There has been a renewed interest to understand the degradation mechanism of concrete under radiation as many nuclear reactors are reaching their expiration date. Much of the information on the degradation mechanism of concrete under radiation comes from the experiments, which are carried out on very small specimens. With the advent of finite element analysis, a numerical predictive tool is desired that can predict the extent of damage in the nuclear concrete structure.

A mesoscale micro-structural framework is proposed in Multiphysics Object-Oriented Simulation Environment (MOOSE) finite element framework which represents the first step in this direction. As part of the framework, a coupled creep damage algorithm was developed and implemented in MOOSE. The algorithm considers creep through rheological models, while damage evolves exponentially as a function of elastic strain and creep strain. A characteristic length is introduced in the formulation such that the energy release rate associated with each element remains the same to avoid vanishing energy dissipation with mesh refinement. A creep damage parameter quantifies the effect of creep strain on the damage that was calibrated using three-point bending experiments with varying rates of loading.

The creep damage model was also validated with restrained ring shrinkage tests on cementitious materials containing compliant/stiff inclusions subjected to variable drying conditions. The simulation approach explicitly considers: (i) moisture diffusion driven differential shrinkage along the depth of the specimen (ii) viscoelastic response of aging cementitious materials (iii) isotropic damage model with Rankine′s failure initiation criterion, and (iv) random distribution of tensile strengths of individual finite elements.

The model was finally validated with experimental results on neutron-irradiated concrete. The simulation approach considers: (i) coupled hygro-thermal model to predict the temperature and humidity profile inside the specimen (ii) radiation-induced volumetric expansion of aggregates (RIVE) (iii) thermal, shrinkage and creep effects based on the temperature and humidity profile and (iv) isotropic damage model with Rankine’s criterion to determine failure initiation.

This paper discusses the design of experimental setup and procedures to characterize polymethyl methylate (PMMA) at its glass transition temperature by studying its strain fields, process zone, and crack speed under different loading conditions. These loading conditions are different steady-state temperatures and initial crack lengths. Steady-state temperature testing uses a temperature control loop. Crack speed / resistivity testing is set up using a voltage drop method. From initial steady-state temperature testing, it was confirmed that the behavior of a PMMA sample becomes more ductile at higher temperatures, and that it is plausible for a crack process zone to be measured using DIC as temperature increases. From finite element simulations, it was validated that the crack speed is not constant relative to an initial crack length.

This research summarizes the characterization of the constituent materials of a unidirectional composite for use in a finite element model. Specifically the T800s-F3900 composite from Toray Composites, Seattle, WA. Testing was carried out on cured polymer matrix provided by the manufacturer and single fiber specimen. The material model chosen for the polymer matrix was MAT 187 (Semi-Analytical Model for Polymers) which allowed for input of the tension, compression, and shear load responses.

The matrix was tested in tension, compression, and shear and was assumed to be isotropic. Ultimate strengths of the matrix were found to be 10 580 psi in tension, 25 900 psi in compression, and 5 940 in shear. The material properties calculated suggest the resin as being an isotropic material with the moduli in tension and compression being approximately equal (3% difference between the experimental values) and the shear modulus following typical isotropic relations. Single fiber properties were obtained for the T800s fiber in tension only with the modulus being approximately 40 500 ksi and the peak stress value being approximately 309 ksi.

The material model predicts the behavior of the multi-element testing simulations in both deformation and failure in the direction of loading.

The preceding paper analyzes the effects of UV radiation in plastic reinforcement and its effects on the fracture properties of cement-based materials. Three point tests were performed on notched beams, which called for the consideration of the Type II Size Effect. A comparison of the ductility of beams with and without polyethylene plastic powder reinforcement was done through the calculation of the fracture parameters Gf and cf, which represent the initial fracture energy and the characteristic length respectively. Although there was an observed increase in ductile behavior and properties in beams with polyethylene reinforcement, there did not seem to be a significant effect caused by the UV radiation. The hydrophilicity of the polyethylene powder was successfully increased through UV radiation and validated through water retention tests, which showed that the UV-treated polyethylene was retaining more water than the non-treated polyethylene, yet there was no extra increase in ductility of the cement beams compared to using non-treated polyethylene. The Type II Size Effect analysis was performed and compared to the stress analysis results of the experiment. For future research, it is recommended that a higher volume of polyethylene per 1000 grams of cement powder be used, as well as increasing the strength of the UV chamber to achieve a larger increase in the hydrophilicity of the polyethylene. Also, perhaps using more precise equipment to cut the notches in the beams would be helpful in ensuring that all specimens are identical and there is no error in notch depth caused by inaccurate use of the hacksaw or radial saw. Further experiments will be conducted.

This research summarizes the validation testing completed for the material model MAT213, currently implemented in the LS-DYNA finite element program. Testing was carried out using a carbon fiber composite material, T800-F3900. Stacked-ply tension and compression tests were performed for open-hole and full coupons. Comparisons of experimental and simulation results showed a good agreement between the two for metrics including, stress-strain response and displacements. Strains and displacements in the direction of loading were better predicted by the simulations than for that of the transverse direction.

Double cantilever beam and end notched flexure tests were performed experimentally and through simulations to determine the delamination properties of the material at the interlaminar layers. Experimental results gave the mode I critical energy release rate as having a range of 2.18 – 3.26 psi-in and the mode II critical energy release rate as 10.50 psi-in, both for the pre-cracked condition. Simulations were performed to calibrate other cohesive zone parameters required for modeling.

Samples of tested T800/F3900 coupons were processed and examined with scanning electron microscopy to determine and understand the underlying structure of the material. Tested coupons revealed damage and failure occurring at the micro scale for the composite material.