EFFECT OF Z-PINS＇ DIAMETER, SPACING AND OVERLAP LENGTH ON CONNECTING PERFORMANCE OF CMC SINGLE LAP JOINT

The effect of through-thickness reinforcement by composite pins （Z-pins） on the static tensile strength and failure mechanisms of the joints made from ceramic matrix composite （CMC） is investigated. Overlap length of the single lap joint is 15 mm, 20 mm, 23 mm, 37 mm, and 60 mm, respectively. The experimental results indicate that the final failure modes of the joints can be divided into two groups, （a） the bond-line stops debonding until crack encounters Z-pins; and then the adherends break at the location of Z-pins, when overlap length is more than 20 mm; （b） the bond-line detaches entirely and Z-pins are drawn from adherends, when overlap length is equal to 15 mm. A simple efficient computational approach is presented for analyzing the benefit of through-thickness pins for restricting failure in the single lap joints. Here, the mechanics problem is simplified by representing the effect of the pins by tractions acting on the fracture surfaces of the cracked bond-line. The tractions are prescribed as functions of the crack displacement, which are available in simple forms that summarize the complex deformations to a reasonable accuracy. The resulting model can be used to track the evolution of complete failure mechanisms, for example, bond-line initial delamination and ultimate failure associated with Z-pin pullout, ultimate failure of the adherends. The paper simulates connecting performance of the single lap joints with different Z-pins＇ diameter, spacing and overlap length; the numerical results agree with the experimental results; the numerical results indicate enlarging diameter and decreasing spacing of Z-pins are in favor of improving the connecting performance of the joints. By numerical analysis method, the critical overlap length that lies between two final failure modes is between 18 mm and 19 mm, when Z-pins＇ diameter and spacing are 0.4 mm, 5 mm, respectively.     

New forced degradation products of vildagliptin: Identification and structural elucidation using LC-MS,with proposed formation mechanisms

Abstract

A new and simple RP-HPLC-UV method was developed for well-separation of vildagliptin raw material and its degradation products at different conditions; it uses of ammonium acetate buffer at pH= 7.5 and methanol with Athena C18 -WP (250?mm) column. Results show that six degradants have been identified using LC–MS technique, in addition to the NMR approach in some cases. One degradant at relative retention time (RRT) 1.3 was formed under acidic condition and designated as 2-((1R, 3S, 5R, 7S)-3-hydroxyadamantan-1-yl) hexahydropyrrolo[1,2-a]pyrazine-1,4-dione at m/z = 304. Three degradants were formed under various conditions of basic hydrolysis at RRTs 1.2, 0.6 and 0.4 with following names and molar masses (m/z), respectively: 1-(((1S, 3S, 5S, 7S)-1,3-dihydroxyadamantan-2-yl)glycyl)pyrrolidine-2-carboxamide at m/z = 337.2, 1-(((1R, 3S, 5R, 7S)-3-hydroxyadamantan-1-yl)glycyl)pyrrolidine-2-carboxamide at m/z = 321.1 and (1,4-dioxo-1,4,6,7,8,8a-hexahydropyrrolo[1,2-a]pyrazin-3-yl)glycylproline at m/z = 322.6. Another three degradants were also formed under oxidative oxidations of vildagliptin, one at RRT 0.38 and designated as N-hydroxy-N-((1R, 3S, 5R, 7S)-3-hydroxyadamantan-1-yl) glycinate with m/z 241.1, the second one was identical to that formed under basic hydrolysis at RRT 0.6 and the last one has RRT 0.8 and was identified as (1S, 3R, 5R, 7S)-3-(hydroxyamino)adamantan-1-ol at m/z 183.1. Formation mechanisms for the degradation products were described.     

White/light white polyethylene joints obtained by diode laser welding process

Diode laser source was successfully employed for the fabrication of joints comprising nanocomposites of biomedical-grade UHMWPE and small amounts of carbon nanoparticles. The joint with 0.016?wt% of filler exhibited mechanical shear strength of 169N and a light-white color, close to the typical milk-white color of polyethylene. A morphological study of the welded area had been performed. The laser energy produced a thermal effect on the heat-altered zone, thereby smoothening out the surface at a depth of about 1.5?mm. Moreover, surface roughness decreased and the permeability of the joint to biological fluids was enhanced.     

OPTIMAL SPECIMEN DESIGN FOR LAP SHEAR TEST

在采用搭接剪切试件进行的剪切强度实验中,试件失效往往是由于试件两端的剥离应力过大,而不是切应力造成的,这往往造成错误的实验结果. 通过有限元和光弹实验相结合的方法研究在搭接结构中引入凹槽以使试件所受的切应力均匀分布并减少两端的剥离应力,从而提高实验精度的可行性. 研究表明,只要凹槽的形状和位置合适,完全可以达到上述效果,从而实现了搭接剪切试件的优化设计.     

高强预应力钢绞线试验研究

为了研究高强钢绞线在多束并联使用情况下，其总体破断强度利用系数的取值范围，以及锚固预紧力与总体破断强度之间的关系。通过对试验结果的分析归纳，给出了最佳试验加载控制曲线，便于在实验室利用计算机对加载系统进行自动控制，得到理想的试验结果。本文对目前使用较为广泛的高强度低松弛钢绞线的力学性能进行了试验研究，对实验过程中安装因素进行了初步分析探讨，提出了相关的最佳实验加载方程和一些可供设计工作参考的安全强度利用系数。为国标中的相应强度标准提供了试验理论依据。     

单轴[110]应力硅电子迁移率

基于k·p微扰法研究单轴[110]应力作用下硅的导带结构,获得单轴[110]应力硅的导带底能量及电子有效质量.在此基础上,考虑电子谷间、谷内及电离杂质散射,采用弛豫时间近似计算单轴[110]应力硅沿不同晶向的电子迁移率.结果表明：单轴[110]应力作用下硅的电子迁移率具有明显的各向异性.在[001]、[110]及[110]输运晶向中,张应力作用下电子沿[110]晶向输运时迁移率有较大的增强,由未受应力时的1 450 cm²·Vs^-1提高到2 GPa应力作用下的2 500 cm²·Vs^-1.迁移率增强的主要原因是电子有效质量的减小,而应力作用下硅导带能谷分裂导致的谷间散射几率的减小对电子迁移率的影响并不显著.     

预应力空心管桩挤土对围护结构的影响

通过施工实施和位移实测结果，分析预应力空心管桩挤土对围护结构位移和土压力的影响，提出了土压力分析方法，反演了地基水平抗力系数的比例常数m值。     

Surface mechanical properties of low‐molecular‐weight polystyrene below its glass‐transition temperatures

Lap shear and friction force measurements were carried out on a series of monodisperse polystyrene (PS) films below the corresponding glass‐transition temperatures. It showed that adhesion between the PS/PS interface was possible at the temperature below the bulk T_g, and the lower the molecular weight of PS, the lower the temperature at which the interfacial strength was detectable. The examination of a series of molecular weights indicated both the surface molecular motion and the magnitude of the interfacial strength were dependent on molecular weight and its distribution. And a steep increase of the friction force with increasing the test temperature was observed around 0 ∼ 30 °C. The contact angle of water versus molecular weight measurements also showed a transition at room temperature. The behavior observed in this study was supposed to be due to the increased molecular mobility, and was in good agreement with the measured surface transition temperatures by DSC. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 654–658, 2000