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Effects of expected service life exposures on the functional properties and impact performance of an American football helmet outer shell material.

机译：预期使用寿命暴露对橄榄球头盔外壳材料的功能特性和冲击性能的影响。

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摘要

The purpose of this dissertation is to gain a greater scientific understanding of the changes in functional material properties and impact performance of an American football helmet outer shell material under expected service life exposures. The research goals are to (i) quantify chemical, physical, thermal, and mechanical degradation of an American football outer shell material under expected environmental conditions and (ii) develop a linear drop test impact protocol to employ expected on-field impact conditions to American football helmet components and a plaque-foam (i.e., shell-liner) surrogate. Overall, a step-wise progression of analysis was demonstrated to concurrently quantify and understand changes in material properties at the molecular, microscopic, and macroscopic levels. Changes across chemical, physical, thermal, and mechanical properties were evaluated following laboratory exposures to 480 hours of accelerated weathering, increasing intensities of n-Butyl acetate solvent, and 12 repetitive linear plaque-foam impacts.;In Chapter II, an instrumented drop test setup was substantiated to investigate linear impact attenuation performance. In Chapter III, laboratory exposure to UV light, oxygen, moisture, and elevated temperatures induced molecular degradative bi-products and physical aging up to ∼1% into the plaque thickness which led to altered aesthetic properties, chemi-crystallization, and an increased resistance to surface indentation and tensile deformation. In Chapter IV, solvent-induced plasticization, crystallization, and stress-cracking of up to ∼3% into the plaque thickness led to an increase in surface porosity which scattered light and decreased tensile properties. In Chapter V, impact exposure induced rubber-toughener (RT) cavitation that generated voids via delamination at the RT-matrix interface at which led to rings of stress-whitening, strain-induced crystallization, increased butadiene RT density, and shifts surface modulus and tensile properties. This dissertation preliminarily substantiated (i) a drop test setup attempting to accurately replicate on-field impact conditions to investigate linear impact attenuation performance, and (ii) polymer techniques and protocols that could elucidate the rates and degrees of material degradation.
机译：本文的目的是对预期使用寿命下的美式橄榄球头盔外壳材料的功能材料性能和冲击性能的变化有更深入的科学认识。研究目标是（i）在预期的环境条件下量化美式橄榄球外壳材料的化学，物理，热和机械降解，以及（ii）制定线性跌落试验冲击规程，以将预期的现场冲击条件应用于美国人橄榄球头盔组件和斑块泡沫（即，衬里）替代物。总体而言，分析的逐步进行被证明可以同时量化和理解分子，微观和宏观层面材料特性的变化。在实验室暴露于480小时的加速风化，乙酸正丁酯溶剂的强度增加以及12次重复线性斑块泡沫影响之后，评估了化学，物理，热和机械性能的变化。;第二章，仪器跌落测试设置得到证实，以研究线性冲击衰减性能。在第三章中，实验室暴露于紫外线，氧气，湿气和高温下会导致分子降解的副产物和物理老化，直至斑块厚度增加约1％，从而导致美学特性发生变化，化学结晶并增加了抵抗力表面压痕和拉伸变形。在第四章中，溶剂诱导的增塑，结晶和应力裂纹直至斑块厚度的约3％导致表面孔隙率增加，从而散射了光并降低了拉伸性能。在第五章中，冲击暴露引起的橡胶-增韧剂（RT）空化通过在RT-基体界面处分层而产生空隙，从而导致应力白化环，应变诱导的结晶，丁二烯RT密度增加以及表面模量变化和拉伸性能。本文初步证实了（i）跌落测试装置，试图精确复制现场冲击条件以研究线性冲击衰减性能，以及（ii）可以阐明材料降解速率和程度的聚合物技术和方案。

著录项

  • 作者

    Krzeminski, David Edward.;

  • 作者单位

    The University of Southern Mississippi.;

  • 授予单位 The University of Southern Mississippi.;
  • 学科 Plastics.;Kinesiology.;Polymer chemistry.
  • 学位 Ph.D.
  • 年度 2015
  • 页码 218 p.
  • 总页数 218
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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