On the Visualization of Localized Porous Media Deformation During an Indentation Process
Soft porous materials widely exist in nature. Animal skins, articular cartilages, and skeletal muscles can all be considered as soft porous media. The deformation of the soft porous material is essential for their normal functionality. For example, the interstitial fluid pressurization of articular cartilage is crucial for the friction reduction of our knee joints. Of particular interest, the localized strain of a porous media under dynamic compression determines the local permeability and hence the pore pressure distribution. From a solid mechanics point of view, localized densification of a porous foam under either uniaxial compression or indentation determines the stress field and hence the load supporting capability during a quasi-static compression process. Despite of its importance, there is no study, to our knowledge, that precisely captures the localized compression of a porous media during an indentation process. The study presented herein is aimed to fill in the gap of literature.
In this paper, we have developed a novel experimental setup to systematically examine the localized densification of a porous foam under indentation. The system consists of a Physik instrument (PI) positioning system and a square flat-punch tip on an isolated optical table. The polyester foam was compressed using indenters of different sizes. The entire surface of the foam was marked with black dots, whose displacements were captured by a high speed camera. The deformation of the porous foam is then precisely recorded. The results were processed with Digital Image Correlation (DIC). It shows that densification of the porous foam, which is related to the collapse of the pores, occurs at the vicinity near the solid loading surface and propagates as the indentation proceeds. This behavior arises from the fact that the Poisson’s ratio changes from a positive to a negative value when the stress continuously increases and exceeds a threshold, a unique feature of porous media. Further analysis using the finite element method (FEM) supports our analysis. When compression is small, the poison’s ratio is positive, and the simulation agrees with the experimental observation. When the compression is getting larger, the simulation deviates from the experiment results as the Poisson’s ratio by nature has changed to a negative value.
The study presented herein, combining a novel indentation system and a comprehensive analysis of the recorded footage, provides a systematic method to capture the non-homogenous behavior of the porous foam under external impaction, which will have a significant impact on the study of soft matters.
On the Visualization of Localized Porous Media Deformation During an Indentation Process
Category
Poster Presentation
Description
Session: 16-01-01 National Science Foundation Posters - On Demand
ASME Paper Number: IMECE2020-25009
Session Start Time: ,
Presenting Author: Qifu Wang
Presenting Author Bio: 2020-present, Ph. D in Villanova University, interested in fluid dynamics, especially in the porous structure.
2016-2020, got a master’s degree from Technical Institute of Physical and Chemistry, CAS, interested in microfluidics field, especially in the micro-thermal sensors and micro-valve.
Authors: Qifu Wang Villanova University
Qiuyun Wang Villanova University
Zenghao Zhu villanova university
Gang Feng Villanova university
Qianhong WuVillanova University