Thermography methodologies for detecting energy related building defects

Thermography is becoming more widely used amongst construction professionals for energy related defect detection in buildings. Until quite recently, most of the research and practical use of building thermography has centred on employing a building walk-around or walk-through methodology to detect sources of unacceptable energy use. However, thermographers are now creating new building thermography methodologies that seek to address some of the known limitations, such as camera spatial resolution, transient climatic conditions and differences in material properties. Often such limitations are misunderstood and sometimes ignored. This study presents a review of the existing literature, covering both well-established and emerging building thermography methodologies. By critically appraising techniques and observing methodology applications for specific energy related defects, a much clearer picture has been formed that will help thermographic researchers and thermographers to decide upon the best methodology for performing building thermography investigations and for the invention of new approaches. Whilst this paper shows that many of the different passive building thermography methodologies seek to address particular building issues such as defects and energy use, it has also demonstrated a lack of correlation between the different methodology types, where one methodology is often chosen over another for a particular reason, rather than making use of several methodologies to better understand building performance. Therefore this paper has identified the potential for using several passive building thermography methodologies together in a phased approach to building surveying using thermography. For example, a less costly and faster survey could be conducted to quickly identify certain defects before enabling more time consuming and expensive surveys to hone in on these with greater detail and spatial resolution if deemed necessary. © 2014 Elsevier Ltd

Compression After Impact and Fatigue of Reconsolidated Fiber-reinforced Thermoplastic Matrix Solid Composite Laminate

AbstractCarbon fiber-reinforced poly-phenylene sulfide laminate coupons were impacted at low-energy in a drop-tower machine and subsequently fatigued in a four-point bending fixture. The doubly damaged test pieces were then hot-press reconsolidated and inspected nondestructively by vibrothermography to check their structural integrity. The residual mechanical properties of the laminate in both the as-damaged and as-repaired conditions were determined by compression loading with the in-plane strain fields determined via a digital image correlation system. Cross-section views of damaged and repaired samples were analyzed by light optical microscopy and correlated to residual mechanical properties, as were the digital image correlation and nondestructive test results. Based on the values of stiffness and ultimate strength of the repaired laminates, 10J was inferred as the maximum impact energy at which it is worthwhile performing hot-press reconsolidation, in view of the applied fatigue history following impact

Thermal stresses applied on helicopter blades useful to retrieve defects by means of infrared thermography and speckle patterns

This work presents a non-destructive analysis based on infrared thermography (IRT) and speckle inspection methods performed on a helicopter blade. In both cases, thermal stresses are needed in order to provoke the visualization of defects. The sample possess fabricated defects, and three techniques were selected, namely, long-pulse thermography, flash thermography, and digital speckle photography (DSP) to retrieve their positions. The first two techniques belong to the group of infrared imaging, that are inherent to the analysis of the infrared thermal patterns to detect internal anomalies in the material, whilst the last one corresponds to the optical imaging group that requires visible light to measure the material response under a thermal stimulus. The active approach, useful to produce a gradient in either, thermal and/or displacement field of the material, was used. In all cases, heat lamps were used to generate the required thermal stresses. Post-processing algorithms were applied to raw data in order to improve the defect detection. Results are finally compared to evaluate pros and cons of each method