Zhongman Ding, Shoujie Li, L. J. Lee, Herbert Engelen
Resin Injection Pultrusion (RIP) is a new composite manufacturing process, which combines the advantages of the conventional pultrusion process and the Resin Transfer Molding (RTM) process. It is sometimes referred to the Continuous Resin Transfer Molding (C-RTM) process. The RIP process differs from the conventional pultrusion process in that the resin is injected into an injection-die (instead of being placed in an open bath) in order to eliminate the emission of volatile organic compounds (styrene) (VOC) during processing. Based on the modeling and simulation of resin/fiber “pultrudability”, resin flow, and heat transfer and curing, a computer aided engineering tool has been developed for the purpose of process design. In this study, the fiber stack permeability and compressibility are measured and modeled, and the resin impregnation pattern and pressure distribution inside the fiber stack are obtained using numerical simulation. Conversion profiles in die heating section of the pultrusion die can also be obtained using the simulation tool. The correlation between the degree-of-cure profiles and the occurrence of blisters in the pultruded composite parts is discussed. Pulling force modeling and analysis are carried out to identify the effect on composite quality due to interface friction between the die surface and the moving resin/fiber mixture. Experimental data are used to verify the modeling and simulation results.
{"title":"Using Computer Simulation as a Process Design Tool for Resin Injection Pultrusion (RIP)","authors":"Zhongman Ding, Shoujie Li, L. J. Lee, Herbert Engelen","doi":"10.1115/imece2000-1236","DOIUrl":"https://doi.org/10.1115/imece2000-1236","url":null,"abstract":"\u0000 Resin Injection Pultrusion (RIP) is a new composite manufacturing process, which combines the advantages of the conventional pultrusion process and the Resin Transfer Molding (RTM) process. It is sometimes referred to the Continuous Resin Transfer Molding (C-RTM) process. The RIP process differs from the conventional pultrusion process in that the resin is injected into an injection-die (instead of being placed in an open bath) in order to eliminate the emission of volatile organic compounds (styrene) (VOC) during processing. Based on the modeling and simulation of resin/fiber “pultrudability”, resin flow, and heat transfer and curing, a computer aided engineering tool has been developed for the purpose of process design. In this study, the fiber stack permeability and compressibility are measured and modeled, and the resin impregnation pattern and pressure distribution inside the fiber stack are obtained using numerical simulation. Conversion profiles in die heating section of the pultrusion die can also be obtained using the simulation tool. The correlation between the degree-of-cure profiles and the occurrence of blisters in the pultruded composite parts is discussed. Pulling force modeling and analysis are carried out to identify the effect on composite quality due to interface friction between the die surface and the moving resin/fiber mixture. Experimental data are used to verify the modeling and simulation results.","PeriodicalId":198750,"journal":{"name":"CAE and Related Innovations for Polymer Processing","volume":"48 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":"124397325","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 numerical scheme that directly calculates the permeability field of the preform during the Resin Transfer Molding (RTM) process. The measured filling front locations as well as the corresponding inlet conditions are used in the proposed scheme to calculate the permeability field. The proposed scheme employs a numerical optimization algorithm to minimize a cost function that leads to the permeability filed of the preform. A time step independent RTM filling algorithm is utilized as a computational kernel to generate the cost function for the subsequent iterative minimization. The proposed permeability identification scheme is applied to test problems that involve isotropic and anisotropic permeability distribution within the perform. The results from these test problems verify the applicability of the proposed scheme.
{"title":"Identification of Preform Permeability Distribution in Resin Transfer Molding","authors":"B. Minaie, Y. Chen, A. Mescher","doi":"10.1115/imece2000-1237","DOIUrl":"https://doi.org/10.1115/imece2000-1237","url":null,"abstract":"\u0000 This paper presents a numerical scheme that directly calculates the permeability field of the preform during the Resin Transfer Molding (RTM) process. The measured filling front locations as well as the corresponding inlet conditions are used in the proposed scheme to calculate the permeability field. The proposed scheme employs a numerical optimization algorithm to minimize a cost function that leads to the permeability filed of the preform. A time step independent RTM filling algorithm is utilized as a computational kernel to generate the cost function for the subsequent iterative minimization. The proposed permeability identification scheme is applied to test problems that involve isotropic and anisotropic permeability distribution within the perform. The results from these test problems verify the applicability of the proposed scheme.","PeriodicalId":198750,"journal":{"name":"CAE and Related Innovations for Polymer Processing","volume":"104 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":"114409823","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 closure model for flow-induced orientation of short fibers is presented and discussed. The model retains all the six-fold symmetry and contraction properties of the fourth order tensor. A derivation of the model is presented and the conditions required for the model to be realizable are discussed. The model is validated against analytical and numerical solutions of the exact distribution function for the fiber orientation state for different flow fields. Variations of this model and its limitations are also discussed.
{"title":"Validation of a New Closure Model for Flow-Induced Alignment of Fibers","authors":"A. Imhoff, S. Parks, C. Petty, A. Benard","doi":"10.1115/imece2000-1246","DOIUrl":"https://doi.org/10.1115/imece2000-1246","url":null,"abstract":"\u0000 A closure model for flow-induced orientation of short fibers is presented and discussed. The model retains all the six-fold symmetry and contraction properties of the fourth order tensor. A derivation of the model is presented and the conditions required for the model to be realizable are discussed. The model is validated against analytical and numerical solutions of the exact distribution function for the fiber orientation state for different flow fields. Variations of this model and its limitations are also discussed.","PeriodicalId":198750,"journal":{"name":"CAE and Related Innovations for Polymer Processing","volume":"52 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":"121565004","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}
H. Wang, S. Ramaswamy, I. Dris, E. M. Perry, Dominic Gao
The objective of this work was to develop a numerical simulation tool that is able to predict the processing window for thin-wall plastic parts made by the injection molding process. This performance predictor links the processing conditions (filling time, resin inlet melt temperature, and so on) to the mechanical properties and failure mechanisms of the part, using empirical data developed for the thermal and shear degradation behavior of the resin. Usage of such a performance predictor will help to expedite the long process development cycle time and to reduce the potentially expensive tooling costs associated with the thin-wall segment of the plastics business.
{"title":"Performance Predictor for Thin-Wall Plastic Parts Produced by Injection Molding","authors":"H. Wang, S. Ramaswamy, I. Dris, E. M. Perry, Dominic Gao","doi":"10.1115/imece2000-1235","DOIUrl":"https://doi.org/10.1115/imece2000-1235","url":null,"abstract":"\u0000 The objective of this work was to develop a numerical simulation tool that is able to predict the processing window for thin-wall plastic parts made by the injection molding process. This performance predictor links the processing conditions (filling time, resin inlet melt temperature, and so on) to the mechanical properties and failure mechanisms of the part, using empirical data developed for the thermal and shear degradation behavior of the resin. Usage of such a performance predictor will help to expedite the long process development cycle time and to reduce the potentially expensive tooling costs associated with the thin-wall segment of the plastics business.","PeriodicalId":198750,"journal":{"name":"CAE and Related Innovations for Polymer Processing","volume":"24 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":"132431595","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}
CAE tools for injection molding have been dramatically improved in the past several years. Prior to this period, advanced simulations provided a wealth of information about a part and mold design. A common complaint was that too much time was required to perform an advanced simulation. This is the part of reason for the rise in popularity of desktop CAE tools, which provide fast, useful results for those who wish to improve quality, increase profitability and eliminate inefficiencies in critical product and mold design. This paper discusses recently developed desktop CAE technology which greatly reduces the time required to run advanced simulations and quickly evaluates material selection, mold filling, part design, and runner balancing issues, and also optimizes cycle time and generates engineering reports.
{"title":"Design to Evaluation: Desktop CAE for Injection Molding","authors":"Jun Hu","doi":"10.1115/imece2000-1230","DOIUrl":"https://doi.org/10.1115/imece2000-1230","url":null,"abstract":"\u0000 CAE tools for injection molding have been dramatically improved in the past several years. Prior to this period, advanced simulations provided a wealth of information about a part and mold design. A common complaint was that too much time was required to perform an advanced simulation. This is the part of reason for the rise in popularity of desktop CAE tools, which provide fast, useful results for those who wish to improve quality, increase profitability and eliminate inefficiencies in critical product and mold design. This paper discusses recently developed desktop CAE technology which greatly reduces the time required to run advanced simulations and quickly evaluates material selection, mold filling, part design, and runner balancing issues, and also optimizes cycle time and generates engineering reports.","PeriodicalId":198750,"journal":{"name":"CAE and Related Innovations for Polymer Processing","volume":"18 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":"122115667","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}
New aluminum alloys, QC-7® and QE-7®, have thermal conductivities four times greater than traditional tool steels, and have significantly increased strength and hardness compared to traditional aluminum materials. Molds were constructed of P-20 tool steel and QE-7® aluminum and were used to provide experimental data regarding thermal mold characteristic and confirm injection molding simulation predictions using C-Mold®. The relationships between cooling time reduction (using aluminum alloys) and polymer type, cooling channel depth, part wall thickness, and coolant temperature were explored both experimentally and using simulation software. It was shown that the potential reduction in cooling time varied from 5% to 25%. The most significant percentage improvements were observed in parts with part wall thickness of 0.05″ to 0.10″ and in molds with cooling channels at a depth ratio (D/d) of 2.0. The thermal pulses in the steel mold 0.10″ from the surface were approximately 63% larger than in aluminum mold.
{"title":"The Use of Advanced Aluminum Alloys for Enhanced Productivity in Plastic Injection Molding","authors":"Jim Nerone, K. Ramani","doi":"10.1115/imece2000-1231","DOIUrl":"https://doi.org/10.1115/imece2000-1231","url":null,"abstract":"\u0000 New aluminum alloys, QC-7® and QE-7®, have thermal conductivities four times greater than traditional tool steels, and have significantly increased strength and hardness compared to traditional aluminum materials. Molds were constructed of P-20 tool steel and QE-7® aluminum and were used to provide experimental data regarding thermal mold characteristic and confirm injection molding simulation predictions using C-Mold®. The relationships between cooling time reduction (using aluminum alloys) and polymer type, cooling channel depth, part wall thickness, and coolant temperature were explored both experimentally and using simulation software. It was shown that the potential reduction in cooling time varied from 5% to 25%. The most significant percentage improvements were observed in parts with part wall thickness of 0.05″ to 0.10″ and in molds with cooling channels at a depth ratio (D/d) of 2.0. The thermal pulses in the steel mold 0.10″ from the surface were approximately 63% larger than in aluminum mold.","PeriodicalId":198750,"journal":{"name":"CAE and Related Innovations for Polymer Processing","volume":"60 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":"129298530","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}
Finite element analysis of thermoforming simulation based on isothermal as well as non-isothermal initial conditions has been applied successfully for predicating final thickness distributions. For these simulations, it is assumed that the initial sheet temperature is known and does not change significantly during forming at a rapid stretch rate. For a non-isothermal analysis, the temperature dependent material properties are necessary. In this paper sample results are presented for the so-called inverse thermoforming problem, where an initial temperature distribution is sought numerically that will result in a specific final thickness distribution. Thus, a finite element simulation is combined with an iterative algorithm to obtain inverse solutions for a thermoformed part. In this example, the required initial temperature distributions that result in a uniform final thickness are determined for a thermoformed part. It is shown that the calculated results are quite sensitive to perturbations in the specified initial temperature profile and thus the practical application of optimal temperature distributions may require high precision thermal sensors and controls. This initial temperature distribution can then be used for the determination of desired heating patterns on zone-controlled heaters of a thermoforming machine using transient heat transfer analysis.
{"title":"A Numerical Solution of the Inverse Problem for Thermoforming Processes Using Finite Element Analysis","authors":"Chao-Hsin Wang, H. F. Nied","doi":"10.1115/imece2000-1240","DOIUrl":"https://doi.org/10.1115/imece2000-1240","url":null,"abstract":"\u0000 Finite element analysis of thermoforming simulation based on isothermal as well as non-isothermal initial conditions has been applied successfully for predicating final thickness distributions. For these simulations, it is assumed that the initial sheet temperature is known and does not change significantly during forming at a rapid stretch rate. For a non-isothermal analysis, the temperature dependent material properties are necessary. In this paper sample results are presented for the so-called inverse thermoforming problem, where an initial temperature distribution is sought numerically that will result in a specific final thickness distribution. Thus, a finite element simulation is combined with an iterative algorithm to obtain inverse solutions for a thermoformed part. In this example, the required initial temperature distributions that result in a uniform final thickness are determined for a thermoformed part. It is shown that the calculated results are quite sensitive to perturbations in the specified initial temperature profile and thus the practical application of optimal temperature distributions may require high precision thermal sensors and controls. This initial temperature distribution can then be used for the determination of desired heating patterns on zone-controlled heaters of a thermoforming machine using transient heat transfer analysis.","PeriodicalId":198750,"journal":{"name":"CAE and Related Innovations for Polymer Processing","volume":"27 33","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2000-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"113954953","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 microelectronics industry continues to grow rapidly in size and importance. As thinner and denser IC packages become, packaging process becomes more challenging and troublesome. The ball grid array (BGA) technology uses substrate and solder balls to replace the traditional leadframe, which offers many advantages over fine pitch technology. These include better assembly yield, superior electrical performance, and higher I/O density. However, the high density of bonding wires form a separating layer which will hold back the molding compound flowing through these regions. The paper presents the simulation of melt-front advancement and wire sweep for BGA 436. The results has been verified by the experimental studies. It is found that the high-density of wires has played a very important role in performing the CAE analysis. It shows that the melt-front advancement can be precisely predicted by CAE simulation software with proper consideration of wire density. With the accurate simulation of melt-front advancement, the CAE results can be further used to perform further engineering analysis. The wire sweep of the package demonstrates the use of CAE analysis, which also shows very good agreement with the experimental study.
{"title":"CAE Simulation and Verification of Wire Sweep for BGA 436","authors":"W. Jong, You-Ren Chen","doi":"10.1115/imece2000-1243","DOIUrl":"https://doi.org/10.1115/imece2000-1243","url":null,"abstract":"\u0000 The microelectronics industry continues to grow rapidly in size and importance. As thinner and denser IC packages become, packaging process becomes more challenging and troublesome. The ball grid array (BGA) technology uses substrate and solder balls to replace the traditional leadframe, which offers many advantages over fine pitch technology. These include better assembly yield, superior electrical performance, and higher I/O density. However, the high density of bonding wires form a separating layer which will hold back the molding compound flowing through these regions.\u0000 The paper presents the simulation of melt-front advancement and wire sweep for BGA 436. The results has been verified by the experimental studies. It is found that the high-density of wires has played a very important role in performing the CAE analysis. It shows that the melt-front advancement can be precisely predicted by CAE simulation software with proper consideration of wire density. With the accurate simulation of melt-front advancement, the CAE results can be further used to perform further engineering analysis. The wire sweep of the package demonstrates the use of CAE analysis, which also shows very good agreement with the experimental study.","PeriodicalId":198750,"journal":{"name":"CAE and Related Innovations for Polymer Processing","volume":"39 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":"124220926","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 cycle time prediction is considered as a critical issue in injection molding. It relates directly to the production rate and the part quality. It is commonly defined as the time duration between the start of the injection and the ejection of the part. When the cycle time exceeds the desired range, the production rate will be compromised. In some cases, due to excessively increased friction force, the part may be subject to severe failure such as breakage during ejection. Another possible situation is that the ejector pins can be damaged because the friction force exceeds the maximum ejection force that the machine can provide through the ejectors. If the part is ejected too early, only a thin layer of polymer is solidified and the ejection may cause the part to be deformed permanently which generally leads to surface defects. For most injection molders, the cycle time is estimated through molding trials, which is very costly and time consuming. In the case of testing a new material, it is even more difficult to determine a proper cycle time ranger due to the lack of knowledge on the material behavior.
{"title":"An Integrated Approach to Evaluate the Cycle Time in Injection Molding","authors":"D. Gao, W. Bushko","doi":"10.1115/imece2000-1222","DOIUrl":"https://doi.org/10.1115/imece2000-1222","url":null,"abstract":"\u0000 The cycle time prediction is considered as a critical issue in injection molding. It relates directly to the production rate and the part quality. It is commonly defined as the time duration between the start of the injection and the ejection of the part. When the cycle time exceeds the desired range, the production rate will be compromised. In some cases, due to excessively increased friction force, the part may be subject to severe failure such as breakage during ejection. Another possible situation is that the ejector pins can be damaged because the friction force exceeds the maximum ejection force that the machine can provide through the ejectors. If the part is ejected too early, only a thin layer of polymer is solidified and the ejection may cause the part to be deformed permanently which generally leads to surface defects. For most injection molders, the cycle time is estimated through molding trials, which is very costly and time consuming. In the case of testing a new material, it is even more difficult to determine a proper cycle time ranger due to the lack of knowledge on the material behavior.","PeriodicalId":198750,"journal":{"name":"CAE and Related Innovations for Polymer Processing","volume":"76 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":"122527373","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 the injection mold process, a pressure gradient exists from the polymer entrance to the last-fill location. At different planar locations of a part, when the polymer melt cools down to the transition temperature and freezes (changes from liquid to solid) at different pressures, shrinkage at the various locations will be different. If cooling channels are not arranged properly, the mold wall temperatures on the cavity and core sides can be different. This unbalanced cooling can also cause the melt at the upper and lower halves of the cavity to shrink differently, because they freeze at different times and different pressures. These two types of non-uniform shrinkage will cause parts to warp. Reducing shrinkage and warpage is one of the top priorities for improving the quality of injection molded parts. In addition to part design and material properties, process conditions are the most important determinants of part quality. In this paper, the relationship between process conditions and in-cavity residual stress will be studied. In-cavity residual stress is the driving force that causes parts to deform after they are taken out of the mold. The effects of process conditions on injection-molded part quality (in terms of shrinkage and warpage) will be discussed. Different packing pressure levels, together with unbalanced cooling from mold wall temperatures, will be examined. Deformation of injection molded parts will be measured. Comparisons between experimental and numerical simulation results will be reported.
{"title":"Effects of Process Conditions on Shrinkage and Warpage: Experiments and Simulations","authors":"James T. Wang, C. Yoon","doi":"10.1115/imece2000-1232","DOIUrl":"https://doi.org/10.1115/imece2000-1232","url":null,"abstract":"\u0000 In the injection mold process, a pressure gradient exists from the polymer entrance to the last-fill location. At different planar locations of a part, when the polymer melt cools down to the transition temperature and freezes (changes from liquid to solid) at different pressures, shrinkage at the various locations will be different. If cooling channels are not arranged properly, the mold wall temperatures on the cavity and core sides can be different. This unbalanced cooling can also cause the melt at the upper and lower halves of the cavity to shrink differently, because they freeze at different times and different pressures. These two types of non-uniform shrinkage will cause parts to warp.\u0000 Reducing shrinkage and warpage is one of the top priorities for improving the quality of injection molded parts. In addition to part design and material properties, process conditions are the most important determinants of part quality. In this paper, the relationship between process conditions and in-cavity residual stress will be studied. In-cavity residual stress is the driving force that causes parts to deform after they are taken out of the mold. The effects of process conditions on injection-molded part quality (in terms of shrinkage and warpage) will be discussed. Different packing pressure levels, together with unbalanced cooling from mold wall temperatures, will be examined. Deformation of injection molded parts will be measured. Comparisons between experimental and numerical simulation results will be reported.","PeriodicalId":198750,"journal":{"name":"CAE and Related Innovations for Polymer Processing","volume":"16 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":"134633611","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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