An indirect tensile testing method is proposed for characterizing low strength graphite platelet reinforced vinyl ester nanocomposites at high-strain rate. In this technique, the traditional Brazilian disk (diametrica...An indirect tensile testing method is proposed for characterizing low strength graphite platelet reinforced vinyl ester nanocomposites at high-strain rate. In this technique, the traditional Brazilian disk (diametrical compression) test method for brittle materials is utilized along with conventional split-Hopkinson pressure bars (SHPB) for evaluating cylindrical disk specimens. The cylindrical disk specimen is held snugly in between two concave end fixtures attached to the incident and transmission bars. To eliminate the complexities of conventional strain gage application, a non-contact Laser Occluding Expansion Gage (LOEG) has been adapted for measuring the diametrical transverse expansion of the specimen under high-strain rate diametrical compressive loading. Failure diagnosis using high-speed digital photography validates the viability of utilizing this indirect test method for characterizing the tensile properties of xGnP (exfoliated graphite nanoplatelets) reinforced and additional CTBN (Carboxyl Terminated Butadiene Nitrile) toughened vinyl ester based nanocomposites. Also, quasi-static indirect tensile response agrees with previous investigations conducted using the traditional dog-bone specimen in direct tensile tests. Investigation of both quasi-static and dynamic indirect tensile test responses shows the strain rate effect on the tensile strength and energy absorbing capacity of the candidate materials. The contribution of reinforcement to the tensile properties of the candidate materials is presented.展开更多
热应激会降低工作效率并导致热相关疾病。为了量化高温环境下环卫工人的热应激水平,建立一个生理状态安全评价指标(physiological state safety evaluation index,PSEI)。首先,引入尖点突变理论分析不同热环境下人体生理状态变化趋势。...热应激会降低工作效率并导致热相关疾病。为了量化高温环境下环卫工人的热应激水平,建立一个生理状态安全评价指标(physiological state safety evaluation index,PSEI)。首先,引入尖点突变理论分析不同热环境下人体生理状态变化趋势。其次,基于信息熵和变权理论计算生理指标的权重,并利用尖点突变级数法建立人体生理状态评价体系。最后,提出新评价指标PSEI以量化生理状态安全水平,并在此基础上确定PSEI的安全等级。结果表明:在不同环境条件和生理状态下,生理指标的权重是变化的;平均皮肤温度、耳膜温度、收缩压和心率的权重范围分别为0.09~0.64、0.08~0.41、0.07~0.74和0.06~0.33;PSEI的安全等级为:非常安全(0.948,1]、相对安全(0.886,0.948]、中等(0.798,0.886]、相对危险(0.649,0.798]和非常危险[0,0.649]。PSEI可为高温环境下环卫工人提供实时的生理状态安全评估和健康预警。展开更多
文摘An indirect tensile testing method is proposed for characterizing low strength graphite platelet reinforced vinyl ester nanocomposites at high-strain rate. In this technique, the traditional Brazilian disk (diametrical compression) test method for brittle materials is utilized along with conventional split-Hopkinson pressure bars (SHPB) for evaluating cylindrical disk specimens. The cylindrical disk specimen is held snugly in between two concave end fixtures attached to the incident and transmission bars. To eliminate the complexities of conventional strain gage application, a non-contact Laser Occluding Expansion Gage (LOEG) has been adapted for measuring the diametrical transverse expansion of the specimen under high-strain rate diametrical compressive loading. Failure diagnosis using high-speed digital photography validates the viability of utilizing this indirect test method for characterizing the tensile properties of xGnP (exfoliated graphite nanoplatelets) reinforced and additional CTBN (Carboxyl Terminated Butadiene Nitrile) toughened vinyl ester based nanocomposites. Also, quasi-static indirect tensile response agrees with previous investigations conducted using the traditional dog-bone specimen in direct tensile tests. Investigation of both quasi-static and dynamic indirect tensile test responses shows the strain rate effect on the tensile strength and energy absorbing capacity of the candidate materials. The contribution of reinforcement to the tensile properties of the candidate materials is presented.
文摘热应激会降低工作效率并导致热相关疾病。为了量化高温环境下环卫工人的热应激水平,建立一个生理状态安全评价指标(physiological state safety evaluation index,PSEI)。首先,引入尖点突变理论分析不同热环境下人体生理状态变化趋势。其次,基于信息熵和变权理论计算生理指标的权重,并利用尖点突变级数法建立人体生理状态评价体系。最后,提出新评价指标PSEI以量化生理状态安全水平,并在此基础上确定PSEI的安全等级。结果表明:在不同环境条件和生理状态下,生理指标的权重是变化的;平均皮肤温度、耳膜温度、收缩压和心率的权重范围分别为0.09~0.64、0.08~0.41、0.07~0.74和0.06~0.33;PSEI的安全等级为:非常安全(0.948,1]、相对安全(0.886,0.948]、中等(0.798,0.886]、相对危险(0.649,0.798]和非常危险[0,0.649]。PSEI可为高温环境下环卫工人提供实时的生理状态安全评估和健康预警。
