Morphological and performance measures of polyurethane foams using X-ray CT and mechanical testing

Area of Science:

• Materials Science
• Polymer Science
• Mechanical Engineering

Background:

• Meso-scale structure dictates polymeric foam mechanical properties.
• Density variations and anisotropic void structure significantly influence compressive and tensile responses.
• Polyurethane (PU) foams are widely used as structural materials and space fillers.

Purpose of the Study:

• To quantitatively measure density and anisotropic structure in PU foams using micro X-ray computed tomography (microCT).
• To correlate microstructural variations with mechanical testing results.
• To understand the impact of regional density and morphology on foam performance.

Main Methods:

• Micro X-ray computed tomography (microCT) for quantitative analysis of density and anisotropic structure.
• In situ imaging during material compression to observe structural response.
• Analysis of cell morphology, size, shape, and orientation in different foam regions.

Main Results:

• MicroCT revealed density variations and anisotropic structural differences across the foam.
• A distinct 6 mm thick high-density "skin" layer with eccentric morphology was identified in molded PU foam.
• Regional variations in density and structure led to significant differences in mechanical performance based on sampling location.

Conclusions:

• The meso-scale structure, particularly density variations, is critical for PU foam mechanical behavior.
• The identified high-density skin layer significantly influences mechanical performance variability.
• Understanding these microstructural heterogeneities is essential for predicting and optimizing PU foam applications.