Mechanical characterization and modeling stress relaxation behavior of acrylic–polyurethane‐based graft‐interpenetrating polymer networks

The stress relaxation behavior of acrylic–polyurethane (PU)‐based graft‐interpenetrating polymer networks (IPNs) was characterized via dynamic mechanical analysis (DMA) and modeled using finite element method (FEM) analysis. Stress relaxation of glassy IPN specimens was experimentally studied under flexural testing, while rubbery IPN specimens were tested in tension. The effects of varying the styrene content in the acrylic copolymer phase, compatibility of the two phases in IPNs, and changing the concentration of acrylic copolymer and PU were studied. A higher percentage of styrene content resulted in higher homogeneity of IPN specimens, and decrease in initial modulus for acrylic copolymer specimens. Additionally, glassy IPN specimens with 90% styrene shows resistance to relaxation as high as acrylic copolymer samples. Experimental results were used to develop a numerical model to study stress relaxation response of specimens. While polymer systems have been studied computationally, numerical modeling of IPN systems is still in its infancy. A three‐dimensional FEM model was developed using the Generalized Maxwell model and four‐term Prony series constants, which were extracted from the stress relaxation experiments. With four terms in the Prony series, a good match was observed between experimental observations and results from the FEM model. Interpenetrating polymer networks (IPNs) have found use in a wide range of applications including biomedicine, dental applications, adhesives, and dampers. In this work, acrylic–polyurethane‐based graft‐IPN specimens were synthesized, and their stress relaxation behavior was studied through experiments and numerical modeling. Increasing styrene content decreases initial modulus of IPN specimens. Glassy IPNs show lower resistance to relaxation than rubbery IPNs. The numerical model captures stress relaxation behavior of samples with good accuracy.