MDF水泥的微观结构和断口分析

应用ＳＥＭ／ＥＤＡＸ、ＳＴＥＭ等仪器比较详细地研究了ＭＤＦ水泥及其断口的微观结构。实验结果表明，ＭＤＦ水泥是由聚合物粘结水泥颗粒构成的新型材料。水泥－聚合物界面粘结良好，界面基本上没有孔隙。聚合物具有较高的孔隙卒，多孔的聚合物是材料的薄弱环节和断裂通道。聚合物的孔隙率和聚合物掺量是影响ＭＤＦ水泥抗弯强度的重要因素。在断裂过程中ＭＤＦ水泥中聚合物具有较高的断裂韧性和断裂伸长。同时探讨了高强ＭＤＦ水泥的结构特征和断裂机理。     

芳纶纤维表面活化的物、化结构本质分析

在深入分析对比聚合物/芳纶纤维复合材料界面改性本质的基础上,将目前世界范围内主要的芳纶纤维表面活化机理重新进行了物理和化学类种属的划分,并着重从物理、化学结构角度剖析了各种机理的优缺点和发展方向。     

水泥基材料聚合物改性机理研究的最新进展

本文介绍了近年来国内外在聚合物改善水泥基材料性能的机理探索方面的研究进展.从理论角度对水泥基材料聚合物改性的机理进行了归纳与总结,着重讨论了聚合物对水泥水化的影响,聚合物改性水泥基材料的微观结构,由此推出复合材料结构形成模型以及聚合物改性水泥基材料的孔结构等几个方面.     

聚合物水泥复合材料的水化机理研究

文章对比单纯硅酸盐水泥和聚合物水泥的水化过程,得出了聚合物水泥复合材料的水化机理,分析了聚合物水泥材料的水化结构,得出了不同比例聚合物水泥材料的性能特点及其原因。     

聚合物水泥改性机理及工程应用

综述了聚合物水泥中的聚合物及其膜的结构组成,探讨了聚合物水泥的组成和形成过程及聚合物改性水泥复合材料的改性机理,分析了聚合物水泥的物理力学性能和工程应用,指出了聚合物水泥的发展趋势和可能的应用途径。     

苯丙乳液改性高强水泥基材料性能及机理

苯丙乳液作为聚合物改性材料已经在水泥基材料中得到应用,而对其改性机理尚不清楚.本文测试了苯丙乳液改性高强水泥基材料的工作性、凝结时间及力学性能,利用微量热仪法与X射线衍射(XRD)分析了苯丙乳液对水泥基材料水化的影响,通过扫描电镜(SEM)及能谱分析(EDS)研究了其微观结构.研究结果表明,苯丙乳液延缓了水泥基材料的水化与二次水化反应,苯丙乳液能有效改善高强水泥基材料界面结构与水泥石结构.苯丙乳液与水泥或其水化产物间存在化学反应的可能性.     

聚合物改性水泥基材料的机理研究进展

综述了近年来聚合物改性水泥基材料(polymer modified cement based materials,PMCBM)改性机理方面的国内外研究进展.从理论角度对PMCBC进行了归纳与总结,重点从4个方面探讨了聚合物改性水泥基材料的改性机理:聚合物对水泥水化过程的影响存在物理作用和化学作用;聚合物对微观结构的主要影响是乳胶粒子的分散和聚合物薄膜的形成;从孔洞结构看,聚合物改变了水泥基材料的孔径分布、特征孔径、平均孔径、最可几孔径、孔隙率等,提高了材料的内聚强度;从聚合物自身结构来看,聚合物的链结构和聚集态结构直接影响水泥基材料的性能.     

石墨烯在水泥基材料中的作用机制研究综述

石墨烯具有优异的力学强度、阻隔性以及超大比表面积,通过对其进行物理或化学分散处理,能够制备高性能石墨烯水泥基复合材料.石墨烯通过调控水泥水化反应、改善孔隙结构以及界面结合等方式,可以改善水泥基材料的力学强度和耐久性能,在水泥基复合材料领域展现出巨大的应用潜力.本文综述了石墨烯水泥基复合材料的研究进展,总结了石墨烯在水泥...     

有机硅助剂在复合材料和填充塑料中的应用

1 填充材料处理有机硅助剂的功能 用于填充材料处理的有机硅助荆通常是具有反应活性的有机硅化合物或聚合物.应用有机硅助剂处理填充材料,通过化学键合或物理作用,改变了填充材料的表面结构或赋予填充材料以附加性能,从而改善填充材料的加工性能,提高复合材料和填充塑料的综合性能.     

碳纤维增强聚合物研究进展

纤维增强聚合物(CFRPs)以其优异的性能,在很多领域代替了传统的金属并得到了广泛应用。CFRPs界面性质决定了复合材料整体性能,因此界面研究一直是复合材料中十分重要的部分。碳纤维(CF)由于优异的性能成为了聚合物复合材料的理想增强材料,然而CF的非极性和光滑表面使其难以提供所需的化学相互作用和有效的物理吸附。本文对碳纤维表面改性从而增强复合材料界面方法做了较为系统的阐述。     

低温覆铝锌钢板搪瓷的密着性能研究

通过对覆铝锌钢板搪瓷样品的密着测试,研究了搪瓷的密着性能。通过金相、扫描电镜等测试,分析了铝锌钢板搪瓷断面结合的微观结构,通过能谱测试分析铝锌钢板搪瓷的元素分布,探讨铝锌搪瓷的密着机制。结果表明,铝锌钢板搪瓷的密着性能良好,铝锌镀层与搪瓷层之间有明显的过渡层和元素扩散,中间过渡层与金属铝的结合主要通过金属键来实现,中间过渡层与瓷釉层的结合主要是通过离子键和共价键来实现。     

Adhesion of polymer coils to a solid surface: influence of the depletion effect

The specific properties of polymer coils are often disregarded in theories of adhesion, but polymer properties are essential for the strength of the adhesive bond. Polymer coils are repelled entropically from impenetrable surfaces. This causes the depletion effect and creates a layer of reduced concentration right at the interface. To bond a polymer coil to a substrate, it must be forced actively towards the interface, driven by the gaining of adsorption energy. The adsorption of specific groups in the (co)polymer, which interact with 'polar' sites on the substrate, must be used to suppress the depletion. Adsorption diminishes the effective distance between the surface and the adhesive polymer. The balance between adsorption and depletion (rather than the effect of polar groups or pretreatments on the work of adhesion as such) is the most important chemical possibility of affecting adhesion. The strength of the bond between polymeric materials and solid surfaces varies as H^-3, with the effective distance H between the polymer and substrate. Therefore, it changes by an order of magnitude when the polymer adhesive is pulled towards the substrate by adsorption.     

Effects of polymer impregnation on mortar-aggregate bond strength

Polymer-impregnated concrete (PIC) is recognized as a superior construction material with higher durability and strength than plain concrete. The increase in strength has been thought to be a result of an increase in bond strength between mortar and aggregate phases and a reduction of the porosity of the mortar. However, there has been no direct evidence to support that an enhanced mortar-aggregate bond is achieved. In this study, modified briquet tension specimens were tested to determine effects of polymer-impregnation on tensile bond strength, and prismatic specimens with inclined aggregates were tested to determine effects on compression-shear bond strength. Plain mortar briquets were also tested. Results indicate that polymer impregnation does not significantly improve interface bond strength in PIC. However, mortar tensile strength is increased. A review of the failure process (microcracking) in plain concrete is presented. It is proposed that if the same microcracking process occurs in PIC, then high compressive strength is a result of high mortar tensile strength.     

UHPC与普通混凝土试件界面黏结抗冻性能试验研究

超高性能混凝土(UHPC)因为其较高的强度和优良的耐久性被认为是极具潜力的结构修补用材料之一。同时,UHPC与普通混凝土(NC)之间的界面黏结性能,是影响UHPC在混凝土加固修复工程中应用可靠性的关键因素。针对严寒环境,本试验对超高性能混凝土与普通混凝土(以下简称UHPC-NC)黏结试件开展－60 ℃的冻融循环试验,分析冻融循环后试件的宏观形态变化、质量变化率。通过黏结强度试验,获得界面的黏结强度以及相应的界面破坏模式。试验主要分析－60 ℃冻融循环对UHPC-NC试件界面黏结性能的影响,以及界面的不同处理方式(钢丝刷刷毛、高压水射流冲毛及劈裂)对抗－60 ℃冻融循环作用的影响,同时,对冻融作用下UHPC-NC试件的界面损伤机理进行初步探索。试验结果表明:－60 ℃冻融循环对UHPC-NC试件黏结强度有较大影响,劈裂组试件的界面黏结强度在经历10次、15次、20次冻融循环后分别下降为界面黏结基准强度的72.94%、55.62%及44.33%,界面黏结强度呈现先急速下降再缓慢下降的趋势;界面粗糙度越高,界面的剩余黏结强度越大,经历20次冻融循环后,劈裂组试件的剩余黏结强度为高压水射流冲毛试件的2.03倍。     

Improved Fracture Toughness of a Titanium Alloy Laminate by Controlled Diffusion Bonding

The use of laminate composites containing a weak interface to increase the fracture toughness of high strength titanium alloys has been studied. Billets were fabricated from Ti-6A1-4V sheet material using a diffusion bonding process. Six billets were fabricated, each billet having an interface with different properties. Results indicate that toughness, as measured by the precracked Charpy test, may be increased when delamination or splitting of the bond occurs.

A simple model to predict the conditions necessary for delamination has been formulated. Correlations between the model and experimental results are made. The model can account for the effect of different base metal and interface material properties and thicknesses. It is seen that a thin, low yield strength interface material with a full strength diffusion bond to a high yield strength, fairly tough base metal leads to optimum composite toughness.     

Mechanical Requirements of the Fiber-Matrix Interface

THE GREAT STRENGTH enhancement and resistance to fracture which occurs when one combines high strength fibers with a low strength, low modulus polymer matrix is well known. The high strength and toughness of the resulting composite material, to a great extent, is dependent upon the many polymer glass interfaces which exist and their ability to deflect cracks propagating normal to them. The presence of these large number of interfaces, however, results in problems which may partially overcome the advantage of their existence. Sufficient adhesive strength must be developed at every point along the polymer-fiber interface so that the maximum stress can be transferred from the polymer matrix to the fiber reinforcement. The critical fiber length or length of fiber required to achieve this maximum stress is thus dependent upon the interfacial strength. A void or an air pocket existing at the interface will cause a stress concentration regardless of the stress state; in addition, this unsupported length of fiber (i.e. the length of the void parallel to the fiber axis) will be subjected to buckling when compressive stresses exist in the fiber. A poorly bonded area at the interface will cause rupture of the interface at very low stresses and the resulting discontinuity will act as a stress concentration.     

Adhesion of a rigid polyurethane foam to zinc phosphated steel

Rigid polyurethane foams were formed on rough zinc phosphate treated steel substrates. The interface between the two materials was investigated using knife peeling, immersion in a solvent which removes amorphous material predominantly, stud pull tests to observe bond failure, and X-ray scattering studies. There were three regions at the interface: an unbonded bare zinc phosphated surface, solid polyurethane areas where foaming did not occur, and foamed regions. These various interfacial regions result from temperature gradients during polymerization and foaming, and poor wetting of the substrate by the polymer. After immersion in a solvent, the solid polyurethane layer bonded to the substrate was completely removed, implying that this area only weakly adheres to the steel substrate. By contrast, the removal of the foamed area exhibited a well-ordered crystalline phase underneath polymer residues. In grazing angle X-ray scattering from the foamed region, a sharp peak from polyurethane crystallites was found on the shoulder of the amorphous peak; this reflection did not appear in the scans for unfoamed solid polymer areas. It is suggested that a greater number of these crystallites results in higher bond strength. A bond failure model was proposed in which fracture takes place along the non-connected regions, with cohesive failure in the foamed areas.     

Interfacial properties of kevlar-49 fiber-reinforced thermoplastics

A single-filament pull-out test was used to study adhesion of Kevlar-49 fibers to thermoplastic polymers. The test involved pulling a partially embedded fiber out of a polymer film. Kevlar-49 fibers with three different surface treatments were used with five thermoplastic materials. The test resulted in the measurement of two properties, an interfacial bond strength and a frictional shear strength. The interfacial bond strength is an essential factor in determining the critical aspect ratio of discontinuous fibers in a composite. The frictional shear strength was found to correlate with the tensile strength of discontinuous fiber composites which fail by fiber pull-out. Scanning electron microscopy was used to examine the fiber pull-out specimens after testing. Observations of the fiber showed that the failure mode at the fiber–matrix interface was complex. The predominant failure mode was fracture at the interface (or in some weak boundary layer). In some cases, cohesive failure of the fiber surface was observed, with the result that strips of material were torn from the fiber surface.     

Grazing incidence X-ray diffraction studies on the structures of polyurethane films and their effects on adhesion to Al substrates

Grazing incidence X-ray diffraction was carried out to analyze the structure of polyurethane films as a function of X-ray penetration depth by varying the angle of incidence. Coherence lengths, interplanar spacings, and crystallinities were obtained for non-aged and aged films of OH numbers of 120, 375, and 600 bonded to an aluminum substrate. Aging led to the improvement of bulk crystallinity of all the samples, particularly in the case of the aged PU-375 film, for which a dramatic increase of the bond strength was observed. The crystallinity of non-aged samples varied from the air/polymer surface down to the polymer/aluminum interface. Invariance of coherence length from air surface to interface was observed for PU-120 and PU-375 samples, implying that substrate-induced ordering has little effect on the average crystallite size. As the X-ray penetration increases near the polymer/Al interface, interplanar spacing of (021) reflection in all the films approach the value found for a bulk polyurethane-urea by Ishihara et al. The bond strength of the polyurethane film to the aluminum was exponentially proportional to the crystallinity including the crystalline interphase formed near the substrate. It is also found that the polymer film containing more (100) planes provided higher bond strength.     

Significance of Peel Test Speed on Interface Strength in Cohesive Zone Modeling

The analysis of the experimental peel test data for obtaining the adhesion fracture energy of an adhesively laminated polymer to the sheet metal surface is considered. The experimental results of the 180° peel test on two types of polymer laminated sheet metal at three different peel speeds are analyzed by two methodological approaches in cohesive zone modeling. These approaches are linear-elastic stiffness approach and critical maximum stress approach. Comparing the results of these two approaches reveals the significance of the peel test speed on the interface strength determination for cohesive zone modeling. It is concluded that a “reference” peel speed may exist at which the interface strength is equal to the yield strength of the peel arm material. A constitutive equation has been proposed which relates the interface strength to the peel test velocity by using the reference peel speed and its corresponding peel arm yield strength.