Modification on epoxy-based adhesive

This research adopted four methods to toughen epoxy adhesives. They were liquid hydroxyl group terminated polybutadiene (HTPB) rubber modification, silicon rubber modification, polyacrylate multiplicity elastomer particulates emulsion modification and chemical grafting modification. After modification, the shearing strength and the rupture elongation were tested. The interface and the chemical reaction between the modifiers and the epoxy were analyzed by scanning electron microscope (SEM) and infrared optical spectrum. The results show that the elastomer particulates modification and the chemical grafting modification can reach the better toughening effects.

传统古法与现代机制宣纸耐久性对比研究

利用QUV/SPRAY型紫外光照老化仪对传统古法和现代机制宣纸进行耐久性试验,并测试和对比老化前后两类宣纸的机械强度及颜色变化。研究结果表明:随着光照老化时间的延长,两类宣纸的机械强度下降明显,但古法宣纸的机械强度始终大于机制宣纸;从颜色变化来看,当光照老化时间小于160h时,两类宣纸的颜色变化不大,而随着光照老化时间的延长,机制宣纸的颜色比古法宣纸更稳定。

核壳共聚耐低温丙烯酸乳液涂料的制备和性能研究

通过预乳化和半连续种子乳液聚合工艺合成核/壳复合结构丙烯酸乳液,以此配制成的涂料具有良好的延弹性、裂断伸长率和抗裂性能,可在0～5℃低温下施工,可望成为性能优良的耐低温涂料。

Structure and properties of AZ31B magnesium alloy sheets processed by repeatedly unidirectional bending at different temperatures

Repeatedly unidirectional bending(RUB) was applied to the magnesium alloy sheet to improve the basal texture.The effect of RUB temperature on resulting structure and room temperature properties was investigated.The texture components of the sheet undergoing RUB at recovery temperature were similar to those of the sheet undergoing RUB at room temperature(RT).As the RUB temperature increased to above recrystallization temperature,the texture components became more disperse and the pyramidal components increased.With the increase of RUB temperature,the grain size near the surface of the sheets undergoing RUB tended to grow up.When the sheets were processed by RUB at medium-high temperature followed by annealing at 533 K,the yield strength and fracture elongation were lower than those of the cold rolled sheet;however,the Erichsen value was slightly higher than that of the cold rolled sheet.The sheet undergoing RUB at RT followed by annealing at 533 K represented the best mechanical properties.

Influence of homogenizing on mechanical properties of as-cast AZ31 magnesium alloy

Forward extrusion experiments of as-cast AZ31 magnesium alloy were conducted at different temperatures and different extrusion ratios using the as-cast billets with and without homogenizing treatment.The mechanical properties of pre-and post-extrusion of the two kinds of billets were investigated.Experimental results show that the mechanical properties of post-extrusion of the two kinds of billets all are obviously improved compared with those of pre-extrusion.The elongation of post-extrusion using the billet with homogenizing is higher than that without homogenizing,but the tensile strength is lower than that without homogenizing.When the extrusion ratio increases,the elongation and tensile strength of post-extrusion of two kinds of billets all will increase obviously.When the extrusion temperature of billet without homogenizing increases,the tensile strength of post-extrusion will decrease obviously and the elongation of post-extrusion will change to a small extent.For the billet with homogenizing,the tensile strength of post-extrusion will decrease in some sort when extrusion temperature increases.

Parametric optimization of friction stir welding process of age hardenable aluminum alloys-ANFIS modeling

A comparative approach was performed between the response surface method(RSM) and the adaptive neuro-fuzzy inference system(ANFIS) to enhance the tensile properties, including the ultimate tensile strength and the tensile elongation, of friction stir welded age hardenable AA6061 and AA2024 aluminum alloys. The effects of the welding parameters, namely the tool rotational speed, welding speed, axial load and pin profile, on the ultimate tensile strength and the tensile elongation were analyzed using a three-level, four-factor Box-Behnken experimental design. The developed design was utilized to train the ANFIS models. The predictive capabilities of RSM and ANFIS were compared based on the root mean square error, the mean absolute error, and the correlation coefficient based on the obtained data set. The results demonstrate that the developed ANFIS models are more effective than the RSM model.

Significant influence of sharp grain boundary corner on tensile elongation of copper bars with columnar grains and its mechanism

The reason why elongation of copper bars with columnar grains drops significantly after small cold-drawing was explored. The copper bars were prepared by warm-mould continuous casting. Tensile test was interrupted at various tensile strains in order to detect crack origin. Electron backscattered diffraction（EBSD） was used to analyze dislocation slip bands. It is found that the as-cast microstructure contains sharp grain boundary（GB） corners nearly parallel to the solidification direction（SD）. Elongation of the copper bars drops significantly from 68.8% in as-cast state to 18.8% in as-drawn state. It is revealed that plastic deformation becomes severer in the vicinity of sharp GB corners. Locally accumulated internal stress even activates a slip system with very low Schmid factor of 0.17. The localized plastic deformation near sharp grain boundary corner promotes crack initiation and propagation, which eventually leads to the significant drop of elongation.

In situ thermomechanical processing to avoid grain boundary precipitation and strength-ductility loss of age hardening alloys

To avoid grain boundary(GB) precipitation during aging, a new strategy of in situ thermomechanical processing for age hardening alloys was proposed. Specifically, high-density nanoscale precipitates were introduced into ultrafine grain(UFG) interiors of 7075 Al alloy by equal-channel-angular(ECAP) processing at 250 ℃ for 8 passes, thus avoiding GB precipitation. Tensile test results indicated that the UFG 7075 Al alloy exhibits superior mechanical properties(yield strength of 350 MPa, ultimate tensile strength of 500 MPa, uniform elongation of 18% and tensile ductility of 19%) compared with the UFG 1050 Al counterpart(yield strength of 170 MPa, ultimate tensile strength of 180 MPa, uniform elongation of 2.5% and tensile ductility of 7%). Fracture surface morphology studies revealed numerous homogeneous micro shear bands in necking shrinkage areas of both UFG 7075 Al and 1050 Al alloys, which are controlled by cooperative GB sliding. Moreover, the introduction of nanoscale precipitates in UFG 7075 Al matrix weakened the tendency of shear fracture, resulting in a higher tensile ductility and more homogeneous deformation. Different from the GB precipitation during postmortem aging, in situ thermomechanical treatment dynamically formed GBs after precipitation, thus avoiding precipitation on GBs.

Theoretical Study on Dihydrogen Bonds of NH3BH3 with Several Small Molecules

The dihydrogen bonds B-H...H-X （X= the complexes of NH3BH3 with HF, HCl, F, Cl, Br, C, O, N） in the dimer （NH3BH3）2 and HBr, H2CO, H20, and CH3OH were theoretically studied. The results show that formation of the dihydrogen bond leads to elongation and stretch frequency red shift of the BH and XH bonds, except that in the H2CO system, the CH bond blue shifts. For （NH3BH3）2 and the complexes of the halogenides, red shifts of the XH bonds are caused by the intermolecular hyperconjugation σ（BH）→σ^＊ （XH）. For the system of H2CO, a blue shift of the CH bond is caused by a decrease of the intramolecular hyperconjugation n（O→σ^＊ （CH）. In the other two systems, the red shift of OH bond is a secondary effect of the stronger traditional red-shifted H-bonds N-H... O. In all these systems, red shifts of the BH bonds are caused by two factors： negative repolarization and negative rehybridization of the BH bond, and decrease of occupancy on σ（BH） caused by the intermolecular hyperconjugation σ（BH）→σ^＊ （XH）.

Influence of Purity Degree on the Evolution the Mechanical Properties of Aluminium Commercial

The influence of the purity degree of the commercial aluminium on the mechanical properties： elastic stress, tensile strength, Brinell hardness, resilience and elongation at break was investigated. It was found that the first three resistance characteristics decrease with the growth of the purity of the material chosen to the detriment of two ductility characteristics that rise to the three states considered： crude of casting noted： F, Annealed noted： O, hardened noted ： H1/4. Furthermore, it is important to note that the hardened and the annealed lead respectively to a considerable hardening and a considerable softening. This hardening and this softening of the material in question can be respectively associated with the increase in dislocation density and immigration impurity elements of dislocations.

聚乙烯醇／半纤维素／纤维素纳米晶复合膜的制备和性能

通过碱解醇沉法从玉米芯中提取半纤维素,进而采用溶液共混流延法制备出不同比例的聚乙烯醇(PVA)/半纤维素共混膜,在此基础上加入通过硫酸水解脱脂棉制备的纤维素纳米晶(NCC),制备了NCC增强的复合膜.DSC、TGA、FTIR、SEM和薄膜拉伸等研究表明,复合膜的各组分间形成了氢键作用,相容性良好.在PVA/半纤维素共混膜中,半纤维素的加入大幅度提高了复合膜的断裂伸长率:当PVA与半纤维素质量比为3∶1时,复合膜的断裂伸长率高达380%,比纯PVA的140%增加了1.7倍,而拉伸强度仍能保持在较高的水平;纤维素纳米晶的加入,还可改善复合膜的韧性;半纤维素对PVA组分的结晶性能产生了影响,而刚性结构的NCC则对PVA的结晶起抑制作用.此外半纤维素和NCC的引入也提高了复合膜的热性能,使第二阶段分解速率峰的温度提高了约50℃.

Rational design of sustainable polyurethanes from castor oil: towards simultaneous reinforcement and toughening

Sustainable polyurethanes prepared from castor oil and diisocyanates show very low strength and toughness, due to the highly cross-linked and flexible structure. Herein, we report a new strategy to simultaneously reinforce and toughen castor oil-based polyurethane via incorporating a stiff component （isosorbide, IS） to enhance network stiffness and reduce crosslink density. The crosslinking degree de- creases while the strength, moduli, ductility and heat re- sistance significantly increase accordingly with increasing IS content. The tensile behaviors are tunable over a broad range （either as elastomers or as plastics） depending on the com- positions. The polyurethanes show excellent thermal stability with onset decomposition temperature higher than 280℃. The investigation provides a new hint for future design and fab- rication of high performance sustainable polymers from other vegetable oils.

Microstructural evolution in 35CrMnSi steel during multi-cyclic quenching and partitioning heat treatment

A novel method,i.e.multi-cyclic quenching and partitioning(M-Q-P)heat treatment,is used to tailor the content of retained austenite(RA)in commercial steels.For 35CrMnSi steel,5 times of Q-P heat treatment can increase the content of RA from 8vol.%to 17 vol.%.As a result,the ultimate elongation of the steel is improved from 17.4%after the typical Q-P heat treatment to 27.1%after 5 times of Q-P treatment.Meanwhile,the improved combination of strength and ductility for steels by typical Q-P heat treatment is retained by the multi-cyclic Q-P heat treatment.It is shown that the content of RA in some specific steels,and furthermore their mechanical properties,can be regulated through the M-Q-P.