BLU-129/B is a low-collateral-damage munition with a Lawrence Livermore developed fiber composite case and metal nose. The munition was fielded in 18 months, compared to a typical timeframe of 4 to 6 years, due largely to advanced design and simulation capabilities.
One of the greatest challenges with BLU-129/B was coupling its parts made of different materials. The fiber-composite case and metal nose coupling was tested using a 1,750-ton press (left). The coupling itself is sprayed with a speckled pattern paint to allow diagnostic cameras to detect specific failure points.
The metal lugs that anchor BLU-129/B to the aircraft presented another challenging coupling point with the fiber composite case. These coupling points were designed to disperse potential stresses, which are shown in the simulations on the right'.
The manufacturing process for two BLU-129/B fiber composite cases begins with the numerically controlled multi-axis filament winder. Carbon fiber strands are visible feeding from the bottom of the image through the yellow carriage, where they are saturated with epoxy. The carriage adjusts its relative position while winding to layer the filament along different paths to maximize strength.
Magnified cross-sections of the fiber-composite cases are examined to determine porosity caused by variances in epoxy saturation. If too large or numerous, the small black pores can be points of weakness in a final case.
The sponsor needed this low-collateral-damage munition fast. A Lawrence Livermore team completed a prototype within 9 months, and BLU-129/B was completely fielded in 18 months, a process that typically takes 4 to 6 years.
Fiber composites play a critical role in the Laboratory's advanced manufacturing capability. They have some of the highest specific strength (strength/density) and specific modulus among structural materials. In addition, the characteristic of orthotropic properties (i.e., differing in three mutually perpendicular directions) has allowed for many unique applications in defense, aerospace, aircraft, and more recently in energy and ground transportation.
At the Laboratory, we have focused on structural applications that can be produced by filament winding of continuous fibers (carbon, glass, etc.) with epoxy-based matrix material systems, while a new generation of composites includes hybrid fibers and modified matrix material such as epoxies with nanoparticles.
Lawrence Livermore's multiscale modeling capability is key to dramatically shortening the development times and minimizing the need for prototype hardware to design systems. Particularly important are understanding mechanical behavior and the processing and deformation mechanisms of these advanced materials.
Lightweight, high-strength "third-generation munitions" have proved to be relatively easy to manufacture and can incorporate specialized effects such as the elimination of shrapnel for certain applications.
The extensive use of simulations has enabled robust designs of joints between composites and metals, which is one of the major challenges in use of composites. Simulations have also been essential to designing and understanding coupling on metal-to-composites joints and the incorporation of essential features that cannot be easily engineered.
Another technology that uses composites is rotors for electromagnetic flywheels for energy storage. Livermore materials engineers have developed a multiple-fiber approach to manage the various types of extreme forces encountered. Some efficient advanced designs call for rotational speeds in the tens of thousands of RPMs. Fiber composites are the only known material than can withstand the stresses that these devices may encounter during service conditions.
Deputy Division Leader, Materials Engineering Division