The sensitivity of the mechanical impedance method of nondestructive testing

1987 ◽  
Vol 20 (4) ◽  
pp. 209-215 ◽  
Author(s):  
P. Cawley
Keyword(s):  
Nondestructive Testing ◽  
Mechanical Impedance ◽  
Impedance Method

scholarly journals Using Hilbert Transform in Diagnostic of Composite Materials by Impedance Method

2020 ◽  
Vol 64 (4) ◽  
pp. 334-342 ◽  
Author(s):  
Volodymyr Eremenko ◽  
Artur Zaporozhets ◽  
Vitalii Babak ◽  
Volodymyr Isaienko ◽  
Kateryna Babikova
Keyword(s):  
Composite Materials ◽  
Nondestructive Testing ◽  
Hilbert Transform ◽  
Instantaneous Frequency ◽  
Information Quality ◽  
Low Frequency ◽  
Mechanical Impedance ◽  
Phase Characteristic ◽  
Impedance Method ◽  
Materials Testing

The article is devoted to the problem of the increasing of information quality for the impedance method of nondestructive testing. The purpose of this article is to get for the pulsed impedance method of nondestructive testing the additional informative parameters. Instantaneous values of the information signal's amplitude is a sensitive parameter to the effects of interference, in particular friction, which necessitates the use of additional informative features. It was experimentally measured signals from defective and defectless areas of the test pattern. Using of the Hilbert transform gave possibility to determine phase characteristics of these signals and realize demodulation to extract a low-frequency envelope for further analysis of its shape. It was received the informative features as a result of researches. Among them are instantaneous frequency of a signal, the integral of a phase characteristic on the selected interval and the integral of a difference signal phase characteristics. In order to compare quality of the defect detection using selected parameters it was carried out evaluation of the testing result reliability for a product fragment made of a composite material. Considering the influence of the change in the mechanical impedance of the researched area on the phase-frequency characteristics of the output signal of the converter, it is proposed to use as the diagnostic signs: the instantaneous frequency and the value of the phase characteristic of the current signal for certain points in time. The proposed informative features enable to increase general reliability of composite materials testing by the pulsed impedance method.

Co-Integration-Based Compensation Technique for Dynamic Load Effects on the Electro-mechanical Impedance Method

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Xiaoluo Jie ◽  
Wenzhong Qu ◽  
Li Xiao ◽  
Ye Lu
Keyword(s):  
Dynamic Load ◽  
Mechanical Impedance ◽  
Piezoelectric Transducers ◽  
Impedance Method ◽  
Operational Conditions ◽  
Load Effects ◽  
Compensation Technique ◽  
Aluminum Beam ◽  
Stress Variations ◽  
Stationary Behavior

Abstract The electro-mechanical (EM) admittance signals acquired from piezoelectric transducers (PZT) surface bonded to the host structure are often used for structural health monitoring (SHM). However, it is well known that the method is susceptible to contamination from environmental and operational conditions. This paper introduces a co-integration method to remove dynamic load effects from electro-mechanical admittance data. The proposed method is based on the concept of co-integration that is partially built on the analysis of the non-stationary behavior of time series. Instead of directly using admittance signatures of PZT for damage detection, the analysis of the co-integrated residual obtained from the co-integration procedure of EM admittance responses and the resonant peaks frequency of the real part of admittance (conductance) are chosen as co-integrated variables. The experiments of aluminum beam bolt loosening identification, which is under dynamic stress, were carried out to verify the effectiveness of the proposed method. The results showed that the method can isolate damage-sensitive features from stress variations, so as to successfully detect the existence of damage.

scholarly journals Detection of Pin Failure in Carbon Fiber Composites Using the Electro-Mechanical Impedance Method

Sensors ◽  
2020 ◽  
Vol 20 (13) ◽  
pp. 3732
Author(s):  
Jochen Moll ◽  
Matthias Schmidt ◽  
Johannes Käsgen ◽  
Jörg Mehldau ◽  
Marcel Bücker ◽  
...  
Keyword(s):  
Carbon Fiber ◽  
Damage Detection ◽  
Fiber Composite ◽  
Mechanical Impedance ◽  
Impedance Method ◽  
Carbon Fiber Composites ◽  
Carbon Fiber Composite ◽  
Bending Loads ◽  
Metallic Parts ◽  
Hybrid Carbon

This paper presents a proof of concept for simultaneous load and structural health monitoring of a hybrid carbon fiber rudder stock sample consisting of carbon fiber composite and metallic parts in order to demonstrate smart sensors in the context of maritime systems. Therefore, a strain gauge is used to assess bending loads during quasi-static laboratory testing. In addition, six piezoelectric transducers are placed around the circumference of the tubular structure for damage detection based on the electro-mechanical impedance (EMI) method. A damage indicator has been defined that exploits the real and imaginary parts of the admittance for the detection of pin failure in the rudder stock. In particular, higher frequencies in the EMI spectrum contain valuable information about damage. Finally, the information about damage and load are merged in a cluster analysis enabling damage detection under load.

scholarly journals Rotordynamic Force Coefficients of Pocket Damper Seals

2006 ◽  
Vol 128 (4) ◽  
pp. 725-737 ◽  
Author(s):  
B. Ertas ◽  
A. Gamal ◽  
J. Vance
Keyword(s):  
Dynamic Pressure ◽  
Mechanical Impedance ◽  
Experimental Tests ◽  
Impedance Method ◽  
Force Density ◽  
Frequency Dependent ◽  
Force Coefficients ◽  
Cross Axis ◽  
Positive Direct ◽  
Stiffness And Damping

This paper presents measured frequency dependent stiffness and damping coefficients for 12-bladed and 8-bladed pocket damper seals (PDS) subdivided into four different seal configurations. Rotating experimental tests are presented for inlet pressures at 69 bar (1000 psi), a frequency excitation range of 20–300 Hz, and rotor speeds up to 20,200 rpm. The testing method used to determine direct and cross-coupled force coefficients was the mechanical impedance method, which required the measurement of external shaker forces, system accelerations, and motion in two orthogonal directions. In addition to the impedance measurements, dynamic pressure responses were measured for individual seal cavities of the eight-bladed PDS. Results of the frequency dependent force coefficients for the four PDS designs are compared. The conclusions of the tests show that the eight-bladed PDS possessed significantly more positive direct damping and negative direct stiffness than the 12-bladed seal. The results from the dynamic pressure response tests show that the diverging clearance design strongly influences the dynamic pressure phase and force density of the seal cavities. The tests also revealed the measurement of same-sign cross-coupled (cross-axis) stiffness coefficients for all seals, which indicate that the seals do not produce a destabilizing influence on rotor-bearing systems.

scholarly journals Rotordynamic Force Coefficients of Pocket Damper Seals

2006 ◽  
Author(s):  
B. Ertas ◽  
A. Gamal ◽  
J. Vance
Keyword(s):  
Dynamic Pressure ◽  
Mechanical Impedance ◽  
Impedance Method ◽  
Force Density ◽  
Frequency Dependent ◽  
Force Coefficients ◽  
Direct Stiffness ◽  
Cross Axis ◽  
Positive Direct ◽  
Stiffness And Damping

This paper presents measured frequency dependent stiffness and damping coefficients for 12 and 8 bladed pocket damper seals (PDS) subdivided into 4 different seal configurations. Rotating experimental test are presented for inlet pressures at 69 bar (1,000 psi), a frequency excitation range of 20–300 Hz, and rotor speeds up to 20,200 rpm. The testing method used to determine direct and cross-coupled force coefficients was the mechanical impedance method, which required the measurement of external shaker forces, system accelerations, and motion in two orthogonal directions. In addition to the impedance measurements, dynamic pressure responses were measured for individual seal cavities of the 8 bladed PDS. Results of the frequency dependent force coefficients for the 4 PDS designs are compared. The conclusions of the test show that the 8 bladed PDS possessed significantly more positive direct damping and negative direct stiffness than the 12 bladed seal. The results from the dynamic pressure response tests show that the diverging clearance design strongly influences the dynamic pressure phase and force density of the seal cavities. The tests also revealed the measurement of same-sign cross-coupled (cross-axis) stiffness coefficients for all seals, which indicate that the seals do not produce a de-stabilizing influence on rotor-bearing systems.

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