A Lightweight Optical Approach to Detect Incipient Heat Damage
Navy SBIR FY2013.1

Sol No.: Navy SBIR FY2013.1
Topic No.: N131-013
Topic Title: A Lightweight Optical Approach to Detect Incipient Heat Damage
Proposal No.: N131-013-0015
Firm: Spectral Sciences, Inc.
4 Fourth Avenue
Burlington, Massachusetts 01803-3304
Contact: Frank Clark
Phone: (781) 273-4770
Web Site: www.spectral.com
Abstract: Composite materials, widely used in aircraft, reduce manufacturing cost, improve structural performance, and boost fuel efficiency. However, composites are susceptible to hidden heat damage, which may occur from fire, exhaust impingement, overheating, or during repairs. The earliest heat damage stage, referred to as "incipient" heat damage, may reduce upper use temperature, cause matrix mass loss, and reduce mechanical flexural strength. We propose an innovative approach that detects this very early matrix damage via changes in the mechanical flexural response of a structure. We use a small lightweight optical imaging detector that can rapidly monitor large structures and identify regions exhibiting incipient heat damage. We combine small mechanical excitation of the structure under test with a lightweight camera that images the surface resonant frequency, directly probing the local flexural strength of the composite material. This technique, called the Fast Imaging Non-Destructive Inspection Technique (FINDIT), can directly and nondestructively test the mechanical flexural properties of composite material. Flexural damage has been shown to provide a first warning of incipient heat damage before visual manifestation. FINDIT quantitatively measures the associated tilt-tip surface changes, and may be automated, removing subjective judgment factors, rendering the approach fully functional under adverse circumstances.
Benefits: This technique will increase safety and reduce cost by accurately detecting incipient heat damage, pinpointing the precise damaged area, and quantifying the degree of damage. This mitigates the need for unnecessary repair or replacement, while at the same time assuring flight safety. The technique may be automated, removing subjective judgment factors and permitting use under adverse conditions. We envision commercial application either by use in normal hangar maintenance, or by imaging commercial aircraft as they are mechanically excited during normal taxi ("drive by safety test"), providing regular autonomous maintenance checks of airframe viability, reducing maintenance costs and increasing safety. We believe this technique has potential for implementation in an inexpensive, lightweight, handheld package (i.e. a modified "smartphone"), which would greatly reduce maintenance costs in the Navy, DoD, and commercial applications. The technique should be applicable to composite production, as a fast inexpensive procedure to test bonding and large structural integrity.