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Acoustoelasticity method for determination of screw joint tightness:
Specialized application «Acoustic tensometer» is intended for testing of tightening force of screw joints containing studs and bolts of steel and titanium alloys with at least 12 mm diameter, when length/diameter ratio does not exceed 7.
Tightening force is tested using acoustic tensometry methods assuming set of testing methods and tools based on the measurement of characteristics of elastic waves propagating in a medium. In practice, these techniques are applied in widest degree in the aerospace and oil-and-gas industries to test the tightening uniformity of screw joints and tensographic imaging.
As a rule, the tested objects are: assemblies with bolted joints in railway vehicles and at iron and steel works, high pressure cylinders at thermal and nuclear power plants, pressure vessels in gas-and-oil producing industry, elements of jet engines of space vehicles, etc.
Tomographic 3.2 implements the method of acoustic (ultrasonic) tensometry based on dependence of the velocity (propagation time) of ultrasonic waves in materials on mechanical stresses these materials are subjected to. Effective values of mechanical stresses are calculated basing on precision measurements of the propagation time of ultrasonic waves in the tested article material under echo-method.
Operation with Tomographic 3.2 is divided into 2 stages: creation and storing in the instrument memory of setting with regard to the tested joint and testing itself of this joint with subsequent saving of test results. If setting for the given joint was already created and stored, the 1st stage is limited by downloading of this setting from the instrument memory for application.
Setting creation process consists of the entry of parameters of a joint to be tested under created setting, as well as parameters of the used PEP. Parameters of sweep and strobes are set automatically depending on entered joint parameters. Nevertheless, they can be adjusted manually, if required. In the entry mode of joint parameters, image of a bolt (stud) is displayed on the screen and the entered parameter is highlighted, which improves significantly visualization of performed actions and facilitates the process of setting creation.
Application is intended for testing of joints, including bolts (studs) of the same type, i.e. of the same size and made of the same material. Therefore, during setting creation, parameters of the only one bolt (stud) are entered, while parameters of remaining bolts (studs) are considered to be identical with parameters of the first bolt (stud). The main parameter of the used PEP to be entered is its frequency. As a rule, in testing of joint tightening forces, PEP’s of P111-5-К12-040 are used. Parameters of the used PEP can be entered manually or downloaded from the PEP archive.
Joints can be tested in 3 modes: assembling, disassembling and reverification.
Assembling – propagation time of ultrasonic waves is measured firstly in bolts (studs) in the non-tightened state. Afterwards, joints are tightened and propagation time of ultrasonic waves is measured in bolts (studs) in the tightened state.
Disassembling – propagation time of ultrasonic waves is measured firstly in bolts (studs) in the tightened state. Afterwards, joints are loosened and propagation time of ultrasonic waves is measured in bolts (studs) in the non-tightened state.
Reverification – for a joint that was tested previously, propagation time of ultrasonic waves is measured repeatedly in bolts (studs) in the tightened state in order to monitor their state. In this case, result of previous testing is downloaded automatically from memory, if it was stored, or is entered manually.
In the testing mode, so called diagram of forces is displayed on the screen; it reflects distribution of stresses in each bolt (stud), which makes it possible to achieve uniform tightening of all parts in joint. Tightening level of the current (tested) element is indicated by means of color scheme. Test results can be presented also in tabular form.
FUNCTIONAL DATA:
Under order of ROSAVIAKOSMOS for NPO Energomash named after V.P.Glushko, additional software and technical modifications were elaborated in accordance with OST 92-9521; these additions to the basic version of Tomographic 3.2 are implemented in the form of separate specialized application "AKON-4М".
