Thermomechanical fatigue and isothermal deformation experiments were conducted on cast Al 319 alloys with small secondary arm spacings (SDAS) in the range of 25 to 35 μm. The alloy was studied in the overaged state designated as T7B. In the case of the T7B treatment the material possesses dimensional stability, but incurs considerable loss of strength with time and cyclic deformation at temperatures exceeding 250°C. A two-state variable unified constitutive model was developed to characterize the stress-strain response for the material. The model handles temperature and strain rate effects and captures the microstructurally induced changes on the stress-strain response. The thermomechanical fatigue response under in-phase (TMF IP) and out-of-phase (TMF OP) conditions was simulated and the material exhibited a decrease in the stress range by as much as 50% with continued cycling. The decrease in strength was attributed to the significant coarsening of the precipitates at high temperatures and was confirmed by transmission electron microscopy.
{"title":"Thermo-mechanical Deformation of Al319 - T7B with Small Secondary Dendrite Arm Spacing","authors":"H. Sehitoglu, Tracy J. Smith, H. Maier","doi":"10.1520/STP15253S","DOIUrl":"https://doi.org/10.1520/STP15253S","url":null,"abstract":"Thermomechanical fatigue and isothermal deformation experiments were conducted on cast Al 319 alloys with small secondary arm spacings (SDAS) in the range of 25 to 35 μm. The alloy was studied in the overaged state designated as T7B. In the case of the T7B treatment the material possesses dimensional stability, but incurs considerable loss of strength with time and cyclic deformation at temperatures exceeding 250°C. A two-state variable unified constitutive model was developed to characterize the stress-strain response for the material. The model handles temperature and strain rate effects and captures the microstructurally induced changes on the stress-strain response. The thermomechanical fatigue response under in-phase (TMF IP) and out-of-phase (TMF OP) conditions was simulated and the material exhibited a decrease in the stress range by as much as 50% with continued cycling. The decrease in strength was attributed to the significant coarsening of the precipitates at high temperatures and was confirmed by transmission electron microscopy.","PeriodicalId":8583,"journal":{"name":"ASTM special technical publications","volume":"75 1","pages":"53-68"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83736275","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 significance and even the existence of crack closure is being questioned by several researchers. The objective of this study was to determine if crack closure occurs and to quantify its significance. An approach combining experimental measurement techniques with finite element analysis techniques was utilized. For two values of compact tension specimen thickness, a series of tests were conducted to determine the effect of maximum stress intensity, load ratio, constraint, and single tensile overload on the crack closure and fatigue crack growth behavior of a modified 1070 steel. Test results indicated that constraint has a significant influence on crack closure and crack growth rate behavior. Thin specimens exhibited consistently lower crack growth rates and higher crack closure levels than the thick specimens, except for tests conducted at a high load ratio, where crack closure did not occur. The thin specimens also exhibited a more significant overload effect. A new finite element modeling technique, which uses substructuring techniques to model the load cycling and crack propagation of an entire compact tension specimen, was developed. Comparison of stationary crack and propagating crack finite element models revealed that plasticity-induced crack closure produces a significant amount of crack tip shielding, which effectively reduces the strain range and mean strain experienced at the crack tip.
{"title":"A Combined Experimental and Finite Element Study of Crack Closure Effects in Modified 1070 Steel","authors":"J. D. Dougherty, T. Srivatsan, J. Padovan","doi":"10.1520/STP13406S","DOIUrl":"https://doi.org/10.1520/STP13406S","url":null,"abstract":"The significance and even the existence of crack closure is being questioned by several researchers. The objective of this study was to determine if crack closure occurs and to quantify its significance. An approach combining experimental measurement techniques with finite element analysis techniques was utilized. For two values of compact tension specimen thickness, a series of tests were conducted to determine the effect of maximum stress intensity, load ratio, constraint, and single tensile overload on the crack closure and fatigue crack growth behavior of a modified 1070 steel. Test results indicated that constraint has a significant influence on crack closure and crack growth rate behavior. Thin specimens exhibited consistently lower crack growth rates and higher crack closure levels than the thick specimens, except for tests conducted at a high load ratio, where crack closure did not occur. The thin specimens also exhibited a more significant overload effect. A new finite element modeling technique, which uses substructuring techniques to model the load cycling and crack propagation of an entire compact tension specimen, was developed. Comparison of stationary crack and propagating crack finite element models revealed that plasticity-induced crack closure produces a significant amount of crack tip shielding, which effectively reduces the strain range and mean strain experienced at the crack tip.","PeriodicalId":8583,"journal":{"name":"ASTM special technical publications","volume":"71 2 1","pages":"227-239"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80818165","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}
L. Heim, M. Tanner, A. Crane, I. Wesenbeeck, R. Velagaleti
The self-contained field lysimeter, patented by ABC Laboratories, Inc. (U.S. Patent # 5,594,185) has been used to test the mobility and dissipation of various agrochemicals in a variety of field sites and soil types. In this paper we present data to support the functionality of the pipe lysimeter design and describe some recent design modifications that have been made to improve its performance. The previous design, presented at the ASTM Eighth Symposium on Environmental Toxicology and Risk Assessment, Atlanta, Georgia, April 1998, used a steel soil core casing, which for some test substances could result in unwanted wall sorption or catalyzed degradation. The use of a stainless steel core casing, while generally considered to be inert for most test substances, can become very expensive, increasing the overall cost of the field project. For these reasons, the modular lysimeter design was modified to allow the use of PVC and other non-metallic soil core casing materials. The utilization of non-metallic soil core casing materials requires the use of a custom manufactured cutting tip and pressing ring for generation of the soil core. Other significant modifications include enhanced methods for the leachate and over-flow module attachment to the soil column, and the instrumentation used for the leachate collection void at the base of the soil column. Development of the monolith lysimeter design to include non-metallic soil core casings provides a comprehensive method for use of all potential core casing materials in the generation of intact, undisturbed soil columns. Benefits of the PVC lysimeter modification include minimal compaction during soil-core generation, chemically inert casing materials for some test substances, and reduced materials costs. In addition, the instrumentation scheme used for the PVC lysimeter allows for more pre-fabrication prior to field deployment, and minimal labor requirements in the field for instrumentation and installation, significantly reducing the overall cost of field lysimeter projects.
{"title":"Advancements in pipe monolith lysimeter designs","authors":"L. Heim, M. Tanner, A. Crane, I. Wesenbeeck, R. Velagaleti","doi":"10.1520/STP14411S","DOIUrl":"https://doi.org/10.1520/STP14411S","url":null,"abstract":"The self-contained field lysimeter, patented by ABC Laboratories, Inc. (U.S. Patent # 5,594,185) has been used to test the mobility and dissipation of various agrochemicals in a variety of field sites and soil types. In this paper we present data to support the functionality of the pipe lysimeter design and describe some recent design modifications that have been made to improve its performance. The previous design, presented at the ASTM Eighth Symposium on Environmental Toxicology and Risk Assessment, Atlanta, Georgia, April 1998, used a steel soil core casing, which for some test substances could result in unwanted wall sorption or catalyzed degradation. The use of a stainless steel core casing, while generally considered to be inert for most test substances, can become very expensive, increasing the overall cost of the field project. For these reasons, the modular lysimeter design was modified to allow the use of PVC and other non-metallic soil core casing materials. The utilization of non-metallic soil core casing materials requires the use of a custom manufactured cutting tip and pressing ring for generation of the soil core. Other significant modifications include enhanced methods for the leachate and over-flow module attachment to the soil column, and the instrumentation used for the leachate collection void at the base of the soil column. Development of the monolith lysimeter design to include non-metallic soil core casings provides a comprehensive method for use of all potential core casing materials in the generation of intact, undisturbed soil columns. Benefits of the PVC lysimeter modification include minimal compaction during soil-core generation, chemically inert casing materials for some test substances, and reduced materials costs. In addition, the instrumentation scheme used for the PVC lysimeter allows for more pre-fabrication prior to field deployment, and minimal labor requirements in the field for instrumentation and installation, significantly reducing the overall cost of field lysimeter projects.","PeriodicalId":8583,"journal":{"name":"ASTM special technical publications","volume":"29 1","pages":"3-15"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86560230","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}
{"title":"History of timber construction","authors":"G. Foliente","doi":"10.1520/STP13370S","DOIUrl":"https://doi.org/10.1520/STP13370S","url":null,"abstract":"","PeriodicalId":8583,"journal":{"name":"ASTM special technical publications","volume":"27 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83623306","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 nonlinear and dynamic behavior of unidirectional composites with fiber waviness under compressive loading was investigated theoretically and experimentally. Unidirectional carbonlepoxy composites with uniform fiber waviness were studied. Complementary strain energy was used to derive the material nonlinear stress-strain relations for the quasi-static case. Nonlinear material properties obtained from shear and longitudinal and transverse compression tests were incorporated into the analysis. An incremental analysis was used to predict the static and dynamic behavior of wavy composites using the basic strain rate characterization data. It is shown that under uniaxial compressive loading, strong nonlinearities occur in the stress-strain curves due to fiber waviness with significant stiffening as the strain rate increases. Stress-strain curves are affected less by fiber waviness under other loading conditions. The major Young's modulus degrades seriously as the fiber waviness increases. It increases moderately as the strain rate increases for the same degree of waviness. Unidirectional composites with uniform waviness across the thickness were prepared by a tape winding method. Compression tests of specimens with known fiber waviness were conducted. Experimental results were in good agreement with predictions based on the complementary strain energy approach and incremental analysis.
{"title":"Nonlinear and Dynamic Compressive Behavior of Composites with Fiber Waviness","authors":"H. Hsiao, I. Daniel","doi":"10.1520/STP15836S","DOIUrl":"https://doi.org/10.1520/STP15836S","url":null,"abstract":"The nonlinear and dynamic behavior of unidirectional composites with fiber waviness under compressive loading was investigated theoretically and experimentally. Unidirectional carbonlepoxy composites with uniform fiber waviness were studied. Complementary strain energy was used to derive the material nonlinear stress-strain relations for the quasi-static case. Nonlinear material properties obtained from shear and longitudinal and transverse compression tests were incorporated into the analysis. An incremental analysis was used to predict the static and dynamic behavior of wavy composites using the basic strain rate characterization data. It is shown that under uniaxial compressive loading, strong nonlinearities occur in the stress-strain curves due to fiber waviness with significant stiffening as the strain rate increases. Stress-strain curves are affected less by fiber waviness under other loading conditions. The major Young's modulus degrades seriously as the fiber waviness increases. It increases moderately as the strain rate increases for the same degree of waviness. Unidirectional composites with uniform waviness across the thickness were prepared by a tape winding method. Compression tests of specimens with known fiber waviness were conducted. Experimental results were in good agreement with predictions based on the complementary strain energy approach and incremental analysis.","PeriodicalId":8583,"journal":{"name":"ASTM special technical publications","volume":"2013 1","pages":"223-237"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86454811","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 is written to honor Dr. George R. Irwin and reviews several key developments in fracture mechanics based on his "stress-intensity factor" concept. The early development of two fundamental crack solutions, (1) an edge crack in a semi-infinite body and (2) the surface crack, are highlighted. Applications of Irwin's early concepts by other researchers to characterize fatigue-crack growth and brittle fracture of metallic materials are presented. The stress-intensity factor is the cornerstone of the damage-tolerance and durability design concepts used by the aerospace community around the world. The stress-intensity factor concept, crack-closure mechanics, and the observation that "fatigue is crack propagation" in many engineering materials has led to a merger of fatigue and fracture mechanics analysis methodologies. Irwin's recognition of the importance of the normal stress parallel to the crack (now referred to as the T-stress) in fracture led many to propose a two-parameter characterization for fracture. The importance of constraint on crack-tip yielding has been further advanced by the use of high-powered computers to calculate a normal-stress constraint parameter following his ideas. The father of fracture mechanics has left a legacy that will endure and provide safer and more reliable structures in the future.
本文是为了纪念George R. Irwin博士而写的，并基于他的“应力强度因子”概念回顾了断裂力学的几个关键发展。重点介绍了两种基本裂纹解的早期发展，即(1)半无限物体的边缘裂纹和(2)表面裂纹。其他研究人员将欧文的早期概念应用于表征金属材料的疲劳裂纹扩展和脆性断裂。应力强度因子是世界各地航空航天界使用的损伤容限和耐久性设计概念的基石。在许多工程材料中，应力强度因子概念、裂纹闭合力学以及“疲劳即裂纹扩展”的观察导致了疲劳力学和断裂力学分析方法的合并。欧文认识到与裂缝平行的法向应力(现在称为t应力)在断裂中的重要性，这使许多人提出了断裂的双参数表征。根据他的思想，利用高性能计算机计算法向应力约束参数，进一步提高了约束对裂纹尖端屈服的重要性。这位断裂力学之父留下的宝贵遗产将在未来提供更安全、更可靠的结构。
{"title":"Irwin's Stress Intensity Factor—A Historical Perspective","authors":"J. Newman","doi":"10.1520/STP14792S","DOIUrl":"https://doi.org/10.1520/STP14792S","url":null,"abstract":"This paper is written to honor Dr. George R. Irwin and reviews several key developments in fracture mechanics based on his \"stress-intensity factor\" concept. The early development of two fundamental crack solutions, (1) an edge crack in a semi-infinite body and (2) the surface crack, are highlighted. Applications of Irwin's early concepts by other researchers to characterize fatigue-crack growth and brittle fracture of metallic materials are presented. The stress-intensity factor is the cornerstone of the damage-tolerance and durability design concepts used by the aerospace community around the world. The stress-intensity factor concept, crack-closure mechanics, and the observation that \"fatigue is crack propagation\" in many engineering materials has led to a merger of fatigue and fracture mechanics analysis methodologies. Irwin's recognition of the importance of the normal stress parallel to the crack (now referred to as the T-stress) in fracture led many to propose a two-parameter characterization for fracture. The importance of constraint on crack-tip yielding has been further advanced by the use of high-powered computers to calculate a normal-stress constraint parameter following his ideas. The father of fracture mechanics has left a legacy that will endure and provide safer and more reliable structures in the future.","PeriodicalId":8583,"journal":{"name":"ASTM special technical publications","volume":"41 1","pages":"39-53"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77288760","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}
Thick thermal barrier coatings (TTBCs) for diesel engine applications are being developed to improve engine performance through increased operating temperatures and lower emissions. To more completely assess the bulk properties of coating materials, a miniature test stand for the mechanical testing of coating materials independent of the substrate was developed. Using a piezoelectric translator as an actuator and a miniature load cell, it was possible to conduct uniaxial testing in both compression and tension of very small samples. In this study, room temperature deformation experiments were conducted on an air plasma-sprayed 24% CeO 2 -ZrO 2 coating material. Mechanical properties in both the in-plane and transverse coating directions were evaluated in both compression and tension. From simple monotonic tests, the anisotropy of the material could be quantified. A key finding was that both the loading modulus and tensile strength were about two to three times higher in the in-plane direction. This anisotropy is believed to be due to the directionality of microcracking in the material. Cyclic loading experiments showed that the coating material also exhibits considerable irreversible strain behavior in both the transverse and in-plane directions. A model describing the irreversible strain behavior based on the combined sliding and closing of pre-existing microcracks is proposed and compared with experimental results. It is shown that the model describes the qualitative and quantitative aspects of the material behavior quite well, especially in compression.
{"title":"Bulk Property Evaluation of a Thick Thermal Barrier Coating","authors":"E. Rejda, D. Socie, Brian P. Nuel","doi":"10.1520/STP14799S","DOIUrl":"https://doi.org/10.1520/STP14799S","url":null,"abstract":"Thick thermal barrier coatings (TTBCs) for diesel engine applications are being developed to improve engine performance through increased operating temperatures and lower emissions. To more completely assess the bulk properties of coating materials, a miniature test stand for the mechanical testing of coating materials independent of the substrate was developed. Using a piezoelectric translator as an actuator and a miniature load cell, it was possible to conduct uniaxial testing in both compression and tension of very small samples. In this study, room temperature deformation experiments were conducted on an air plasma-sprayed 24% CeO 2 -ZrO 2 coating material. Mechanical properties in both the in-plane and transverse coating directions were evaluated in both compression and tension. From simple monotonic tests, the anisotropy of the material could be quantified. A key finding was that both the loading modulus and tensile strength were about two to three times higher in the in-plane direction. This anisotropy is believed to be due to the directionality of microcracking in the material. Cyclic loading experiments showed that the coating material also exhibits considerable irreversible strain behavior in both the transverse and in-plane directions. A model describing the irreversible strain behavior based on the combined sliding and closing of pre-existing microcracks is proposed and compared with experimental results. It is shown that the model describes the qualitative and quantitative aspects of the material behavior quite well, especially in compression.","PeriodicalId":8583,"journal":{"name":"ASTM special technical publications","volume":"110 1","pages":"143-161"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87714426","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 high-temperature titanium alloy IMI 834 was studied with regard to the stress-strain response under thermo-mechanical fatigue conditions, the evolution of the microstructure, the relevant damage mechanisms and their implications for fatigue life. For this purpose isothermal and thermo-mechanical fatigue tests were performed in the temperature range from 350°C to 650°C in vacuum and air, respectively, and changes in the microstructure were determined by means of transmission electron microscopy. It was found that planar dislocation slip prevails in all tests in which the temperature does not exceed 600°C. Hence, in this temperature range the stress-strain response under thermo-mechanical conditions can be predicted solely based on the isothermal behavior. By contrast, a transition to wavy slip takes place at higher temperatures, affecting significantly the stresses in the low-temperature part of the corresponding thermo-mechanical fatigue tests. Fatigue life was generally observed to be lower in out-of-phase tests as compared to in-phase loading. Furthermore, the tests performed in high vacuum demonstrated that oxidation strongly affects fatigue life, but does not basically change the influence of testing mode on cyclic life. This can mainly be attributed to the additional effect of the acting mean stress.
{"title":"Behavior of the High-Temperaturse Titanium Alloy IMI 834 Under Thermo-mechanical and Isothermal Fatigue Conditions","authors":"P. Pototzky, H. Maier, H. Christ","doi":"10.1520/STP15251S","DOIUrl":"https://doi.org/10.1520/STP15251S","url":null,"abstract":"The high-temperature titanium alloy IMI 834 was studied with regard to the stress-strain response under thermo-mechanical fatigue conditions, the evolution of the microstructure, the relevant damage mechanisms and their implications for fatigue life. For this purpose isothermal and thermo-mechanical fatigue tests were performed in the temperature range from 350°C to 650°C in vacuum and air, respectively, and changes in the microstructure were determined by means of transmission electron microscopy. It was found that planar dislocation slip prevails in all tests in which the temperature does not exceed 600°C. Hence, in this temperature range the stress-strain response under thermo-mechanical conditions can be predicted solely based on the isothermal behavior. By contrast, a transition to wavy slip takes place at higher temperatures, affecting significantly the stresses in the low-temperature part of the corresponding thermo-mechanical fatigue tests. Fatigue life was generally observed to be lower in out-of-phase tests as compared to in-phase loading. Furthermore, the tests performed in high vacuum demonstrated that oxidation strongly affects fatigue life, but does not basically change the influence of testing mode on cyclic life. This can mainly be attributed to the additional effect of the acting mean stress.","PeriodicalId":8583,"journal":{"name":"ASTM special technical publications","volume":"65 1","pages":"18-35"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73071576","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}
Constant ramp strength tests on unidirectional thermoplastic composite specimens oriented in the 90 deg. direction were conducted at constant temperatures ranging from 149 C to 232 C. Ramp rates spanning 5 orders of magnitude were tested so that failures occurred in the range from 0.5 sec. to 24 hrs. (0.5 to 100,000 MPa/sec). Below 204 C, time-temperature superposition held allowing strength at longer times to be estimated from strength tests at shorter times but higher temperatures. The data indicated that a 50% drop in strength might be expected for this material when the test time is increased by 9 orders of magnitude. The shift factors derived from compliance data applied well to the strength results. To explain the link between compliance and strength, a viscoelastic fracture model was investigated. The model, which used compliance as input, was found to fit the strength data only if the critical fracture energy was allowed to vary with temperature reduced stress rate. This variation in the critical parameter severely limits its use in developing a robust time-dependent strength model. The significance of this research is therefore seen as providing both the indication that a more versatile acceleration method for strength can be developed and the evidence that such a method is needed.
{"title":"Accelerated Strength Testing of Thermoplastic Composites","authors":"J. Reeder, D. Allen, W. Bradley","doi":"10.1520/STP15841S","DOIUrl":"https://doi.org/10.1520/STP15841S","url":null,"abstract":"Constant ramp strength tests on unidirectional thermoplastic composite specimens oriented in the 90 deg. direction were conducted at constant temperatures ranging from 149 C to 232 C. Ramp rates spanning 5 orders of magnitude were tested so that failures occurred in the range from 0.5 sec. to 24 hrs. (0.5 to 100,000 MPa/sec). Below 204 C, time-temperature superposition held allowing strength at longer times to be estimated from strength tests at shorter times but higher temperatures. The data indicated that a 50% drop in strength might be expected for this material when the test time is increased by 9 orders of magnitude. The shift factors derived from compliance data applied well to the strength results. To explain the link between compliance and strength, a viscoelastic fracture model was investigated. The model, which used compliance as input, was found to fit the strength data only if the critical fracture energy was allowed to vary with temperature reduced stress rate. This variation in the critical parameter severely limits its use in developing a robust time-dependent strength model. The significance of this research is therefore seen as providing both the indication that a more versatile acceleration method for strength can be developed and the evidence that such a method is needed.","PeriodicalId":8583,"journal":{"name":"ASTM special technical publications","volume":"10 1","pages":"318-337"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75136824","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 proposed thermo-mechanical fatigue test rig is based on a rotating bending machine and employs a high and a low temperature sources. This permits imposing thermal and mechanical loading at relatively high frequencies on a portion of a surface generatrix of a tubular specimen. Using this rig, a series of experiments was carried out on superalloy test specimens. These tests were conducted at various mechanical loadings with the temperature cycling between 600 and 1050°C in 10 seconds. The temperature distribution on the test specimen was measured under stabilized conditions and the same was calculated using a finite element code. Good correlation was found between the experimental and simulated temperature distributions. The thermal stress field, hence calculated, enables us to identify the critical crack initiation sites of the specimen and to calculate the applied thermo-mechanical cycle. In this way, an equivalent constant temperature can be defined and fatigue life has been predicted using isothermal fatigue results only.
{"title":"A New Technique for High Frequency Multiaxial Thermo-mechanical Fatigue Testing of Materials","authors":"R. Chieragatti, Florin Calin Paun","doi":"10.1520/STP15269S","DOIUrl":"https://doi.org/10.1520/STP15269S","url":null,"abstract":"The proposed thermo-mechanical fatigue test rig is based on a rotating bending machine and employs a high and a low temperature sources. This permits imposing thermal and mechanical loading at relatively high frequencies on a portion of a surface generatrix of a tubular specimen. Using this rig, a series of experiments was carried out on superalloy test specimens. These tests were conducted at various mechanical loadings with the temperature cycling between 600 and 1050°C in 10 seconds. The temperature distribution on the test specimen was measured under stabilized conditions and the same was calculated using a finite element code. Good correlation was found between the experimental and simulated temperature distributions. The thermal stress field, hence calculated, enables us to identify the critical crack initiation sites of the specimen and to calculate the applied thermo-mechanical cycle. In this way, an equivalent constant temperature can be defined and fatigue life has been predicted using isothermal fatigue results only.","PeriodicalId":8583,"journal":{"name":"ASTM special technical publications","volume":"253 1","pages":"319-332"},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75054635","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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