Advances in Structural Engineering Research
341320 - Softening visco-elasto-plastic response of polyurethanes for damage-resistant structures: Experimental characterization and constitutive modeling
Friday, April 20
3:30 PM - 5:00 PM
Polymers are highly customizable materials, which present high potential for applications in the development of damage-resistant structural systems. Out of the various polymeric materials, polyurethanes combine high strength (2-3 times that of concrete) with high deformation capacity (~4% strain at yielding), and have been recently considered in the development of damage resistant bridges. However, development of structural systems incorporating polyurethanes requires fundamental understanding of their mechanical properties under various loading and environmental conditions, as well as development of constitutive models describing such responses. Compared to conventional structural materials, the response properties of polyurethanes include hysteresis, damage (softening), and rate dependence (viscosity) in both the elastic and inelastic range. For this reason, experimental mechanical characterization and constitutive modeling of polyurethanes requires rigorous experimental investigations.
This presentation describes: (i) an experimental program to characterize the mechanical behavior of amorphous thermoset polyurethanes of two different compositions, and (ii) a visco-elastic softening visco-plastic uniaxial material model to capture the observed response. The experimental program included different loading and environmental conditions. Loading conditions included: (a) monotonic/cyclic compression-only and tension-only tests for various strain rates (up to 5% per second), (b) monotonic compressive and tensile loading (at various strain rates) including constant deformation segments to quantify relaxation and capture the so-called equilibrium path (c) cyclic combined tension-compression uniaxial loading, and (d) relaxation and creep compressive tests. Environmental effects were considered via combinations of temperature (-25oC to 50oC) and relative humidity (25% to 98%). The test results showed rate dependence, asymmetric response in tension and compression, monotonic/cyclic damage, hysteresis, and environment dependence of both elastic and inelastic properties.
On the basis of these test results, a visco-elastic softening visco-plastic constitutive model is developed, which is composed of set of rheological networks in series. Different networks represent different processes during material deformation. Visco-elastic response is represented by a generalized Maxwell network of nonlinear elements, which can also capture relaxation and creep. Inelastic response is captured by an elasto-visco-plastic network that incorporates a smooth kinematic visco-plasticity law and softening through “shrinking” of the yield surface as a function of the plastic strain. Coupling between the networks is also considered to capture the interdependence of different processes during material deformation. A novel structured approach for decomposing the response into a rate-independent part and a rate-dependent part is adopted for model calibration. The developed constitutive relations are implemented in the OpenSees structural analysis, which is then used for the analysis, under dynamic and environmental conditions, of benchmark structures, such as buildings and bridges, where the polyurethane materials are used in the location of the plastic hinges for damage resistance.
• Considering the low performance of traditional structural materials under dynamic loads from various natural hazards, exploration of advanced materials for structural applications, which is the focus of this presentation, will be of national and international interest.
• The target audience will include structural and materials engineers from academia and industry that are interested in use of advanced materials to improve structural performance under natural hazards.
• The audience will be introduced to novel polymeric materials, their fundamental mechanical properties, and their advantages over traditional structural materials, such as concrete.