Dual roles of pearlite microstructure to interfere/facilitate gaseous hydrogen-assisted fatigue crack growth in plain carbon steels

Fatigue crack growth of two carbon steels with different pearlite volume fractions were studied in pressurized gaseous hydrogen environment. Notably, pearlite was found to mitigate hydrogen-assisted fatigue crack acceleration. This positive impact of pearlite was ascribed to ferrite/cementite lamellar aligned perpendicularly to the cracking direction, which functioned as barriers to intermittently arrest the crack propagation. Meanwhile, brittle delamination fracture ensued in the pearlite lamellar lying parallel to the crack-plane increased the crack growth rate and compromised the above positive effect to some extent. The material behavior is rationalized in light of fractographical observations and microstructural analyses of the crack-wake.acceptedVersio

Three lateral osteotomy designs for bilateral sagittal split osteotomy: biomechanical evaluation with three-dimensional finite element analysis

<p>Abstract</p> <p>Background</p> <p>The location of the lateral osteotomy cut during bilateral sagittal split osteotomy (BSSO) varies according to the surgeon's preference, and no consensus has been reached regarding the ideal location from the perspective of biomechanics. The purpose of this study was to evaluate the mechanical behavior of the mandible and screw-miniplate system among three lateral osteotomy designs for BSSO by using three-dimensional (3-D) finite element analysis (FEA).</p> <p>Methods</p> <p>The Trauner-Obwegeser (TO), Obwegeser (Ob), and Obwegeser-Dal Pont (OD) methods were used for BSSO. In all the FEA simulations, the distal segments were advanced by 5 mm. Each model was fixed by using miniplates. These were applied at four different locations, including along Champy's lines, to give 12 different FEA miniplate fixation methods. We examined these models under two different loads.</p> <p>Results</p> <p>The magnitudes of tooth displacement, the maximum bone stress in the vicinity of the screws, and the maximum stress on the screw-miniplate system were less in the OD method than in the Ob and TO methods at all the miniplate locations. In addition, Champy's lines models were less than those at the other miniplate locations.</p> <p>Conclusions</p> <p>The OD method allows greater mechanical stability of the mandible than the other two techniques. Further, miniplates placed along Champy's lines provide greater mechanical advantage than those placed at other locations.</p

Hydrogen trapping in X70 structural pipeline steel and weldments

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Hydrogen trapping in X70 structural pipeline steel and weldments

Diffusion measurements and thermal desorption measurements have been performed on a X70 pipeline steel, in as received and normalized and quenched condition, after being hydrogen charged for 200 h at 100 MPa hydrogen gas pressure and 85°C. Numerical simulations based on the assumption of thermodynamic equilibrium were performed, aiming to compare the trapping energies when fitting to the TDS spectra. TDS experiments revealed a reversible trap site with activation energy of 26.2 kJ.mol−1. Irreversible trap sites with an activation energy of >100 kJ.mol−1 were observed from both as-received and heat-treated condition. In contrast, a reversible trap site with an activation energy of 49.2 kJ.mol−1 was observed only from the heat-treated condition. The numerical modelling based on the assumption of equilibrium between hydrogen in traps and hydrogen in lattice is seen to provide a good fit to the experimental data.acceptedVersio

Hydrogen-assisted crack propagation in α-iron during elasto-plastic fracture toughness tests

Elasto-plastic fracture toughness tests of a commercially pure iron were performed in air and in hydrogen gas at two different pressures. Some unique characteristics of hydrogen-enhanced cracking were exhibited at both the macroscopic and microscopic length scales, based on the observation of fracture surface, fracture plane, plasticity distribution and dislocation structure. The possible mechanisms responsible for the hydrogen-induced degradation of fracture toughness are discussed.acceptedVersio

Effect of orientation of small defects on fatigue limit of steels

In order to clarify the effect of defect orientation on the fatigue limit of three types of steels; JIS-S15C, JIS-S45C and JIS-SNCM439, a small semi-circular slit was introduced into the surface of a round specimen. The slits were tilted at 0∘, 30∘ or 60∘ with respect to the plane normal to the loading axis, but all of them had the same defect size, \vec{area} = 188 μm, where the area denotes the area of the domain defined by projecting the defect on a plane normal to the loading axis. In all the combinations of the materials and tilting angles, a non-propagating crack was found at the fatigue limit, i.e. the fatigue limit was determined by the non-propagation condition of crack initiated from the defect. In JIS-S15C and JIS-S45C, the fatigue limit was nearly independent of the tilting angle, which was in good agreement with the predicted value by the \vec{area} parameter model. On the other hand, in JIS-SNCM439, the fatigue limit was also in agreement with the prediction at the tilting angle of 0∘, but it increased with an increase in the tilting angle. These results indicated that the \vec{area} parameter model can predict a conservative fatigue limit for the tilted defects. In this paper, the mechanistic reason for the effect of the tilting angle on the fatigue limit will be discussed by paying special attention to the crack path and length of non-propagating crack

Follow-up Study of Latex-allergic Health Care Workers in Japan

Background: While many cases of latex allergy have been reported in Japanese health care workers (HCWs) since 1992, there have been no follow-up studies after removing latex from the workplace. We had previously replaced all working environment latex gloves and latex products with low-allergen or non-latex products. The purpose of the investigation was to evaluate the benefits of the latex allergy countermeasures that were taken in our hospital, and the effects of life guidance education. Methods: We investigated 16 latex-allergic HCWs in our hospital. We gave them a detailed questionnaire and tested them by a skin prick test (SPT) with latex extract and specific IgE antibodies against latex using the Pharmacia CAP RAST system, RAST FEIA. We compared these results with earlier results from the time of diagnosis. Results: According to the questionnaire, none of the HCWs had changed their work habits, though all were avoiding the use of latex products as much as possible. Of the 16 patients, 81.2% were eating foods for which cross reactivity with latex has been reported. However, the foods had not induced severe allergic symptoms. In the SPT, 62.5% of scores decreased and 81.2% of patients had decreases in specific IgE antibody levels. Conclusions: After avoiding latex products and following our educational suggestions, the patients' allergy symptoms had generally improved. This indicates that our countermeasures against latex allergy were largely successful

Shear-mode Crack Initiation Behavior in the Martensitic and Bainitic Microstructures

Fully reversed torsional fatigue tests were conducted to elucidate the behaviour of shear-mode crack initiation and propagation in one martensitic and two bainitic steels. The relationship between the crack initiation site and microstructure was investigated by means of an electron backscatter diffraction (EBSD) technique. From the S-N diagram, two notable results were obtained: (i) the shear-mode crack was initiated on the prior austenitic grain boundary in martensitic steel, while in bainitic steels, the crack was initiated along the {110} plane; one of the slip planes of bcc metals, and (ii) the torsional fatigue limit of lower bainitic steel with finer grains was 60 MPa higher than that of upper bainitic steel with coarser grains even though the hardnesses were nearly equivalent. The mechanism determining the torsional fatigue strength in these steels is discussed from the viewpoint of microstructure morphology

The influence of interacting small defects on the fatigue limits of a pure iron and a bearing steel

This study investigates the effect of interacting small cracks on the fatigue limits of two types of pure iron of varying strengths and of a bearing steel. The experimental results revealed that although the fatigue limits were essentially controlled by the mechanics of interacting cracks, the non-propagating crack features and the severity of crack coalescence varied greatly among the different materials. In addition, it is demonstrated that the material-independent, analytical, interaction-criterion alone is not sufficient to estimate interaction effects in reality. This research shows that the material effect can be considered in terms of hardness and non-propagating crack size.Peer reviewe