Investigation on the phase shifts of extinction and phase gratings in polymethyl methacrylate

The phase shifts of the extinction and refractive index gratings to the illumination pattern are revealed in doped polymethyl methacrylate （PMMA）. The dynamic process of these shifts is studied via two-wave coupling at 351 nm. It is shown that these shifts are from the strain and the shrinkage inside the sample and accompanied with the photo-repolymerization process during the building process of the holographic grating. Such shifts will cause obvious energy exchange between the two recording beams and enough attention should be paid to the nonlocal property of the holographic gratings of the material in the application.     

Water Surface Wave in a Trough with Periodical Topographical Bottom under Vertical Vibration

We investigate the water surface waves in a vertically vibrated long rectangular trough with several identical Plexiglas rectangles lined periodically on the bottom. The band structure is computed theoretically by the method of transfer matrix. Some interesting phenomena, such as the localized wave, especially the solitary-like wave inside the band gap . are observed in the experiments.     

在气炮上应用恒磁质点速度计对有机玻璃冲击的试验研究

详细介绍应用恒磁质点速度计对有机玻璃冲击研究的全过程。研究结果表明,它具有较高的准确度和时空分辨率,是探测材料动态性质的一种较好手段。     

超声频谱法对固体内薄夹层的检测

用常规超声脉冲反射法对固体内薄夹层的检测是一个较为难以解决的课题,我们用超声频谱法对此课题进行了实验研究和理论分析.结果表明:1 有薄夹层的反射回波频谱将出现缺口,缺口频率刚好对应薄层的厚度共振频率;2 缺口下陷深浅由薄层反射率所决定.因此,通过反射回波缺口频率和缺口下陷深浅的测量,有可能为探测薄层的厚度和其性质提供一种有意义的方法.     

高压重复频率快脉冲下变压器油中的闪络

介绍了重复频率快脉冲下固/液体介质交接面闪络初步的实验结果.脉冲功率源为基于半导体断路开关(SOS)的SPG200,固体介质为有机玻璃和尼龙,液体介质为变压器油.在相对低频阶段,闪络耐压时间与闪络场强随外加电压脉冲频率的增加非线性迅速减小,在约200 Hz以后,两者下降的趋势明显减缓.随着脉冲频率的增加,闪络耐压时间在统计上变小的同时,在一定区间内的分布也更均匀.分析表明,在不同实验条件下,重复频率显著低于单次下的沿面闪络和体击穿场强.两类场强都随脉冲频率增加非线性下降,在约200 Hz以后,下降的程度减弱.闪络场强随重复频率电压脉冲频率的变化表明,电压作用时间是绝缘介质击穿的根本要素,脉冲电压对绝缘介质的作用时间越长,沿面闪络越容易发生.     

两种类型的剪切断裂韧性及其裂纹扩展

利用紧凑剪切断裂试验和有限元方法数值模拟对TC4（Ti6Al4V)钛合金及PMMA有机玻璃II型断裂行为进行了研究,试验结果表明：存在两种不同的断裂模式,（a)裂纹起裂方向以相对于原裂纹面70－83度扩展为特征的断裂形态,简称拉伸型扩展。（b)型纹开裂方向以几乎沿原裂纹面方向扩展为特征的韧性剪切断裂形态,简称箭切型扩展,文中着重就后一种开裂方式存在的一些问题进行了探讨。