Session: 02-05-02: Experimental Studies in Structural Dynamics - II

Paper Number: 110930

110930 - Characteristics and Dynamics of Asymmetric Bolted-Joint Beams Under the Influence of Wear 

Wear in structures often occurs at an interface between two components that are in contact with each other. The type of wear can be determined by the material of the components that are in contact, and the amount of force causing them to be in contact can give insight into how fast the wear is developing. The current benchmark bolted-joint structure that is used to test joint dynamics is the Brake-Reuss beam, and that is due to its nonlinearities. This beam is composed of two identical component beams with extensions that are half of the initial height. These extensions connect through a lap joint with three bolts. In this study, the effect of the development of wear at the lap joint of the Brake-Reuss beam on the structural dynamics of the system is investigated for two different materials: aluminum and steel. The aim is to examine how differently wear affects the dynamic properties of structures made of different materials in order to gain a higher level of understanding of the dynamics of systems affected by wear.

To achieve this, modal testing on two identical cantilevered Brake-Reuss beams with dimensions of 60 x 1 x 1 cm is first performed with the goal of fully defining their dynamic profiles and categorizing them before any substantial wear has developed within the joint interface. One of the beams is made of Aluminum 6061-T6 while the other is made of low carbon steel. Accelerometers are placed above the beams’ axial centerline at the tip, 14 cm from the tip, and 33 cm from the tip. Only the accelerometer at the tip is used to measure data. These accelerometers weigh 6.3 g and have dimensions of 1.016 x 1.016 x 1.016cm. Three forms of modal testing are considered: free, random, and harmonic. The free vibration testing is conducted by constraining the beams to a smart table with a steel plate, leaving 50 cm of the beams extended to implement pseudo cantilever conditions. A large manual displacement is then applied and the response is measured and recorded using Siemens Testlab time data acquisition software. Time history data for high, medium, and low excitations is retrieved. Fast Fourier Transform analysis is performed on these time histories and the data is processed to determine backbone curves that serve as a basis for comparison for the random and harmonic tests.

Next, the beams are fixed onto a slip table similar to the free vibration experiments to achieve a pseudo cantilevered condition with a 50cm length. A modal shop shaker attached to the slip table via a stinger then output a signal to the slip table. Through this, random testing is examined at three levels of excitations: 1e-6, 1e-5, and 1e-4 V^2/Hz. The data is measured and the frequency response functions are obtained and normalized by the input values to verify that the nonlinear characteristics are consistent with the free vibration results. Then, harmonic testing is performed at four levels of excitation: 10, 20, 50, and 70 mV. Experimental results indicate the presence of nonlinear damping and softening as the excitation increases, which is expected due to energy dissipation at the joint. The next phase of the project is to conduct long harmonic tests near resonance to induce the most damage to the interface. This is done in order to later measure the development of the wear throughout the lifetime of these beams and see what changes in the beams’ dynamic profiles can be observed. At regular intervals between these long harmonic tests, free vibration is performed and the changes of the systems is tracked and compared between the aluminum and steel beams.

Presenting Author: Tharwat Elkabani New Mexico State University

Presenting Author Biography: My name is Tharwat Elkabani. I am a junior undergraduate in Mechanical & Aerospace engineering at New Mexico State University. I work on vibration and environmental testing of structures in the Nonlinear Dynamics and Energy Harvesting Laboratory at NMSU. I am also participating in Los Alamos Dynamic Summer School in Summer 2023. My interests include nonlinear dynamics, structural testing, and aeroelasticity.

Authors:

Tharwat Elkabani New Mexico State University
Dylan Allen New Mexico State University
Marina Espinosa New Mexico State University
Abdessattar Abdelkefi New Mexico State University