MILITARY-STEEL AND NEW DESIGN OF DEEP PENETRATING BOMB

Introduction

The BLU-122 deep penetrating bomb (BLU-122 penetrator) was developed by the Air Force in 2003 made improvements upon the BLU-113 penetrator which would enable it to have significant penetration through hard targets.  The weapon incorporates more energetic explosive fill, higher strength case material, and modified nose shape for increased penetration. Despite the improved case, the BLU-122 possesses only 18-20 ft (5.4-6.0 m) penetrability in 5.0 ksi (34.5 MPa) strength reinforced concrete. A composite case made from the joined different super-high strength materials has several improvements compared to the monolithic case. Penetrator with the composite case is able to penetrate the Ultra-High Performance Concrete. 

Description

The well-known Eglin steel [1] is utilized for manufacturing cases for the BLU-122 penetrator [2]. Low alloy steel improves impact toughness of Eglin steel, but its 245 ksi strength cannot be enough to penetrate highly defended targets [3]. New developed high strength steel (“Military-Steel”) exhibits superior strength to Eglin steel at the same level of ductility and toughness [4]. Concentrations of expensive elements and the cost of raw materials of Military-Steel are significantly lower than Eglin steel, while the cost of melting, hot forging, and heat treatment are comparable. Table shows the typical room temperature quasi-static tensile test results of the air melted quenched and low tempered Grades #1-4 of the Military-Steel, Eglin steel, and USAF-96 steel [5], wherein HRC, YS, UTS, El, RA, and CVN are Rockwell hardness scale C, a yield strength at 0.2% offset, an ultimate tensile strength, an elongation at break, a reduction of area, and Charpy v-notch impact toughness energy respectively. . Graph under Table shows tensile diagram of of the Grade#2 of the Military-Steel having a yield strength (YS) of 225 ksi (1600 MPa), an ultimate tensile strength of 285 ksi (1967 MPa), a total elongation of 13%, a reduction of area of 48%, and Charpy v-notch impact toughness energy (CVN) of 32 ft-lbs (43 J) at r.t. and of 24 ft-lbs (33 J) at -40°F (-40°C).

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Eglin steel exhibits a ~10% increase in yield and tensile strength when strain-rates are increased from quasi-static to 200 s-1 [3], Military-Steel shows approximately the same sensitivity to increasing strain-rates. The tensile and yield strengths of the steels at high strain-rates will be referred as the dynamic tensile and yield strength.

           Grade #2 and Grade#4 superiors to the Eglin steel due to:

•           Higher hardness and strength at the same ductility and toughness

•           Reduction in total raw material cost of 50% or more by lower concentration of Mo and eliminating of W

•           Better formability at hot working

•           Better machinability.

Grade #1 superiors to the USAF-96 steel due to:

·                     Higher hardness and strength at the same ductility and toughness

·                     Better formability at hot working

New designs of the monolithic cases of for deep penetrating bombs BLU-122, BLU-109 and its improvement BLU-137/B have been developed to increase their penetration distances. The new designs are based on the concept that the material and nose of a penetrator play crucial roles in the strength and durability of their cases. If the material of the penetrator does not have enough strength, large deformation of the nose and wall occurs, and as a result, the nose is flattened, and the wall is warped. On the other hand, if the high strength material of the penetrator does not have enough impact toughness, a fracture of the nose and wall occurs. Both scenarios lead to a reduction of penetration distance and do not meet the strict requirements for the penetrators. Therefore, the main parameters that affect penetration distance are: strength and toughness of the case material; shape and length of nose; thickness of the wall; length and diameter of the case. The new monolithic cases have the same weight as the standard cases and the same capacities of explosive materials. Projected penetration distance in 5.0 ksi (34.5 MPa) strength reinforced concrete of the BLU-122 penetrator with the new monolithic case made from Military-Steel is 50% higher than the penetration distance of the standard case made from Eglin steel [6]. Recently developed Ultra-High Performance Concrete (UHPC) can withstand bombs and bunker penetrators, making it a unique new material that can be utilized for bunkers [7]. UHPC made by combining pure powdered quartz with a mixture of metals and nanofibers, has compression strength of 30 ksi (207 MPa) compared to traditional concrete at just 4.0 ksi (27.6 MPa). To reach and destroy well protected bunkers, new weapon systems such as the 30,000 lbs (13,600 kg) Massive Ordnance Penetrator (MOP) and the High Velocity Penetrating Weapons (HVPW) have been designed. However, neither BLU-122 bomb nor MOP or HVPW bombs can penetrate the bunkers made from UHPC with compression strength of >20 ksi (138 MPa) and thickness of >20 ft (6 m). Penetrators with monolithic cases made from materials such as 250-260 ksi (1725-1800 MPa) strength Eglin steel or 280-300 ksi (1930-1970 MPa) strength Military-Steel cannot penetrate bunkers made from UHPC. To penetrate bunkers made from UHPC, the new composite case has been designed. The composite case has the following improvements compared to the monolithic case:

·         Utilizing materials with strength of >400 ksi (2,750 MPa) to increase strength

·         Nose made from joined different super-strength materials and it has complex shape to increase penetrability

·         Walls made from super-strength and high impact toughness materials and it joins with the nose

·         Walls have reinforced components to increase general, bending, and compression stiffness and reduce dynamic vibration

·         Uniform distribution of weight through its length of case to supply its dynamic stability

·         High wear resistance of the composite case.

The composite case has the same weight and the same capacity of explosive materials as the new monolithic case and the standard case while the projected cost of production of the composite case 10-20% higher. The composite case is applicable for the BLU-122, BLU-109, and BLU-137/B penetrators, MOP, and HVPW to pierce bunkers made from UHPC.  

For more information, contact: info@amdoncorp.com            

Summary

New design of the monolithic cases of the BLU-122 penetrator has been developed to increase its penetration distance. Projected penetration distance in 5.0 ksi (34.5 MPa) strength reinforced concrete of the BLU-122 penetrator with the new monolithic case made from Military-Steel is 50% higher than the penetration distance of the standard case made from Eglin steel. New design of a composite case provides piercing of penetrators in UHPC. Penetrator with the composite case is able to penetrate bunkers made from UHPC with compression strength of >20 ksi (138 MPa) and thickness of >20 ft (6 m). The composite case can be utilized for the different types of penetrators, including BLU-122, BLU-109, BLU-137/B, MOP, and the high velocity HVPW. 

References

[1]               Dilmore, Morris; Rahlman, James D.: “EGLIN STEEL-A LOWALLOY HIGH STRENGTH COMPOSITION”, U.S. patent No 7,537,727

[2]               BLU-122/B Penetrator Brochure: General Dynamics Ordnance and Tactical Systems, approved for public release 08/22/07; http://www.gd-ots.com/download/BLU-122-B.pdf

[3]               Abrahams, Rachel Ann: “Low alloy high performance steel”, U.S. patent application No 15/160,221

[4]               Vartanov, Gregory: “High Strength Military Steel”, U.S. patent No 8,414,713

[5] U.S. Air Force Research Laboratory at Eglin AFB: “Low Alloy, High Impact Toughness Steel”, TechLink, 2019 https://techlinkcenter.org/technologies/low-alloy-high-impact-toughness-steel/

[6]               Vartanov, Gregory: “A new design for a better bunker buster”, DSIAC Journal, Volume 5, Number 1, Winter 2018, p.p. 13-14; www.dsiac.org

[7]               HDIAC Staff: “Developments in Ultra-High Performance Concrete and Bunker-Busting Bombs”, HDIAC Journal, October 12, 2015; https://www.hdiac.org/wp-content/uploads/Spotlight_Developments_in_Ultra-High_Performance_Concrete_and_Bunker-Busting_Bombs.pdf   

Publications:

U.S. Patent No 8,414,713 B2 “High Strength Military Steel”

“A new design for a better bunker buster”: DSIAC Journal, Volume 5, Number 1, 2018, p. 12-14

“New Design of Deep Penetrating Bomb”: Military Technology Magazine, Vol. XLIII, Issue 7-8, 2019, p. 34