Composite durability under conditions where the material survives the initial application of load but then deteriorates with time is a major issue in most engineering applications of composites. The degradation can be caused by the propagation of many damage modes: delamination, matrix cracking, interface degradation, creep, and fiber degradation, among others. In many situations, ultimate and total failure is associated with failure of the fiber bundle supporting the dominant portion of the applied load. Here, the lifetime of a composite due to fiber degradation is investigated for two important modes of fiber degradation: fatigue crack growth under cyclic loading and slow crack growth under stress rupture conditions of constant load. In both cases, individual fiber failure is caused by the growth of pre-existing cracks to a critical size via fatigue or rupture, which is modeled here by a Paris law. A simulation model is used to determine the time-dependent stresses on a bundle of uniaxial brittle fibers, each containing an initial distribution of cracks corresponding to a Weibull strength distribution. As individual fibers fail, their stresses are transferred to nearby fibers, which increases the rate of degradation of the nearby fibers. The damage evolution thus accelerates locally, culminating in the very rapid growth of damage across the entire specimen at the failure time. The average failure time for a set of nominally identical specimens is primarily a function of the fiber Weibull modulus, the Paris law exponent in the fatigue or rupture model, the initial fiber strength, and the rate coefficient of the Paris law. Guidance for the major dependencies of the failure time is obtained by considering an analogous “Global Load Sharing” (GLS) model in which broken fibers transfer load equally to all remaining fibers in the same cross-section. The statistical distribution of failure times at fixed composite size and the size scaling of the mean failure time with increasing size, neither of which can be obtained from the GLS model, are presented and discussed.
{"title":"Failure by Fatigue and Stress Rupture in Fiber-Reinforced Composites","authors":"W. Curtin","doi":"10.1115/imece2000-2665","DOIUrl":"https://doi.org/10.1115/imece2000-2665","url":null,"abstract":"\u0000 Composite durability under conditions where the material survives the initial application of load but then deteriorates with time is a major issue in most engineering applications of composites. The degradation can be caused by the propagation of many damage modes: delamination, matrix cracking, interface degradation, creep, and fiber degradation, among others. In many situations, ultimate and total failure is associated with failure of the fiber bundle supporting the dominant portion of the applied load. Here, the lifetime of a composite due to fiber degradation is investigated for two important modes of fiber degradation: fatigue crack growth under cyclic loading and slow crack growth under stress rupture conditions of constant load. In both cases, individual fiber failure is caused by the growth of pre-existing cracks to a critical size via fatigue or rupture, which is modeled here by a Paris law. A simulation model is used to determine the time-dependent stresses on a bundle of uniaxial brittle fibers, each containing an initial distribution of cracks corresponding to a Weibull strength distribution. As individual fibers fail, their stresses are transferred to nearby fibers, which increases the rate of degradation of the nearby fibers. The damage evolution thus accelerates locally, culminating in the very rapid growth of damage across the entire specimen at the failure time. The average failure time for a set of nominally identical specimens is primarily a function of the fiber Weibull modulus, the Paris law exponent in the fatigue or rupture model, the initial fiber strength, and the rate coefficient of the Paris law. Guidance for the major dependencies of the failure time is obtained by considering an analogous “Global Load Sharing” (GLS) model in which broken fibers transfer load equally to all remaining fibers in the same cross-section. The statistical distribution of failure times at fixed composite size and the size scaling of the mean failure time with increasing size, neither of which can be obtained from the GLS model, are presented and discussed.","PeriodicalId":324509,"journal":{"name":"Materials: Book of Abstracts","volume":"40 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":"117162185","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}
Thermal protection systems based on thermal barrier coatings are widely used in turbine engines for propulsion and power generation. They commonly comprise oxide thermal barriers coatings (TBCs) deposited on an intermetallic bond coat (BC), and provide simultaneous thermal and oxidation protection. The benefit of these coatings resides in their ability to inhibit degradation of the underlying structural superalloy component by thermo-mechanical fatigue and oxidation. Existing commercial coatings are well-engineered with established durability and cost benefits. However, they lose adhesion and spall from the underlying metal with cyclic thermal exposure. Because coating failure occurs in a stochastic manner, with no assured cyclic life, the coatings cannot be used in a prime-reliant manner. Prime reliability is only achievable if a high level of basic understanding is gained about failure mechanisms, and material responses, that arise upon thermal cycling. Because of differing manufacturing approaches and operating scenarios, several specific mechanisms are involved. Present understanding of these phenomena has highlighted several nuances and challenges in developing thermal barrier coatings for use as prime-reliant components. This talk will review the current understanding of factors affecting coating durability and presents relationships between the durability, the governing material properties and the salient morphological features. The durability of thermal barrier coatings is governed by a sequence of crack nucleation, propagation and coalescence events that accumulate prior to final failure by large scale buckling and spalling.
{"title":"Challenges and Opportunities for Prime Reliant Thermal Barrier Coating Systems","authors":"A. Evans","doi":"10.1115/imece2000-2677","DOIUrl":"https://doi.org/10.1115/imece2000-2677","url":null,"abstract":"\u0000 Thermal protection systems based on thermal barrier coatings are widely used in turbine engines for propulsion and power generation. They commonly comprise oxide thermal barriers coatings (TBCs) deposited on an intermetallic bond coat (BC), and provide simultaneous thermal and oxidation protection. The benefit of these coatings resides in their ability to inhibit degradation of the underlying structural superalloy component by thermo-mechanical fatigue and oxidation. Existing commercial coatings are well-engineered with established durability and cost benefits. However, they lose adhesion and spall from the underlying metal with cyclic thermal exposure. Because coating failure occurs in a stochastic manner, with no assured cyclic life, the coatings cannot be used in a prime-reliant manner. Prime reliability is only achievable if a high level of basic understanding is gained about failure mechanisms, and material responses, that arise upon thermal cycling. Because of differing manufacturing approaches and operating scenarios, several specific mechanisms are involved. Present understanding of these phenomena has highlighted several nuances and challenges in developing thermal barrier coatings for use as prime-reliant components. This talk will review the current understanding of factors affecting coating durability and presents relationships between the durability, the governing material properties and the salient morphological features. The durability of thermal barrier coatings is governed by a sequence of crack nucleation, propagation and coalescence events that accumulate prior to final failure by large scale buckling and spalling.","PeriodicalId":324509,"journal":{"name":"Materials: Book of Abstracts","volume":"17 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":"124946482","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 probabilistic framework is presented for the modeling of the variability in crack-tip opening displacement (fracture toughness) during the fracture of coarse grained heat affected zones in A707 steel welds. The variability in inclusion distribution and fracture conditions is modeled using weak link statistics in physically-based fracture mechanics models that describe the fracture behavior in the lower-shelf and transition-temperature regimes. The models are used to explain the measured trends in experiments designed to explore the effects of heat input on crack-tip opening displacement. The implications of the results are also analyzed for the design of welded structures.
{"title":"A Probabilistic Approach to the Modeling of Coarse Grain Heat Affected Zone Fracture in A707 Steel Welds","authors":"J. Zhou, W. Soboyejo","doi":"10.1115/imece2000-2666","DOIUrl":"https://doi.org/10.1115/imece2000-2666","url":null,"abstract":"\u0000 A probabilistic framework is presented for the modeling of the variability in crack-tip opening displacement (fracture toughness) during the fracture of coarse grained heat affected zones in A707 steel welds. The variability in inclusion distribution and fracture conditions is modeled using weak link statistics in physically-based fracture mechanics models that describe the fracture behavior in the lower-shelf and transition-temperature regimes. The models are used to explain the measured trends in experiments designed to explore the effects of heat input on crack-tip opening displacement. The implications of the results are also analyzed for the design of welded structures.","PeriodicalId":324509,"journal":{"name":"Materials: Book of Abstracts","volume":"423 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":"123556435","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 Corrosion behavior of aluminum alloys coated with intrinsically conducting polymers, ICPs, such as polyaniline, polypyrrole and their composites has been determined. The corrosion rate of the coated substrates is significantly reduced in the presence of the ICP coating. However, the corrosion resistance of the coated Al was found to be strongly dependent on the electrochemical processing variables such as the applied current density, pH and the deposition time. Both low current densities, i 3/4 2 mA/cm2 and high current densities, i > 6 mA/cm2, resulted in high corrosion currents and low corrosion rates. Also the ICP coatings deposited at very short and very long deposition times, respectively, show decreased corrosion performance. In our presentation, we will discuss the effects of electrochemical processing variables on the surface structure and corrosion performance of ICPs coated Al.
{"title":"Corrosion and Wear Behavior of Al 2024 Alloy Coated With Intrinsically Conductive Polymers, ICPs","authors":"K. Shah, J. Iroh, G. Akundy, Y. Zhu, O. Popoola","doi":"10.1115/imece2000-2679","DOIUrl":"https://doi.org/10.1115/imece2000-2679","url":null,"abstract":"\u0000 The Corrosion behavior of aluminum alloys coated with intrinsically conducting polymers, ICPs, such as polyaniline, polypyrrole and their composites has been determined. The corrosion rate of the coated substrates is significantly reduced in the presence of the ICP coating. However, the corrosion resistance of the coated Al was found to be strongly dependent on the electrochemical processing variables such as the applied current density, pH and the deposition time. Both low current densities, i 3/4 2 mA/cm2 and high current densities, i > 6 mA/cm2, resulted in high corrosion currents and low corrosion rates. Also the ICP coatings deposited at very short and very long deposition times, respectively, show decreased corrosion performance. In our presentation, we will discuss the effects of electrochemical processing variables on the surface structure and corrosion performance of ICPs coated Al.","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":"128262401","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 a statistical framework for the modeling of fatigue in gamma-based titanium aluminide intermetallics. Following an initial description of the physics of fatigue crack growth, a deterministic fracture mechanics model is presented for the estimation approaches are of fatigue life. This is used as a basis for the development of a probabilistic model for the estimation of fatigue life due to variabilities in the initial flow size. The predicted variabilities are compared with measured variabilities from multiple fatigue life experiments performed on three cast lamellar gamma alloys. The implications of the results are then discussed for the estimation of material reliability in gamma-based titanium aluminide intermetallics.
{"title":"A Probabilistic Approach to the Modeling of Fatigue in Gamma-Based Titanium Aluminides","authors":"J. Lou, W. Shen, W. Soboyejo","doi":"10.1115/imece2000-2648","DOIUrl":"https://doi.org/10.1115/imece2000-2648","url":null,"abstract":"\u0000 This paper presents a statistical framework for the modeling of fatigue in gamma-based titanium aluminide intermetallics. Following an initial description of the physics of fatigue crack growth, a deterministic fracture mechanics model is presented for the estimation approaches are of fatigue life. This is used as a basis for the development of a probabilistic model for the estimation of fatigue life due to variabilities in the initial flow size. The predicted variabilities are compared with measured variabilities from multiple fatigue life experiments performed on three cast lamellar gamma alloys. The implications of the results are then discussed for the estimation of material reliability in gamma-based titanium aluminide intermetallics.","PeriodicalId":324509,"journal":{"name":"Materials: Book of Abstracts","volume":"13 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":"128645002","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}
Pyrolytic carbons have a long successful history in mechanical heart valve prosthesis applications. Originally pyrolytic carbons had been developed for use in nuclear reactors. But in a chance interaction between a scientist studying nuclear energy and another searching for blood compatible materials, the blood compatibility of pyrolytic carbon was discovered. This discovery of blood compatibility prompted an effort that resulted in the development of a form of pyrolytic carbon specifically tailored for use in mechanical heart valves. This form developed by General Atomic Co. was an alloy of approximately 5 to 12 weight percent silicon codeposited with pyrolytic carbon. Fine silicon carbide particles dispersed in the carbon matrix increased the hardness and wear resistance of the pyrolytic carbon, which compensated for difficulties in manufacturing using the process control capabilities available at the time. Use of pyrolytic carbon instead of polymers in the early valve designs allowed the durability, stability and compatibility needed for true long-term implants. Since the first pyrolytic carbon heart valve component implant in 1968, more than 4 million pyrolytic carbon components in more than 25 different valve designs have been implanted to accumulate a clinical experience on the order of 18 million patient years. The physiochemical and mechanical properties of silicon-alloyed pyrolytic carbon, while enabling the practical utilization of mechanical heart valves, placed some severe restrictions upon design. Silicon-alloyed pyrolytic carbon is an extremely hard and nearly ideal linear elastic material with a strain to failure of approximately 1.2 percent. Traditional machining and joining techniques are not feasible, rather the carbon is prepared as a coating upon a pre-form and the coated components are then finished to size using diamond impregnated tools, grinding forms and abrasive polishing techniques. While the silicon-alloyed material was very successful, design features of known hydrodynamic advantage, such as a flared inlet, were not possible and in some valve designs annular area was sacrificed by the addition of metallic rings used to increase stiffness. As a result, mechanical valve designs in the small aortic sizes tended to be stenotic. In the early 1990’s, pyrolytic carbon coating technology was re-examined and methods of process control were redesigned in order to produce pure carbon. The resulting pure pyrolytic carbon had sufficient hardness and wear resistance, but, in addition, had higher strength and toughness with higher deformability than the silicon-alloyed material. The new material eliminated the need for the silicon and improved the carbon mechanical properties. With the improved mechanical properties, it is now possible to manufacture valve designs with greater hydrodynamic efficiency, and eliminate the need for stiffening rings, thus improving the flow behavior in the small aortic valve sizes. A mechanical valve
{"title":"Pyrolytic Carbons and the Design of Mechanical Heart Valve Prostheses","authors":"R. More","doi":"10.1115/imece2000-2672","DOIUrl":"https://doi.org/10.1115/imece2000-2672","url":null,"abstract":"\u0000 Pyrolytic carbons have a long successful history in mechanical heart valve prosthesis applications. Originally pyrolytic carbons had been developed for use in nuclear reactors. But in a chance interaction between a scientist studying nuclear energy and another searching for blood compatible materials, the blood compatibility of pyrolytic carbon was discovered. This discovery of blood compatibility prompted an effort that resulted in the development of a form of pyrolytic carbon specifically tailored for use in mechanical heart valves. This form developed by General Atomic Co. was an alloy of approximately 5 to 12 weight percent silicon codeposited with pyrolytic carbon. Fine silicon carbide particles dispersed in the carbon matrix increased the hardness and wear resistance of the pyrolytic carbon, which compensated for difficulties in manufacturing using the process control capabilities available at the time. Use of pyrolytic carbon instead of polymers in the early valve designs allowed the durability, stability and compatibility needed for true long-term implants. Since the first pyrolytic carbon heart valve component implant in 1968, more than 4 million pyrolytic carbon components in more than 25 different valve designs have been implanted to accumulate a clinical experience on the order of 18 million patient years.\u0000 The physiochemical and mechanical properties of silicon-alloyed pyrolytic carbon, while enabling the practical utilization of mechanical heart valves, placed some severe restrictions upon design. Silicon-alloyed pyrolytic carbon is an extremely hard and nearly ideal linear elastic material with a strain to failure of approximately 1.2 percent. Traditional machining and joining techniques are not feasible, rather the carbon is prepared as a coating upon a pre-form and the coated components are then finished to size using diamond impregnated tools, grinding forms and abrasive polishing techniques. While the silicon-alloyed material was very successful, design features of known hydrodynamic advantage, such as a flared inlet, were not possible and in some valve designs annular area was sacrificed by the addition of metallic rings used to increase stiffness. As a result, mechanical valve designs in the small aortic sizes tended to be stenotic.\u0000 In the early 1990’s, pyrolytic carbon coating technology was re-examined and methods of process control were redesigned in order to produce pure carbon. The resulting pure pyrolytic carbon had sufficient hardness and wear resistance, but, in addition, had higher strength and toughness with higher deformability than the silicon-alloyed material. The new material eliminated the need for the silicon and improved the carbon mechanical properties. With the improved mechanical properties, it is now possible to manufacture valve designs with greater hydrodynamic efficiency, and eliminate the need for stiffening rings, thus improving the flow behavior in the small aortic valve sizes. A mechanical valve","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":"134282006","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 development of stochastic models for representing the uncertainties present in a problem is a very important component of probabilistic reliability analysis. Stochastic modeling of engineering parameters require the determination of appropriate probability distribution functions and their associated statistical parameters. In cases that of practical interest, there are usually two or more random variables or processes involved, and hence it is further necessary to establish the correlations between the uncertain parameters or functions. The choice of stochastic models often influences the reliability values as well as the probabilistic sensitivity factors computed from analyses. This is especially so for probabilistic fracture mechanics and fatigue reliability calculations which constitute the cornerstone for durability and damage tolerance assessments. The present paper reports the development of a methodology for probabilistic fatigue data characterization. The characterization utilizes raw fatigue damage (crack initiation or crack growth) data to determine the most appropriate probability distributions, statistical parameters and confidence bounds for the modeling parameters that are involved in fatigue damage initiation and propagation relations used in durability and damage tolerance prediction. Correlations between different parameters are also computed on the basis of well established deterministic models and standards (such as the ASTM E647-93 standard) that have been widely accepted in the industry. Statistical tests are implemented on the basis of Kolmogorov-Smirnov measures of model acceptability. The probabilistic models are determined using both the method of moments (MOM) and maximum likelihood estimators (MLE) and are packaged within the framework of a user-friendly computational tool (PRADAC). Illustrative practical examples are presented to demonstrate the utility of this probabilistic pre-processing computational tool and the important effects on fatigue reliability prediction of aerospace structural components.
{"title":"Probabilistic Characterization of Fatigue Damage Data for Aerospace Materials","authors":"I. Orisamolu","doi":"10.1115/imece2000-2644","DOIUrl":"https://doi.org/10.1115/imece2000-2644","url":null,"abstract":"\u0000 The development of stochastic models for representing the uncertainties present in a problem is a very important component of probabilistic reliability analysis. Stochastic modeling of engineering parameters require the determination of appropriate probability distribution functions and their associated statistical parameters. In cases that of practical interest, there are usually two or more random variables or processes involved, and hence it is further necessary to establish the correlations between the uncertain parameters or functions. The choice of stochastic models often influences the reliability values as well as the probabilistic sensitivity factors computed from analyses. This is especially so for probabilistic fracture mechanics and fatigue reliability calculations which constitute the cornerstone for durability and damage tolerance assessments.\u0000 The present paper reports the development of a methodology for probabilistic fatigue data characterization. The characterization utilizes raw fatigue damage (crack initiation or crack growth) data to determine the most appropriate probability distributions, statistical parameters and confidence bounds for the modeling parameters that are involved in fatigue damage initiation and propagation relations used in durability and damage tolerance prediction. Correlations between different parameters are also computed on the basis of well established deterministic models and standards (such as the ASTM E647-93 standard) that have been widely accepted in the industry. Statistical tests are implemented on the basis of Kolmogorov-Smirnov measures of model acceptability. The probabilistic models are determined using both the method of moments (MOM) and maximum likelihood estimators (MLE) and are packaged within the framework of a user-friendly computational tool (PRADAC). Illustrative practical examples are presented to demonstrate the utility of this probabilistic pre-processing computational tool and the important effects on fatigue reliability prediction of aerospace structural components.","PeriodicalId":324509,"journal":{"name":"Materials: Book of Abstracts","volume":"10 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":"132808487","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 discusses the application of probabilistic design methodology for the optimum design of aircraft structures. Material properties and loads are considered as stochastic data in formulating the optimization model for the design. The procedure accommodates various types of sensitivity analyses. Attention is focused on studies in which both the aerodynamic and structural designs are optimized simultaneously. Tradeoffs between drag and structural weight for aircraft wings are affected by two aerodynamic-structural interactions. First, structural weight affects the required lift and, thus drag. Second, structural deformations change the aerodynamic shape. Design results obtained using the Monte Carlo simulation method, and the limit state function approach, are presented. The limit state function method applies the Most Probable Point (MPP) search approach. Some of the approximate methods that have been applied for the search are FORM, AMV, AIS, etc.
{"title":"Probabilistic Optimum Design of Aircraft Structures","authors":"L. Onyebueke, Ikechukwu Nnamani","doi":"10.1115/imece2000-2655","DOIUrl":"https://doi.org/10.1115/imece2000-2655","url":null,"abstract":"\u0000 This paper discusses the application of probabilistic design methodology for the optimum design of aircraft structures. Material properties and loads are considered as stochastic data in formulating the optimization model for the design. The procedure accommodates various types of sensitivity analyses. Attention is focused on studies in which both the aerodynamic and structural designs are optimized simultaneously. Tradeoffs between drag and structural weight for aircraft wings are affected by two aerodynamic-structural interactions. First, structural weight affects the required lift and, thus drag. Second, structural deformations change the aerodynamic shape.\u0000 Design results obtained using the Monte Carlo simulation method, and the limit state function approach, are presented. The limit state function method applies the Most Probable Point (MPP) search approach. Some of the approximate methods that have been applied for the search are FORM, AMV, AIS, etc.","PeriodicalId":324509,"journal":{"name":"Materials: Book of Abstracts","volume":"77 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":"114412316","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 the three step approach to computing the probability of high cycle fatigue in turbine engine components that has been implemented in the ProFES probabilistic finite element software. The first step is to develop a probabilistic Campbell Diagram for mode interaction screening. The probabilistic diagram is developed considering uncertainties in material properties, boundary conditions, geometry, and operating conditions. This approach is an improvement over the deterministic approach as the closeness of a mode to an operating frequency can be measured in a probabilistic sense and gives engineers the capability to answer questions of the type, “What is the probability that modes interact within 5Hz over the lifetime of the engine.” The second step is to perform a probabilistic dynamic analysis. This step is done for interactions that are deemed critical from the step one analysis. The actual structural response is determined and the probability of exceeding a critical level is determined. The third step applies a cumulative damage model to the stress distributions from step two to find the fatigue failure probability. This step is applied for modes that are found to be critical in the step two analysis. The complete process is automated using the ProFES probabilistic finite element software which allows pre and post processing of the FEM model to be integrated into one probabilistic analysis.
{"title":"Probabilistic High Cycle Fatigue Analysis of Turbine Engine Components","authors":"M. Cesare, R. Sues","doi":"10.1115/imece2000-2653","DOIUrl":"https://doi.org/10.1115/imece2000-2653","url":null,"abstract":"\u0000 This paper presents the three step approach to computing the probability of high cycle fatigue in turbine engine components that has been implemented in the ProFES probabilistic finite element software. The first step is to develop a probabilistic Campbell Diagram for mode interaction screening. The probabilistic diagram is developed considering uncertainties in material properties, boundary conditions, geometry, and operating conditions. This approach is an improvement over the deterministic approach as the closeness of a mode to an operating frequency can be measured in a probabilistic sense and gives engineers the capability to answer questions of the type, “What is the probability that modes interact within 5Hz over the lifetime of the engine.” The second step is to perform a probabilistic dynamic analysis. This step is done for interactions that are deemed critical from the step one analysis. The actual structural response is determined and the probability of exceeding a critical level is determined. The third step applies a cumulative damage model to the stress distributions from step two to find the fatigue failure probability. This step is applied for modes that are found to be critical in the step two analysis. The complete process is automated using the ProFES probabilistic finite element software which allows pre and post processing of the FEM model to be integrated into one probabilistic analysis.","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":"131011247","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}
In some oxide thin film systems, such thermal barrier coating systems (TBCs), thermal cycling leads to the development of geometric irregularities in the film. The evolution of these irregularities involves very large changes in aspect-ratio and often occurs rapidly over several hundreds of cycles. A key aspect of this behavior is the development of tensile stresses in the irregularity due to plastic yielding of the surrounding metal. These stresses can accelerate the elongation of the oxide (which translates into shape evolution of the irregularity) by various mechanisms, including enhanced oxide formation, inelastic stretching (creep) and failure of the oxide. An idealized analytical model consisting of a thin elastic shell embedded in an elastic-plastic matrix is used to explore the interactions between geometry, thermal strains, plasticity and oxide growth. Boundaries between purely elastic deformation, uni-directional yielding and reversed plasticity are shown to have a strong dependence on the size of the irregularity relative to the oxide thickness. For any given thermal strain, there is a critical aspect ratio of the irregularity that leads to maximum tensile stress in the oxide. The resulting closed-form solutions allow for quick and easy evaluations of various oxide-growth scenarios, including stress-dependent oxide formation. This talk will present the application of these models to TBC thermal cycling experiments, and discuss how stress-dependent oxide formation plays a role in the rapid evolution of these irregularities. A variety of oxide growth scenarios will be illustrated, and used to demonstrate that oxide failure and subsequent oxide formation in the cracked region is the most likely explanation for the rapid shape evolution seen in the experiments.
{"title":"Growth and Failure of Oxide Irregularities During Thermal Cycling: Interactions Between Stress, Geometry and Oxide Formation","authors":"M. Begley, J. M. Ambrico, E. Jordan","doi":"10.1115/imece2000-2686","DOIUrl":"https://doi.org/10.1115/imece2000-2686","url":null,"abstract":"\u0000 In some oxide thin film systems, such thermal barrier coating systems (TBCs), thermal cycling leads to the development of geometric irregularities in the film. The evolution of these irregularities involves very large changes in aspect-ratio and often occurs rapidly over several hundreds of cycles. A key aspect of this behavior is the development of tensile stresses in the irregularity due to plastic yielding of the surrounding metal. These stresses can accelerate the elongation of the oxide (which translates into shape evolution of the irregularity) by various mechanisms, including enhanced oxide formation, inelastic stretching (creep) and failure of the oxide. An idealized analytical model consisting of a thin elastic shell embedded in an elastic-plastic matrix is used to explore the interactions between geometry, thermal strains, plasticity and oxide growth. Boundaries between purely elastic deformation, uni-directional yielding and reversed plasticity are shown to have a strong dependence on the size of the irregularity relative to the oxide thickness. For any given thermal strain, there is a critical aspect ratio of the irregularity that leads to maximum tensile stress in the oxide. The resulting closed-form solutions allow for quick and easy evaluations of various oxide-growth scenarios, including stress-dependent oxide formation. This talk will present the application of these models to TBC thermal cycling experiments, and discuss how stress-dependent oxide formation plays a role in the rapid evolution of these irregularities. A variety of oxide growth scenarios will be illustrated, and used to demonstrate that oxide failure and subsequent oxide formation in the cracked region is the most likely explanation for the rapid shape evolution seen in the experiments.","PeriodicalId":324509,"journal":{"name":"Materials: Book of Abstracts","volume":"11 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":"114821714","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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