Solid Work 2012 Crack 13 Fixed
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This paper studies the thermoelastic fracture in a solid under non-classical Fourier heat conduction. The temperature field and the associated thermal stresses are solved by the dual integral equation technique. Both thermally insulated crack and heated crack are considered. It is found that the crack tip thermal stress is singular and can be expressed in terms of the thermal stress intensity factor in a closed-form. Numerical results show that the crack considerably amplifies the local thermal stresses, confirming the significance of the effect of non-classical heat conduction on the thermoelastic fracture mechanics of materials.
We show that one-level criteria for crack propagation in fracture mechanics should be supplemented by taking into account structure transformations in the local curvature regions of the crystal lattice in front of the crack tip. We develop a modified method of excitable cellular automata that takes into account the local torques in the crystal lattice with broken translational invariance and permits calculating the work of rotational deformation modes in crack propagation. Experimental data confirming the multilevel criteria of fracture mesomechanics are presented.
The study is concerned with the simulation of cracks in finitely deforming viscoelastic media. The main goal is to establish a computational methodology for crack propagation analyses in bulk material and interface debonding using an extended finite element method and cohesive zone modeling. First, a linear elastic plate with a single-edge crack and a linear viscoelastic plate with a double-edge crack are selected as benchmark problems. Upon verification of the extended finite element method and cohesive zone modeling results against those from the conventional crack propagation method and those from the literature, a nonlinear viscoelastic solid rocket motor subjected to various thermal loadings is analyzed for failure due to bore cracking or interface debonding. For a cooldown the stress distribution along the bond line is determined for the bore cracking mode and results are compared with those from the literature. For the cyclic temperature, the propagation of bore cracks is analyzed using an extended finite element method, and the propagation of initial debonding is studied using cohesive zone modeling. For both failure modes, crack propagation occurs only during the first cooldown. The relation between the crack growth and the initial crack size show parabolic behavior. Overall, it is concluded that the extended finite element method and cohesive zone modeling are suitable methods for crack propagation analysis in nonlinear viscoelastic media.
The overall objective of this work has been to develop and evaluate tools for designing against fatigue in gas turbine applications, with special focus on the nickel-based superalloy Inconel 718. The fatigue crack propagation behaviour under high temperature hold times has been studied. Firstly, the main fatigue crack propagation phenomena have been investigated with the aim of setting up a basis for fatigue crack propagation modelling. Secondly, modelling of the observed behaviour has been performed. Finally, the constitutive behaviour of the material has been studied, where focus has been placed on trying to describe the mean stress relaxation and initial softening of the material under intermediate temperatures.
This thesis is divided into two parts. The first part describes the general framework, including basic observed fatigue crack propagation behaviour of the material when subjected to hold times at high temperature as well as a background for the constitutive modelling of mean stress relaxation. This framework is then used in the second part, which consists of the seven included papers.
In this work, fatigue crack growth measurements have been made on center-cracked tension specimens of Inconel 718, where the focus has been to observe the effect of high temperature hold times on the fatigue crack growth behaviour of the material. The material testing has been done at three different temperatures, namely 450 degrees C, 550 degrees C and 650 degrees C. All testing were done in an isothermal LCF context with a standard test method for measuring the fatigue crack growth rates.
For those who participated in this study, crack plays an important mediating role between the different possible affective agreements in their daily lives. These findings, in a similar way to other studies, indicate a predominance of men and women with a profle of low levels of education and informal working practices88. Rodrigues DS, Backes DS, Freitas HMB, Zamberlan C, Gelhen MH, Colomé JS. Conhecimentos produzidos acerca do crack: uma incursão nas dissertações e teses brasileiras. Cien Saude Colet 2012; 17(5):1247-1258.,1010. Seleghim MR, Inoue KC, Santos JAT, Oliveira MLF. Aspectos da estrutura familiar de jovens usuários de crack: um estudo do genograma. Cienc Cuid Saude 2012; 10(4):795-802.,3030. Malta M, Monteiro S, Lima RMJ, Bauken S, Marco A, Zuim GC, Bastos FI, Singer M, Strathdee SA. HIV/AIDS risk among female sex workers who use crack in Southern Brazil. Rev Saude Publica 2008; 42(5):830-837.. 2b1af7f3a8