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Blast-induced traumatic brain injury (bTBI) is a rising health concern of soldiers deployed in modern-day military conflicts. For bTBI, blast wave loading is a cause, and damage incurred to brain tissue is the effect. There are several proposed mechanisms for the bTBI, such as direct cranial entry, skull flexure, thoracic compression, blast induced acceleration, and cavitation, that are not mutually exclusive. So the cause-effect relationship is not straightforward. The efficiency of protective headgears against blast waves is relatively unknown as compared with other threats. Proper knowledge about standard problem space, underlying mechanisms, blast reconstruction techniques, and biomechanical models are essential for protective headgear design and evaluation. Various researchers from cross disciplines analyze bTBI from different perspectives. From the biomedical perspective, the physiological response, neuropathology, injury scales, and even the molecular level and cellular level changes incurred during injury are essential. From a combat protective gear designer perspective, the spatial and temporal variation of mechanical correlates of brain injury such as surface overpressure, acceleration, tissue-level stresses, and strains are essential. This paper outlines the key inferences from bTBI studies that are essential in the protective headgear design context.

The results of an experimental investigation of the performance characteristics of concrete reinforced with a newly developed synthetic synergy fiber are presented. A number of three-dimensionally reinforced concrete specimens (beams and cylinders) using four fiber dosages (0.5, 1.0, 1.5, and 2.0 vol%) were cast and tested to evaluate the strength and toughness characteristics. The strength tests included compressive strength, flexural strength (modulus of rupture), first crack strength, and impact strength. The toughness properties evaluated were modulus of elasticity; the toughness indices I5, I10, I20, and I30 and residual strengths calculated according to ASTM C1018 test procedure; and the flexural toughness factor and the equivalent flexural strength calculated according to the Japanese Society of Civil Engineers standard specifications. A new test method (ASTM C1399-98) was also used to determine the average residual strength (ARS) of the concretes reinforced with the four synthetic synergy fiber dosages. The fiber-reinforced concretes were mixed, placed, consolidated, finished, and cured under identical conditions. There was a significant increase in the flexural strength and a slight increase in the first crack strength as the fiber content was increased from 0.5 to 2.0 vol%. The ASTM toughness indices and the Japanese toughness factors and equivalent flexural strengths also increased significantly as fiber content increased. There was a tremendous increase in impact strength for an increase in fiber content. Very high average residual strengths (ASTM C1399) were obtained, and ARS values increased as fiber content increased.

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