Kimberly Maciejewski 1 , Yaofeng Sun 1 , Otto Gregory 2 , Hamouda Ghonem 1 1 Department of Mechanical Engineering and Applied Mechanics, 2 Department of Chemical Engineering, University of Rhode Island, Kingston, RI, 02881, USA The microstructural and mechanical properties of low carbon steel as a function of temperature and post thermal exposure are characterized. The amounts and morphology of carbides present were monitored as a function of thermal exposure parameters. An Internal State Variable (ISV) model has been employed to simulate the flow behavior of the steel for multiple temperatures, ranging from 20-700°C and loading rate conditions. Low cycle fatigue tests are carried out to determine the material parameters required for implementation in constitutive equations. This work provides a fundamental understanding of the deformation response associated with fire loadings. It also gives insight on the effects of microstructural components related to the deformation response of post-fire loading conditions. This knowledge represents the foundation of predictive modeling of new designs, materials and protocols for mitigation methods aiming at infrastructure protection. This material is based upon work supported by the U.S. Department of Homeland Security under Award Number 2008-ST-061-ED0001. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied of the U.S. Department of Homeland Security. This ISV model is being extended to 2-D and 3-D simulations suitable for implementation of steel-structures subjected to fire and loading conditions. It will also be extended for simulation of deformation response of structural steel under combined blast/fire loadings K. Maciejewski, Y. Sun, O. Gregory and H. Ghonem, Time-Dependent Deformation of Low Carbon Steel at Elevated Temperatures, Int. J. Steel and Iron Research, March 2011 Deformation and Hardening Characteristics of Structural Steel Under Post-Fire and Fire Conditions Abstract Relevance 1) Effects of temperature and time on Vol% pearlite and grain size of low carbon steel have been examined. 2) An ISV material model combining kinematic and isotropic hardening has been employed. 3) An experimental program was carried out to determine material parameters for model implementation. 4) Numerical modeling was carried out for 1-D simulation to check validity of model and its ability to predict material behavior for variable loading conditions. Accomplishments Through Current Year Future Work Journal Publications Technical Approach 4. Microstructural 5. Heat Treatment Characterization Test Setup v R k ij X ij p ij v R k ij X 1 2 1 μq max p 1 ( ) ( ) Q Q 1 e max( ε ,q) exp ( ) ( ) i v r i i i p i p i i i p n n v v p t p X R k X X X X Ca X X X R bQ R q sign X K K E Extensometer Induction Coil TC 1 TC 2 TC 3 Specimen Extensometer Specimen Alpha-Ferrite Pearlite Colony/ Plates - Cementite - Ferrite Temperature range: 300-700°C Exposure times range: 0-200min Vertical Furnaces Ice Salt Water Baths Nickel-Chromium Wire Temperature (°C) 0 200 400 600 800 Vol% Pearlite 0 2 4 6 8 10 12 14 Marked decrease in Vol% Pearlite at 700°C Exposure Time (minutes) -50 0 50 100 150 200 250 Vol% Pearlite 0 2 4 6 8 10 12 14 20°C, 300°C, 500°C, 600°C 700°C Exposure Time (minutes) -50 0 50 100 150 200 250 Grain Size (micrometers) 30 40 50 60 70 80 90 100 20°C, 300°C, 500°C, 600°C 700°C Temperature (°C) 0 200 400 600 800 Grain Size (micrometers) 30 40 50 60 70 80 90 100 Increase in variations of grain size at 700°C (bimodal distribution) As Received 600°C, 200min 700°C, 200min Critical Post Fire Conditions • As Received • 600°C, 200min, Quenched in Ice Salt Water Bath • 700°C, 200min, Quenched in Ice Salt Water Bath Grain Size (micrometers) 30 40 50 60 70 80 90 Vol% Pearlite 0 2 4 6 8 10 12 14 20°C - 600°C 700°C Bimodal Distribution Formation of Spheroidized Carbide For the same temperature, exposure time had less than 2% effect on Vol% Pearlite 600°C, 200min Spheroidized Carbide 700°C, 200min Spheroidized Carbide Strain controlled tests carried at 5 temperatures to determine Kinematic Hardening, Isotropic Hardening, and Viscous Stress Material Constants. Tests required at each temperature are: 1. Monotonic – constant strain rate 2. Stress Relaxation – constant strain rate with hold at constant strain values 3. Cyclic – constant strain rate with fully reversed loading at different strain ranges 4. Strain Rate Sensitivity – varying strain rates 2. High & Room Temperature Test Setup 3. Experimental Program & Parameter Determination 1. Internal State Variable Model Digital Temperature Readout 6. Quantitative Analysis For T 20°C- 600°C, exposure time has no effect on grain size. At 700°C, “average” GS increases with exposure time Strain (mm/mm) -0.006 -0.004 -0.002 0.000 0.002 0.004 0.006 Stress (MPa) -200 -150 -100 -50 0 50 100 150 200 600°C - Experimental Strain (mm/mm) -0.008 -0.006 -0.004 -0.002 0.000 0.002 0.004 0.006 0.008 Stress (MPa) -80 -60 -40 -20 0 20 40 60 80 700°C - Experimental Strain (mm/mm) -0.006 -0.004 -0.002 0.000 0.002 0.004 0.006 Stress (MPa) -400 -200 0 200 400 300°C - Experimental Numerical Strain (mm/mm) -0.006 -0.004 -0.002 0.000 0.002 0.004 0.006 Stress (MPa) -300 -200 -100 0 100 200 300 500°C - Experimental 500°C 300°C 600°C 700°C Strain (mm/mm) 0.000 0.002 0.004 0.006 0.008 0.010 Stress (MPa) 0 100 200 300 400 500 300°C - Experimental 500°C - Experimental 600°C - Experimental 700°C - Experimental Numerical Strain (mm/mm) 0.000 0.005 0.010 0.015 0.020 0.025 Stress (MPa) 0 50 100 150 200 250 300 5e-4 s -1 5e-6 s -1 5e-7 s -1 500°C - Numerical Strain (mm/mm) 0.000 0.002 0.004 0.006 0.008 0.010 Stress (MPa) 0 100 200 300 400 500 5e-6s -1 5e-5s -1 5e-4s -1 300°C - Numerical 300°C 500°C Strain (mm/mm) 0.000 0.005 0.010 0.015 0.020 Stress (MPa) 0 100 200 300 400 500 20°C - Experimental 20°C - Numerical Strain (mm/mm) 0.000 0.005 0.010 0.015 0.020 Stress (MPa) 0 100 200 300 400 500 20°C - Post 600°C - Experimental 20°C - Post 600°C - Numerical Strain (mm/mm) 0.000 0.005 0.010 0.015 0.020 Stress (MPa) 0 100 200 300 400 500 20°C - Post 700°C - Experimental 20°C - Post 700°C - Numerical Strain (mm/mm) -0.008 -0.006 -0.004 -0.002 0.000 0.002 0.004 0.006 0.008 Stress (MPa) -600 -400 -200 0 200 400 600 20°C - Post 600°C - Experimental 20°C - Post 600°C - Numerical Strain (mm/mm) -0.010 -0.008 -0.006 -0.004 -0.002 0.000 0.002 0.004 0.006 0.008 0.010 Stress (MPa) -600 -400 -200 0 200 400 600 20°C - Post 700°C - Experimental 20°C - Post 700°C - Numerical Strain (mm/mm) -0.004 -0.003 -0.002 -0.001 0.000 0.001 0.002 0.003 0.004 Stress (MPa) -600 -400 -200 0 200 400 600 20°C - Experimental 20°C - Numerical As Received Post 600°C Post 700°C Strain Rate Independent The ISV model is capable of modeling: Monotonic and cyclic loading for all temperature conditions: A) 20°C and 300°C - strain rate independent behavior B) 500°C, 600°C, and 700°C - strain rate dependent behavior 7. Simulation Results & Validation Fire Conditions Post-Fire Conditions Strain Rate Dependent