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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

New Insights on the Mechanical Characterization of Kerogen-Rich Shale, KRS

In the past decade, mechanical, physical, and chemical characterization of reservoir shale rocks, such as the Woodford shale, which is kerogen-rich shale (KRS), has moved toward micro- and nanoscale testing and analyses. Nanoindentation equipment is now widely used in many industrial and university laboratories to measure shale anisotropic Young’s moduli, kerogen stiffness, plastic yield parameters, and other isotropic and anisotropic poromechanical and viscoelastic properties. However, to date, failure analyses of KRS and the effects of organic components on the tensile strength have not been observed or measured at the micro- or nanoscales. In this study, preserved kerogen-rich Woodford shale samples manufactured in micro-beam and micro-pillar geometries were mechanically tested and brought to failure in tension and compression, respectively. These tests were conducted in situ using a nanoindenter inside a scanning electron microscope (SEM). The load versus displacement curves of prismatic micro-cantilever beams were analyzed in light of high-resolution images collected during tensile fracture initiation, propagation, and ultimately sample failure. The micro-pillar geometries were subjected to a uniaxial compressive load and were also brought to failure while capturing measurements of stress and strain. It was found that, within just a few hundred microns of the KRS microcantilever beams, both brittle and ductile failure modes were observed. In the ductile plastic domain, strain-softening and strain-hardening behaviors were identified and characterized. These were not due to confining stress variations, but due to the volume of the organic matter and the way it is interlaced with the shale minerals in and around the failure planes. The tensile strength characteristics and the large modulus of toughness of kerogen, which is a cross-linked polymer, definitely weigh heavily in our engineering field applications, such as hydraulic fracking, which is a Mode I tensile fracture opening and propagation phenomenon. This practice demands that, due to the complex composite nature of KRS, mechanical characterization be not only for unconfined compressive strength but also for unconfined tensile strength and moduli of ruptures. At the end of this study, the need for nanometer scale mechanical characterization of KRS will become apparent. These nano- and micro-scale shale failure tests reinforce our previous understanding of the heterogeneous composite nature of Woodford KRS and its complex behavior, as well as other source shale reservoir formations.

58 GEOSCIENCES↗
DOE OSTI2016

The granular and polymer composite nature of kerogen-rich shale

In the past decade, mechanical, physical, and chemical characterization of reservoir shale rocks, such as the Woodford shale, which is kerogen-rich shale (KRS), has moved toward micro- and nanoscale testing and analyses. Nanoindentation equipment is now widely used in many industrial and university laboratories to measure shale anisotropic Young’s moduli, kerogen stiffness, plastic yield parameters, and other isotropic and anisotropic poromechanical and viscoelastic properties. However, to date, failure analyses of KRS and the effects of organic components on the tensile strength have not been observed or measured at the micro- or nanoscales. In this study, preserved kerogen-rich Woodford shale samples manufactured in micro-beam and micro-pillar geometries were mechanically tested and brought to failure in tension and compression, respectively. These tests were conducted in situ using a nanoindenter inside a scanning electron microscope (SEM). The load versus displacement curves of prismatic micro-cantilever beams were analyzed in light of high-resolution images collected during tensile fracture initiation, propagation, and ultimately sample failure. The micro-pillar geometries were subjected to a uniaxial compressive load and were also brought to failure while capturing measurements of stress and strain. It was found that, within just a few hundred microns of the KRS microcantilever beams, both brittle and ductile failure modes were observed. In the ductile plastic domain, strain-softening and strain-hardening behaviors were identified and characterized. These were not due to confining stress variations, but due to the volume of the organic matter and the way it is interlaced with the shale minerals in and around the failure planes. The tensile strength characteristics and the large modulus of toughness of kerogen, which is a cross-linked polymer, definitely weigh heavily in our engineering field applications, such as hydraulic fracking, which is a Mode I tensile fracture opening and propagation phenomenon. This practice demands that, due to the complex composite nature of KRS, mechanical characterization be not only for unconfined compressive strength but also for unconfined tensile strength and moduli of ruptures. At the end of this study, the need for nanometer scale mechanical characterization of KRS will become apparent. Furthermore, these nano- and micro-scale shale failure tests reinforce our previous understanding of the heterogeneous composite nature of Woodford KRS and its complex behavior, as well as other source shale reservoir formations.

58 GEOSCIENCES↗
NASA NTRS1998

Evaluation of Composite Honeycomb Sandwich Panels Under Compressive Loads at Elevated Temperatures

Fourteen composite honeycomb sandwich panels were tested to failure under compressive loading. The test specimens included panels with both 8 and 24-ply graphite-bismaleimide composite facesheets and both titanium and graphite-polyimide core materials. The panels were designed to have the load introduced through fasteners attached to pairs of steel angles on the ends of the panels to simulate double shear splice joints. The unloaded edges were unconstrained. Test temperatures included room temperature, 250F, and 300F. For the room and 250F temperature tests, the 24-ply specimen failure strains were close to the unnotched allowable strain values and failure loads were well above the design loads. However, failure strains much lower than the unnotched allowable strain values, and failure loads below the design loads were observed with several of the 8-ply specimens. For each individual test temperature, large variations in the failure strains and loads were observed for the 8-ply specimens. Dramatic decreases in the failure strains and loads were observed for the 24-ply specimens as the test temperature was increased from 250F to 300F. All 8-ply specimens appeared to have failed in a facesheet strength failure mode for all test temperatures. The 24-ply specimens displayed appreciably greater amounts of bending prior to failure than the 8-ply specimens, and panel buckling occurred prior to facesheet strength failure for the 24-ply room and 250F temperature tests.

Walker, Sandra P.↗
NASA NTRS2020

Comparison of Compressive Stress-Strain Responses at High Temperatures for Representative Single Crystal and Polycrystal Superalloys

Polycrystalline disk superalloys and single crystal blade superalloys have divergent grain and precipitate microstructures but can each display reduced strength and increasing deformation for certain test conditions at high temperatures. To allow thermo-mechanical processes such as forging and rolling to be applied, favorable temperatures and strain rates must first be identified using compression testing. The objective of this study was to perform compression tests at high temperatures on a polycrystalline disk superalloy and a single crystal blade superalloy in order to compare their stress-strain responses for given test conditions and determine preferred conditions. It was determined that the conditions required for stable flow differed significantly between the polycrystalline and single crystal superalloys. The conditions leading to unstable flow were also identified for each alloy. The microstructural deformation modes for both stable and unstable flow are discussed.

compression, superalloy, turbine engine↗
NASA NTRS2003

Thermal Effects on the Compressive Behavior of IM7/PET15 Laminates

The effect of changing operating temperature on the compressive response of IM7/PETI5 composite laminates is investigated within this paper. The three temperatures evaluated for this study were 129 C, 21 C, and 177 C, a spectrum from cryogenic to an elevated operating temperature. Laminate compressive strength property testing was conducted using the Wyoming Combined Load Compression fixture to generate strength data at the three operating temperatures of interest for several lay-ups. A three-dimensional finite element analysis model of a [90/0]8s composite laminate subject to compressive loading is developed. The model is used to study the key attributes of the laminate that significantly influence the state of stress in the laminate. Both the resin rich layer located between lamina and the thermal residual stresses present in the laminate due to curing are included in the analysis model. For the laminate modeled, the effect of modeling temperature dependent material properties was determined to be insignificant for the operating temperatures studied. Simply using the material properties measured at the operating temperature of interest was sufficient for predicting stresses accurately in a linear analysis for the current problem. The three-dimensional analysis results revealed that the application of an applied compressive axial load in the 0-degree direction decreased the interlaminar stresses present in the laminate initially due to curing. Therefore, failure was concluded not be attributable to the interlaminar stresses in the composite laminate being studied when a compressive load is applied. The magnitude of the measured laminate compressive strength change with a change in temperature is concluded to be dominated by the change in the lamina compressive axial strength with a change in temperature.

Walker, Sandra Polesky↗
NASA NTRS1992

Compression failure of angle-ply laminates

Test results from the compression loading of (+ or - Theta/ - or + Theta)(sub 6s) angle-ply IM7-8551-7a specimens, 0 less than or = Theta less than or = 90 degs, are presented. The observed failure strengths and modes are discussed, and typical stress-strain relations shown. Using classical lamination theory and the maximum stress criterion, an attempt is made to predict failure stress as a function of Theta. This attempt results in poor correlation with test results and thus a more advanced model is used. The model, which is based on a geometrically nonlinear theory, and which was taken from previous work, includes the influence of observed layer waviness. The waviness is described by the wave length and the wave amplitude. The theory is briefly described and results from the theory are correlated with test results. It is shown that by using levels of waviness observed in the specimens, the correlation between predictions and observations is good.

Peel, L. D.↗
NASA NTRS1995

Effects of Yarn Crimping on Braided Composite Design Allowables

Braided composite materials are currently being evaluated for wing skin stiffeners on commercial aircraft. These carbon-fiber/epoxy materials allow for low-cost manufacturing while maintaining high strength-to-weight and stiffness-to-weight ratios. The proposed braid architecture consists of axial carbon fiber yarns and braider carbon fiber yarns making 60 deg to 70 deg angles with respect to the axial yarns. These 2-D triaxial braids are produced as long, continuous tubes, which are flattened, cut, and stacked to produce the desired part thickness and shape. When infiltrated with epoxy resin and cured under a compaction pressure, the fiber yarns become crimped, allowing for higher fiber packing. Although high fiber packing is desirable, yarn crimping (especially in the axial fiberyarns) is undesirable. Significant axial yarn crimp angles (greater than 10 deg) have been measured in braided composites. Comparable levels of crimping have been found to produce significant compressive strength reductions in laminated composites consisting of planar fiber sheets. Thus, axial yarn crimping is suspected of producing significant reductions in compressive strength allowables for braided composites. The objective of this research is to quantify the reduction in compressive strength as a function of axial yarn crimp severity. Since crimp severity can be reduced by lowering the compaction pressure during curing, the resulting compressive strengths may be used to determine optimum processing conditions. A 'cure-on-the-loom' manufacturing process was developed to produce braided composites with controlled levels of crimping. This method allowed for controlled levels of tension to be placed on the axial yarns and maintained during the curing process. With increasing tension, the crimp severity in the axial yarns was reduced. Thus, varying crimp severities were produced ranging from conventional levels (greater than 10 deg) to virtually straight axial yarns. Test results indicate that a 30% increase in compressive strength is obtainable by eliminating axial yarn crimping. Further compression testing is underway to quantify the relationship between crimp severity and compressive strength. Additional testing is planned to investigate the effect of crimping on the open-hole compressive strength, often considered a more significant design allowable.

Adams, Dan↗
NASA NTRS2004

A Preliminary Study on the Toxic Combustion Products Testing of Polymers Used in High-Pressure Oxygen Systems

One likely cause of polymer ignition in a high-pressure oxygen system is adiabatic-compression heating of polymers caused by pneumatic impact. Oxidative _ pyrolysis or combustion of polymers in a high-pressure oxygen system could generate toxic gases. This paper reports the preliminary results of toxic combustion product testing of selected polymers in a pneumatic-impact test system. Five polymers commonly used in high-pressure oxygen systems, Nylon 6/6, polychlorotrifluoroethylene (CTFE), polytetrafluoroethylene (PTFE), fluoroelastomer (Viton(TradeMark) A), and nitrile rubber (Buna N), were tested in a pneumatic-impact test system at 2500- or 3500-psia oxygen pressure. The polymers were ignited and burned, then combustion products were collected in a stainless-steel sample bottle and analyzed by GC/MS/IRD, GC/FID, and GC/Methanizer/FID. The results of adiabatic-compression tests show that combustion of hydrocarbon polymers, nitrogen-containing polymers, and halogenated polymers in high-pressure oxygen systems are relatively complete. Toxicity of the combustion product gas is presumably much lower than the combustion product gas generated from ambient-pressure oxygen (or air) environments. The NASA-Lewis equilibrium code was used to determine the composition of combustion product gas generated from a simulated, adiabatic-compression test of nine polymers. The results are presented and discussed.

Hshieh, Fu-Yu↗
NASA NTRS1992

Hydrogen no-vent fill testing in a 5 cubic foot (142 liter) tank using spray nozzle and spray bar liquid injection

A total of 38 hydrogen no-vent fill tests were performed in this test series using various size spray nozzles and a spray bar with different hole sizes in a 5 cubic foot receiver tank. Fill levels of 90 percent by volume or greater were achieved in 26 of the tests while maintaining a receiver tank pressure below 30 psia. Spray nozzles were mounted at the top of the tank, whereas, the spray bar was centered in the tank axially. The spray nozzle no-vent fills demonstrated tank pressure and temperature responses comparable to previous test series. Receiver tank pressure responses for the spray bar configuration were similar to the spray nozzle tests with the pressure initially rising rapidly, then leveling off as vapor condenses onto the discharging liquid streams, and finally ramping up near the end of the test due to ullage compression. Both liquid injection techniques tested were capable of filling the receiver tank to 90 percent under variable test conditions. Comparisons between the spray nozzle and spray bar configurations for well matched test conditions indicate the spray nozzle injection technique is more effective in minimizing the receiving tank pressure throughout a no-vent fill compared to the spray bar under normal gravity conditions.

Moran, Matthew E.↗
NASA NTRS1992

Hydrogen no-vent testing in a 5 cubic foot (142 liter) tank using spray nozzle and spray bar liquid injection

A total of 38 hydrogen no-vent fill tests were performed in this test series using various size spray nozzles and a spray bar with different hole sizes in a 5 cubic foot receiver tank. Fill levels of 90 percent by volume or greater were achieved in 26 of the tests while maintaining a receiver tank pressure below 30 psia. Spray nozzles were mounted at the top of the tank, whereas, the spray bar was centered in the tank axially. The spray nozzle no-vent fills demonstrated tank pressure and temperature responses comparable to previous test series. Receiver tank pressure responses for the spray bar configuration were similar to the spray nozzle tests with the pressure initially rising rapidly, then leveling off as vapor condenses onto the discharging liquid streams, and finally ramping up near the end of the test due to ullage compression. Both liquid injection techniques tested were capable of filling the receiver tank to 90 percent under variable test conditions. Comparisons between the spray nozzle and spray bar configurations for well matched test conditions indicate the spray nozzle injection technique is more effective in minimizing the receiving tank pressure throughout a no-vent fill compared to the spray bar under normal gravity conditions.

Moran, Matthew E.↗
NASA NTRS1995

Out-of-plane properties

This paper summarizes three areas of research which were performed to characterize out-of-plane properties of composite materials. In the first investigation, a series of tests was run to characterize the through-the-thickness tensile strength for a variety of composites that included 2D braids, 2D and 3D weaves, and prepreg tapes. A new test method based on a curved beam was evaluated. Failures were significantly different between the 2D materials and the 3D weaves. The 2D materials delaminated between layers due to out-of-plane tensile stresses while the 3D weaves failed due to the formation of radial cracks between the surface plies caused by high circumferential stresses along the inner radius. The strength of the 2D textile composites did not increase relative to the tapes. Final failure in the 3D weaves was caused by a circumferential crack similar to the 2D materials and occurred at a lower bending moment than in other materials. The early failures in the 3D weaves were caused by radial crack formation rather than a low through-the-thickness strength. The second investigation focused on the development of a standard impact test method to measure impact damage resistance. The only impact tests that currently exist are compression after impact (CAI) tests which incorporate elements of both damage resistance and damage tolerance. A new impact test method is under development which uses a quasi-static indentation (QSI) test to directly measure damage resistance. Damage resistance is quantified in terms of the contact force to produce a unit of damage where a metric for damage may be area in C-scan, depth of residual dent , penetration, damage growth, etc. A final draft of an impact standard that uses a QSI test method will be presented to the ASTM Impact Task Group on impact. In the third investigation, the impact damage resistance behavior of a variety of textile materials was studied using the QSI test method. In this study, the force where large damage initiates was measured and the delamination size as a function of force was determined. The force to initiate large damage was significantly lower in braids and weaves. The delamination diameter - impact forace relationship was quanitfied using a damage resistance parameter, Q(*), which related delamination diameter to imapct force over a range of delamination sizes. Using this Q(*) parameter to rate the materials, the stitched uniweaves, toughened epoxy tapes, and through-the-thickness orthogonal interlock weave were the most damage resistant.

Jackson, Wade C.↗
NASA NTRS1984

Durability and damage tolerance of Large Composite Primary Aircraft Structure (LCPAS)

Analysis and testing addressing the key technology areas of durability and damage tolerance were completed for wing surface panels. The wing of a fuel-efficient, 200-passenger commercial transport airplane for 1990 delivery was sized using graphite-epoxy materials. Coupons of various layups used in the wing sizing were tested in tension, compression, and spectrum fatigue with typical fastener penetrations. The compression strength after barely visible impact damage was determined from coupon and structural element tests. One current material system and one toughened system were evaluated by coupon testing. The results of the coupon and element tests were used to design three distinctly different compression panels meeting the strength, stiffness, and damage-tolerance requirements of the upper wing panels. These three concepts were tested with various amounts of damage ranging from barely visible impact to through-penetration. The results of this program provide the key technology data required to assess the durability and damage-tolerance capability or advanced composites for use in commercial aircraft wing panel structure.

Mccarty, John E.↗
NASA NTRS1994

Performance considerations for the application of the lossless browse and residual model

A hybrid lossless compression model employing both the (lossy) JPEG DCT algorithm and one of a selection of lossless image compression methods has been tested. The hybrid model decomposes the original image into a low-loss quick-look browse and a residual image. The lossless compression methods tested in the model are Huffman, arithmetic, LZW, lossless JPEG, and diagonal coding. For both the direct and the hybrid application of these lossless methods, the compression ratios (CR's) are calculated and compared on three test images. For each lossless method tested, the hybrid model had no more than a nominal loss in compression efficiency relative to the direct approach. In many cases, the hybrid model provided a significant compression gain. When used in the hybrid model, lossless JPEG outperformed the other lossless methods over a broad range of browse image qualities.

Abbott, Walter D., III↗
DOE OSTI2022

Effect of Moisture and Feedstock Variability on the Rheological Behavior of Corn Stover Particles

Continuous feeding, processing, and handling of biomass powders is pivotal to the economic viability of integrated biorefineries. However, current challenges associated with the operational reliability of bulk solids handling and transport greatly impact the process economics and ultimately the widespread commercialization of integrated biorefineries. In this work, we examine the effect of moisture and feedstock variability on the flow behavior of corn stover biomass particles. The total flow energy, compressibility, shear properties, and wall friction angles were measured for corn stover samples A and B containing 0%, 15%, 25%, 50%, and 75% (mass fraction) moisture contents using a FT4 powder rheometer. In general, the flowability of both A and B was reduced when moisture was present as indicated by the stability and variable flow rate, compressibility, and shear tests. The 15% moisture sample had the highest flow energy, revealing the interplay between the increased surface tension and looser packing both of which were caused by liquid bridging. The 75% moisture sample had the highest compressibility and the lowest flowability factor (ff c ). The trend in wall friction angle was found to be dependent upon the surface hydrophobicity of the wall material. The wall friction angle on the hydrophilic, stainless-steel surface increased with moisture and therefore poses additional handling challenges. On the other hand, the wall friction angle on the hydrophobic polymer surfaces were the lowest for samples with intermediate moisture contents. Sample B had greater bulk density, smaller compressibility, and greater flowability than the sample A , as suggested by the compressibility and shear tests. The wall friction angle of sample B was higher than or equal to that of sample A depending on both the type and the surface roughness of the wall material.

09 BIOMASS FUELS↗
NASA NTRS1973

An investigation of the compressive strength of PRD-49-3/Epoxy composites

The development of unidirectional fiber composite materials is discussed. The mechanical and physical properties of the materials are described. Emphasis is placed in analyzing the compressive behavior of composite materials and developing methods for increasing compressive strength. The test program for evaluating the various procedures for improving compressive strength are reported.

Kulkarni, S. V.↗
NASA NTRS1984

Effect of Impact Damage and Open Holes on the Compression Strength of Tough Resin/high Strain Fiber Laminates

Tests to assess the performance of composite structures damaged by impact or containing local discontinuities such as cutouts are discussed. In particular, two plate specimen test configurations which were developed to define the serverity of compression strength reduction are described; one for impact damage and the other open hole specimens. The test technique for impact specimens involves damaging the plate at selected energies, measuring the size of damage by ultrasonic C-scan techniques and measuring the residual strength in a compression load test. Open-hole specimen compression tests are conducted for several different hole diameters and the failure strain and load and mode of failure recorded. The plate specimen used in these tests is designed with length, width, thickness and laminate stiffness to ensure that overall plate buckling is not responsible for initiating failure.

Williams, J. G.↗
NASA NTRS1992

The Utilization of Advanced Composites in Military Aircraft

The purpose of this workshop was to identify the current state of the art in key issues related to compression loading and fluid effects in composite materials. In the area of compression loading, there was considerable concern over the different results obtained from various test methods. It was agreed that failure modes produced by the various test methods along with a better fundamental understanding of compression failure were key issues in the development of compression test methods. In the area of fluid effects, a lack of a comprehensive data base hampers identification of key mechanisms leading to fluid degradation. This is further complicated by the fact that interactions depend on the fluid and composite under consideration.

Advisory Group for Aerospace Research and Developm↗