Ваш браузер устарел и не обеспечивает полноценную и безопасную работу с сайтом.
Установите актуальную версию вашего браузера или одну из современных альтернатив.
Carrying out multi-cycle tests of samples from VT-6, subjected to repair by fusion welding.
Krylov K.A.1,2, Lastovirya V.N.1,3
1 Department of equipment and technology of welding production, Moscow Polytechnic University, 38, st. B. Semyonovskaya, Moscow, 107223, Russian Federation.
2 Kirill.Krylov.94@mail.ru
3 Slava.Lastovirya@gmail.com
Annotation. The most important element of a gas turbine aircraft engine is a monolithic fan aircraft wheel. Simulator samples are used to confirm the properties of an expensive fan wheel. The paper considers testing of samples for high-cycle fatigue in comparison with repair methods by fusion welding methods. It is concluded that the destruction of samples from electron beam welding occurred due to machining defects.
Key words: gas turbine engine, fan, monolithic fan wheel, wheel defects, repair of fan wheels, manufacturing and operation stages.
Introduction
One of the most complex engineering structures is a gas turbine. An important part of the turbine is the fan, which consists of several stages.
Initially, the fan wheels were made with replaceable blades, but to improve flight performance, they began to be made monolithic. After this change, it became a question of repairing defective fan wheels.
During the work on the restoration of the fan wheel of a gas turbine engine, 29 samples of high-cycle fatigue were tested to confirm the performance.
Multi-cycle tests
High-cycle fatigue tests were carried out on a VEDS-1500 vibration electrodynamic test facility.
Three types of samples were tested: control specimens, samples with welded-on TIG joint (sample size 9x11mm) and samples with EBW joint (straight weld).
On the basis of OST1 00303-79 «Blades of gas turbine engines. Periodic fatigue tests» [1], a procedure for testing monowheel blades has been developed. A similar technology was used in the work described in the article «Development and justification of a method for repairing unicycles by argon arc welding and surfacing» [2].
The tests were carried out at room temperature according to the following regime: initial loading level: σ = 392.27 MPa, loading change step: ∆σ = ± 29.42 MPa, test base N = 2*107 cycles.
Control samples
σ = 392.27 MPa, N = 0.38*107 cycles, collapsed
σ = 362.85 MPa, N = 1.45*107 cycles, collapsed
σ = 333.43 MPa, N = 2*107 cycles, withstood
Samples with welded TIG connection
σ = 392.27 MPa, N = 0.18*107 cycles, collapsed
σ = 362.85 MPa, N = 0.23*107 cycles, collapsed
σ = 333.43 MPa, N = 0.82*107 cycles, collapsed
σ = 304.01 MPa, N = 2*107 cycles, withstood
Samples with EBW connection
σ = 392.27 MPa, N = 0.03 * 107 cycles, collapsed on clamping *
The sample stood 3 modes
σ = 392.27 MPa, N = 2*107 cycles, withstood
σ = 421.69 MPa, N = 2*107 cycles, withstood
σ = 451.11 MPa, N = 1.01*107 cycles, collapsed
σ = 421.69 MPa, N = 2*107 cycles, collapsed
σ = 392.27 MPa, N = 2*107 cycles, withstood
σ = 392.27 MPa, N = 0.12*107 cycles, collapsed
σ = 362.85 MPa, N = 2*107 cycles, withstood
σ = 362.85 MPa, N = 0.06 * 107 cycles, collapsed on clamping *
σ = 362.85 MPa, N = 2*107 cycles, withstood
* Samples with EBW connection No. 1 and No. 8 were destroyed along the clamping part. When analyzing the test results, these samples were not taken into account.
Endurance limit of control samples σ-1= 333.43 MPa, samples with welded TIG joint σ-1= 304.01 MPa, samples with EBW joint σ-1= 362.85 MPa, with test base N = 2*107 cycles. In all cases, this is above 300 MPa, set as the required minimum by instruction 2220000000I18.2 «Instruction for checking the blades of fan and compressor unicycles for fatigue strength» [3].
Investigation of samples with EBW connection No. 2 and No. 3
After testing, samples No. 2, No. 3 with the EBW connection were checked by the LUM1-OV method according to GOST R50.05.09-2018 [4] and the glow of the phosphor was found:
— on sample No. 2 in the form of a thin transverse line, at the exit from the transition radius with a length of 17 mm, crossing the edge.
— on sample No. 3 in the form of a thin line, at a distance of 2 mm from the radius, 11 mm long, crossing the edge
When examined under a microscope after removing the paint, non-through cracks are observed on the flat surface of samples 2 and 3.
After etching the samples, it was revealed that cracks on sample No. 2 were formed at a distance of 3 mm, on sample No. 3 at a distance of 1.5 mm from the EBW.
Fractures were exposed along the cracks. A fractographic study on an electron microscope has established that the destruction is of a fatigue nature with centers of the onset of destruction:
— on sample No. 2, the center was an unrounded radius, in the form of an angle, of two surfaces, where irregularities and risks from the mechanical processing of these surfaces converge.
— on sample No. 3, the burr and risks located at a distance of ~ 5.5 mm from the end of the sample, formed during mechanical processing, served as the focus.
Findings
Endurance limit of control samples σ-1= 333.43 MPa, specimens with welded TIG joint σ-1= 304.01 MPa, specimens with EBW joint σ-1= 362.85 MPa, with test base N = 2*107 cycles.
The results show that with this configuration of joints in electron-beam welding, the endurance limit is higher, and in case of surfacing with TIG, it is lower than that of the control group.
The destruction of the samples with the EBW connection occurred along the base material or the place where the samples were clamped in the installation; no damage was found along the weld or near-weld zone.
Thus, the technology of electron beam welding provides the best quality of repair and restoration of the fan wheels of a gas turbine engine and is more promising due to the fact that:
First, it provides a higher tensile strength of the restored joint.
Secondly, the welded joint is of equal strength with the main material of the repaired wheel.
Thirdly, the technology of electron beam welding has a high repeatability of properties and does not depend on the skill of the welder.
References
1. OST 1-00303-79. Blades of gas turbine engines. Periodic fatigue testing. — Input. 1980–01–01 — M.: Publishing house of standards, 1979. — 36 p.
2. Fomichev, E. O. Development and substantiation of a method for repairing unicycles by argon arc welding and surfacing / Welding production. — 2014 — No. 4 p. 29-34.
3. 2220000000 I 18.2 Instructions for testing the blades of the fan and compressor unicycles for fatigue strength. — Input. 2001-01-01. — Zaporozhye: ZMKB «Progress» them. A. G. Ivchenko, 2000. — 18 p.
4. GOST R50.05.09-2018 Conformity assessment in the form of control Unified methods. Capillary control Input. 2019–03–01.
