Tensometry by means of electromagnetic-acoustic method for controlling the bolt tightening connections on the parts of the liquid rocket engines

Speaker:
Gulshin, Andrey; NPO Energomash; Russian Federation

Authors:
Bobrov, V.T.; Research Institute of Introscopy of MSIA Spectrum; Russia
Bobrenko, V.M.; Research Institute of Introscopy of MSIA Spectrum; Russia
Gulshin, A.V.; NPO Energomash; Russia
Lebedev, V.V.; NPO Energomash; Russia

ID: ECNDT-0039-2018

The problem of monitoring mechanical stress in structural elements is important for many industries, in particular, aerospace, automotive, energy, chemical, etc.
In NPO Energomash, the technology of acoustic strain gauging of threaded tightening connectors has been well developed and tested by measuring the time increment caused by propagation of longitudinal waves in fastening elements using piezoelectric transducers. According to this technology, preliminary calibration of devices is carried out, then zero values of longitudinal waves propagation time in non-fastened bolts (or studs) and after fastening are measured. Using the calibration data, the force value in the fastening elements is calculated.
Despite all the advantages, this technique has two significant drawbacks: 1) the necessity for con-tact lubricants and de-oiling operations; 2) systematic error which appears after the re-measurement (for example, after various tests or after a certain period of continuous operation). Inaccuracy arises because of the elongation of the studs and can reach significant values.
In this research, we analyzed the effectiveness of the electromagnetic-acoustic (EMA) method for controlling the bolt tightening connections on the parts of the liquid rocket engines in real production conditions. We used various designs of EMA transducers and tried to optimize the inspection process by means of simultaneous excitation of longitudinal and shear waves. A few measurement and data processing methods were tested after loading the studs and bolts on the hydraulic bench. Statistical processing of experimental results and error estimation for various measurement methods is carried out.
The principal possibility of using the EMA method for controlling the bolt tightening connections is shown experimentally and recommendations for the further development of this method is given.