# Design of a Spin Test System for Burst Phenomen Considering Nonlinear Rotordynamic Effects
## 1 Introduction  
Spin test rigs are systems used to test the dynamic phenomena and structural strength limits of components operating at high speeds [1; 2]. The purpose of the applications carried out in the test rig is to examine phenomena such as plastic deformation, crack propagation, and burst by rotating the part under test at high angular speeds and exposing it to centrifugal load [3]. Tests can be performed under vacuum and at high temperatures, depending on the operating conditions of the test rig. Components operating at high speeds, such as turbines and compressors of gas turbine engines, high-speed gears, and rotating parts of turbochargers and centrifugal pumps, can be tested under maximum load conditions in spin test rigs [4; 5; 6; 7; 8]. During the test stages, the aim is to expose the disc structure to burst by accelerating to the targeted speeds. However, before the disc bursts, plastic deformation will occur in the material. This associated plastic deformation will cause crack propagation [9; 10]. The burst phenomenon will occur as the crack size increases and the disc continues to be exposed to centrifugal force. The spin test rigs operate under vacuum and are driven by an electric motor running at high speeds for structures with a low inertia tensor [11; 12; 13; 14; 15]. The most important reason for operating the system under vacuum is to reduce the aerodynamic torque to zero, making electric motor selection easier and eliminating aerodynamic effects during the test. With vacuum, both aerodynamic damping is eliminated and convective heat transfer is prevented [16; 17; 18; 19]. In this way, a temperature gradient is achieved on the part. Without a vacuum, it would be almost impossible to capture the temperature gradient on the test specimen, which would be exposed to convective heat transfer [20; 21; 22]. It is crucial that the spin test system operates smoothly in terms of rotor dynamics [23]. The most important factor here is ensuring that any natural frequency of the part, shaft, or assembly does not resonate at a speed close to the test speed [24; 25; 26; 27]. If such a situation occurs, suitable test conditions may be disrupted. Particularly, when examining the natural frequencies obtained from the entire assembly of the part to be tested, it is essential that there is no critical speed in the range corresponding to \(\pm\)20% of the test RPM [28; 29]. For these reasons, detailed modal analysis must be performed, and the part test range must be kept away from rotor dynamic effects [30; 31]. This study conducted in [32] highlights the importance of flywheel strength in energy storage systems and addresses the challenges of high-speed spin tests in vacuum environments. By implementing a small stiffness pivot-jewel bearing and a spring squeeze film damper, these researchers designed a cost-effective, long-lasting spin system, achieving stable operation at 50,000 rpm with the theoretical results aligning with experimental findings. In another study [33], due to the limited data on the performance of burst containments for high-speed rotating machines, there was a need for low-cost test methods to develop optimized containment structures. Consequently, a low-cost test rig was designed to systematically investigate the performance of different containment structures and materials, with the collected data and subsequent analyses enabling the assessment of the effectiveness of various burst containments. This paper focused on examining the rotor dynamic effects for the spin test rig in detail. First, a Discrete Model (henceforth DM) of the system was established in the Matlab/Simulink environment to develop a preliminary design of the drive shaft, which rotates the test specimens. Then, both two- and three-dimensional modal and harmonic response analysis were carried out using the finite element approach to verify numerical results obtained from DM studies. These numerical results were validated with the Hummer test, and it was observed that the maximum error percentage was as small as 4.85.