Hole-edge damage of joint structure is one type of the most closely watched damages for ultrahigh buildings, bridges, aircrafts, etc., due to stress concentration at the bolt hole and complex load conditions. This paper employs an eddy current array sensor, made by flexible printed circuit technology, bonded on the bolt screw to monitor the growth of hole-edge damage. Coil winding configuration of the eddy current array sensor made by one actuation coil throughout all depth and several sensing coils along the depth is proposed to quantify the damage growth, especially the damage depth. Simulation and experimental study were conducted to verify the ability of quantitatively monitoring the hole-edge damage growth.
Guided wave-based structural health monitoring (SHM) has been given considerable attention and widely studied for large-scale aircraft structures. Nevertheless, it is difficult to apply SHM systems on board or online, for which one of the most serious reasons is the environmental influence. Load is one fact that affects not only the host structure, in which guided wave propagates, but also the PZT, by which guided wave is transmitted and received. In this paper, numerical analysis using finite element method is used to study the load effect on guided wave acquired by PZT. The static loads with different grades are considered to analyze its effect on guided wave signals that PZT transmits and receives. Based on the variation trend of guided waves versus load, a load compensation method is developed to eliminate effects of load in the process of damage detection. The probabilistic reconstruction algorithm based on the signal variation of transmitter-receiver path is employed to identify the damage. Numerical tests is conducted to verify the feasibility and effectiveness of the given method.
Advanced fiber reinforced composite materials are becoming the main structural materials of next generation of aircraft because of their high strength and stiffness to weight ratios, and excellent designability. As key components of large composite structures, joints play important roles to ensure the integrity of the composite structures. However, it is very difficult to analyze the strength and failure modes of composite joints due to their complex nonlinear coupling factors. Therefore, there is a need to monitor, diagnose, evaluate and predict the structure state of composite joints. This paper proposes a multi-field coupled sensing network for health monitoring of composite bolted joints. Major work of this paper includes: 1) The concept of multifunctional sensor layer integrated with eddy current sensors, Rogowski coil and arrayed piezoelectric sensors; 2) Development of the process for integrating the eddy current sensor foil, Rogowski coil and piezoelectric sensor array in multifunctional sensor layer; 3) A new concept of smart composite joint with multifunctional sensing capability. The challenges for building such a structural state sensing system and some solutions to address the challenges are also discussed in the study.
Damage monitoring is of great concern to manufacturers as well as maintenance personnel for significantly improving safety
and reliability of aircrafts. Delamination and corrosion are among the most interested types of damage which the industries
want to monitor for composites and metals correspondingly. In plate-like structures, the aforementioned damage can all
practically be treated as 2-dimensional damage. Many progresses have been made on monitoring the location of the damage;
however, to monitor the size of the damage is still very challenging. It is known from dynamic theory that elastic waves will
be scattered and reflected at the interface of two different media. Thus scattered and reflected waves will be generated at the
boundaries of the damage. By analyzing these scattered and reflected waves, the boundaries of the damage can be determined,
then, not only the location, but also the size of 2-dimensional damage can be given. In this study, to get as exact monitoring
results as possible, two types of locating curves are used: one type acquired by pitch-catch mode and the other type by pulseecho
mode. By taking the inner most locating curves, the boundaries of the damage can be given. Experimental results
showed that the size of ahole damage can be monitored quite well by the envelop locating curves method.
KEYWORDS: Temperature metrology, Waveguides, Structural health monitoring, Ferroelectric materials, Sensors, Composites, Damage detection, Electronic filtering, Digital filtering, Signal detection
A new temperature compensation technique combining optimal baseline selection and the filter based on Adaptive
Linear Neuron Network was developed to enhance the robustness and effectiveness of guided Lamb wave-based damage
detection. This paper focuses on three main issues for practically implementing the proposed method: (a) Establishment
of temperature compensation standard; (b) Parameters design of compensation filter; (c) Determination of temperature
gradient of baseline signals. Experiments were conducted on two stiffened composite plates to demonstrate the feasibility
of proposed method under a temperature range from -40°C to 80°C for compensating temperature effects. Results
showed that a reasonable temperature step for providing good temperature compensation can be up to 20°C in a baseline
dataset.
The integrity monitoring of foam based thermal insulation systems is investigated under a load-temperature environment.
Guided wave propagation studies are conducted on two specimens using the pitch-catch approach. To receive only the
guided wave, the interval distance is 15mm and 20 mm between two adjacent sensors for specimens. The appropriate
guided wave modes are generated by changing the excitation signal. To simulate the thermal and load environment of the
thermal insulation system, the test piece is assembled on the load-temperature test machine, where the compression load
gradually up to 3 tons is applied to the test piece along its axial direction. Different temperatures are applied to two sides
of the test piece. The side without the foam is cooled using Liquid nitrogen to -196°C, while the other side with the foam
is heated by the thermocouple to 120 °C. The guided wave signals are obtained before/after the experiment begins/ends,
and also received periodically in the joint work process of the pressure and the different temperatures. Signals processing
and damage imaging techniques are combined to demonstrate the possible disbond defect. Experimental results show
that the disbond defect between the foam and the substrate can be qualitatively detected, and its expansion could be
identified.
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