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Laser Ablation Surface Treatment of Structural Aerospace Composites and Metal Alloys for Adhesive BondingNASA 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.
Document ID
20180006285
Acquisition Source
Langley Research Center
Document Type
Conference Paper
Authors
Connell, John W. (NASA Langley Research Center Hampton, VA, United States)
Yi, Lin (National Inst. of Aerospace Hampton, VA, United States)
Wohl, Christopher J. (NASA Langley Research Center Hampton, VA, United States)
Hopkins, John W. (NASA Langley Research Center Hampton, VA, United States)
Ledesma, Rodolfo I. (Virginia Univ. Charlottesville, VA, United States)
Palmieri, Frank L. (NASA Langley Research Center Hampton, VA, United States)
Date Acquired
October 16, 2018
Publication Date
February 25, 2018
Subject Category
Composite Materials
Report/Patent Number
NF1676L-28021
Meeting Information
Meeting: 2018 Annual Meeting of the Adhesion Society
Location: San Diego, CA
Country: United States
Start Date: February 25, 2018
End Date: March 1, 2018
Sponsors: Adhesion Society, Inc.
Funding Number(s)
WBS: WBS 826611.04.07.03.05
Distribution Limits
Public
Copyright
Public Use Permitted.

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