D. J. Grove

A void growth-based failure model to describe spallation

A new dynamic failure model to describe void nucleation, growth, and coalescence in ductile metals is reported. The model is based on a pressure‐dependent yield criterion for compressible plastic flow. This three‐dimensional, plasticity‐based continuum damage model is incorporated into a finite difference, wave propagation code. A procedure to determine the failure model parameters is proposed. In this procedure, the model parameters are calibrated based on the ability to match the experimental free‐surface velocity history with code simulations. Model parameters for oxygen‐free high‐conductivity copper have been determined successfully using this procedure.

Determination of Rajendran-grove ceramic constitutive model constants

This paper presents a methodology to determine the constitutive/damage model constants for silicon carbide for penetration modeling applications. The ceramic constitutive model describes the total strain as the sum of elastic, plastic, and microcracking components. There are effectively nine model constants to be determined. Six constants are adequate to describe the microcracking strain. The pulverized ceramic strength is described through one constant. The plastic strain description involves two which can be determined from a flow stress vs. strain rate plot. By matching the measured velocity vs. time or stress vs. time profiles from plate impact experiments with numerical simulations, the microcracking model constants can be determined. The fracture toughness value is available in material handbooks. In a two dimensional hydrocode analysis, the pulverized ceramic strength model parameter is adjusted to match the measured depth of penetration in a ballistic test.

Effects of pulverized material strength on penetration resistance of ceramic targets

Constitutive/damage model constants are traditionally determined from quasi-static, split Hopkinson bar, and plate impact experimental data. While some constants can be directly determined from these data, others must be calibrated through a trial and error procedure involving numerical simulations of various experimental configurations. In the Rajendran-Grove ceramic failure model, essentially one parameter is used to describe the strength of the pulverized ceramic material. Since the pulverized material strength significantly influences the penetration process in a confined ceramic target, this model parameter can be effectively determined through numerical simulations of ballistic penetration experiments. Using the 1995 version of EPIC, we simulated three penetration experiments in which the thicknesses of the confined ceramic plates were 25.4 mm, 38.1 mm, and 50.8 mm. The Rajendran-Grove model was used to describe the ceramic material’s response to the ballistic impact. The pulverized material strengt...

RESPONSE OF THIN SHEET DUE TO DEBRIS CLOUD IMPACT

The basic architecture for a space structures meteoriod shield consists of two spaced thin metal sheets. Protection of the space structure may be enhanced through the use of intermediate layers of material placed between the two thin sheets. In this work we used the STEALTH and EPIC-2 Lagrangian codes to simulate the effects of a debris cloud impact on a thin aluminum sheet, including the effects of intermediate layers. We employed Wilkinsons impulse-velocity based model in the simulations of the rear wall response. Computational results were verified through comparison with existing experimental results. The computed final thickness profile compared favorably with the experimental measurements.

MODELING OF DYNAMIC FRACTURE IN A SOLID CONE TARGET

Spall under a three dimensional strain state was modeled using the RDG ductile failure model1−3. Using this model, we simulated a plate impact configuration in which a flyer plate impacts the base of a solid right circular cone. The RDG model simulated spall pattern compared extremely well with the experimental results.

Dynamic Ductile Failure under Multi-Axial Loading

Dynamic ductile failure under a three dimensional strain state was modeled using a recently developed spall model. We considered a plate impact configuration in which a flyer plate impacts the base of a solid right circular cone. At high velocity impact, a complex spall pattern was generated in the cone. The pattern consisted of radial cracks at the base and tunnel (longitudinal) cracks inside. The failure model simulated spall pattern matched reasonably well with the experimental results.