Stephen A. Akers

The Influence of Soil Parameters on the Impulse and Airblast Overpressure Loading above Surface-Laid and Shallow-Buried Explosives

The dynamic airblast, fragmentation, and soil ejecta loading environments produced by the detonation of surface-laid and shallow-buried mines are major threats to lightweight military vehicles. During the past several years, the US Army has focused considerable attention on developing improved methods for predicting the below-vehicle environment from these threats for use by vehicle/armor analysts; thereby, improving the survivability of these platforms. The US Army Engineer Research and Development Center recently completed the first year of a three-year effort to experimentally and numerically quantify the blast and fragment loading environments on vehicles due to surface and subsurface mine and IED detonations. As part of this research effort, a series of experiments was conducted to quantify the effects of soil parameters on the aboveground blast environments produced by the detonation of aboveground bottom-surface-tangent, buried top-surface-tangent, and shallow-buried 2.3-kg (5-lb) Composition C4 charges. The experiments were conducted using three different well characterized soils; 10.8% air-filled-voids (AFV) silty sand, 5.4% AFV clay, and 29.8% AFV poorly graded sand. The combined aboveground loads due to airblast and soil debris were measured by an impulse measurement device. The near-surface airblast overpressure was quantified by a series of side-on measurements above the charges at one elevation and three radial distances. This paper summarizes and compares the results of the experimental program with emphasis on defining the effect of soil parameters on the aboveground blast environment.

Numerical Simulations of Explosive Wall Breaching

Explosive wall breaching will be a key war fighter capability in future military operations by dismounted soldiers in urban terrain environments where the close proximity of urban structures, possibly occupied by noncombatants, significantly restricts the use of large demolition charges or large caliber direct-fire weapons. The US Army Engineering Research and Development Center (ERDC) is currently investigating new explosive wall breaching systems and numerical techniques to model the breaching system interaction with the wall targets. The experimental and numerical programs will conduct comprehensive demolition breaching research on a full range of construction and material types and will fully validate new multi-functional breaching procedures across the spectrum of desired missions. As a first step in this process, the ERDC conducted a baseline study of C-4 breaching effectiveness against steel-reinforced concrete walls in FY04. The goal of this effort was to develop improved methods for breaching these walls with simple arrangements of C-4. The experimental breaching scenarios addressed: (1) a baseline study of C-4 breaching, (2) optimal use of C-4 for concrete removal, and (3) optimal use of C-4 for concrete and reinforcing steel removal. Numerical simulations of two selected experiments were conducted using the coupled Eulerian and Lagrangian code Zapotec. In these simulations, the concrete and reinforcing steel were modeled as Lagrangian materials, and the C-4 and air were modeled as Eulerian materials. Two different concrete constitutive models were used in the simulations: the Karagozian and Case concrete model, which is included with Zapotec, and the Microplane model, which was implemented in Zapotec by ERDC personnel. Comparisons between the experimental results and the numerical simulations will be described.

Numerical Simulations of Explosive Blast Pressures During Wall Breaching

During the past several years, the US Army has focused considerable attention toward developing improved methods for breaching walls and determining weapon-target interaction effects from direct- and indirect-fire weapons in the urban combat environment. A major thrust area is centered on developing methods for predicting the blast and fragmentation environment behind a breached wall. This information is important to the warfighter in terms of recognizing the expected impact on both enemy combatants, and non-combatants or friendly forces. One impediment to this effort is that little data exist to document the behind-wall blast environment produced by the detonation of explosives against or within walls. As part of the Armys effort, the US Army Engineer Research and Development Center (ERDC) is conducting experimental and numerical investigations to improve wall breaching methods. In the experimental and numerical programs, the ERDC conducts comprehensive research on a full range of urban construction materials. As a first step in this process, the ERDC conducted a baseline study of C-4 breaching effectiveness against steel-reinforced-concrete (RC) walls. A goal of this effort was to better define the behind wall blast environment produced by various C-4 charges placed in contact with RC walls. Numerical simulations of selected experiments were conducted using the coupled Eulerian-Lagrangian code Zapotec. In these simulations, the concrete and reinforcing steel were modeled as Lagrangian materials, and the C-4 and air were modeled as Eulerian materials

Breaching of Triple-Brick Walls: Numerical Simulations

Explosive wall breaching will be a key war-fighter capability in future military operations by dismounted soldiers in urban terrain environments where the close proximity of urban structures, possibly occupied by noncombatants, significantly restricts the use of large demolition charges or large caliber direct-fire weapons. Because of this requirement, the US Army has focused considerable attention and resources to optimize breaching activities in urban terrain. As part of the Armys effort, the US Army engineer research and development center (ERDC) is conducting experimental and numerical investigations to improve wall breaching methods. The ongoing experimental and numerical programs will conduct comprehensive breaching research on a full range of urban construction materials. As a first step in this process, the ERDC conducted a successful baseline study of Composition C4 (C-4) breaching effectiveness against steel-reinforced-concrete walls. Recently, the research effort was extended to triple-brick walls. Numerical simulations of two selected experiments were conducted using the coupled Eulerian- Lagrangian code Zapotec. In these simulations, the brick and mortar were modeled as Lagrangian materials, and the C-4 was modeled as an Eulerian material.

Explosive Removal of Concrete From Reinforced Walls

During the past several years, the US Army has focused considerable attention toward developing improved methods for breaching walls in the urban combat environment. A major thrust area is centered on finding improved methods to breach the toughest wall type that Army units are likely to face: a double (steel) reinforced concrete (RC) wall. One impediment to this effort is that the relationship between the contact explosive charge configuration and the quantity of concrete removed has not been thoroughly understood. The U.S. Army Engineer Research and Development Center has conducted a research effort to better define the effectiveness of various explosive charge configurations in breaching RC walls. This paper presents a discussion of results from this research.© 2007 ASME

Parallel computation methods for large-scale nonlinear CSM

Publisher Summary In this chapter, a parallel explicit dynamic finite element code, “ParaAble”, is used for the three-dimensional analysis of penetration and blast loading events. The analysis of structures undergoing complex inelastic responses to load—such as those resulting from explosive detonations or high-speed impact—are challenging mechanics problems, which can typically require significant computational resources. The analyses presented in the chapter involve large models (up to several million elements) and different types of material models with varying levels of complexity and computational expense. The parallel computational strategy includes an overlapping computation/message passing algorithm and a material-weighting mesh partitioning scheme. These procedures are implemented into a parallel finite element code, “ParaAble”, and then it is used for several large-scale applications.

Constitutive Property Behavior of Type N and Type S Mortars

An extensive program of quasi-static mechanical property tests was conducted to characterize the mechanical behavior of type N and type S mortars under various stress and strain boundary conditions to decide which mortar to use in the construction of triple-brick and brick-over-block walls. The material characterization effort consisted of hydrostatic compression, unconfined compression, triaxial compression, direct pull, reduced triaxial extension, and uniaxial strain tests. The results from all of the quasi-static tests provided the mechanical properties required for determining which mortar to use in the construction of target walls for projectile perforation experiments as well as the constitutive model coefficients for numerical simulations of these experiments. This paper provides a summary of the mechanical property test results obtained for type N and type S mortars and the rational for using type S mortar in the construction of triple-brick and brick-over-block walls.

Vulnerability of Structures to Weapons Effects

The Geotechnical and Structures Laboratory (GSL) has a number of funded research efforts to support Department of Defense (DoD) requirements for understanding the response of structures to explosives/weapons. These efforts are all heavily dependent on high performance computing (HPC) simulations to meet research needs. The research efforts to be supported include Force Protection, Military Operations in Urban Terrain, and Homeland Defense. HPC simulations are used to enhance ongoing experimental programs. The simulations are used to assist in designing experiments, to aid in understanding the experiments, to extend the knowledge beyond the limitations of the experiments, and to develop numerical databases. High priority HPC hours available through the High Performance Computing Modernization Program (HPCMP) Challenge Project were used to perform these simulations. Simulation results are compared with experimental results when available.