Uniaxial tensile tests are routinely conducted to obtain stress-strain data for forming applications. It is important to understand the deformation behavior of test specimens at plastic strains, temperatures, and strain rates typically encountered in metal forming processes. In this study, the Johnson-Cook (J-C) flow stress model was used to describe the constitutive behavior of ASTM International (ASTM) A 1008 steel specimens during uniaxial tensile tests at three different average strain rates (10(-5)s(-)(1), 10(-3) s(-1), and 10(-1) s(-1)). The digital image correlation (DIC) technique was used for displacement and strain measurement, and two-dimensional (2D) infrared (IR) imaging was employed for temperature measurement. Separate optimization studies involving relevant finite element (FE) modeling with appropriate measured data yielded optimum values of convective heat transfer coefficients, J-C parameters, and inelastic heat fraction variables. FE modeling employing these optimum parameter values was then used to study the mechanical behavior. While FE predictions matched measured strain localization and thermal field very well in the intermediate- and low-rate experiments, the high-rate test showed narrower strain localization and a sharper temperature peak in the experiment. Possible use of a higher steel thermal conductivity value and/or exclusion of material inhomogeneities may have resulted in discrepancies between computed and measured temperature and strain fields. The study shows that an optimized set of parameters obtained with a controlled test could be reasonably applied for other tests conducted at very different strain rates.

Structural design for fire is conceptually similar to structural design conducted under ambient temperature conditions. Such design requires an establishment of clear objectives and determination of the severity of the design fire. In the commonly used prescriptive design method for fire, fire resistance (expressed in hours) is the primary qualification metric. This is an artifact of the standard fire tests that are used to determine this quantity. When conducting a performance-based approach for structural design for fire, it is important to determine structural member temperatures accurately when the members are exposed to a real fire. In order to evaluate the fire resistance of structural members such as structural steels and concrete, both the temporal and spatial variation of temperatures must be accurately determined. The transient temperature profiles in structural members during exposure to a fire can be determined from a heat transfer analysis. There are several models/approaches for analyzing heat transfer that have been used to determine the transient structural temperatures during a fire event. These range from simple models to advanced models involving three-dimensional heat transfer analysis employing finite element or finite difference techniques. This document provides a brief summary of some of the common simple and advanced approaches that have been used for conducting heat transfer analysis of both steel and concrete members when exposed to fire.