The collapse timing and rate of closed cell foams: revealing a conceptual misunderstanding of foam mechanics
conference contribution
posted on 2024-10-31, 09:28authored byFranz Fuss
The collapse stress and strain was determined in a closed cell PE foam according to the traditional method
(intersection of tangents at the linear elastic segment and at the beginning of the collapse plateau) and a new
method presented in this article. The new model consists of a normalized number of elements; each element
comprises the vertical cell wall members, in parallel with the cell gas and the horizontal members, the latter
two in series. The vertical members have two different moduli, depending on the pre- and post-buckling
phase. From this model, the normalized number of buckled elements and its collapse rate are calculated as a
function of strain and stress, and the onset of foam collapse is determined. The new method delivers a
collapse strain of 0.0224±0.0013; at the collapse strain determined with the traditional method
(0.0634±0.0048), on average 93% of all vertical members are already buckled. The traditional method is
incorrect as the foam starts to collapse once its modulus decreases.