1,720,984 research outputs found
Stress intensity factor in alumina-zirconia composites by a hybrid finite element method
No full textThe present paper describes a numerical method which is able to calculate the stress intensity factor in two dimensional heterogeneous materials under mechanical and thermal loads. The proposed method uses two hybrid element formulations to model the second phase heterogeneities of the material and the crack tips. The method was used to analyse alumina-zirconia ceramic materials, and the effects due to the zirconia t→m phase transformation and the thermal stresses, which develop during the cooling stage of sintering, were taken into account in calculating the stress intensity factor
Structural transition under uniaxial deformation in a NiTi pseudo-elastic alloy
No full textNiTi shape memory alloys (SMAs) are increasingly used in many engineering and medical
applications, because they combine special functional properties, such as shape memory effect and pseudoelasticity,
with good mechanical strength and biocompatibility. However, the microstructural changes associated
with these functional properties are not yet completely known. In this work a NiTi pseudo-elastic alloy was
investigated by means of X-ray diffraction in order to assess micro-structural transformations under mechanical
uniaxial deformation. The results have been compared with those obtained after complete shape recovery
Numerical simulations and experimental measurements of the stress intensity factor in perforated plates
No full textA numerical procedure, which combines two hybrid finite element formulations, was developed to analyse the stress intensity factors in cracked perforated plates with a periodic distribution of holes and square representative volume elements. The accuracy of the method in predicting the stress intensity factor was verified by a comparison with experimental measurements, carried out by a photoelasticity method, and by commercial finite element software. Several simulations were executed by varying both the crack length and the hole diameters, and the effects of the holes on the stress intensity factor are illustrated. The method shows high accuracy and efficiency, as small differences were observed when compared with the traditional finite element method, notwithstanding a strong reduction in degrees of freedom and mesh complexity
A novel methodology for the prediction of the stress–strain response of laser powder bed fusion lattice structure based on a multi-scale approach
Full text linkAdditive manufacturing (AM), and in particular laser powder bed fusion (LPBF), is a technology that allows to easily produce geometrically complex structural components. Among others, an example is represented by lattice structures which allow to obtain lightweight components with enhanced mechanical properties. Despite a large number of papers available in the literature, mechanical behavior of lattice structures made by LPBF is still difficult to predict, due to microstructure modifications induced by their small features, scanning strategy and building direction. In this regard, a multi-scale approach to predict the effective response within the lattice structure is proposed in this investigation. It mainly consists in local measurements by nano-indentation tests, carried out at different portion of the lattice structure and along different orientation to build the effective constitutive response of the component. In this way, possible modifications induced by the LPBF process within the microstructure can be captured. Relying on experimental investigations at both macro and nano-scale, a numerical model for stainless steel 316L octet-truss lattice specimen has been calibrated. To improve the accuracy of the simulations, the geometrical model was built starting from the real geometry of the component through micro-CT images. Obtained results revealed that using the as-built geometry and effective local properties is fundamental for an accurate prediction of the mechanical behavior of lattice structures made by LPBF manufacturing process
Three-point bending tests of zirconia core/veneer ceramics for dental restorations
No full textIntroduction. The mechanical strength and the surface hardness of commercially available yttrium-doped zirconia were investigated. Furthermore, a comparative study of eight different ceramic veneers, to be used for the production of two-layered all-ceramic restorative systems, was carried out. Materials and Methods. Four types of zirconia specimens were analyzed, according to a standard ISO procedure (ISO 6872). Besides, two-layered zirconia-veneer specimens were prepared for three-point bending tests. Results. A strong effect of the surface roughness on the mechanical strength of zirconia specimens was observed. Finally, a comparative study of eight commercially available veneering ceramics shows different modes of failure between the selected veneers. Conclusion. The results indicate that close attention should be paid to the preparation of zirconia-based crowns and bridges by CAD/CAM process, because surface roughness has an important effect on the mechanical strength of the material. Finally, the results of the mechanical tests on two-layered specimens represent an important support to the choice of the veneering ceramic. Copyright © 2013 Massimo Marrelli et al
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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