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.
