Modeling of Hydrogen-Charged Notched Tensile Tests of an X70 Pipeline Steel with a Hydrogen-Informed Gurson Model.

Hydrogen can degrade the mechanical properties of steel components, which is commonly referred to as "hydrogen embrittlement" (HE). Quantifying the effect of HE on the structural integrity of components and structures remains challenging. The authors investigated an X70 pipeline steel through uncharged and hydrogen-charged (notched) tensile tests. This paper presents a combination of experimental results and numerical simulations using a micro-mechanics-inspired damage model. Four specimen geometries and three hydrogen concentrations (including uncharged) were targeted, which allowed for the construction of a fracture locus that depended on the stress triaxiality and hydrogen concentration. The multi-physical finite element model includes hydrogen diffusion and damage on the basis of the complete Gurson model. Hydrogen-Assisted degradation was implemented through an acceleration of the void nucleation process, as supported by experimental observations. The damage parameters were determined through inverse analysis, and the numerical results were in good agreement with the experimental data. The presented model couples micro-mechanical with macro-mechanical results and makes it possible to evaluate the damage evolution during hydrogen-charged mechanical tests. In particular, the well-known ductility loss due to hydrogen was captured well in the form of embrittlement indices for the different geometries and hydrogen concentrations. The limitations of the damage model regarding the stress state are discussed in this paper.

Effects of Fixture Configurations and Weld Strength Mismatch on J-Integral Calculation Procedure for SE(B) Specimens.

This work presents the development of a J-integral estimation procedure for deep and shallow cracked bend specimens based upon plastic ηpl factors for a butt weld made in an S690 QL high strength low alloyed steel. Experimental procedures include the characterization of average material properties by tensile testing and evaluation of base and weld metal resistance to stable tearing by fracture testing of square SE(B) specimens containing a weld centerline notch. J-integral has been estimated from plastic work using a single specimen approach and the normalization data reduction technique. A comprehensive parametric finite element study has been conducted to calibrate plastic factor ηpl and geometry factor λ for various fixture and weld configurations, while a corresponding plastic factor γpl was computed on the basis of the former two. The modified ηpl and γpl factors were then incorporated in the J computation procedure given by the ASTM E1820 standard, for evaluation of the plastic component of J and its corresponding correction due to crack growth, respectively. Two kinds of J-R curves were computed on the basis of modified and standard ηpl and γpl factors, where the latter are given by ASTM E1820. A comparison of produced J-R curves for the base material revealed that variations in specimen fixtures can lead to ≈10% overestimation of computed fracture toughness JIc. Furthermore, a comparison of J-R curves for overmatched single-material idealized welds revealed that the application of standard ηpl and γpl factors can lead to the overestimation of computed fracture toughness JIc by more than 10%. Similar observations are made for undermatched single material idealized welds, where fracture toughness JIc is overestimated by ≈5%.

Are panoramic images reliable in planning sinus augmentation procedures?

OBJECTIVE: The inherent deformation and two-dimensional nature of panoramic radiographs jeopardise their interpretation and quantitative measurements. This study aims to estimate the degree of underestimation of available mesio-distal bone in the premolar area (comparing panoramic radiographs with multi-slice/cone-beam computer tomography [CT]) to determine the prevalence, width, length and position of the bony canal [artery] in the lateral sinus wall and to explore the prevalence, width and length of another (newly detected) bony canal at the palatal aspect of the upper canine. MATERIAL AND METHODS: The distance between the distal side of the canine/first premolar and the mesial side of the first molar or the anterior wall of the maxillary sinus was measured on panoramic radiographs and corresponding multi-slice/cone-beam CT images (65 patients). Measurements were made at apical, mid-radicular and crestal regions, parallel to the occlusal plane. The presence and dimensions of the two above-mentioned intra-osseous canals were verified on multi-slice CT scans (144 patients) using reformatted cross-sectional images and/or axial slices. RESULTS: For all 65 patients, panoramic radiographs underscored the mesio-distal distance of available bone in the upper premolar region (mean 2.9 mm, range 0.1-7.5 mm). An intra-osseous canal in the lateral maxillary sinus wall was clearly visible in 49.5% of the cases (mean diameter 1.4 mm). In the canine region, a bony canal was obvious in 32.9% of the cases, with a mean diameter of 1.23 mm. For both canals, there was no correlation between diameter and patient's age. CONCLUSIONS: Based on the present data, cone-beam CT imaging can be recommended for visualising anatomical structures during planning of sinus augmentation procedures.