Dynamic compressive behavior of metallic particulate-reinforced cementitious composites: SHPB experiments and numerical simulations

An experimental and numerical evaluation on the dynamic compressive response of mortars containing up to 20% waste iron powder as sand replacement is presented in this paper. The dynamic response is evaluated using split Hopkinson pressure bar (SHPB) apparatus under high strain rates (up to 250/s). The elongated iron particulates present in the iron powder-incorporated mortars warrant significantly improved compressive strength and energy absorption capacity at high strain rates. Multiscale numerical simulations are performed with a view to develop a tool that facilitates microstructure-guided design of these particulate-reinforced mortars for efficient dynamic performance. The dynamic compressive response of particulate-reinforced mortars is simulated adopting a numerical approach that incorporates strain rate-dependent damage in a continuum micromechanics framework. The simulated dynamic compressive strengths and energy absorption capacities for mortars with various iron powder content exhibit good correlation with the experimental observations thereby validating the efficacy of the simulation approach

Dynamic response of closed cell PVC foams subjected to underwater shock loading

A dynamic loading facility is developed to investigate the underwater shock response of poly vinyl chloride foams of varying densities. The shock loading facility consists of a water filled hollow cylindrical structure, with one end fully closed and the other end fitted with a nylon piston. A rigid striker is used to impact the piston, which creates an underwater shockwave. The facility is comprised of four separate sections, where the middle section is an optically clear acrylic window, and the other three sections are aluminum. The optically clear acrylic window is utilized for the employment of three-dimensional Digital Image Correlation in conjunction with high-speed photography (90,000–100,000 frames per second) to obtain full-field deformation data of the foams during shock loading. Pressure data is recorded using piezoelectric pressure sensors at different locations along the underwater shock tube. Peak pressures in the range of 1–10 MPa with exponential decays are generated by changing the striker velocity. Furthermore, quasi-static hydrostatic response of pre shocked foams is evaluated using a previously developed underwater loading facility. Strain rate of 103 s −1 is obtained in foam specimens during the experiments. Findings showed substantial delay between the underwater shock loading and material response. Polyvinyl chloride foams recovered 80–90% of their original shape after underwater shock loading and also retained much of their energy absorption capacity

Underwater mechanical behavior of closed cell PVC foams under hydrostatic loading through 3D DIC technique

The underwater constitutive behavior of poly vinyl chloride foams with varying densities was investigated in this study. The experiments were conducted in an optically clear acrylic tube, which allowed for visualization of the specimen and the application of 3D Digital Image Correlation. A series of calibration experiments was conducted to investigate the applicability of the Digital Image Correlation technique for measuring the deformation of objects underwater inside of a curved acrylic tube of considerable thickness. The results of the calibration experiments demonstrated that a submerged object located in the middle of the acrylic tube appears magnified in the radial direction. This apparent magnification was taken into account during the analysis of the deformation for all underwater experiments. The hydrostatic loading was achieved by fitting the acrylic tube with a nylon piston, and compressing the piston with an Intron testing machine. Hydrostatic load of up to 5 MPa was achieved during quasi-static compression of the piston. The load applied by the Instron machine was coupled with the Digital Image Correlation data to analyze the constitutive behavior of the PVC foams. The hydraulic crush pressure, bulk modulus, and energy stored up to densification strain were determined for each foam density

Underwater implosion pressure pulse interactions with submerged plates

An experimental and analytical investigation is conducted to study the underwater interaction of implosion pressure pulses with large plates. Two plates with stiffnesses significantly apart are investigated experimentally in a large-diameter pressure vessel for their Fluid-Structure Interaction (FSI) phenomena during proximal implosions of low stiffness metallic shells. High-speed photography, in conjunction with 3D Digital Image Correlation (DIC) measurements, is employed to obtain full-field displacements of the plates. Local dynamic pressure histories are also simultaneously recorded to investigate the incident, reflected and transmitted fluid pressures across the plates during dynamic loading. The lesser stiffness plate showed higher deflection, allowed a weaker reflected pressure pulse and allowed a stronger transmitted pressure pulse as compared to the higher stiffness plate. The peak deflections of the plates occurred during the underpressure phase of the implosion event. Four analytical modeling iterations with increasing complexities starting from Taylor\u27s FSI model are considered to assess the response of water backed plates to dynamic pressure pulse loadings. Each iteration is analyzed individually in an experimental context to understand its role as a building block in a final analytical model. The final model developed is based on the classical plate-bending equation and fluid velocity corrected for ‘afterflow’ effects and performed better than Taylor\u27s original model in predicting pressure-time history of the plates’ reflected pressure and transmitted pressure. The plates’ mid-point deflection profiles are also better predicted using this model. Furthermore, the model showed that the response of a plate during a dynamic implosion pressure pulse interaction is weakly dependent on its bending stiffness. Instead, it is observed that for a large plate, its areal mass density is the dominant factor in determining the reflected pressure, the transmitted pressure and the plate mid-point deflection profiles

Mitigation of shock loading on structures using aqueous methylcellulose solution

Shock mitigation performance of aqueous methylcellulose hydrogel and water for structural applications was investigated through two dynamic loading instruments: Instrumented bar and shock tube. While aqueous methylcellulose solutions have previously been found to attenuate impact-induced forces passing through them by a unique liquid-to-solid phase transition, this is the first time studied as shock mitigators to structural elements. The results obtained with aqueous methylcellulose as mitigator were compared with an equivalent experiment conducted with water as damping medium. The liquid was loaded into a specially designed hollow aluminum box, built to allow transmission of dynamic stress waves to a thin back plate. Determination of the liquid\u27s attenuation performance was based on the 3D Digital Image Correlation technique with high-speed photography to obtain the full-field real-time deformation data of the back-face plate throughout the dynamic loading event. It was found that upon high rate loading with the instrumented bar, the aqueous methylcellulose solution decreases the maximum out of plane displacement resulting from the dynamic loading by as much as 40% compared to water, and significantly damps the structural vibrations of the back-face plate. On the other hand, upon relatively low rate loading with shock tubes, water and aqueous methylcellulose solutions provide the same magnitude of out of plane displacement, however, the damping ratio (Logarithmic Decrement) of the structure through aqueous methylcellulose solutions is 45% greater than through water. The findings are analyzed and rationalized in terms of imparted mechanical power