Severe Shock Loads Research Articles

An innovative design of a compact shock isolation system to protect sensitive weapons from underwater shock & validated by shock testing for naval applications

This paper presents an innovative solution to protect the sensitive weapons stored inside strategic submerged platforms from severe shock loads (170 g) due to underwater explosions. The shock loads mainly resulted from the underwater explosion of a nuclear warhead, mines, and bomb nearby platform. The underwater shock load has been analyzed, and a shock response spectrum (SRS) method has been developed to calculate peak responses during shock. The frequency of shock isolation has been selected from SRS to meet the requirement of shock isolation and sensitive weapon. Stiffness and damping characteristics were finalized to reduce the shock load of 179 g to an acceptable limit of 5 g for a sensitive weapon. The single-degree freedom system analytical model was formulated, and the ANSYS tool was used for modeling and simulation. The stiffness has been distributed over the weapon's length at multiple locations such that the weapon will oscillate in the translational mode under shock load from the elastic model. This paper explains the novel approach and technique for the design of a simple, unique, compact, reliable, electromagnetically compatible shock isolation system for underwater sensitive weapons. A parametric study was undertaken to compute the dimensions and configuration of shock isolators. Experimental tests were performed on the prototype to validate the design of the shock isolator. The maximum displacement of the isolator and maximum force transmitted to the sensitive weapon was found by shock testing. Finally, Transient dynamic analysis was performed to evaluate the actual motion of isolators during shock.

Survivability of embedded microelectronics in precision guided projectiles: Modeling and characterization

Precision guided projectiles (PGPs) experience severe shock loads during launch emanating from the propellant gasses and the surrounding air. Our most recent multiphysics effort showed that the complex flow environment during launch would result in the development of severe shock loads in the confined barrel space and at muzzle exit. The focus of the current effort is the survivability of the embedded integrated circuit chips and printed circuit boards (PCB). Four aspects of the work were accordingly examined. The first is concerned with the development of a new polymeric encapsulation technique to protect the embedded microelectronic systems (EMES). The second with testing the effectiveness and endurance of the newly proposed encapsulation techniques using instrumented pneumatic drop weight impact test facility. The third with constructing bottom-up multi-level micromechanics based homogenization schemes, accounting for complex constitutive material models of a multilayer circuit board, to determine the effective elastic properties of the PCB for the numerical FE simulations. The fourth with conducting three-dimensional high-resolution dynamic FE simulations to evaluate the structural integrity of the potted PCB assembly in response to the short duration impulse and to elucidate the experimental findings. The results of our experimental and numerical efforts reveal that the newly devised encapsulation technique is highly effective in protecting EMES and can be used to audit the survivability of the microelectronics that are embedded in PGPs.

Dynamics of precision-guided projectile launch: fluid–structure interaction

Precision-guided projectiles (PGPs) experience severe shock loads during launch emanating from the propellant gases and the surrounding air. The complex flow environment that exists within the confined space of the barrel and at muzzle exit is significantly influenced by the speed of the projectile, the compressibility of the air, and the rapid state transition of the projectile from the confined volume of the barrel to the surrounding free space. In this effort, we extend our earlier vacuum work (Yin et al. in Int J Mech Mater Des 10:439–450. https://doi.org/10.1007/s10999-014-9255-0 , 2014) by performing comprehensive and a more realistic multiphysics simulations of the dynamics of the entire launch process of a projectile accounting for the intense combustion pressures of the propellant, the large accelerations experienced during the launch, and the induced shock waves. Our numerical model successfully captured the development and progression as well as the interaction of the projectile with the induced shock waves. Specifically, the model identifies the intense pressures generated by the propellant that result in supersonic flow conditions within the confined space of the barrel. This supersonic flow within the barrel leads to a wave front that travels ahead of the projectile creating a normal shock wave in the barrel. Once the normal shock crosses the muzzle exit, it diffracts into three types of shock waves: precursor, bow, and base. These shock loads pose a significant threat to the embedded electronic systems (EES) necessary for the operation, guidance and control of these PGPs. Our model further reveals that the projectile will experience a reduction in velocity as a result of induced frictional drag and interaction with the induced shock waves. This study will assist in the design and development of appropriate encapsulation techniques necessary for the protection of EES.

Dynamics of Precision Guided Projectile Launch: Solid–Solid Interaction

Precision guided projectiles (PGPs) experience severe shock loads during launch emanating from the propellant gases inside the barrel and the surrounding air. The complex flow environment that exists within the confined space of the barrel and at muzzle exit is greatly influenced by the supersonic speed of the projectile, the compressibility of the air, and the rapid state transition of the projectile from the confined volume of the barrel to the surrounding free-space. In our earlier efforts (X. W. Yin, P. Verberne and S. A. Meguid, Multiphysics modelling of the coupled behaviour of precision-guided projectiles subjected to intense shock loads, Int. J. Mech. Mater. Des. 10 (2014) 439–450; P. Verberne and S. A. Meguid, The coupled behaviour of precision-guided projectiles subject to propellant induced shock loads using multiphysics analysis, in 8th Int. Conf. Mech. Mater. Des. (2019); P. Verberne and S. A. Meguid, Dynamics of precision guided projectile launch: Fluid-structure interaction, Acta Mech. (2020)) examined the fluid–solid interaction problem. In this paper, we expand our earlier effort by examining the underlying mechanisms associated with the solid–solid interaction between the projectile and the barrel walls that severely govern the survivability of the embedded electronic systems (EES). This was achieved by conducting comprehensive finite element (FE) simulations of the dynamics of the entire launch process of a projectile accounting for the intense combustion pressures of the propellant, the large accelerations experienced during the launch and the induced shock waves. Our FE simulations successfully capture the interaction of the projectile with the barrel. Our work reveals that frictional forces due to contact inside the barrel significantly affect the projectile’s acceleration response at muzzle exit. Immediately following muzzle exit, the rapid reduction of the frictional forces inside the barrel results in a rapid increase of the projectile acceleration followed by a rapid reduction due to the free expansion of the propellant gases and air drag, leading to large acceleration fluctuations.

Effective Mitigation of Shock Loads in Embedded Electronic Packaging Using Bilayered Potting Materials

Shock loads which are characterized by high intensity, short duration, and vibration at varied frequencies can lead to the failure of embedded electronics typically used to operate/control numerous devices. Failure of electronics renders these devices ineffective, since they cannot carry out their intended function. It is therefore the objective of this work to determine the behavior of a typical electronic board assembly subject to severe shock loads and the means to protect the electronics. Specifically, three aspects of the work were considered using 3D finite element (FE) simulations in supercomputer environment. The first was concerned with the dynamic behavior of selected electronic devices subject to shock loads. The second with the ability of different potting materials to attenuate the considered shock loads. The third was with the use of a new bilayer potting configurations to effectively attenuate the shock load and vibration of the electronic board. The shock loads were delivered to the Joint Electron Device Engineering Council (JEDEC) standard board using simulated drop impact test. The effectiveness of different protective potting designs to attenuate the effect of shock loads was determined by considering the two key factors of electronics reliability: the stress in the interconnection and deformation of the printed circuit board. Our results reveal the remarkable effectiveness of the bilayer potting approach over the commonly adopted single potting attenuation strategy.

Multiphysics modelling of the coupled behaviour of precision-guided projectiles subjected to intense shock loads

Precision-guided projectiles (PGPs) typically deployed in smart munitions are operated and guided by highly sophisticated embedded electronic systems (EES). These PGPs are subjected to severe shock loads resulting from the ignition of the propellant during their launch. These shock loads, which are typically characterised by high intensity, short duration and wave reflections at varied frequencies, often lead to the failure of the EES. It is the objective of this work to conduct a comprehensive multiphysics analysis of the launch process of PGPs accounting for coupling and interaction effects between the different media (propellant, PGP, confined volume and free space). Specifically, we investigated the entire launch process that include the ignition of the propellant to observe local and global features of the setback, set forward pressure and acceleration histories using explicit axisymmetric Lagrangian–Eulerian finite element simulations. In this work, we also examine the severity and frequency of the reflected waves as well as the springback of the PGPs resulting from these local oscillations as they exit the muzzle. In addition, the flight state transition due to muzzle exit in terms of pressure and flow velocity is also discussed. Our results reveal the complex phenomena associated with the dynamic response of the PGPs and pressurization process resulting from the ignition of propellant during launch that are characterized by high oscillatory pressure profiles and projectile springback.

Mechanism of shock wave merging in a laser jet engine

A new approach based on the mechanism of the merging of shock waves generated by an optical pulsating discharge (OPD) is considered for developing laser jet engines (LJE). It is proposed to use high-power repetitively pulsed laser radiation of small duration (150–250 ns), energy 20–200 J, and a pulse repetition rate of up to 100 kHz for producing an OPD. The formation of an OPD with the help of an array of reflectors allows a manifold increase in the efficiency of laser radiation used for developing an LJE and prevents severe shock loading of the engine, excludes thermal action of laser plasma on the reflector, and decreases the shielding of laser radiation by plasma. Possible values of the LJE thrust are estimated under conditions of the proposed mechanism of merging of shock waves into a quasistationary high-pressure wave.

Dynamic behavior of the activated sludge process under shock loading: Application of the floc model

An integrated system model is developed for an activated sludge system which not only couples the floc behavior to changes in the bulk liquid characteristics but also takes into account the floc size distribution in terms of mass in the reacting system. Intensive simulation is then carried out based on the comprehensive model developed to assess the impact of shock loading on the plant dynamic behavior and to build an understanding of the importance of the floc effects. Simulation results show that more complex dynamic behavior due to the floc effects is likely to occur under severe shock loads which must be considered in the development of the control policy for a safer and better operating performance.

Elevated-temperature mechanical properties of sintered iron-base materials containing calcium fluoride additions

1. It has been established that the alloying of sintered Fe-CaF2 materials with molybdenum (15 wt.%) increases their hardness 2.5–8.6 times and raises their transverse rupture strength to 70–60 kg/mm2 and their compressive strength to 110–70 kg/mm2 at temperatures of up to 650°C.0 2. Raising the CaF2 content of sintered iron decreases its impact strength at temperatures of up to 650°C. It was found that for Fe6CaF2, Fe9CaF2, and Fe (porous) materials the variation of impact strength as a function of testing temperature is similar in character to that observed with cast Armco iron. The blue-brittleness range for sintered Fe-CaF2 materials extends from 350 to 450°C. 3. It is shown that the impact strength of sintered Fe15Mo6CaF2 material, unlike that of unalloyed materials, increases up to a temperature of 500°C as a result of migration of the molybdenum from the grain boundaries into the grains. In tests Fe15Mo6CaF2 material cracks by a brittle intergranular rupture mechanism. 4. Fe15Mo6CaF2 material surpasses in heat resistance all the other sintered CaF2-containing ironbase materials investigated, and can therefore be recommended for operation at temperatures of up to 650°C in friction units which do not experience severe shock loads.