User friendly assessment of stress intensity factor in thermal shocked cracked structures with finite boundary restraint

Brent Fillery

    Research output: ThesisDoctoral Thesis

    230 Downloads (Pure)

    Abstract

    The storage, transportation and processing of thermo-fluids is an essential part of numerous engineering processes. An interaction between thermo-fluids and associated engineering structures often induces thermal fatigue cracking and the prediction of fitness-for-purpose assessment under worst case severe thermal shock conditions is thus an important problem. In creep-free thermal shock conditions this fitness-for-purpose or structural integrity and remaining life assessment is closely associated with a mode I thermal shock stress intensity factor (KTSI ) evaluation, and the ease at which such a fitness-for-purpose can be performed is also dependent on the ‘user-friendliness‘ of the KTSI evaluation procedure. The aim of this thesis is to propose and demonstrate how a Compliance Adjusted Weight Function (CAWF) approach can enable the ‘user-friendly‘ estimation of KTSI associated with finite length elastically/ thermo-elastically restrained cracked plates and cracked hollow cylinders. The underlying CAWF approach will be shown to utilise an easily formularised analysis of elastic Line-Spring compliance, a crackfree finite element analysis, well known and easily documented geometry factors and mechanical weight functions for an equivalent semi-infinite cracked plate or cracked hollow cylinder configuration. The plate and hollow cylinder CAWF philosophies for the cases outlined, the CAWF‘s finite element implementation and a description of the aforementioned elastic Line-Spring compliance analysis are detailed herein. A validation of each CAWF formulation will also be provided and these verification analyses demonstrate that CAWF estimates associated with the targeted edge cracked plate and edge cracked hollow cylinder configurations are vastly improved over reference mechanical weight function evaluations and are within ±5% of benchmark fracture mechanic finite element results for the majority of analysed configurations. A similar outcome ensues when verifying the CAWF formulations associated with the targeted semielliptical surface cracked plate and semi-elliptical surface cracked hollow cylinder configurations. In this case the CAWF estimates are within ±10% of benchmark fracture mechanic finite element analyses and vastly improved over reference mechanical weight function evaluations. However, the CAWF estimates attributed to the semi-elliptical surface cracked plate and semi-elliptical surface cracked hollow cylinder configurations did show a distinctive departure from the benchmark fracture mechanic finite element analyses at large crack depth as well as low boundary restraint stiffness where a length associative free boundary effect is apparent. The maximum magnitude of this length associative free boundary effect was observed at a near zero boundary restraint stiffness and observed to be proportional to the tensile force and bending moment that encompass the boundary restraint reaction behaviour in an equivalent rigid boundary restraint configuration. Based upon this observation a sigmoidal adjustment was proposed to enable the CAWF approach to capture the instance of this length associative free boundary effect. In the targeted plate configurations this procedure appears relatively simple as the behaviour of the length associative free boundary effect was observed to exhibit a consistent and constant behaviour for estimates at the deepest and surface points on the semi-elliptical crack front. The characterisation of the length associative free boundary effect is more complicated in the targeted hollow cylinder configurations. Estimates of the length associative free boundary effect at the surface points on these semi-elliptical surface cracked hollow cylinders were observed to be a function of the surface points position around the hollow cylinder circumference. Estimates of the length associative free boundary effect at the deepest and surface points on these semi-elliptical surface cracked hollow cylinder
    Original languageEnglish
    QualificationDoctor of Philosophy
    Publication statusUnpublished - 2010

    Fingerprint Dive into the research topics of 'User friendly assessment of stress intensity factor in thermal shocked cracked structures with finite boundary restraint'. Together they form a unique fingerprint.

  • Cite this