Simulation of hypervelocity penetration in limestone

A parameter study was performed to examine the (shock) damage obtained with long-rod and spherical mono-material penetrators impacting two varieties of limestone. In all cases, the impacts were assumed to be normal to the plane of the rock and at zero angle of attack (in the case of the rods). Impact velocities ranged to 15 km/s but most calculations were performed at 4 and 6 km/s and the penetrator mass was fixed at 1000 kg. For unlined underground structures, incipient damage was defined to occur when the peak stress, σ_pk, exceeds 1 kb (100 MPa) and the applied impulse per unit area, I_pk, exceeds 1 ktap (1 kb μs). Severe damage was assumed to occur when σ_pk exceeds 1 kb and I_pk exceeds 1000 ktaps. Using the latter definition it was found that severe damage in hard, non-porous limestone with spherical impactors extended to a depth of 9 m on-axis for an impact velocity of 4 km/s and 12 m at 6 km/s. Cylinders with length-to-diameter (L/D) ratio of 8.75 achieved depth to severe damage of 23 and 40 m, respectively, under the same conditions. For a limestone medium with 2% initial gas porosity, the latter numbers were reduced to 12 and 18 m.     

Equivalent continuum modeling for non‐linear wave propagation in jointed media

This paper describes a methodology to build equivalent continuum (ECC) models to represent jointed media for non‐linear wave propagation. In the present work, we study the response of randomly jointed rock media both to quasi‐static and dynamic loadings. We have found that, unlike in the quasi‐static case where no relaxation is observed, during dynamic loading, the deviatoric stress drops in the plastic wave after reaching its peak. Such stress relaxation phenomenon is calculated in jointed media, although the model used for intact rock blocks is rate‐independent. This is a strong indication that EC models for jointed rock should include some rate‐dependence when used in wave propagation simulations. Copyright © 2010 John Wiley & Sons, Ltd.     

An extended Eulerian method for contacts in Godunov formulations

This paper offers a new method to treat contacts in Eulerian Godunov formulations. The inadequacy of classic Eulerian formulations to describe contacts behavior is identified in the lack of degrees of freedom. This limitation is overcome by employing a set of state variables per material for the calculation of multi‐material elements and faces. The extra state variables allow for the independent analysis of the materials present in the problem; materials interactions are characterized by introducing contact constraints in the formulation. The locality of the method limits the memory burden. Copyright © 2012 John Wiley & Sons, Ltd.     

Evaluation of the skull base by SPECT. A comparison with planar scintigraphy and computed tomography

Computed tomography is currently the standard diagnostic tool for the evaluation of the skull base. The complex anatomy of this area is the primary reason why planar bone scintigraphy is often unsatisfactory; exact localization of abnormalities may be very difficult. These limitations may be overcome by SPECT. Seventeen patients with clinical features of basal skull involvement were assessed by CT, SPECT, and planar scintigraphy. Subsequent clinical diagnoses were malignancy in 15 patients, vasculitis in 1 patient, and osteomyelitis in 1 patient. Computed tomography with IV contrast was performed through the skull base at 5 mm intervals. Planar scintigraphy with Tc-99m MDP was followed by SPECT. Bony involvement compatible with the clinical findings was demonstrated by CT scans in 6 patients, by planar scintigraphy in 7 patients, and by SPECT in 9 patients. The abnormalities that were identified by CT were all identified by SPECT. This study suggests that, in imaging the skull base, SPECT is more sensitive and provides better anatomical localization than planar imaging and appears useful in patients with a negative CT study.