Low temperature cracking is one of the main distresses of asphalt pavement in cold regions. Stress relaxation characteristics is critical for cracking resistance of asphalt materials, especially at low temperatures, but there are few studies on the relaxation characteristic of asphalt mastics. To evaluate the effects of relaxation characteristics of asphalt binders and mastics on its low temperature performance, beam bending relaxation test was carried out through dynamic thermomechanical analyzer at low temperatures. Relaxation rate and relaxation time were proposed to illustrate the relaxation characteristics of asphalt binders and mastics. Then, the low-temperature performance of asphalt binders and mastics was evaluated by bending beam rheometer (BBR), glass transition temperature (Tg), and single edge notch beam bending test. Finally, the correlation of relaxation characteristics with low-temperature properties was analyzed based on Pearson’s correlation coefficient and Spearman rank correlation coefficient. The results show that the elasticity of asphalt mastics increases with incorporation of mineral fillers and thus the viscous deformation potential is reduced, which affects the stress relaxation capability. The low-temperature cracking performance of asphalt mastics is indeed compromised as compared with asphalt binders, and the asphalt mastics prepared with fly ash performs the worst since it presents a stronger hardening effect. Fracture energy is determined not to be suitable for evaluating the low-temperature performance of asphalt mastics since its results contradict the BBR and Tg tests. The maximum displacement at fracture can better characterize the brittleness of asphalt materials at low temperatures. The relaxation characteristic index has the strongest correlation with Tg of asphalt binders and mastics, followed by maximum displacement at fracture and comprehensive compliance parameter (Jc). The correlation coefficients are almost larger than 0.5, suggesting that relaxation time and relaxation rate can characterize the low-temperature properties of asphalt binders and mastics.
: DSA (dynamic strain aging) phenomenon in SUS316 steel was investigated using isothermal and non-isothermal tensile tests of simulated HAZ (heat-affected zone) thermal cycles. Isothermal tensile tests were performed on SUS316 in the peak temperature range of 20-700 °C, with strain rates varying from 4.2 × 10 -3 to 4.2 × 10 -5 s -1 . Based on the appearance of discontinuous plastic flows, expressed as serrations, and the hardening phenomenon of the tensile samples, the conditions for the occurrence of DSA in the SUS316 steel were investigated. Furthermore, the extent of hardening due to DSA was evaluated by comparing the hardness values of the SUS316 and SUS316EHP steels after the tensile tests. To confirm the effect of DSA on hardness in the HAZ of the welded SUS316 steel, non-isothermal tensile tests of the simulated HAZ thermal cycles were performed using a Thermec Master. The relationship between the increase in Vickers hardness due to DSA and the strain in the HAZ was determined; the effect of DSA on hardness in the HAZ could be predicted. The DSA in SUS316 steel was found to be mainly attributed to the dynamic interaction of dislocations with C and N interstitial atoms during high-temperature deformation.
: This review and research study provides conclusive discussion on the electron and hole effective masses in thermal silicon dioxide placing their values at 0.42 m and 0.58 m , where m is the free electron mass, correct to two decimal places. Only one of the masses needs to be determined as the electron and hole masses in materials add up to be equal to free electron mass with the hole effective mass being larger than the electron effective mass. The review also convinces the reader that the CBO (conduction band offset) or the Si-SiO 2 barrier height at the oxide/silicon interface of a Si MOS (metal-oxide-semiconductor) device is 3.20 eV.
采用化学气相浸渗(CVI)与聚合物浸渍裂解法(PIP)相结合的工艺制备碳/碳(C/C)复合材料,利用CFT-I型材料表面性能综合试验仪对C/C复合材料进行往复摩擦磨损测试,采用扫描电镜对C/C复合材料的微观组织与摩擦磨损试验后的表面形貌进行表征,研究了沉积温度对CVI+PIP工艺C/C复合材料微观组织与摩擦磨损性能的影响规律.结果表明:与石墨材料相比,C/C复合材料具有更加理想的摩擦磨损性能;沉积温度为1050℃制得的C/C复合材料具有稳定的摩擦系数和最低的磨损率,在该温度下产生的孔洞和裂纹极少,浸渗效果最为理想.
本研究采用微波烧结技术制备了不同 Ni3Al 含量的硼掺杂 WC-Ni3Al 硬质合金材料,研究了烧结工艺和Ni3Al含量对力学性能和微观组织的影响.研究表明,使用微波烧结可以在较短的时间内制备出性能优异的 WC-Ni3Al-B合金.随烧结温度升高,合金的相对密度和弯曲强度先升后降.Ni3Al含量的增加可以降低合金的烧结温度,随 Ni3Al 含量增加其弯曲强度和断裂韧性升高,硬度下降.当Ni3Al含量为 10%、在 1450℃、烧结 15 min时,合金具有较高的综合力学性能.
: The issue of determining the maximum compressive residual stress that can be induced through mechanical surface treatment is of great significance. There are two possible approaches, namely stress peening and stress rolling, both to determine the limit. Steel with high hardness may be under the yield strength, while for those with lower tensile strength, the hardness is increased, and the limit is above the tensile strength.
采用纯Cu箔作中间层,利用瞬间液相扩散焊(TLP)技术对2195铝锂合金进行连接,研究了焊接温度对铝锂合金TLP连接接头的显微组织形貌、元素扩散以及力学性能的影响.结果表明,随焊接温度升高,扩散更均匀,接头结合处组织更均匀,但焊缝区域会出现晶粒越粗大的现象,焊接温度对焊接接头区域的物相种类影响不大;显微硬度随焊接温度增加而下降,剪切强度随焊接温度增加先上升后下降,焊接温度为570℃时,剪切强度最大为108.6 MPa.
以拜耳法赤泥、偏高岭土和水泥为原料,将拜耳法赤泥与偏高岭土按不同配合比制备水泥胶砂,分析了赤泥和偏高岭土掺合料对水泥胶砂的力学性能的影响,并借助X射线衍射仪(XRD)、傅里叶变换红外光谱仪(FTIR)、扫描电子显微镜(SEM)对复合水泥胶砂的物相组成及微观形貌进行表征.研究结果表明:当赤泥掺量10％、偏高岭土掺量10％时,水泥胶砂28 d抗压强度最高,可达到47.38 MPa;赤泥和偏高岭土中的活性SiO2和Al2O3掺入能消耗水泥产生的Ca(OH)2,发生二次水化反应,生成水化硅酸钙及斜方钙沸石(CaAl2Si2O8·4H2O)填充于内部空隙,增加了结构密实度,提高了复合水泥胶砂的力学性能.
通过计算机模拟建立了一种确定导电填料/高分子复合材料理论渗流阈值的方法.首先,通过以一定比例混合而构成的二相石墨烯/聚氨酯复合材料建模;其次,利用有效介质理论进行计算机模拟计算,得出石墨烯/聚氨酯二相复合电热材料理论渗流阈值.模拟结果表明石墨烯/聚氨酯复合材料中,当石墨烯添加量为3.4 wt％时,该复合电热材料达到了理论渗流阈值.实验以上述模拟结果为基础,采用溶液共混法成功制备出了石墨烯/聚氨酯复合水溶液;实验结果表明,该石墨烯浆料中石墨烯添加量在3.7 wt％时,电热复合材料达到渗流阈值,表明该理论模拟结果与实际实验结果相吻合.使用实验制备的石墨烯/聚氨酯浆料涂覆而成的电热网状材料,在24 V时温度可达50℃.
镁合金存在腐蚀速度过快以及打磨后表面因其光滑平整而无法直接沉积涂层的问题.使用HF处理后,表面具有一定的粗糙度,有利于沉积层的附着.同时,HF处理后的镁合金表面会生成一层致密的氟化镁(MgF2)化学层,更加提高了对于腐蚀介质的抵抗作用.本研究采用电泳沉积的方法在镁合金表面制备羟基磷灰石(HA)-氧化石墨烯(GO)复合涂层.随后热处理,使GO转变为还原氧化石墨烯(RGO).通过设置悬浮液中GO的不同含量,以探究RGO含量对HA-RGO/MgF2复合涂层形貌和耐腐蚀性的影响.结果表明,当GO含量为0.33 mg/mL时,HA-RGO/MgF2复合涂层具有最佳耐腐蚀性.
本实验研究了SBS改性沥青、偶联剂及其复合改性技术对提升铁尾矿与沥青界面粘附效果.针对2个不同铁尾矿掺量、2种结合料及3种不同改性工艺进行了混合料配比设计及路用性能研究,分析了粘附效果的同时利用汉堡实验对长期水稳性能效果进行了相关研究.结果表明,通过SBS改性沥青、偶联剂及其复合改性可以明显提高含铁尾矿混合料的水稳定性,整体路用性能也获得一定的提升,从宏观效果及微观指标证实了复合改性的粘附改性功效,并证实了复合改性技术显著提升含铁尾矿的耐久性.
为研究温拌剂PN2217对氢氧化铝(ATH)/有机改性蒙脱土(OMMT)沥青混合料阻燃抑烟与路用性能的影响,采用高速剪切法制备ATH/OMMT复合阻燃沥青与温拌阻燃沥青并测试了常规物理性能;采用锥形量热仪测试PN2217对ATH/OMMT复合改性沥青混合料阻燃抑烟性能的影响;对ATH/OMMT复合阻燃沥青与温拌阻燃沥青进行热重试验,研究PN2217对ATH/OMMT复合阻燃沥青热解特性的影响机理;采用车辙试验与低温弯曲试验研究了PN2217对ATH/OMMT复合改性沥青混合料路用性能的影响.研究表明,PN2217抑制燃烧过程中惰性炭层的形成降低了ATH/OMMT复合改性沥青混合料的阻燃抑烟性能,加入PN2217后,燃烧过程中形成的炭层表面出现了空隙与裂隙,无法有效阻止与外界的热量与气体交换;PN2217通过降低了ATH/OMMT复合改性沥青与集料之间的粘附作用,对高温性能有一定的抑制作用,同时改善了低温抗裂性能.
研究石墨烯、层状双金属氢氧化物(LDHs)及石墨烯复配LDHs对SBS改性沥青物理性能和抗热氧老化、紫外光氧老化性能的影响,并采用傅立叶变换红外光谱(FTIR)分析了改性沥青老化前后化学结构的变化.结果表明,石墨烯、LDHs及石墨烯复配LDHs均能提高SBS改性沥青的高温性能和抗老化性能.与单掺石墨烯和LDHs相比,石墨烯复配LDHs能同时减少SBS改性沥青热氧老化和紫外光氧老化前后软化点和粘度的变化,提高其延度和针入度保留率.FTIR分析显示,掺入石墨烯复配LDHs的SBS改性沥青老化前后羰基指数变化率和碳碳双键指数变化率均最小,表明石墨烯复配LDHs对SBS改性沥青耐老化性能具有更好的改善效果.
