1,720,986 research outputs found
Comparative Analysis of Thermal Processing Approaches for a CFRP Element Aided by UT Control
No full textThe present work resumes thermal data processing with most common algorithms in literature and introduces in addition a different data processing strategy, proposed to improve subsurface defect detection on industrial composites. These materials are successfully controlled with infrared Non-Destructive Investigations, since defects are easily detected by temperature response under thermal pulses with reliable results. To reduce application limits for non-destructive inspections, the proposed research shows possibility to combine pulsed thermographic technique with accurate image-processing methods implemented in Matlab environment for a reliable and rapid characterization of subsurface and internal damage. Thermal processing methods are evaluated for the proposed case of study, as the well-established DAC, PCT, TSR procedures. In addition, the authors proposed a better defect characterization that is achieved with refined data processing and accurate experimental procedures, providing detailed contrast maps where defects are easily distinguished. This improved algorithm automates the defect mapping and enhances the accuracy of defects inspection, optimized to identify defect boundaries according to spatial variations in neighboring of each calculation point of the whole thermal frame. Thermal data are evaluated with standard methods and the local boundary method is for carbon-fiber composite specimens with artificial defects, evaluating processed images obtained by different methods employing the Tanimoto criterion. Proposed thermal computation method is found suitable for automatic mapping of defect distribution and optimized for simultaneous defect boundaries’ detection in terms of Tanimoto criterion, in the inspected structure. In addition, ultrasonic controls are carried out for detection comparison between different control procedures
Application of Pulsed Thermography and Post-processing Techniques for CFRP Industrial Components
No full textSeveral studies demonstrate the effectiveness of pulsed thermography for detection and visualization of sub-superficial flaws in composites. Continuous improvement of thermal data manipulation makes active thermography an attractive and powerful inspection method for industrial process control and maintenance aims. Therefore, temperature image-processing is the major ongoing challenge in the thermographic research field. However, the particular interest for thermographic inspections is to be more addressed to its simple and relatively fast industrial application; an appropriate image processing tool should be implemented and verified on industrial components, containing manufacturing and in-service defects. In the proposed research, well-established and previously proposed methods were analysed and compared for different defect typology inside three CFRP components. The main goal is not solely focused on establishing the suitable data processing approach, providing detection limits of processed data in terms of damage type, size and distribution. The aim of proposed work is to present detailed examples of thermal imaging methods applied on similar critical defects, evaluating different results among methods in terms of defects mapping capabilities and Tanimoto evaluation criterion, coupled also with the signal-to-noise ratio as assessment of defect detectability
Microstructural analysis of AISI 304 bars welded with high speed pulsed discharges
No full textIn a way similar to the resistance welding the high speed pulsed welding exploits the power of elevated discharging current through an electrical circuit, which contains the two parts to be welded. During welding edges profile interact with the process parameters to determine both the weld microstructure and mechanical strength.
In this paper, the welding profiles at the opposite surfaces was machined so to have linear contacts instead of a classic single protrusion contact. The effect of this multilinears contact geometry was a weld that was in the midway between the capacitor discharge welding (CDW) and the projection welding (PW).
Pulsed welding experiments were performed using AISI 304 cylindrical bars in butt configuration. The welded microstructures were studied using an optical microscope and image analysis software. The Vickers microhardness tests were performed to a better characterization of the welding microstructure
Fatigue and damage analysis on aeronautical CFRP elements under tension and bending loads: Two cases of study
No full textThe present work is focused on experimental monitoring procedures to investigate stresses and damage settlement during fatigue tests of CFRP elements under bending and tensile loads. Continuous damage accumulation, coupled with mechanical properties degradation are monitored with ultrasonic inspection and with thermographic full field analysis, during long lasting HC fatigue loads. Effects of localized bending loads and artificial composite wrinkle presence within a notch are source of delamination initiation, investigated two different types of specimens under fatigue. Combined monitoring approaches, based on thermo-elastic and dissipative phenomena, together with ultrasonic through thickness properties variations are claimed to offer precise damage state and localization during tests, subsequently aided by FEM damage model analysis in case of static failure zone identification, to be compared with experimental data; in addition, experimental DIC computation of deformation on specimen critical zones is performed in order to check failure and delamination initiation spot. The thermal parameters and experimental compliance correlation seem to indicate a similar signal variation during damage progress, verified also by contemporaneous ultrasonic inspections of some specimens in the failure zones of CFRP elements
A Brief Review and Advances of Thermographic Image - Processing Methods for IRT Inspection: a Case of Study on GFRP Plate
No full textThe present work introduces a different data processing strategy, proposed in order to improve sub-surface defect detection on industrial composites; in addition, a resume of thermal data processing with most common algorithms in literature is presented and applied with new data. A deep comparison between the common absolute contrast, DAC, PCT, TSR and derivative methods and a new proposed contrast mapping procedure is implemented. Thermographic inspection was done in reflection mode on a Glass Fiber Reinforced Plastic plate, with flat bottom hole defects. Thermal data computation method is found to be critical for simultaneous defect detection and automatic mapping, optimized to identify defect boundaries at specific depth, with help of accurate image processing, implemented in a Matlab GUI for a reliable and rapid characterization of internal damage. The new processing approach, the Local Boundary Contrast method, elaborates different contrast maps and facilitates recognition of damage extension. Tanimoto criterion and the signal-to-noise ratio method were applied as a criterion to assess defect detectability of various processing methods
Stress/strain state for critical components of a jet engine aeronautical compressor
No full textIn order to prevent in-flight fatigue failure, a numerical analysis of in service-operative cases is an useful approach for preliminary evaluation of most stressed and critical zones in components of aeronautical engine. The zero-stage compressor rotor disk and blades represent one of the most critical part of aircraft turbojet. This paper presents a verification FEM analysis of this component. An accurate 3D scanning was performed to reconstruct both blade and disk real geometry and the detailed point cloud was obtained and opportunely elaborated by using specific software to generate CAD sections and volumes given in input to finite element analysis. The stress field due to different operating conditions is studied for a suitable evaluation of the most stressed and critical areas where a failure may occur, particularly near the rotor connection under contact conditions. FEM and flight data analysis are finally used for a subsequent fatigue life verification, based on classical Palmgren Miner’ rule. The suggested procedure for verification of engine aeronautical component is here optimized for maintenance program improvements
Full-field monitoring methods for damage analysis on aeronautical CFRP specimens under fatigue loads
No full textThe present paper is focused on full-field experimental monitoring procedures to be employed during HCF fatigue testing on two series of CFRP open hole samples. Two different experimental methodologies based on thermographic techniques and displacement measurements with Digital Image Correlation (DIC) analysis are employed for damage settlement and evolution to be detected up to failure, together with correspondent compliance analysis. Combined monitoring approaches, based on thermo-elastic and dissipative phenomena, together with stiffness properties variations, are claimed to offer precise damage state localization during tests in real time; in addition, DIC analysis is performed during lowfrequency fatigue cycle is studied for better failure prediction and damage location.
The thermal parameters and experimental compliance correlation seem to indicate similar signal variation during damage progress and after proper data elaboration; contemporaneous raw thermal measurements in critical zones of specimens under fatigue life offer a kind of delamination recognition at specific layer interface and location, as well as propagation before final failure. Sample under tensile load on the other hand reveal delaminations indirectly on the surface. In addition, non-destructive thermographic and ultrasound tests are performed at regular intervals during fatigue life
Real-time monitoring of damage evolution by nonlinear ultrasonic technique
Full text linkIn this work, the ultrasound technique was used to monitor the damage of material subjected to fatigue loads. Prediction of structural damage is critical for safe and reliable operation of engineered complex systems. In these measurements, conventional ultrasonic probes (transmitter and receiver) were stably fixed to the tested samples with steel brackets, in order to eliminate ever possible variability associated with the coupling of probes. The transmitted and received ultrasonic signals were recorded and analyzed using a digital oscilloscope. The data were converted into the frequency domain using an algorithm developed in Matlab based on Fast Fourier Transform (FFT) for received signal in dependence of the applied stress level and the accumulated fatigue damage was deeply studied in order to recognize quantitative effects, suitable for an experimental prediction of the integrity of the material. The acquired data were compared with the reference signal, at the beginning of the fatigue tests. Particular care has been paid to UT signal attenuation and to the study of the frequency spectrum as the number of load cycles varies. The applied experimental technique has proved efficient for detecting damage induced by mechanical stress
Advanced NDT methods and data processing on industrial CFRP components
Full text linkIn this work, enhanced thermal data processing is developed with experimental procedures, improving visualization algorithm for sub-surface defect detection on industrial composites. These materials are prone to successful infrared nondestructive investigation analyses, since defects are easily characterized by temperature response under thermal pulses with reliable results.
Better defect characterization is achieved analyzing data with refined processing and experimental procedures, providing detailed contrasts maps where defects are better distinguished. Thermal data are analyzed for different CFRP specimens with artificial defects and experimental procedures are verified on real structural aeronautical component with internal anomalies due to impact simulation. A better computation method is found to be useful for simultaneous defect detection by means of automatic mapping of absolute contrast, optimized to identify defect boundaries
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