAROLCZUK A. , MACHA E. 
Published: January 2005

ABSTRACTFatigue behaviour under multiaxial variable amplitude loading can be examined by applying the failure criteria based on the critical plane approach. Positions of the critical plane can be determined in relation to the principal stress or strain directions. In the present paper, the expected directions of the principal stresses under proportional and non‐proportional loading have been obtained by averaging the instantaneous values of the Euler angles through special weight functions. The known weight functions based on stress parameters appear not to be efficient for each loading or material being analysed. Thus, the authors consider new weight functions based on energy parameters. The presented forms of weight functions are assessed by testing 18G2A steel specimens. It is concluded that the fatigue fracture plane position under multiaxial loading can efficiently be determined on the basis of an averaged direction of the maximum principal stress by employing a suitable weight function.
Fatigue crack path in Cu–Ni–Mo alloyed PM steel
Authors: BERGMARK A. , ALZATI L. 
Published: January 2005

ABSTRACTA detailed qualitative fatigue crack path study is made on Ni–Cu alloyed powder metallurgy (PM) steel with Mo prealloyed base powder. The microstructure is characterized by upper bainitic cores of the base powder particles surrounded by a Cu‐rich martensite with islands of Ni‐rich austenite. Earlier observations have shown that the visible surface cracks do not pass through the Ni‐rich areas. The aim of the present study is to find the crack path in relation to the Cu‐rich martensite and the Ni‐rich austenite also below the surface. Successive grinding in steps of about 20 μm is made, and the surface crack in each level is recorded by light optical microscope (LOM). The main part of the crack path is found through high temperature bainite or along the interface between martensite and high temperature bainite. Ni‐rich austenite is surrounded by martensite that hinders the crack from entering into austenite. The result indicates that austenite as such is not a strong crack stopper.
Multiple surface crack propagation: numerical simulations and experimental tests
Authors: CITARELLA R. , PERRELLA M. 
Published: January 2005

ABSTRACTIn‐house experimental observations of three‐dimensional fatigue crack growth are compared to numerical predictions by the Boundary Element code BEASY. Fracture analysis results for a complex geometry specimen, undergoing a general load spectrum, are presented with regard to three‐dimensional crack propagation and mode coupling effects. The specimens under consideration are cracked tension specimens, with a through‐crack or a quarter/semicircular crack that proceed inclined to the remote loading direction. Mixed mode conditions along the crack edge are characterized: the stress intensity factors are determined using the crack opening displacement (COD) method and the crack growth direction is computed by the minimum strain energy density criterion. Effects of specimen complex geometry, produced by a part‐through thickness hole near the initial saw‐cut notch, on fracture crack path are analysed. Moreover, multiple interacting three‐dimensional cracks are simulated correspondingly to experiments: a satisfactory agreement between numerical and experimental crack growth direction and crack growth rates are displayed.
The effects of loading waveform and microstructure on the fatigue response of Ti–6Al–2Sn–4Zn–2Mo alloy
Authors: SHANIAVSKI A. A. 
Published: January 2005

ABSTRACTA fractographic analysis was performed to estimate the crack‐growth period in specimens of Ti–6AL–2Sn–4Zn–2Mo–0.1Si titanium alloy with two types, α/β and β, of microstructure. The fatigue load cycle shape was triangular or trapezoidal. It was shown that a facetted pattern predominantly forms under the trapezoidal wave shape of cyclic loads for both the investigated microstructures. A special methodology was introduced for quantitative fractographic analysis in the case of locally formed fatigue striations between facetted patterns. Crack‐growth periods, estimated on the basis of the striation spacing measurements, were used to determine lifetime to failure for the tested specimens. The results of the performed investigations are briefly discussed and compared with experimental data.
A model for fatigue strength of welded lap joints
Authors: BERETTA S. , SALA G. 
Published: January 2005

ABSTRACTThe most advanced structural frames of cars and motorcycles are made from welded box beams of aluminium alloys. A recent technological solution for the beams consists of press‐formed metal sheets joined by welded single‐lap joints. Because the frames undergo cyclic loading, the evaluation of the fatigue endurance of this kind of connections plays a crucial role in the development of the frames. The present research deals with the evaluation of the fatigue behaviour of welded lap joints, subjected to tensile and bending loads. Fractographic evidence and numerical analyses show that the fatigue strength is controlled by the presence of defects and inhomogeneities at the tip of the weld root. In particular, these defects, which appear to lie on the maximum Kθθ path, increase the stress intensity factor (SIF) at the weld root. Such an analysis, together with a statistical description of the population defects, allows us to develop a methodology to predict the fatigue strength of lap joints. A simple method for SIF computation based on finite‐element (FE) analyses and structural stresses at the lap joints is then presented.
Computational prediction of fatigue crack paths in ship structural details
Authors: SUMI Y. , MOHRI M. , KAWAMURA Y. 
Published: January 2005

ABSTRACTThe characteristics of fatigue crack propagation and the remaining life assessment of ship structures are investigated focusing attention on a curved crack path due to the effects of welds, complicated stress distributions at three‐dimensional structural joints and structural redundancy. An advanced numerical simulation method is demonstrated for the remaining life assessment for curved crack propagation. The simulation method is based on a step‐by‐step finite‐element analysis. The crack path is predicted by the perturbation method with the local symmetry criterion, which gives a higher order approximation of the crack path, while the finite‐element re‐zoning is carried out by an improved paving method. Fatigue crack paths in the welded structural details of the transverse girder of a ship structure are investigated by experiments and simulation. The present method may offer an efficient simulation‐based tool for the design of critical details, which prevents the failure of the plates forming a compartment boundary.
Theoretical crack path prediction
Authors: RICHARD H. A. , FULLAND M. , SANDER M. 
Published: January 2005

ABSTRACTIn many practical cases, the crack growth leads to abrupt failure of components and structures. For reasons of a reliable quantification of the endangerment due to sudden fracture of a component, therefore, it is of enormous importance to know the threshold values, the crack paths and the growth rates for the fatigue crack growth as well as the limiting values for the beginning of unstable crack growth (fracture toughness). This contribution deals with the complex problem of a—however initiated—crack, that is subjected to a mixed‐mode loading. It will present the hypotheses and concepts, which describe the superposition of Mode I and Mode II (plane mixed mode) as well as the superposition of all three modes (Mode I, II and III) for spatial loading conditions. Those concepts admit a quantitative appraisal of such crack situations and a characterization of possible crack paths.
The effect of microtexture evaluated by electron backscatter diffraction method on fatigue crack propagation behaviour in rolled copper film
Authors: SHIMIZU K. , TORII T. 
Published: January 2005

ABSTRACTUsing a fatigue‐testing method by which a fatigue crack can be propagated in a film adhered to cover an elliptical through‐hole in a base plate, annealed rolled copper films have been fatigued. The effects of rolling textures and annealing twin boundaries on fatigue crack propagation behaviour are discussed. The fatigue crack propagates in a large zigzag pattern in the TC specimen (crack perpendicular to the rolling direction), while the crack propagation path in the RC specimen (crack parallel to the rolling direction) is nearly straight. Further, the fatigue cracks propagate slower toward the perpendicular direction than toward the parallel direction. After fatigue testing, the crystallographic characteristic of rolling textures around the fatigue crack in the annealed film is analysed using the EBSD (electron backscatter diffraction) system. Because the annealing twin boundary is in the same plane as the slip of the face‐centred‐cubic metal, the fatigue crack tends to propagate along the slip line initiated along the annealing twin boundary.
Quantitative palaeoclimatic inference based on terrestrial mammal faunas
Authors: Fernández Manuel Hernández , Peláez‐Campomanes Pablo 
Published: January 2005

ABSTRACTAim  The main goal of this paper is to propose a new tool, in the form of Quantitative Bioclimatic Models (QnBMs), for reconstructing past climates based on fossil mammal associations. As a case study, European climatic conditions during the basal early Pleistocene will be inferred using QnBMs.Location  The study uses faunas throughout the world to develop a quantitative bioclimatic model, which is then applied to Quaternary faunas from Eurasia.Methods  The models were constructed by applying multivariate linear regression to modern mammal faunas and climates from all over the world. The models were validated with a second group of modern faunas, which includes several from transitional zones between different climates (ecotones). To test the reliability of the method when applied to fossil associations, the results obtained for the Pleistocene have been compared with those obtained from palynology.Results  Validation of the models shows that as many as 11 climatic factors can be inferred with high reliability using the regression models developed in this work. Comparisons of results in the late Pleistocene–Holocene of Barová (Czech Republic) between a palynological study and the quantitative bioclimatic analysis show a high degree of similarity. The results for the early Pleistocene show colder and drier climatic conditions for Europe than today.Main conclusions  The application of the quantitative bioclimatic models to present day as well as Quaternary mammal faunas proves to be a useful tool for palaeoclimatic reconstruction during the Quaternary and probably most of the Neogene. Transfer functions are presented for a complete set of climatic factors, allowing a precise estimation of the climate in a locality from its mammal fauna.
Carbon sequestration rates in organic layers of boreal and temperate forest soils — Sweden as a case study
Authors: Akselsson Cecilia , Berg Björn , Meentemeyer Vernon , Westling Olle 
Published: January 2005

ABSTRACTAim The aim of this work was to estimate C sequestration rates in the organic matter layer in Swedish forests.Location  The region encompassed the forested area (23 × 106 ha) of Sweden ranging from about 55° N to 69° N.Methods  We used the concept of limit values to estimate recalcitrant litter remains, and combined it with amount of litter fall. Four groups of tree species were identified (pine, spruce, birch and ‘other deciduous species’). Annual actual evapotranspiration (AET) was estimated for 5 × 5 km grids covering Sweden. For each grid, data of forested area and main species composition were available. The annual input of foliar litter into each grid was calculated using empirical relationships between AET and foliar litter fall in the four groups. Litter input was combined with average limit values for decomposition for the four groups of litter, based on empirical data. Finally, C sequestration rate was calculated using a constant factor of the C concentration in the litter decomposed to the limit value, thus forming soil organic matter (SOM).Results  We obtained a value of 4.8 × 106 metric tons of C annually sequestered in SOM in soils of mature forests in Sweden, with an average of 180 kg ha−1 and a range from 40 to 410 kg ha−1. Norway spruce forests accumulated annually an average of 200 kg C ha−1. The pine and birch groups had an average of 150 kg ha−1 and for the group of other deciduous trees, which is limited to south Sweden, the C sequestration was around 400 kg ha−1.Conclusions  There is a clear C sequestration gradient over Sweden with the highest C sequestration in the south‐west, mainly corresponding to the gradient in litter fall. The limit‐value method appears useful for scaling up to a regional level to describe the C sequestration in SOM. A development of the limit value approach in combination with process‐orientated dynamic models may have a predictive value.