SEARCH · Search NASA
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Quick-release cover includes pin-retraction mechanism releasing cover quickly from lower of two sets of pin connections holding cover. Cover released at top by pulling lever as described in "Lever-Arm Pin Puller" (NPO-18788). Removal of cover begins when technician or robot pulls upper-pin-release lever. Cover swings downward until tabs on lower pins are pulled through slots in their receptacles. Lower pins are then free.
Pip pins are used in many engineering applications. Of particular interest to the aerospace industry is their use in various mechanism designs. Many payloads that fly aboard our nation's Space Shuttle have at least one actuated mechanism. Often these mechanisms incorporate pip pins in their design in order to fasten interfacing parts or joints. Pip pins are most often used when an astronaut will have a direct interface with the mechanism. This interfacing can be done during Space Shuttle mission EVA's (ExtraVehicular Activity). The main reason for incorporating pip pins is convenience and their ability to provide a quick release for interfacing parts. However, there are some issues that must be taken into account when using them in a design. These issues include documented failures and quality control problems when using substandard pip pins. A history of pip pins as they relate to the aerospace industry as well as general design features is discussed.
An improved quick-release pin mechanism supplants a prior such mechanism in which the pin bears a shear load to hold two objects together. The prior mechanism, of a ball-locking design, can fail when vibrations cause balls to fall out. The load-bearing pin is an outer tube with a handle at one end (hereafter denoted the near end). Within the outer tube is a spring-loaded inner tube that includes a handle at its near end and a pivoting tab at its far end. The pin is inserted through holes in the objects to be retained and the inner tube is pushed against an offset pivot inside the outer tube to make the tab rotate outward so that it protrudes past the outer diameter of the outer tube, and the spring load maintains this configuration so that the pin cannot be withdrawn through the holes. Pushing the handles together against the spring load moves the locking tab out far enough that the tab becomes free to rotate inward. Then releasing the inner-tube handle causes the tab to be pulled into a resting position inside the outer tube. The pin can then be pulled out through the holes.
Disclosed is a method and apparatus for strongly enhancing vortex pinning by conformal crystal arrays. The conformal crystal array is constructed by a conformal transformation of a hexagonal lattice, producing a non-uniform structure with a gradient where the local six-fold coordination of the pinning sites is preserved, and with an arching effect. The conformal pinning arrays produce significantly enhanced vortex pinning over a much wider range of field than that found for other vortex pinning geometries with an equivalent number of vortex pinning sites, such as random, square, and triangular.
Heat sinks and methods of using the same include a top and bottom plate, at least one of which has a plurality of pin contacts flexibly connected to one another, where the plurality of pin contacts have vertical and lateral flexibility with respect to one another; and pin slice layers, each having multiple pin slices, arranged vertically between the top and bottom plates such that the plurality of pin slices form substantially vertical pins connecting the top and bottom plates.
For extrusion-based additive manufacturing, the mechanical performance in vertical direction (z-direction) is significantly lower than that in the printed layer plane (xy-direction). This paper presents a vertical extrusion approach across several layers to improve the mechanical properties of a 3D printed part. This approach is patent pending, and it involves depositing pins in the z-direction into predefined holes. It requires the vertical pins to mechanically engage with the surrounding structure of the holes. To maximize the mechanical performance of the printed structures with pins, we then analyzed the penetration quality of the pins with a wide range of hole depths, hole sizes, and pin volumes and obtained the relationship between the hole width and the hole depth for the full penetration of pins.
A method of testing a PIN diode for a power limiter circuit comprises measuring a reverse bias current of the PIN diode; applying a reverse bias voltage to the PIN diode; increasing the reverse bias voltage until the reverse bias current of the PIN diode reaches a threshold current indicative of a reverse voltage breakdown; and determining whether the reverse bias breakdown voltage of the PIN diode is within an acceptable range of reverse bias breakdown voltages corresponding to a power range at which the power limiter circuit would enter power limiting mode with the PIN diode.
Pinning of dislocations at nanosized obstacles like precipitates, voids, and bubbles is a crucial mechanism in the context of phenomena like hardening and creep. The interaction between such an obstacle and a dislocation is often studied at fundamental level by means of analytical tools, atomistic simulations, and finite element methods. Nevertheless, the information extracted from such studies cannot be utilized to its maximum extent on account of insufficient information about the underlying statistics of this process comprising a large number of dislocations and obstacles in a system. Here, we propose a new statistical approach, where the statistics of pinning of dislocations by idealized spherical obstacles is explored by taking into account the generalized size-distribution of the obstacles along with the dislocation density within a three-dimensional framework. Starting with a minimal set of material parameters, the framework employs the method of geometrical statistics with a few simple assumptions compatible with the real physical scenario. The application of this approach, in combination with the knowledge of fundamental dislocation-obstacle interactions, has successfully been demonstrated for dislocation pinning at nanovoids in neutron irradiated type 316-stainless steel in regard to the non-conservative motion of dislocations. An interesting phenomenon of transition from rare pinning to multiple pinning regimes with increasing irradiation temperature is revealed.
Isothermal magnetic field dependence of magnetization and magnetic relaxation measurements were performed for the $H\parallel {\rm{c}}$ axis on a single crystal of Ba(Fe 0.935 Co 0.065 ) 2 As 2 pnictide superconductor having T c = 21.7 K. The second magnetization peak (SMP) for each isothermal M(H) was observed in a wide temperature range from T c to the lowest temperature of measurement (2 K). The magnetic field dependence of relaxation rate R(H), showed a peak (H spt) between H on (onset of SMP in M(H)) and H p (peak field of SMP in M(H)), which is likely to be related to a vortex-lattice structural phase transition, as suggested in the literature for a similar sample. In addition, the magnetic relaxation measured for magnetic fields near H spt showed some noise, which might be the signature of the structural phase transition of the vortex lattice. Analysis of the magnetic relaxation data using Maley's criterion and the collective pinning theory suggested that the SMP in the sample was due to the collective (elastic) to plastic creep crossover, which was also accompanied by a rhombic to square vortex lattice phase transition. The analysis of the pinning force density suggested a single dominating pinning mechanism in the sample, which did not showing the usual $\delta {l}$ and $\delta {T}_{{\rm{c}}}$ nature of pinning. Furthermore, the critical current density (J c ), estimated using the Bean critical state model, was found to be 5 × 10 5 A cm - 2 at 2 K in the zero magnetic field limit. Surprisingly, the maximum of the pinning force density was not responsible for the maximum value of the critical current density in the sample.
REBa 2 Cu 3 O 7-x (REBCO, RE: rare earth) coated conductors (CCs) suffer from great critical current I c differences between different manufacturers, I c variations within individual manufacturers, and often significant lengthwise fluctuations. The understanding of such variations is complicated by the lack of a direct correlation between I c and the critical current density J c . In fact, although J c is the fundamental property determined by the local vortex pinning landscape, I c is often limited by variable current blocking mechanisms. An important practical complexity is commercial practices of performing J c and I c evaluations based on I c at 77 K and self-field (sf), where connectivity variation dominates over vortex pinning variations. However, at higher fields and lower temperatures, vortex pinning becomes more complex and highly variable, making predictions of I c and J c at arbitrary temperature T, magnetic field H, and field orientation θ, quite uncertain. To address some aspects of this problem, we conducted detailed spool-to-spool performance characterization on recently manufactured REBCO CCs. Despite J c (77 K, sf) varies by only ∼11%, J c (77 K, 1 T) of its minimum and maximum (for H//ab-plane) show variations of ∼21% and ∼32%, respectively. This emphasizes the shortcoming in using J c (77 K, sf) as parameter for evaluating even the low field performance. An even more remarkable spool-to-spool J c variation of ∼68% was observed at 20 K and 15 T for H//ab-plane. To identify the origin of such lack of reproducibility we performed microstructural characterizations, which revealed, within the REBCO layer, large variation in the density of copper oxide (CuO x ) particles ranging from 0.1 to 2 μm in size. We believe that they play a decisive role in reducing the effective cross-section of the REBCO layer by not simply blocking current themselves, but also by nucleating off-axis REBCO grains, whose misoriented grain boundaries adversely impact REBCO grain-to-grain connectivity. The REBCO growth associated with high density CuO x particles also leads to the more disordered spatial arrangement of BaHfO 3 precipitate arrays, which, when self-aligning along the ab-planes, generate stronger pinning enhancing J c (H//ab) at all temperatures. In this way, we established that variations of both connectivity and vortex pinning are thus directly coupled. Our results also explain why the so-called ‘lift-factor’, typically defined by the ratio between I c (T, H) and I c (77 K, sf), frequently turns out to be unreliable.
Radioxenon detectors are used for the verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) in a network of detectors throughout the world called the International Monitoring System (IMS). The Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) Provisional Technical Secretariat (PTS) has tasked Pacific Northwest National Laboratory (PNNL) with testing a V.G. Khlopin Radium Institute (KRI) and Lares Ltd-developed Silicon PIN detector for radioxenon detection. PNNL measured radioxenon with the silicon PIN detector and determined its potential compared to current plastic scintillator beta cells. While the PNNL tested Si detector experienced noise issues, a second detector was tested in Russia at Lares Ltd, which did not exhibit the noise issues. Without the noise issues, the Si detector produces much better energy resolution and isomer peak separation than a conventional plastic scintillator cell used in the SAUNA systems in the IMS. Under the assumption of 1 cm 3 of Xe in laboratory-like conditions, 24-hr count time (12-hr count time for the SAUNA), with the respective shielding the minimum detectable concentrations for the Si detector tested by Lares Ltd (and a conventional SAUNA system) were calculated to be: 131m Xe – 0.12 mBq/m 3 (0.12 mBq/m 3 ); 133 Xe – 0.18 mBq/m 3 (0.21 mBq/m 3 ); 133m Xe – 0.07 mBq/m 3 (0.15 mBq/m 3 ); 135 Xe – 0.45 mBq/m 3 (0.67 mBq/m 3 ). Detection limits, which are one of the important factors in choosing the best detection technique for radioxenon in field conditions, are significantly better than for SAUNA-like detection systems for 131m Xe and 133m Xe, but similar for 133 Xe and 135 Xe. Another important factor is the amount of “memory effect” or carry over signal from one radioxenon measurement to the subsequent sample. The memory effect is reduced by a factor of 10 in the Si PIN detector compared to the current plastic scintillator cells. There is potential for further reduction with the removal of plastics within the cell, which will need to be explored in future work. A third important parameter in choosing the best detection technique for radioxenon is the resolution of the electron detection. While the resolution is important in determining the minimum detectable concentration, it plays a larger role in source identification when there is a visible signal. The Silicon PIN diodes generated improved resolution over a similar plastic scintillator cell. With the improved resolution, it becomes easier to distinguish the radioxenon isomers ( 133m Xe and 131m Xe) from the 133 Xe beta continuum background. With the beta background from 133 Xe ever present with the detection of the isomers, the improved resolution proves vital in calculating the ratios of the three isotopes. With an accurate measurement of the isotopic ratios, the anthropogenic sources of radioxenon (medical isotope production and nuclear reactors) can be more accurately distinguished. Based on the results shown within this report, a Si PIN beta cell shows the potential to aid in the operation and discriminating power of the IMS for the CTBTO. However, there are a number of issues that need attention before a detector of this design would be reliable enough for field operations in the IMS. Issues that need develop include, but are not limited to: studying the robustness of the design in field conditions, eliminating or minimizing the noise and variability of individual Si detector elements, understanding the long-term gain stability of the Si detectors, and reducing the non-Si materials within the cell (i.e. the plastic housing).
Most PWR spent fuel pool criticality analyses assume that the burnup is uniformly distributed among the fuel pins in the assembly. This assumption is accurate for PWR cores that have the typical small inter-assembly gap. The Palisades reactor core, however, is different in that it uses cruciform control rods in between fuel assemblies. Every interior assembly has two sides having a wide water gap and two sides having a narrow water gap. After depleting under these conditions, the pins near the wide water gap will have a higher burnup than the pins in the center. If the burnup is distributed uniformly among the pins, the resulting k calculation will be conservative but excessively so. The excess conservatism was found to be on the order of 1% in k. For this analysis, SCALE 6.1 depletion with TRITON is used followed by the CSAS5 module for the Palisades pool analysis. Several burnup zoning arrangements (uniform enrichment) were investigated ranging from 3 zones to as many as 19 zones. The 19 zone analysis agreed well with a CASMO analysis where every pin was its own depletion zone. It was found that 8 fuel zones gave essentially the same result as 19 zones with less complexity. The depletion calculation using 8 fuel zones instead of a single zone is more complicated but the resulting k calculation no longer has the excessive conservatism seen in a one zone model. (authors)
A common fuel arrangement for Sodium Fast Reactors (SFR) designs are hexagonal arrays of wire wrapped fuel pins. The helically wound wires redirect coolant to neighboring subchannels and increases mixing. The increased mixing of the coolant is beneficial to heat transfer from the fuel and prevents temperature peaking in hot channels that may occur. The purpose of this study is to observe the effect of bundle size on the temperature distribution of a coolant when a constant heat flux is implemented. Bundles of 19, 37, 61, and 91 pins were modeled. The wire-wrapping on fuel pins encourages interchannel mixing. With a constant heat flux the enhanced interchannel mixing has little observable effect. The temperature distributions of the subchannels has negligible dependence on radial or angular position. The temperature distribution additionally shows negligible dependence on the bundle size. The subchannel average temperatures further illustrate the homogeneity of the temperature across the bundles. Similarly oriented subchannels differ by less than two Kelvin. The temperature distribution within a single subchannel is fairly uniform, differing by about 15 K between the wall and the bulk flow, with the exception of two hot spots. The two hot spots, however, occur in two non-geometrically accurate locations, so little analysis can be performed. To better illustrate the effect of the enhanced mixing of the wire-wrapped fuel pins, a hot pin analysis should be performed to observe how the additional, non-uniform heat is dispersed. (authors)
The pinning of grain interfaces plays an important role in determining the coercivity of nanocomposite magnets. Here, based on pinning effect, a simple model was proposed to correlate the pinning strength with microstructural parameters. A structural factor K has been used to describe the contribution of the phase composition and grain size of hard and soft phases to pinning strength. The model can be used to estimate the pinning strength of nanocomposite magnets, which is important for the design and fabrication of nanocomposite magnets with high coercivity.
Friction stir welding (FSW), as a solid-state welding technology invented by TWI in 1991, has potential to join dissimilar Al/Mg alloys. In this study, the pin adhesion phenomenon affecting joint quality during FSW of 6061-T6 aluminum and AZ31B magnesium alloys was investigated. The adhesion phenomenon induced by higher heat input easily transformed the tapered-and-screwed pin into a tapered pin, which greatly reduced the tool’s ability to drive the plasticized materials and further deteriorated joint formation. Under the condition without the pin adhesion, the complex intercalated interlayer at the bottom of stir zone was beneficial to mechanical interlocking of Al/Mg alloys, improving tensile properties. However, the formation of intermetallic compounds was still the main reason of the joint fracture, significantly deteriorating tensile properties. Under the welding speed of 60 mm/min without the pin adhesion phenomenon, the maximum tensile strength of 107 MPa and elongation of 1.2% were achieved.
Conventional 3D printing approaches are restricted to building up material in a layer-by-layer format, which is more appropriately considered “2.5-D” printing. The layered structure inherently results in significant mechanical anisotropy in printed parts, causing the tensile strength in the build direction (z-axis) to be only a fraction of the in-plane strength – a decrease of 50–75% is common. In this study, a novel “z-pinning” approach is described that allows continuous material to be deposited across multiple layers within the volume of the part. Here, the z-pinning process is demonstrated using a Fused Filament Fabrication (FFF) printer for polylactic acid (PLA) and carbon fiber reinforced PLA. For both materials, z-pinning increased the tensile strength and toughness in the z-direction by more than a factor of 3.5. Direct comparisons to tensile strength in the x-axis showed a significant decrease in mechanical anisotropy as the volume of the pin was increased relative to the void in the rectilinear grid structure. In fact, the PLA sample with the largest pin volume demonstrated mechanically isotropic properties within the statistical uncertainty of the tests. Tensile test results were also analyzed relative to the functional area resisting deformation for each sample.
In this paper we report on measurements of critical current densities J c and flux creep rates S of freestanding Ca(Fe 1–x Co x ) 2 As 2 (x ≈ 0.033) single crystals with T c ≈ 15.7 K by performing magnetization measurements. The magnetic field dependences of J c at low temperature display features related to strong pinning. In addition, we find that the system displays small flux creep rates. The characteristic glassy exponent, μ, and the pinning energy, U 0 , display exceptional high values for pristine crystals. We find that for magnetic fields between 0.3 T and 1 T, μ decreases from ≈ 2.8 to ≈ 2 and U 0 remains ≈ 300 K. Analysis of the pinning force indicates that the mechanism is similar to the observed in polycrystalline systems in which grain boundaries and random disorder produce the vortex pinning. Considering the large U 0 observed in the single crystal, we attempt to improve the pinning by adding random point disorder by 3 MeV proton irradiation with a fluence of 2 × 10 16 proton/cm 2 . The results show that, unlike other iron-based superconductors, the superconducting fraction is sharply reduced by irradiation. This fact indicates that the superconductivity in the system is extremely fragile to an increment in the disorder. The superconducting volume fraction in the irradiated crystal systematically recovers after removal disorder by thermal annealing, which evidences as to the observation of critical state in curves of magnetization versus magnetic field. No features related to a reentrant antiferromagnetic transition are observed for the irradiated sample.
We demonstrate that for multilayered magnetic nanowires, where the thickness and composition of the individual layers have been carefully chosen, domain walls can be pinned at non-topographic sites created purely by ion irradiation in a focused ion beam system. The pinning results from irradiation induced alloying leading to magnetic property modification only in the affected regions. Using Lorentz transmission electron microscopy, we have studied the pinning behavior of domain walls at the irradiation sites. Depending on the irradiation dose, a single line feature not only pinned the domain walls but also acted to control their structure and the strength of their pinning.