填充环氧树脂界面残余应力研究——Ⅲ.界面残余应力的热行为

本文针对橡胶填充环氧树脂体系和玻璃珠填充环氧树脂体系,研究了界面残余应力的退火效应和温度变化行为。样品的残余应力与退火时间有关。温度与界面残余应力成线性反比关系。在两体系中,界面残余应力随温度升高而下降的速度不相同。     

填充环氧树脂界面残余应力研究 Ⅴ.界面应力集中及残余应力的影响

本文针对橡胶和玻璃珠填充环氧树脂体系,通过显微光弹法测定填充粒子的界面应力集中系数,发现橡胶填充体系的应力集中发生在粒子赤道处,而玻璃珠体系发生在粒子两极。在低拉伸时,界面残余应力对应力集中的影响较大,但在高拉伸,特别是达到材料伸长率时,界面残余应力的作用可忽略。     

填充环氧树脂界面残余应力研究 Ⅱ.影响界面残余应力的因素

本文针对橡胶改性环氧树脂体系和玻璃珠改性环氧树脂体系,研究了影响界面残余应力的因素.填料的粒径不影响界面残余应力的测量.界面键合强弱的影响在两体系中不相同.     

填充环氧树脂界面残余应力研究——Ⅳ.界面残余应力形成的分子机理

本文针对橡胶改性环氧树脂体系,从微观分子运动角度对界面残余应力形成原因进行了初步探索,发现复合材料界面残余应力的生成是界面处分子运动不平衡所导致的。同时界面残余应力有效体积是一个重要参数,它和材料温度以及界面键合强弱有关。     

固化降温速率对环氧复合材料性能的影响

通过重点关注氧化铝(Al2O3)填充环氧树脂(EP)的固化冷却过程,并通过内应力在线监测分析了不同降温速率下EP体系的残余应力,系统研究了不同降温速率对EP体系力学性能的影响.结果 表明,选择合适的降温速率对提高EP制品质量有重要意义.     

用应力跟踪测试仪测量环氧树脂的残余应力

介绍了我们研制的应力跟踪测试仪,并用它测量了环氧树脂在固化过程和降温冷却过程中的残余应力.     

环氧树脂基固体浮力材料的研制及表征

采用空心玻璃微珠填充环氧树脂研制固体浮力材料。间苯二胺 (MPD)、顺丁烯二酸酐 (MA)、二氨基二苯砜(DDS)及 593四种固化剂对比研究表明,MPD和DDS环氧树脂固化体系轴向压缩强度可达 210MPa。γ 氨丙基三乙氧基硅烷(KH—550)偶联剂在无机玻璃微珠与有机环氧树脂的复合过程中,可增加环氧树脂与微珠之间的亲合,电镜照片观察到微珠与环氧树脂间无界面沟隙,粘结界面均匀。空心玻璃微珠质量填充量为 25%时,复合材料密度降低至 0. 61g/cm3,轴向压缩强度仍能保持在 40MPa以上。     

环氧树脂塑封过程残余应力研究

利用Moldfl ow和Ansys对环氧树脂塑封过程进行模拟,并且用应力偏光仪获得应力条纹,然后与模拟结果进行对比。结果表明,环氧树脂热固性塑料在完成塑封后,其残余应力基本呈均匀分布。然而由于条带和塑封体热膨胀系数不同,在条带和塑封体接触部位会形成应力集中。并发现塑封体的残余应力和塑封体与条带接触部位的最大残余应力会随着保压压力的增大呈线性降低趋势。残余应力的降低不仅能够保证尺寸精度,而且塑封件在使用时还能减少塑封体与条带开裂的可能性。     

不同界面形态聚晶金刚石复合片热残余应力分析

聚晶金刚石复合片（Polycrystalline Diamond Compact,简称PDC）钻头因具有极高的耐磨性、抗冲击韧性以及锐利的切削刃,在地质和石油钻探中受到了广泛的应用。但目前国内外油田钻探中所使用的复合片有80%的非正常失效断裂是由于PDC的残余应力致裂及界面结构问题引起的,热残余应力是造成PDC非正常失效的主要因素。文章根据PDC制造过程中的热力学工艺条件,对平面界面及其他几种典型不规则界面的PDC热残余应力作详尽的数值计算和分析比较,对PDC热残余应力的分布规律作深入研究。研究结果表明,界面形态与热残余应力的大小及其分布规律密切相关,不同界面形态热残余应力大小和分布均不相同,并提出了优化PDC界面结构、有效降低界面残余应力的措施。这对提高PDC生产合格率及使用寿命具有重要意义。     

固化环氧树脂中残余应力的研究

环氧树脂等热固性树脂中的残余应力是由固化时树脂的体积收缩,不同材质热膨胀系数的差异以及聚合物树脂本身的粘弹性本质所引起的。残余应力可以用应力松驰法、电阻应变丝法、逐步除层法和光弹技术来测定。针对其产生原因。在工艺上可通过降低官能团浓度,加入增韧剂和无机粉状填料,改进固化工艺等办法来消除残余应力。同时也探讨了利用膨胀性单体来根本消除残余应力的方法。     

Influence of network chain orientation on the mechanical property of epoxy resin filled with silica particles

When tensile stress was applied to epoxy resin filled with silica particles, we expected that the stress concentration would occur in the epoxy matrix near the interface between the matrix and the silica particles. We investigated the plastic deformation of the network chains near the interface, which was quantitatively evaluated using a polarized microscope FTIR technique. A biphenol‐type epoxy resin, which has a mesogenic group in the backbone moiety, was used as the matrix resin. As a result, reorientation of the network chains along the direction of the tensile stress near the interface with the silica particles was observed. Especially when the silica/matrix interface has good bonding properties, the reorientation of the network chains was observed at a larger area around the silica particles. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 787–794, 2003     

Residual stress in particulate epoxy resin by X-ray diffraction

Residual stress in particulate epoxy resin was investigated by X-ray diffraction. Microdeformation of incorporated Al and α-SiO₂ crystal, which was induced by the residual stress, could be detected as a shift of X-ray diffraction peak. The residual stress at the interface between the adherend and the particulate epoxy resin was found to decrease with the increase of volume fraction of filler. It was shown that the difference in the thermal expansion coefficients between the adherend and the particulate epoxy resin is much more effective on residual stress than the increment of Young's modulus owing to the incorporation of filler. When epoxy resin was cured on the Al plate, incorporated particles were subjected to a tensile stress; while cured on polytetrafluoroethylene sheet, particles were subjected to a compressive stress. The incorporation of some inorganic particles is considered effective to reduce the residual stress.     

动态固化聚丙烯／马来酸酐接枝聚丙烯／滑石粉／环氧树脂复合材料研究

将动态硫化技术应用于热塑性树脂／填料／热固性树脂复合体系，制备了动态固化聚丙烯(PP)／马来酸酐接枝PP(PP-g-MAH)/滑石粉(Talc)／环氧树脂(EP)复合材料。研究了动态固化PP／PP-g-MAH/Talc／EP复合材料的界面作用、形态结构、力学性能以及热稳定性。实验结果表明：PP／PP-g—MAH的加入，可明显增加PP/Talc复合材料的界面作用。在动态固化PP／PP-g-MAH/Talc／EP复合材料中，PP和Talc两相界面更加模糊，动态固化EP进一步增加了PP和Talc间的界面作用。当EP的用量超过5份时，部分EP呈颗粒状分布在PP基体中。与PP／PP-g-MAH/Talc／EP和PP／PP-MAH-Talc／EP复合材料相比，动态固化PP／PP-g-MAH/Talc／EP复合材料的冲击强度、拉伸强度和弯曲模量均有明显提高。当EP用量超过5份时，复合材料的冲击强度和断裂伸长率明显降低，但拉伸强度和弯曲模量继续增加。热分析表明动态固化PP／PP-g-MAH/Talc／EP复合材料具有较高的热稳定性。     

Interfacial stress concentration and the effect of residual microstress on tensile fracture in filled epoxy resins

Interfacial stress concentrations in rubber-filled epoxy resin and glass bead–filled epoxy resin systems were studied by a photoelastic method. We found that the stress concentration is independent of the applied stress and the particle size, but decreases with increasing chemical bonding at the interface between rubber and matrix. For the rubber-filled system, stress concentration is present at the equator of particles, while for either the untreated or treated glass bead-filled system, it is on the two poles. The effect of interfacial residual microstress on tensile fracture was studied, and results showed that the function of residual microstress is limited as tensile elongation increases.     

Adhesive Strength of Deformed Epoxy and Polyester Coatings

The adhesive strengths of a soft, ductile polyester paint and a stiff, brittle epoxy resin on metal substrates equibiaxially strained to different levels were investigated by pull-off testing. The stress state in the samples after straining was estimated from relaxation tests on unsupported films. It was found that the epoxy behaved elastically at low strains and plastically at higher strains, whereas the polyester responded plastically at all levels of imposed strain. The pull-off stress of the polyester decreased strongly with increasing strain, indicating the formation of defects at the interface. No influence of the elastic strain in the epoxy coating on the pull-off stress could be detected. In both the epoxy and the polyester the location of failure moved towards the interface with increasing strain. After the onset of interfacial failure, the increase in area fraction interfacial failure with strain was found to proceed similarly in both materials.     

Delamination mechanism of high‐voltage coil insulators made from mica flakes and thermosetting epoxy resin

To clarify the delamination mechanism of high‐voltage coil insulators made from mica flakes and epoxy resin due to static mechanical stress, the relationships between the shear strength of the insulator and the physical properties of the component materials were studied. The mechanism of their delamination was thought to be either a lack of epoxy resin between the mica flakes, interface failure between the mica flakes and the epoxy resin, or cleavage of the mica flakes. The first two mechanisms were discounted because the shear strength of the insulator was found to be independent of both the contact angle of the corresponding liquid epoxy resin on the mica flakes and the critical surface tension of the epoxy resin. Furthermore, the shear strength of the model insulator was improved by using an epoxy resin with a higher bending elastic modulus, implying that the delamination mechanism in this system is the cleavage of mica flakes. Therefore, the epoxy resin should have a high elastic modulus to ensure high delamination resistance, that is, the temperature to which the insulators are exposed should be lower than the glass transition temperature of the corresponding epoxy resin. Optical microscope studies also supported these results. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2164–2169, 2001     

Calendar of events

Printed circuit boards are subject to increasingly hostile environment, for example, to a higher reflow temperature with the new lead-free solders. Consequently, thermal stability of copper clad laminates, a major component in printed circuit boards, is a critical issue in electronic packaging industries. In order to understand thermal degradation behavior, popcorn blister tests were performed at high temperatures for three different brands of copper clads laminated with FR-4 epoxy-saturated glass fabrics. Regardless of the brand, all the specimens became defective with blisters at about 250 °C. Detailed examination of fracture morphology with a scanning electron and an optical interferometric microscope revealed that popcorn blisters started not at the interface between copper foil and epoxy resin but at the interface between epoxy resin and glass yarns inside the FR-4 fabric. Sizing agent, an organic lubricant used for glass fibers, is suspected for the initial breakdown of the interface between glass yarns and epoxy resin. As epoxy resin degraded through decomposition of amino-alcohol portion or some other reaction, the gas products then diffused to the yarn-resin interface area. When the temperature reached about 250 °C, the pressure of such gas pockets became strong enough to rupture the laminate under both tension and shear stresses or to advance the fracture through the epoxy via cleavage fracture. Fracture patterns displayed both river and hackle markings, typical characteristics of epoxy fracture. The river markings seemed to indicate cleavage fracture of the epoxy (mode I) which was in close contact with glass yarns. The hackle markings, on the other hand, suggested rupturing of epoxy under both tension and shear stresses (modes I and II), which were most likely caused by a change in the maximum principal tensile stress direction due to interlocked copper nodules.     

Incorporation of hyperbranched polyamide‐functionalized graphene oxide into epoxy for improving interfacial and mechanical properties

The incorporation of hyperbranched polyamide‐functionalized graphene oxide (HPA‐GO) into epoxy was proposed to improve the interfacial and mechanical properties. Benefiting from improved dispersion and strengthened interfacial interaction, epoxy composites with HPA‐GO showed significant improvements in mechanical and thermomechanical properties at low GO loading. The interaction at the HPA‐GO/epoxy interface was investigated to confirm the occurrence of chemical bonding. Strong interfacial bonding improved the stress transfer and distribution of HPA‐GO/epoxy interface. Accordingly, the overall strength of epoxy composites was effectively improved on account of the uniform dispersion of HPA‐GO and interfacial chemical interaction between HPA‐GO and epoxy. Compared with neat epoxy resin, the inclusion of 0.10 wt% HPA‐GO led to 310.5 and 37.2% increase in impact strength and tensile strength, respectively. © 2019 Society of Chemical Industry     

Effect of rubber/matrix interfacial modifications on the properties of a rubber-toughened epoxy resin

The interface of a rubber-toughened epoxy resin was modified by using epoxide end-capped carboxyl-terminated butadiene and acrylonitrile random copolymer (CTBN). The end-capping epoxides were formulated with different ratios of flexible diglycidyl ether of propylene glycol (DER732) and rigid diglycidyl ether of bisphenol-A (Epon 828). The microstructure and the fracture behavior of these rubber-modified epoxy resins were studied by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. The thermal and mechanical properties were also investigated. With an increase in the amount of end-capping DER732, the interfacial zone of an undeformed rubber particle and the degree of cavitation of the rubber cavity on the fracture surface were greatly increased. At the maximal addition of DER732, fracture energy (GIc) for this toughened epoxy resin containing 10phr CTBN rubber increases up to 2.4 fold compared to that of a conventional CTBN-toughened epoxy resin, but the thermal and the mechanical properties remained quite unaffected. The modification on the interfacial property provides a new technique in the improvement of fracture toughness of a rubber-toughened epoxy resin.     

Influence of plasma treatment on properties of ramie fiber and the reinforced composites

In this research, 9 series of ramie fibers were treated under low-temperature plasma with diverse output powers and treatment times. By analysis of the surface energy and adhesion power with epoxy resin, 3 groups as well as control group were chosen as reinforced fibers of composites. The influences of these parameters on the ramie fiber and its composites such as topography and mechanical properties were tested by scanning electron microscopy (SEM), atomic force microscopy (AFM), tensile property and fragmentation test of single-fiber composites. Contact angle and surface free energy results indicated that with the increased treatment times and output powers, surface energy and adhesion work with epoxy resin improved. Compared with the untreated fibers, surface energy and adhesion work with epoxy resin grew 124.5 and 59.1% after 3 min-200 w treatment. SEM and AFM showed low temperature plasma treatment etched the surface of ramie fiber to enhance the coherence between fiber and resin, consequently fiber was not easy to pull-out. After 3 min-200 w treatment, tensile strength of ramie fiber was 253.8 MPa, it had about 30.5% more than that of untreated fiber reinforced composite. Interface shear stress was complicated which was affected by properties of fiber, resin and interface. Fragmentation test showed biggest interface shear stress achieved 17.2 MPa, which represented a 54.0% increase over untreated fiber reinforced composites.