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}
Al2O3 coatings produced by plasma spray have been considered for wear resistance and corrosion protection. Mechanical investigations of these coatings are often performed when the coating is still on the metallic substrate, hiding the intrinsic response of the coatings and the lamellae that make up their microstructure. The development of a compression test for stand-alone coatings will be described. Cyclic compression loading with monotonically increased peak stresses was employed to study the deformation and damage of the coatings. Transmission electron microscopy and acoustic emission were also used to identify damage mechanisms that ultimately lead to failure. It is proposed that numerous defects that exist in plasma-sprayed coatings, including porosity and microcracks, serve as sites for crack nucleation and/or propagation. As these small cracks extend subcritically under an applied stress that ultimately propagate parallel to the loading direction along inter-lamella boundaries. With increasing stress, these cracks ultimately link resulting in catastrophic failure.
{"title":"Damage Mechanisms in Plasma-Sprayed Alumina Coatings","authors":"R. Trice, D. Prine, K. Faber","doi":"10.1115/imece2000-2690","DOIUrl":"https://doi.org/10.1115/imece2000-2690","url":null,"abstract":"\u0000 Al2O3 coatings produced by plasma spray have been considered for wear resistance and corrosion protection. Mechanical investigations of these coatings are often performed when the coating is still on the metallic substrate, hiding the intrinsic response of the coatings and the lamellae that make up their microstructure. The development of a compression test for stand-alone coatings will be described. Cyclic compression loading with monotonically increased peak stresses was employed to study the deformation and damage of the coatings. Transmission electron microscopy and acoustic emission were also used to identify damage mechanisms that ultimately lead to failure. It is proposed that numerous defects that exist in plasma-sprayed coatings, including porosity and microcracks, serve as sites for crack nucleation and/or propagation. As these small cracks extend subcritically under an applied stress that ultimately propagate parallel to the loading direction along inter-lamella boundaries. With increasing stress, these cracks ultimately link resulting in catastrophic failure.","PeriodicalId":324509,"journal":{"name":"Materials: Book of Abstracts","volume":"17 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":"134367977","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}
E. Kung, C. Mercer, S. Allameh, O. Popoola, W. Soboyejo
The fatigue behavior of Fe-Ni-base metal/polymer composites is discussed in this paper. These are proposed as self lubricating surfaces with the potential to replace conventionally lubricated pistons in automotive engines. Following a description of composite microstructure and basic mechanical properties, the paper examines the effects of polymer volume fraction on long fatigue crack growth. The effects of temperature on fatigue crack growth are then elucidated before presenting some initial fracture mechanics concepts for the prediction of fatigue life. The implications of the results are assessed for the design of durable surfaces.
{"title":"An Investigation of Fatigue in Polymer/Metal Composites","authors":"E. Kung, C. Mercer, S. Allameh, O. Popoola, W. Soboyejo","doi":"10.1115/imece2000-2694","DOIUrl":"https://doi.org/10.1115/imece2000-2694","url":null,"abstract":"\u0000 The fatigue behavior of Fe-Ni-base metal/polymer composites is discussed in this paper. These are proposed as self lubricating surfaces with the potential to replace conventionally lubricated pistons in automotive engines. Following a description of composite microstructure and basic mechanical properties, the paper examines the effects of polymer volume fraction on long fatigue crack growth. The effects of temperature on fatigue crack growth are then elucidated before presenting some initial fracture mechanics concepts for the prediction of fatigue life. The implications of the results are assessed for the design of durable surfaces.","PeriodicalId":324509,"journal":{"name":"Materials: Book of Abstracts","volume":"27 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":"115442741","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}
A design concept for potentially hard damage-resistant ceramic coatings on relatively soft substrates is proposed. Such coating structures are of direct relevance to biomechanical structures, especially teeth and dental crowns. In this study failure modes in bilayers and trilayers with relatively hard, brittle coating outerlayers on soft, tough substrate underlayers are evaluated. Coating/substrate systems of interest include ceramic/ceramic, ceramic/metal, and ceramic/polymer. A key element of these structures is a well-bonded interface, to prevent delamination during stressing. The objective is to arrest intrusive coating cracks in a tough sublayer, rather than merely to deflect them along a weak interface.
{"title":"Failure of Ceramic Coatings on Soft Substrates","authors":"B. Lawn","doi":"10.1115/imece2000-2661","DOIUrl":"https://doi.org/10.1115/imece2000-2661","url":null,"abstract":"\u0000 A design concept for potentially hard damage-resistant ceramic coatings on relatively soft substrates is proposed. Such coating structures are of direct relevance to biomechanical structures, especially teeth and dental crowns. In this study failure modes in bilayers and trilayers with relatively hard, brittle coating outerlayers on soft, tough substrate underlayers are evaluated. Coating/substrate systems of interest include ceramic/ceramic, ceramic/metal, and ceramic/polymer. A key element of these structures is a well-bonded interface, to prevent delamination during stressing. The objective is to arrest intrusive coating cracks in a tough sublayer, rather than merely to deflect them along a weak interface.","PeriodicalId":324509,"journal":{"name":"Materials: Book of Abstracts","volume":"71 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":"122611905","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}
Laser shock peening is developing into a commercial surface enhancement process for increasing the fatigue life of metal components. The process produces deep residual compressive stresses into treated surfaces which inhibit the initiation and propagation of fatigue cracks. The process has been particularly effective in increasing the resistance to foreign object damage in fan and compressor blades of aircraft gas turbine engines. However, the potential application of this process is much broader, encompassing automotive, tooling and dies, and others. Significant effort is being made to lower the cost and increase the throughput of the process, to make it an affordable process for many more applications. This describes the process and reviews the progress being made in the technology, both in material property enhancement and use of the process, and towards reducing cost and increasing throughput.
{"title":"Laser Shock Peening for Fatigue Resistance","authors":"A. Clauer","doi":"10.1115/imece2000-2681","DOIUrl":"https://doi.org/10.1115/imece2000-2681","url":null,"abstract":"\u0000 Laser shock peening is developing into a commercial surface enhancement process for increasing the fatigue life of metal components. The process produces deep residual compressive stresses into treated surfaces which inhibit the initiation and propagation of fatigue cracks. The process has been particularly effective in increasing the resistance to foreign object damage in fan and compressor blades of aircraft gas turbine engines. However, the potential application of this process is much broader, encompassing automotive, tooling and dies, and others. Significant effort is being made to lower the cost and increase the throughput of the process, to make it an affordable process for many more applications. This describes the process and reviews the progress being made in the technology, both in material property enhancement and use of the process, and towards reducing cost and increasing throughput.","PeriodicalId":324509,"journal":{"name":"Materials: Book of Abstracts","volume":"66 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":"130500787","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：