High Rate Tensile Strength Measurements of Frangible Bullets Using a Kolsky Bar | NIST
The tensile strength of frangible bullets is measured by a high rate diametral compression test (DCT) performed with a Kolsky Bar. Frangible bullets, meant to disintegrate on impact by brittle failure, also exhibit significant plasticity in compression. As a result, the elastic stress analysis usually used for the DCT cannot accurately deduce a tensile strength from the test results. To account for plasticity effects, finite element analysis is used to calculate the stress throughout the disk as it deforms under diametral loading prior to failure. Two cases are examined. The first involves a standard disk-shaped sample, and the second involves a disk with its contact points pre-flattened to reduce the amount of plastic strain prior to failure. With the standard sample, plastic flow produces tensile stresses at failure that are 80 % larger than those predicted by the usual elastic analysis of the DCT. Stresses at failure with the pre-flattened sample are 33 % lower than the elastic prediction, owing to load distribution and three dimensional effects. Results with the pre-flattened sample are considered more reliable since the finite element calculation does not account for crushing damage that is observed at the contacts points with the standard sample but is avoided with the pre-flattened sample.
Stresses and failure in the diametral compression test
The validity of the diametral disc test with a small flat ground has been established. The stress distribution was determined by a finite element method for a range of loading conditions. The results show that for the case of a point load, the failure is due to shear and compressive stresses at the loading point. Application of the diametral disc test for a ground flat was proposed and tested. The width of the flattened area must be less than 0.2 times the diameter of the disc to obtain accurate tensile strength.
Comparison between Two Chemicals for Reducing Scale Formation in Reverse Osmosis Systems
In this present research was transacted with the calcium carbonate scale inhibition on the membrane surface of the reverse osmosis desalination system. Influence of changing feed solution flow rate (10-25)l/h, pH of the feed solution (6-10) on the recovery ,penetrate flow rate and total dissolved solid in (RO) system by using solution of calcium carbonate as feed solution was investigated, furthermore the effect of adding two types of scale inhibitor ,zinc chloride and polyamino polyether methylene phosphonate with difference concentration (2-8)mg/l for zinc chloride and (8-15) mg/l for polyamino polyether methylene phosphonate was calculated. The results showed that the permeate rate increases as the feed flow rate augmentation ,while it reducing with time, the total dissolved solids decreases as the feed flow rate increases while it increases with time and recovery rate decreases as the feed flow rate increases and it also decreases with time. It was concluded that the permeate rate decreases as the feed solution pH value increases and it cause high scale forming thus decrease the permeate TDS.By adding the scale inhibitor, it was found that the permeate rate and recovery rates increases as the concentration of inhibitor increases while the total dissolved solids decreases in the permeate with increasing the concentration of both inhibitors .It was discovered that Polyamino polyether methylene phosphonate more sturdy than zinc chloride as scale inhibitor for reverse osmosis desalination system in all concentrations was studied in this article.