Strainassisted corrosion cracking and growth rate inhibitors
(2002) Abstract
 A model for evolution of cracks as a result of strainassisted corrosion is presented. The considered cracks possess a realistic geometry, where the tip region is an integral part of the crack surface instead of being a singular point. This geometry is either implicitly defined or is a consequence of crack nucleation from surface irregularities. The evolution model poses a moving boundary value problem, where material dissolution advances the boundary exposed to the corrosive environment. A controlling mechanism for the boundary advancement is the rupture of a brittle corrosionprotective film, which is continually buildingup along the corroding surface. The rate of boundary evolution is a function of the degree of the protective film... (More)
 A model for evolution of cracks as a result of strainassisted corrosion is presented. The considered cracks possess a realistic geometry, where the tip region is an integral part of the crack surface instead of being a singular point. This geometry is either implicitly defined or is a consequence of crack nucleation from surface irregularities. The evolution model poses a moving boundary value problem, where material dissolution advances the boundary exposed to the corrosive environment. A controlling mechanism for the boundary advancement is the rupture of a brittle corrosionprotective film, which is continually buildingup along the corroding surface. The rate of boundary evolution is a function of the degree of the protective film damage, caused by mechanical straining. Thus, no crack growth criterion is needed for the analysis. A FEM based program with various procedures for tracking the moving boundary is used as a solution tool. A number of problems are considered – cracks with realistic geometries with tips embedded in a squareroot singular stress field, and cracks nucleating from surface pits and propagating in either a homogeneous material or in a bimaterial system. The presented results show the importance of the crack width, interpreted as grain boundaries interphase thickness, as well as the various shape parameters describing the crack tip region, for the stress corrosion crack growth rate. Further, the results clearly demonstrate that the interaction between the surface deformation and the protective film is primarily responsible for the dissolution localisation along a narrow surface region, such that a crack is formed from a pit and the crack shape is maintained during the evolution. The influence of the initial pit aspect ratio on the crack nucleation phase is investigated, as well as the competition of cracks evolving from closely situated pits. It is shown how these results could be used for estimation of the arrested cracks distribution along a corroding surface. In the cases of corrosion cracks growing across bimaterial interfaces the numerical results for the crack morphology are shown to be in qualitative agreement with a real life example. In all these cases the cracks pass the interface being either accelerated or inhibited, depending on the elastic mismatch of the bimaterial system. Design recommendations are proposed on the bases of the presented results. Finally, a perturbation model for a nonhomogeneous material is proposed. The model is used in the analysis of an ideal crack with one tip interfering with an inclusion, introduced in a plane homogeneous elastic body, and having arbitrarily varying elastic characteristics. The solution is given in terms of an area integral and further specialised to an inclusion shaped as a layer stretching perpendicularly to the crack plane. A closed form result for this special case is derived and compared with numerical results obtained for finite variations of the elastic modulus. A wide range of validity of the perturbation solution is discovered. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/record/465280
 author
 Jivkov, Andrey P ^{LU}
 opponent

 Professor Varna, Janis, Luleå University of Technology
 organization
 publishing date
 2002
 type
 Thesis
 publication status
 published
 subject
 keywords
 vacuum technology, vibration and acoustic engineering, Maskinteknik, hydraulik, vakuumteknik, vibrationer, akustik, materialteknik, Mechanical engineering, Material technology, Materiallära, Stress intensity factor, Inhomogeneous materials, Crack evolution, Stress corrosion cracking, Moving boundary, hydraulics
 pages
 148 pages
 publisher
 Andrey Jivkov, Solid Mechanics, Malmö University, SE205 06 Malmö, Sweden,
 defense location
 Room M:B of the Mbuilding, Lund Institute of Technology, Ole Römers väg 1, Lund
 defense date
 20021219 10:15
 ISBN
 9162854720
 language
 English
 LU publication?
 yes
 id
 48e9832680e34e079d25296426b17c14 (old id 465280)
 date added to LUP
 20070910 10:45:01
 date last changed
 20160919 08:45:11
@phdthesis{48e9832680e34e079d25296426b17c14, abstract = {A model for evolution of cracks as a result of strainassisted corrosion is presented. The considered cracks possess a realistic geometry, where the tip region is an integral part of the crack surface instead of being a singular point. This geometry is either implicitly defined or is a consequence of crack nucleation from surface irregularities. The evolution model poses a moving boundary value problem, where material dissolution advances the boundary exposed to the corrosive environment. A controlling mechanism for the boundary advancement is the rupture of a brittle corrosionprotective film, which is continually buildingup along the corroding surface. The rate of boundary evolution is a function of the degree of the protective film damage, caused by mechanical straining. Thus, no crack growth criterion is needed for the analysis. A FEM based program with various procedures for tracking the moving boundary is used as a solution tool. A number of problems are considered – cracks with realistic geometries with tips embedded in a squareroot singular stress field, and cracks nucleating from surface pits and propagating in either a homogeneous material or in a bimaterial system. The presented results show the importance of the crack width, interpreted as grain boundaries interphase thickness, as well as the various shape parameters describing the crack tip region, for the stress corrosion crack growth rate. Further, the results clearly demonstrate that the interaction between the surface deformation and the protective film is primarily responsible for the dissolution localisation along a narrow surface region, such that a crack is formed from a pit and the crack shape is maintained during the evolution. The influence of the initial pit aspect ratio on the crack nucleation phase is investigated, as well as the competition of cracks evolving from closely situated pits. It is shown how these results could be used for estimation of the arrested cracks distribution along a corroding surface. In the cases of corrosion cracks growing across bimaterial interfaces the numerical results for the crack morphology are shown to be in qualitative agreement with a real life example. In all these cases the cracks pass the interface being either accelerated or inhibited, depending on the elastic mismatch of the bimaterial system. Design recommendations are proposed on the bases of the presented results. Finally, a perturbation model for a nonhomogeneous material is proposed. The model is used in the analysis of an ideal crack with one tip interfering with an inclusion, introduced in a plane homogeneous elastic body, and having arbitrarily varying elastic characteristics. The solution is given in terms of an area integral and further specialised to an inclusion shaped as a layer stretching perpendicularly to the crack plane. A closed form result for this special case is derived and compared with numerical results obtained for finite variations of the elastic modulus. A wide range of validity of the perturbation solution is discovered.}, author = {Jivkov, Andrey P}, isbn = {9162854720}, keyword = {vacuum technology,vibration and acoustic engineering,Maskinteknik,hydraulik,vakuumteknik,vibrationer,akustik,materialteknik,Mechanical engineering,Material technology,Materiallära,Stress intensity factor,Inhomogeneous materials,Crack evolution,Stress corrosion cracking,Moving boundary,hydraulics}, language = {eng}, pages = {148}, publisher = {Andrey Jivkov, Solid Mechanics, Malmö University, SE205 06 Malmö, Sweden,}, school = {Lund University}, title = {Strainassisted corrosion cracking and growth rate inhibitors}, year = {2002}, }