Barenblatt's idea of modeling the crack process zone by means of a cohesive zone has attracted considerable attention for predicting ductile crack growth. The model allows separation of the energy necessary for material separation from global plastic work. This has been a key problem in ductile fracture when searching for reasons for the geometry dependence of crack growth resistance curves. When using cohesive zone models, the correct determination of the cohesive zone material parameters is of eminent importance. In the past these parameters-the cohesive strength and the separation energy-were assumed to be material constants. However, micromechanical considerations show that this assumption is only an approximation in the case of ductile fracture. Here, the underlying mechanisms of void nucleation, growth, and coalescence are dependent on the stress triaxiality. This effect is accounted for in the new constitutive equation for cohesive zone models as presented here. In this new "triaxiality-dependent cohesive zone model," the cohesive material properties are taken to be dependent on the stress triaxiality in the solid element adjacent to the cohesive element. For low triaxiality, low values of cohesive strength and large values of the separation energy are observed; the opposite holds true for cases of high triaxiality. Ductile crack growth in a mild steel under quasistatic loading was investigated. The results from the use of the triaxiality-dependent cohesive zone model are compared to those of the Gurson-Tvergaard-Needleman (GTN) model as well as to the cohesive zone model with constant material parameters. The dissipation rate is shown to be a favorable measure for the characterization of the crack growth resistance. It allows the description of both the (global) plastic dissipation and the (local) work of fracture.
{"title":"The Role of Cohesive Strength and Separation Energy for Modeling of Ductile Fracture","authors":"T. Siegmund, W. Brocks","doi":"10.1520/STP13400S","DOIUrl":"https://doi.org/10.1520/STP13400S","url":null,"abstract":"Barenblatt's idea of modeling the crack process zone by means of a cohesive zone has attracted considerable attention for predicting ductile crack growth. The model allows separation of the energy necessary for material separation from global plastic work. This has been a key problem in ductile fracture when searching for reasons for the geometry dependence of crack growth resistance curves. When using cohesive zone models, the correct determination of the cohesive zone material parameters is of eminent importance. In the past these parameters-the cohesive strength and the separation energy-were assumed to be material constants. However, micromechanical considerations show that this assumption is only an approximation in the case of ductile fracture. Here, the underlying mechanisms of void nucleation, growth, and coalescence are dependent on the stress triaxiality. This effect is accounted for in the new constitutive equation for cohesive zone models as presented here. In this new \"triaxiality-dependent cohesive zone model,\" the cohesive material properties are taken to be dependent on the stress triaxiality in the solid element adjacent to the cohesive element. For low triaxiality, low values of cohesive strength and large values of the separation energy are observed; the opposite holds true for cases of high triaxiality. Ductile crack growth in a mild steel under quasistatic loading was investigated. The results from the use of the triaxiality-dependent cohesive zone model are compared to those of the Gurson-Tvergaard-Needleman (GTN) model as well as to the cohesive zone model with constant material parameters. The dissipation rate is shown to be a favorable measure for the characterization of the crack growth resistance. It allows the description of both the (global) plastic dissipation and the (local) work of fracture.","PeriodicalId":8583,"journal":{"name":"ASTM special technical publications","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90601895","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}
Elastic-plastic fracture mechanics (EPFM) is the name given to a body of fracture technology that includes parameters, test methods, and analysis techniques. EPFM began in the 1960s, soon after it was recognized that the linear elastic approach to fracture mechanics was too limited to cover many engineering applications. It began in response to real engineering problems and continues to develop in the same application-driven mode. The development of EPFM spans more than three decades. It involved many people and a multitude of good ideas. Some of the people have gone on to other pursuits, and many of the ideas have been set aside or discarded in the never-ending debate about which is the best approach. The development of EPFM is not complete, nor is the controversy ended. It is important to look back at the factors that influenced such a vast development of technology before trying to forge ahead. This paper takes a look at the area of fracture mechanics called EPFM. It considers the development of a technology that involved people, places, and a seemingly inexhaustible supply of technical ideas. It considers what happened in the past, what is going on in the present, and speculates about what will happen for the future. Its purpose is to stop for a moment and consider for EPFM: Where has it been? Where is it going?
{"title":"Elastic-plastic fracture mechanics: Where has it been? Where is it going?","authors":"J. Landes","doi":"10.1520/STP13391S","DOIUrl":"https://doi.org/10.1520/STP13391S","url":null,"abstract":"Elastic-plastic fracture mechanics (EPFM) is the name given to a body of fracture technology that includes parameters, test methods, and analysis techniques. EPFM began in the 1960s, soon after it was recognized that the linear elastic approach to fracture mechanics was too limited to cover many engineering applications. It began in response to real engineering problems and continues to develop in the same application-driven mode. The development of EPFM spans more than three decades. It involved many people and a multitude of good ideas. Some of the people have gone on to other pursuits, and many of the ideas have been set aside or discarded in the never-ending debate about which is the best approach. The development of EPFM is not complete, nor is the controversy ended. It is important to look back at the factors that influenced such a vast development of technology before trying to forge ahead. This paper takes a look at the area of fracture mechanics called EPFM. It considers the development of a technology that involved people, places, and a seemingly inexhaustible supply of technical ideas. It considers what happened in the past, what is going on in the present, and speculates about what will happen for the future. Its purpose is to stop for a moment and consider for EPFM: Where has it been? Where is it going?","PeriodicalId":8583,"journal":{"name":"ASTM special technical publications","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90777807","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}
An overstress viscoplasticity model is proposed to describe the rate-dependent behavior of a polymeric composite during loading and unloading. In the model, a three-parameter function is used to describe viscoplastic strain rate. In the loading stage, the equilibrium stress is determined using a multi-step relaxation test performed during loading. During the initial unloading stage, owing to the fact that the viscoplastic strain rate is still positive, the material still experiences "loading," and the corresponding equilibrium stress is the equilibrium stress-strain curve for loading. In the second unloading stage, the viscoplastic strain rate becomes negative, and the material is in a true unloading mode for which the equilibrium stress is determined again using the multi-step "relaxation" test. The viscoplasticity model is found to be capable of capturing the characteristics of the rate-dependent loading and unloading behavior.
{"title":"A Viscoplasticity Model for Characterizing Loading and Unloading Behavior of Polymeric Composites","authors":"Chang-ming Zhu, C. Sun","doi":"10.1520/STP15838S","DOIUrl":"https://doi.org/10.1520/STP15838S","url":null,"abstract":"An overstress viscoplasticity model is proposed to describe the rate-dependent behavior of a polymeric composite during loading and unloading. In the model, a three-parameter function is used to describe viscoplastic strain rate. In the loading stage, the equilibrium stress is determined using a multi-step relaxation test performed during loading. During the initial unloading stage, owing to the fact that the viscoplastic strain rate is still positive, the material still experiences \"loading,\" and the corresponding equilibrium stress is the equilibrium stress-strain curve for loading. In the second unloading stage, the viscoplastic strain rate becomes negative, and the material is in a true unloading mode for which the equilibrium stress is determined again using the multi-step \"relaxation\" test. The viscoplasticity model is found to be capable of capturing the characteristics of the rate-dependent loading and unloading behavior.","PeriodicalId":8583,"journal":{"name":"ASTM special technical publications","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83983992","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 Washington State Department of Ecology (Ecology) is revising the Model Toxics Control Act (MTCA: WAC 173-340-7490 to 7494) to include terrestrial food pathways in an ecological risk evaluation and to set cleanup levels. One of the key provisions of the ecological risk assessment approach proposed by Ecology is a generic simplified "foodweb" model that would be used to set cleanup levels. The terrestrial model is based on four feeding guilds and default species are the earthworm, shrew, vole, and robin. The use of a foodweb model implies that the results should in some way be descriptive of the ecosystem being evaluated. Any decision criterion (e.g., a benchmark or cleanup level) should be site-specific, and based on species present at the site. The default species are not representative of the fauna in the native shrub-steppe ecosystem of the Hanford Site. Therefore, the use of species not present at the site to set soil cleanup levels seems flawed. Alternative species for the four feeding guilds have been selected. Species specific exposure parameters were developed from the literature.
{"title":"Evaluation of a Terrestrial Foodweb Model to Set Soil Cleanup Levels","authors":"P. Doctor, K. A. Gano, N. K. Lane","doi":"10.1520/STP14416S","DOIUrl":"https://doi.org/10.1520/STP14416S","url":null,"abstract":"The Washington State Department of Ecology (Ecology) is revising the Model Toxics Control Act (MTCA: WAC 173-340-7490 to 7494) to include terrestrial food pathways in an ecological risk evaluation and to set cleanup levels. One of the key provisions of the ecological risk assessment approach proposed by Ecology is a generic simplified \"foodweb\" model that would be used to set cleanup levels. The terrestrial model is based on four feeding guilds and default species are the earthworm, shrew, vole, and robin. The use of a foodweb model implies that the results should in some way be descriptive of the ecosystem being evaluated. Any decision criterion (e.g., a benchmark or cleanup level) should be site-specific, and based on species present at the site. The default species are not representative of the fauna in the native shrub-steppe ecosystem of the Hanford Site. Therefore, the use of species not present at the site to set soil cleanup levels seems flawed. Alternative species for the four feeding guilds have been selected. Species specific exposure parameters were developed from the literature.","PeriodicalId":8583,"journal":{"name":"ASTM special technical publications","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85562778","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":null,"pages":null},"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}
The cumulative fatigue behavior of a cobalt-base superalloy, Haynes 188, was investigated at 760°C in air. Initially, strain-controlled tests were conducted on solid cylindrical gage section specimens of Haynes 188 under fully reversed, tensile and compressive mean strain-controlled fatigue tests. Fatigue data from these tests were used to establish the baseline fatigue behavior of the alloy with (1) a total strain range type fatigue life relation and (2) the Smith-Watson-Topper (SWT) parameter. Subsequently, two load-level multi-block fatigue tests were conducted on similar specimens of Haynes 188 at the same temperature. Fatigue lives of the multi-block tests were estimated with (1) the linear damage rule (LDR) and (2) the nonlinear damage curve approach (DCA) both with and without the consideration of mean stresses generated during the cumulative fatigue tests. Fatigue life predictions by the nonlinear DCA were much closer to the experimentally observed lives than those obtained by the LDR. In the presence of mean stresses, the SWT parameter estimated the fatigue lives more accurately under tensile conditions than under compressive conditions.
{"title":"Fatigue life estimation under cumulative cyclic loading conditions","authors":"S. Kalluri, M. Mcgaw, G. Halford","doi":"10.1520/STP14796S","DOIUrl":"https://doi.org/10.1520/STP14796S","url":null,"abstract":"The cumulative fatigue behavior of a cobalt-base superalloy, Haynes 188, was investigated at 760°C in air. Initially, strain-controlled tests were conducted on solid cylindrical gage section specimens of Haynes 188 under fully reversed, tensile and compressive mean strain-controlled fatigue tests. Fatigue data from these tests were used to establish the baseline fatigue behavior of the alloy with (1) a total strain range type fatigue life relation and (2) the Smith-Watson-Topper (SWT) parameter. Subsequently, two load-level multi-block fatigue tests were conducted on similar specimens of Haynes 188 at the same temperature. Fatigue lives of the multi-block tests were estimated with (1) the linear damage rule (LDR) and (2) the nonlinear damage curve approach (DCA) both with and without the consideration of mean stresses generated during the cumulative fatigue tests. Fatigue life predictions by the nonlinear DCA were much closer to the experimentally observed lives than those obtained by the LDR. In the presence of mean stresses, the SWT parameter estimated the fatigue lives more accurately under tensile conditions than under compressive conditions.","PeriodicalId":8583,"journal":{"name":"ASTM special technical publications","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89493916","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 broadly reviews the stress-based, strain-based, and crack growth approaches to fatigue life prediction, and it attempts to suggest some choices and variations of these that might enhance their inclusion in undergraduate education and their more routine use by practicing engineers. For the stress-based approach, emphasis should shift toward the use of data on actual components, and it should be recognized that damage below the usual fatigue limit may occur. Also, evaluation of mean stress effects by the modified Goodman diagram should be replaced by other methods. The usefulness of the strain-based approach for simple situations may be extended by adding empirical adjustments for surface finish and size. It may also be desirable to lower the long-life end of the strain-life curve to obtain agreement with limited component test data, producing a component-specific strain-life curve. Use of the crack growth approach is hampered by the lack of a widely accepted set of materials constants for describing da/dN versus ΔK curves. It is recommended that this situation be remedied by representing the intermediate growth rate region with a Paris-type exponent, an associated coefficient, and a third constant that characterizes the sensitivity to R-ratio according to the equation of Walker. Limits or asymptotic behavior for the low and high growth rate regions should then be handled separately.
{"title":"An overview and discussion of basic methodology for fatigue","authors":"N. Dowling, S. Thangjitham","doi":"10.1520/STP14791S","DOIUrl":"https://doi.org/10.1520/STP14791S","url":null,"abstract":"This paper broadly reviews the stress-based, strain-based, and crack growth approaches to fatigue life prediction, and it attempts to suggest some choices and variations of these that might enhance their inclusion in undergraduate education and their more routine use by practicing engineers. For the stress-based approach, emphasis should shift toward the use of data on actual components, and it should be recognized that damage below the usual fatigue limit may occur. Also, evaluation of mean stress effects by the modified Goodman diagram should be replaced by other methods. The usefulness of the strain-based approach for simple situations may be extended by adding empirical adjustments for surface finish and size. It may also be desirable to lower the long-life end of the strain-life curve to obtain agreement with limited component test data, producing a component-specific strain-life curve. Use of the crack growth approach is hampered by the lack of a widely accepted set of materials constants for describing da/dN versus ΔK curves. It is recommended that this situation be remedied by representing the intermediate growth rate region with a Paris-type exponent, an associated coefficient, and a third constant that characterizes the sensitivity to R-ratio according to the equation of Walker. Limits or asymptotic behavior for the low and high growth rate regions should then be handled separately.","PeriodicalId":8583,"journal":{"name":"ASTM special technical publications","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83349510","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 main elements of implementation into a finite-element analysis (FEA) package of the earlier developed model for nonlinear viscoelastic behavior of plastics are described. The Henriksen scheme of discretization of the hereditary integral has been chosen for implementation. This scheme enables development of a fast procedure for modeling of viscoelastic behavior. As a result, the time necessary for calculation of problems of viscoelasticity is not much larger than the calculation time required for simulation of elasto-plastic behavior. Several discretization schemes have been analyzed, implemented in FEA software MARC and verified. The numerical algorithm, which is chosen as a result of comparison, allows us to reach a total deviation of less than 8% to 10% for the modeling of creep and recovery of PMMA and HDPE for the broad range of loading levels. The case study of a thick plate under distributed transversal loading is examined to compare the results achieved using the Schapery model with the newly proposed approach.
{"title":"Implementation of Constitutive Model in FEA for Nonlinear Behavior of Plastics","authors":"I. Skrypnyk, J. Spoormaker, W. Smit","doi":"10.1520/STP15830S","DOIUrl":"https://doi.org/10.1520/STP15830S","url":null,"abstract":"The main elements of implementation into a finite-element analysis (FEA) package of the earlier developed model for nonlinear viscoelastic behavior of plastics are described. The Henriksen scheme of discretization of the hereditary integral has been chosen for implementation. This scheme enables development of a fast procedure for modeling of viscoelastic behavior. As a result, the time necessary for calculation of problems of viscoelasticity is not much larger than the calculation time required for simulation of elasto-plastic behavior. Several discretization schemes have been analyzed, implemented in FEA software MARC and verified. The numerical algorithm, which is chosen as a result of comparison, allows us to reach a total deviation of less than 8% to 10% for the modeling of creep and recovery of PMMA and HDPE for the broad range of loading levels. The case study of a thick plate under distributed transversal loading is examined to compare the results achieved using the Schapery model with the newly proposed approach.","PeriodicalId":8583,"journal":{"name":"ASTM special technical publications","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78663578","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}
Estimation of closure-corrected fatigue crack propagation (FCP) data in monolithic metal alloys was reported recently by the author, using a simple computational method. The quantity E√b, where E = the modulus of elasticity, and b, the dislocation Burgers vector, is used to define a stress intensity factor, corresponding to an FCP rate of b/cyc. The remainder of the FCP curve at higher FCP rates (where daldN > b) is found to follow a relation of the form: da/dN = (ΔK/E) 3 (1/√b). Good agreement is found between computed FCP data and recently reported experimental test results for various aluminum, titanium, and steel alloys. Such computations allow for a rapid and inexpensive way to estimate the FCP response of metals under both long and short crack growth conditions.
{"title":"Estimation Procedure for Determination of Fatigue Crack Propagation in Metal Alloys","authors":"R. Hertzberg","doi":"10.1520/STP13408S","DOIUrl":"https://doi.org/10.1520/STP13408S","url":null,"abstract":"Estimation of closure-corrected fatigue crack propagation (FCP) data in monolithic metal alloys was reported recently by the author, using a simple computational method. The quantity E√b, where E = the modulus of elasticity, and b, the dislocation Burgers vector, is used to define a stress intensity factor, corresponding to an FCP rate of b/cyc. The remainder of the FCP curve at higher FCP rates (where daldN > b) is found to follow a relation of the form: da/dN = (ΔK/E) 3 (1/√b). Good agreement is found between computed FCP data and recently reported experimental test results for various aluminum, titanium, and steel alloys. Such computations allow for a rapid and inexpensive way to estimate the FCP response of metals under both long and short crack growth conditions.","PeriodicalId":8583,"journal":{"name":"ASTM special technical publications","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2000-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77793239","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":null,"pages":null},"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}
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