Stephen A. Akers

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The new microplane model developed in the preceding companion paper is calibrated and verified by comparison with test data. A new approximate method is proposed for data delocalization, i.e., decontami-nation of laboratory test data afflicted by localization of strain-softening damage and size effect. This method, applicable more generally to any type of(More)
The first part of this two-part study presents a new improved microplane constitutive model for concrete, representing the fourth version in the line of microplane models developed at Northwestern University. The constitutive law is characterized as a relation between the normal, volumetric, deviatoric, and shear stresses and strains on planes of various(More)
The formulation of the microplane model for concrete and development of model M4 in the three preceding companion papers in this study is here extended to large strains. After giving examples of certain difficulties with the second Piola-Kirchhoff stress tensor in the modeling of strength and frictional limits on weak planes within the material, the(More)
The formulation of microplane model M4 in Parts I and II is extended to rate dependence. Two types of rate effect in the nonlinear triaxial behavior of concrete are distinguished: (1) Rate dependence of fracturing (microcrack growth) associated with the activation energy of bond ruptures, and (2) creep (or vis-coelasticity). Short-time linear creep(More)
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(More)
We have demonstrated in our in vitro system that an extracorporeal lithotripter utilizing a movable ultrasound probe can fragment gallstones more effectively when the ultrasound probe is not partially blocking shock waves. Using a pressure transducer we measured the pressures in the focal volume of a Wolf Piezolith 2300 lithotripter with the ultrasound(More)
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(More)
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