Hamid Reza Madadi Varzaneh, SFB 1313 doctoral researcher at the Institute of Applied Mechanics (CE) (research project B05), will give his milestone presentation on 28 March 2025: "Dynamic Characterization under Multiaxial Stresses and High Frequency Fatigue Tesing".
Date: Friday, 28 March 2025
Time: 9:00 am CET
Title: "Dynamic Characterization under Multiaxial Stresses and High Frequency Fatigue Tesing"
Venue: Seminar Room MIB, Pfaffenwaldring 9, Room: 3.141. If you are interested to participate online in Hamid Madadi's milestone presentation, please contact Samaneh Vahid Dastjerdi to receive the Webex link >>> samaneh.vahiddastjerdi@mechbau.uni-stuttgart.de
Abstract
Visco-porous materials such as rocks and concrete exhibit different mechanical behaviors in response to varying frequencies and multiaxial boundary conditions.A lack of understanding of how these materials respond under such conditions results in almost unknown outcomes and significant engineering costs.
In this research, an innovative measurement system for dynamic mechanical analysis (DMA) was designed. This mechanical characterization technique utilizes finite amplitude excitations at the µm level. The DMA Frequencies were here from 0.01 to 1 kHz. Complex Poisson's ratio and Young's modulus and attenuation coefficient of them were measured directly. In the next phase, the DMA setup was integrated with a triaxial apparatus to investigate the mechanical response of visco-porous rocks and concretes materials under varying boundary conditions. The response of these materials to different confining pressures exhibited a distinct fingerprint effect, enabling differentiation between their behaviors and facilitating the detection of internal fractures. This approach allows for the extraction of mechanical properties, permeability and transition frequencies and changing in attenuation coefficients of Poisson's ratio and Young's modulus.
Also, this research aims to develop a high-frequency fatigue testing (HFFT) method were performed dynamic cyclic loading at high frequencies. Cyclic loading tests were conducted at frequencies ranging from 20 Hz to 200 Hz. The characteristics of property degradation and topological changes in rock and concrete materials were examined. The behavior of these materials was analyzed across different phases of fatigue testing. Ultimately, crack initiation, propagation, and final fatigue failure were investigated using micro X-ray Computed Tomography (µXRCT) imaging combined with the DMA method.
Finally, the DMA-HFFT-Triaxial method, coupled with µXRCT, was developed to characterize various materials, in both intact and fractured states. This characterization can be performed continuously and in real time under different boundary conditions.