Life-time Modelling of thermoset Polymers in Structural Engineering

In recent years, polymers have joined the traditional infrastructure materials timber, steel, concrete, and brick in structural engineering applications. However, compared to classical aerospace or automotive applications the polymers typically do not undergo the full curing process. This has far reaching consequences as the material is likely to change its properties during service. Currently, the scientific community is lacking concepts to predict the changing material properties and thus accurately predict the performance of structures and structural components in the presence of polymers. The project Life-time Modelling of thermoset Polymers in Structural Engineering (LiMoPoSE) pursues an interdisciplinary approach combining experimental investigations and computer-based simulations on the level of the structure, the material, and the material constituents. By creating the necessary background knowledge, a truly predictive model for structural applications will be developed. The models quality will be verified by three typical and independent case studies, one classical problem from aerospace engineering and two representative cases in structural engineering.

Thermoset polymers play an increasingly important role in structural engineering. Compared to classical aerospace or automotive applications the polymers typically do not reach a fully cured state during construction. The material will consequently undergo post-curing during it's lifetime, changing significantly it's material characteristics. Currently, the scientific community is lacking modeling concepts for the temperature and curing level dependent mechanical response of set-cast polymers, in particular with regard to visco-elasticity. Due to aging, these materials defy all known concepts for accelerated testing. Hence, the performance prediction for structural life-times of 50 years or longer remains an unsolved challenge. In this proposal an interdisciplinary approach combining experiments and simulations on multiple length and time scales aims at delivering a physically based and thus truly predictive multi-physics multi-scale model for structural applications. The model's quality will be established by two typical and independent representative cases in structural engineering. The data collected on the mechanical behavior at different degrees of cure of 2-4 typical thermosets represents one of the most comprehensive data collections available on this topic. In addition to the development of mechanical and visco-elastic properties, water absorption and the associated changes in mechanical behavior were also investigated. In addition to the experimental data, models were also developed to predict the exothermal curing reaction, associated volume changes, the curing-dependent mechanical properties, including rate+dependence and, in particular, a novel creep model that allows extrapolations far beyond the period under investigation. The latter was validated on basis of an almost 2-year long data set after calibration on a 24-hour data set.