No abstract

The objective of this work was to demonstrate the use of ultrasonics to determine the end-of-cure for autoclave cured, graphite/epoxy composite laminates. The fundamental benefit of this work will be understanding when to complete the temperature hold and cool down the autoclave and, therefore, consistently produce composite laminates with the desired material properties. An additional benefit is the ability to follow the changing viscosity of the resin during the initial part ofthe cure.The general approach to this program involved using pulse-echo ultrasonics to measure the transit time for longitudinal ultrasonic waves to pass through a graphite/epoxy composite laminate during cure. Sixteen, 32 and 64 ply [0/90]s graphite/Fiberite 934 epoxy panels were fabricated and cured to various end-ofcure conditions. Additionally, panels with various starting conditions were run. Sound speed was calculated using the panel thickness (number of plies multiplied by the manufacturer specified thickness of each ply) divided by the measured transit time. * formerly of the carderock Division Naval Surface Warfare Center, Annapolis, MD 21402 72 / SPIE Vol. 2948 O-8194-2352-1/96/$6.OO Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/21/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspxMechanical (maximum fiber stress and maximum strain) and glass transition temperature (Tg) tests are being performed on all the fabricated panels. Determining the relationships between the velocity profiles, mechanical properties, and Tg data is in progress. Ultimately, the goal is to understand the relationship between the ultrasonic data and state-of-cure, and to incorporate the ultrasonic sensor into an operational expert system for sensor feedback control of the autoclave process.BACKGROUND

The Pacific Northwest National Laboratory (PNNL) is conducting studies for the U.S. Nuclear Regulatory Commission (NRC) to assess the capability, effectiveness, and reliability of ultrasonic testing (UT) as a replacement method for radiographic testing (RT) for volumetric examination of nuclear power plant (NPP) components. This particular study focused on evaluating the use of phased-array (PA) UT on carbon steel plate welds. Welding fabrication flaws included a combination of planar and volumetric types; for example, incomplete fusion, lack of penetration, cracks, porosity, and slag inclusions. The examinations were conducted using PAUT techniques applied primarily for detection and flaw type characterization. This paper will discuss the results of using PAUT in lieu of RT for detection and classification of fabrication flaws in carbon steel plate welds.

We compare results of ultrasonic, microwave, and thermal imaging of graphite-epoxy composite panels with artificial defect structures.

The Knowledge Based Inspection System (KBIS), comprised ofneural network classification ofultrasonic data and advanced ultrasonic sizing methodologies, is being developed under a Navy Manufacturing Technology Program. The intent of the KBIS program is to provide a tool with which an ultrasonic inspector can obtain enhanced information to improve the probability of correctly accepting or rejecting weld discontinuities. Ultimately, the use of KBIS should reduce the long-term cost of ownership ofvessels due to elimination of detrimental discontinuities only.