Effect of natural aging on microstructure and mechanical properties of friction stir welded 7050-T7451 joints

The microstructure and mechanical properties of friction stir welded 2.5 mm 7050-77451 aluminum alloy natural aging 72 h and 17 520 h were investigated,respectively.The uniaxial tensile test showed that yield strength,tensile strength and elongation of the joints 17 520 h natural aging were about 20%,12%and 24%higher than those joints natural aging72 h.Hardness profile of natural aging 17 520 h joint witnessed significant enhancement in nugget zone,compared with 72 h natural aging.Differential scanning calorimetry(DSC) and transmission electron microscopy(TEM) test revealed that more Guinier-Preston zone,η' and η phase emerged in nugget zone as natural aging duration increased,high density of dislocation located within grain boundary in nugget zone of joints natural aging 72 h.It is concluded that natural aging was feasible to enhance strength and plasticity of FSW joints simultaneously.     

低应变瞬态荷载作用下基桩动力响应解析解

目前广泛采用的基桩低应变检测问题的理论基础是基于平截面假定的一维应力波理论。而实际上,锤击产生的应力波是三维应力波,不仅沿桩身纵向传播,还沿径向传播,对于基桩低应变检测问题平截面假定实际上是不成立的。此时,一维纵波传播问题转换为应力波沿三维柱体传播问题。文章从基桩三维理论出发,忽略桩土径向位移,考虑桩体中应力波沿纵向和径向传播与桩土的相互作用,建立三维条件下桩土系统瞬态振动计算模型,推导得到低应变瞬态荷载作用下基桩三维动力响应的解析解,以期为基桩低应变检测提供新的理论指导。     

宽条带与离层注浆开采地表移动计算

本文根据宽条带与离层注浆联合开采的工程实践,推导了该种采矿方法地表移动理论计算公式,从理论上完善了该项技术,为更好地推广该技术打下理论基础.     

Rheological studies of hyaluronan solutions based on the scaling law and constitutive models

We have investigated the scaling relationship between rheological behavior and concentration for both salt-free and saline solutions of hyaluronan (HA), and adopted three viscoelastic constitutive models to predict the linear/non-linear viscoelastic behavior of these aqueous solutions of HA with different molecular weights at different concentrations up to 20 mg/ml. A series of concentration equations are obtained to describe the influence of HA concentration on solution viscosity. Corresponding to dilute and semi-dilute concentration region, salt-free HA solutions have scaling relationship between specific viscosity and HA concentration as η_sp ∼ c^1.0 and η_sp ∼ c^3.5, respectively, while for 0.15 M NaCl HA solutions, the scaling exponents are 1.5 and 4.2, respectively. Simulation results indicate that these constitutive models have good applicability to describe quantitatively the rheological properties of HA entangled solutions under either dynamic or steady shear flow. In addition, the plateau modulus scaling of HA solutions can be well described by the concentration-dependent length scale.     

环氧固化剂硫脲改性四乙烯五胺的合成及性能研究

用硫脲改性四乙烯五胺合成了环氧树脂固化剂。通过测量初凝时间和接触角,讨论了反应时间、合成温度和单体投料比对固化剂性能的影响。通过热效应法考查了固化剂与环氧树脂的最佳配比。实验结果表明,反应时间为3 h,反应温度为130℃,四乙烯五胺与硫脲的质量比为1.4∶1时,合成的固化剂较好。当m固化剂∶m环氧=1∶4时,胶粘剂能在-5℃/8 d内固化,有效提高固化体系在低温下的固化能力。     

固相萃取净化-气相色谱法同时测定茶叶中16种有机氯、拟除虫菊酯农药残留

对茶叶中多种农药残留气相色谱测定方法做了改进,建立了茶叶中16种农药残留同时测定的新方法.待测组分经提取、净化后进行气相色谱测定.淋洗液为石油醚和乙酸乙酯混合溶液,对两者的比例作了优化(石油醚:乙酸乙酯=7∶3,v/v).16种农药残留组分的标准加入回收率为92.7%～102.9%,检出下限为0.1～3.3μg/kg,相对标准偏差为3.4%～8.9%(0.04～0.2μg/kg,n=5),能满足出口企业对产品质量控制的要求.     

挤出滚圆法制备天麻粉球形微丸的实验研究

采用挤出滚圆法制备天麻粉球形微丸,为有效提高高主药比例造粒的容易程度,首次引入粉体表面改性技术,并对改性前后的天麻进行了造粒的对比实验。结果表明改性效果明显,为中药造粒提供了新的工艺思路。     

大连港大窑湾吹填区软基的堆载预压处理研究

结合大连港大窑湾吹填区软土地基处理具体工程,通过现场试验与监测比较详细地介绍了堆载预压方法中关于分级堆载设计、施工及监测等各方面的技术问题。通过对监测结果的综合分析,探讨了堆载预压处理过程中地表沉降、深层沉降等关键参数的变化规律及堆载级数、堆载高度与固结时间等参数之间的依赖关系,为吹填造陆地区软基处理提供了经验和依据。     

三乙胺、乙醇和水混合物分离工艺模拟与优化

以化工流程模拟软件Aspen Plus为工具,通过模拟数据与文献数据对比,确定选用SR-POLAR热力学方程模拟研究体系.利用残余曲线、蒸馏边界理论对三乙胺、乙醇和水混合液模拟分析,确定采用变压精馏技术分离共沸混合物设计方案,利用灵敏度分析对流程进行优化设计.结果表明:低压精馏塔理论塔板数为25、回流比为5,原料进料位...     

焦化废水用改性斜发沸石吸附水中氨氮的研究

研究了焦化废水用改性斜发沸石对水中氨氮的吸附行为,考察了pH值、氨氮初始浓度以及竞争阳离子等对钠型沸石吸附氨氮的影响,同时进行了钠型沸石的吸附动力学研究.