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A study of impact damage morphology in unidirectional carbon/epoxy laminates was performed. A 'load drop' method was investigated for prediction of the delamination threshold energy (EDT) for impact. The impacted samples were subjected to uniaxial, in-plane compression to observe the growth of damage, failure modes, and residual strength. Samples were scanned before and after CAI using air-coupled through-transmission ultrasound and amplitude C-scans were collected for visual inspection of damage. [ABSTRACT FROM AUTHOR]

Previously we have described the Computer Aided Tap Tester (CATT), a simple instrumented probe and software that facilitates the generation of tap test C-scans in field environments. Early in the CATT development it was noted that inspectors prefer hand tapping at random locations over the part, eventually covering the part to the satisfaction of the inspector. To speed inspections, a regimented method of tapping was incorporated into the CATT via a grid laid over the part. Although the CATT system is quite simple to use, the method of tapping at each grid location in a pre-determined raster pattern continues to encounter resistance from the inspectors. The preferred free scanning of the inspection area dovetails nicely with the GenScan system previously reported on, where the operator scans over the inspection area freely, starting with larger pixels, and refines the geometry of flaw indications with finer pixels. As part of an Air Force project, we are merging the CATT instrumented tap data with position encoding and pixel change on-the-fly features of the GenScan. A description and demonstration of its operation will be presented. This material is based on work supported by the Air Force Research Laboratory under Contract[sharp/mesh/hash_synonym]FA8650-04-C-5228 at Iowa State University’s Center for NDE. [ABSTRACT FROM AUTHOR]

Metallic inserts are embedded into composite honeycomb sandwiches as hard points for mechanical connections. Air-coupled ultrasound can be used for detecting disbonds between the insert and the facesheet. It was discovered in such inspections that a surprisingly large amplitude could be transmitted through thick metallic inserts (e.g. 0.75″ thick and 1.5″ diameter), whereas a thin plate of the same material will transmit a much weaker signal. This paper reports an experimental and analytic study of the geometrical effect of inserts on transmitted UT signals. Modal analyses of cylindrical inserts were made using the finite element code ANSYS. The transmission efficiency or air-coupled ultrasound correlated well with the longitudinal vibration mode of the cylinder. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper describes the development of a non-mechanically encoded, simple, field-worthy air-coupled ultrasonic scanning system that gives quantitative information about the size of damage and underlying structure in composite and aluminum aerospace structures. The system consists of the AIRSCAN® air-coupled ultrasonic testing system, the Flock of Birds® real-time motion tracking equipment, a lightweight composite yoke, and laptop PC with data acquisition and processing software. Through transmission C-scan images are generated manually by moving transducers attached to a yoke across the part’s surface. The prototype has produced images for a variety of aircraft composite and metal honeycomb structures containing flaws, damages, and repairs. Field tests on commercial and military aircraft as well as rotor blades have begun. Initial test results are shown. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper describes the development and implementation of two complementary nondestructive inspection methods for repairs made on aircraft composite honeycomb structures: computer aided tap testing (CATT) and air-coupled ultrasonic testing (AC-UT). The CATT, being a semi-automated and quantitative technique, is exploited to map out the interior conditions of a repaired part. The same repair is also imaged with air-coupled ultrasound and both compared with the results from destructive sectioning. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

Standard linear ultrasonic testing techniques have long been employed for locating and characterizing relatively open cracks in a wide variety of materials, from metallic alloys and ceramics to composites. In all these materials, the detection of open cracks easily accomplished because the void between the two crack surfaces provides sufficient acoustic impedance mismatch to reflect the incident energy. Closed or partially closed cracks, however, may often go undetected because contacting interfaces allow transmission of ultrasound. In the green (unsintered) state, powder metallurgy compacts typically contain high residual stresses that have the ability to close cracks formed during the compaction process, a result of oxide films, improper powder lubricant, mold design, etc. After sintering, the reduction of residual stresses may no longer be sufficient to close the crack. Although the crack may be more easily detected, it is obvious most desirable to discover defects prior to sintering. It has been shown that the displacements of an interface may be highly nonlinear if a stress wave of sufficient intensity propagates across it, a result of the stress wave either opening or closing the interface. Current efforts involve the application of nonlinear acoustic techniques, in particular acoustic harmonic generation measurements, for the detection and characterization of tightly closed cracks in powder metallurgy parts. A description of the equipment and the measurement technique will be discussed and initial experimental results on sintered and green compacts will be presented.—This work was performed at the Ames Laboratory, Iowa State University under USDOE Contract No. W-7405-ENG-82. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This paper describes a simple, field-worthy tap test imaging system that gives quantitative information about the size, shape, and severity of defects and damages. The system consists of an accelerometer, electronic circuits for conditioning the signal and measuring the impact duration, a laptop PC and data acquisition and processing software. The images are generated manually by tapping on a grid printed on a plastic sheet laid over the part’s surface. A mechanized scanner is currently under development. The prototype has produced images for a variety of aircraft composite and metal honeycomb structures containing flaws, damages, and repairs. Images of the local contact stiffness, deduced from the impact duration using a spring model, revealed quantitatively the stiffness reduction due to flaws and damages, as well as the stiffness enhancement due to substructures. The system has been field tested on commercial and military aircraft as well as rotor blades and engine decks on helicopters. Field test results will be shown and the operation of the system will be demonstrated.—This material is based upon work supported by the Federal Aviation Administration under Contract #DTFA03-98-D-00008, Delivery Order No. IA016 and performed at Iowa State University’s Center for NDE as part of the Center for Aviation Systems Reliability program. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]