{"id":{"repo_id":"oxford-brookes","oai_identifier":"tle:3b3cc3a1-b87c-4458-9257-eab7ef2d43a6:d6bd9758-527a-46cd-bfe2-c433766e8fca:1"},"canonical_url":"https://search.dev.ndltd.org/etd/oxford-brookes/tle:3b3cc3a1-b87c-4458-9257-eab7ef2d43a6:d6bd9758-527a-46cd-bfe2-c433766e8fca:1","repository":{"repo_id":"oxford-brookes","name":"Oxford Brookes University","base_url":"https://radar.brookes.ac.uk/radar/oai"},"display":{"title":"Effect of Variable Amplitude Loading on Fatigue Crack Growth Rate","abstract":"Fatigue crack growth (FCG) is a major cause of failure in many engineering component and structure that are subjected to dynamic loading conditions. Several models have been proposed for estimating crack growth rate da/dN under various conditions. The majority of work reported has focused on constant amplitude (CA) loading and some for variable amplitude (VA) loading. The estimation of da/dN under VA loading is complex due to effect of several factors such as plasticity, crack tip blunting, residual stresses, crack tip closure and crack tip branching which are associated with different levels of loading. These factors which cause acceleration or deceleration of the crack growth are known as interaction effects. Crack closure has been identified to be one of the main interaction factors, and finite element (FE) models have been developed to quantify it in terms of crack opening stresses. There are however still a number of issue regarding the modelling parameters such as mesh size, element type number of loading increment and material hardening model that should be used and on whether crack closure represents the interaction effect sufficiently. Also modelling long crack length has been perceived to be too computationally intensive and therefore studies focus on hort crack length only. This thesis has studied several VA loading cases with a view to establish quantifiable parameters for the effects of plasticity induced crack closure and to assess its significance for representing interaction effect in estimating crack growth rate. A two dimensional FE model was used to simulate the fatigue crack growth. The modelling considered long cracks by dividing a whole crack in consecutive mall lengths. For this purpose the restart capability included in the ABAQUS code was employed, also the mesh refinement strategy optimised and reduced memory requirements for the thousands of cycles analysed. In addition elastic-perfect plastic and work hardening propertie were used to study the influence of work hardening on da/dN under VA loading. In order to validate the numerical model extensive experimental work was carried out to obtain data for comparison with numerical results. The experimental work implemented an optical method to measure the opening and closure loads in situ at 950x magnification. Also a technique to measure da/dN by employing a stroboscope lamp is presented. The FE results were in good agreement for most of the experiments and possible reasons are provided for some minor discrepancies observed.","abstract_html":"Fatigue crack growth (FCG) is a major cause of failure in many engineering component and structure that are subjected to dynamic loading conditions. Several models have been proposed for estimating crack growth rate da/dN under various conditions. The majority of work reported has focused on constant amplitude (CA) loading and some for variable amplitude (VA) loading. The estimation of da/dN under VA loading is complex due to effect of several factors such as plasticity, crack tip blunting, residual stresses, crack tip closure and crack tip branching which are associated with different levels of loading. These factors which cause acceleration or deceleration of the crack growth are known as interaction effects. Crack closure has been identified to be one of the main interaction factors, and finite element (FE) models have been developed to quantify it in terms of crack opening stresses. There are however still a number of issue regarding the modelling parameters such as mesh size, element type number of loading increment and material hardening model that should be used and on whether crack closure represents the interaction effect sufficiently. Also modelling long crack length has been perceived to be too computationally intensive and therefore studies focus on hort crack length only. This thesis has studied several VA loading cases with a view to establish quantifiable parameters for the effects of plasticity induced crack closure and to assess its significance for representing interaction effect in estimating crack growth rate. A two dimensional FE model was used to simulate the fatigue crack growth. The modelling considered long cracks by dividing a whole crack in consecutive mall lengths. For this purpose the restart capability included in the ABAQUS code was employed, also the mesh refinement strategy optimised and reduced memory requirements for the thousands of cycles analysed. In addition elastic-perfect plastic and work hardening propertie were used to study the influence of work hardening on da/dN under VA loading. In order to validate the numerical model extensive experimental work was carried out to obtain data for comparison with numerical results. The experimental work implemented an optical method to measure the opening and closure loads in situ at 950x magnification. Also a technique to measure da/dN by employing a stroboscope lamp is presented. The FE results were in good agreement for most of the experiments and possible reasons are provided for some minor discrepancies observed.","abstract_has_math":false,"creators":["Aguilar Espinosa, Aaron Alejandro"],"institution":"Oxford Brookes University","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":["Fellows, Neil"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":null,"date_issued":"","date_published":null,"updated_at":"2026-07-24T03:42:17Z","subjects":[],"languages":["en"],"rights":["All rights reserved"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://doi.org/10.24384/w93k-1k42","outbound_label":"DOI","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Aguilar Espinosa, Aaron Alejandro","Fellows, Neil"]},{"key":"dc:creator","label":"Author","values":["Aguilar Espinosa, Aaron Alejandro"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:publisher","label":"Institution","values":["Oxford Brookes University"]},{"key":"dc:type","label":"Dc Type","values":["thesis"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["All rights reserved"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://doi.org/10.24384/w93k-1k42","https://radar.brookes.ac.uk/radar/file/3b3cc3a1-b87c-4458-9257-eab7ef2d43a6/1/AguilarEspinosa_2009_E229.pdf"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Fatigue crack growth (FCG) is a major cause of failure in many engineering component and structure that are subjected to dynamic loading conditions. Several models have been proposed for estimating crack growth rate da/dN under various conditions. The majority of work reported has focused on constant amplitude (CA) loading and some for variable amplitude (VA) loading. The estimation of da/dN under VA loading is complex due to effect of several factors such as plasticity, crack tip blunting, residual stresses, crack tip closure and crack tip branching which are associated with different levels of loading. These factors which cause acceleration or deceleration of the crack growth are known as interaction effects. Crack closure has been identified to be one of the main interaction factors, and finite element (FE) models have been developed to quantify it in terms of crack opening stresses. There are however still a number of issue regarding the modelling parameters such as mesh size, element type number of loading increment and material hardening model that should be used and on whether crack closure represents the interaction effect sufficiently. Also modelling long crack length has been perceived to be too computationally intensive and therefore studies focus on hort crack length only. This thesis has studied several VA loading cases with a view to establish quantifiable parameters for the effects of plasticity induced crack closure and to assess its significance for representing interaction effect in estimating crack growth rate. A two dimensional FE model was used to simulate the fatigue crack growth. The modelling considered long cracks by dividing a whole crack in consecutive mall lengths. For this purpose the restart capability included in the ABAQUS code was employed, also the mesh refinement strategy optimised and reduced memory requirements for the thousands of cycles analysed. In addition elastic-perfect plastic and work hardening propertie were used to study the influence of work hardening on da/dN under VA loading. In order to validate the numerical model extensive experimental work was carried out to obtain data for comparison with numerical results. The experimental work implemented an optical method to measure the opening and closure loads in situ at 950x magnification. Also a technique to measure da/dN by employing a stroboscope lamp is presented. The FE results were in good agreement for most of the experiments and possible reasons are provided for some minor discrepancies observed."]},{"key":"dc:format","label":"Dc Format","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Effect of Variable Amplitude Loading on Fatigue Crack Growth Rate"]}]}],"canonical_facts":{"dc:contributor":["Aguilar Espinosa, Aaron Alejandro","Fellows, Neil"],"dc:creator":["Aguilar Espinosa, Aaron Alejandro"],"dc:description":["Fatigue crack growth (FCG) is a major cause of failure in many engineering component and structure that are subjected to dynamic loading conditions. Several models have been proposed for estimating crack growth rate da/dN under various conditions. The majority of work reported has focused on constant amplitude (CA) loading and some for variable amplitude (VA) loading. The estimation of da/dN under VA loading is complex due to effect of several factors such as plasticity, crack tip blunting, residual stresses, crack tip closure and crack tip branching which are associated with different levels of loading. These factors which cause acceleration or deceleration of the crack growth are known as interaction effects. Crack closure has been identified to be one of the main interaction factors, and finite element (FE) models have been developed to quantify it in terms of crack opening stresses. There are however still a number of issue regarding the modelling parameters such as mesh size, element type number of loading increment and material hardening model that should be used and on whether crack closure represents the interaction effect sufficiently. Also modelling long crack length has been perceived to be too computationally intensive and therefore studies focus on hort crack length only. This thesis has studied several VA loading cases with a view to establish quantifiable parameters for the effects of plasticity induced crack closure and to assess its significance for representing interaction effect in estimating crack growth rate. A two dimensional FE model was used to simulate the fatigue crack growth. The modelling considered long cracks by dividing a whole crack in consecutive mall lengths. For this purpose the restart capability included in the ABAQUS code was employed, also the mesh refinement strategy optimised and reduced memory requirements for the thousands of cycles analysed. In addition elastic-perfect plastic and work hardening propertie were used to study the influence of work hardening on da/dN under VA loading. In order to validate the numerical model extensive experimental work was carried out to obtain data for comparison with numerical results. The experimental work implemented an optical method to measure the opening and closure loads in situ at 950x magnification. Also a technique to measure da/dN by employing a stroboscope lamp is presented. The FE results were in good agreement for most of the experiments and possible reasons are provided for some minor discrepancies observed."],"dc:format":["application/pdf"],"dc:identifier":["https://doi.org/10.24384/w93k-1k42","https://radar.brookes.ac.uk/radar/file/3b3cc3a1-b87c-4458-9257-eab7ef2d43a6/1/AguilarEspinosa_2009_E229.pdf"],"dc:language":["en"],"dc:publisher":["Oxford Brookes University"],"dc:rights":["All rights reserved"],"dc:title":["Effect of Variable Amplitude Loading on Fatigue Crack Growth Rate"],"dc:type":["thesis"]},"updated_at":"2026-07-24T03:42:17Z"}