The local mechanics of macroscopic heterogeneous photoelastic polymer networks

Stress localization and fracture within networks are common observations but predicting failure relies on a complex interplay between each connected component or beam. Simulations on model networks have shown intriguing connections between connectivity and stress. But do these results translate into physical experiments? To explore this, we produce macroscopic (~cm), heterogeneous (removing beams or varying beam thickness), 2D networks by using a 3D printed mold that is cast first with a silicone rubber, and then with a highly responsive photoelastic resin. Upon straining these networks to failure, each beam experiences a local stress resulting in a proportional photoelastic signal which is captured with a camera while measuring the bulk force with a capacitive load cell. This signal is compared to a previously measured force-intensity calibration curve from a single beam. Concomitantly, a second camera captures brightfield images, used to calculate the local strain. This local stress/strain information in programmable heterogenous networks is used as input for spring network simulations. We will present the comparisons between simulations/experiments and explore the underlying mechanics of a polymer network in both the linear and non-linear regime just before network failure.