Bead‐to‐Bead Analysis: Introducing an Innovative Methodology for Accelerated Quantitative Analysis of the Welding Behavior of Bead Foams

Abstract

Performant lightweight components made of bead foams are essential for a sustainable transformation of industry in multiple areas. An in‐depth understanding of the welding process is key in reaching maximum mechanical properties. This study presents the novel methodology of Bead‐to‐Bead analysis, providing a superior way in directly and quantitatively evaluating the welding behavior of bead foams compared with current approaches. Individual beads of expanded polystyrene (EPS) and expanded thermoplastic polyurethane (ETPU) are welded in a rheometer at defined parameters. A subsequent tensile test in combination with the analysis of the welded surface allows the evaluation of shrinkage/softening of the beads during welding and their tensile strength. For EPS, softening of the amorphous material is observed at the beginning of glass transition (~95°C) in addition to an increased welding quality. Residual stresses in ETPU lead to initial shrinkage followed by softening above 140°C. Welding of ETPU starts at 100°C and reaches a maximum at 140°C. The subsequent thermal analysis of the welded beads show the importance of recrystallization processes during cooling due to the formation of new crystalline domains across the bead interfaces. In the absence of such domains, sufficient bonding between beads is not possible.