202
A. Rabiei et al.
Keywords Composite metal foams · Hazardous materials · Tank car · Iron and
steel · Characterization
Introduction
According to the US Department of Transportation (DOT), each year millions of
liters of hazardous materials (hazmat) is transported through railroads [1]. Despite
of all safety measures and regulations, rail car accidents are reported every now
and then resulting in hazmat spills that even some times cause fire, explosion, and
massive fatalities [1]. The most important recent rail car accident is the 2013 LacMégantic, Quebec accident where the train carrying 7.7 M liters of petroleum crude
oil burst into flames after crashing and ending up with multiple fires and explosions
that destroyed most of the downtown area leaving 47 casualties [2].
The Lac-Mégantic accident led to the development of the DOT-117 tank car [3].
The DOT 117R set standards for the thermal protection system of tank cars [4] in
which the tank car must have sufficient thermal resistance so that there will be no
release of any lading within the tank car, except release through the pressure release
device, when subjected to a pool fire for 100 min, and a torch fire for 30 min. [5] Even
the DOT-117 specifications were deemed not strict enough resulting in the need for
additional thermal blanket protection for tank cars, which eventually phase out tank
cars carrying flammable liquids starting with crude oil tank cars first, followed by tank
cars carrying ethanol, then followed by tank cars carrying other flammable liquids
and required top fittings protection on tank car retrofits [1]. These enhancements
raise an immediate need for novel material with superior puncture resistance, impact
energy absorption capability and fire insulation properties to improve the safety of
tank cars carrying Hazmat.
Composite metal foam (CMF) is a unique novel material based on a combination
of properties of metal matrix composites and metal foams. CMF is known for its high
strength to density ratio, high specific stiffness, extraordinary energy absorption, and
superior thermal characteristics [6–10]. CMF is comprised of hollow metal spheres
surrounded by a metallic matrix. The two components can be made of any metal
or alloy combination and manufactured through either powder metallurgy sintering
or casting [6]. Steel-steel composite metal foam (S-S CMF) is comprised of steel
hollow spheres embedded in steel matrix. CMF is 60–70% lighter than its parent
bulk material with a relative density of approximately 30–40% [6]. CMF can be
made out of 100% stainless steel and be as light as aluminum while offering close
to two orders of magnitude higher energy absorption in compression compared to
its parent material. Due to the regularity of its pore structure, uniform deformation
under compression, and the presence of a matrix between the pores, CMF is able to
maintain a very high plateau stress over large amounts of strain when loaded under
compression, which offers higher energy absorption capability compared to other
metal foams [7]. Further studies of composite metal foams showed an increase in
performance under higher loading rates [7, 11], which makes CMF more suitable for
A. Rabiei et al.
Keywords Composite metal foams · Hazardous materials · Tank car · Iron and
steel · Characterization
Introduction
According to the US Department of Transportation (DOT), each year millions of
liters of hazardous materials (hazmat) is transported through railroads [1]. Despite
of all safety measures and regulations, rail car accidents are reported every now
and then resulting in hazmat spills that even some times cause fire, explosion, and
massive fatalities [1]. The most important recent rail car accident is the 2013 LacMégantic, Quebec accident where the train carrying 7.7 M liters of petroleum crude
oil burst into flames after crashing and ending up with multiple fires and explosions
that destroyed most of the downtown area leaving 47 casualties [2].
The Lac-Mégantic accident led to the development of the DOT-117 tank car [3].
The DOT 117R set standards for the thermal protection system of tank cars [4] in
which the tank car must have sufficient thermal resistance so that there will be no
release of any lading within the tank car, except release through the pressure release
device, when subjected to a pool fire for 100 min, and a torch fire for 30 min. [5] Even
the DOT-117 specifications were deemed not strict enough resulting in the need for
additional thermal blanket protection for tank cars, which eventually phase out tank
cars carrying flammable liquids starting with crude oil tank cars first, followed by tank
cars carrying ethanol, then followed by tank cars carrying other flammable liquids
and required top fittings protection on tank car retrofits [1]. These enhancements
raise an immediate need for novel material with superior puncture resistance, impact
energy absorption capability and fire insulation properties to improve the safety of
tank cars carrying Hazmat.
Composite metal foam (CMF) is a unique novel material based on a combination
of properties of metal matrix composites and metal foams. CMF is known for its high
strength to density ratio, high specific stiffness, extraordinary energy absorption, and
superior thermal characteristics [6–10]. CMF is comprised of hollow metal spheres
surrounded by a metallic matrix. The two components can be made of any metal
or alloy combination and manufactured through either powder metallurgy sintering
or casting [6]. Steel-steel composite metal foam (S-S CMF) is comprised of steel
hollow spheres embedded in steel matrix. CMF is 60–70% lighter than its parent
bulk material with a relative density of approximately 30–40% [6]. CMF can be
made out of 100% stainless steel and be as light as aluminum while offering close
to two orders of magnitude higher energy absorption in compression compared to
its parent material. Due to the regularity of its pore structure, uniform deformation
under compression, and the presence of a matrix between the pores, CMF is able to
maintain a very high plateau stress over large amounts of strain when loaded under
compression, which offers higher energy absorption capability compared to other
metal foams [7]. Further studies of composite metal foams showed an increase in
performance under higher loading rates [7, 11], which makes CMF more suitable for