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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

Supersonic Retropulsion Surface Preparation of Carbon Fiber Reinforced Epoxy Composites for Adhesive Bonding

Surface preparation is widely recognized as a key step to producing robust and predictable bonds in a precise and reproducible manner. Standard surface preparation techniques, including grit blasting, manual abrasion, and peel ply, can lack precision and reproducibility, which can lead to variation in surface properties and subsequent bonding performance. The use of a laser to ablate composite surface resin can provide an efficient, precise, and reproducible means of preparing composite surfaces for adhesive bonding. Advantages include elimination of physical waste (i.e., grit media and sacrificial peel ply layers that ultimately require disposal), reduction in process variability due to increased precision (e.g. increased reproducibility), and automation of surface preparation, all of which improve reliability and process control. This paper describes a Nd:YAG laser surface preparation technique for composite substrates and the mechanical performance and failure modes of bonded laminates thus prepared. Additionally, bonded specimens were aged in a hot, wet environment for approximately one year and subsequently mechanically tested. The results of a one year hygrothermal aging study will be presented.

Palmieri, Frank L.↗
NASA NTRS2003

Shearography for Non-Destructive Evaluation with Applications to BAT Mask Tile Adhesive Bonding and Specular Surface Honeycomb Panels

In this report we examine the applicability of shearography techniques for nondestructive inspection and evaluation in two unique application areas. In the first application, shearography is used to evaluate the quality of adhesive bonds holding lead tiles to the BAT gamma ray mask for the NASA Swift program. By exciting the mask with a vibration, the more poorly bonded tiles can be distinguished by their greater displacement response, which is readily identifiable in the shearography image. A quantitative analysis is presented that compares the shearography results with a destructive pull test measuring the force at bond failure. Generally speaking, the results show good agreement. Further investigation would be useful to optimize certain test parameters such as vibration frequency and amplitude. The second application is to evaluate the bonding between the skin and core of a honeycomb structure with a specular (mirror-like) surface. In standard shearography techniques, the object under test must have a diffuse surface to generate the speckle patterns in laser light, which are then sheared. A novel configuration using the specular surface as a mirror to image speckles from a diffuser is presented, opening up the use of shearography to a new class of objects that could not have been examined with the traditional approach. This new technique readily identifies large scale bond failures in the panel, demonstrating the validity of this approach. For the particular panel examined here, some scaling issues should be examined further to resolve the measurement scale down to the very small size of the core cells. In addition, further development should be undertaken to determine the general applicability of the new approach and to establish a firm quantitative foundation.

Lysak, Daniel B.↗
NASA NTRS2001

Heat Transfer in Adhesively Bonded Honeycomb Core Panels

The Swann and Pittman semi-empirical relationship has been used as a standard in aerospace industry to predict the effective thermal conductivity of honeycomb core panels. Recent measurements of the effective thermal conductivity of an adhesively bonded titanium honeycomb core panel using three different techniques, two steady-state and one transient radiant step heating method, at four laboratories varied significantly from each other and from the Swann and Pittman predictions. Average differences between the measurements and the predictions varied between 17 and 61% in the temperature range of 300 to 500 K. In order to determine the correct values of the effective thermal conductivity and determine which set of the measurements or predictions were most accurate, the combined radiation and conduction heat transfer in the honeycomb core panel was modeled using a finite volume numerical formulation. The transient radiant step heating measurements provided the best agreement with the numerical results. It was found that a modification of the Swann and Pittman semi-empirical relationship which incorporated the facesheets and adhesive layers in the thermal model provided satisfactory results. Finally, a parametric study was conducted to investigate the influence of adhesive thickness and thermal conductivity on the overall heat transfer through the panel.

Daryabeigi, Kamran↗
DOE OSTI2025

Adhesively Bonded Copper and Polyimide for Flexible Printed Circuit Boards: A Data-Driven Degradation Study Under Accelerated Aging

The long-term durability of polyimide laminated adhesive based flexible printed circuit boards (PCBs) is critical to the microelectronics industry. The interface of the adhesive layer binding the polyimide and copper layers is particularly vulnerable since decreased bonding strength can lead to deadhesion, performance loss, and premature device failure. Here, in this study, adhesive-bonded polyimide and copper samples are subjected to 1000 h of damp heat exposure (85 °C/85%RH) to evaluate the impact of moisture and copper inclusion on the adhesive bonding performance. Significant copper diffusion through the adhesive layer is observed, which, combined with moisture uptake, is found to substantially weaken interfacial adhesion in copper-containing samples, thereby reducing device lifetime. Observed surface and bulk material changes are correlated to adhesion strength using the network structural equation modeling (netSEM) approach, resulting in a robust predictive model of performance degradation based on measurable materials properties.

Chemistry↗
NASA NTRS2018

Laser Ablation Surface Treatment of Structural Aerospace Composites and Metal Alloys for Adhesive Bonding

NASA Langley Research Center (LaRC) has been involved over the past decade in the development of laser ablation as a method to surface treat aerospace structural fiber reinforced composites (CFRPs) and metal alloys. [1- 18] Laser surface treatment has been shown to be a rapid, high precision, and reproducible method for surface treatment of these materials, and is amenable to automation. The laser ablation process removes surface contamination such as silicones, creates surface roughness, and chemically activates a surface for bonding. The degree of ablation is controllable by adjusting laser parameters. In the case of CFRPs, ablation can be performed without damage to any underlying carbon fibers. In the case of metal alloys, ablation is possible without surface embrittlement, heat damage or creation of undesirable grain structures or morphologies. The optimum laser treatment conditions are substrate dependent and generally are influenced by laser wavelength and pulse duration (typically fixed for a laser system), and laser power. In the case of metal alloys such as Ti-6Al-4V, the laser ablation process eliminates the need for several steps of the conventional processes, including hydrofluoric (HF) acid and caustic treatment. These steps are often conducted in dip tanks and require costly facilities and environmentally unfriendly liquids. In addition, the laser can create nano-porosity on the Ti-6Al-4V alloy surface allowing for sol-gel penetration and thereby creating a gradient interface with improved temperature and mechanical performance. NASA LaRC has also been involved with the development of in-line characterization methods compatible with the laser treatment process to rapidly determine the presence of key contaminates such as silicones that, even at very low concentrations, are a threat to adhesive bonding. A spectroscopic technique called micro-laser induced breakdown spectroscopy (u-LIBS) has been developed to rapidly detect silicones at concentrations below those known to cause bonding problems. This technique requires no sample preparation, vacuum or inert atmosphere, has no practical size limitations, and provides nearly instantaneous feedback to the operator. This presentation will give an overview and update of these developments with specific examples highlighted.

Connell, John W.↗
NASA NTRS1985

Mixed-mode cyclic debonding of adhesively bonded composite joints

A combined experimental-analytical investigation to characterize the cyclic failure mechanism of a simple composite-to-composite bonded joint is conducted. The cracked lap shear (CLS) specimens of graphite/epoxy adherend bonded with EC-3445 adhesive are tested under combined mode 1 and 2 loading. In all specimens tested, fatigue failure occurs in the form of cyclic debonding. The cyclic debond growth rates are measured. The finite element analysis is employed to compute the mode 1, mode 2, and total strain energy release rates (i.e., GI, GII, and GT). A wide range of mixed-mode loading, i.e., GI/GII ranging from 0.03 to 0.38, is obtained. The total strain energy release rate, G sub T, appeared to be the driving parameter for cyclic debonding in the tested composite bonded system.

Rezaizadeh, M. A.↗
NASA NTRS1970

Nondestructive sonic testing of adhesive-bonded composites

System detects and determines the location, depth, and areas of crushed core or of breaks in bonding between core and adhesive, adhesive and face sheet, or face sheet and external doubler. It is applicable to honeycomb panels of metal and/or plastics and to metal-to-metal laminates.

Caustin, E. L.↗
NASA NTRS1971

New primers for adhesive bonding of aluminum alloys

Synthetic polypeptide adhesive primers are effective, with high temperature epoxy resins, at temperatures from 100 deg to 300 deg C. Lap-shear failure loads and lap-shear strength of both primers are discussed.

Burrell, B. W.↗
NASA NTRS1986

Effect of adherend thickness and mixed mode loading on debond growth in adhesively bonded composite joints

Symmetric and unsymmetric double cantilever beam (DCB) specimens were tested and analyzed to assess the effect of: (1) adherend thickness, and (2) a predominantly mode I mixed mode loading on cyclic debond growth and static fracture toughness. The specimens were made of unidirectional composite (T300/5208) adherends bonded together with EC3445 structural adhesive. The thickness was 8, 16, or 24 plies. The experimental results indicated that the static fracture toughness increases and the cyclic debond growth rate decreases with increasing adherend thickness. This behavior was related to the length of the plastic zone ahead of the debond tip. For the symmetric DCB specimens, it was further found that displacement control tests resulted in higher debond growth rates than did load control tests. While the symmetric DCB tests always resulted in cohesive failures in the bondline, the unsymmetric DCB tests resulted in the debond growing into the thinner adherend and the damage progressing as delamination in that adherend. This behavior resulted in much lower fracture toughness and damage growth rates than found in the symmetric DCB tests.

Mangalgiri, P. D.↗
DOE OSTI2024

Final Report on Characterization of Irradiated Sensors and Coupling Adhesive Bonds

This report summarizes characterization via scanning/transmission electron microscopy of the microstructures of the unirradiated and irradiated piezoelectric ultrasonic sensor/aluminum substrate assemblies using four commercially available inorganic coupling adhesives to bond two types of piezoelectric crystals to the substrates. The sample assemblies were irradiated in the PULSTAR reactor at NC State University and ultrasonic data was collected in-situ. ORNL LAMDA Laboratory capabilities were utilized to perform pre- and post-irradiation examination of the sensor assemblies. This document summarizes the PIE performed at the ORNL LAMDA laboratory. The results of the PIE described in this report are consistent with the ultrasonic data collected during irradiation – in particular, high temperature epoxy adhesive seemed to provide the best coupling as compared to the refractory ceramic adhesives. It was determined that the quality of the sensor-adhesive-substrates governed the ultrasonic performance of the sensors. It was also apparent that irradiation did not significantly affect bond quality, which is also supported by the ultrasonic data collected during irradiation. A more comprehensive DOE NSUF Final Report including details of materials selection, sample fabrication, initial ultrasonic testing, irradiation and in-situ ultrasonic testing, positron annihilation lifetime spectroscopy and doppler broadening spectroscopy performed at EPRI and NC State University will be published at the conclusion of the project.

36 MATERIALS SCIENCE↗
NASA NTRS1970

Improvement of adhesive-bonded structural joints

Investigation is described of methods for obtaining uniform shear stress distribution in adhesives used in double-lap bonded joints. Design rules for reducing adhesive peak shear stresses are listed. Test results of an analysis of straight-lap joint design and stepped-lap joint design are given.

Evensen, H. A.↗
NASA NTRS1983

Viscoelastic study of an adhesively bonded joint

The plane strain problem of two dissimilar orthotropic plates bonded with an isotropic, linearly viscoelastic adhesive is considered. Both the shear and the normal stresses in the adhesive are calculated for various geometries and loading conditions. Transverse shear deformations of the adherends are taken into account, and their effect on the solution is shown in the results. All three inplane strains of the adhesive are included. Attention is given to the effect of temperature, both in the adhesive joint problem and to the heat generation in a viscoelastic material under cyclic loading. This separate study is included because heat generation and or spatially varying temperature are at present too difficult to account for in the analytical solution of the bonded joint, but whose effect can not be ignored in design.

Joseph, P. F.↗
NASA NTRS2006

Adhesive Bonding of Titanium to Carbon-Carbon Composites for Heat Rejection Systems

High temperature adhesives with good thermal conductivity, mechanical performance, and long term durability are crucial for the assembly of heat rejection system components for space exploration missions. In the present study, commercially available adhesives were used to bond high conductivity carbon-carbon composites to titanium sheets. Bonded pieces were also exposed to high (530 to 600 Kelvin for 24 hours) and low (liquid nitrogen 77K for 15 minutes) temperatures to evaluate the integrity of the bonds. Results of the microstructural characterization and tensile shear strengths of bonded specimens will be reported. The effect of titanium surface roughness on the interface microstructure will also be discussed.

Cerny, Jennifer↗
NASA NTRS1983

A fracture mechanics approach for designing adhesively bonded joints

An analytical and experimental investigation was undertaken to determine if the adhesive debond initiation stress could be predicted for arbitrary joint geometries. The analysis was based upon a threshold total strain-energy-release rate (Gth) concept. Two bonded systems were tested: T300/5208 graphite/epoxy adherends bonded with either EC-3445 or FM-300 adhesive. The Gth for each adhesive was determined from cracked-lap-shear (CLS) specimens by initiation tests. Finite-element analyses of various tapered CLS specimen geometries predicted the specimen stress at which the total strain-energy-release rate (GT) equaled Gth at the joint tip. Experiments verified the predictions. The approach described herein predicts the maximum stress at which an adhesive joint can be cycled yet not debond. Furthermore, total strain-energy-release rate appeared to be the driving parameter for cyclic debonding and debond initiation in structural adhesives. In addition, debond initiation and growth were found to occur with virtually no peel stress present.

Johnson, W. S.↗