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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

The Effect of Stainless Steel 304 Surface Roughness on Ice Adhesion Shear Strength of Accreted Impact Ice

Aircraft in-flight icing is problematic due to the ad-verse effect on vehicle performance. It occurs when supercooled water droplets (SCWD) present in clouds, under the appropriate environmental conditions, col-lide with the aircraft surface resulting in accretion of ice (i.e., impact icing). Impact ice can range from clear/glaze to rime or a combination of the two (i.e., mixed) with the type determined by the air temperature (0 to -20°C), liquid water content (LWC, 0.3-0.6 g/cu.m), and droplet size [median volumetric diameter (MVD) of 15-40 µm] present during accretion.1 These impact icing events generally occur at temperatures ranging from 0 to -20°C. Below -20°C, ice crystals dominate the environment and typically do not adhere to the aircraft surface. A main difference between an impact icing occurrence and a slow growth icing (i.e., freezer ice) one is the speed of the icing event. Besides environmental conditions, ice adhesion strength (IAS) to a metallic substrate depends upon surface roughness. It is known that increasing surface roughness and decreasing temperature lead to in-creases in IAS.

Smith, Joseph G., Jr.↗
NASA NTRS1983

Synthesis and characterization of bisimide amines and bisimide amine-cured epoxy resins

An attempt is made to develop tough, moisture resistant, high char yield epoxy resins by means of novel bisimide amine (BIA) hardener curing agents and a state-of-the-art epoxy resin system. The BIAs are isolated as mixtures containing monomer, oligomer, and polymeric species, and then characterized by elemental analysis and high pressure liquid chromatography. The bisimide amine-cured epoxies (IMEs) were characterized with respect to moisture absorption, thermal properties, and physical and mechanical properties, as well as in the role of matrices in Celion 6000/IME composites. The relative toughness characteristics of each IME formulation was measured by the 10 deg off-axis tensile test, measuring the uniaxial tensile strength, shear strength, and shear-strain-to-failure of the composite systems.

Scola, D. A.↗
NASA NTRS1985

Evaluation of a high temperature adhesive for fabricating graphite/PMR-15 polyimide structures

Tests are conducted to measure shear strength, shear modulus and flatwise tensile strength of the A7F (amide-imide modified LARC-13) adhesive system. An investigation is also conducted to determine the effect of geometric material parameters, and elevated temperature on the static strength of standard joints. Single-lap and double-lap composite joints, and single, double and step lap composite to metal joints are characterized. A series of advanced joints consisting of preformed adherends, adherends with scalloped edges and joints with hybrid interface plies are tested and compared to baseline single and double-lap designs.

Hill, S. G.↗
DOE OSTI2026

Multi-Objective design of interlocking metasurfaces using conditional diffusion models

Unit cell design remains a major challenge for interlocking metasurfaces, a promising joining technology for dissimilar materials, due to the complex, competing, multivariate design space and the need for rapid adaptation to varying performance requirements. This study explores Conditional Diffusion Models as a design optimization tool for interlocking metasurfaces. Given the complex, competing, multivariate design space for interlocking metasurfaces, unit cell design remains a major challenge for this joining technology. We trained a conditional diffusion model on 25,000 finite element analysis-simulated interlocking metasurface unit cells to generate designs with tailored thermo-mechanical properties (tensile strength, shear strength, and thermal conductivity) based on specified performance criteria. The model demonstrated a success rate of approximately 72 % in producing designs that met specified property bounds. The conditional diffusion model generated both thermally resistive and conductive designs, revealing clear trends in design characteristics: taller, dendritic structures were advantageous for tensile loads, while shorter, robust designs excelled in shear applications. Our findings indicate that the model's performance is more influenced by the breadth of the design space than by the quantity of training data, highlighting the importance of expansive design domains for generating innovative solutions. This work establishes conditional diffusion models as a highly efficient and adaptable tool for rapid interlocking metasurface unit cell design, paving the way for advancements in multi-material joining technologies, as well as highlighting the justification to leverage conditional diffusion models as design tools across complex design domains.

Conditional diffusion models↗
NASA NTRS1973

Characterization of the mechanical and physical properties of TD-NiCr (Ni-20Cr-2ThO2) alloy sheet

Sheets of TD-NiCr processed using techniques developed to produce uniform material were tested to supply mechanical and physical property data. Two heats each of 0.025 and 0.051 cm thick sheet were tested. Mechanical properties evaluated included tensile, modulus of elasticity, Poisson's Ratio, compression, creep-rupture, creep strength, bearing strength, shear strength, sharp notch and fatigue strength. Test temperatures covered the range from ambient to 1589K. Physical properties were also studied as a function of temperature. The physical properties measured were thermal conductivity, linear thermal expansion, specific heat, total hemispherical emittance, thermal diffusivity, and electrical conductivity.

Fritz, L. J.↗
NASA NTRS1975

Mechanical behavior of the directionally solidified gamma/gamma prime - delta eutectic alloy

The eutectic alloy Ni-20.0%Cb-2.5%Al-6.0%Cr was tested in short-term creep and long-term exposure to service conditions to assess its suitability for high temperature turbine blade applications. Long-time exposure showed the lamellar microstructure of the alloy to be exceptionally stable. Other properties tested were notch sensitivity, isothermal and thermomechanical fatigue strength, shear strength, and transverse ductility. It was shown that this alloy is superior to the best currently available directionally solidified superalloys over the temperature/stress conditions encountered in turbine airfoils.

Barkalow, R. H.↗
NASA NTRS1987

Materials property definition and generation for carbon-carbon and carbon phenolic materials

A data base program to generate statistically significant material-property data for carbon-carbon and carbon phenolic materials to be used in designs of Space Shuttle is described. The program, which will provide data necessary for thermal and stress modeling of Shuttle nozzle and exit cone structures, includes evaluation of tension, compression, shear strength, shear modulus, thermal expansion, thermal conductivity, permeability, and emittance for both materials; the testing of carbon phenolic materials also includes CTE, off-gassing, pyrolysis, and RTG. Materials to be tested will be excised from Space Shuttle inlet, throat, and exit cone billets and modified involute carbon-carbon exit cones; coprocessed blocks, panels, and cylinders will also be tested.

Canfield, A. R.↗
NASA NTRS1984

Processing study of a polyimidesulfone adhesive

An adhesive bonding process cycle study was performed for a polyimidesulfone (PISO2) recently developed as a promising structural adhesive. The high molecular weight, linear aromatic system possesses properties which make it attractive as a processable, low-cost material for elevated temperature applications. The results of a study to better understand the parameters that affect the adhesive properties of the polymer for titanium alloy adherends are detailed. These include the tape preparation, the use of a primer, and press and simulated autoclave processing conditions. The polymer was characterized using Fourier Transform Infrared Spectroscopy, glass transition temperature determination, flow measurements, and weight loss measurements. The adhesive's strength determined by lap shear strength tests was used to evaluate the effects of the bonding process variations. Higher lap shear strengths were obtained at room temperature when a primer (PISO2) was used; however, the results were the same at 232 C (450 F) with or without a primer. The use of a vacuum (simulated autoclave cycle) during titanium bonding produced similar lap shear strengths to those specimens bonded without a vacuum.

Progar, D. J.↗
NASA NTRS1986

Specimen geometry effects on graphite/PMR-15 composites during thermo-oxidative aging

Studies were conducted to establish the effects of specimen geometry on the thermo-oxidative stability and the mechanical properties retention of unidirectional Celion 12000 graphite fiber reinforced PMR-15 polyimide composites. Weight loss, flexural strength and interlaminar shear strength are measured at isothermal aging times as long as 1639 hr at a temperature of 316 C for three different specimen geometries. It is found that the three different types of specimen surfaces exhibit different values of weight loss/unit area. The mechanical properties retention is also found to be dependent on geometry for these composites. The interlaminar shear strength decreases significantly over the complete range of aging times. The flexural strength retention starts showing geometric dependency after about 1000 hr of aging at 316C. Weight loss fluxes, associated with the three different types of exposed surfaces, are calculated and used to develop an empirical mathematical model for predicting the weight loss behavior of unidirectional composites of arbitrary geometries. Data are presented comparing experimentally determined weight loss with weight loss values predicted using the empirical model.

Bowles, K. J.↗
NASA NTRS1986

Specimen geometry effects on graphite/PMR-15 composites during thermo-oxidative aging

Studies were conducted to establish the effects of specimen geometry on the thermo-oxidative stability and the mechanical properties retention of unidirectional Celion 12000 graphite fiber reinforced PMR-15 polyimide composites. Weight loss, flexural strength and interlaminar shear strength are measured at isothermal aging times as long as 1639 hr at a temperature of 316 C for three different specimen geometries. It is found that the three different types of specimen surfaces exhibit different values of weight loss/unit area. The mechanical properties retention is also found to be dependent on geometry for these composites. The interlaminar shear strength decreases significantly over the complete range of aging times. The flexural strength retention starts showing geometric dependency after about 1000 hr of aging at 316 C. Weight loss fluxes, associated with the three different types of exposed surfaces, are calculated and used to develop an empirical mathematical model for predicting the weight loss behavior of unidirectional composites of arbitrary geometries. Data are presented comparing experimentally determined weight loss with weight loss values predicted using the empirical model.

Bowles, K. J.↗
NASA NTRS1982

Mechanics aspects of NDE by sound and ultrasound

Nondestructive evaluation (NDE) is considered as a means to detect the energy release mechanism of defects and the interaction of microstructures within materials with sound waves and/or ultrasonic waves. Ultrasonic inspection involves the frequency range 20 kHz-1 GHz with amplitudes depending on the sensitivity of the test instrumentation. Pulse echo systems are most frequently used in NDE. Information is extracted from the signals through measurements of the signal velocity, attenuation, the acoustic emission when stress is applied, and calculation of the acoustoelastic coefficients. Fracture properties, tensile and shear strengths, the interlaminar shear strength, the cohesive strength, yield and impact strengths, the hardness, and the residual stress can be assayed by ultrasonic methods. Finally, attention is given to analytical treatment of the derived data, with mention given to transition matrix, integral equation, and eigenstrain approaches.

Fu, L. S.↗
NASA NTRS1983

Interlaminar shear properties of graphite fiber, high-performance resin composites

Short beam testing was used to determine the shear properties of laminates consisting of T-300 and Celion 3000 and 6000 graphite fibers, in epoxy, hot melt and solvent bismaleimide, polyimide and polystyrylpyridine (PSP). Epoxy, composites showed the highest interlaminar shear strength, with values for all other resins being substantially lower. The dependence of interlaminar shear properties on the fiber-resin interfacial bond and on resin wetting characteristics and mechanical properties is investigated, and it is determined that the lower shear strength of the tested composites, by comparison with epoxy resin matrix composites, is due to their correspondingly lower interfacial bond strengths. An investigation of the effect of the wettability of carbon fiber tow on shear strength shows wetting variations among resins that are too small to account for the large shear strength property differences observed.

Needles, H. L.↗
NASA NTRS1995

Evaluation of Rhenium Joining Methods

Coupons of rhenium-to-Cl03 flat plate joints, formed by explosive and diffusion bonding, were evaluated in a series of shear tests. Shear testing was conducted on as-received, thermally-cycled (100 cycles, from 21 to 1100 C), and thermally-aged (3 and 6 hrs at 1100 C) joint coupons. Shear tests were also conducted on joint coupons with rhenium and/or Cl03 electron beam welded tabs to simulate the joint's incorporation into a structure. Ultimate shear strength was used as a figure of merit to assess the effects of the thermal treatment and the electron beam welding of tabs on the joint coupons. All of the coupons survived thermal testing intact and without any visible degradation. Two different lots of as-received, explosively-bonded joint coupons had ultimate shear strengths of 281 and 310 MPa and 162 and 223 MPa, respectively. As-received, diffusion-bonded coupons had ultimate shear strengths of 199 and 348 MPa. For the most part, the thermally-treated and rhenium weld tab coupons had shear strengths slightly reduced or within the range of the as-received values. Coupons with Cl03 weld tabs experienced a significant reduction in shear strength. The degradation of strength appeared to be the result of a poor heat sink provided during the electron beam welding. The Cl03 base material could not dissipate heat as effectively as rhenium, leading to the formation of a brittle rhenium-niobium intermetallic.

Reed, Brian D.↗