Experimental measurement of intracranial strains under breacher-level blast exposure

Abstract

Blast-induced traumatic brain injury (bTBI) is an ongoing concern for military and law enforcement personnel exposed to repeated low-level blasts. While strain-driven axonal damage has been proposed as a mechanism of primary blast injury, the role of strain under occupationally relevant conditions remains poorly defined. To investigate the role of strain in blast-induced injury, we measured strain in a Sylgard 527-filled surrogate headform exposed to shock-tube blasts of ~75-kPa incident overpressure and ~5-ms positive-phase duration, which is representative of breacher-level blast exposures. High-speed imaging and digital image correlation revealed that intracranial strains are consistently below 0.5%. These values are much lower than the reported thresholds for both long-term potentiation (3.7–6.7% strain) and moderate-to-severe axonal injury (5–10% strain). Our findings are consistent with prior finite element simulations of comparable blast exposures (50–100  kPa, 4–8  ms) which similarly found less than 1% strains for 50–100  kPa incident overpressures. In this head surrogate, the results indicate that strain is unlikely to be a dominant mechanism of injury at breacher-level exposures and instead emphasize the importance of experimental testing for other potential injury mechanisms, such as cavitation.