The specialized "Acoustic tensometer" application is intended to test tensile strength of threaded connections, having studs and bolts of at least 12mm diameter, the length-to-diameter ratio not more than 7, manufactured from steels and titanium alloys. Tensile strength is tested with the acoustic tensometry methods; it means a set of testing techniques and tools, based on measurement of characteristics of the propagating elastic waves. This application is widely used in the airspace and oil-and-gas industries to test uniform tension of threaded connections and build tensographic images.
In general, testing objects are assemblies of bolted connections of the rail transport and metallurgical works, high-pressure cylinders of thermal and nuclear power stations, high-pressure vessels of the oil-and-gas industry, elements of spacecraft reaction engines, etc.
The program implements the acoustic (ultrasonic) tensometry method, based on dependence of the ultrasonic vibrations velocity (propagation time) within the material on the mechanical stresses. Current value of mechanical stresses is estimated on the basis of precision measurements of the ultrasonic waves propagation time for the tested object material, using the echo method (Fig. 1).
Program operation consists of two steps:
creation and saving of the setting for tested connection
and
testing with further saving of testing results.
If this connection’s setting has already been created and stored, the 1st step is just loading of this setting from the archive.
The setting is created by input of the tested connection’s parameters and used probe parameters. The scan and gates parameters are automatically set, depending on the input connection’s parameters. If necessary, they can be manually corrected. The bolt (stud) image is displayed in the connection’s parameters input mode; the input parameter is highlighted (Fig. 2,3); it improves the visual presentation of executed actions and simplifies the setting creation process.
The program is intended to test connections, having the one-type bolts (studs), i.e. they have the same size and are manufactured of the same material. Therefore, the parameters of only one bolt (stud) are input by creating setting; the parameters of other bolts (studs) are considered to be identical to the parameters of the first bolt (stud). The used probe frequency is its main parameter, which must be input. While testing the connection’s tensile strength, the probes of the P111-5-K12-040 type are usually used. The used probe parameters can be either manually input or loaded from the probes archive.
There are three modes: of connection’s testing: assembling, disassembling and retest.
Assembling - at first, the ultrasonic vibrations propagation times for untightened bolts (studs) are measured. Then the connection is tightened and ultrasonic vibrations propagation times for tightened bolts (studs) are measured
Disassembling - at first, the ultrasonic vibrations propagation times for tightened bolts (studs) are measured. Then the connection is weakened and ultrasonic vibrations propagation times for tightened bolts (studs) are measured.
Retest - the ultrasonic vibrations propagation time of for tightened bolts (studs) is repeatedly measured in the connection, which has already been tested earlier, to monitor its state. The earlier testing result is then automatically loaded from the memory (if it was stored)or manually input.
The so-called force diagram is displayed on the screen in the testing mode (Fig. 4); it displays the distribution of tensions in each bolt (stud), allowing to reach uniform tension of all connection’s parts. Tension degree of the current (tested) element is displayed with the help of the color range. Testing results can be also displayed as a table (Fig. 5).
In the retest mode, the force diagrams of current and previous testings are displayed (Fig. 6). It allows to monitor the connection’s state during its operation. | 
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fig. 5
fig. 6 |
Testing results are processed both on the device and PC. To process the results and form testing protocols on PC, the specialized Operator's Workbench program is used.
The acoustic tensometry technique was tested in the Russian Aviation and Space Agency (NPO "Energomash named after academician V.P.Glushko") and and in the Vyksa Steel Works and patented. Copyright belongs to the company Votum. Functional data: - Visualization and simplicity of input of the tested connection’s parameters;
- Built-in database of acoustic properties of different materials;
- Automatic setting of gates to the backwall echo signals;
- Automatic adjustment of the backwall echo signals amplitude;
- Estimation of current value of mechanical stresses in kgf/mm2 or MPa (force, Ts) in each part of the connection;
- Representation of testing results as a table or force (strength) diagram, displaying the “tension” degree with a color range;
- Possibility to re-test the earlier tested connection with simultaneous displaying of some testing results of this connection;
- Representation of testing results on the device and PC.
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