Computational investigation of shock‐mitigation efficacy of polyurea when used in a combat helmet

Tse

Numer Methods Biomed Eng

et al. 2017

Blast-induced traumatic brain injury has been on the rise in recent years because of the increasing use of improvised explosive devices in conflict zones. Our study investigates the response of a helmeted human head subjected to a blast of 1 atm peak overpressure, for cases with and without a standard polycarbonate (PC) face shield and for face shields comprising of composite PC and aerogel materials and with lateral edge extension. The novel introduction of aerogel into the laminate face shield is explored and its wave-structure interaction mechanics and performance in blast mitigation is analysed. Our numerical results show that the face shield prevented direct exposure of the blast wave to the face and help delays the transmission of the blast to reduce the intracranial pressures (ICPs) at the parietal lobe. However, the blast wave can diffract and enter the midface region at the bottom and side edges of the face shield, resulting in traumatic brain injury. This suggests that the bottom and sides of the face shield are important regions to focus on to reduce wave ingress. The laminated PC/aerogel/PC face shield yielded higher peak positive and negative ICPs at the frontal lobe, than the original PC one. For the occipital and temporal brain regions, the laminated face shield performed better than the original. The composite face shield with extended edges reduced ICP at the temporal lobe but increases ICP significantly at the parietal lobe, which suggests that a greater coverage may not lead to better mitigating effects.

Section: Resultssupporting

confidence: 70%

“…Extra padding had been reported to mitigate the blast wave effects on the head. 46,47 Even though the head and helmet models may be different, comparison of our results with the published values showed that similar magnitudes of ICPs were obtained, and hence ascertain the appropriate modelling methodology used.…”

Section: Analysis Landmarkssupporting

confidence: 75%

Face shield design against blast‐induced head injuries

Tse

Numer Methods Biomed Eng

et al. 2017

J of Applied Polymer Sci

“…This class of elastomer has gained a lot of interest by both academia and industry in the last few years, in view of their ability to exhibit a range of mechanical properties, which in turn is an indirect manifestation of its composite microstructure . Polyurea is finding interesting applications in specialized fields, especially as linings in personnel‐protective gear, retrofits for unreinforced structures, and as ballistic‐penetration resistant metallic armor …”

Section: Introductionmentioning

confidence: 99%

“…1 This class of elastomer has gained a lot of interest by both academia and industry in the last few years, in view of their ability to exhibit a range of mechanical properties, which in turn is an indirect manifestation of its composite microstructure. [2][3][4] Polyurea is finding interesting applications in specialized fields, especially as linings in personnel-protective gear, 5 retrofits for unreinforced structures, 6,7 and as ballistic-penetration resistant metallic armor. 8 The inherent microstructure of polyurea comprise of two distinct types of domains: "hard" realms formed by hydrogen bonded polar urea linkages (ANHACOANHA) and "soft" domains, consisting of long aliphatic polyether chains.…”

Section: Introductionmentioning

confidence: 99%

Understanding the role of isocyanate dilution toward spraying of polyurea

Iqbal

Kumar

Roy

2017

An experimental study into the consequences of diluting isocyanate toward processing of polyurea has been reported. The effect of introducing increasing amount of propylene carbonate into a representative isocyanate precursor has been established. Viscosity‐blending index based equations were found to be more reliable toward prediction of isocyanate precursor‐propylene carbonate blend viscosity. Spraying of undiluted isocyanate precursor with amine formulations led to formation of “noodle‐like” fibrous product, irrespective of the type of chain extender being used. Diluting isocyanate with propylene carbonate (10% v/v), lowered the viscosity of the precursor from 85 to 48 mPa s (at 70 °C), and the resulting formulations could be effectively sprayed to form polyurea films with excellent mechanical properties. Dilution with propylene carbonate also increased the “tack free” time appreciably from ∼1 to ∼4 s, which directly reflects on the improved processability. Rheological studies were performed to quantify the activation energy associated with the isocyanate‐amine reaction for polyurea preparation. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45869.

J of Applied Polymer Sci

“…Certain products, i.e., pipes, freight wagon liners, industrial floors, need to be brought back to service as soon as possible, and in such cases, the fast curing nature of polyurea is extremely beneficial. Polyurea is also entering into areas like personnel‐protective gear, retrofits for unreinforced structures, and as ballistic‐penetration resistant metallic armor, where rapid curing has enormous advantages.…”

Section: Introductionmentioning

confidence: 99%

Emergence of time‐dependent material properties in chain extended polyureas

Iqbal

Kumar

Roy

2018

In this article, we report the emergence of material properties of polyurea over a finite time frame. Due to the rapid isocyanate–amine reaction, polyurea formation occurs practically instantaneously. Despite being an “instant‐curing” system, the material properties of polyurea evolve substantially with time: phenomenon, which warrants a methodical study. The curing process of polyurea formulations, containing both aliphatic and aromatic chain extender, has been studied systematically with an aim to gain insight into the time frame associated with its curing and subsequent stress relaxation. Formulations containing aromatic chain extender mandated relatively lesser time to “gel,” but the complete disappearance of NCO absorbance mandated much longer periods ∼7 h. Interestingly, in all the formulations, mechanical properties improved with time and reached their optimal properties over a period of 15 days. This improvement has been attributed to several processes simultaneously occurring within the matrix; the foremost being the relaxation of internal stresses which tend to buildup in the polymer during the spray coating process. In addition, significant changes occur in the internal morphology of segmented polymers, which in turn is a result of H‐bond rearrangement.