School of Mechanical and Industrial Engineering

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Browsing School of Mechanical and Industrial Engineering by Subject "Adiabatic crack"

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    Numerical Modeling of Thermo-Mechanical Stress Field Associated with Mode-I and Mixed-Mode Fracture in Homogenous Isotropic Materials
    (Addis Ababa University, 2021-11) Wondimu, Dessalegn; Addis, Kidane (PhD); Araya, Abera (PhD) Co-Advisor
    Engineering components exposed to different loading include mechanical, thermal or combined thermo-mechanical loading. Some of the components subjected to thermomechanical loading are gas turbines, engines, reactor components, fuel chambers, and so forth. Defects and flaws are primal causes for materials failure and exist in almost all materials. In this work, the effect of thermomechanical loading on the stress fields was investigated under pure Mode-I and Mixed Mode fracture by assuming a two-dimensional model under plane strain condition. To study the combined effect of thermo-mechanical loading on the stress field around the crack tip, sequentially coupled thermal-stress analysis employed by ABAQUS software was used under different conditions. The parameters used in this work i.e., material dimension selected based on BS standard, the applied remote stress also calculated analytically using limit load formula as 20MPa, 50MPa and 100MPa. The temperature gradient employed at the surface of the model is taken from literature ranges from��20℃ to 89℃. The crack was considered as thermally insulated means adiabatic crack and the temperature field used as an input for the thermomechanical stress. This temperature field was solved by the assumption of steady-state heat transfer and the heat transfer procedure is utilized to solve it. The temperature field is incorporated as an input for the stress analysis as a predefined field in the static general procedure for developing a thermomechanical stress field. The extended finite element method (XFEM) was employed to model the crack for reducing the time of meshing and processing and to define the temperature and displacement discontinuity along the crack. The thermomechanical stress field was solved by applying different parameters i.e., remote stress, crack angle, crack length and temperature gradient. The mechanical and thermo-mechanical stress fields were evaluated and extracted from the crack tip for the radian value of �� �� 0.002�� and angular position value between ��180° ≤ �� ≤ 180° for both Mode–I and Mixed Mode fracture cases. Based on the result, the stress fields i.e.,��������, ������ and ������ around the crack tip were affected by the temperature gradients. The extreme thermo-mechanical stress field values ������ and ������ were rise by 13.4 to 36.39% and 4 to 17.6% respectively while the in-plane stress ������ drop by 8 to 43.49% relative to extreme mechanical stress value for temperature change Δ���� to Δ���� in case of considering the maximum value in pure mode-I loading case. Even though, the phenomenon of the extreme values for the case of mixed and pure mode-I loading cases are differ, the mixed mode thermo-mechanical stress field values ������ and ������ are drop by 6.78 to 25.64% and 12.85 to 30.3% respectively while the in-plane stress ������ rise by 4.75 to 25.09% in rising of temperature change Δ���� to Δ���� in case of considering the maximum value. This extreme values variation was because of the temperature gradient from the boundary of the plate as compared to mechanical stress field. Besides the angular position of the extreme stress field values shifted for a certain angle as compared to the isothermal stress field. The contour of these stress fields around the crack tip developed numerically has a good agreement with the analytical developed results.