Experimental investigation of macroscopic material nonlinear behavior and microscopic void volume fraction change for porous materials under uniaxial compression

The purpose of this study was to simultaneously analyze the nonlinear behavior and the void volume fraction change of polyurethane foam (PUF) under a uniaxial compressive load through micro-scale and macro-scale viewpoints. The influence of micro-scale factors on the macroscopic properties of PUF was analyzed, along with the interrelationships between micro-scale and macroscopic properties. The microstructure of PUF was observed by analyzing the density. Various micro-analyses were also conducted, including those for energy absorption, Young's modulus, and recovery behaviors. Internal structure changes such as those in density and degree of compressive strain were analyzed by measuring the void volume fraction of each region in the specimen under a uniaxial compressive load. The elastic, plateau, densification, and fracture regions of the compressive test stress strain curve were divided, analyzed, and compared with microscopic analysis results. Based on the results of the macro-micro-scale experiment, we analyzed influence and change process of microstructures on the compressive behavior of the PUF specimen in detail. This study shows that internal and overall changes in the compression process of various porous materials can be predicted under a uniaxial compressive load.