Potted electronics are becoming more common in precision-guided artillery due to demands for increased structural-robustness. In field artillery applications, the potted electronics are inactive for most of their lifetime. Projectiles may be stored in a bunker without environmental (temperature and humidity) controls for up to 20 years. In contrast, the electronics for most commercial applications tend to be active for most of their lifetime and the operating environment is more predictable. This difference makes the thermal management task for the artillery application challenging. The ability to accurately analyze these designs requires the use of fully coupled thermal-stress transient-analysis with accurate material properties over the full temperature range. To highlight the thermal-stress transient effects, the potted configuration of a typical electronics assembly is analyzed. The thermal analysis indicates that significant stresses can develop in critical locations as a result of temperature cycles. The structural dynamic responses of unpotted and potted assemblies, subjected to gun-launch environments, are also compared. The results indicate that for the potted design, the dynamic response of the processor board is attenuated by the potting material.

The U.S. Army uses several types of tests to increase the reliability of gun-fired munitions. Systems, subsystems, and components are gun fired to assess reliability. When failures are found, root-cause investigations are completed and parts may be redesigned. For instance, the 155 mm projectile Excalibur uses several types of tests to find failures and build reliability. Components are tested in a rail gun, a new soft-catch gun, and in soft recovery vehicles. With the rail gun, test projectiles are fired from a worn gun tube into a trough of water. The soft-catch gun, a hybrid system using both air and water, has a standard cannon tube and a series of catch tubes to stop a projectile. The third type of test, a soft recovery vehicle, uses a modified tactical Excalibur with a parachute for a soft landing. All three types of tests have on-board recorders to capture ballistic accelerations. Accelerometer data are used in failure investigations, redesign parts, and to design new projectiles. The purpose of this paper is to compare accelerations from different types of ballistic tests. Comparisons were done to determine if the tests were in the same statistical family. Comparisons are made for a United States MACS 5 charge. The maximum axial forces were the same for the soft-catch gun and the soft recovery vehicle. In the balloting directions, the rail gun and soft recovery vehicle had similar forces. The set forward forces differed in all three cases, reflecting the different catch mechanisms for the projectiles. Comparisons of g-forces were also made using shock response spectra. The shock response indicated that the damage potential is greatest for the rail gun tests, consistent with an increase rate of failures for some electronics.

The resulting vibration after the removal of the load would be a free vibration if it were not for material damping, Coulomb damping (friction) at all of the interfaces and joints, aerodynamic drag, and any other damping caused by the cargo or warhead material (fig. 1). In figure 1, we see that during the set back event all of the material, and therefore the center of gravity (C.G.), moves rearward relative to the base when a force is applied to the base. Upon release of this load, the ends of the projectile oscillate about the C.G. Equilibrium position of the C.G. Equilibrium State C.G. moves rearward with compression Accelerating, Axial Force Pressure C.G. back to equilibrium position-structure exhibits damped oscillation about C.G.

Smart projectiles use electronic components such as circuit boards with integrated circuits to control guidance and fusing operations. During gun-launch, the electronics are subjected to 3-dimensional g-forces as high as 15,000 G, The U.S. Army uses finite element analysis to simulate electronics with high-g, dynamic loads. Electronics are difficult to model due to the large variation in size, from large circuit boards, to very small solder joints and solder pads. This means that to accurately model such small features would require very large models that are computationally expensive to analyze; often beyond the capability of resources available. Therefore, small features such as solder joints are often not included in the finite element models to make the models computationally tractable. The question is: what is the effect on model accuracy without these small features in the model? The purpose of this paper is to evaluate the effect that solder joints and solder pads have on the accuracy of the structural analysis of electronic components mounted on circuit boards during gun shot. Finite element models of simplified circuit boards, chips, and potting were created to do the evaluation. Modal analysis and dynamic structural analysis using typical gun loads were done. Both potting at high temperature (soft) and potting at low temperature (stiff) were used in the dynamic analysis. In the modal analysis there was no potting. All of these models were run with and without solder. In all cases, the results differed between the models with solder and those without. In the models with potting, there was a difference in magnitude and stress distribution between the models with and without solder. This indicates that there is a significant reduction in accuracy when solder is not included in the model.

Tensile and fracture tests were conducted on thin panels of a fiber-reinforced bioabsorbable material. The composites were made of polycarbonate matrix and calcium phosphate fibers. Both matrix and fibers were bioabsorbable orthopaedic biomaterials. The fibers were short and randomly distributed. The properties were compared for composites with and without a coating of methane on the fibers. Composites with the methane coating had a higher elastic modulus, a higher proportional limit, but a lower load at failure on pre-cracked panels. Electron microscopy showed that the coating resulted in a better bond between the matrix and the fiber.