1
Effects of High Strain Rates on ASTM A992 and A572
Grade 50 Steel
Matthew P. Murray; U.S. Army Engineer Research and Development Center; Vicksburg, Mississippi, USA
Stephen P. Rowell; U.S. Army Engineer Research and Development Center; Vicksburg, Mississippi, USA
Trace A. Thornton; U.S. Army Engineer Research and Development Center, Vicksburg, Mississippi, USA
Keywords: dynamic increase factor, dynamic strength properties, A572, A992, structural steel, yield strength.
ABSTRACT
Uniaxial tension tests were conducted on ASTM A572-50 and A992 steel at increasing strain rates to determine
material strength properties of structural members subjected to dynamic loadings. The increase in dynamic yield
strength and ultimate tensile strength, defined as the dynamic increase factor (DIF), versus strain rate was determined
to provide the necessary information to efficiently design blast resistant structures utilizing modern day structural
steel. Dynamic strength properties were determined by high-rate tensile tests using a hydraulic testing apparatus and
compared to static values obtained from ASTM E8 standard tension tests. The comparisons were used to calculate the
DIF of each steel at strain rates ranging from 0.002 to 2.0 inch/inch/second. Experiments revealed that A572-50 steel
exhibited an increase in yield strength up to 35% and ultimate tensile strength up to 20% as strain rate increased over
the range tested. A992 steel exhibited a similar increase in yield strength up to 45% and ultimate tensile strength up
to 20%. DIF versus strain rate curves obtained during this research will be used to develop criteria within the structural
steel design chapter of Unified Facilities Criteria (UFC) 3-340-02 (2014) for A572-50 and A992 steel.
INTRODUCTION
Understanding the change in material properties with change in loading rates has been addressed by many researchers
over the past century and is vital to accurate design and evaluation of structural members subjected to blast loads [1–
10]. The ratio of dynamic yield strength to static is defined as the dynamic increase factor for yield (DIF
y
) and is
known to be a function of strain rate [11–18]. Similarly, the ratio of dynamic to static ultimate tensile strength (UTS)
is defined as the dynamic increase factor for UTS (DIF
u
). Specification of the DIF of a material provides engineers
with the capability to efficiently design structural members to resist large loads produced during dynamic blast
phenomena [19–21]. DIF design curves for different materials are empirically derived from experimental material
property tests conducted at increasing strain rates.
Engineers and scientists throughout the protective design community have recognized cost and performance benefits
of incorporating newer, readily available, advanced construction materials into hardened structure designs for
protection of personnel, critical assets, and facilities. The reinforced concrete design chapter of UFC 3-340-02,
Structures to Resist the Effects of Accidental Explosions [19], uses DIF design curves developed by Malvar and
Crawford [22,23] for different grades of ASTM A615 reinforcing steel. The structural steel design chapter of the UFC
currently provides DIF design curves for ASTM A36 and A514 structural steel [19]. However, there is limited design
guidance available in the current UFC to permit efficient use of more modern steels, specifically A572-50 and A992,
due to the lack of research on these steels under high strain rates.
The U.S. Army Engineer Research and Development Center (ERDC) was tasked by the Department of Defense
Explosives Safety Board (DDESB) to conduct a series of static and dynamic, uniaxial tension tests on A572-50 and
A992 steel. The material strength data were used to develop DIF
y
and DIF
u
versus strain rate curves for these steels.
The experimental curves will later be used to develop design DIF curves for incorporation into future revisions of the
structural steel design chapter in the UFC.