PSI - Issue 68

Büşra Eyri et al. / Procedia Structural Integrity 68 (2025) 332 – 338 B. Eyri et al. / Structural Integrity Procedia 00 (2025) 000–000

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Figure 1. The cell structure types of the samples. a) Diamond b) Overexpanded c) Re-entrant

2.2. Three Point Bending Test Three-point bending tests were performed on the samples using the Instron 4411 model universal testing machine in alignment with the standards set forth by the ASTM D7249 at room temperature and with a bending speed of 5 mm/min. A minimum of three tests were conducted. The flexural strength (σ), flexural modulus (E), and flexural strain (ε) values of the samples were determined (Table 2.) and subsequently analyzed. The bending curves obtained for each sample are presented in Figure 2, and the energy absorption performances derived from the curves were evaluated. 2.3. Modal Tests Modal tests were conducted to analyze the vibration behavior and structural damping properties of samples with three distinct cell structures, produced via 3D printing. The samples are fixed at one end to simulate the physical boundary conditions that would be present in a real-world scenario and tested using the impact hammer method, which is a non-destructive material testing technique (Noel et al. 2024). The test was conducted with a Dytran brand 5800B4 model impulse hammer and a sensitivity of 2.25 mV/N. A Dytran brand 3055d2 model and 100 mV/g sensitivity uniaxial accelerometer was employed to evaluate the response of the sample. The accelerometer probe is attached to the sample, and an impact stimulus is applied to the sample using the impact hammer. The natural frequencies of each sample have been analyzed using an OROS O4 4-channel vibration analyzer as a result of the impact hammer test. In order to obtain displacement data in the vibration of samples with various cell structures, a Micro-Epsilon brand OptoNCDT 1420 model laser measurement sensor is employed. This sensor is a high-precision non-contact displacement sensor that employs the technique of optical triangulation to measure distance, displacement and position. The device operates on the principle of transmitting a laser beam to a surface and calculating the distance according to the reflection angle, utilizing a position-sensitive detector. The OptoNCDT utilizes voltage readings within the acceptable range of 40mm-70mm. The linear regression model was employed to obtain the correlation between the analog voltage reading and the distance, which was found to be = 36,5 + 35,1 (1) In this equation, the dependent variable, y, represents the distance in millimeters, while the independent variable, x, represents the analogue voltage reading. The Logarithmic Decrement and Damping Factor, derived from the aforementioned measurements, are calculated using the prescribed formulas. = " ! ( # ! # " ) (2) = %& ( $ # )$ # (3)