Search

A test setup consisting of a shock-tube with an instrumented short rod is developed for investigating the blast response of cellular concrete foams. In the shock tube facility, blast pressure wave is generated by the rupture of a notched Aluminum membrane. An instrumented rod is calibrated for measuring transmitted stress from the cellular foam. Experiments are conducted on brittle cellular concrete foam, which exhibits non-linear stress-strain behavior associated with crushing of the cellular structure and subsequent densification. Crushing is initiated when the stress exceeds the crushing strength and continued crushing produces an upward concave stress-strain curve leading to densification of the material. Foams with two different crushing strengths are evaluated. The influence of length of the foam is investigated. For an applied blast pressure amplitude which is higher than the crushing strength of foam, the wave structure in the foam consists of an elastic precursor wave followed by a compaction front which produces crushing of the cellular structure of the material. From the experimental investigation, the existence of a critical length for completely attenuating the applied blast pressure wave is established. For a given blast pressure loading, when the length of foam is larger the critical length, the applied blast pressure wave is transmitted as a rectangular pulse of nominally constant magnitude, which is slightly higher than the crushing strength of the foam. The foam is compacted without significant densification. The critical length depends on the crushing strength of the foam and the blast pressure amplitude and duration. If the length of foam is smaller than the critical length, there is an enhancement in the transmitted stress amplitude. If the length of foam is significantly smaller than the critical length, the transmitted stress is enhanced to a magnitude higher than the applied blast pressure amplitude and the compaction of foam leads to signifi

A one-dimensional (1D) finite-volume implementation, based on the second-order Godunov method for predicting dynamic response of foams that exhibit irreversible compaction, is presented. Cellular foams, with an upward concave stress-strain relationship associated with densification of the material resulting from collapse of the cell structure, have the possibility of a strong discontinuity with shock-type characteristics. An approximate solution to the local Riemann problem is developed considering all possible wave structure(s) in the material based on the quasi-static response of the material. The prediction of dynamic compaction response of the foam subjected to solid impact is shown to compare favorably with experimental results. For an applied blast pressure loading, attenuation of transmitted stress wave in the foam is shown to be a result of the energy dissipation provided by compaction of the foam.

Results from an experimental investigation of the dynamic response of cellular concrete subjected to blast-pressure loading are presented. The cellular concrete has large entrained porosity in the form of uniformly distributed air cells in a matrix of hardened cement. Under quasi-static loading, once the applied stress exceeds the crushing strength of the cellular concrete, crushing and densification of material results in an upward concave stress-strain response. The shock-tube experimental test setup used for generating blast-pressure loading in a controlled manner is described. Experimental results from the cellular concrete subjected to blast-pressure loading with pressure amplitude greater than its crushing strength indicate that a compression stress wave, which produces compaction of the material due to collapse of the cellular structure, is produced in the material. As the compaction front propagates in the material, there is a continuous decrease in its amplitude. The impulse of the blast pressure wave is conserved. When a sufficient length of the cellular concrete is present, the applied blast pressure wave is completely attenuated to a rectangular stress pulse. The transmitted stress to a substrate from cellular concrete when an applied blast pressure wave is completely attenuated resembles a rectangular stress pulse of amplitude slightly higher than the crushing strength of the material with a duration predicted by the applied blast impulse.

Results from an experimental investigation into the dynamic response of cement foams subjected to blast pressure loading are reported in this paper. Cement foams with a cellular structure consisting of large entrained porosity in the form of uniformly distributed air cells were used in the study. The quasi-static response of such foams exhibits a distinctive concave shape associated with crushing of cell, which follows an initial linear elastic response. Experimental results from cement foam subjected to different blast pressure loadings using a shock tube are presented. Experimental results show a clear beneficial effect in reducing the amplitude of the transmitted stress. Results indicate that crushing of foam produces a continuous decrease in the amplitude of the stress wave produced in the foam. The blast pressure loading applied at one end of foam specimen is transmitted to the substrate as a stress pulse of reduced amplitude. When sufficient length of the foam is present, the transmitted stress history due to an applied blast pressure wave resembles a rectangular stress pulse of amplitude slightly higher than the crushing strength of the foam. The transmitted stress amplitude to the structure can effectively be controlled by varying the crushing strength of the foam

A numerical approach for one-dimensional dynamic compaction of foam produced by a blast pressure wave is presented. Approximate numerical procedures for solving the Riemann problem associated with shock are implemented within the Godunov finite volume scheme for the fluid domain. A numerical framework for enforcing the traction and velocity continuity across the fluid–solid interface is presented. Numerical evaluation is performed considering foams of different strengths. Results of the analysis indicate that the fluid-structure interaction effects are significant only in the early part of the blast pressure history. The energy consumed during the dynamic compaction of foam produced by a blast pressure wave is higher than the energy obtained as the area under the quasi-static stress-strain curve of the material. During the dynamic compaction of foam, there is a difference between the energy absorbed by the foam and the total energy consumed in the compaction of foam, which is available as kinetic energy of the compacted foam. The compaction of the porous material continues even after the blast over-pressure decreases below the crushing strength of the foam because of the kinetic energy available in the compacted foam. The energy transferred from the blast pressure wave to weaker foam is higher than the energy transferred to foam with higher crushing strength. There is a critical length of the foam when the energy absorbed by the foam is totally dissipated by the compaction of the material and the kinetic energy in the compacted foam becomes equal to zero. When the length of foam is greater than the critical length, the impulse of the transmitted pressure pulse is equal to the impulse of the reflected blast over-pressure. There is however a decrease in the pressure amplitude which depends upon the crushing strength of the foam.