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2005 Contents


COMPARISON OF NORMAL AND PHASE STEPPING SHEAROGRAPHIC NDE (2005)

ABSTRACT

The paper presents results of non-destructive testing of composite main rotor helicopter blade calibration specimens using the laser based optical NDE technique known as Shearography. The tests were performed initially using the already well established near real-time non-destructive technique of Shearography, with the specimens perturbed during testing for a few seconds using the hot air from a domestic hair dryer. Subsequent to modification of the shearing device utilized in the shearographic setup, phase stepping of one of the sheared images to be captured by the CCD camera was enabled and identical tests were performed on the composite main rotor helicopter blade specimens. Considerable enhancement of the images manifesting or depicting the defects on the specimens is noted suggesting that phase stepping is a desirable enhancement technique to the traditional Shearographic setup.

Complete Paper (1507kB)


PHASE STEPPING SHEAROGRAPHY AND ELECTRONIC SPECKLE PATTERN INTERFEROMETRY (2005)

ABSTRACT

Electronic Speckle Pattern Interferometry (ESPI) and Digital Shearography have been shown to be of great value for the Non-destructive Evaluation of the integrity of materials and manufactured components. The NDT Laboratory in the Department of Mechanical Engineering at the University of Cape Town has an active research group focused on the research, development and the various applications of ESPI and Digital Shearography. This work culminated in the development of portable prototype inspection systems based on Digital Shearography and ESPI.

The current portable systems, mentioned above, generate intensity based fringe patterns. By introducing a known phase shift into the speckle pattern during the image recording process, displacement fringe patterns, based on the change in phase of the laser light, can be generated. These fringe patterns differ in that they reveal distinct 2Ï€ discontinuities and are thus suited for automated inspection techniques and are also suited for object surface displacement mapping techniques.

This paper reports on the progress made in developing phase stepped ESPI and Digital Shearography. The techniques are described and applied to selected flawed composite samples. The findings are presented and comparisons are drawn between the results obtained from both phase stepping and conventional intensity based optical interference techniques. The possibility of applying phase stepping techniques to portable inspection systems is also discussed.

Complete Paper ((7200kB)


IMPACT DAMAGE DETECTION ON COMPOSITES USING ELECTRONIC SPECKLE PATTERN INTERFEROMETRY (2005)

ABSTRACT

The paper presents the results from an attempt to detect damage resulting from impact loading events such as tool drop or bird collisions etc. on composite materials designed for structural applications in the aerospace industry. The investigation attempted to establish the possibility of detecting; beyond of what is obviously visible to the naked eye, the extent of damage inflicted on composite panels which were subjected to controlled impact. For the purpose, Electronic Speckle Pattern Interferometry was chosen as the Non Destructive Evaluation technique to be employed in this study, because it is non-contacting, whole field, non limited to particular material types and provides fast and easy results in real-time. The specimens were subjected to low velocity impact energy levels by using an instrumented drop-weight impact tester.

Complete Paper ((1186kB)


SIMULTANEOUS SHEAROGRAPHIC AND THERMOGRAPHIC NDT OF AEROSPACE MATERIALS (2005)

ABSTRACT

The paper describes the simultaneous use of Digital Shearographic and Infrared Thermographic techniques when testing aerospace structures made of honeycomb and composite materials. Non Destructive Testing of the structures was accomplished using a proprietary portable Shearographic system, produced at the Mechanical Engineering department of the University of Cape Town, and a relatively inexpensive new comer to the Infrared Thermography field, known as IRISYS Universal Thermal Imager.

Simply,both systems were employed to image the component simultaneously and record the effect of it cooling down after heated with the hot air from a hair drier or a heating lamp. The techniques proved effective in identifying defects such as the crushed honeycomb core in a section of the wing of an unmanned aerial vehicle (UAV) and the de-laminations at different depths in the main rotor blade of an Oryx helicopter. The images indicating the defects as produced by the Shearographic system are visually more dramatic, particularly when enhanced by phase stepping and colour techniques.

On the other hand the Thermographic images besides indicating the position of the flaw, gave information regarding the temperature of the region of the defect relative to the cooler surrounding material. In addition there was the indication that during the cooling down, the infrared system continued to indicate the presence of the flaws/defects for longer period of time than the Shearographic system. It is suggested that in similar tests, the temperature data be coupled to the out of plane displacement gradients with view to provide quantitative thermal stress results.

Complete Paper ((1023kB)


PHASE STEPPING SHEAROGRAPHY AND ELECTRONIC SPECKLE PATTERN INTERFEROMETRY (2005)

ABSTRACT

Electronic Speckle Pattern Interferometry (ESPI) and Digital Shearography have been shown to be of great value for the Non-destructive Evaluation of the integrity of materials and manufactured components. The NDT Laboratory in the Department of Mechanical Engineering at the University of Cape Town has an active research group focused on the research, development and the various applications of ESPI and Digital Shearography. This work culminated in the development of portable prototype inspection systems based on Digital Shearography and ESPI.

The current portable systems, mentioned above, generate intensity based fringe patterns. By introducing a known phase shift into the speckle pattern during the image recording process, displacement fringe patterns, based on the change in phase of the laser light, can be generated. These fringe patterns differ in that they reveal distinct 2Ï€ discontinuities and are thus suited for automated inspection techniques and are also suited for object surface displacement mapping techniques.

This paper reports on the progress made in developing phase stepped ESPI and Digital Shearography. The techniques are described and applied to selected flawed composite samples. The findings are presented and comparisons are drawn between the results obtained from both phase stepping and conventional intensity based optical interference techniques. The possibility of applying phase stepping techniques to portable inspection systems is also discussed.

Complete Paper ((2135kB)