壁厚对HR2钢柱壳爆轰加载下膨胀断裂行为的影响

通过对6、12 mm两种不同壁厚的HR2钢柱壳进行爆轰加载实验,对其断裂碎片的宏观形貌、断口的微观形貌以及横截面的变形微观结构进行系统表征,研究了金属柱壳在爆轰加载下的膨胀断裂机理。结果表明,在膨胀断裂过程中壳壁厚度的增大导致HR2钢柱壳由纯剪切断裂变为拉剪混合的断裂模式。断裂碎片的微观结构分析结果表明,柱壳的断裂实际上是剪切裂纹从样品内部剪切带形核并扩展、和拉伸裂纹沿柱壳外表面的形核扩展的共同作用及竞争的结果。薄壁柱壳断裂由样品内裂纹沿剪切带的形核和扩展主导发生剪切断裂,而厚壁柱壳中内侧的裂纹沿剪切带的形核和扩展,但是最外侧则为环向拉应力主导发生拉伸断裂,因此表现出拉剪结合的断裂模式。     

制备工艺对Ag/SnO2材料力学性能的影响

采用粉末冶金和反应合成两种工艺制备了Ag/SnO2电接触材料,分析了两种工艺对显微组织的影响,发现反应合成法制备的Ag/SnO2材料经热挤压后,SnO2颗粒呈纤维状排列,颗粒细小,分散均匀,与基体浸润良好.断裂拉伸测试和分析表明,粉末冶金法制备的Ag/SnO2材料的拉伸断口形貌由许多互相连接的撕裂棱和韧窝组成,表现为韧断;而反应合成法制备的断口形貌韧窝更加细小,显示出近脆性断裂特征.最后比较了两种方法制备的Ag/SnO2材料的抗拉强度、延伸率、硬度等力学性能.     

Double-phase morphology of high molecular weight poly(methyl methacrylate)-epoxy blend

The double-phase morphology of 5 wt% high molecular weight poly(methyl methacrylate) (PMMA) modified epoxy system was investigated by optical and scanning electron microscopic (SEM) techniques. PMMA-epoxy blend cured at 100 °C revealed that a bicontinuous secondary phase separation was observed in both epoxy and PMMA phases in the early stages of curing. Epoxy-rich particles were dispersed in the PMMA-rich phase, while PMMA-rich particles were segregated in the epoxy-rich phase, leading to double-phase bicontinuous morphology. The spinodal decomposition mechanism could probably be responsible for this secondary phase separation. From the SEM analysis, a morphology consisting of a rough striated continuous phase along with large smooth regions was observed. Rough striated domains are ascribed to the PMMA-rich phase and the smooth domains are assigned to the epoxy-rich phase, thus confirming the secondary phase separation. The PMMA-epoxy blend showed a slight increase in flexural properties and about 20% improvement in the fracture toughness.     

带有环氧基的反应型聚丙烯酸酯乳液的合成及表征

以甲基丙烯酸甲酯、丙烯酸-2-乙基己酯和甲基丙烯酸缩水甘油酯等为单体,制备了以PMMA-BA为"核"、PEHA-GMA为"壳"的微相复合乳液.利用透射电镜和激光动态光散射对乳胶粒子的形态和粒径分布进行了表征.研究了乳液聚合物和乳液与水溶性脲醛树脂共混物经不同温度热处理后的物理性能.结果表明,合成乳液的乳胶粒子具有预期的核-壳结构,粒度分布窄,平均粒径为132 nm;乳液聚合物和乳液与脲醛树脂共混物均随着热处理温度的升高,玻璃化转变温度升高,拉伸强度增大,断裂伸长率变小,吸水率降低.     

Toughened carbon/epoxy composites made by using core/shell particles

Toughened epoxy resin composites have been prepared by resin-transfer moulding by using a range of toughening agents. Two types of epoxy-functional preformed toughening particles were investigated and have a three-layer morphology in which the inner core is crosslinked poly(methyl methacrylate), the intermediate layer is crosslinked poly(butyl acrylate) rubber and the outer layer is a poly[(methyl methacrylate)-co-(ethyl acrylate)-co-(glycidyl methacrylate)]. The presence of glycidyl groups in the outer layer facilitates chemical reaction with the matrix epoxy resin during curing. Comparisons were made with acrylic toughening particles that have a similar structure, but which do not have the epoxy functionality in the outer shell, and with a conventional carboxy-terminated butadiene acrylonitrile (CTBN) liquid rubber toughening agent. The composites were characterised by using tensile, compression and impact testing. The fracture surfaces and sections through the moulded composites were examined by means of optical and scanning electron microscopy. Short-beam shear tests and fragmentation tests were used to investigate the interfacial properties of the composites. In general, use of the epoxy-functionalised toughening particles gave rise to superior properties compared with both the non-functionalised acrylic toughening particles and CTBN.     

聚砜改性环氧树脂共混体系相结构的控制

研究了双官能团环氧树脂（Ｅ５１，Ｅ３９）与聚砜（ＰＳＦ）共混体系，在用二氨基二苯基砜（ＤＤＳ）固化时相分离结构的控制，在反应初期为均相体系，随固化反应的进行，环氧的分子量增大，体系发生相分离，相差异微镜观察的结果表明，温度较低时相分离进行缓慢，遵循旋节相分离的机理，利用这一特点，在低温进行共混物预固化，调控反应程度，在环氧树脂达到不同的分子量时再行固化，电子显微镜（ＳＥＭ），红外（ＦＴＩＲ）分析，     

Synthesis and characterization of core–shell nanoparticles and their influence on the mechanical behavior of acrylic bone cements

Core–shell nanoparticles consisting of polybutyl acrylate (PBA) rubbery core and a polymethyl methacrylate (PMMA) shell, with different core–shell ratios, were synthesized in order to enhance the fracture toughness of the acrylic bone cements prepared with them. It was observed by TEM and SEM that the core–shell nanoparticles exhibited a spherical morphology with ca. 120 nm in diameter and that both modulus and tensile strength decreased by increasing the PBA content; the desired structuring pattern in the synthesized particles was confirmed by DMA. Also, experimental bone cements were prepared with variable amounts (0, 5, 10 and 20 wt.%) of nanoparticles with a core–shell ratio of 30/70 in order to study the influence of these nanostructured particles on the physicochemical, mechanical and fracture properties of bone cements. It was found that the addition of nanostructured particles to bone cements caused a significant reduction in the peak temperature and setting time while the glass transition temperature (T_g) of cements increased with increasing particles content. On the other hand, modulus and strength of bone cements decreased when particles were incorporated but fracture toughness was increased.     

稀土元素对原位合成TiB_2/Al复合材料组织和性能的影响

采用原位合成法研究稀土元素Ce,Sc,Er对TiB_2/Al复合材料TiB_2颗粒和基体组织的影响,并对复合材料的拉伸性能进行分析。结果表明,稀土元素的添加显著改善了复合材料的组织和性能。添加0.3%(质量分数)Sc和Er的复合材料的TiB_2颗粒分布相对均匀,稀土元素Er对基体合金的组织细化效果最显著,其次是Sc。添加稀土Sc和Er元素的复合材料拉伸强度较好,分别提高了32%和31%,添加稀土Er元素的复合材料伸长率最佳,提高了85%,因此,其拉伸性能也最佳。添加稀土元素Sc和Er后,复合材料的断裂形式为微孔聚集型的韧性断裂。稀土元素对复合材料的作用机理表现在两方面:一是稀土元素的添加改善了复合材料的润湿性,并抑制了TiB_2颗粒的团聚;另一方面,稀土元素的添加使得基体合金组织细化,从而提高了复合材料的拉伸强度。     

聚合物共混初期形态结构发展的研究进展

就国外近期研究内容,介绍了熔融共混过程初期的形态结构发展模式。在聚合诉共混初期,分散相首先先形成片状物（带状物）,进而在剪切力场作用下碎裂成球形粒子,完全熔融以后,粒径变化很小;此模式对反应性体系和非反应性体系均适合。对于弹性体含量低的橡塑共混体系,在共混初期弹性粒子首先成为连续相,可用一“四阶段”相反转模式;对于反应性体系,此模式不会发迹但是相反转延迟发生,并伴有转矩增大现象。     

Predicting Effective Elastic Moduli and Strength of Ternary Blends with Core–Shell Structure by Second–Order Two–Scale Method

Core–shell particle–filled PA6/EPDM–g–MA/HDPE ternary blend has excellent mechanical properties. In this paper, effective elastic properties and tensile yield strength of the ternary blend are predicted by the second–order two– scale method, to investigate the relationship between morphology and mechanical properties. The method and the limit analysis for predicting mechanical properties of random heterogeneous materials are briefly introduced. Realistic morphology of the ternary blend including both core–shell particles and pure particles is simulated, and finite element mesh is generated. The unified strength theory is embedded in the method for the convenience of selecting a suitable yield criterion. The effective elastic moduli and tensile yield strength predicted by the method in this paper are compared with analytical and experimental results. Finally, effect of shell thickness in the core–shell particles on the effective elastic moduli and tensile yield strength is investigated.     

Effects of microstructure on crack tip fields and fracture toughness in PC/ABS polymer blends

Numerical simulations are performed in order to gain a better understanding of the effects of various microstructural features and toughening mechanisms in amorphous PC/ABS polymer blends. Crack tip loading under global small-scale yielding conditions is considered with the blend microstructure explicitly resolved in the near-tip process zone. Constitutive models are employed which account for large visco-plastic deformations, the characteristic softening- rehardening behavior of glassy polymers, as well as the effect of plastic dilatancy in the ABS phase due to rubber particle cavitation. The influence of blend composition and morphology on the local stress distribution and the development of the plastic zone at a stationary crack tip are analyzed. Furthermore, crack propagation and the evolution of fracture toughness are studied using different cohesive surface models for failure in the different phases of the blend microstructure.     

The effects of phase morphology and adhesion between phases on fracture of ethylene-vinylalcohol copolymer/nylon 6/12 copolymer blends

The effects of phase morphology and the adhesion between phases of ethylene-vinylalcohol copolymer(EVOH)/nylon 6/12 copolymer blends on the fracture properties were estimated. Films of the blends which were obtained by extrusion processing showed different phase morphologies depending on the composition of the nylon 6/12 copolymer. The morphology of the partially miscible blend (EVOH and nylon 6f-nylon121-f where f=0.8) was needle-like in appearance. On the other hand the immiscible blend (EVOH and nylon 6f-nylon121-f where f=0.5) had equiaxed particles of nylon 6/12. The plastic deformation of films of the blends was observed using transmission electron microscopy. Deformation zones were observed for both blends but extensive debonding of particle interfaces was observed in the immiscible blend system. These observations are reinforced by our measurements of the interfacial fracture energy, Gc, between EVOH and nylon 6f-nylon121-f made using a double cantilever beam test. Gc decreases monotonically as 1–f increases. The fracture toughness of the partially miscible blend film measured at low temperature (–80°C) was higher than that of EVOH alone and there was fractographic evidence of a larger crack tip plastic deformation zone. In contrast, the fracture toughness of the immiscible blend was lower than that of EVOH and there was fractographic evidence of extensive debonding of the second phase nylon particles. This result suggests that it is important to have good adhesion between phases to achieve the optimum fracture toughness of these polymer blends. © 1998 Chapman & Hall     

Epoxy modified with triblock copolymers: morphology, mechanical properties and fracture mechanisms

The morphology, fracture toughness and mechanical properties of an anhydride-cured diglycidylether of bisphenol-A epoxy polymer modified with poly(methyl methacrylate)-b-poly(butylacrylate)-b-poly(methyl methacrylate) (MAM) have been investigated. The addition of three different MAM triblock copolymers (M22N, M52N and M52) to the epoxy polymer gives two different microstructures. A nanostructure with well-dispersed worm-like micelles (or a bicontinuous gyroid structure if the micelles are connected into a network) was obtained using M22N. The addition of M52N or M52 gives dispersed micron-size particles in the epoxy matrix for ≤7 wt% MAM, and a co-continuous microstructure at higher MAM contents. These triblock copolymers toughen the epoxy polymer significantly, with only slight reductions in the mechanical and thermal properties of the epoxy polymer. The maximum values of fracture toughness and fracture energy (1.22 MPa m^1/2 and 450 J/m², respectively) were measured using 12 wt% M22N, which is an increase of 100 and 350%, respectively, compared with the unmodified epoxy. The M52- and M52N-modified materials show a maximum toughness when a co-continuous microstructure is formed. The potential toughening mechanisms are identified and discussed.     

紫外光固化导电胶的制备及固化动力学机制

为研究紫外光固化导电胶的性能及固化机制,以银包铜粉、环氧丙烯酸树脂为原料制备固化胶,采用刮涂法将浆料涂覆到载玻片上,置于紫外光下固化获得导电涂层。对试样的微观结构、力学和电学性能进行表征,对固化体系的热行为及固化反应动力学机理进行了研究,并利用Kissinger和Grane模型计算固化反应的活化能和反应级数。研究结果表明:光辐射下导电胶层可快速固化;当填料含量为70wt%时,浆料达最低电阻率1.122mΩ·cm;填料含量75wt%时剪切值最大为57.4MPa;活性稀释剂含量为35wt%时,浆料具有最佳的固化速度和网联结构;固化反应过程中表观活化能为15.17kJ/mol,固化工艺为172.3℃→302.05℃→369.35℃,为一级固化反应;浆料在200℃以下具有较好的抗氧化性能。     

Micromechanism of failure of thermoplastic rubber

The fracture surface morphology of various thermoplastic rubber and rubber vulcanizates based on natural rubber (NR), ethylene propylene diene rubber (EPDM), nitrile rubber (NBR), polyethylene (PE) and polypropylene (PP), namely NR-PE, NR-PP, EPDM-PE, EPDM-PP and NBR-PP, has been studied over a range of blend ratios, levels of interaction, rates, temperatures and modes of testing. The fracture surface changes with changes in blend ratio. Incorporation of a third component like EPDM or chlorinated polyethylene (CPE) to a certain percentage does not change the fracture morphology. Sulphur curing in the NR-PE blend generates a ductile matrix like rubber whereas large fissures are observed for peroxide-cured systems. Modification of both rubber and plastic also changes the surface morphology. The samples tested at various temperatures, rates and modes show similar features on the fracture surface.     

Toughening of polystyrene by natural rubber-based composite particles: Part I Impact reinforcement by PMMA and PS grafted core-shell particles

This work was focused on the influence of the morphology of composite natural rubber (NR)-based particles on the toughness of polystyrene (PS). Emulsion polymerization processes were used to adjust the microstructure of the latex particles. In order to be suitable for the reinforcement of PS, the NR-based particles were coated with a shell of crosslinked polymethyl methacrylate (PMMA) or PS. Furthermore, PS subinclusions were introduced into the natural core. A continuous extrusion process was adapted for the incorporation of these natural rubber based impact modifiers into thermoplastics. High deformation speeds (impact testing) were necessary in order to evaluate the mechanical properties of PS blends with a series of the prepared structured latexes. PS could only be toughened by core-shell particles. A PMMA shell proved to be advantageous because it is easier to produce by emulsion polymerization than a hydrophobic PS shell. Pre-vulcanized NR-based particles, which do not cavitate easily, were ineffective. Core-shell particles based on NR-containing PS subinclusions toughened PS more effectively. Solid NR particles caused premature craze and polymer fracture, as the rubber particles break down, debond from the matrix and form large voids at the craze/particle interface. Scanning electron microscopy (SEM) of Izod fracture surfaces showed clearly the cavities of debonded solid rubber particles and demonstrated that subinclusions within the rubber core permitted a larger volume of plastic deformation before failure. This revised version was published online in November 2006 with corrections to the Cover Date.     

云母粉表面改性提高云母纸拉伸强度的研究

利用硅烷偶联剂"分子桥"作用对云母粉进行表面处理,通过自乳化改性的环氧树脂和聚丙烯酰胺,使云母粉表面桥联的环氧基团发生交联反应,显著提高云母纸拉伸强度。结果表明:当硅烷偶联剂、改性环氧树脂、聚丙烯酸胺的质量分数分别为0.5%、1.0%、0.5%时,云母纸拉伸强度由72.17 N/m提高到151.3 N/m。硅烷偶联剂水解产生的硅羟基与云母表面的羟基发生化学键的结合,另一端的氨基与改性环氧树脂中的环氧基团反应,增强了改性环氧树脂对云母表面的结合力。     

PSF/环氧共混基体体系增韧机理研究

通过对PSF/环氧共混体系剥离强度、DMA 及SEM 断口图象的分析研究, 揭示了共混体系相结构演变与脆韧转变的对应关系和增韧机理。研究表明, 当共混体系形成较均匀完整的PSF 连续网膜包覆环氧球粒分散相结构,并且网膜厚度小于0. 04 Lm 时, 体系呈现高韧性, 此时体系由断面上高韧性的PSF 网膜产生大量的塑性变形吸收能量而使体系增韧, 不同于传统“海岛结构”的增韧结构和机理, 研究结果对开发高韧性先进复合材料基体和结构胶粘剂具有重要意义。     

Toughening of polystyrene by natural rubber-based composite particles: Part II Influence of the internal structure of PMMA and PS-grafted core-shell particles

This work was focused on the influence of the internal structure of natural rubber (NR)-based core-shell particles on the toughness of polystyrene (PS). Several emulsion polymerization processes were used to control the degree of grafting of the NR phase and the site of polymerization, which determines the final morphology of the prepared composite NR-based particles. PS subinclusions were introduced into the NR core in order to determine their influence on the deformation behaviour of PS. A continuous extrusion process was adapted for the direct feeding of the wet NR-based latexes into the molten PS matrix. Impact testing indicated that core-shell particles based on NR containing a large number of small crosslinked PS subinclusions toughened PS most effectively. A very effective toughening agent is obtained if a hard shell of 25 wt% crosslinked PMMA surrounds the composite rubber particle. Grafting of NR chains during the subinclusion synthesis has to be avoided since a high rubber particle modulus is detrimental for craze nucleation in PS. From the fracture surface morphology the craze nucleating and stabilizing efficiency of composite NR particles having different morphologies or grafting degrees could be deduced. This revised version was published online in November 2006 with corrections to the Cover Date.     

多孔壳微胶囊对硬化砂浆抗渗性的影响

采用原位聚合与水解缩聚法,以四乙氧基硅烷（TEOS）、环氧树脂（E51）、苯乙烯（St）等为主要原料,合成了一种二氧化硅多孔壳微胶囊（Porous silica shell microcapsules,PSSM）。分别采用SEM、FTIR、TGA对PSSM外观形貌、化学组分、核壳比进行表征。通过对掺加PSSM的砂浆试块进行80%抗压强度荷载预压、养护（浸水或干湿循环养护）处理后,运用交流阻抗法与压汞法研究了PSSM对硬化砂浆抗渗性与孔结构的影响规律。结果表明:制备的PSSM粒径约为10~100 μm,其含有聚苯乙烯网络支架、环氧树脂和聚硅氧烷囊芯,支架聚合物和多孔壳,核壳质量比为1.54。与未预压-养护处理的试块相比,经预压-养护处理后的空白试块的连通孔溶液电阻R_CH和扩散阻抗系数σ均降低,孔隙率升高,表明预压使试块内形成微裂纹缺陷,经养护仍未愈合,因此试块抗渗性降低;而对于掺加8% PSSM的试块,经预压-养护处理后其R_CH和σ均增加,孔隙率降低,表明试块抗渗性提高。这是由于PSSM的破壳-固化作用以及长期浸水或干湿循环养护,导致试块中PSSM发生了渗出-固化作用,封堵愈合了试块内的微裂隙,抗渗性得到提高。