Thermal Inspection Research Articles

Investigation of Uncooled Microbolometer Focal Plane Array Infrared Camera for Quantitative Thermography

Thermal nondestructive evaluation has shown promise as a potential NDE technology for next generation US Army rotorcraft structures because it is rapid, noncontacting, and able to inspect complex geometries. To successfully apply thermal inspection systems for field use, the cost and size must be lowered. The infrared camera is a major factor contributing to the overall cost of commercially available thermal inspection systems. Recent advances in uncooled microbolometer focal plane array detectors have resulted in low cost, small size/weight, and low power consumption cameras. These attributes make this technology well suited for portable low cost thermal inspection systems. The purpose of this paper is to investigate the capabilities of the new microbolometer infrared cameras for quantitative thermal nondestructive evaluation. Quantitative thermal diffusivity and thickness images are obtained by minimizing the squared difference between the data and a thermal model on samples with fabricated defects. Critical infrared camera features such as spatial and temperature resolution, detector response time, and detector stability are studied by comparing results to a conventional thermal imaging camera using a cooled InSb focal plane array detector. Finally several techniques are presented to improve the camera’s performance. These techniques include temporal background subtraction, use of a synchronized electronic shutter system, and cyclic flash heating.

Integration of multiple range and intensity image pairs using a volumetric method to create textured three-dimensional models

We present a volumetric approach to three-dimensional (3D) object modeling that differs from previous techniques in that both object texture and geometry are considered in the reconstruc- tion process. The motivation for the research is the simulation of a thermal tire inspection station. Integrating 3D geometry information with two-dimensional thermal images permits the thermal informa- tion to be displayed as a texture map on the tire structure, enhanc- ing analysis capabilities. Additionally, constructing the tire geometry during the inspection process allows the tire to be examined for structural defects that might be missed if the thermal data were textured onto a predefined model. Experimental results demonstrate the efficacy of the proposed approach and quantitative experiments indicate that the volumetric integration technique compares favor- ably to a state-of-the-art, mesh-based integration approach in terms of geometrical accuracy. Future research goals are also noted.

Optimization of heating protocol in thermal NDT, short and long heating pulses: A discussion

Flash and continuous heating are widely used in transient thermal NDT. Choice of the most appropriate heating protocol leads to multiparametric optimization involving temperature resolution of an IR imager, injected energy, noise on the surface being tested, temperature signal, and contrast over defect as well as times when maximum signals occur. A theoretical analysis of the thermal inspection of glass fiber-steel and carbon epoxy plastic specimens is given. Experimental illustration is performed by testing Plexiglass specimens using both flash and continuous heating techniques. Decision-making rules and limits of the thermal NDT are discussed as well.

A Field Deployable Nondestructive Impact Damage Assessment Methodology for Composite Structures

A technique is being developed for rapid in-service detection and quantification of damage in composite airframe structures combining thermal and ultrasonic nondestructive evaluation (NDE). Thermal inspection techniques can be used to identify impact damage areas because it is fast, inspects large areas, and is noncontacting. Once an area of concern is identified, characterization of the depth and extent of the damage can be determined using ultrasonic volumetric imaging. Ultrasonic volumetric imaging quantifies the damage by giving a ply-by-ply view of the damage. Single-sided measurements were made on two types of samples, flat panels with through-the-thickness reinforcements and a “Y”-stiffened skin. These samples were impacted with an aluminum ball at various velocities. The thermal results were compared with ultrasonic C-scans and the ultrasonic volumetric results were compared with destructive tests. The thermal images compared well with the C-scan images in both relative size and shape. It was found that the ultrasonic volumetric results gave a better indication of damage than achievable with the destructive specimen evaluation method. It has been shown that a multidisciplinary approach using thermal and ultrasonic NDE techniques is an efficient and informative inspection method for identifying and quantifying damage.

Evaluation of the sensitivity of contact thermal inspection methods : Platonov, V.V.; Dymchenko, V.V.; Ivanova, E.G. Soviet Journal of Non-Destructive Testing, Vol. 24, No. 11, pp. 726–732 (Jul. 1989)

Evaluation of the sensitivity of contact thermal inspection methods : Platonov, V.V.; Dymchenko, V.V.; Ivanova, E.G. Soviet Journal of Non-Destructive Testing, Vol. 24, No. 11, pp. 726–732 (Jul. 1989)

Thermal imaging of graphite/epoxy composite samples with fabricated defects : Zalameda, J.N.; Winfree, W.P. Review of Progress in Quantitative Nondestructive Evaluation, La Jolla, California (United States), 15–20 Jul. 1990. Vol. 10A, pp. 1065–1072. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1991). ISBN 0-306-43903-4

Consideration is given to a thermal inspection system for quickly inspecting large area composites for increased reliability and maintainability of helicopters resulting from improved quality assurance manufacturing. The infrared camera/image processor-based inspection system was used to image defects in composites. Noncontacting and single-sided measurements were performed on graphite/epoxy samples with fiber volume fraction variations, fabricated porosity, impact damage, and inclusions in incurred lay ups. These defects were imaged by determining the variations in the cooling rates caused by differences in through ply thermal diffusivity. Attention is also given to the system's sensitivity to measuring the defects due to sample thickness.

Thermal inspection of carbon-reinforced plastic-aluminum parts : Vavilov, V.P.; Okonechnikov, V.K. Soviet Journal of Nondestructive Testing, Vol. 22, No. 12, pp. 845–848 (Aug. 1987)

Thermal inspection of carbon-reinforced plastic-aluminum parts : Vavilov, V.P.; Okonechnikov, V.K. Soviet Journal of Nondestructive Testing, Vol. 22, No. 12, pp. 845–848 (Aug. 1987)

Finite-element thermal modeling of casting microstructures and defects

Finite-element thermal modeling offers the capability of simulating casting solidification conditions. By combining thermal modeling and inspection, a defect map can be established to enable prediction of casting microstructures and defects. Gamma-prime size, dendrite-arm spacing, equiaxed grain size, shrink, hot tearing, misrun, and other features can all be predicted.

VLSI Package Reliability

The challenge presented by advanced package development in the past five years has further accentuated the constant need for package quality and reliability monitoring through extensive laboratory testing and evaluation. As pin counts and chip geometries have continued to increase, there has been additional pressure from the military and commercial sectors to improve interconnect designs for packaged chips, including chips directly attached to the printed wiring board (PWB). One of the options employed has been tape automated bonding (TAB). However, this assembly technique also presents new standardisation, qualification and reliability problems. Therefore, at Rome Air Development Center (RADC), there is regular assessment (through in‐house failure analysis studies) of parts destined for military and space systems. In addition, Department of Defense (DoD) high tech development programmes, such as very high speed integrated circuits (VHSIC), have utilised all present screening methods for package evaluation, and have addressed the need for development of more definitive non‐destructive tests. To answer this need, two RADC contractual efforts were awarded on laser thermal and ultrasonic inspection techniques. Through these package evaluations, a number of potential reliability problems are identified and the results provided to the specific contractors for corrective action implementation. Typical problems uncovered are lid material and pin corrosion, damage to external components and adhesion problems between copper leads and polyimide supports, hermeticity failures, high moisture content in sealed packages and particle impact noise detection (PIND) test failures (internal particles). Further tests uncover bond strength failures, bond placement irregularities, voids in die attach material (potential heat dissipation problems), and die surface defects such as scratches and cracks. This presentation will review the specific package level physical test methods that are employed as a means of evaluating reliable package performance. Many of the tests, especially the environmental tests—e.g., salt atmosphere and moisture resistance—provide accelerated forms of anticipated conditions and are therefore applied as destructive tests to assess package quality and reliability in field use. In addition to a manufacturer's compliance with designated qualification procedures, the key to package quality lies in utilising good materials and well‐controlled assembly techniques. This practice, along with effective package screen tests, will ensure reliable operation of very large scale integration (VLSI) devices in severe military and commercial environment applications.

The Final Thermal Inspection of Buildings by Means of Short Period Performance Monitoring: Two Case Studies

Thermal performance monitoring of buildings and heating systems has been used in Italy since 1979. The main purposes were to assess both the typical energy con sumption of the different construction technologies used, and the amount of saving obtained by energy conservation measures or solar energy applications. For the purposes of research, the data acquisition systems used were quite sophisti cated, and the monitoring period very long (up to 3 years). In this paper the author discusses the possiblity of making use of short period performance monitoring as a basis for the final thermal evaluation of a building; this is done by presenting two relevant case studies. The first case regards a school building (17,750 m3) where the heating system is solar assisted by 800 m2 of air collectors. The working of the system was specially designed to take into account the complex utilization pattern of the building. The second case regards a convertible mobile home (140 m3) designed for emergency assistance in case of earthquake: in this case the heating system is electric. After outlining the buildings' construction and physical parameters, the author de scribes the testing procedure adopted. The results obtained are then presented, comparing the measured behaviour of the buildings and systems with the expected ones. Starting from these first experiences, some aspects regarding the possibility of per forming a final thermal evaluation of buildings based on this technique are discussed, such as: • the shortest significant performance monitoring period • types and minimum significant number of parameters to be measured • physical parameters qualifying the energy consumption of buildings • complementary measurements (useful or necessary) Finally, the author gives a short account of future work on the possibility to use low-cost instrumentation.