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

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

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

Effects of sintering profile on the densification behaviour of forsterite ceramics

The sintering behaviour of forsterite prepared by mechanical activation and heat treatment has been studied. The green compacts were sintered using two different sintering profiles. The first was based on the conventional sintering (CS) profile in which the powder compact was sintered at the desired temperature, holding for 2 hours and then cooled to room temperature. The second was based on a two-step sintering (TSS) profile in which the samples were sintered at a temperature T1 = 1400 degrees C for 6 minutes and then continued sintering at a lower temperature T2 (i.e. 750 degrees C, 850 degrees C and 950 degrees C) for 15 hours before cooling to room temperature. It was found that a minimum ball milling time of 7 h was necessary to completely eliminate secondary phases from developing in the forsterite matrix after sintering at 1400 degrees C. The sintering study indicated that the CS profile was effective in enhancing the fracture toughness of the sintered body when sintered at 1400 degrees C but this was accompanied by exaggerated grain growth. In addition, it was found that sintering below 1400 degrees C was not effective in preventing the formation of secondary phases in the sintered body. On the other hand, the TSS profile (T1 = 1400 degrees C, T2 = 950 degrees C) was found to be most beneficial in promoting densification and more importantly, to suppress grain coarsening of the forsterite body

Mechanochemical synthesis of nanohydroxyapatite bioceramics

Nanosized hydroxyapatite powder has been synthesized by the mechanochemical method using a dry mixture of calcium hydroxide and diammonium hydrogen phosphate. The effect of mechanochemical process on powder properties has been investigated. Three rotation speeds of 170 rpm, 270 rpm and 370 rpm have been employed with 15 hours milling time. Characterization of the nanopowders has been accomplished by Fourier transform infra red, X-ray diffraction and transmission electron microscopy analyses. The samples have been prepared and sintered in air at varying temperatures ranging from 1050–1350 °C. Results show that increase in rotation speed (370 rpm) increases the crystallite size (9–21 nm). Agglomerate formation with irregular shapes is found in the samples prepared at 270 and 370 rpm. The sintering process influences the stability of powder by yielding TCP phase at all the sintering temperatures. At 370 rpm, the sample sintered at 1250 °C shows the maximum relative density of 95.3% as well as hardness of 5.3 GPa