brian grimsley - Academia.edu (original) (raw)

Papers by brian grimsley

The vacuum assisted resin transfer molding (VARTM) process is a low-cost, innovative method that ... more The vacuum assisted resin transfer molding (VARTM) process is a low-cost, innovative method that is being considered for manufacture of large aircraft-quality components where high mechanical properties and dimensional tolerance are essential. In the present work a rigorous science-based approach is used to study the VARTM processing of high performance complex shape components. A process model, COMPRO © , is used to simulate the cure of panels produced by VARTM. It was found that the presence of the distribution media significantly affects the magnitude of the exotherm particularly for thick panels. For C-shaped laminates, the part distortion was a function of fiber volume fraction distribution and was affected by the presence of the distribution media.

American Society for Composites 2017, 2017

Wrinkles, puckers and fiber bridging are among the major issues encountered in Automated Fiber Pl... more Wrinkles, puckers and fiber bridging are among the major issues encountered in Automated Fiber Placement (AFP) process. These defects are all different manifestations of fiber misalignment. Residual stresses introduced in the tow during the deposition stage by the AFP head are the main driver for these defects. Tack between the deposited tape and the substrate is the resisting force against formation of such defects. Tack is a very complex phenomenon that is influenced by a variety of process parameters including temperature, head pressure and speed, as well as prepreg aging, moisture content and surface condition. A physics-based modelling framework for simulation of tack is developed in this study that allows for prediction of tack response. A model is also developed to simulate the deposition of the prepreg tape by the AFP head. It is shown that the model is capable of predicting AFP-induced puckers.

SAMPE 2019 - Charlotte, NC, 2019

SAMPE 2019 - Charlotte, NC, 2019

Vacuum assisted resin transfer molding is a promising process in advanced composite manufacturing... more Vacuum assisted resin transfer molding is a promising process in advanced composite manufacturing with a wide range of applications in industry. That potential is often misused, though, because of the lack of an efficient and reliable simulation tool to support product development. Most of the simulation methods in use today are based on Darcy's law, which explains the permeation of a fluid in a porous medium. However, it is known that this law has limitations when applied to the context of dual-scale fibrous reinforcements: macro porosity given by fiber architecture generates resistance to flow, while the inner porosity inherent to fiber tows causes it to absorb resin, affecting the flow. The latter effect cannot be explained by traditional theory. In order to explore these limitations, this work proposes a simplified model to vacuum assisted resin transfer molding process from the point of view of system dynamics, and to prove the viability of such theory. The ultimate goal is to propose a more complete model in light of system dynamics that saves time and cost while offering the same reliability as current simulation models. In order to provide an explanation to both dual-scale phenomena, a parallel association between a resistance and a fluid capacitance is proposed. Model validation is then performed through the analysis of experimental data followed by the comparison between the Darcy infusion profile and the one predicted by the resistor-capacitor-parallel (RC-parallel) circuit model. Thus, this work is able to perform a proof of concept that leads to a novel and yet unexplored field of study.

Curved honeycomb sandwich panels composed of carbon fiber reinforced toughened-epoxy polymer face... more Curved honeycomb sandwich panels composed of carbon fiber reinforced toughened-epoxy polymer facesheets are being evaluated for potential use as payload fairing components on the NASA heavy-lift space launch system (HL-SLS). These proposed composite sandwich panels provide the most efficient aerospace launch structures, and offer mass and thermal advantages when compared with existing metallic payload fairing structures. NASA and industry are investigating recently developed carbon fiber epoxy prepreg systems which can be fabricated using out-of autoclave (OOA) processes. Specifically, OOA processes using vacuum pressure in an oven and thereby significantly reducing the cost associated with manufacturing large (up to 10 m diameter) composite structures when compared with autoclave. One of these OOA composite material systems, CYCOM(R) 5320-1, was selected for manufacture of a 1/16th scale barrel portion of the payload fairing; such that, the system could be compared with the well-characterized prepreg system, CYCOM(R) 977-3, typically processed in an autoclave. Notched compression coupons for each material were obtained from the minimum-gauge flat laminate [60/-60/0]S witness panels produced in this manufacturing study. The coupons were also conditioned to an effective moisture equilibrium point and tested according to ASTM D6484M-09 at temperatures ranging from 25 C up to 177 C. The results of this elevated temperature mechanical characterization study demonstrate that, for thin coupons, the OHC strength of the OOA laminate was equivalent to the flight certified autoclave processed composite laminates; the limitations on the elevated temperature range are hot-wet conditions up to 163 C and are only within the margins of testing error. At 25 C, both the wet and dry OOA material coupons demonstrated greater OHC failure strengths than the autoclave processed material laminates. These results indicate a substantial improvement in OOA material development and processing since previous studies have consistently reported OOA material strengths on par or below those of autoclave processed composite laminates.

Recent work at NASA Langley Research Center (LaRC) has concentrated on developing new polyimide r... more Recent work at NASA Langley Research Center (LaRC) has concentrated on developing new polyimide resin systems for advanced aerospace applications that can be processed without the use of an autoclave. Polyimide composites are very attractive for applications that require a high strength to weight ratio and thermal stability. Vacuum assisted resin transfer molding (VARTM) has shown potential to reduce the manufacturing cost of composite structures. In VARTM, the fibrous preform is infiltrated on a rigid tool surface contained beneath a flexible vacuum bag. Both resin injection and fiber compaction are achieved under pressures of 101.3 KPa or less. Recent studies have demonstrated the feasibility of the VARTM process for fabrication of void free structures utilizing epoxy resin systems with fiber volume fractions approaching 60%. In this work, the VARTM process has been extended to the fabrication of composite panels from polyimide systems developed at the Langley Research Center. Thi...

Due to a demand by the aerospace industry, NASA has begun developing the next generation of polyi... more Due to a demand by the aerospace industry, NASA has begun developing the next generation of polyimide foams which will be utilized to reduce vehicle weight for the X-33 Program and Reusable Launch Vehicle (RLV) Program. The research activity at NASA Langley Research Center (LaRC) focuses on developing foam and foam structures which are made from a polyimide using monomeric solutions or salt solutions formed from the reaction of a dianhydride dissolved in a mixture of foaming agents and alkyl alcohols at room temperature. This process can produce polyimide foams with varying properties from a large number of monomers and monomer blends. The specific densities of these foams can range from 0.008 g/cc to 0.32 g/cc. Polyimide foams at densities 0.032 g/cc and 0.08 g/cc were tested for a wide range of physical properties. The foams demonstrated excellent thermal stability at 321°C, good thermal conductivity at 25°C of 0.0003 W/cm-K, compressive strengths as high as 0.84 MPa at 10% deflection, and a limiting oxygen index of 51%. Thermomechanical cyclic testing was also performed on these materials for 50 cycles at temperatures from -253°C to 204°C. The foams survived the cyclic testing without debonding or cracking.

A three-dimensional model was developed to simulate the VARTM composite manufacturing process. Th... more A three-dimensional model was developed to simulate the VARTM composite manufacturing process. The model considers the two important mechanisms that occur during the process: resin flow, and compaction and relaxation of the preform. The model was used to simulate infiltration of a carbon preform with an epoxy resin by the VARTM process. The model predicted flow patterns and preform thickness changes agreed qualitatively with the measured values. However, the predicted total infiltration times were much longer than measured most likely due to the inaccurate preform permeability values used in the simulation.

Vacuum-Assisted Resin Transfer Molding (VARTM) is a Liquid Composite Molding (LCM) process where ... more Vacuum-Assisted Resin Transfer Molding (VARTM) is a Liquid Composite Molding (LCM) process where both resin injection and fiber compaction are achieved under pressures of 101.3 kPa or less. Originally developed over a decade ago for marine composite fabrication, VARTM is ...

Materials Science and Engineering: A, 2007

... TEM samples were prepared by lift-out method under FEI Dual-Beam DB-235 focused ion beam (FIB... more ... TEM samples were prepared by lift-out method under FEI Dual-Beam DB-235 focused ion beam (FIB). The solder/surface finish interface was then examined in a JEOL 2010 F transmission electron microscope operated at 200 kV. ...

High Performance Polymers, 2000

ABSTRACT Due to a demand by the aerospace industry, NASA has begun developing the next generation... more ABSTRACT Due to a demand by the aerospace industry, NASA has begun developing the next generation of polyimide foams which could be utilized to reduce vehicle weight for the X-33 and Reusable Launch Vehicle (RLV) programmes. The activity at NASA Langley Research Center focuses on developing polyimide foam and foam structures which are made using monomeric solutions or salt solutions formed from the reaction of a dianhydride and diamine dissolved in a mixture of foaming agents and alkyl alcohols. This process can produce polyimide foams with varying properties from a large number of monomers and monomer blends. The specific densities of these foams can range from 0.008 g cc−1 to 0.32 g cc−1.Polyimide foams at densities of 0.032 g cc−1 and 0.08 g cc−1 were tested for a wide range of physical properties. The foams demonstrated excellent thermal stability at 321°C, a good thermal conductivity at 25°C of 0.03 W m−1 K−1, compressive strengths as high as 0.84 MPa at 10% deflection and a limiting oxygen index of 51%. Thermomechanical cyclic testing was also performed on these materials for 50 cycles at temperatures from −253°C to 204°C. The foams survived the cyclic testing without debonding or cracking. Thermal forming of the 0.032 g cc−1 foam was performed and a minimum radius curvature of 0.0711 m was achieved. The foams exhibited excellent properties overall and are shown to be viable for use as cryogenic insulation on the next generation RLV.

Polymers for Advanced Technologies, 2005

Activity at the NASA Langley Research Center (LaRC) has focused on developing low density polyimi... more Activity at the NASA Langley Research Center (LaRC) has focused on developing low density polyimide foam and foam structures which are made using monomeric solutions or salt solutions formed from the reaction of a dianhydride and diamine dissolved in a mixture of foaming agents and alkyl alcohol at room temperature. Monomer blends may be used to make a variety of polyimide foams with varying properties. The first foaming process developed consisted of thermal cycling the polymer precursor residuum and allowing the inflation of the particles to interact to create the foam. This process has resulted in foam structures with higher percentages of open cell content. Another innovative foaming process has been developed that begins with partially inflated microspheres, “friable balloons”, with incomplete polymer molecular weight gain, which when fully cured into a foam results in more closed cell structures.In a research study performed by NASA Kennedy Space Center (KSC) and LaRC, two closely related polyimide foams, TEEK-H series and TEEK-L series, (4,4′-oxydiphthalic anhydride/3,4′-oxydianiline and 3,3′,4,4′-benzophenonetetracarboxylic acid dianhydride/4,4′-oxydianiline) were investigated for density effects and closed versus open cell effects on the thermal, mechanical, and flammability properties. Thermal conductivity data under the full range of vacuum pressures indicate that these materials are effective insulators under cryogenic conditions. Contributing factors such as cell content, density, and surface area were studied to determine the effects on thermal conductivity. Cone calorimetry data indicated decreased peak heat release rates for the closed cell system, TEEK-H friable balloons, compared to the TEEK foams with higher open cell content. Mechanical properties including tensile strength and compressive strength indicated that the materials have good structural integrity. Foams with more open cell content resulted in greater tensile and compressive strengths than the closed cell foams. The maximum closed cell content achieved in the “friable balloon” system was 78% at a foam density of 0.048 gm/cm3. Published in 2005 by John Wiley & Sons, Ltd.

Page 1. POLYIMIDE FOAMS FROM FRIABLE BALLOONS Erik S. Weiser and Brian W. Grimsley NASA Langley R... more Page 1. POLYIMIDE FOAMS FROM FRIABLE BALLOONS Erik S. Weiser and Brian W. Grimsley NASA Langley Research Center Hampton, VA 23681 R. Byron Pipes University of Akron Akron, OH 44325 Martha K. Williams NASA ...

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007

... TEM samples were prepared by lift-out method under FEI Dual-Beam DB-235 focused ion beam (FIB... more ... TEM samples were prepared by lift-out method under FEI Dual-Beam DB-235 focused ion beam (FIB). The solder/surface finish interface was then examined in a JEOL 2010 F transmission electron microscope operated at 200 kV. ...

The application of lightweight carbon fiber reinforced plastics (CFRP) as structure for cryogenic... more The application of lightweight carbon fiber reinforced plastics (CFRP) as structure for cryogenic fuel tanks is critical to the success of the next generation of Reusable Launch Vehicles (RLV). The recent failure of the X-33 composite fuel tank occurred in part due to microcracking of the polymer matrix, which allowed cryogen to permeate through the inner skin to the honeycomb core. As part of an approach to solve these problems, NASA Langley Research Center (LaRC) and Marshall Space Flight Center (MSFC) are working to develop and investigate polymer films that will act as a barrier to the permeation of LH2 through the composite laminate. In this study two commercially available films and eleven novel LaRC films were tested in an existing cryogenics laboratory at MSFC to determine the permeance of argon at room temperature. Several of these films were introduced as a layer in the composite to form an interleaved, or hybrid, composite to determine the effects on permeability. In addition, the effects of the interleaved layer thickness, number, and location on the mechanical properties of the composite laminate were investigated. In this initial screening process, several of the films were found to exhibit lower permeability to argon than the composite panels tested.

Abstract: The curing kinetics and viscosity of an epoxy resin system, SI-ZG-5A, have been charact... more Abstract: The curing kinetics and viscosity of an epoxy resin system, SI-ZG-5A, have been characterized for application in the vacuum assisted resin transfer molding (VARTM) process. Impregnation of a typical carbon fiber perform provided the test bed for the characterization. Process simulations were carried out using the process model, COMPRO [8], to examine heat transfer and curing kinetics for a fully impregnated panel, neglecting resin flow. The predicted viscosity profile and final degree...

The vacuum assisted resin transfer molding (VARTM) process is a low-cost, innovative method that ... more The vacuum assisted resin transfer molding (VARTM) process is a low-cost, innovative method that is being considered for manufacture of large aircraft-quality components where high mechanical properties and dimensional tolerance are essential. In the present work a rigorous science-based approach is used to study the VARTM processing of high performance complex shape components. A process model, COMPRO © , is used to simulate the cure of panels produced by VARTM. It was found that the presence of the distribution media significantly affects the magnitude of the exotherm particularly for thick panels. For C-shaped laminates, the part distortion was a function of fiber volume fraction distribution and was affected by the presence of the distribution media.

American Society for Composites 2017, 2017

Wrinkles, puckers and fiber bridging are among the major issues encountered in Automated Fiber Pl... more Wrinkles, puckers and fiber bridging are among the major issues encountered in Automated Fiber Placement (AFP) process. These defects are all different manifestations of fiber misalignment. Residual stresses introduced in the tow during the deposition stage by the AFP head are the main driver for these defects. Tack between the deposited tape and the substrate is the resisting force against formation of such defects. Tack is a very complex phenomenon that is influenced by a variety of process parameters including temperature, head pressure and speed, as well as prepreg aging, moisture content and surface condition. A physics-based modelling framework for simulation of tack is developed in this study that allows for prediction of tack response. A model is also developed to simulate the deposition of the prepreg tape by the AFP head. It is shown that the model is capable of predicting AFP-induced puckers.

SAMPE 2019 - Charlotte, NC, 2019

SAMPE 2019 - Charlotte, NC, 2019

Vacuum assisted resin transfer molding is a promising process in advanced composite manufacturing... more Vacuum assisted resin transfer molding is a promising process in advanced composite manufacturing with a wide range of applications in industry. That potential is often misused, though, because of the lack of an efficient and reliable simulation tool to support product development. Most of the simulation methods in use today are based on Darcy's law, which explains the permeation of a fluid in a porous medium. However, it is known that this law has limitations when applied to the context of dual-scale fibrous reinforcements: macro porosity given by fiber architecture generates resistance to flow, while the inner porosity inherent to fiber tows causes it to absorb resin, affecting the flow. The latter effect cannot be explained by traditional theory. In order to explore these limitations, this work proposes a simplified model to vacuum assisted resin transfer molding process from the point of view of system dynamics, and to prove the viability of such theory. The ultimate goal is to propose a more complete model in light of system dynamics that saves time and cost while offering the same reliability as current simulation models. In order to provide an explanation to both dual-scale phenomena, a parallel association between a resistance and a fluid capacitance is proposed. Model validation is then performed through the analysis of experimental data followed by the comparison between the Darcy infusion profile and the one predicted by the resistor-capacitor-parallel (RC-parallel) circuit model. Thus, this work is able to perform a proof of concept that leads to a novel and yet unexplored field of study.

Curved honeycomb sandwich panels composed of carbon fiber reinforced toughened-epoxy polymer face... more Curved honeycomb sandwich panels composed of carbon fiber reinforced toughened-epoxy polymer facesheets are being evaluated for potential use as payload fairing components on the NASA heavy-lift space launch system (HL-SLS). These proposed composite sandwich panels provide the most efficient aerospace launch structures, and offer mass and thermal advantages when compared with existing metallic payload fairing structures. NASA and industry are investigating recently developed carbon fiber epoxy prepreg systems which can be fabricated using out-of autoclave (OOA) processes. Specifically, OOA processes using vacuum pressure in an oven and thereby significantly reducing the cost associated with manufacturing large (up to 10 m diameter) composite structures when compared with autoclave. One of these OOA composite material systems, CYCOM(R) 5320-1, was selected for manufacture of a 1/16th scale barrel portion of the payload fairing; such that, the system could be compared with the well-characterized prepreg system, CYCOM(R) 977-3, typically processed in an autoclave. Notched compression coupons for each material were obtained from the minimum-gauge flat laminate [60/-60/0]S witness panels produced in this manufacturing study. The coupons were also conditioned to an effective moisture equilibrium point and tested according to ASTM D6484M-09 at temperatures ranging from 25 C up to 177 C. The results of this elevated temperature mechanical characterization study demonstrate that, for thin coupons, the OHC strength of the OOA laminate was equivalent to the flight certified autoclave processed composite laminates; the limitations on the elevated temperature range are hot-wet conditions up to 163 C and are only within the margins of testing error. At 25 C, both the wet and dry OOA material coupons demonstrated greater OHC failure strengths than the autoclave processed material laminates. These results indicate a substantial improvement in OOA material development and processing since previous studies have consistently reported OOA material strengths on par or below those of autoclave processed composite laminates.

Recent work at NASA Langley Research Center (LaRC) has concentrated on developing new polyimide r... more Recent work at NASA Langley Research Center (LaRC) has concentrated on developing new polyimide resin systems for advanced aerospace applications that can be processed without the use of an autoclave. Polyimide composites are very attractive for applications that require a high strength to weight ratio and thermal stability. Vacuum assisted resin transfer molding (VARTM) has shown potential to reduce the manufacturing cost of composite structures. In VARTM, the fibrous preform is infiltrated on a rigid tool surface contained beneath a flexible vacuum bag. Both resin injection and fiber compaction are achieved under pressures of 101.3 KPa or less. Recent studies have demonstrated the feasibility of the VARTM process for fabrication of void free structures utilizing epoxy resin systems with fiber volume fractions approaching 60%. In this work, the VARTM process has been extended to the fabrication of composite panels from polyimide systems developed at the Langley Research Center. Thi...

Due to a demand by the aerospace industry, NASA has begun developing the next generation of polyi... more Due to a demand by the aerospace industry, NASA has begun developing the next generation of polyimide foams which will be utilized to reduce vehicle weight for the X-33 Program and Reusable Launch Vehicle (RLV) Program. The research activity at NASA Langley Research Center (LaRC) focuses on developing foam and foam structures which are made from a polyimide using monomeric solutions or salt solutions formed from the reaction of a dianhydride dissolved in a mixture of foaming agents and alkyl alcohols at room temperature. This process can produce polyimide foams with varying properties from a large number of monomers and monomer blends. The specific densities of these foams can range from 0.008 g/cc to 0.32 g/cc. Polyimide foams at densities 0.032 g/cc and 0.08 g/cc were tested for a wide range of physical properties. The foams demonstrated excellent thermal stability at 321°C, good thermal conductivity at 25°C of 0.0003 W/cm-K, compressive strengths as high as 0.84 MPa at 10% deflection, and a limiting oxygen index of 51%. Thermomechanical cyclic testing was also performed on these materials for 50 cycles at temperatures from -253°C to 204°C. The foams survived the cyclic testing without debonding or cracking.

A three-dimensional model was developed to simulate the VARTM composite manufacturing process. Th... more A three-dimensional model was developed to simulate the VARTM composite manufacturing process. The model considers the two important mechanisms that occur during the process: resin flow, and compaction and relaxation of the preform. The model was used to simulate infiltration of a carbon preform with an epoxy resin by the VARTM process. The model predicted flow patterns and preform thickness changes agreed qualitatively with the measured values. However, the predicted total infiltration times were much longer than measured most likely due to the inaccurate preform permeability values used in the simulation.

Vacuum-Assisted Resin Transfer Molding (VARTM) is a Liquid Composite Molding (LCM) process where ... more Vacuum-Assisted Resin Transfer Molding (VARTM) is a Liquid Composite Molding (LCM) process where both resin injection and fiber compaction are achieved under pressures of 101.3 kPa or less. Originally developed over a decade ago for marine composite fabrication, VARTM is ...

Materials Science and Engineering: A, 2007

... TEM samples were prepared by lift-out method under FEI Dual-Beam DB-235 focused ion beam (FIB... more ... TEM samples were prepared by lift-out method under FEI Dual-Beam DB-235 focused ion beam (FIB). The solder/surface finish interface was then examined in a JEOL 2010 F transmission electron microscope operated at 200 kV. ...

High Performance Polymers, 2000

ABSTRACT Due to a demand by the aerospace industry, NASA has begun developing the next generation... more ABSTRACT Due to a demand by the aerospace industry, NASA has begun developing the next generation of polyimide foams which could be utilized to reduce vehicle weight for the X-33 and Reusable Launch Vehicle (RLV) programmes. The activity at NASA Langley Research Center focuses on developing polyimide foam and foam structures which are made using monomeric solutions or salt solutions formed from the reaction of a dianhydride and diamine dissolved in a mixture of foaming agents and alkyl alcohols. This process can produce polyimide foams with varying properties from a large number of monomers and monomer blends. The specific densities of these foams can range from 0.008 g cc−1 to 0.32 g cc−1.Polyimide foams at densities of 0.032 g cc−1 and 0.08 g cc−1 were tested for a wide range of physical properties. The foams demonstrated excellent thermal stability at 321°C, a good thermal conductivity at 25°C of 0.03 W m−1 K−1, compressive strengths as high as 0.84 MPa at 10% deflection and a limiting oxygen index of 51%. Thermomechanical cyclic testing was also performed on these materials for 50 cycles at temperatures from −253°C to 204°C. The foams survived the cyclic testing without debonding or cracking. Thermal forming of the 0.032 g cc−1 foam was performed and a minimum radius curvature of 0.0711 m was achieved. The foams exhibited excellent properties overall and are shown to be viable for use as cryogenic insulation on the next generation RLV.

Polymers for Advanced Technologies, 2005

Activity at the NASA Langley Research Center (LaRC) has focused on developing low density polyimi... more Activity at the NASA Langley Research Center (LaRC) has focused on developing low density polyimide foam and foam structures which are made using monomeric solutions or salt solutions formed from the reaction of a dianhydride and diamine dissolved in a mixture of foaming agents and alkyl alcohol at room temperature. Monomer blends may be used to make a variety of polyimide foams with varying properties. The first foaming process developed consisted of thermal cycling the polymer precursor residuum and allowing the inflation of the particles to interact to create the foam. This process has resulted in foam structures with higher percentages of open cell content. Another innovative foaming process has been developed that begins with partially inflated microspheres, “friable balloons”, with incomplete polymer molecular weight gain, which when fully cured into a foam results in more closed cell structures.In a research study performed by NASA Kennedy Space Center (KSC) and LaRC, two closely related polyimide foams, TEEK-H series and TEEK-L series, (4,4′-oxydiphthalic anhydride/3,4′-oxydianiline and 3,3′,4,4′-benzophenonetetracarboxylic acid dianhydride/4,4′-oxydianiline) were investigated for density effects and closed versus open cell effects on the thermal, mechanical, and flammability properties. Thermal conductivity data under the full range of vacuum pressures indicate that these materials are effective insulators under cryogenic conditions. Contributing factors such as cell content, density, and surface area were studied to determine the effects on thermal conductivity. Cone calorimetry data indicated decreased peak heat release rates for the closed cell system, TEEK-H friable balloons, compared to the TEEK foams with higher open cell content. Mechanical properties including tensile strength and compressive strength indicated that the materials have good structural integrity. Foams with more open cell content resulted in greater tensile and compressive strengths than the closed cell foams. The maximum closed cell content achieved in the “friable balloon” system was 78% at a foam density of 0.048 gm/cm3. Published in 2005 by John Wiley & Sons, Ltd.

Page 1. POLYIMIDE FOAMS FROM FRIABLE BALLOONS Erik S. Weiser and Brian W. Grimsley NASA Langley R... more Page 1. POLYIMIDE FOAMS FROM FRIABLE BALLOONS Erik S. Weiser and Brian W. Grimsley NASA Langley Research Center Hampton, VA 23681 R. Byron Pipes University of Akron Akron, OH 44325 Martha K. Williams NASA ...

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2007

... TEM samples were prepared by lift-out method under FEI Dual-Beam DB-235 focused ion beam (FIB... more ... TEM samples were prepared by lift-out method under FEI Dual-Beam DB-235 focused ion beam (FIB). The solder/surface finish interface was then examined in a JEOL 2010 F transmission electron microscope operated at 200 kV. ...

The application of lightweight carbon fiber reinforced plastics (CFRP) as structure for cryogenic... more The application of lightweight carbon fiber reinforced plastics (CFRP) as structure for cryogenic fuel tanks is critical to the success of the next generation of Reusable Launch Vehicles (RLV). The recent failure of the X-33 composite fuel tank occurred in part due to microcracking of the polymer matrix, which allowed cryogen to permeate through the inner skin to the honeycomb core. As part of an approach to solve these problems, NASA Langley Research Center (LaRC) and Marshall Space Flight Center (MSFC) are working to develop and investigate polymer films that will act as a barrier to the permeation of LH2 through the composite laminate. In this study two commercially available films and eleven novel LaRC films were tested in an existing cryogenics laboratory at MSFC to determine the permeance of argon at room temperature. Several of these films were introduced as a layer in the composite to form an interleaved, or hybrid, composite to determine the effects on permeability. In addition, the effects of the interleaved layer thickness, number, and location on the mechanical properties of the composite laminate were investigated. In this initial screening process, several of the films were found to exhibit lower permeability to argon than the composite panels tested.

Abstract: The curing kinetics and viscosity of an epoxy resin system, SI-ZG-5A, have been charact... more Abstract: The curing kinetics and viscosity of an epoxy resin system, SI-ZG-5A, have been characterized for application in the vacuum assisted resin transfer molding (VARTM) process. Impregnation of a typical carbon fiber perform provided the test bed for the characterization. Process simulations were carried out using the process model, COMPRO [8], to examine heat transfer and curing kinetics for a fully impregnated panel, neglecting resin flow. The predicted viscosity profile and final degree...