Microstructural observations of TBCs failed under thermal cycling conditions reveal that failure is associated with extensive local separations between either the thermally grown oxide and the TBC or within the TBC itself close to the thermally grown oxide. Based on extensive microstructural characterization and measurements of concentration profiles within the bond-coat, we present a new model for the cause of these separations based on local increases in the density of the bond coat associated with the beta-NiAl to gamma-prime Ni3Al phase transformation. The phase transformation, driven by aluminum depletion required to form the protective alumina thermally grown oxide, is constrained by the overlying TBC thereby generating tensile stresses across the TBC/TGO interface and its vicinity. The observations and evidence for the new model will be described together with the role of thermal cycling.
{"title":"Thermal Cycling Induced Bond-Coat Rumpling as a Precursor to TBC Failure","authors":"D. Clarke, V. Tolpygo","doi":"10.1115/imece2000-2682","DOIUrl":"https://doi.org/10.1115/imece2000-2682","url":null,"abstract":"\u0000 Microstructural observations of TBCs failed under thermal cycling conditions reveal that failure is associated with extensive local separations between either the thermally grown oxide and the TBC or within the TBC itself close to the thermally grown oxide. Based on extensive microstructural characterization and measurements of concentration profiles within the bond-coat, we present a new model for the cause of these separations based on local increases in the density of the bond coat associated with the beta-NiAl to gamma-prime Ni3Al phase transformation. The phase transformation, driven by aluminum depletion required to form the protective alumina thermally grown oxide, is constrained by the overlying TBC thereby generating tensile stresses across the TBC/TGO interface and its vicinity. The observations and evidence for the new model will be described together with the role of thermal cycling.","PeriodicalId":324509,"journal":{"name":"Materials: Book of Abstracts","volume":"19 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124829533","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper presents probabilistic methodologies being developed at Vanderbilt University for the reliability analysis of aging structures. Several deterioration mechanisms such as fatigue, corrosion, creep, and fretting are considered, and probabilistic models are developed. Interactions between the different mechanisms are considered. The effects of various uncertain parameters on the overall life prediction estimates are quantified. The fatigue damage process induced by pitting corrosion in aging aircraft is composed of seven stages: pitting nucleation, pit growth, transition from pit growth to short crack, short crack growth, transition from short crack to long crack, long crack growth and fracture. A comprehensive mechanics-based probabilistic model for pitting corrosion fatigue life prediction by including all the stages is presented. Analytical FORM/SORM methods as well as advanced Monte Carlo simulation methods are implemented with the proposed model, and probabilistic sensitivity analysis and parametric studies are performed. Fretting fatigue is one of the main mechanisms of the formation of cracks in riveted lap joint assemblies in aging aircraft and can reduce the fatigue life significantly. A macro-mechanics-based probabilistic model is developed to give the quantitative description of crack nucleation life. Fretting conditions in an idealized, cyclic-loaded pinned connection having dimensions typical of riveted panels are studied. ANSYS finite element analysis is applied to provide the stress, displacement and strain fields in the neighborhood of the contacts between the panel and pin. Creep is one of the principal damage mechanisms for materials operating at elevated temperatures, such as in aircraft and space propulsion engines. It can produce larger strain deformation, stress relaxation, and crack initiation and growth. Current creep-fatigue life prediction methods use a code-specified bilinear model that has several uncertainties and assumptions regarding material behavior. A new continuous creep-fatigue failure criterion function is introduced directly based on experimental data to facilitate analytical reliability approximations. Such a model is advantageous for new high performance materials where previous experience is limited. A linear damage accumulation rule is used. The use of analytical and simulation methods for reliability analysis with the proposed model is investigated. The effects of the scatter and distributions of different random variables on the creep-fatigue life are studied. This study is supported by funds from the National Science Foundation.
{"title":"Fatigue Reliability Under Corrosion, Creep, and Fretting Damage","authors":"S. Mahadevan","doi":"10.1115/imece2000-2670","DOIUrl":"https://doi.org/10.1115/imece2000-2670","url":null,"abstract":"\u0000 This paper presents probabilistic methodologies being developed at Vanderbilt University for the reliability analysis of aging structures. Several deterioration mechanisms such as fatigue, corrosion, creep, and fretting are considered, and probabilistic models are developed. Interactions between the different mechanisms are considered. The effects of various uncertain parameters on the overall life prediction estimates are quantified.\u0000 The fatigue damage process induced by pitting corrosion in aging aircraft is composed of seven stages: pitting nucleation, pit growth, transition from pit growth to short crack, short crack growth, transition from short crack to long crack, long crack growth and fracture. A comprehensive mechanics-based probabilistic model for pitting corrosion fatigue life prediction by including all the stages is presented. Analytical FORM/SORM methods as well as advanced Monte Carlo simulation methods are implemented with the proposed model, and probabilistic sensitivity analysis and parametric studies are performed.\u0000 Fretting fatigue is one of the main mechanisms of the formation of cracks in riveted lap joint assemblies in aging aircraft and can reduce the fatigue life significantly. A macro-mechanics-based probabilistic model is developed to give the quantitative description of crack nucleation life. Fretting conditions in an idealized, cyclic-loaded pinned connection having dimensions typical of riveted panels are studied. ANSYS finite element analysis is applied to provide the stress, displacement and strain fields in the neighborhood of the contacts between the panel and pin.\u0000 Creep is one of the principal damage mechanisms for materials operating at elevated temperatures, such as in aircraft and space propulsion engines. It can produce larger strain deformation, stress relaxation, and crack initiation and growth. Current creep-fatigue life prediction methods use a code-specified bilinear model that has several uncertainties and assumptions regarding material behavior. A new continuous creep-fatigue failure criterion function is introduced directly based on experimental data to facilitate analytical reliability approximations. Such a model is advantageous for new high performance materials where previous experience is limited. A linear damage accumulation rule is used. The use of analytical and simulation methods for reliability analysis with the proposed model is investigated. The effects of the scatter and distributions of different random variables on the creep-fatigue life are studied.\u0000 This study is supported by funds from the National Science Foundation.","PeriodicalId":324509,"journal":{"name":"Materials: Book of Abstracts","volume":"28 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127785552","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
W. Soboyejo, C. Mercer, S. Allameh, B. Nemetski, N. Marcantonio, J. Ricci
This paper presents the results of a multi-scale microstructural characterization of micro-textured Ti-6Al-4V surfaces that are used in biomedical implants. The hierarchies of substructural and microstructural features associated with laser micro-texturing, polishing and surface blasting with alumina pellets are elucidated via atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and optical microscopy (OM). The nano-scale roughness profiles associated with the different surface textures are elucidated via AFM. Sub-micron precipitates and dislocation substructures associated with wrought processing and laser processing are revealed by TEM. Micro- and meso-scale images of the groove structures are then discussed using OM and SEM. The implications of the results are discussed for the optimization of laser processing schemes for the fabrication of micro-textured surfaces that will facilitate the self organization of proteins, and the attachment of mammalian cells to the Ti-6Al-4V surfaces in biomedical implants.
{"title":"Microstructural Characterization of Micro-Textured Titanium Surfaces","authors":"W. Soboyejo, C. Mercer, S. Allameh, B. Nemetski, N. Marcantonio, J. Ricci","doi":"10.1115/imece2000-2674","DOIUrl":"https://doi.org/10.1115/imece2000-2674","url":null,"abstract":"\u0000 This paper presents the results of a multi-scale microstructural characterization of micro-textured Ti-6Al-4V surfaces that are used in biomedical implants. The hierarchies of substructural and microstructural features associated with laser micro-texturing, polishing and surface blasting with alumina pellets are elucidated via atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and optical microscopy (OM). The nano-scale roughness profiles associated with the different surface textures are elucidated via AFM. Sub-micron precipitates and dislocation substructures associated with wrought processing and laser processing are revealed by TEM. Micro- and meso-scale images of the groove structures are then discussed using OM and SEM. The implications of the results are discussed for the optimization of laser processing schemes for the fabrication of micro-textured surfaces that will facilitate the self organization of proteins, and the attachment of mammalian cells to the Ti-6Al-4V surfaces in biomedical implants.","PeriodicalId":324509,"journal":{"name":"Materials: Book of Abstracts","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121333568","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The paper discusses an enhanced analytical modeling approach to characterize and understand fatigue crack initiation and growth in gas turbine engine intermetallics. It is recognized that the design of components subjected to fatigue cannot be based on average material behavior but that designs must consider −3σ or some other appropriate extreme value material properties. Thus, a life prediction capability useful in a design application must address the scatter inherent in material response to fatigue. The paper addresses the scatter in fatigue life of gamma titanium aluminide by investigating the microstructural variables responsible for the scatter and developing analytical and semi-analytical models to quantitatively relate the variables to the response. The model is general and considers the entire range of damage accumulation sequences; from crack nucleation of the initially unflawed structure to final fast fracture. However, the model also allows failure to be defined as any subset of damage accumulation i.e., crack initiation life to a particular crack size or the number of cycles to grow a crack from a particular size to final fracture. The models allows the structural engineer to systematically and quantitatively assess the influence of the material uncertainties on the overall reliability of the structure.
{"title":"Probabilistic Micromechanical Fatigue Model for High Temperature Materials","authors":"R. Tryon","doi":"10.1115/imece2000-2654","DOIUrl":"https://doi.org/10.1115/imece2000-2654","url":null,"abstract":"\u0000 The paper discusses an enhanced analytical modeling approach to characterize and understand fatigue crack initiation and growth in gas turbine engine intermetallics. It is recognized that the design of components subjected to fatigue cannot be based on average material behavior but that designs must consider −3σ or some other appropriate extreme value material properties. Thus, a life prediction capability useful in a design application must address the scatter inherent in material response to fatigue. The paper addresses the scatter in fatigue life of gamma titanium aluminide by investigating the microstructural variables responsible for the scatter and developing analytical and semi-analytical models to quantitatively relate the variables to the response. The model is general and considers the entire range of damage accumulation sequences; from crack nucleation of the initially unflawed structure to final fast fracture. However, the model also allows failure to be defined as any subset of damage accumulation i.e., crack initiation life to a particular crack size or the number of cycles to grow a crack from a particular size to final fracture. The models allows the structural engineer to systematically and quantitatively assess the influence of the material uncertainties on the overall reliability of the structure.","PeriodicalId":324509,"journal":{"name":"Materials: Book of Abstracts","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125527375","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hydrogels have become increasingly important for use in the biomedical field. They are used diagnostic, therapeutic and implantable devices(e.g. catheter, biosensor, artificial skin, controlled release drug delivery system and contact lenses). Also silicone derivatives are widely used owing to their favorable properties such as low-glass transition temperature, high gas permeability, high thermal stability and good biocompatibility. We have studied the interpenetrating polymer networks(IPN) by previous reports, and to report on the preparation and properties of poly(vinyl alcohol), (PVA) and vinyl terminated polydimethylsiloxane(PDMS) IPN hydrogel in this presentation. The IPN composed of PVA and PDMS was synthesized by the following method. PVA was dissolved in the water to make 10wt% aqueous solution. And PDMS was mixed with 0.5wt% 2,2-dimethyl-2-phenylacetophenone(DMPAP) and 0.5mol% methylenebis acrylicamide(MBAAm). This mixture was added to PVA aqueous solution and heated at 90oC for 3hrs. Various IP{Ns were prepared from different mol ratios of PVA/PDMS. Hydrogels obtained were characterized by using FT-IR, wide angle X-ray diffractometry(WAXD), differential scanning calorimetry(DSC), dielectric analysis(DEA), and equilibrium water content(EWC).
{"title":"Synthesis and Characteristics of Interpenetrating Polymer Network Hydrogels Based on Silicone and Poly(vinyl alcohol)","authors":"S. J. Kim, M. Shin","doi":"10.1115/imece2000-2700","DOIUrl":"https://doi.org/10.1115/imece2000-2700","url":null,"abstract":"\u0000 Hydrogels have become increasingly important for use in the biomedical field. They are used diagnostic, therapeutic and implantable devices(e.g. catheter, biosensor, artificial skin, controlled release drug delivery system and contact lenses). Also silicone derivatives are widely used owing to their favorable properties such as low-glass transition temperature, high gas permeability, high thermal stability and good biocompatibility. We have studied the interpenetrating polymer networks(IPN) by previous reports, and to report on the preparation and properties of poly(vinyl alcohol), (PVA) and vinyl terminated polydimethylsiloxane(PDMS) IPN hydrogel in this presentation. The IPN composed of PVA and PDMS was synthesized by the following method. PVA was dissolved in the water to make 10wt% aqueous solution. And PDMS was mixed with 0.5wt% 2,2-dimethyl-2-phenylacetophenone(DMPAP) and 0.5mol% methylenebis acrylicamide(MBAAm). This mixture was added to PVA aqueous solution and heated at 90oC for 3hrs. Various IP{Ns were prepared from different mol ratios of PVA/PDMS. Hydrogels obtained were characterized by using FT-IR, wide angle X-ray diffractometry(WAXD), differential scanning calorimetry(DSC), dielectric analysis(DEA), and equilibrium water content(EWC).","PeriodicalId":324509,"journal":{"name":"Materials: Book of Abstracts","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127762193","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Clinical performance of an prosthesis is directly dependent on damage introduced during fabrication and during fatigue loading associated with function. The relation between shaping damage and fatigue damage on clinical performance of all-ceramic dental crowns was investigated. Materials used commercially for all-ceramic crowns and investigated in this study included a series of different microstructures of machinable glass ceramics (Corning), aluminas and porcelains (Vita Zahnfabrik), and zirconias (Norton).
{"title":"Clinical Performance: A Reflection of Damage Accumulation","authors":"E. Rekow, V. Thompson","doi":"10.1115/imece2000-2662","DOIUrl":"https://doi.org/10.1115/imece2000-2662","url":null,"abstract":"\u0000 Clinical performance of an prosthesis is directly dependent on damage introduced during fabrication and during fatigue loading associated with function. The relation between shaping damage and fatigue damage on clinical performance of all-ceramic dental crowns was investigated. Materials used commercially for all-ceramic crowns and investigated in this study included a series of different microstructures of machinable glass ceramics (Corning), aluminas and porcelains (Vita Zahnfabrik), and zirconias (Norton).","PeriodicalId":324509,"journal":{"name":"Materials: Book of Abstracts","volume":"33 3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116741368","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The connection between processing and performance in thermal barrier coatings produced by electron-beam physical-vapor-deposition is not well understood. A significant component of the problem is the limited understanding of the role that microstructure (including defects) plays in this connection, and the relationships between microstructure and process parameters. This presentation will review recent work aimed at understanding these relationships. The focus will be on the evolution of porosity within the TBC, which is of paramount importance to both thermal conductivity and strain tolerance. Porosity is a result of shadowing processes in the presence of insufficient surface diffusion, and thus deposition temperature and vapor incidence pattern are major parameters. The presentation will highlight the interplay between vapor flux and surface topography, illustrating the relevant phenomena with experimental and modeling results. (Work sponsored by ONR under Grant N00014-99-1-0471 and the UC-LANL Collaborative Research Program.)
{"title":"Processing and Microstructure Evolution in EB-PVD TBCs","authors":"S. G. Terry, Junghyun Cho, C. Levi","doi":"10.1115/imece2000-2683","DOIUrl":"https://doi.org/10.1115/imece2000-2683","url":null,"abstract":"\u0000 The connection between processing and performance in thermal barrier coatings produced by electron-beam physical-vapor-deposition is not well understood. A significant component of the problem is the limited understanding of the role that microstructure (including defects) plays in this connection, and the relationships between microstructure and process parameters. This presentation will review recent work aimed at understanding these relationships. The focus will be on the evolution of porosity within the TBC, which is of paramount importance to both thermal conductivity and strain tolerance. Porosity is a result of shadowing processes in the presence of insufficient surface diffusion, and thus deposition temperature and vapor incidence pattern are major parameters. The presentation will highlight the interplay between vapor flux and surface topography, illustrating the relevant phenomena with experimental and modeling results. (Work sponsored by ONR under Grant N00014-99-1-0471 and the UC-LANL Collaborative Research Program.)","PeriodicalId":324509,"journal":{"name":"Materials: Book of Abstracts","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117225391","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The paper addresses significant aspects of stochastic modeling for jet engine component life prediction. Probabilistic life prediction for gas turbine engine components represents a very difficult engineering problem involving stochastic modeling of multiple, complex random phenomena. A key aspect for developing a probabilistic life prediction tool is to incorporate, and to be open to modeling advances related to dynamic complex random phenomena, including space-time random variabilities of mission environment and material parameters, aero-elastic interactions, friction at contact interfaces, multi-site fatigue, progressive damage mechanism, including loading interactions, etc.. The paper addresses the main aspects involved in stochastic modeling of component fatigue life prediction for jet engine rotating components, specifically fan blades. The paper highlights the need of the use of stochastic process and field models for including space-time varying random aspects. Mission speed profiles produced by pilot’s random maneuvers are modeled by pulse non-Gaussian stochastic processes. These pulse processes are approximated using linear recursive models when the cluster effects are not significant. A more general approach, useful when cluster effects are significant, based on a combination of two pulse processes is used. Aero-pressure distribution on blade as well as blade surface geometry deviations due to manufacturing are idealized by using factorable stochastic field models. Also, stochastic field models are used for modeling strain-life and damage accumulation curves. Stochastic damage accumulation models are based on randomized stress-dependent models (nonlinear damage rule models). The paper also addresses mathematical modeling of stochastic nonlinear responses in multidimensional parameter spaces. Stochastic response surface techniques based on factorable stochastic fields or optimum stochastic models are suggested. An illustrative example of a jet engine blade is used for discussion and to show the consequences of different modeling assumptions.
{"title":"Advanced Stochastic Techniques for Jet Engine Component Life Prediction","authors":"D. Ghiocel","doi":"10.1115/imece2000-2650","DOIUrl":"https://doi.org/10.1115/imece2000-2650","url":null,"abstract":"\u0000 The paper addresses significant aspects of stochastic modeling for jet engine component life prediction. Probabilistic life prediction for gas turbine engine components represents a very difficult engineering problem involving stochastic modeling of multiple, complex random phenomena. A key aspect for developing a probabilistic life prediction tool is to incorporate, and to be open to modeling advances related to dynamic complex random phenomena, including space-time random variabilities of mission environment and material parameters, aero-elastic interactions, friction at contact interfaces, multi-site fatigue, progressive damage mechanism, including loading interactions, etc.. The paper addresses the main aspects involved in stochastic modeling of component fatigue life prediction for jet engine rotating components, specifically fan blades. The paper highlights the need of the use of stochastic process and field models for including space-time varying random aspects.\u0000 Mission speed profiles produced by pilot’s random maneuvers are modeled by pulse non-Gaussian stochastic processes. These pulse processes are approximated using linear recursive models when the cluster effects are not significant. A more general approach, useful when cluster effects are significant, based on a combination of two pulse processes is used. Aero-pressure distribution on blade as well as blade surface geometry deviations due to manufacturing are idealized by using factorable stochastic field models. Also, stochastic field models are used for modeling strain-life and damage accumulation curves. Stochastic damage accumulation models are based on randomized stress-dependent models (nonlinear damage rule models).\u0000 The paper also addresses mathematical modeling of stochastic nonlinear responses in multidimensional parameter spaces. Stochastic response surface techniques based on factorable stochastic fields or optimum stochastic models are suggested.\u0000 An illustrative example of a jet engine blade is used for discussion and to show the consequences of different modeling assumptions.","PeriodicalId":324509,"journal":{"name":"Materials: Book of Abstracts","volume":"318 ","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"120866001","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The human heat rate is roughly 40 million beats per year. To prosthetic implants such as mechanical heart valves and endovascular stents, this means that they must endure almost 109 fatigue cycles during the patient’s lifetime. To prevent premature mechanical failures of such devices, which inevitably lead to patient fatalities, considerations of damage-tolerant design and life-prediction methodologies represent a preferred approach. In this presentation, a damage-tolerant approach to life prediction and “quality control” for both metallic and ceramic heart valve prostheses is presented, based on the notion that the useful life of the device is governed by the time for incipient defects in the material to propagate, by stress corrosion or more critically fatigue, to failure. Based on these analyses, the relative benefits of metallic (Co-Cr, Ti-6Al-4V) vs. ceramic (pyrolytic carbon) valves are discussed. Finally, analogous considerations are presented for endovascular stents, particularly those processed by laser cutting of the superelastic Ni-Ti alloy Nitinol. Again, the relative benefits of Nitinol vs. more traditional metallic implant materials (stainless steel, Co-Cr, titanium, titanium alloys) are discussed.
{"title":"Damage Tolerance in Biomedical Implants: Cardiac Valves and Endovascular Stents","authors":"R. Ritchie","doi":"10.1115/imece2000-2671","DOIUrl":"https://doi.org/10.1115/imece2000-2671","url":null,"abstract":"\u0000 The human heat rate is roughly 40 million beats per year. To prosthetic implants such as mechanical heart valves and endovascular stents, this means that they must endure almost 109 fatigue cycles during the patient’s lifetime. To prevent premature mechanical failures of such devices, which inevitably lead to patient fatalities, considerations of damage-tolerant design and life-prediction methodologies represent a preferred approach. In this presentation, a damage-tolerant approach to life prediction and “quality control” for both metallic and ceramic heart valve prostheses is presented, based on the notion that the useful life of the device is governed by the time for incipient defects in the material to propagate, by stress corrosion or more critically fatigue, to failure. Based on these analyses, the relative benefits of metallic (Co-Cr, Ti-6Al-4V) vs. ceramic (pyrolytic carbon) valves are discussed. Finally, analogous considerations are presented for endovascular stents, particularly those processed by laser cutting of the superelastic Ni-Ti alloy Nitinol. Again, the relative benefits of Nitinol vs. more traditional metallic implant materials (stainless steel, Co-Cr, titanium, titanium alloys) are discussed.","PeriodicalId":324509,"journal":{"name":"Materials: Book of Abstracts","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129368937","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fatigue and fracture are typical random phenomena due to various uncertainty sources, including material property, initial flaw and crack shape, structural configuration and geometry around crack tip, load fluctuation, and other environmental factors. As contrast to the most commonly used probabilistic fatigue growth models, which are built based on simplified fatigue crack growth law, a framework of probabilistic fracture mechanics based fatigue damage assessment methodology for small crack propagation is presented here. The proposed modeling is developed based on a comprehensive fatigue crack growth model, which accounts the effect of crack aspect ratio, stress ratio, and crack closure and retardation. Due to the complicated nature of the fatigue damage modeling adopted, a high non-linear limit state function with discontinuity resulted from physical domain jumping and overlapping are encountered. The advanced fast probability integration techniques in conjunction with response surface methodology and Monte Carlo simulation are used and the accuracy of the analysis is verified. The interface between probabilistic analysis package and the deterministic fracture mechanics analysis program is developed for the purpose of uncertainty propagation. The probability of failure of fatigue damage is computed first. The statistical characteristics of estimated fatigue life and critical crack size are obtained and presented through CDF/PDF curves. The sensitivity analysis is also performed, which provides an indication of the order of importance for the random variables considered. The results of the study have shown robustness and efficiency of the probabilistic analysis to deal with the real world challenge of uncertainty modelling, propagation, and quantification. Currently, possibility to combine the subject probabilistic damage assessment methodology with reliability updating techniques is under the investigation. The successfulness of the presented research activity will address an important issue of quantitative risk analysis for aging structures subjected to accumulative material damage.
{"title":"Probabilistic Fatigue Damage Assessment for Small Crack Growth","authors":"Zhengwei Zhao, Irewole Wally Orisamolu","doi":"10.1115/imece2000-2647","DOIUrl":"https://doi.org/10.1115/imece2000-2647","url":null,"abstract":"\u0000 Fatigue and fracture are typical random phenomena due to various uncertainty sources, including material property, initial flaw and crack shape, structural configuration and geometry around crack tip, load fluctuation, and other environmental factors. As contrast to the most commonly used probabilistic fatigue growth models, which are built based on simplified fatigue crack growth law, a framework of probabilistic fracture mechanics based fatigue damage assessment methodology for small crack propagation is presented here. The proposed modeling is developed based on a comprehensive fatigue crack growth model, which accounts the effect of crack aspect ratio, stress ratio, and crack closure and retardation. Due to the complicated nature of the fatigue damage modeling adopted, a high non-linear limit state function with discontinuity resulted from physical domain jumping and overlapping are encountered. The advanced fast probability integration techniques in conjunction with response surface methodology and Monte Carlo simulation are used and the accuracy of the analysis is verified. The interface between probabilistic analysis package and the deterministic fracture mechanics analysis program is developed for the purpose of uncertainty propagation. The probability of failure of fatigue damage is computed first. The statistical characteristics of estimated fatigue life and critical crack size are obtained and presented through CDF/PDF curves. The sensitivity analysis is also performed, which provides an indication of the order of importance for the random variables considered. The results of the study have shown robustness and efficiency of the probabilistic analysis to deal with the real world challenge of uncertainty modelling, propagation, and quantification. Currently, possibility to combine the subject probabilistic damage assessment methodology with reliability updating techniques is under the investigation. The successfulness of the presented research activity will address an important issue of quantitative risk analysis for aging structures subjected to accumulative material damage.","PeriodicalId":324509,"journal":{"name":"Materials: Book of Abstracts","volume":"110 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127978867","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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