Resonance testers

Resonance testers A number of devices are available. In Europe, the Fokker bond tester is commonly used. This was developed by the Fokker Aircraft Company in order to... 

The performance of the classifier has been verified using a number of practical applications, such as civil engineering [3], inspection of aerospace composite structures, ball bearings and aircraft multi-layer structures. Here we present shortly some results, focusing on detection of disbonds in adhesively joint multi-layer aerospace structures using Fokker Bond Tester resonance instrument, details can be found in [1]. 

Fokker Bond Tester. An ultrasonic inspection technique commonly used for aircraft structures is based on ultrasonic spectroscopy [2]. Commercially available instruments (bond testers) used for this test operate on the principle of mechanical resonance in a multi-layer structure. A piezoelectric probe shown in Figure 3b, excited by a variable frequency sine signal is placed on the surface of the inspected structure. A frequency spectrum in the range of some tens of kHz to several MHz is acquired by the instrument, see Figure 3a. 

Dynamic mechanical testers apply a small sinusoidal stress or strain to a small sample of the polymer to be examined and measure resonant frequency and damping versus temperature and forced frequency. Instrument software computes dynamic storage modulus (G ), dynamic loss modulus (G") and tan delta or damping factor. Measurements over a wide range of frequency and temperature provide a fingerprint of the polymer with sensitivity highly superior to DSC. 

One of the oldest and best known ultrasonic testing systems for NDT is the Fokker Bond Tester. This method uses a sweep frequency resonance method of ultrasonic inspection. Some degree of quantitative analysis is claimed with the Fokker Bond Tester in the aircraft industry. 

Ultrasonic properties Ultrasonic resonance method, Fokker Bond Tester A—>C 50,51... 

Another transducer resonance system is the Fokker Stack Tester, developed to examine ply orientation and stacking sequence in the different layers of CFRP composites. This computer-controlled system displays the signal output in a graphical format. It consists of passing a probe into a rivet or fastener hole and scanning the material surface by a focused laser beam. The intensity of the reflected light is correlated to the orientation of each ply and can provide information on the ply number, the thickness of each ply, and fiber orientation. 

Non-destructive testing of adhesively-bonded structures G J CURTIS Acoustic wave techniques, resonance and pulse-echo testers... 

After plasma modification, the polymers were melt mixed at different composition in the Brabender Plasticorder, at 175EC. Samples from unmodified polymers were prepared under identical conditions. The test specimens were prepared by pressing at 190EC, then annealing. For the mechanical tests, an Instron TM 1102 tester at room temperature was used with crosshead speed of 12.4 mm/min. The dynamic mechanical tests were performed using a TA 983 dynamic mechanical analyzer (DMA), at a resonant fi equency of 0.2 Hz. 

Several nanomechanical characterization techniques have been suggested to measure the elastic properties of individual electrospun nanofibers, such as AFM cantilevers, universal tensile tester, and AFM-based nanoindentation system [133, 134]. Among them AFM-based techniques have been widely used to measure the mechanical properties of single electrospun nanofibers. This technique was carried out by attaching nanofiber to two AFM cantilever tips and recording the cantilever resonances for both the free cantilever vibrations and for the case where the microcantilever system has nanofibers attached. The Young s modulus of the nanofiber is then derived from the measured resonant frequency shift resulting from the nanofiber. A similar experiment has been carried out for electros-... 

Figure 6.34 The typical relationship between single lap-shear strength and response from the Fokker Bond Tester A-scale . With strengths increasing from zero up to 50% of the maximum, the resonance peak moves to the left further increases in the quality of the joints brings the peak back to the far right-hand side of the oscilloscope, whereupon it continues to move to the left as the strength increases to a maximum [138].

A different principle is used in ultrasonic resonance testing. Here, thickness vibrations are induced in the adherend/adhesive/adherend sandwich in which the two adherends eire considered to act as rigid masses while the adhesive is an almost massless spring. If the type and thickness of the metal sheets is constant, then the resonant frequency is a function of the thickness and bulk modulus of the adhesive. The well-known Fokker Bond Tester (Mark II) overcomes the difficulty of the many variables in the ultrasonic resonance test by coupling the joint to a system of well-defined resonance characteristics. Changes in the frequencies of the joint-transducer system are correlated with known defects and a calibration curve obtained. The calibration curves can then be used to establish acceptance limits which can be (and are extensively) used for quality control in production. 

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