Stress concentration factor for interacting notch and subsurface pore

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Insinööritieteiden korkeakoulu | Master's thesis
Mechanics of materials
Degree programme
Master’s Programme in Mechanical Engineering
Machineries, vehicles, ships and airliners have numerous components that inevitably have stress concentrations. These concentrations are mainly due to abrupt geometrical alteration caused by manufacturing processes and design. The magnitude of a stress concentration depends on the geometry, loading and interaction between two distinct geometrical features. Geometrical discontinuities occur in numerous forms; mostly as external surface notch or subsurface defects e.g., circular or elliptical porosities or inclusions. These surface and subsurface defects have long been identified as detrimental factors which reduce the fatigue life of components. To avoid catastrophic failures related to stress concentrations, detailed analysis of them in engineering design is required. This thesis focuses on the interaction of stress concentrations between a surface notch and a subsurface porosity. The motivation behind this thesis work has been the unavailability of related studies despite of its significance. The thesis work uses a stress averaging method of the tangential stress component to determine the maximum interacting stress concentration factors of semi-circular notch-hole and equivalent elliptical notch-hole configurations in a semi-infinite plate. The study of the maximum stress concentration factor of the notch-hole configurations uses global and local stress averaging techniques that strongly depend on the extent of notch-hole gap distances. Three cases with relative notch-hole radii ratios of 20:1, 10:1, and 1:1 are investigated to determine the interacting stresses concentration factors with subsequent gap increments. In addition, the developed method is further utilized to analyse the interacting stress concentration factors of an equivalent elliptical notch and a hole that represents surface roughness with a subsurface porosity. The results of this work are compared with analytical solutions for two interacting holes and finite element simulations carried out using Abaqus simulation software. Based on the results, the stress averaging methods can be used to analyse the interacting stress concentration factors of notch-hole configurations with a specified range of gaps. The limitations of estimations using stress averaging approach are observed when the notch-hole gap is substantially reduced. The differences between the results obtained using stress averaging and the corresponding benchmarks of two holes solutions as well as finite element simulations are discussed. The study also discusses the limitations of using the stress averaging method in determining the interacting stress concentrations between semi-circular notch-hole and equivalent elliptical notch-hole configurations. In this study, porosity is represented by a circular hole. As the thesis is a single case of study in terms of relative notch-hole orientation, there is a variety of further study possibilities that could incorporate different notch-hole arrangements, loading conditions and varying material properties, which are suggested as possible future works.
Remes, Heikki
Thesis advisor
Karttunen, Anssi
interacting stress concentration factor, hole, semi-circular notch, equivalent elliptical notch, geometrical discontinuities, stress averaging
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