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This document is a technical assessment of the Defense Advanced Research Projects Agency (DARPA) Affordable Polymer Matrix Composite (PMC) program. The projects under this program were initiated to develop and demonstrate technologies that would reduce the acquisition costs of composites for high performance air vehicles and other platforms by 30+ percent, develop a composite structure equal to or lower than the cost of a metallic structure for transports and other 'lower performance' applications, and reduce prototype tooling costs and lead times by 40+ percent. The projects that were originally planned had to refocus their efforts and/or finish earlier than planned. This document summarizes the technical achievements of these projects, assesses the readiness of the technologies for systems applications, and discussed the process and exit criteria that were developed to assess the technology readiness.

Polymer matrix composite mechanical properties have been shown to decrease significantly with the presence of thermal damage. For aerospace applications, this type of damage typically occurs as a result of exposure to elevated temperatures from localized heating, such as lightning strikes, exhaust wash, or improper maintenance/repair procedures. Mechanical testing has shown that this type of damage, known as incipient damage, is present even when no visible damage is observable and can cause significant reduction in mechanical properties. Incipient damage is not currently readily detected with conventional nondestructive evaluation (NDE) tools. This presentation describes a NDE method that combines mechanical excitation with thermal imaging to detect the presence of surface and through-the-thickness incipient thermal damage without direct contact to the part being tested. It compares the results from samples with and without known damage using the thermo-elastic technique with similar inspection results from conventional NDE techniques, such as ultrasonic C-scan and thermography. These results indicate the thermo-elastic method identifies incipient damage that the other techniques fail to detect. In addition, an approach to analyze the thermo-elastic data to potentially determine the severity of the thermal damage is reviewed.

The concept of molecular composites utilizing rod-like aromatic heterocyclic polymers as reinforcements in coil-like heterocyclic polymer matrices has been demonstrated. A series of polymer films, prepared by vacuum casting from various solutions of rod-like polymer, amorphous polymer, and solvent, were fabricated and tested. Morphological studies of these films were conducted using x-ray diffraction and scanning electron microscopy. The results of the morphology studies showed pronounced structure and definite evidence of the ordering of the rod-like polymer. In some cases, a second phase or conglomeration was evidenced. Analysis of the scanning electron microscopy pictures indicated that the second phase was itself a composite of rod-like and amorphous polymer. The mechanical testing showed significant increases in tensile modulus and strength with only ten percent rod-like polymer in the matrix; this was especially true after stretching of the film had been performed. Analytical equations developed for composite materials were used to calculate theoretical properties of the conglomerates and rods. All results and conclusions are presented in detail in this report.

The main objective of the project Structural Foaming at the Nano-, Micro-, and Macro-Scales of Continuous Carbon Fiber Reinforced Polymer Matrix Composites, was to create fractal structures within each composite lamina and introduce scaled porosity. As this fractal structure was being created, it was observed that the structure imitated that of naturally occurring bird feathers. Consequently, the name given to this new generation of fractal structured composite materials with scaled porosity was deemed Featherweight(trademark) Composites. The idea was to create lighter composites, and at the same time increase material strength. Through extensive characterization, two main interlayer enabling fractal systems were manufactured and characterized, first Carbon fiber - Epoxy Foam - CNTs, and second Carbon Fiber - Electrospun Nano-Fiber - CNTs, with both becoming transformed from the macro-, to micro-, and then nano-dimension. By focusing on low cost, the nano-materials utilized were not of the highest performance and quality. Nonetheless, with both interlayer systems, strength increased in several forms, such as fracture toughness (400%), stiffness (150%), flexural strength (80%), and tensile strength (20%), with percentages based on maximum values observed. At the same time, an experimental weight reduction of 10% was achieved. Finally, it is expected that if higher quality CNTs and matrix materials are used, the weight reduction can be higher, or even double that observed.

Fiber-reinforced polymer matrix composite materials display quite complex deformation and failure behavior under ballistic/blast impact loading conditions. This complexity is generally attributed to a number of factors such as (a) hierarchical/multi-length scale architecture of the material microstructure; (b) nonlinear, rate-dependent and often pressure-sensitive mechanical response; and (c) the interplay of various intrinsic phenomena and processes such as fiber twisting, interfiber friction/sliding, etc. Material models currently employed in the computational engineering analyses of ballistic/blast impact protective structures made of this type of material do not generally include many of the aforementioned aspects of the material dynamic behavior. Consequently, discrepancies are often observed between computational predictions and their experimental counterparts. To address this problem, the results of an extensive set of molecular-level computational analyses regarding the role of various microstructural/morphological defects on the Kevlar fiber mechanical properties are used to upgrade one of the existing continuum-level material models for fiber-reinforced composites. The results obtained show that the response of the material is significantly affected as a result of the incorporation of microstructural effects both under quasi-static simple mechanical testing condition and under dynamic ballistic-impact conditions.

Polymer matrix composite mechanical properties have been shown to decrease significantly with the presence of thermal damage. For aerospace applications, this type of damage typically occurs as a result of exposure to elevated temperatures from localized heating, such as lightning strikes, exhaust wash, or improper maintenance/repair procedures. Mechanical testing has shown that this type of damage, known as incipient damage, is present even when no visible damage is observable and can cause significant reduction in mechanical properties. Incipient damage is not currently readily detected with conventional nondestructive evaluation (NDE) tools. This presentation describes a NDE method that combines mechanical excitation with thermal imaging to detect the presence of surface and through-the-thickness incipient thermal damage without direct contact to the part being tested. It compares the results from samples with and without known damage using the thermo-elastic technique with similar inspection results from conventional NDE techniques, such as ultrasonic C-scan and thermography. These results indicate the thermo-elastic method identifies incipient damage that the other techniques fail to detect. In addition, an approach to analyze the thermo-elastic data to potentially determine the severity of the thermal damage is reviewed.

A novel experimental configuration that can record projectile velocity histories and target back surface out-of-plane motion in penetration experiments has been developed. The technique was used to investigate failure mechanisms during ballistic impact of an S-2 glass fiber woven composite with 60% fiber volume fraction. Microscopy studies performed on recovered samples clearly show interply delamination, fiber breakage, ply inelasticity, and fiber kinking as the major failure modes in these composites. Recorded penetrator velocity histories indicate these failure mechanisms are rate dependent. Pressure-shear recovery experiments were performed to investigate the out-of-plane dynamic shear resistance of the composite. Microstructural analyses revealed that at low impact velocities, 2 GPa compressive stresses, matrix cracking and matrix-fiber debonding are the primary damage mechanisms. At higher impact velocities, 4 GPa compressive stresses, fiber microcracking becomes pronounced.

This report describes a thermal-vacuum outgassing model and test protocol for predicting outgassing times and dimensional changes for polymer matrix composites. Experimental results derived from 'control' samples are used to provide the basis for analytical predictions to compare with the outgassing response of Long Duration Exposure Facility (LDEF) flight samples. Coefficient of thermal expansion (CTE) data are also presented. In addition, an example is given illustrating the dimensional change of a 'zero' CTE laminate due to moisture outgassing.

Advanced polymer matrix composites (PMC's) are desirable for structural materials in diverse applications such as aircraft, civil infrastructure and biomedical implants because of their improved strength-to-weight and stiffness-to-weight ratios. For example, the next generation military and commercial aircraft requires applications for high strength, low weight structural components subjected to elevated temperatures. A possible disadvantage of polymer-based composites is that the physical and mechanical properties of the matrix often change significantly over time due to the exposure of elevated temperatures and environmental factors. For design, long term exposure (i.e. aging) of PMC's must be accounted for through constitutive models in order to accurately assess the effects of aging on performance, crack initiation and remaining life. One particular aspect of this aging process, physical aging, is considered in this research.

The Long Duration Exposure Facility (LDEF) was deployed on April 7, 1984 in low earth orbit (LEO) at an altitude of 482 kilometers. On board experiments experienced the harsh LEO environment including atomic oxygen (AO), ultraviolet radiation (UV), and thermal cycling. During the 5.8 year mission, the LDEF orbit decayed to 340 kilometers where significantly higher AO concentrations exist. LDEF was retrieved on January 12, 1990 from this orbit. One experiment on board LDEF was M0003, Space Effects on Spacecraft Materials. As a subset of M0003 nearly 500 samples of polymer, metal, and glass matrix composites were flown as the Advanced Composites Experiment M0003-10. The Advanced Composites Experiment is a joint effort between government and industry with the Aerospace Corporation serving as the experiment integrator. A portion of the graphite reinforced polymer matrix composites were furnished by the Boeing Defense and Space Group, Seattle, Washington. Test results and discussions for the Boeing portion of M0003-10 are presented. Experiment and specimen location on the LDEF are presented along with a quantitative summary of the pertinent exposure conditions. Matrix materials selected for the test were epoxy, polysulfone, and polyimide. These composite materials were selected due to their suitability for high performance structural capability in spacecraft applications. Graphite reinforced polymer matrix composites offer higher strength to weight ratios along with excellent dimensional stability. The Boeing space exposed and corresponding ground control composite specimens were subjected to post flight mechanical, chemical, and physical testing in order to determine any changes in critical properties and performance characteristics. Among the more significant findings are the erosive effect of atomic oxygen on leading edge exposed specimens and microcracking in non-unidirectionally reinforced flight specimens.

These are the proceedings of the High Temperature Polymer Matrix Composites Conference held at the NASA Lewis Research Center on March 16 to 18, 1983. The purpose of the conference is to provide scientists and engineers working in the field of high temperature polymer matrix composites an opportunity to review, exchange, and assess the latest developments in this rapidly expanding area of materials technology. Technical papers are presented in the following areas: (1) matrix development; (2) adhesive development; (3) characterization; (4) environmental effects; and (5) applications.

A research program is underway to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to high strain rate impact loads. Under these types of loading conditions, the material response can be highly strain rate dependent and nonlinear. State variable constitutive equations based on a viscoplasticity approach have been developed to model the deformation of the polymer matrix. The constitutive equations are then combined with a mechanics of materials based micromechanics model which utilizes fiber substructuring to predict the effective mechanical and thermal response of the composite. To verify the analytical model, tensile stress-strain curves are predicted for a representative composite over strain rates ranging from around 1 x 10(exp -5)/sec to approximately 400/sec. The analytical predictions compare favorably to experimentally obtained values both qualitatively and quantitatively. Effective elastic and thermal constants are predicted for another composite, and compared to finite element results.

NASA's Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC) is used to predict the elastic properties of plain weave polymer matrix composites (PMCs). The traditional one step three-dimensional homogertization procedure that has been used in conjunction with MAC/GMC for modeling woven composites in the past is inaccurate due to the lack of shear coupling inherent to the model. However, by performing a two step homogenization procedure in which the woven composite repeating unit cell is homogenized independently in the through-thickness direction prior to homogenization in the plane of the weave, MAC/GMC can now accurately model woven PMCs. This two step procedure is outlined and implemented, and predictions are compared with results from the traditional one step approach and other models and experiments from the literature. Full coupling of this two step technique with MAC/ GMC will result in a widely applicable, efficient, and accurate tool for the design and analysis of woven composite materials and structures.

NASA's Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC) is used to predict the elastic properties of plain weave polymer matrix composites (PMCs). The traditional one step three-dimensional homogertization procedure that has been used in conjunction with MAC/GMC for modeling woven composites in the past is inaccurate due to the lack of shear coupling inherent to the model. However, by performing a two step homogenization procedure in which the woven composite repeating unit cell is homogenized independently in the through-thickness direction prior to homogenization in the plane of the weave, MAC/GMC can now accurately model woven PMCs. This two step procedure is outlined and implemented, and predictions are compared with results from the traditional one step approach and other models and experiments from the literature. Full coupling of this two step technique with MAC/ GMC will result in a widely applicable, efficient, and accurate tool for the design and analysis of woven composite materials and structures.

A methodology to compute the fatigue life for different ratios, r, of applied stress to the laminate strength based on first ply failure criteria combined with thermal cyclic loads has been developed and demonstrated. Degradation effects resulting from long term environmental exposure and thermo-mechanical cyclic loads are considered in the simulation process. A unified time-stress dependent multi-factor interaction equation model developed at NASA Lewis Research Center has been used to account for the degradation of material properties caused by cyclic and aging loads. Effect of variation in the thermal cyclic load amplitude on a quasi-symmetric graphite/epoxy laminate has been studied with respect to the impending failure modes. The results show that, for the laminate under consideration, the fatigue life under combined mechanical and low thermal amplitude cyclic loads is higher than that due to mechanical loads only. However, as the thermal amplitude increases, the life also decreases. The failure mode changes from tensile under mechanical loads only to the compressive and shear at high mechanical and thermal loads. Also, implementation of the developed methodology in the design process has been discussed.

A research program is in progress to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to impact loads. Previously, strain rate dependent inelastic constitutive equations developed to model the polymer matrix were incorporated into a mechanics of materials based micromechanics method. In the current work, the micromechanics method is revised such that the composite unit cell is divided into a number of slices. Micromechanics equations are then developed for each slice, with laminate theory applied to determine the elastic properties, effective stresses and effective inelastic strains for the unit cell. Verification studies are conducted using two representative polymer matrix composites with a nonlinear, strain rate dependent deformation response. The computed results compare well to experimentally obtained values.

The results of a program designed to determine the extent to which elemental boron and boron containing fillers added to the matrix resin of graphite/epoxy composites prevent the release of graphite fibers when the composites are exposed to fire and impact conditions are described. The fillers evaluated were boron, boron carbide and aluminum boride. The conditions evaluated were laboratory simulations of those that could exist in the event of an aircraft crash and burn situation. The baseline (i.e., unfilled) laminates evaluated were prepared from commercially available graphite/epoxy. The baseline and filled laminates' mechanical properties, before and after isothermal and humidity aging, also were compared. It was found that a small amount of graphite fiber was released from the baseline graphite/epoxy laminates during the burn and impact conditions used in this program. However, the extent to which the fibers were released is not considered a severe enough problem to preclude the use of graphite reinforced composites in civil aircraft structure. It also was found that the addition of boron and boron containing fillers to the resin matrix eliminated this fiber release. Mechanical properties of laminates containing the boron and boron containing fillers were lower than those of the baseline laminates. These property degradations for two systems: boron (5 micron) at 2.5 percent filler loading, and boron (5 micron) at 5.0 percent filler loading do not appear severe enough to preclude their use in structural composite applications.

A methodology to compute cumulative probability distribution functions (CDF) of fatigue life for different ratios, r of applied stress to the laminate strength based on first ply failure criteria has been developed and demonstrated. Degradation effects due to long term environmental exposure and mechanical cyclic loads are considered in the simulation process. A unified time-stress dependent multi-factor interaction equation model developed at NASA Lewis Research Center has been used to account for the degradation/aging of material properties due to cyclic loads. Fast probability integration method is used to perform probabilistic simulation of uncertainties. Sensitivity of fatigue life reliability to uncertainties in the primitive random variables are computed and their significance in the reliability based design for maximum life is discussed. The results show that the graphite/epoxy (0/+45/90) deg laminate with ply thickness 0.125 in. has 500,000 cycles life for applied stress to laminate strength ratio of 0.6 and a reliability of 0.999. Also, the fatigue life reliability has been found to be most sensitive to the ply thickness and matrix tensile strength. Tighter quality controls must therefore be enforced on ply thickness and matrix strength in order to achieve high reliability of the structure.

A research program is in progress to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to high strain rate impact loads. Strain rate dependent inelastic constitutive equations have been developed to model the polymer matrix, and have been incorporated into a micromechanics approach to analyze polymer matrix composites. The Hashin failure criterion has been implemented within the micromechanics results to predict ply failure strengths. The deformation model has been implemented within LS-DYNA, a commercially available transient dynamic finite element code. The deformation response and ply failure stresses for the representative polymer matrix composite AS4/PEEK have been predicted for a variety of fiber orientations and strain rates. The predicted results compare favorably to experimentally obtained values.

This study provides methods by which composite prepreg materials can be characterized at the microscopic level. By applying established spatial tessellation schemes developed by Dirichlet, a means by which fiber packing may be conveniently characterized at a number of different length scales is provided. New micrographic preparation techniques are presented, that allow microscopic characterization of uncured prepreg material. This provides the starting point for an analysis that is intended to uncover the links between processing sequence, micro-structural variation and attendant variability in structural performance. A computer code is presented that allows automatic characterization, in terms of fiber volume fraction maps, of micrographic images including those from previously published articles. A preliminary version of a finite element model that interrogates the effect of fiber packing on stress profiles and associated microcracking patterns is also presented.

In this Research effort, the tension-compression fatigue behavior of the 3D and 2D PMCs with 0/90 deg fiber orientation (newly developed) was investigated. These polymer composites consist of an NRPE (high-temperature polyimide) matrix with carbon fiber reinforcement. Compressive properties were assessed at (1) room temperature and (2) elevated temperature with one side, T(sub right), at 329 deg C and the other side open to the ambient air. Tension-compression fatigue tests were conducted at elevated temperature with a frequency of 1 Hz and a ratio of minimum to maximum stress of -1.

In this Research effort, the tension-compression fatigue behavior of the 3D and 2D PMCs with 0/90 deg fiber orientation (newly developed) was investigated. These polymer composites consist of an NRPE (high-temperature polyimide) matrix with carbon fiber reinforcement. Compressive properties were assessed at (1) room temperature and (2) elevated temperature with one side, T(sub right), at 329 deg C and the other side open to the ambient air. Tension-compression fatigue tests were conducted at elevated temperature with a frequency of 1 Hz and a ratio of minimum to maximum stress of -1.

Polymer Matrix Composites (PMCs) offer lightweight and frequently low cost alternatives to other materials in many applications. High temperature PMCs are currently used in limited propulsion applications replacing metals. Yet in most cases, PMC propulsion applications are not in the direct engine flow path since particulate erosion degrades PMC component performance and therefore restricts their use in gas turbine engines. This paper compares two erosion resistant coatings (SANRES and SANPRES) on PMCs that are useful for both low and high temperature propulsion applications. Collaborating over a multi-year period, researchers at NASA Glenn Research Center, Allison Advanced Developed Company, and Rolls-Royce Corporation have optimized these coatings in terms of adhesion, surface roughness, and erosion resistance. Results are described for vigorous hot gas/particulate erosion rig and engine testing of uncoated and coated PMC fan bypass vanes from the AE 3007 regional jet gas turbine engine. Moreover, the structural durability of these coatings is described in long-term high cycle fatigue tests. Overall, both coatings performed well in all tests and will be considered for applications in both commercial and defense propulsion applications.

Polymer Matrix Composites (PMCs) offer lightweight and frequently low cost alternatives to other materials in many applications. High temperature PMCs are currently used in limited propulsion applications replacing metals. Yet in most cases, PMC propulsion applications are not in the direct engine flow path since particulate erosion degrades PMC component performance and therefore restricts their use in gas turbine engines. This paper compares two erosion resistant coatings (SANRES and SANPRES) on PMCs that are useful for both low and high temperature propulsion applications. Collaborating over a multi-year period, researchers at NASA Glenn Research Center, Allison Advanced Developed Company, and Rolls-Royce Corporation have optimized these coatings in terms of adhesion, surface roughness, and erosion resistance. Results are described for vigorous hot gas/particulate erosion rig and engine testing of uncoated and coated PMC fan bypass vanes from the AE 3007 regional jet gas turbine engine. Moreover, the structural durability of these coatings is described in long-term high cycle fatigue tests. Overall, both coatings performed well in all tests and will be considered for applications in both commercial and defense propulsion applications.

With this research we explore interfacial functionality in polymer matrix composites from sensing and monitoring of mechanical damage to the active control of interfacial phenomena, such as the transport of heat and mass. We use a combined computational and experimental approach. Structures generated using our simulation framework allow us to gain unprecedented insights into anomalous diffusion behavior of water in polyimides and reveal that non-bonding interactions play a more important role in the thermal conductivity of polymers than expected. At 20%-30% of the nominal breakdown voltage we observe small changes in the elastic modulus of PVDF as a result of applying this field, but these changes dissipate with time. Closer inspection of the time dependence of elastic property changes under the influence of external constrains reveal that, as long as the deformation remains within the elastic regime, the elastic modulus gradually returns to the value that corresponds to the unstrained state, presumably as a result of structural reconstitution. Two different relaxation rates govern this process, and they differ by up to two orders of magnitude, depending on the amount of strain applied and the deformation history. The slower processes are only observable in the adiabatic modulus. These results provide insights into the relative magnitudes of entropic and enthalpic changes that occur upon deforming PVDF. We attribute theenthalpic changes predominantly to nonbonding interactions, since in the elastic regime we do not expect covalent bonds to rupture under deformation.

A series of samples of graphite/epoxy, glass/epoxy, and Kevlar epoxy were prepared. In addition, hybrids of glass epoxy and Kevlar epoxy were laid up in various configurations. The samples were subjected to hygro-thermal cycling and properties in the through-the-thickness direction were measured as a function of cycling. Thermal expansion and residual stress measurements were made and the effect of ply orientation was determined on both the hybrid and standard composites.

Equipment was purchased to carry out experiments to characterize the dynamic response and failure of polymer composites under dynamic compressive loads. A high speed framing camera with variable frames, instrumentation amplifiers for load cells, strain gage signals, and high-speed data acquisition were purchases. Details are given in the report. The total budget with cost sharing was $370,000.

Polymer matrix composites are increasingly used in demanding structural applications in which they may be exposed to harsh environments. The durability of such materials is a major concern, potentially limiting both the integrity of the structures and their useful lifetimes. The goal of the current investigation is to develop a mechanism-based model of the chemical degradation which occurs, such that given the external chemical environment and temperatures throughout the laminate, laminate geometry, and ply and/or constituent material properties, we can calculate the concentration of diffusing substances and extent of chemical degradation as functions of time and position throughout the laminate. This objective is met through the development and use of analytical models, coupled to an analysis-driven experimental program which offers both quantitative and qualitative information on the degradation mechanism. Preliminary analyses using a coupled diffusion/reaction model are used to gain insight into the physics of the degradation mechanisms and to identify crucial material parameters. An experimental program is defined based on the results of the preliminary analysis which allows the determination of the necessary material coefficients. Thermogravimetric analyses are carried out in nitrogen, air, and oxygen to provide quantitative information on thermal and oxidative reactions. Powdered samples are used to eliminate diffusion effects. Tests in both inert and oxidative environments allow the separation of thermal and oxidative contributions to specimen mass loss. The concentration dependency of the oxidative reactions is determined from the tests in pure oxygen. Short term isothermal tests at different temperatures are carried out on neat resin and unidirectional macroscopic specimens to identify diffusion effects. Mass loss, specimen shrinkage, the formation of degraded surface layers and surface cracking are recorded as functions of exposure time. Geometry effects in the neat resin, and anisotropic diffusion effects in the composites, are identified through the use of specimens with different aspect ratios. The data is used with the model to determine reaction coefficients and effective diffusion coefficients. The empirical and analytical correlations confirm the preliminary model results which suggest that mass loss at lower temperatures is dominated by oxidative reactions and that these reaction are limited by diffusion of oxygen from the surface. The mechanism-based model is able to successfully capture the basic physics of the degradation phenomena under a wide range of test conditions. The analysis-based test design is successful in separating out oxidative, thermal, and diffusion effects to allow the determination of material coefficients. This success confirms the basic picture of the process; however, a more complete understanding of some aspects of the physics are required before truly predictive capability can be achieved.

Polymer matrix composites are increasingly used in demanding structural applications in which they may be exposed to harsh environments. The durability of such materials is a major concern, potentially limiting both the integrity of the structures and their useful lifetimes. The goal of the current investigation is to develop a mechanism-based model of the chemical degradation which occurs, such that given the external chemical environment and temperatures throughout the laminate, laminate geometry, and ply and/or constituent material properties, we can calculate the concentration of diffusing substances and extent of chemical degradation as functions of time and position throughout the laminate. This objective is met through the development and use of analytical models, coupled to an analysis-driven experimental program which offers both quantitative and qualitative information on the degradation mechanism. Preliminary analyses using coupled diffusion/reaction model are used to gain insight into the physics of the degradation mechanisms and to identify crucial material parameters. An experimental program is defined based on the results of the preliminary analysis which allows the determination of the necessary material coefficients. Thermogravimetric analyses are carried out in nitrogen, air, and oxygen to provide quantitative information on thermal and oxidative reactions. Powdered samples are used to eliminate diffusion effects. Tests in both inert and oxidative environments allow the separation of thermal and oxidative contributions to specimen mass loss. The concentration dependency of the oxidative reactions is determined from the tests in pure oxygen. Short term isothermal tests at different temperatures are carried out on neat resin and unidirectional macroscopic specimens to identify diffusion effects. Mass loss, specimen shrinkage, the formation of degraded surface layers and surface cracking are recorded as functions of exposure time. Geometry effects in the neat resin, and anisotropic diffusion effects in the composites, are identified through the use of specimens with different aspect ratios. The data is used with the model to determine reaction coefficients and effective diffusion coefficients. The empirical and analytical correlations confirm the preliminary model results which suggest that mass loss at lower temperatures is dominated by oxidative reactions and that these reaction are limited by diffusion of oxygen from the surface. The mechanism-based model is able to successfully capture the basic physics of the degradation phenomena under a wide range of test conditions. The analysis-based test design is successful in separating out oxidative, thermal, and diffusion effects to allow the determination of material coefficients. This success confirms the basic picture of the process; however, a more complete understanding of some aspects of the physics are required before truly predictive capability can be achieved.

This effort examines the combined effects of temperature and strain- rate upon the Mode I fracture toughness of advanced composites. The material systems used were As4/APC-2, a semi-crystalline thermoplastic matrix system; and AS4/3502, a thermosetting epoxy matrix system. The focus of this effort was to investigate whether the Mode I fracture toughness varies with temperature and strain-rate for these systems. The applied crack opening displacement rates utilized were from 0.02 to 20.0 inches per minute and a temperature range from ambient to 350 deg F. Post failure fractographic examinations were utilized to correlate significant variations in mechanical properties with fractographic features. Mechanical test results were summarized via data plots with error bars to show which effects were statistically significant.

The objective of the Accelerated Insertion of Materials - Composites (AIM-C) program is to provide concepts, and approach and tools that can accelerate the insertion of composite materials into DoD systems. It will evaluate the historical roadblocks to effective implementation of composites and offer a process or protocol to eliminate these roadblocks and a strategy to expand the use of the systems and processes developed.

The objective of the Accelerated Insertion of Materials - Composites (AIM-C) program is to provide concepts, and approach and tools that can accelerate the insertion of composite materials into DoD systems. It will evaluate the historical roadblocks to effective implementation of composites and offer a process or protocol to eliminate these roadblocks and a strategy to expand the use of the systems and processes developed.

NAS 1.55:2385 Digitized from IA1177306-12-0033 , IA1177306-12-0034 , IA1177306-12-0035 , IA1177306-12-0036 , IA1177306-12-0037 .

NAS 1.55:2385 Digitized from IA1177306-12-0033 , IA1177306-12-0034 , IA1177306-12-0035 , IA1177306-12-0036 , IA1177306-12-0037 .

Aliphatic polymers were identified as optimum radiation polymeric shielding materials for building multifunctional structural elements. Conceptual damage-tolerant configurations of polyolefins have been proposed but many issues on the manufacture remain. In the present paper, we will investigate fabrication technologies with e-beam curing for inclusion of high-strength aliphatic polymer fibers into a highly cross-linked polyolefin matrix. A second stage of development is the fabrication methods for applying face sheets to aliphatic polymer closed-cell foams.

The mechanical properties of two neat resin systems for use in carbon fiber epoxy composites were characterized. This included tensile and shear stiffness and strengths, coefficients of thermal and moisture expansion, and fracture toughness. Tests were conducted on specimens in the dry and moisture-saturated states, at temperatures of 23, 82 and 121 C. The neat resins tested were American Cyanamid 1806 and Union Carbide ERX-4901B(MPDA). Results were compared to previously tested neat resins. Four unidirectional carbon fiber reinforced composites were mechanically characterized. Axial and transverse tension and in-plane shear strengths and stiffness were measured, as well as transverse coefficients of thermal and moisture expansion. Tests were conducted on dry specimens only at 23 and 100 C. The materials tested were AS4/3502, AS6/5245-C, T300/BP907, and C6000/1806 unidirectional composites. Scanning electron microscopic examination of fracture surfaces was performed to permit the correlation of observed failure modes with the environmental test conditions.

The mechanical properties of two neat resin systems for use in carbon fiber epoxy composites were characterized. This included tensile and shear stiffness and strengths, coefficients of thermal and moisture expansion, and fracture toughness. Tests were conducted on specimens in the dry and moisture-saturated states, at temperatures of 23, 82 and 121 C. The neat resins tested were American Cyanamid 1806 and Union Carbide ERX-4901B(MPDA). Results were compared to previously tested neat resins. Four unidirectional carbon fiber reinforced composites were mechanically characterized. Axial and transverse tension and in-plane shear strengths and stiffness were measured, as well as transverse coefficients of thermal and moisture expansion. Tests were conducted on dry specimens only at 23 and 100 C. The materials tested were AS4/3502, AS6/5245-C, T300/BP907, and C6000/1806 unidirectional composites. Scanning electron microscopic examination of fracture surfaces was performed to permit the correlation of observed failure modes with the environmental test conditions.

This report provides a review of select Soviet and Russian (SIR) literature from the mid 1960s to the mid 199Os related to residual stresses in wound composite articles. Through a compilation of SIR review articles. a historical overview of the development of this SIR knowledge base is first provided. This overview is then followed by detailed compilations of the following topics: experimental measurement of residual stress development in wound composites. cure shrinkage in neat polymers. residual microsstress development. modeling residual macrostress development. and manufacturing methods for controlling residual macrosnesses in wound composites. This study though not a comprehensive review of SIR residual stress literature. provides a general survey which should prove useful for identifying published sources of SIR technical expertise.

Support of the metal matrix composites effort, as the equivalent of a MIL-HDBK-17 working group, is included in the Secretariat contract. Preparation, of a document for publication was not included in the revised proposal since this was not mentioned in the RFP. The draft outline of the metal matrix handbook was revised. A volume with three parts is planned. Volunteers will draft some of the sections and additional sections will be written by the MMCIAC. The goal is a draft handbook by the New Orleans meeting, sufficient to be assigned a military handbook number. In addition to draft handbook sections, test matrix information is under development. Buchanan at McDonald Douglas has a MMC database he is willing to contribute to the handbook.

Some recent developments on integrated damping mechanics for unidirectional composites, laminates, and composite structures are reviewed. Simplified damping micromechanics relate the damping of on-axis and off-axis composites to constituent properties, fiber volume ratio, fiber orientation, temperature, and moisture. Laminate and structural damping mechanics for thin composites are summarized. Discrete layer damping mechanics for thick laminates, including the effects of interlaminar shear damping, are developed and semianalytical predictions of modal damping in thick simply supported specialty composite plates are presented. Applications show the advantages of the unified mechanics, and illustrate the effect of fiber volume ratio, fiber orientation, structural geometry, and temperature on the damping. Additional damping properties for composite plates of various laminations, aspect ratios, fiber content, and temperature illustrate the merits and ranges of applicability of each theory (thin or thick laminates).

A study was conducted to relate the impact resistance of graphite fiber reinforced composites with matrix properties through gaining an understanding of the basic mechanics involved in the deformation and fracture process, and the effect of the polymer matrix structure on these mechanisms. It was found that the resin matrix structure influences the composite impact resistance in at least two ways. The integration of flexibilizers into the polymer chain structure tends to reduce the T sub g and the mechanical properties of the polymer. The reduction in the mechanical properties of the matrix does not enhance the composite impact resistance because it allows matrix controlled failure to initiate impact damage. It was found that when the instrumented dropweight impact tester is used as a means for assessing resin toughness, the resin toughness is enhanced by the ability of the clamped specimen to deflect enough to produce sufficient membrane action to support a significant amount of the load. The results of this study indicate that crossplied composite impact resistance is very much dependent on the matrix mechanical properties.

This work addresses the problem of multi length scale modeling of polymer matrix composites reinforced with high specific strength, high specific stiffness continuous aramid fibers. These composite materials are commonly used in various light weight protective systems the main requirement of which is a high level of penetration resistance against high kinetic energy projectiles (e.g. bullets, exploded mine propelled soil ejecta, fragments of improvised explosive devices, turbine blades, etc.). Within the proposed multi length scale modeling approach, the following distinct length scales have been identified and their respective mechanical constitutive relations derived and parameterized: (a) molecular chain; (b) fibril; (c) fiber; (d) yarn; (e) fabric/ply; (f) single lamina; (g) stacked lamina; and (h) laminate. In addition, issues related to identification of the type and the extent of data generated at a finer length scale to the adjacent coarser length scale, as well as seamless integration of different length scales into a unified material model, are addressed. Finally, results are presented pertaining to the implementation of the multi scale material model into a transient, nonlinear dynamics/finite element analysis of a few simplified ballistic impact scenarios.

This project was concerned with the link between transport and fracture in composite materials with emphasis on degradation of properties on aqueous exposure. The dependence of transport and fracture on volume fraction of a particulate filler was considered in terms of the percolation properties of the connected and unconnected particles. This report describes: validation of the percolation approach; mechanical properties ad effect of water absorption; electrical and gravimetric measurements; and ternary composites with glass and rubber.

The major objective of this material program is to develop an improved epoxy nanocomposite for carbon fiber-reinforced polymer matrix composite (CPMC) with higher temperature performance capability, mechanical performance, damage resistance, extreme environment corrosion resistance, and improved dimensional control. We proposed that a nanophase be introduced into specific components of an epoxy resin system, prior to cure, to provide improved Tg and mechanical strength of the composites. In this study, we used Cytec Engineered Materials (CEM) CYCOM 977-3, a high temperature damage tolerant tetrafunctional epoxy resin system; and three types of nanoparticles: chemically modified montmorillonite (MMT) organoclays, surface treated nanosilica, and surface modified carbon nanofibers (CNF) to create new types of epoxy nanocomposites. Wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) were used to determine the degree of dispersion. Dynamic mechanical thermal analysis (DMTA) was used to determine the Tg and complex modulus of the polymer nanocomposites. The TEM analyses indicated that the MMT clay, nanosilica, and CNF dispersed very well in the epoxy resin system. Evidence is presented that a nanophase is formed when nanoparticles such as surface treated clay, surface treated nanosilica, or carbon nanofibers are introduced into the epoxy resin. Higher Tg and complex modulus values from DMTA for the nanomodified materials are presented as evidence for nanophase presence in the epoxy resin system as compared to lower Tg and complex modulus for the epoxy resin control. The DMTA data of the neat epoxy nanosilica nanocomposite (2% Aerosil R202) show the highest Tg (258C) and the highest complex modulus (964 MPa). Five epoxy nanocomposites were selected to produce prepregs using AS4-6K carbon woven cloth at CEM. The prepregs were fabricated into composites.

This study program has defined design approaches and materials from which can be fabricated pyrostatic graphite/epoxy (Gr/Ep) laminates that show improved retention of graphite particulates when subjected to burning. Sixteen hybridized plus two standard Gr/Ep laminates were designed, fabricated, and tested in an effort to eliminate the release of carbon (graphite) fiber particles from burned/ burning, mechanically disturbed samples. (The term pyrostatic is defined as meaning mechanically intact in the presence of fire.) The main thrust of this program was aimed at the formulation of graphite particulate retentive laminates whose constituent materials, cost of fabrication, and physical and mechanical properties were not significantly different from existing Gr/Ep composites. Therefore, all but one laminate (a Celion graphite/bis-maleimide polyimide) were based on an off-the-shelf Gr/Ep, the AS-1/35O1-5A system. Of the 16 candidates studied, four thin (10-ply) and four thick (50-ply) hybridized composites are recommended. Panels of the selected laminates were delivered to the NASA-Lewis Research Center. jg p.3

A three-dimensional thermo-chemical simulation of the curing phase of Resin Transfer Molding (RTM) Process and process-induced stress and deformation analysis methodologies are developed. The mechanics model considers orthotropic and thermo-chemically varying viscoelastic stiffness of the composite material and varying boundary conditions during the process cycle. The residual stress and deformation profiles resulting from several processing histories including the effect of thermal expansion, and chemical shrinkage are studied. Several numerical simulations are performed to compare and validate the developed method with the existing solutions.

The mechanical properties of two neat resin systems for use in carbon fiber/epoxy composites were characterized. This included tensile and shear stiffnesses and strengths, coefficients of thermal and moisture expansion, and fracture toughness. Tests were conducted on specimens in the dry and moisture-saturated states, at temperatures of 23 deg C, 82 deg C, and 121 deg C. The neat resins tested were American Cyanamid 1806 and Union Carbide ERX-4901B(MPDA). Results were compared to previously tested neat resins. Four unidirectional carbon fiber-reinforced composites were mechanically characterized. Axial and transverse tension and in-plane shear strengths and stiffnesses were measured, as well as transverse coefficients of thermal and moisture expansion. Tests were conducted on dry specimens only at 23 deg C and 100 deg C. The materials tested were AS4/3502, AS6/5245-C, T300/BP907, and 06000/1806 unidirectional composites. Scanning electron microscopic examination of fracture surfaces was performed to permit the correlation of observed failure modes with the environmental test conditions.

A variety of environmental factors can influence the performance of advanced polymers and composites. In particular, exposure to a combination of moisture and elevated temperature can significantly alter properties. The extent of chemical and physical changes is a function of exposure time and the temperature and humidity of the environment. This work discusses the effects of chemical and physical aging of AFR700B, a high-temperature addition polyimide resin. Neat resin samples were isothermally aged for 500 and 1000 hours at 250 deg C in dry air, humid air, and dry nitrogen. Changes in the dynamic mechanical properties and weight of the resin samples after these different exposures are discussed. An accelerated aging process was developed to facilitate the study of hydrolytic degradation. The effect of degradation on the Tg, weight, and mechanical behavior is discussed. The use of a silicon-nitride moisture barrier proved ineffective.

Outline: Simulation approach, Generating Realistic Structures, Structural Ubiquities, Property Prediction and Analysis of governing Principles and Summary and Outlook.

Carbon nanotubes (CNTs) have been studied extensively since their discovery and demonstrated at the nanoscale superior mechanical, electrical and thermal properties in comparison to micro and macro scale properties of conventional engineering materials. This combination of properties suggests their potential to enhance multi-functionality of composites in regions of primary structures on aerospace vehicles where lightweight materials with improved thermal and electrical conductivity are desirable. In this study, hybrid multifunctional polymer matrix composites were fabricated by interleaving layers of CNT sheets into Hexcel® IM7/8552 prepreg, a well-characterized toughened epoxy carbon fiber reinforced polymer (CFRP) composite. The resin content of these interleaved CNT sheets, as well as ply stacking location were varied to determine the effects on the electrical, thermal, and mechanical performance of the composites. The direct-current electrical conductivity of the hybrid CNT composites was characterized by in-line and Montgomery four-probe methods. For [0](sub 20) laminates containing a single layer of CNT sheet between each ply of IM7/8552, in-plane electrical conductivity of the hybrid laminate increased significantly, while in-plane thermal conductivity increased only slightly in comparison to the control IM7/8552 laminates. Photo-microscopy and short beam shear (SBS) strength tests were used to characterize the consolidation quality of the fabricated laminates. Hybrid panels fabricated without any pretreatment of the CNT sheets resulted in a SBS strength reduction of 70 percent. Aligning the tubes and pre-infusing the CNT sheets with resin significantly improved the SBS strength of the hybrid composite To determine the cause of this performance reduction, Mode I and Mode II fracture toughness of the CNT sheet to CFRP interface was characterized by double cantilever beam (DCB) and end notch flexure (ENF) testing, respectively. Results are compared to the control IM7/8552 laminate.