Fatigue behaviors and cellular damages of bead-welded foam of poly(ether-b-amide) under cyclic compression

Abstract

Two polymer foams with density of 0.10 and 0.13 g/cm³ (F10 and F13) respectively were fabricated by steam-welding of expanded beads, obtained from super-critical foaming of poly(ether-b-amide). The compression fatigue behaviors were first characterized by step-increase strain tests up to −60 %, with an increment of 10 %. The stress relaxation rates during every one thousand cycles of compression was approximately 5.5 % and 4 % respectively for F10 and F13, while the energy return rate was kept more than 90 % and 85 % respectively. The stiffness of F13 can be largely kept stable, while that of F10 dropped evidently. Setting the strain from −30 % to −50 %, the long-term dynamic compression tests were performed with 4 Hz for 1 million cycles and 2 million cycles. The compression stress was generally kept unchanged after the foams were stabilized. Four types of damages were found i.e. the fine cracks, the detachment, the penetrated pinholes, and the rupture. Micro-computer tomography quantitatively revealed that the average fraction of damages is 8.95 % and 30.53 % in the visualized slices for the inter-bead surface and intra-bead walls. However, both foams showed nearly zero residual compression set, no detachment of single bead, which denotes the superior fatigue properties of the PEBA foams.