System for the non-destructive testing of components

Abstract

In the system, two ultrasonic transducers, which form a pair and each have a piezoelectric ceramic plate-shaped element with a rectangular geometry, can be fastened to a surface of a component. The two ultrasonic transducers are arranged at a distance from one another such that there is no direct mechanical contact and they are arranged beside one another with a parallel orientation of their central longitudinal axes. The two elements have a different polarization along their width and are connected with the same polarity to an electrical voltage source. The two plate-shaped elements can also have an identical polarization along their width and can be connected in this case with opposite polarity to an electrical voltage source. At least one ultrasonic transducer and/or at least one further ultrasonic transducer is/are designed to detect ultrasonic waves reflected by defects and/or shear waves simultaneously emitted by the two ultrasonic transducers.

Claims

1. A system for the non-destructive testing of components, comprising two ultrasonic transducers, which form a pair and each have a piezoelectric ceramic plate-shaped element with a rectangular geometry with a width, length, and thickness, which are formed on two opposite surfaces each with an electrode, fastened to a surface of a component, wherein the two ultrasonic transducers in the pair are arranged at a distance from one another such that there is no direct mechanical contact and the two ultrasonic transducers in the pair are arranged beside one another with a parallel orientation of their central longitudinal axes, and the two piezoelectric ceramic plate-shaped elements have a different polarization along their width, and the two ultrasonic transducers in the pair are connected in this case with the same polarity to an electrical voltage source which can be operated in a pulsed manner, or the two piezoelectric ceramic plate-shaped elements have an identical polarization along their width, and the two ultrasonic transducers in the pair are connected in this case with opposite polarity to an electrical voltage source which can be operated in a pulsed manner, and the electrical voltage source is designed to apply electrical voltages in a frequency range of 10 kHz to 1 MHz to the two ultrasonic transducers, and at least one of the two ultrasonic transducers in the pair and at least one further ultrasonic transducer arranged at a known distance from the two ultrasonic transducers in the pair are designed to detect ultrasonic waves reflected by defects on the component and/or shear waves simultaneously emitted by the two ultrasonic transducers in the pair, whereby a pulse echo measurement is carried our using the at least one pair of ultrasonic transducers or a transmission/reception measurement is carried out between the at least one pair of ultrasonic transducers and the at least one further ultrasonic transducer which is arranged at a known distance from the respective pair and the detected ultrasonic waves are transmitted to an electronic evaluation and control unit, wherein the electronic evaluation unit is designed to evaluate the detected ultrasonic waves with respect to their amplitude and/or their temporal sequence.

2. The system according to claim 1, wherein the centre or area centroid spacing of the piezoelectric ceramic plate-shaped elements of the ultrasonic transducers in the pair is an odd integer multiple of half the wavelength of the emitted ultrasonic waves.

3. The system according to claim 1, wherein the ratio of the width to the length of the piezoelectric ceramic plate-shaped elements at least 3 to 1.

4. The system according to claim 1, wherein the piezoelectric ceramic plate-shaped elements have a maximum thickness of 1 mm.

5. The system according to claim 1, wherein the ultrasonic transducers in the pair can be fastened to the respective component by means of an elastically deformable material.

6. The system according to claim 1, wherein the at least two ultrasonic transducers in the pair are embedded or laminated in an elastically deformable material.

7. The system according to claim 1, wherein a sleeve is formed with elastically deformable material which fastens the ultrasonic transducers in the pair to the surface of the respective component such that the ultrasonic transducers rest on the respective component surface in a flat manner.

Description

DESCRIPTION OF THE DRAWINGS

(1) The invention shall be explained in more detail by way of example below. In this case, features can be combined with one another independently of the respective example or the respective illustration.

(2) In the figures:

(3) FIG. 1 shows two views of an example of a pair of ultrasonic transducers which can be used in the invention;

(4) FIG. 2 shows two views of a further example of a pair of ultrasonic transducers which can be used in the invention;

(5) FIG. 3 shows the effective direction of emitted shear waves (plan view);

(6) FIG. 4 shows an example of transmission functions which can be carried out as a broadband transmission signal (Sinc, at the top) or as a bandwidth-limited transmission signal (RC4);

(7) FIG. 5 shows a graph of the frequency-dependent achievable vibration speed of the SH0 mode in the comparison; excitation by means of a simple ultrasonic transducer 40 mm×10 mm (black curve) vs. two ultrasonic transducers 40 mm×5 mm (×2) forming a pair (grey curve), as can be used in the invention (recorded by means of laser vibrometry at a distance of 200 mm from the centre of the ultrasonic transducers), and

(8) FIG. 6 shows a typical phase speed graph of the shear wave modes for the material steel.

DETAILED DESCRIPTION OF THE INVENTION

(9) FIG. 1 shows a sectional illustration and a perspective illustration of an example of two ultrasonic transducers 1 and 2 which are arranged beside one another. In this case, their central longitudinal axes are oriented parallel to one another, in which case the two central longitudinal axes are also each oriented parallel to the edges with the length b. The two ultrasonic transducers 1 and 2 form a pair. At least one further ultrasonic transducer 4 is arranged at a known distance from the two ultrasonic transducers in the pair.

(10) As can be gathered from FIG. 2, in particular, an electrode 1.2 and 2.2 is respectively present on the two opposite surfaces of the piezoelectric ceramic elements 1.1 and 2.1, which electrodes are connected to an electrical voltage source (not shown). The electrical voltage source can be operated in a pulsed manner directly or via a frequency generator and can be controlled by an electronic evaluation and control unit (likewise not shown). The electrical power and the frequency with which shear waves are emitted can therefore be influenced in a defined manner.

(11) The spacing a of the area centroids of the two piezoelectric ceramic plate-shaped elements 1.1 and 2.1 is selected in the manner mentioned in the general part of the description. The spacing a is selected such that there is no direct touching mechanical contact, with the result that said elements do not directly mechanically influence one another during their operation.

(12) The actual detection of defects can be carried out as described in the general part of the description or as known, in principle, from the prior art.

(13) The two ultrasonic transducers 1 and 2 which form a pair can be laminated in an elastically deformable material 3.

(14) The amplitudes which can be captured can be gathered in a time-resolved manner or on the basis of the respective frequency from the graphs shown in FIG. 4 for emitted shear waves which are referred to as a broadband transmission signal (Sinc function, windowed) or as a bandwidth-limited transmission signal (RC4). These are a broadband transmission signal of up to 200 kHz (Sinc) and a bandwidth-limited transmission signal (RC4 at 100 kHz).

(15) The speed of shear waves is defined as follows:

(16) $c\left(\omega \right)=\frac{c_s}{\sqrt{1-{\left(\eta d\right)}^2{\left(\frac{c_s}{\omega d}\right)}^2}}$$c_s=\sqrt{\frac{G}{\rho }}$ with G . . . shear modulus, ρ . . . density

(17) $\omega =2\pi f$$\eta d=k\frac{\pi }{2},k=0,1,2,3,\mathrm{.Math.}$ d . . . half the structure thickness f . . . frequency

(18) In this case, k describes the order of the wave mode (SH0, SH1, SH2, . . . ). For the fundamental shear wave mode (k=0), the formula is reduced to the pure transverse wave speed. The wavelength can be calculated from the known propagation speed cs and the frequency f of the transmission signal.

(19) $\lambda =\frac{c_s}{f}$

(20) Laboratory measurements showed that the efficiency of the two ultrasonic transducers 1 and 2 can be increased in comparison with a simple arrangement by virtue of the two opposite piezoelectric ceramic plate-shaped elements 1.1 and 2.1, that is to say the proportion of energy of the shear waves emitted in the intended propagation direction increases for the same volume of piezoelectric ceramic material.

(21) The frequency-dependent achievable amplitudes in the comparison of simple ultrasonic transducers 40 mm×10 mm (black curve profile) in comparison with the two ultrasonic transducers 40 mm×5 mm (×2) forming a pair, as can be used in the invention (grey curve profile), can be gathered from the graph shown in FIG. 5.