Cavitation Instabilities in Plastics and Rubber-Modified Plastics

Spherical void expansion in plastics and rubber-modified plastics is investigated under radial traction conditions. The plastics are modeled as elastic-plastic pressure-sensitive materials and the rubbers are modeled as nonlinearly elastic materials. First, the growth of a spherical void in an infinite plastic matrix is investigated under remote radial traction conditions. The results show that the cavitation stress of the plastic decreases significantly as the pressure sensitivity increases. Then, the growth of a spherical void located at the center of a spherical rubber particle in an infinite plastic matrix is investigated under remote radial traction conditions. The results indicate that without any failure criteria for the rubber, the cavitation stress does not exist when the void is small and the rubber is characterized by high-order strain energy functions. However, when a failure criterion for the rubber is considered at a finite stretch ratio, the results show that the cavitation stress for the plastic with the rubber particle becomes close to that for the plastic without the rubber particle. This revised version was published online in August 2006 with corrections to the Cover Date.     

Factors affecting the shelf-life of precooked chilled roast pork

The microbiological, sensory and physicochemical changes in precooked chilled pork were measured over 8 days storage at 1°C and 5°C. Microbial growth was limited, but marked sensory and physicochemical changes occurred within the 5-day period currently recommended as the maximum storage time in the DHSS guidelines on precooked chilled foods (DHSS, 1980). At 1°C, marked toughening occurred after only 1 day; whilst at 5°C adverse flavour and odour changes were noticeable by the fourth day of storage. The amount of volatile compounds, especially n-hexanal, stripped from the pork increased significantly over the 8-day storage period, particularly at 5°C.     

动态应变时效对奥氏体不锈钢静拉伸强度的影响

本文研究了动态应变时效(DSA)对18—8型奥氏体不锈钢静拉伸性能的影响。结果表明,(1),在 DSA 发生的温区,强度与温度关系曲线上出现流变应力平台(2),室温屈服强度随DSA 预处理温度升高和预应变量增加而提高,DSA 预处理具有比冷变形处理更佳的强化效果,且经873K 预处理后的室温强度达最大值,而塑性不下降.电镜观察结果报好地解释了这种 DSA强化的机理。同时表明,DSA 有可能作为一种强韧化工艺应用于生产实际。     

现代混凝土增韧防裂原理及应用

从水泥基体和增强纤维两个方面综述混凝土增韧防裂的原理,分析增韧防裂技术的影响因素和作用效果,介绍了典型应用工程。从分子、微观和细观三个层次,阐述了纳米材料、有机高分子材料和聚合物对水泥基体增韧的作用机制。从纤维 基体界面作用力、裂缝形成和非稳态扩展抑制等方面,论述纤维种类和特性对混凝土硬化前后阶段增韧防裂的作用规律。基体增韧与纤维增韧相结合,能够提高混凝土的抗拉强度、拉伸应变和断裂能,并有效降低裂缝宽度,抑制裂缝扩展。     

芳纶纤维/环氧树脂预浸料界面相容性的方法探究

预浸料要求树脂基体和增强纤维具有良好的匹配性,为了提高芳纶纤维/环氧树脂预浸料的界面相容性,本文从芳纶纤维表面改性及增韧技术两个方面进行综述,讨论了芳纶纤维物理改性和化学改性方法的优缺点,分析了界面增韧及环氧树脂基体的不同增韧途径,重点介绍了聚氨酯/环氧树脂互穿网络体系.认为芳纶纤维的偶联剂表面处理和聚氨酯增韧环氧树脂相结合,是提高芳纶纤维/环氧树脂预浸料层间剪切强度的的可行途径.     

混凝土修复用抗紫外改性异佛尔酮二胺

以液体双酚A环氧树脂为基体,采用腰果酚和甲醛对异佛尔酮二胺(IPDA)固化剂进行改性.结果 表明:在腰果酚、甲醛和IPDA的质量比为1.0∶1.1∶1.2,反应时间为3h,反应温度为90℃的条件下,改性IPDA固化剂性能最优;改性IPDA固化剂不仅符合混凝土路面修复的力学性能要求,还大幅提高了其抗UV老化性能.     

回收轮胎粉反应增韧PVC性能的研究

将甲基丙烯酸缩水甘油酯(GMA)、丙烯酸(AA)、马来酸酐(MAH)3种不同单体分别通过开炼机剪切加入废旧轮胎粉(GRT)后与聚氯乙烯(PVC)直接反应挤出,制备了3种PVC/GRT复合材料。利用万能电子试验机测定了材料的力学性能,实验结果表明:3种不同单体修饰的GRT/PVC复合材料中PVC/GRTg-GMA复合材料韧性提高显著,在GRT用量为5 phr,GMA、St、DCP用量分别为4、4、0.15 phr时,PVC/GRT复合材料缺口冲击强度提高25.6%。扫描电镜结果显示GMA的加入改善了界面相容性。     

高光泽高玻璃纤维含量增强增韧PA6复合材料的开发

研究了不同螺杆组合和增韧剂种类、用量对玻璃纤维(GF)增强尼龙(PA)6复合材料性能的影响.结果表明,当使用复配增韧剂体系、控制材料中GF长度为0.3～0.6 mm和使用塑化、剪切适当的螺杆组合时,可制得GF质量分数为50%、拉伸强度为205 MPa、缺口冲击强度为26 kJ/m2、低温(-30℃)缺口冲击强度为22 kJ/m2、注射成型制品表面无浮纤、光泽度高的PA6复合材料.     

导热环氧灌封胶的研制

以环氧AG-80为主体树脂,端羧基液体丁腈橡胶与1,6-已二醇二缩水甘油醚的反应产物为活性增韧稀释剂,纳米AlN为导热填料,缩胺-105为固化剂制备导热灌封胶。实验结果表明,每100份环氧树脂中活性增韧稀释剂为20份时,灌封胶的力学性能、耐热性能良好;纳米AlN的质量分数为12％,灌封胶的热导率达到0．85W／m·k,可满足使用要求。     

酯交换反应制备端羟基聚氨酯预聚物的研究

本文介绍了二苯基甲烷二氨基甲酸酯与聚酯多元醇的酯交换反应,考察了催化剂、温度、时间对反应的影响,合成了分子量达21500的羟基封端的聚氨酯预聚体,并将该预聚物用于环氧树脂灌封胶中,收到良好的增韧效果。