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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Mechanical and Corrosion Assessment of Friction Self-Piercing Rivet Joint of Carbon Fiber-Reinforced Polymer and Magnesium Alloy AZ31B

In the present work, thermoset carbon fiber–reinforced polymer (CFRP) was spot joined to magnesium alloy AZ31B by a friction self-piercing riveting (F-SPR) process. Lap shear tensile and cross-tension testing were used to evaluate the mechanical joint performance. An average lap shear tensile load of 5.18 kN was achieved, while an average of 2.81 kN was found from cross-tension testing. All F-SPR samples showed a pullout of AZ31B after mechanical testing, indicating good mechanical interlocking between the steel rivet and AZ31B. Corrosion potential was measured for each material to establish the galvanic corrosion characteristics. As expected, AZ31B was found to be the most active, while thermoset CFRP was the most noble. The steel rivet fell between the AZ31B (active) and the thermoset CFRP (noble). Salt fog corrosion testing (ASTM B-117) was performed to evaluate the corrosion performance of the uncoated F-SPR joint. With up to 200 h of exposure, the post-corroded F-SPR joint integrity retained 81.2% of the pre-exposure F-SPR joint strength with AZ31B pullout failure mode. From cross-sectional analysis of the F-SPR joint, extensive corrosion of AZ31B was observed at the joint and other exposure areas. However, steel rivet was not significantly corroded due to sacrificial anode effect by which AZ31B corroded first in the galvanic couple.

36 MATERIALS SCIENCE↗
DOE OSTI2020

MECHANICAL AND CORROSION ASSESSMENT OF FRICTION SELF-PIERCING RIVET JOINT OF CARBON FIBER-REINFORCED POLYMER AND MAGNESIUM ALLOY AZ31B

In the present work, thermoset carbon fiber–reinforced polymer (CFRP) was spot joined to magnesium alloy AZ31B by a friction self-piercing riveting (F-SPR) process. Lap shear tensile and cross-tension testing were used to evaluate the mechanical joint performance. An average lap shear tensile load of 5.18 kN was achieved, while an average of 2.81 kN was found from cross-tension testing. All F-SPR samples showed pull-out of AZ31B after mechanical testing, indicating good mechanical interlocking between the steel rivet and AZ31B. Corrosion potential was measured for each material to establish the galvanic corrosion characteristics. As expected, AZ31B was found to be the most active, while thermoset CFRP was the most noble. The steel rivet fell between the AZ31B (active) and the thermoset CFRP (noble). Salt fog corrosion testing (ASTM B-117) was performed to evaluate the corrosion performance of the uncoated F-SPR joint. With up to 200 h of exposure, the post-corroded F-SPR joint integrity retained 81.2% of the pre-exposure F-SPR joint strength with AZ31B pull-out failure mode. From cross-sectional analysis of the F-SPR joint, extensive corrosion of AZ31B was observed at the joint and other exposure areas. However, steel rivet was not significantly corroded potentially due to sacrificial anode effect by which AZ31B corroded first in the galvanic couple.

Lim, Yong Chae↗
NASA NTRS1969

Flexible rivet-set

Tool sets rivets in tight places where the riveting head of the gun cannot be laid on the rivet. Tool may be made in any of many diameters and lengths, and its principle and use are not restricted to riveting.

Hespenhide, W. H.↗
NASA NTRS1994

Detection of Fatigue Cracks at Rivets with Self-Nulling Probe

A new eddy current probe developed at NASA Langley Research Center has been used to detect small cracks at rivets in aircraft lap splices [1]. The device has earlier been used to detect isolated fatigue cracks with a minimum detectable flaw size of roughly 1/2 to 1/3 the diameter of the probe [2]. The present work shows that the detectable flaw size for cracks originating at rivets can be greatly improved upon from that of isolated flaws. The use of a rotating probe method combined with spatial filtering has been used to detect 0.18 cm EDM notches, as measured from the rivet shank, with a 1.27 cm diameter probe and to detect flaws buried under the rivet head, down to a length of 0.076 cm, using a 0.32 cm diameter probe. The Self-Nulling Electromagnetic Flaw Detector induces a high density eddy current ring in the sample under test. A ferromagnetic flux focusing lens is incorporated such that in the absence of any inhomogeneities in the material under test only a minimal magnetic field will reach the interior of the probe. A magnetometer (pickup coil) located in the center of the probe therefore registers a null voltage in the absence of material defects. When a fatigue crack or other discontinuity is present in the test article the path of the eddy currents in the material is changed. The magnetic field associated with these eddy currents then enter into the interior of the probe, producing a large output voltage across the pickup coil leads. Further

Wincheski, Buzz↗
DOE OSTI2023

Wire rivet

A rivet assembly for securing a wire in electrical communication with a substrate having a hollow cylindrical body with a first opening at a proximal end and a second opening at a distal end. The rivet assembly further includes a wire with a portion in electrical communication with the cylindrical body. The rivet assembly yet further includes a compression mechanism configured for use selectively compressing the cylindrical body along an axial direction. Compression of the cylindrical body can cause diametric expansion of an outer diameter of the cylindrical body to retain the cylindrical body within a substrate. The rivet assembly additionally includes wire retention structure configured for holding the wire in electrical contact with the compressed cylindrical body.

Briggs, Timothy↗
DOE OSTI2023

Crack-Free Joining of High-Strength AA7055 Sheets by Friction Based Self-Piercing Riveting with the Aid of Numerical Design

Unique friction-based self-piercing riveting (F-SPR) was employed to join high-strength, low-ductility aluminum alloy 7055 for lightweight vehicle applications. This study aimed to maximize the joint strength of the AA7055 F-SPR joint while avoiding cracking issues due to low ductility at room temperature. A fully coupled Eulerian–Lagrangian (CEL) model was employed to predict the process temperature during F-SPR, and the temperature field was then mapped onto a 2D axisymmetric equivalent model for accelerated numerical analysis. The geometry, dimensions, and material strength of the rivet, as well as the depth of the die cavity and plunging depth, were investigated to enhance joint formation. Also, a static finite-element analysis model was developed to predict and analyze the stress distribution in the rivet under different mechanical testing loading conditions. Overall, the numerical model showed good agreement with the experiment results, such as joint formation and mechanical joint strength. With the aid of virtual fabrication through numerical modeling, the joint design iterations and process development time of F-SPR were greatly reduced regarding the goal of lightweight, high-strength aluminum joining.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Robust Independent Validation of Experiment and Theory: Rivet version 3

First released in 2010, the Rivet library forms an important repository for analysis code, facilitating comparisons between measurements of the final state in particle collisions and theoretical calculations of those final states. We give an overview of Rivet's current design and implementation, its uptake for analysis preservation and physics results, and summarise recent developments including propagation of MC systematic-uncertainty weights, heavy-ion and ep physics, and systems for detector emulation. In addition, we provide a short user guide that supplements and updates the Rivet user manual.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1975

High-strength rivet does not require aging

Aluminum rivet is simpler to handle. It does not need aging and provides better high-temperature and shear properties than conventional rivets. Tests at upset height of up to 1.7 diameters have shown rivets to have exceptionally good crack resistance.

Charles, J. F.↗
NASA NTRS1947

Effect of rivet or bolt holes on the ultimate strength developed by 24S-T and Alclad 75S-T sheet in incomplete diagonal tension

Strength tests were made of a number of 24S-T and Alclad 75S-T aluminum alloy shear webs to determine the effect of rivet or bolt holes on the shear strength. Data were obtained for webs which approached a condition of pure shear stress as well as for webs with well-developed diagonal tension. The rivet factor (pitch minus diameter), divided by pitch, was varied from approximately 0.81 to 0.62. These tests indicated that the shear stresses on the gross section were nearly constant for all values of the rivet factor investigated if the other properties of the web were not changed.

Levin, L Ross↗
NASA NTRS1955

An Analysis of the Stability and Ultimate Compressive Strength of Short Sheet-Stringer Panels with Special Reference to the Influence of Riveted Connection Between Sheet and Stringer

A method of strength analysis of short sheet-stringer panels subjected to compression is presented which takes into account the effect that the riveted attachments between the plate and the stiffeners have on the strength of the panels. An analysis of experimental data shows that panel strength is highly influenced by rivet pitch, diameter, and location and that the degree of influence for a given riveting depends on the panel configuration and panel material. (author)

Semonian, Joseph W↗
NASA NTRS1955

An Analysis of the Stability and Ultimate Compressive Strength of Short Sheet-stringer Panels with Special Reference to the Influence of the Riveted Connection Between Sheet and Stringer

A method of strength analysis of short sheet-stringer panels subjected to compression is presented which takes into account the effect that the riveted attachments between the plate and the stiffeners have on the strength of panels. An analysis of experimental data shows that panel strength is highly influenced by rivet pitch, diameter, and location and that the degree of influence for a given riveting depends on the panel configuration and panel material.

Semonian, Joseph W↗
NASA NTRS1930

Riveted joints in thin plates

The method of riveting by forming the closing head under increasing pressure or by a series of hammer blows is investigated. The question as to the best edge distance, i.e. that distance from the rivet center to the plate edge below which it is unadvisable to go and, at the same time useless to go beyond, was examined. The slippage of plates which occurs under the effect of a certain stress, does not completely disappear on unloading. The elastic form change is essentially a function of the elasticity modulus, the slip modulus, the supporting moment, the rivet spacing, etc.

Hilbes, W↗
NASA NTRS1994

Statistical investigation of fatigue crack initiation and growth around chamfered rivet holes in Alclad 2024 T3 as affected by corrosion

In panel specimens with rivet holes cracks initiate in the blunted knife edge of the chamfered rivet hole and propagate inward as well as along the hole. The fatigue lifetime to dominant crack information was defined as the number of cycles, N500 micrometer, to formation of a 500 micrometer long crack. Statistical data on N500 micrometer and on crack propagation after N500 micrometer were obtained for a large number of uncorroded specimens and specimens corroded in an ASTM B 117 salt spray. Considerable variation in N500 micrometer and crack propagation behavior was observed from specimen to specimen of the same nominal geometry with chamfered rivet holes increased the probability for both early formation and later formation of a propagating 500 micrometer fatigue crack. The growth of fatigue cracks after 500 micrometer size was little affected by prior salt spray.

Fadragas, M. I.↗
NASA NTRS1947

The Load Distribution in Bolted or Riveted Joints in Light-Alloy Structures

This report contains a theoretical discussion of the load distribution in bolted or riveted joints in light-alloy structures which is applicable not only for loads below the limit of proportionality but also for loads above this limit. The theory is developed for double and single shear joints. The methods given are illustrated by numerical examples and the values assumed for the bolt (or rivet) stiffnesses are based partly on theory and partly on known experimental values. It is shown that the load distribution does not vary greatly with the bolt (or rivet) stiffnesses and that for design purposes it is usually sufficient to know their order of magnitude. The theory may also be directly used for spot-welded structures and, with small modifications, for seam-welded structures, The computational work involved in the methods described is simple and may be completed in a reasonable time for most practical problems. A summary of earlier theoretical and experimental investigations on the subject is included in the report.

Vogt, F.↗
NASA NTRS1943

Effect of Rivet Holes on the Ultimate Strength Developed by 24S-T and Alclad 75S-T Sheet in Incomplete Diagonal Tension

Strength tests were made of a number of 24S-T and Alclad 75S-T aluminum-alloy shear webs to determine the effect of rivet or bolt holes on the shear strength. Data were obtained for webs which approached a condition of pure shear stress as well as for webs with well-developed diagonal tension. The rivet factor, (pitch minus diameter) divided by pitch, was varied from approximately 0.81 to 0.62. These tests indicated that the shear stresses on the gross section were nearly constant for all values of the rivet factor investigated if the other properties of the web were not changed.

Levin, L. Ross↗
DOE OSTI2026

Elucidating microstructural evolution and hardness variation across friction self-piercing riveted Al-7055 using synchrotron X-ray scattering and advanced microscopy techniques

Friction self-piercing riveting (FSPR) is a unique hybrid joining technique that combines the advantages of mechanical interlocking, frictional heat, and solid-state joining (if metallurgically compatible) to produce crack free joints in high strength and/or low-ductility alloys at room temperature. Here, in the current study, Al-7055 sheets were joined using FSPR for lightweight automotive applications and significant microhardness variations were observed across the joint cross-section. A detailed microstructural characterization at multiple length scales was carried out using advanced electron microscopy and X-ray scattering techniques to provide a fundamental understanding of the process-structure-property relationships. The relative contributions of microstructural characteristics at various length scales (i.e., grain size, dislocation density, solute concentration, precipitate nature) to strengthening were estimated using existent formulations (i.e., Hall-Petch, Taylor, precipitate bypass/shear equations) and correlated to the observed microhardness values across different regions. Small-angle X-ray scattering and scanning transmission electron microscopy revealed significant changes in the size and volume fraction of precipitate species, i.e., GP-I Zones, η′, and Mg/Zn solute co-clusters, depending on the process region. It was observed that the dissolution of the small η′/GP-I zones (T ∼ 150–200 °C) in the heat-affected zone were the key reason for the hardness drop. Further, it was shown that solid-solution, dislocation, grain size and solute co-cluster strengthening played a key role in the thermo-mechanically affected zone and grain-refined zone (GRZ). Finally, these observations were leveraged along with the Zener-Holloman relationship and grain size in the GRZ to estimate the peak joining temperature of the GRZ (∼ 350 °C) near the steel rivet.

aluminum 7xxx alloy↗
NASA NTRS1938

Tank Tests to Show the Effect Rivet Heads on the Water Performance of a Seaplane-Float

A 1/3.5 full-sized model of a seaplane float constructed from lines supplied by the Bureau of Aeronautics, Navy Department, was tested first with smooth painted bottom surfaces and then with round-head rivets, plate laps, and keel plates fitted to simulate the actual bottom of a metal float. A percentage increase in water resistance caused by the added roughness was found to be from 5 to 20 percent at the hump speed and from 15 to 40 percent at high speeds. The effect of the roughness of the afterbody was found to be negligible except at high trims. The model data were extrapolated to full size by the usual method that assumes the forces to vary according to Froude's law and, in the case of the smooth model, by a method of separation that takes into account the effect of scale on the frictional resistance. It was concluded that the effect of rivet heads on the take-off performance of a relatively high-powered float seaplane is of little consequence, but it may be of greater importance in the case of more moderately powered flying boats.

FLOATS - RESISTANCE EFFECT OF SURFACE ROUGHNESS↗