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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 19 records

All sources NASA NTRS DOE OSTI

NASA NTRS1980

Use of two-dimensional transmission photoelastic models to study stresses in double-lap bolted joints: Load transfer and stresses in the inner lap

The determination of the stress distribution in the inner lap of double-lap, double-bolt joints using photoelastic models of the joint is discussed. The principal idea is to fabricate the inner lap of a photoelastic material and to use a photoelastically sensitive material for the two outer laps. With this setup, polarized light transmitted through the stressed model responds principally to the stressed inner lap. The model geometry, the procedures for making and testing the model, and test results are described.

Hyer, M. W.↗

NASA NTRS1938

The Effect of Surface Irregularities on Wing Drag. II - Lap Joints: Lap Joints - 2

Tests have been made in the NACA 8-foot high-speed wind tunnel of the drag caused by four types of lap joint. The tests were made on an airfoil of NACA 23012 section and 5-foot chord and covered in a range of speeds from 80 to 500 miles per hour and lift coefficients from 0 to 0.30. The increases in profile drag caused by representative arrangements of laps varied from 4 to 9%. When there were protruding rivet heads on the surface, the addition of laps increased the drag only slightly. Laps on the forward part of a wing increased the drag considerably more than those farther back.

Hood, Manley J.↗

DOE OSTI2020

Numerical Simulation and Experimental Validation of Joint Performance in Aluminum-Steel Lap Welds Formed by Friction Stir Dovetailing

Friction stir dovetailing (FSD) is a new dissimilar material joining process that simultaneously forms a mechanical interlock and metallurgical bond at the dissimilar material interface. This work presents development of a modeling and simulation approach to predict mechanical performance of FSD thick section aluminum to steel joints. A finite element analysis (FEA) was carried out in order to predict the load-carrying capacity and failure location for aluminum thicknesses between 12.7 mm and 50.8 mm with different numbers of dovetails. The numerical results and corresponding experimental investigation are in agreement and suggest that the developed methods can be used effectively for design and analysis of FSD joints using standard FEA tools.

Friction stir dovetailing, Friction stir welding, ↗

NASA NTRS1977

Abernathy's Lap

A lap in this instance is not a midriff but a tool for presision.polishing and grinding. During the Saturn V moonbooster program, Marshall Space Flight Center found a need for a better lap. The need arose from the exquisitely precise tolerances required for parts of the launch vehicle's guidance,and control system. So William J. Abernathy, a former Marshall employee, built a better lap; he invented a method for charging aluminum lap plates with diamond powder, then hard-anodizing them. The resulting lap produces a high polish on materials ranging from the softest aluminum to the hardest ceramics. It operates faster, wears longer and requires less reworking. Abernathy got NASA's permission to obtain a personal patent and he formed the one-man Abernathy Laps Co. in Huntsville, which produces a variety of laps. One of Abernathy's customers is Bell Aerospace Textron, Buffalo, which uses the laps to finish polish delicate instrument parts produced for NASA's Viking and other space programs. Says a Bell official: "Time needed (with the Abernathy lap) is a fraction of that required by conventional methods. The result is extremely accurate flatness and surface finish." Abernathy is providing laps for other manufacturing applications and for preparation of metallurgical specimens. The business is small but steady, and Abernathy plans expansion into other markets.

Source record↗

DOE OSTI2014

A Lapping Technique for Metallic, Alpha-Phase, Plutonium: Achieving and Measuring Nano-Meter Roughness and Sub-Micron Flatness

There are various processes and techniques by which one can achieve well polished (highly reflective) and smooth, flat (low roughness) surfaces on a wide variety of materials. Historically, precision lapping processes were first applied to optical materials for the production of lenses for telescopes and microscopes. These processes have been developed by a multitude of technicians over the centuries and reported in countless publications. These same grinding, lapping and polishing processes have been of great importance in the fabrication and structural characterization of countless optical materials and engineering structures, e.g. optics, Si wafers, precision machined surfaces, engineered devices, low-friction surfaces, mechanical systems, metallographic examination of microstructures, to name but a few. The development of lapping and polishing processes and techniques as applied to extremely hazardous and highly (chemically) reactive materials, such as metallic plutonium (Pu), has been limited. This is due in part due to the sensitive nature of the work as applied to nuclear applications, and limited access and need to work with these materials. For the limited information regarding polishing and lapping of Pu materials that has been documented, there has been virtually no quantitative assessment of qualities such as surface roughness and flatness on the nanometer scale. In this report we use the word “lapping” to refer to the traversing of a specimen surface across an abrasive surface in a controlled manner in order to achieve smooth/flat surfaces. We differentiate lapping from polishing, in that we define polishing as traversing of a sample surface across a non-abrasive surface that contains loose abrasive particles, e.g. diamond paste on nylon nap, in order to achieve a highly reflective surface. In this report, we will detail a simple and repeatable lapping process as applied to alpha-phase metallic Pu. We will provide quantitative measurements of the surface roughness and flatness. We will demonstrate the ability to achieve sub-10 nm surface roughness and to lap millimeter-size areas to a flatness of approximately 1.0 µm. Additionally, we will assess the current limitations and discuss any artifacts that arise as a result of our polishing processes applied to metallic Pu materials.

36 MATERIALS SCIENCE↗

NASA NTRS1981

Use of two-dimensional transmission photoelastic models to study stresses in double-lap bolted joints

The stress distribution in two hole connectors in a double lap joint configuration was studied. The following steps are described: (1) fabrication of photoelastic models of double lap double hole joints designed to determine the stresses in the inner lap; (2) assessment of the effects of joint geometry on the stresses in the inner lap; and (3) quantification of differences in the stresses near the two holes. The two holes were on the centerline of the joint and the joints were loaded in tension, parallel to the centerline. Acrylic slip fit pins through the holes served as fasteners. Two dimensional transmission photoelastic models were fabricated by using transparent acrylic outer laps and a photoelastic model material for the inner laps. It is concluded that the photoelastic fringe patterns which are visible when the models are loaded are due almost entirely to stresses in the inner lap.

Hyer, M. W.↗

NASA NTRS2003

Flaw Tolerance in Lap Shear Brazed Joints

Furnace brazing is a joining process used in the aerospace and other industries to produce strong permanent and hermetic structural joints. As in any joining process, brazed joints have various imperfections and defects. At the present time, our understanding of the influence of the internal defects on the strength of the brazed joints is not adequate. The goal of this 3-part investigation is to better understand the properties and failure mechanisms of the brazed joints containing defects. This study focuses on the behavior of the brazed lap shear joints because of their importance in manufacturing aerospace structures. In Part 1, an average shear strength capability and failure modes of the single lap joints are explored. Stainless steel specimens brazed with pure silver are tested in accordance with the AWS C3.2 standard. Comparison of the failure loads and the ultimate shear strength with the Finite Element Analysis (FEA) of the same specimens as a function of the overlap widths shows excellent correlation between the experimental and calculated values for the defect-free lap joints. A damage zone criterion is shown to work quite well in understanding the failure of the braze joints. In Part 2, the findings of the Part 1 will be verified on the larger test specimens. Also, various flaws will be introduced in the test specimens to simulate lack of braze coverage in the lap joints. Mechanical testing and FEA will be performed on these joints to verify that behavior of the flawed ductile lap joints is similar to joints with a reduced braze area. Finally, in Part 3, the results obtained in Parts 1 and 2 will be applied to the actual brazed structure to evaluate the load-carrying capability of a structural lap joint containing discontinuities. In addition, a simplified engineering procedure will be offered for the laboratory testing of the lap shear specimens.

Flom, Yury↗

NASA NTRS2003

Flaw Tolerance In Lap Shear Brazed Joints

This paper presents results of the second part of an on-going effort to gain better understanding of defect tolerance in braze joints. In the first part of this three-part series, we mechanically tested and modeled the strength of the lap joints as a function of the overlap distance. A failure criterion was established based on the zone damage theory, which predicts the dependence of the lap joint shear strength on the overlap distance, based on the critical size of a finite damage zone or an overloaded region in the joint. In this second part of the study, we experimentally verified the applicability of the damage zone criterion on prediction of the shear strength of the lap joint and introduced controlled flaws into the lap joints. The purpose of the study was to evaluate the lap joint strength as a function of flaw size and its location through mechanical testing and nonlinear finite element analysis (FEA) employing damage zone criterion for definition of failure. The results obtained from the second part of the investigation confirmed that the failure of the ductile lap shear brazed joints occurs when the damage zone reaches approximately 10% of the overlap width. The same failure criterion was applicable to the lap joints containing flaws.

Wang, Len↗

DOE OSTI2017

Defect features, texture and mechanical properties of friction stir welded lap joints of 2A97 Al-Li alloy thin sheets

1.4 mm 2A97 Al-Li alloy thin sheets were welded by friction stir lap welding using the stirring tools with different pin length at different rotational speeds. The influence of pin length and rotational speed on the defect features and mechanical properties of lap joints were investigated in detail. Microstructure observation shows that the hook defect geometry and size mainly varies with the pin length instead of the rotational speed. The size of hook defects on both the advancing side (AS) and the retreating side (RS) increased with increasing the pin length, leading to the effective sheet thickness decreased accordingly. Electron backscatter diffraction analysis reveals that the weld zones, especially the nugget zone (NZ), have the much lower texture intensity than the base metal. Some new texture components are formed in the thermo-mechanical affected zone (TMAZ) and the NZ of joint. Lap shear test results show that the failure load of joints generally decreases with increasing the pin length and the rotational speed. The joints failed during the lap shear tests at three locations: the lap interface, the RS of the top sheet and the AS of the bottom sheet. The fracture locations are mainly determined by the hook defects. - Highlights: • Hook defect size mainly varies with the pin length of stirring tool. • The proportion of LAGBs and substructured grains increases from NZ to TMAZ. • Weld zones, especially the NZ, have the much lower texture intensity than the BM. • Lap shear failure load and fracture location of joints is relative to the hook defects.

36 MATERIALS SCIENCE↗

NASA NTRS1973

Adhesive-bonded scarf and stepped-lap joints

Continuum mechanics solutions are derived for the static load-carrying capacity of scarf and stepped-lap adhesive-bonded joints. The analyses account for adhesive plasticity and adherend stiffness imbalance and thermal mismatch. The scarf joint solutions include a simple algebraic formula which serves as a close lower bound, within a small fraction of a per cent of the true answer for most practical geometries and materials. Digital computer programs were developed and, for the stepped-lap joints, the critical adherend and adhesive stresses are computed for each step. The scarf joint solutions exhibit grossly different behavior from that for double-lap joints for long overlaps inasmuch as that the potential bond shear strength continues to increase with indefinitely long overlaps on the scarf joints. The stepped-lap joint solutions exhibit some characteristics of both the scarf and double-lap joints. The stepped-lap computer program handles arbitrary (different) step lengths and thickness and the solutions obtained have clarified potentially weak design details and the remedies. The program has been used effectively to optimize the joint proportions.

Hart-Smith, L. J.↗

NASA NTRS1989

Apparatus and method for lapping an edge surface of an object

An apparatus for lapping an edge surface of an object comprises a block having a side adapted to engage a wide surface of an object, adjustable spacers disposed on the block and adapted to engage a lap plate, and a weighted spring disposed on the block for urging the spacers and the object edge surface towards the lap plate. A method for lapping comprises setting surfaces of adjustable spacers disposed on a block to be substantially the same distance from the block, affixing a wide surface of an object to the block, urging an edge surface of the object and the spacers towards a lap plate, lapping the edge of the object, inspecting the edge for parallelism to a reference line, resetting the spacers and relapping the edge surface.

Rossi, Vito N.↗

NASA NTRS1988

Large-scale Advanced Prop-fan (LAP) high speed wind tunnel test report

High Speed Wind Tunnel testing of the SR-7L Large Scale Advanced Prop-Fan (LAP) is reported. The LAP is a 2.74 meter (9.0 ft) diameter, 8-bladed tractor type rated for 4475 KW (6000 SHP) at 1698 rpm. It was designated and built by Hamilton Standard under contract to the NASA Lewis Research Center. The LAP employs thin swept blades to provide efficient propulsion at flight speeds up to Mach .85. Testing was conducted in the ONERA S1-MA Atmospheric Wind Tunnel in Modane, France. The test objectives were to confirm that the LAP is free from high speed classical flutter, determine the structural and aerodynamic response to angular inflow, measure blade surface pressures (static and dynamic) and evaluate the aerodynamic performance at various blade angles, rotational speeds and Mach numbers. The measured structural and aerodynamic performance of the LAP correlated well with analytical predictions thereby providing confidence in the computer prediction codes used for the design. There were no signs of classical flutter throughout all phases of the test up to and including the 0.84 maximum Mach number achieved. Steady and unsteady blade surface pressures were successfully measured for a wide range of Mach numbers, inflow angles, rotational speeds and blade angles. No barriers were discovered that would prevent proceeding with the PTA (Prop-Fan Test Assessment) Flight Test Program scheduled for early 1987.

Campbell, William A.↗

NASA NTRS1997

The Characteristics of Fatigue Damage in the Fuselage Riveted Lap Splice Joint

An extensive data base has been developed to form the physical basis for new analytical methodology to predict the onset of widespread fatigue damage in the fuselage lap splice joint. The results of detailed destructive examinations have been cataloged to describe the physical nature of MSD in the lap splice joint. ne catalog includes a detailed description, e.g., crack initiation, growth rates, size, location, and fracture morphology, of fatigue damage in the fuselage lap splice joint structure. Detailed examinations were conducted on a lap splice joint panel removed from a full scale fuselage test article after completing a 60,000 cycle pressure test. The panel contained a four bay region that exhibited visible outer skin cracks and regions of crack link-up along the upper rivet row. Destructive examinations revealed undetected fatigue damage in the outer skin, inner skin, and tear strap regions. Outer skin fatigue cracks were found to initiate by fretting damage along the faying surface. The cracks grew along the faying surface to a length equivalent to two to three skin thicknesses before penetrating the outboard surface of the outer skin. Analysis of fracture surface marker bands produced during full scale testing revealed that all upper rivet row fatigue cracks contained in a dim bay region grow at similar rates; this important result suggests that fracture mechanics based methods can be used to predict the growth of outer skin fatigue cracks in lap splice structure. Results are presented showing the affects of MSD and out-of-plane pressure loads on outer skin crack link-up.

Piascik, Robert S.↗

NASA NTRS1999

Determination of the Corrosive Conditions Present within Aircraft Lap-Splice Joints

The complexity of airframe structure lends itself to damage resulting from crevice corrosion. Fuselage lap-splice joints are a particularly important structural detail in this regard because of the difficulty associated with detection and measurement of corrosion in these occluded regions. The objective of this work is to develop a laboratory corrosion test protocol to identify the chemistry to which lap joints are exposed and to develop a model of the corrosion within the joints. A protocol for collecting and identifying the chemistry of airframe crevice corrosion has been developed. Capillary electrophoresis (CE) is used to identify the ionic species contained in corrosion product samples removed from fuselage lap splice joints. CE analysis has been performed on over sixty corrosion product samples removed from both civilian and military aircraft. Over twenty different ions have been detected. Measurements of pH of wetted corroded surfaces indicated an alkaline occluded solution. After determining the species present and their relative concentrations, the resultant solution was reproduced in bulk and electrochemical tests were performed to determine the corrosion rate. Electrochemical analyses of the behavior of AA2024-T3 in these solutions gave corrosion rates of up to 250 microns per year (10 mpy). Additional tests have determined the relative importance of each of the detected ions in model solutions used for future predictive tests. The statistically significant ions have been used to create a second generation solution. Laboratory studies have also included exposure tests involving artificial lap joints exposed to various simulated bulk and crevice environments. The extent and morphology of the attack in artificial lap joints has been compared to studies of corroded samples from actual aircraft. Other effects, such as temperature and potential, as well as the impact of the environment on fatigue crack growth have also been studied.

Lewis, Karen S.↗

NASA NTRS2002

Flaw Tolerance in Lap Shear Brazed Joints

Vacuum brazing is a viable process to achieve strong permanent and hermetic joints in space. As in any joining process, brazed Joints have various imperfections and defects. It is important to understand the impact that flaws have on the load carrying capacity and performance of the brazed joints. This study focuses on the behavior of lap shear joints due to their engineering importance in brazed aerospace structures. In Part 1 an average shear strength capabilitY and failure modes of the single lap joints are explored. Specimens comprised of 0.090 inch thick 347 stainless steel sheet brazed with pure silver are tested in accordance with the AWS C3.2 standard. Comparison of the measured loads and average shear stresses at failure with the Finite Element Analysis (FEA) of the same specimens as a function of the overlap lengths shows excellent correlation between the experimental and calculated values for the defect-free lap joints. In Part 2, various flaws will be introduced in the test specimens to simulate lack of braze coverage in the lap joints. Mechanical testing and FEA will be performed on these joints to verify if behavior of ductile ]appoints containing flaws is similar to the joints with the reduced braze area. Finally, in Part 3, the results obtained in Part 1 and 2 will be applied to the brazed assembly to evaluate a load carrying capability of the structural lap joint containing defects.

Flom, Yury↗

DOE OSTI2015

FRICTION STIR LAP WELDING OF ALUMINUM - POLYMER USING SCRIBE TECHNOLOGY

Friction Stir Scribe (FSS) technology is a relatively new variant of Friction Stir Welding (FSW) which enables lap joining of dissimilar material with very different melting points and different high temperature flow behaviors. The cutter scribe attached at the tip of FSW tool pin effectively cuts the high melting point material such that a mechanically interlocking feature is created between the dissimilar materials. The geometric shape of this interlocking feature determines the shear strength attained by the lap joint. This work presents first use of scribe technology in joining polymers to aluminum alloy. Details of the several runs of scribe welding performed in lap joining of ~3.175mm thick polymers including HDPE, filled and unfilled Nylon 66 to 2mm thick AA5182 are presented. The effect of scribe geometry and length on weld interlocking features is presented along with lap shear strength evaluations.

Upadhyay, Piyush↗

NASA NTRS1966

Device spot-laps spheres to very close tolerances

Device laps precise amounts of metal from high spots on a spherical body to correct minute surface imperfections. The device generates the lapped surface with reference to an existing true surface on the spherical workpiece. Lapping is performed by applying a rotary and oscillatory motion to the workpiece while the lapping tool is held on the workpiece high spot.

Avery, H. W.↗

NASA NTRS1935

Effect of Viscosity on Fuel Leakage Between Lapped Plungers and Sleeves and on the Discharge from a Pump-Injection System

Test data and analysis show that the rate of fuel leakage between a lapped plunger and sleeve varies directly with the density of the fuel, the diameter of the plunger, the pressure producing the leakage, and the cube of the mean clearance between the plunger and sleeve. The rate varies inversely as the length of the lapped fit and the viscosity of the fuel. With a mean clearance between the plunger and sleeve of 0.0001 inch the leakage amounts to approximately 0.2 percent of the fuel injected with gasoline and as low as 0.01 percent with diesel fuel oils. With this mean clearance an effective seal is obtained when the length of the lap is three times the diameter of the lap. The deformation of the sleeve and plunger under pressure is sufficient to change the rate of leakage appreciably from that which would be obtained if the clearance was constant under pressure.

Rothrock, A M↗