Repetitive impact exposure and characterization of stress-whitening of an American football helmet outer shell material

Mechanical stress exerted upon impact-modified polycarbonate (PC) and poly(ethylene terephthalate) (PET) blends has been reported to generate microscopic voids via rubber-toughener (RT) particle cavitation which can macroscopically manifest to visibly whiten the material. Previous work has revealed a whitening phenomenon in collegiate American football helmet outer shells after a single season and in helmet-grade plaques following linear impact testing. The purpose of this research was to quantify the effects of repetitive linear drop exposures on the (i) impact performance; (ii) physical and thermal properties; and (iii) surface and tensile mechanical properties of a stress-whitened American football helmet outer shell material. Statistically significant changes in plaque impact performance corresponded to substantial stress-whitening that penetrated up to 40–45% into the plaque thickness and elicited shifts in surface and tensile mechanical properties. Nanoscale microscopy revealed elongation of the PC/PET matrix and delamination at the RT-matrix interface. Thermal property analysis suggested the concomitant occurrence of RT cavitation and strain-induced PET crystallization. Overall, the research identified a battery of diagnostic tools to characterize material property changes of stress-whitening in rubber-toughened helmet outer shell materials.     

基于双CCD的某型光电式头盔瞄准具改进方法研究

为了提高某型光电式头盔瞄准具的精度以及响应时间等性能,根据对其工作过程和主要不足的分析,提出了一种基于双CCD的改进方法,运用双目视觉原理,推导出了相应的数学模型,并对该模型进行了验证和误差分析,结果表明新系统的方位角和俯仰角误差均小于0．5°,小于原系统的0．75°,基于双CCD的改进方法能有效提高某型光电式头盔瞄准具的整体性能。     

折/衍混合超轻小型投影式头盔光学系统设计

投影式头盔系统具有成像质量高,结构轻便等特点。分析投影式头盔光学系统设计参数的选择原则,并基于投影式物镜引入对角为1.55 cm的新型OLED显示器作为图像源,采用折射/衍射混合结构来减轻光学系统的体积和重量。通过ZEMAX软件对系统进行优化,设计得到一款质量仅1.35 g,直径11.32 mm的超轻小型三片式头盔显示器光学系统。系统中心视场MTF在32lp/mm处达到了0.52,在该空间频率下对应人眼的分辨率为1.85,′在大视场处,子午和弧矢MTF也均大于0.2,分辨率满足SVGA显示模式要求。     

X‐ray,synchrotron, and neutron diffraction analysis of Roman cavalry parade helmet fragment

A partially corroded fragment of the neck guard of a Roman cavalry helmet excavated in the former military camp of Gerulata, a part of the Limes Romanus on the River Danube, was analysed by laboratory X‐ray, synchrotron and neutron powder diffraction. The approximate phase composition determined by the neutron diffraction of the bulk, 82% (wt) of the copper alloy phase, 12 % (wt) of cuprite and 6% of nantokite indicate a significant degree of corrosion of the artefact. Elemental EDX analysis of cleaned surface showed that the chemical composition of the original alloy is 78 to 82 % (wt) of Cu and 21.4 to 16.5 % of Zn with minute amounts of Sn, Si and S. High contents of Cu and Zn with the negligible amount of Sn showed that the body of the helmet was made of brass and not of bronze as expected before. The amount of zinc in the copper alloy calculated from the refined lattice parameter agrees fairly well with the value determined by EDX. The most abundant phase in the synchrotron powder diffraction pattern of the corrosion products scrapped from the artefact is cuprite, but presence of atacamite, malachite, brochantite, nantokite, mixed Cu‐Zn hydroxyl carbonates and probably also of simonkolleite (Zn₅(OH)₈Cl₂·H₂O) have been detected. In contrast, the X‐ray pattern taken directly from the surface of the artefact is dominated by atacamite with some traces of malachite and quartz. Because the penetration depth of laboratory X‐rays is in order of tens of microns, the phase analysis based only on a diffraction pattern taken from a surface can lead to erroneous conclusions concerning the phase composition of the patina. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

头盔的声学性能测试与分析

本文设计了使用自关函数以测试混响声衰变速度、自功率谱以测试插入损失的方法，用于头盔的回声与隔声效果分析。结果表明，这一方法物理概念明确，测试简单，可以定量地说明头盔的声学性能可能存在的问题，可望用于头盔的声学性能额 观测试与分析方法的建立。     

头盔显示器的光学设计方案

本文介绍了几种头盔式显示器的光学设计方案,并从提高系统的分辨率、对比度,重量等各方面作了比较。     

头盔的声学性能测试与分析

本文设计了使用自相关函数以测试混响声衰变速度、自功率谱以测试插入损失的方法，用于头盔的回声与隔声效果分析．结果表明，这一方法物理概念明确，测试简单，可以定量地说明头盔的声学性能可能存在的问题，可望用于头盔的声学性能客观测试与分析方法的建立．