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NASA NTRS1979

Tests of a protective shell passive release mechanism for hypersonic wind-tunnel models

A protective shell mechanism for wind tunnel models was developed and tested. The mechanism is passive in operation, reliable, and imposes no new structural design changes for wind tunnel models. Methods of predicting the release time and the measured loads associated with the release of the shell are given. The mechanism was tested in a series of wind tunnel tests to validate the removal process and measure the pressure loads on the model. The protective shell can be used for wind tunnel models that require a step input of heating and loading such as a thin skin heat transfer model. The mechanism may have other potential applications.

Puster, R. L.↗

NASA NTRS1985

Tensile testing apparatus

An improved mechanical extensometer is described for use with a constant load creep test machine. The dead weight of the extensometer is counterbalanced by two pairs of weights connected through a pulley system and to rod extension and leading into the furnace where the test sample is undergoing elevated temperature (above 500 F.) tensile testing. Novel gripper surfaces, conical tip and flat surface are provided in each sampling engaging platens to reduce the grip pressure normally required for attachment of the extensometer to the specimen and reduce initial specimen bending normally associated with foil-gage metal testing.

Blackburn, L. B.↗

NASA NTRS1974

Low voltage 30-cm ion thruster development

The basic goal was to advance the development status of the 30-cm electron bombardment ion thruster from a laboratory model to a flight-type engineering model (EM) thruster. This advancement included the more conventional aspects of mechanical design and testing for launch loads, weight reduction, fabrication process development, reliability and quality assurance, and interface definition, as well as a relatively significant improvement in thruster total efficiency. The achievement of this goal was demonstrated by the successful completion of a series of performance and structural integrity (vibration) tests. In the course of the program, essentially every part and feature of the original 30-cm Thruster was critically evaluated. These evaluations, led to new or improved designs for the ion optical system, discharge chamber, cathode isolator vaporizer assembly, main isolator vaporizer assembly, neutralizer assembly, packaging for thermal control, electrical terminations and structure.

King, H. J.↗

NASA NTRS1987

Energy-Absorbing Passenger Seat for Aircraft

Development of energy-absorbing passenger seat, designed to minimize injury in commercial-aircraft crash, part of joint FAA/NASA controlledimpact flight test of transport-category commercial aircraft. Modified seat mechanism collapses under heavy load to absorb impact energy and thereby protect passenger. Results of simulation tests indicate probability of passenger survival high. Proposed seat mechanism mitigates passenger injuries by reducing impact forces in crash.

Eichelberger, C. P.↗

NASA NTRS1997

Experimental Investigation of a Graphite-Composite Intertank Section for a Reusable Launch Vehicle

The use of graphite-composites as primary structure is essential for the development of a cost effective single-stage-to-orbit reusable launch vehicle (RLV). A full-scale segment of a graphite-composite intertank was designed and fabricated by an industry team and tested at NASA Langley Research Center as a part of the RLV technology development program. The intertank test component was approximately 3.0 m long by 6.7 m wide and included slightly less than a 90deg section of a cylindrical intertank. The test article was fabricated using graphite-bismaelimide composite material and consisted of a hat-stiffened skin with five ring frames. The stiffeners were secondarily bonded to the panel skin and the ring frames were mechanically attached. The test article was loaded to failure with a uniform compression load applied by 21 individually controlled hydraulic actuators. Resistance strain gages, linear variable differential transformers and video cameras were used to measure and record the test results. A linear f d t e element analysis of the test article and test fixture was performed. The test results verified the structural integrity cf the intertank test article up to the design limit load. However, the test article failed in general skin buckling between the ring frames at a load 1.08 times design limit load. This load was considerably lower than the expected failure load. The cause of premature failure is being investigated. Good correlation of the test and analysis results was obtained for loads up to the design limit load.

Sawyer, James Wayne↗

NASA NTRS2020

Design and Development of a Robust Chuck Mechanism for the Mars2020 Coring Drill

The Sampling and Caching Subsystem (SCS) onboard the Mars2020 rover includes a coring drill that can perform coring, abrasion, and regolith collection operations. The coring drill requires a chuck mechanism to allow for the changing of the bits needed to perform sampling. The chuck mechanism must be capable of securely connecting a bit under drilling, rover slip, and pullout loads, but also readily release a bit after application of these loads. The Mars2020 chuck consists of a ball lock mechanism that allows for robust engagement and release of bit assemblies that is preloaded to ensure a secure, stiff connection between the bit assembly and the rest of the corer. To prevent jamming, the chuck incorporates rollers to preload the ball lock. The rollers are mounted onto a flexured cam that minimizes changes in internal mechanism loads that result from thermally induced dimensional changes, further mitigating the potential for jamming. The chuck mechanism is moved between engaged, disengaged, and loose chuck positions by rotating the cam with a gearmotor that incorporates a magnetic detent brake that prevents inadvertent mechanism motion under design loads. Ongoing testing is occurring on the qualification model in a dirty environment while coring and abrading rocks in a Mars representative environment.

Barletta, Anthony↗

NASA NTRS2015

Preparation for Testing a Multi-Bay Box Subjected to Combined Loads

The COmbined Loads Test System (COLTS) facility at NASA Langley Research Center provides a test capability to help develop validated structures technologies. The test machine was design to accommodate a range of fuselage structures and wing sections and subject them to both quasistatic and cyclic loading conditions. The COLTS facility is capable of testing fuselage barrels up to 4.6 m in diameter and 13.7 m long with combined mechanical, internal pressure, and thermal loads. The COLTS facility is currently being prepared to conduct a combined mechanical and pressure loading for a multi-bay pressure box to experimentally verify the structural performance of a composite structure which is 9.1 meters long and representative of a section of a hybrid wing body fuselage section in support of the Environmentally Responsible Aviation Project at NASA. This paper describes development of the multi-bay pressure box test using the COLTS facility. The multi-bay test article will be subjected to mechanical loads and internal pressure loads up to design ultimate load. Mechanical and pressure loads will be applied independently in some tests and simultaneously in others.

Rouse, Marshall↗

NASA NTRS1991

Fracture mechanics analysis for various fiber/matrix interface loadings

Fiber/matrix (F/M) cracking was analyzed to provide better understanding and guidance in developing F/M interface fracture toughness tests. Two configurations, corresponding to F/M cracking at a broken fiber and at the free edge, were investigated. The effects of mechanical loading, thermal cooldown, and friction were investigated. Each configuration was analyzed for two loadings: longitudinal and normal to the fiber. A nonlinear finite element analysis was performed to model friction and slip at the F/M interface. A new procedure for fitting a square-root singularity to calculated stresses was developed to determine stress intensity factors (K sub I and K sub II) for a bimaterial interface crack. For the case of F/M cracking at a broken fiber with longitudinal loading, crack tip conditions were strongly influenced by interface friction. As a result, an F/M interface toughness test based on this case was not recommended because nonlinear data analysis methods would be required. For the free edge crack configuration, both mechanical and thermal loading caused crack opening, thereby avoiding frictional effects. A F/M interface toughness test based on this configuration would provide data for K(sub I)/K(sub II) ratios of about 0.7 and 1.6 for fiber and radial normal loading, respectively. However, thermal effects must be accounted for in the data analysis.

Naik, R. A.↗

NASA NTRS1991

Fracture mechanics analysis for various fiber/matrix interface loadings

Fiber/matrix (F/M) cracking was analyzed to provide better understanding and guidance in developing F/M interface fracture toughness tests. Two configurations, corresponding to F/M cracking at a broken fiber and at the free edge, were investigated. The effects of mechanical loading, thermal cooldown, and friction were investigated. Each configuration was analyzed for two loadings: longitudinal and normal to the fiber. A nonlinear finite element analysis was performed to model friction and slip at the F/M interface. A new procedure for fitting a square-root singularity to calculated stresses was developed to determine stress intensity factors (K sub I and K sub II) for a bimaterial interface crack. For the case of F/M cracking at a broken fiber with longitudinal loading, crack tip conditions were strongly influenced by interface friction. As a result, an F/M interface toughness test based on this case was not recommended because nonlinear data analysis methods would be required. For the free edge crack configuration, both mechanical and thermal loading caused crack opening, thereby avoiding frictional effects. An F/M interface toughness test based on this configuration would provide data for K(sub I)/K(sub II) ratios of about 0.7 and 1.6 for fiber and radial normal loading, respectively. However, thermal effects must be accounted for in the data analysis.

Naik, R. A.↗

NASA NTRS1992

Fracture mechanics analysis for various fiber/matrix interface loadings

Fiber/matrix (F/M) cracking was analyzed to provide better understanding and guidance in developing F/M interface fracture toughness tests. Two configurations, corresponding to F/M cracking at a broken fiber and at the free edge, were investigated. The effects of mechanical loading, thermal cooldown, and friction were investigated. Each configuration was analyzed for two loadings: longitudinal and normal to the fiber. A nonlinear finite element analysis was performed to model friction and slip at the F/M interface. A new procedure for fitting a square-root singularity to calculated stresses was developed to determine stress intensity factors (K sub I and K sub II) for a bimaterial interface crack. For the case of F/M cracking at a broken fiber with longitudinal loading, crack tip conditions were strongly influenced by interface friction. As a result, an F/M interface toughness test based on this case was not recommended because nonlinear data analysis methods would be required. For the free edge crack configuration, both mechanical and thermal loading caused crack opening, theory avoiding fractional effects. A F/M interface toughness test based on this configuration would provide data for K(sub I/K(sub II) ratios of about 0.7 and 1.6 for fiber and radial normal loading, respectively. However, thermal effects must be accounted for in the data analysis.

Naik, Rajiv A.↗

NASA NTRS1971

An experimental study of the mechanism of failure of rocks under borehole jack loading

Laboratory and field tests with an experimental jack and an NX-borehole jack are reported. The following conclusions were made: Under borehole jack loading, a circular opening in a brittle solid fails by tensile fracturing when the bearing plate width is not too small. Two proposed contact stress distributions can explain the mechanism of tensile fracturing. The contact stress distribution factor is a material property which can be determined experimentally. The borehole tensile strength is larger than the rupture flexural strength. Knowing the magnitude and orientation of the in situ stress field, borehole jack test results can be used to determine the borehole tensile strength. Knowing the orientation of the in situ stress field and the flexural strength of the rock substance, the magnitude of the in situ stress components can be calculated. The detection of very small cracks is essential for the accurate determination of the failure loads which are used in the calculation of strengths and stress components.

Van, T. K.↗

NASA NTRS1993

Micromechanical simulation of damage progression in carbon phenolic composites

Carbon/phenolic composites are used extensively as ablative insulating materials in the nozzle region of solid rocket motors. The current solid rocket motor (RSRM) on the space shuttle is fabricated from woven rayon cloth which is carbonized and then impregnated with the phenolic resin. These plies are layed up in the desired configuration and cured to form the finished part. During firing, the surface of the carbon/phenolic insulation is exposed to 5000 F gases from the rocket exhaust. The resin pyrolizes and the material chars to a depth which progresses with time. The rate of charring and erosion are generally predictable, and the insulation depth is designed to allow adequate safety margins over the firing time of the motor. However, anomalies in the properties and response of the carbon/phenolic materials can lead to severe material damage which may decrease safety margins to unacceptable levels. Three macro damage modes which were observed in fired nozzles are: ply lift, 'wedge out', and pocketing erosion. Ply lift occurs in materials with plies oriented nearly parallel to the surface. The damage occurs in a region below the charred material where material temperatures are relatively low - about 500 F. Wedge out occurs at the intersection of nozzle components whose plies are oriented at about 45 deg. The corner of the block of material breaks off along a ply interface. Pocketing erosion occurs in material with plies oriented normal to the surface. Thermal expansion is restrained in two directions resulting in large tensile strains and material failure normal to the surface. When a large section of material is removed as a result of damage, the insulation thickness is reduced which may lead to failure of the nozzle due to excessive heating of critical components. If these damage events cannot be prevented with certainty, the designer must increase the thickness of the insulator thus adding to both weight and cost. One of the difficulties in developing a full understanding of these macro damage mechanisms is that the loading environment and the material response to that environment are extremely complex. These types of damage are usually only observed in actual motor firings. Therefore, it is difficult and expensive to evaluate the reliability of new materials. Standard material tests which measure mechanical and thermal properties of test specimens can only provide a partial picture of how the material will respond in the service environment. The development of the ANALOG test procedure which can combine high heating rates and mechanical loads on a specimen will improve the understanding of the interactive effects of the various loads on the system. But a mechanistic model of material response which can account for the heterogeneity of the material, the progression of various micromechanical damage mechanisms, and the interaction of mechanical and thermal stresses on the material is required to accurately correlate material tests with response to service environments. A model based on fundamental damage mechanisms which is calibrated and verified under a variety of loading conditions will provide a general tool for predicting the response of rocket nozzles. The development of a micromechanical simulation technique was initiated and demonstrated to be effective for studying across-ply tensile failure of carbon/phenolic composites.

Slattery, Kerry T.↗

NASA NTRS1996

Thermomechanical Multiaxial Fatigue Testing Capability Developed

Structural components in aeronautical gas turbine engines typically experience multiaxial states of stress under nonisothermal conditions. To estimate the durability of the various components in the engine, one must characterize the cyclic deformation and fatigue behavior of the materials used under thermal and complex mechanical loading conditions. To this end, a testing protocol and associated test control software were developed at the NASA Lewis Research Center for thermomechanical axial-torsional fatigue tests. These tests are to be performed on thin-walled, tubular specimens fabricated from the cobalt-based superalloy Haynes 188. The software is written in C and runs on an MS-DOS based microcomputer.

Source record↗

NASA NTRSDate not supplied

Experimental Methods Using Force Application of A Single Boom for A 500-M²-Class Solar Sail

Solar sailing missions rely on deployable systems for large area-to-mass ratios once in space, while still being small enough for launcher envelopes in the stowed configuration. Many of these deployable systems feature booms that are flattened and subsequently coiled onto a spool / hub. As part of a collaborative deployable space structures research effort between the National Aeronautics and Space Administration (NASA) and German Aerospace Center (DLR), a boom deployment system for a future 500 m² solar sail has been developed. To achieve the respective solar sail size goal, 16.5-m-long booms produced by NASA were integrated into a DLR-designed deployer mechanism. This considerable size, as well as the lightweight construction of the booms and respective deployable systems makes testing on the ground a significant challenge. Some systems for gravity compensation as well as vertical testing to minimize the influence of gravity have been used in the past. However, an uncertainty factor remains towards the behaviour in the space environment. The focus of this paper is the load application testing of the integrated boom-deployment mechanism system under microgravity condition, as well as a comparison to vertical testing under gravity. Testing in microgravity was performed during a parabolic flight test inside an aircraft and it included stowage and full deployment of a single boom along the longitudinal axis of the aircraft. The load application was split into two categories: static testing, which induced a linear force ramp to the static boom for either compression or compression-bending; and dynamic testing, which applied a constant force to a boom during extension provided by the deployer mechanism. Both types of tests were performed multiple times at two distinct lengths of the boom, fully deployed (12.76 m) and ~28.6 % deployed (3.65 m). More parameters that are vital to the test philosophy are the angles of attack in the force application and the highest force applied. The data acquisition used for the applied load and deflection measurements of the boom is also presented.

Martin Richter↗

NASA NTRSDate not supplied

Experimental Methods Using Force Application of A Single Boom for A 500-M²-Class Solar Sail

Martin Richter↗

NASA NTRS2007

Apparent-Strain Correction for Combined Thermal and Mechanical Testing

Combined thermal and mechanical testing requires that the total strain be corrected for the coefficient of thermal expansion mismatch between the strain gage and the specimen or apparent strain when the temperature varies while a mechanical load is being applied. Collecting data for an apparent strain test becomes problematic as the specimen size increases. If the test specimen cannot be placed in a variable temperature test chamber to generate apparent strain data with no mechanical loads, coupons can be used to generate the required data. The coupons, however, must have the same strain gage type, coefficient of thermal expansion, and constraints as the specimen to be useful. Obtaining apparent-strain data at temperatures lower than -320 F is challenging due to the difficulty to maintain steady-state and uniform temperatures on a given specimen. Equations to correct for apparent strain in a real-time fashion and data from apparent-strain tests for composite and metallic specimens over a temperature range from -450 F to +250 F are presented in this paper. Three approaches to extrapolate apparent-strain data from -320 F to -430 F are presented and compared to the measured apparent-strain data. The first two approaches use a subset of the apparent-strain curves between -320 F and 100 F to extrapolate to -430 F, while the third approach extrapolates the apparent-strain curve over the temperature range of -320 F to +250 F to -430 F. The first two approaches are superior to the third approach but the use of either of the first two approaches is contingent upon the degree of non-linearity of the apparent-strain curve.

Johnson, Theodore F.↗

NASA NTRS1984

Antiwear Additive Mechanisms in Sliding Contacts

The possible mechanisms associated with wear in a sliding contact and how an oil and antiwear additive can mitigate wear or prevent catastropic seizure of the contacting parts was examined. The various load and temperature regimes are examined and the mechanisms which are predominant under these conditions are determined. The critical mechanism(s) depend on the test parameters, particularly load and temperature, although sliding speed is also a factor. Different ways to improve the efficiency of antiwear additives are suggested.

Baldwin, B. A.↗

NASA NTRS1998

Open Architecture Data System for NASA Langley Combined Loads Test System

The Combined Loads Test System (COLTS) is a new structures test complex that is being developed at NASA Langley Research Center (LaRC) to test large curved panels and cylindrical shell structures. These structural components are representative of aircraft fuselage sections of subsonic and supersonic transport aircraft and cryogenic tank structures of reusable launch vehicles. Test structures are subjected to combined loading conditions that simulate realistic flight load conditions. The facility consists of two pressure-box test machines and one combined loads test machine. Each test machine possesses a unique set of requirements or research data acquisition and real-time data display. Given the complex nature of the mechanical and thermal loads to be applied to the various research test articles, each data system has been designed with connectivity attributes that support both data acquisition and data management functions. This paper addresses the research driven data acquisition requirements for each test machine and demonstrates how an open architecture data system design not only meets those needs but provides robust data sharing between data systems including the various control systems which apply spectra of mechanical and thermal loading profiles.

Lightfoot, Michael C.↗