Evaluating the freeze–thaw phenomenon in sandwich-structured composites via numerical simulations and infrared thermography

The water ingress phenomenon in sandwich-structured composites used in the aerospace/aeronautical sector is a current issue. This type of defect can cause in the course of time several other defects at the boundary, such as corrosions, deformations, detachments. In fact, water may change its state of physical matter going towards the freeze–thaw cycle caused by the atmosphere re-entry of, e.g. space probes. In this work, the alveoli of a composite laminate have been filled with water, which was initially transformed into ice. By taking into account, the known quantity of water, the freeze–thaw cycle was simulated by Comsol Multiphysics® software, reproducing exactly the shape of the sandwich as well as the real conditions in which it was subsequently subjected in a climatic chamber. The experimental part consisted of monitoring the front side of the specimen by means of a thermal camera operating into the long-wave infrared spectrum, and by setting both the temperature and the relative humidity of the test chamber according to the values imposed during the numerical simulation step. It was found that the numerical and experimental temperature trends are in good agreement with each other since the model was built by following a physico-chemical point-of-view. It was also seen that the application of the independent component thermography (ICT) technique was able both to retrieve the positions of the defects (i.e. the water inclusions) and to characterize the defects in which a detachment (fabricated between the fibres and the resin) is present; the latter was realized above an inclusion caused by the water ingress. To the best of our knowledge, this is the first time that ICT is applied to satisfy this purpose.Postprint (author's final draft

Ensemble Joint Sparse Low Rank Matrix Decomposition for Thermography Diagnosis System

Composite is widely used in the aircraft industry and it is essential for manufacturers to monitor its health and quality. The most commonly found defects of composite are debonds and delamination. Different inner defects with complex irregular shape is difficult to be diagnosed by using conventional thermal imaging methods. In this paper, an ensemble joint sparse low rank matrix decomposition (EJSLRMD) algorithm is proposed by applying the optical pulse thermography (OPT) diagnosis system. The proposed algorithm jointly models the low rank and sparse pattern by using concatenated feature space. In particular, the weak defects information can be separated from strong noise and the resolution contrast of the defects has significantly been improved. Ensemble iterative sparse modelling are conducted to further enhance the weak information as well as reducing the computational cost. In order to show the robustness and efficacy of the model, experiments are conducted to detect the inner debond on multiple carbon fiber reinforced polymer (CFRP) composites. A comparative analysis is presented with general OPT algorithms. Not withstand above, the proposed model has been evaluated on synthetic data and compared with other low rank and sparse matrix decomposition algorithms

Spinoff 2010

Topics covered include: Burnishing Techniques Strengthen Hip Implants; Signal Processing Methods Monitor Cranial Pressure; Ultraviolet-Blocking Lenses Protect, Enhance Vision; Hyperspectral Systems Increase Imaging Capabilities; Programs Model the Future of Air Traffic Management; Tail Rotor Airfoils Stabilize Helicopters, Reduce Noise; Personal Aircraft Point to the Future of Transportation; Ducted Fan Designs Lead to Potential New Vehicles; Winglets Save Billions of Dollars in Fuel Costs; Sensor Systems Collect Critical Aerodynamics Data; Coatings Extend Life of Engines and Infrastructure; Radiometers Optimize Local Weather Prediction; Energy-Efficient Systems Eliminate Icing Danger for UAVs; Rocket-Powered Parachutes Rescue Entire Planes; Technologies Advance UAVs for Science, Military; Inflatable Antennas Support Emergency Communication; Smart Sensors Assess Structural Health; Hand-Held Devices Detect Explosives and Chemical Agents; Terahertz Tools Advance Imaging for Security, Industry; LED Systems Target Plant Growth; Aerogels Insulate Against Extreme Temperatures; Image Sensors Enhance Camera Technologies; Lightweight Material Patches Allow for Quick Repairs; Nanomaterials Transform Hairstyling Tools; Do-It-Yourself Additives Recharge Auto Air Conditioning; Systems Analyze Water Quality in Real Time; Compact Radiometers Expand Climate Knowledge; Energy Servers Deliver Clean, Affordable Power; Solutions Remediate Contaminated Groundwater; Bacteria Provide Cleanup of Oil Spills, Wastewater; Reflective Coatings Protect People and Animals; Innovative Techniques Simplify Vibration Analysis; Modeling Tools Predict Flow in Fluid Dynamics; Verification Tools Secure Online Shopping, Banking; Toolsets Maintain Health of Complex Systems; Framework Resources Multiply Computing Power; Tools Automate Spacecraft Testing, Operation; GPS Software Packages Deliver Positioning Solutions; Solid-State Recorders Enhance Scientific Data Collection; Computer Models Simulate Fine Particle Dispersion; Composite Sandwich Technologies Lighten Components; Cameras Reveal Elements in the Short Wave Infrared; Deformable Mirrors Correct Optical Distortions; Stitching Techniques Advance Optics Manufacturing; Compact, Robust Chips Integrate Optical Functions; Fuel Cell Stations Automate Processes, Catalyst Testing; Onboard Systems Record Unique Videos of Space Missions; Space Research Results Purify Semiconductor Materials; and Toolkits Control Motion of Complex Robotics

Damage monitoring of aircraft structures made of composite Materials using wavelet transforms

Due to the significant increase in composite materials that can be used in aviation structural elements, there is a strong need for their operational control. It is estimated that a significant part of the average modern aircraft lifecycle costs is related to inspection and repair, thus it is important to perform efficient and cost-effective maintenance and monitoring techniques to reduce lifetime costs. This study is concerned with integral state monitoring of aircraft structures made from composite materials. It deals with techniques for damage monitoring and quality control, equipment observation, planned prototype testing and research into the vibration properties of different composite structures. Operation, maintenance and condition forecasting of components, such as aircraft composite blades, airplane spoilers, ailerons, aircraft airframe components, are the areas that should be properly investigated, in order to enhance the future of the industry. The aim of this research is to investigate usable signs of vibration characteristics that can reflect the effects of the damage and integral changes of advanced composite structures. The main goals are a universal approach to integral condition monitoring for all kinds of composite materials and research into the vibration property alterations of a new generation of composite materials during their operation. The modern generation of large aircraft can be designed with all-composite fuselage, frames and wing structures. The main advantages of composite materials are their high strength, relatively low weight, corrosion resistance and flexibility in implementation. Control and diagnostics of this kind of composites require deep knowledge of composite structures, materials, their failure behaviour, and tooling. Aerospace structures are suffering from damage as a result of fatigue, overloading, partial or integral material destruction and degradation in consequence of environmental factors, and extemporaneous incidents such as seismic events or impacts. There is also uncertainty connected to understanding the outcome of operational damage of aircraft composite structures. Non-destructive inspection and evaluation techniques are recommended in many cases, but still, represent significant downtime and labour costs and, in many cases, require highly skilled personnel to perform them. Linked to structures and onboard built-in structural health monitoring systems could be used for improving the reliability and safety of composites while reducing lifecycle costs and improving the design and manufacture processes. However, they also have their own disadvantages like the cost of implementation, cost of operation of the system itself and impact to the structure during production and maintenance. This research is therefore mainly focused on vibration properties of advanced composite materials and simple control procedures that can be conducted by an engineering technician during light maintenance checks (including both routine and detailed inspections). The decision on the schedule for the checks to be performed can vary by aircraft type, the cycle count, or the number of hours flown since the last check. Another important subtask is the prediction of the object condition in operation. A significant part of the research is concerned with the collection of statistical information, and experiments with different objects made of composite materials, using the proposed methodology. An additional part is linked to the optimization of equipment for the future demands of the industry in operational control and diagnostics. It is concluded that the technique of combining wavelet analysis is an effective and appropriate tool for vibration analysis to determine the modal parameters of free and forced oscillations, especially in the integral control of composite structural elements. The novel aspect of the research is the practical experimental work that has been executed on real advanced composite material objects (metal-polymer-metal composites as well), and its subsequent analysis

Detection and characterization of impact damage in carbon fiber aircraft fuselage structure

As the use of advanced composite materials continues to grow in the aviation industry, damage detection techniques need to be developed and tested. Impact damage on aluminum aircraft structures can be detected from obvious surface indications. This is not the case in composite aircraft structure. Large interply delaminations and substructure disbonding may occur as a result of an impact, often leaving no visual indications of damage. This research investigates the use of conventional hand-deployed ultrasonic (UT) inspection techniques and more advanced UT pulse-echo and resonance scanning techniques to detect and characterize damage in full-scale carbon fiber fuselage structure. It also examines embedded and bonded methods of deploying an in-situ fiber optic (FO) Swept Wavelength Interferometry (SWI) strain sensing system for damage detection. The hypothesis is that the more advanced scanning nondestructive inspection (NDI) techniques used in the study will more effectively detect and characterize damage modes in the fuselage panels than hand-deployed UT techniques. It is further hypothesized that impact damage created by both simulated hail and steel spherical tip impacts will create a permanent, detectable strain change that can be detected by the FO strain measurement system. Two fuselage panels representative of structures seen on advanced composite transport category aircraft were fabricated. They each measured approximately 56 x 76\u27. The structural components consisted of a 16 ply skin, co-cured, hat-section stringers, fastened shear ties and frames. The material used to fabricate the panels was T800 unidirectional, carbon pre-preg and was processed in an autoclave. Simulated hail impact testing was conducted on the panels using a high velocity gas gun with 2.4\u27 diameter ice balls. The ice impact tests were performed in collaboration with the University of California San Diego (UCSD). In addition to the simulated hail impact testing, 2\u27 diameter spherical tip steel impacts were conducted to simulate impact damage introduced during heavy ground maintenance operations. The extent of 16 ply skin damage induced on the panels ranged from less than 1 in2 to 55 in2 of interply delamination. Substructure damage on the panels included shear tie cracking, delamination of the built-up pad sections behind the fastened shear ties, and stringer-to-flange disbonding. Substructure damage away from the site of high energy ice impacts was often not detected with hand-deployed UT, which can be attributed to failure to inspect far enough away from the impact site. This additional damage was detected using the more advanced scanning techniques. Data collection from the embedded FO was not possible due to light attenuation caused by micro-bending induced in the fiber. It was determined that increasing both the numerical aperture of the FO and the diameter, in combination with adjusting the layout orientation used, may make it possible to measure strain change using this technique. Detectable strain indications were obtained using the backside bonded FO in 15 of the 25 interrogated steel tip impacts. Increasing the robustness of this deployment method could provide a means for in-situ damage detection.\u2

Aiding the conservation of two wooden Buddhist sculptures with 3D imaging and spectroscopic techniques

The conservation of Buddhist sculptures that were transferred to Europe at some point during their lifetime raises numerous questions: while these objects historically served a religious, devotional purpose, many of them currently belong to museums or private collections, where they are detached from their original context and often adapted to western taste. A scientific study was carried out to address questions from Museo d'Arte Orientale of Turin curators in terms of whether these artifacts might be forgeries or replicas, and how they may have transformed over time. Several analytical techniques were used for materials identification and to study the production technique, ultimately aiming to discriminate the original materials from those added within later interventions