Measuring Residual Concrete Strength After Penetration and Blast
Agency / Branch:
DOD / DTRA
OBJECTIVE: Find a reliable inexpensive way to measure resistance to penetration (for subsequent weapons) in damaged concrete. DESCRIPTION: When munitions are used in multiple strikes against reinforced concrete slabs (for example, burster slabs over cut and cover targets with concrete layers), if the first weapon does not penetrate all the way to the target room, it is important to know the remaining strength of the damaged slabs. For subsequent strikes, the remaining strength determines the time for penetration to the target room, from which the fuze setting must be determined. In the test environment, current methods of measuring residual strength include coring the slab and measuring compressive strength, and shooting instrumented penetrators through the slab, observing acceleration, and backing in the strength by running trial and error simulations. The first method can not be used when the slab is heavily damaged, as frequently occurs. The second method costs $10,000 per data point and is time consuming. PHASE I: Identify concept. Design a device (and methodology) perhaps used for direct, but preferably remote, measurement. The device shall have the ability to measure, or predict based on measured damage, a damaged slab's remaining ability to subtract kinetic energy from subsequent penetration at location (x,y). The device shall use the remaining strength measurement at (x,y) to predict the time elapsed from impact until a penetrator tail exits the damaged concrete slab and the exit velocity. In subsequent penetrations, the device (perhaps a second device) shall measure the actual exit velocity and elapsed time. Impact velocities are on the order of 1 foot per millisecond. The 90% confidence interval width for measuring or predicting penetrator tail exit velocity from a damaged concrete slab shall be near 1/2 foot per millisecond. It is acceptable to predict (or measure) the velocity and time of arrival at depth d (in soil) below the slab. It is acceptable to specify (x,y) coordinates of subsequent penetrations prior to the test. PHASE II: Prototype development. Build the device, and confirm it meets the accuracy specified above. Use designed experimentation, collect data by blowing up slabs of varying strength and thickness and measuring residual strength using the device from Phase I. Predict penetrator tail exit time and velocity. Perform confirmation penetration shots. PHASE III DUAL USE APPLICATIONS: (1) The device might be used to measure the remaining strength of concrete walls damaged by terrorist bombs. (2) Given the confirmation data, slab attributes can be determined so as to minimize damage. This might allow specification of construction parameters to resist damage. (3) This may have use in evaluating hypervelocity penetration. REFERENCES: 1. Adley, M.D., Berger, R.P., and Creighton, D. C. (1994). ""Two-Dimensional Projectile Penetration Into Curvilinear Geologic/Structural Targets: User's Guide for PENCURV-PC,"" V1.5, Instruction Report SL-94-1, US Army Engineer Waterways Experiment Station, Vicksburg, MS. 2. Curry, T.F., and E.J. Jerome, Discriminant Analysis Models for Unified Damage Prediction Across Failure Modes, Journal of the International Test and Evaluation Association, Vol. 23. No. 4 (December 2002, January 2003).
Small Business Information at Submission:
INTELLIGENT FIBER OPTIC SYSTEMS CORPORAT
2363 Calle Del Mundo Santa Clara, CA 95054
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