Damage Detection Technology Research Articles

Distributed Fiber Optic Strain Sensing with Embedded Small-Diameter Optical Fibers in CFRP Laminate

Although demand for composite structures rapidly increase due to the advantages in weight, there are few effective assessment techniques to enable the quality control and guarantee the durability. In particular, an invisible microscopic damage detection technology is highly required because damages such as transverse cracks, debondings, or delaminations can lead to the critical failure of the structures. Among many non-destructive evaluation (NDE) methods for composite structures, fiber optic sensors are especially attractive due to the high sensitivity, the lightweight, and the small size. In the current trend of the structural health monitoring technology, fiber Bragg gratings (FBG) sensors are frequently used as strain or temperature sensors, and Brillouin scattering sensors are also often used for a long distance distributed measurement. The Brillouin distributed sensors can measure strain over a distance of 10km while a spatial resolution was limited to 1m. Some novel sensing method is proposed to improve the spatial resolution. The pulse-prepump Brillouin optical time domain analysis (PPP-BOTDA) is one of the latest distributed sensing applications with a cm-order high spatial resolution. The PPP-BOTDA commercial product has the spatial resolution of 10cm, and can measure the strain with a precision of ±25og. This precision, however, can be achieved by using conventional single-mode optical fibers. In our research, small-diameter optical fibers with a cladding diameter of 40om were embedded in the CFRP laminate to avoid the deterioration of the CFRP mechanical properties. Thus, in order to verify the performance of PPP-BOTDA, the distributed strain measurement was conducted with the small-diameter optical fibers embedded in the CFRP laminate.

Creep degradation in welds of Mod.9Cr-1Mo steel

Creep life assessment technology has not yet been developed for Mod.9Cr-1Mo steel welded joints due to the unique degradation and failure mechanisms in the heat affected zone. Nevertheless, there is strong demand from power plant operators for the development of nondestructive damage detection and life assessment technology for weldments of this steel. In this study creep rupture testing using a large-size welded joint was conducted, and creep and damage detection tests were carried out to elucidate the degradation mechanism. Also the microstructure and hardness changes in the heat affected zones of the welds were investigated to clarify the degradation mechanisms of such welds in comparison with base metal during creep. In general, the changes in hardness distribution along the welds were difficult to correlate with the life consumption, although degradation in welds due to creep was successfully detected. Accordingly, a new approach to degradation evaluation and creep life assessment by hardness measurement method for Mod.9Cr-1Mo steel welds is proposed.

Damage detection of composite material intelligent structure with a new photoelectric system

A kind of photoelectric system that is suitable to measuring and to testing the damage of the composite material intelligent structure was presented. It can measure the degree of damage of the composite intelligent structure and it also can tell us the damage position in the structure. This system consists of two parts: software and hardware. Experiments of the damage detection and the analysis of the composite material structure with the photoelectric system were performed, and a series of damage detection experiments was conducted. The results prove that the performance of the system is well and the effects of the measure and test are evident. Through all the experiments, the damage detection technology and test system are approved to be real-time, effective and reliable in the damage detection of the composite intelligent structure.

熱画像解析を用いたコンクリート構造物の欠陥検出に関する研究

One of the damage detection technologies of highly elevated concrete structure is the method using infrared thermography. Because it is difficult to detect the damage visually from the unclear distribution of temperature, it depends on seat-of-the-pants approach. In this paper, the authors propose a method to identify the location and the geometrical shape of the damage quantitatively by processing the thermal image of the surface of the concrete structure. In the proposed method, a layer-by-layer inverse analysis using the boundary element method is carried out to obtain the sharper image of the damage as well as the depth of the damage layer. The effectiveness of the proposed technique is examined by a numerical study.

Damage Detection on Typical Aeronautical Structures

The paper pursues the exploration of the feasibility and reliability of current damage detection technologies, evaluating their detection capabilities, environmental factors effects, false alarms rate, adaptability to complex geometries, etc. The method to be used is based on finite element modal updating. Three aspects, as outlined below, are covered: testing samples will be aluminium sheets (0.6m x 0.4m x 1.6mm) strengthened with riveted L-shaped stiffeners. Data will be presented from the undamaged specimens. Secondly, the testing of the samples with damage simulated at different places by temporary removal of specific rivets, thus affecting the overall structural characteristics of the structure. The models used for damage identification methods will be fine tuned to properly detect the simulated damages. Finally, using this information, the paper resumes the capabilities of the method to detect and locate the simulated damage.

Integrating Oil Debris and Vibration Gear Damage Detection Technologies Using Fuzzy Logic

A diagnostic tool for detecting damage to spur gears was developed. Two different measurement technologies, wear debris analysis and vibration, were integrated into a health monitoring system for detecting surface fatigue pitting damage on gears. This integrated system showed improved detection and decision-making capabilities as compared to using individual measurement technologies. This diagnostic tool was developed and evaluated experimentally by collecting vibration and oil debris data from fatigue tests performed in the NASA Glenn Spur Gear Fatigue Test Rig. Experimental data were collected during experiments performed in this test rig with and without pitting. Results show combining the two measurement technologies improves the detection of pitting damage on spur gears.

Impact damage detection system using small-diameter optical-fiber sensors embedded in CFRP laminate structures

The mechanical properties of composites subjected to out-of-plane impact decrease markedly from even barely visible damage. In this study, three damage detection technologies are explained: (1) Technologies for the arrangement of embedded small-diameter optical fibers that have no serious effect on the mechanical properties of composites; (2) Technologies for the egress of the optical fibers using 'the embedded connector for smart structures' that can be trimmed without damaging the optical fibers; and (3) Technologies for a damage detection system that has data acquisition and analysis functions, evaluates the initiation and the position of damage, and visualizes damage information. We conducted an impact test using the composite airframe demonstrator. FBG sensors are embedded in the upper panel of the 1.5 m diameter, 3 m long stiffened cylindrical composite structure for strain measurement, and optical fibers are embedded for optical loss measurement. Damage detection in composite structures using the developed damage detection system was demonstrated.

Monitoring on-line integrated technologies for operational reliability — monitor

This article presents an overview of the European Union supported project MONITOR (Monitoring ON-line Integrated Technologies for Operational Reliability). The project has attempted to provide the tools by which the diagnosis of a fault or the prognosis of impending failure can be given for airframe structures. MONITOR has revealed a number of important facts related to aircraft end-user requirements and emerging damage detection technologies.