The mechanical failure properties of rigid polyurethane foam treated under random vibration were studied experimentally and by numerical simulation. The random vibration treatments were carried out in the frequency range of 5–500 Hz, 500–1000 Hz, and 1000–1500 Hz, respectively. The influence of the vibration frequency, mass block and acceleration on the mechanical performance of rigid polyurethane foam was further investigated by compression testing. The experimental results showed that the compression performance and energy absorption of foams decreased the least between 500–1000 Hz. In addition, in the 5–500 Hz range, the reduction rate of compression performance and energy absorption increased with the increase of the vibration mass block and acceleration. The resulting simulation indicated that the deformation degree of the sample was the most serious under the condition of 5–500 Hz. With the increase of deformation, the damage of the sample during the vibration process increased, which led to the decrease of compression property and energy absorption of rigid polyurethane foam. This further explained the variation mechanism of the compression test performance.
In order to study the relationship between the molecular structure and mechanical properties of rigid polyurethane foam (RPUF) during the mechanical and chemical failure process, the variation of the molecular structure and mechanical properties of RPUF treated in temperature range of 323–473 K were characterized by both theoretical and experimental methods. The molecular structure stability of RPUF varied with thermal treatment temperature was characterized by density functional theory method. The mechanical properties of base material of RPUF were simulated by means of molecular dynamics (MD) simulation. Then the related parameters obtained from the MD simulation were assigned into a representative volume element model of RPUF for the finite element analysis. The results indicated that the vibrational frequencies of isocyanate groups and amino acid ester groups in RPUF molecule increased while the molecular orbital energy gap of RPUF decreased with the increase of treatment temperature. It indicated that the RPUF molecule had high chemical reactivity at high temperature. The results of the multiscale simulation of mechanical properties showed that the defects and voids in RPUF generated under high temperature would grow with the increase of thermal treatment temperature, which intensified the stress concentration in RPUF and decreased the tensile properties of RPUF.
The thermal stability and tribological properties of cyanate ester (CE) composites filled with Zirconium boride (ZrB 2 ) particles were investigated by experimental and numerical simulation. The results of thermogravimetric analysis and differential scanning calorimetry showed that the thermal stability of composites was improved by introduction of ZrB 2 particles. The tribological properties of composites including friction coefficient and wear rate measured by pinon-disk friction and wear tester were enhanced. Friction coefficient and wear rate of composites were decreased significantly with an increase of ZrB 2 particles content under dry and oil sliding conditions. The 5 wt% ZrB 2 particles reinforced CE resin composite presented optimal thermal stability and tribological performance due to good dispersion of ZrB 2 particles. The worn surfaces of composites were observed by scanning electron microscopy to explore wear mechanism, indicating that the dominant wear mechanism of composites was transformed from adhesive wear to abrasive wear after incorporation of ZrB 2 particles. Finite element model was established to study the distribution of friction stress. The results revealed that filling ZrB 2 particles in the friction process of composites could bear more friction stress than CE resin matrix, which further illustrated that abrasive wear is main wear mechanism of ZrB 2 /CE resin composites. POLYM. ENG. SCI., 59:602-607, 2019.
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