A new displacement-based approach to calculate stress intensity factors with the boundary element method

The analysis of cracked brittle mechanical components considering linear elastic fracture mechanics is usually reduced to the evaluation of stress intensity factors (SIFs). The SIF calculation can be carried out experimentally, theoretically or numerically. Each methodology has its own advantages but the use of numerical methods has be-come very popular. Several schemes for numerical SIF calculations have been developed, the J-integral method being one of the most widely used because of its energy-like formulation. Additionally, some variations of the J-integral method, such as displacement-based methods, are also becoming popular due to their simplicity. In this work, a simple displacement-based scheme is proposed to calculate SIFs, and its performance is compared with contour integrals. These schemes are all implemented with the Boundary Element Method (BEM) in order to exploit its advantages in crack growth modelling. Some simple examples are solved with the BEM and the calculated SIF values are compared against available solutions, showing good agreement between the different schemes

EFFECT OF CALCINATION ON THE SINTERING BEHAVIOUR OF HYDROXYAPATITE

In this study, a wet chemically produced hydroxyapatite (HA) powder was subjected to calcination at 700, 800, 900 and 1000oC. Subsequently, the sintering behaviour of these calcined powders was studied at various temperatures, ranging from 1050 to 1350oC. XRD results revealed that calcination has no effect on the phase stability of hydroxyapatite. However, the XRD peaks showed that the crystallinity of the powder increased with increasing calcination temperature. The specific surface area of powder reduced drastically from 60.74 m2 ∙g-1 to 9.45 m2 ∙g-1 with increasing calcination temperature. The SEM micrographs of calcined powder showed the coarsening of powder particles as the calcination temperature was increased. In terms of sinterability, the uncalcined HA powder sintered at 1150oC was found to possess the optimum properties with the following values being recorded: ~ 99 % relative density, Vickers hardness of 7.23 GPa and fracture toughness of 1.12 MPa∙m1/2. The present research indicated that calcination of the HA powder prior to sintering has a negligible effect on the sintering behaviour of the HA compacts and that calcination at 1000oC was found to be unfavourable to the properties of sintered HA

Exact solution for stresses/displacements in a multilayered hollow cylinder under thermo-mechanical loading

In this study, a new analytical solution by the recursive method for evaluating stresses/displacements in multilayered hollow cylinder under thermo-mechanical loading was developed. The results for temperature distribution, displacements and stresses obtained by using the proposed solution were shown to be in good agreement with the FEM results. The proposed analytical solution was also found to produce more accurate results than those by the analytical solution reported in literature

Assessment of a planar inclusion in a solid cylinder

As a planar inclusion in a solid cylinder can lead to a catastrophic failure of a whole structure, relevant studies on evaluating quantitative fracture values are always sought for supporting the investigations. In line with the use of nondestructive evaluation technique for quantifying the embedded defects in structures, relevant research findings would be usable to contribute to the structural integrity analyses. It is also intended to have the possibility of the use of the data in a preliminary structural design stage. Since the complexity of the experimental setup for evaluating a planar inclusion in a solid component, numerical modeling is always desirable. There are currently very few available solutions of stress intensity factors for the embedded cracks in a solid cylinder in literature. In this work, the planar inclusion was considered as an embedded (penny/elliptical) crack. Stress intensity factors (SIFs) of an embedded crack for different crack aspect ratios, crack eccentricities and crack inclinations are presented. All the analyses were carried out by using a dual boundary element method (DBEM) based software. (C) 2014 Elsevier Ltd. All rights reserved

Low-temperature degradation and defect relationship in yttria-tetragonal zirconia polycrystal ceramic

In this work, the relationship between tetragonal to monoclinic phase transformation and photoluminescence spectrum were studied for 3 mol% yttria-tetragonal zirconia polycrystal samples sintered in air and argon atmosphere at 1500 degrees C. A low-temperature degradation study was conducted under autoclave conditions containing superheated steam at 180 degrees C and 10 bar vapour pressure for periods up to 12 hours. Photoluminescence studies were conducted using a photoluminescence spectroscope with helium-cadmium laser at a wavelength of 325 nm as the excitation source, and the phase content in the zirconia samples was measured using X-ray diffractometer. The studies concluded that argon gas sintered samples have higher structural vacancy than air sintered samples; the argon gas sintered sample showed a more rapid phase transformation than the air sintered sample and also showed that the defect associated with oxygen vacancies in the zirconia lattice increases with increasing aging time