拉伸速度对ETFE薄膜力学性能的影响

对厚度为250μm的长条形ETFE(乙烯-四氟乙烯共聚物)薄膜试样进行了6种定速(应变速率分别为10%/min,25%/min,50%/min,100%/min,200%/min,500%/min)单向拉伸试验,得到了相应的抗拉强度、断裂延伸率、屈服应力以及弹性模量等力学参数的变化规律.结果表明:ETFE薄膜的抗拉强度随拉伸速度的增加略有增加,而断裂延伸率随拉伸速度的增加略有减小;ETFE薄膜的屈服强度随拉伸速度的增加而有所增加,但第二屈服强度增加不大;ETFE薄膜的屈服应变随拉伸速度的增加略有增加,第二屈服应变则略有减少;ETFE薄膜的切线弹性模量以及第二弹性模量随拉伸速度的增加呈下降趋势,割线弹性模量和第三弹性模量则没有明显的变化.通过分析,给出了以应变速率对数为变量的线性拟合公式,可用于计算在不同应变速率下ETFE薄膜的相关力学参数.

A method of determining nonlinear large strain consolidation parameters of dredged clays

A method of obtaining the large strain consolidation parameters of dredged clays considering the influence of the initial water content is investigated in this study. According to the test results of remolded clays with high initial water contents reported by Hong et al. （2010）, a relationship between the void ratio （e） and effective stress （a3 is established. Furthermore, based on the available permeability data from the literature, a new relationship between the permeability coefficient （k） and the ratio （e/eL） of the void ratio to the void ratio at the liquid limit （eL） is proposed. The new proposed expression considering the initial water content improves the e-k equation established by Nagaraj et al. （1994）. Finally, the influence of the initial void ratio and effective stress on the large strain consolidation coefficient g（e） defined by Gibson et al. （1981） and k/（1 ＋e） in large strain analysis is discussed. The results show that, under a constant effective stress, the value of k/（1 ＋e） increases with the initial void ratio. The large strain consolidation coefficient shows the law of segmentation change, which decreases with the increase of the effective stress when the effective stress is less than the remolded yield stress, but increases rapidly with the effective stress when the effective stress is larger than the remolded yield stress.

为什么地球上超大陆的寿命变得越来越短了?

地球上的主要大陆地块在过去的20亿年间以来曾经三次聚合成一个超大陆,但一段时间以后又发生裂解.这种大陆地块的周期性聚合和裂解现象被称为超大陆旋回.地球通过超大陆旋回控制着地表的造山运动、成矿过程、大洋及超大洋的形成与闭合,甚至大气圈与生命圈的演化.但一个有趣的观察是,已知的由老到新的努纳(也称哥伦比亚)、罗迪尼亚(最早音译鲁迪尼亚)和盘古三个超大陆的寿命显示出一个逐渐递减的趋势,其分别为大约3亿年,2~2.5亿年和1.5亿年,反映出控制地球长期演化过程的某种重要的内在原因.本文通过超级电脑地球动力学三维建模发现,导致超大陆寿命不断减短的主要原因在于形成于超大陆内部的新的造山带的强度随着地球的年龄增大而逐渐减小,并进而提出这与地球的长期冷却过程有关.因为地幔温度随着地球年龄的增长在不断降低,上地幔岩石部分熔融的程度也在不断降低,因此造成新生造山带的岩石圈厚度不断减薄,强度降低.此外,沿新生造山带的岩浆底侵对板块缝合线及大断裂的岩浆缝合作用可能也会随之减弱.