Study of Blast Wave Pressure Modification through Rubber Foam

Testing the blast response of foam inserts for helmets

“…This corresponds with explanations posed in literature [33], which suggest that the implementation of foam padding amplifies the peak overpressure transmitted to the head, as the larger contact area between head and helmet more effectively couples the energy to the brain than would occur in a helmet without padding. As the samples used in this study exhibited amplification effects of the reflected shockwave, they do not possess sufficient energy absorption capacity prior to the point of densification.…”

“…It is expected that there will be an increase in normalised impulse with increase in density of a foam sample, as explained in the literature [33]. For a positive blast mitigation effect in the context of this study, a value of normalised reflective impulse as a percentage of incident impulse (calculated using Equation 3) measurably below 100 would be required.…”

“…This equates to requiring a thicker layer of foam for a more flexible material of the type used in helmets. Sandhu et al [33] showed that for increasing thicknesses an open cell rubber foam, the peak overpressure transmitted is initially amplified until a point of critical thickness is reached, at which point the transmitted pressure decreases and blast mitigation is observed. For the material used the critical thickness was 40 cm, a size which would not be Table 1.…”

“…Polyurethane foams are widely used for comfort padding including in combat helmets, as they are lightweight, readily available and low cost. However, Sandhu et al discovered that they also amplify the peak overpressure as the thickness increases when tested using a shocktube, but blast mitigation has been observed in explosive experiments [33]. This discrepancy highlights the importance of creating as representative an environment as possible during experimentation, to allow reasonable extrapolation of data and meaningful conclusions.…”

“…Table 2 lists the different types of foam used across both test series, where the majority of samples were open cell polyurethane foams of different pores per inch (PPI) supplied by Reticel, UK. These samples were used as they were inexpensive, readily available, and their properties were well investigated in wider literature [23,33,44]. Due to the similar mass and density ranges of the Reticel foams, additional foam specimens were investigated to ascertain if any notable relationship between mass and density also existed (see Figure 4a).…”