Mechanical properties of asphalt binders evaluated by atomic force microscopy

Atomic Force Microscopy was employed in order to relate the features observed on the surface of a 50/70 asphalt binder according to its local stiffness and elastic recovery. Indentations were performed in different points of the surface and a significant variation of elasticity was observed between the points on the so-called bee structure and the matrix. Also, indentations varying the maximum force were performed on similar white spots in the bee structure and the recovery was followed up to 1 h after indentation. It was observed that the elastic recovery is very much dependent on the colloidal structure of the bee. The final surface state of the binder, close to the bee for usual bees is not the same as the initial one indicating severe plastic deformation. Also, permanent phase change could be observed for bright spots presented in not well-structured bee arrangements. A surface hardening was observed in the bee region.     

Evolution of the microstructure of unmodified and polymer modified asphalt binders with aging in an accelerated weathering tester

This paper presents findings on the evolution of the surface microstructure of two asphalt binders, one unmodified and one polymer modified, directly exposed to aging agents with increasing durations. The aging is performed using an accelerated weathering tester, where ultraviolet radiation, oxygen and an increased temperature are applied to the asphalt binder surface. Ultraviolet and dark cycles, which simulated the succession of day and night, alternated during the aging process, and also the temperature varied, which corresponded to typical summer day and night temperatures registered in the state of Qatar. Direct aging of an exposed binder surface is more effective in showing microstructural modifications than previously applied protocols, which involved the heat treatment of binders previously aged with standardized methods. With the new protocol, any molecular rearrangements in the binder surface after aging induced by the heat treatment is prevented. Optical photos show the rippling and degradation of the binder surface due to aging. Microstructure images obtained by means of atomic force microscopy show gradual alteration of the surface due to aging. The original relatively flat microstructure was substituted with a profoundly different microstructure, which significantly protrudes from the surface, and is characterized by various shapes, such as rods, round structures and finally ‘flower’ or ‘leaf’ structures.     

Observation of asphalt binder microstructure with ESEM

The observation of asphalt binder with the environmental scanning electron microscope (ESEM) has shown the potential to observe asphalt binder microstructure and its evolution with binder aging. A procedure for the induction and identification of the microstructure in asphalt binder was established in this study and included sample preparation and observation parameters. A suitable heat‐sampling asphalt binder sample preparation method was determined for the test and several stainless steel and Teflon sample moulds developed, finding that stainless steel was the preferable material. The magnification and ESEM settings conducive to observing the 3D microstructure were determined through a number of observations to be 1000×, although other magnifications could be considered. Both straight run binder (PG 58‐28) and an air blown oxidised binder were analysed; their structures being compared for their relative size, abundance and other characteristics, showing a clear evolution in the fibril microstructure. The microstructure took longer to appear for the oxidised binder. It was confirmed that the fibril microstructure corresponded to actual characteristics in the asphalt binder. Additionally, a ‘bee’ micelle structure was found as a transitional structure in ESEM observation. The test methods in this study will be used for more comprehensive analysis of asphalt binder microstructure.     

Multiscale imaging and characterization of the effect of mixing temperature on asphalt concrete containing recycled components

When producing asphalt concrete mixture with high amounts of reclaimed asphalt pavement (RAP), the mixing temperature plays a significant role in the resulting spatial distribution of the components as well as on the quality of the resulting mixture, in terms of workability during mixing and compaction as well as in service mechanical properties. Asphalt concrete containing 50% RAP was investigated at mixing temperatures of 140, 160 and 180°C, using a multiscale approach. At the microscale, using energy dispersive X‐ray spectroscopy the RAP binder film thickness was visualized and measured. It was shown that at higher mixing temperatures this film thickness was reduced. The reduction in film thickness can be attributed to the loss of volatiles as well as the mixing of RAP binder with virgin binder at higher temperatures. X‐ray computer tomography was used to characterize statistically the distribution of the RAP and virgin aggregates geometric features: volume, width and shape anisotropy. In addition using X‐ray computer tomography, the packing and spatial distribution of the RAP and virgin aggregates was characterized using the nearest neighbour metric. It was shown that mixing temperature may have a positive effect on the spatial distribution of the aggregates but did not affect the packing. The study shows a tendency for the RAP aggregates to be more likely distributed in clusters at lower mixing temperatures. At higher temperatures, they were more homogeneously distributed. This indicates a higher degree of blending both at microscale (binder film) and macroscale (spatial distribution) between RAP and virgin aggregates as a result of increasing mixing temperatures and the ability to quantify this using various imaging techniques.     

Investigation of porous asphalt microstructure using optical and electron microscopy

Direct observations of porous asphalt concrete samples in their natural state using optical and electron microscopy techniques led to useful information regarding the microstructure of two mixes and indicated a relationship between microstructure and in situ performance. This paper presents evidence that suboptimal microstructure can lead to premature failure thus making a first step in defining well or suboptimal performing pavements with a bottom-up approach (microstructure). Laboratory and field compaction produce different samples in terms of the microstructure. Laboratory compaction using the gyratory method has produced more microcracks in mineral aggregates after the binder had cooled. Well-performing mixes used polymer-modified binders, had a more homogeneous void structure with fewer elongated voids and better interlocking of the aggregates. Furthermore, well-performing mixes showed better distribution of the mastic and better coverage of the aggregates with bitumen. Low vacuum scanning electron microscopy showed that styrene butadiene styrene polymer modification in binder exists in the form of discontinuous globules and not continuous networks. A reduction in the polymer phase was observed as a result of aging and in-service use.     

Effect of treatment temperature on the microstructure of asphalt binders: insights on the development of dispersed domains

This paper offers important insights on the development of the microstructure in asphalt binders as a function of the treatment temperature. Different treatment temperatures are useful to understand how dispersed domains form when different driving energies for the mobility of molecular species are provided. Small and flat dispersed domains, with average diameter between 0.02 and 0.70 μm, were detected on the surface of two binders at room temperature, and these domains were observed to grow with an increase in treatment temperature (up to over 2 μm). Bee‐like structures started to appear after treatment at or above 100°C. Moreover, the effect of the binder thickness on its microstructure at room temperature and at higher treatment temperatures was investigated and is discussed in this paper. At room temperature, the average size of the dispersed domains increased as the binder thickness decreased. A hypothesis that conciliates current theories on the origin and development of dispersed domains is proposed. Small dispersed domains (average diameter around 0.02 μm) are present in the bulk of the binder, whereas larger domains and bee‐like structures develop on the surface, following heat treatment or mechanical disturbance that reduces the film thickness. Molecular mobility and association are the key factors in the development of binder microstructure.     

Effect of rubber component on the performance of brake friction materials

Various composite friction materials containing 40 vol.% organic binder (phenolic resin plus styrene–butadiene–rubber (SBR)) with varying phenolic-resin/SBR ratio were prepared. The content of phenolic resin in each composite was indicated by the resin value (RV) index ranging between 0 and 100%. The composites with RVs greater than 50% form resin-based friction materials in which the primary binder is the phenolic resin. For RVs less than 50%, the composites become the rubber-based materials where the primary binder is the SBR. The analysis of mechanical properties exhibited that the conformability of the composites increases upon incorporation of SBR. The frictional analysis revealed that type of polymeric binder, i.e. resin or rubber, dominates greatly the frictional behavior of the composites. The increment of friction force and higher improvement in the frictional fade and recovery with sliding velocities are the general features of rubber-based friction materials. It was attributed to the inherent properties of rubber on the viscoelastic response at higher sliding velocities and entropic contribution on the mechanical properties at higher temperatures. The wear rate of resin-based materials and its drum temperature is lower than those of rubber-based materials. It was attributed to the strongly adhered multilayer secondary plateaus formed on the surface of resin-based materials.     

含弹性杆件的并联机器人刚度分析

通过分析包含弹性杆件的并联机器人的刚度系数的性质,计算了机器人在各方向上的刚度,绘制了最小刚度系数的变化曲线,研究了刚度与奇异位形、机器人的固有频率及弹性振动振幅的关系.计算实例表明,刚度系数和奇异位形、机器人的固有频率有密切的联系,可用于预测含弹性杆件的并联机器人的弹性动力学特性和响应,不需要进行弹性动力学计算,计算时间节省94%.     

Fine-particle slurry wear resistance of selected tungsten carbide thermal spray coatings

The surface degradation of tungsten carbide based thermal spray coatings when exposed to fine-particle slurry abrasion has been investigated. The coatings that were studied contain binder-phase constituents consisting of either nickel or cobalt. The coatings were deposited onto test cylinders using a detonation gun device. After applying approximately 0.15 mm thickness of thermal spray coating, the coatings were ground, then diamond polished to achieve surface roughnesses of 0.03 μm Ra or less. The coatings were exposed to a three-body abrasive wear test involving zirconia particles (less than 3 μm diameter) in a water-based slurry. Results show that preferential binder wear plays a significant role in the wear of these tungsten carbide coatings by fine abrasives. In the comparison presented here, the coating containing nickel-based binder with a dense packing of primary carbides was superior in terms of retaining its surface finish upon exposure to abrasion. The coating containing a cobalt binder showed severe surface degradation.     

文物蛋白胶料的气相色谱-质谱分析方法探讨

为了探讨文物蛋白胶结材料的气相色谱-质谱（GC-MS）分析方法，以正亮氨酸为内标，N-(叔丁基二甲硅烷基)-N-甲基三氟乙酰胺(简称MTBSTFA)+1%特丁基二甲基氯代硅烷作为衍生化试剂，建立了蛋白胶料中常见的丙氨酸、甘氨酸等11种氨基酸的标准曲线，测定了每种氨基酸的精密度和检出限，并将该方法用于现代参考胶料和文物样品的分析测量。结果表明，GC-MS法对氨基酸的分离效果较好，除羟脯氨酸的稳定性略差外，其余10种氨基酸标准曲线的相关系数（R）均大于0.99，11种氨基酸的相对标准偏差（RSD）为2.7%~6.3%。甘氨酸的检出限最低，为0.066 μg/g；亮氨酸的检出限最高，为0.676 μg/g。在对猪皮胶、全蛋和牛奶3种现代参考胶料氨基酸分析的基础上，结合主成分分析（PCA）法揭示了3种胶料的特征性，并采用该方法鉴定了广西服饰金线文物样品中的蛋白胶料，表明该方法适用于文物蛋白胶料的定量分析。     

Measurements of polyphosphoric acid on HOPG

As a sample for initial study on biological materials by using scanning tunnelling microscope (STM), we selected phosphoric acid consisting of phosphorous atoms which play biologically an important role. We measured polyphosphoric acid coated on HOPG by STM and scanning tunnelling spectroscopy (STS) in air. In order to identify molecules on STM images, local I-V curves were taken simultaneously. The averaged I-V curves and the normalized conductance spectra of graphite coated with the acid show characteristics different from those of clean graphite surface. Around a step of the substrate, we found domains where normalized conductance spectra were different from those of clean graphite surface and ascribable to that of the adsorbed molecules.     

Effects of layer thickness and binder saturation level parameters on 3D printing process

Various parameters, such as binder properties, printing layer thickness, powder size, and binder saturation level, have effects on the strength and surface finish of the three-dimensional printing (3D printing) process. The objective of this research is to study the effects of two parameters of layer thickness and binder saturation level on mechanical strength, integrity, surface quality, and dimensional accuracy in the 3D printing process. Various specimens include tensile and flexural test specimens and individual network structure specimens are made by the 3D printing process under different layer thicknesses and binder saturation by use of ZCorp.'s ZP102 powder and Zb56 binder. Two printing layer thicknesses, 0.1 and 0.087 mm, are evaluated at 90% and 125% binder saturation levels. Experimental findings show that under the same layer thickness, increment of binder saturation level from 90% to 125% would result in an increase of tensile and flexural strengths of the specimens and decrease of dimensional accuracy and surface uniformity of specimens. On the other hand, under the same binder saturation conditions, increase in layer thickness from 0.087 to 0.1 mm would decrease tensile strength and increase flexural strength. Also, it gives better uniformity on the surface.     

V形压料面在汽车覆盖件拉深模设计中的应用

采用冲压成形分析软件Dynaform对汽车车身A柱内板的拉深成形过程进行了有限元模拟分析,研究了拉深过程中压边状态和后期出现的皱折问题,得到了皱折产生的趋势曲线。曲线显示,压料面高度差越大,皱折越严重。针对皱折提出了一种新的V形压料面的模具结构,改善了压边时材料的流动方向,有效避免了皱折的
产生。采用一种新的球面侧壁取代传统的斜面侧壁,消除了零件圆弧形边缘的开裂,使拉深零件的最大变薄率由54.2%降为28.5%。最终按此优化型面加工模具,并成功获得了合格产品。

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Development of a feedstock formulation based on polypropylene for micro-powder soft embossing process of 316L stainless steel micro-channel part

To exploit the potential of micro-system technology, the micro-powder embossing process, a rapid manufacturing production technology of microstructured die mould, was currently being investigated. Present work focused on establishing a suitable binder system for micro-powder embossing process. Multi-component binder systems, comprising of different weight percentages of paraffin wax, stearic acid and polypropylene were investigated. The compatibility between binder constituents was studied by thermogravimetric analysis (TGA) showing a partial miscibility between both components. The feedstock comprised of 316L stainless steel powder, and a wax-based thermoplastic binder was used to achieve a feedstock with 60 to 68 vol.% powder loading. The degradation temperature of binders was determined by using TGA and flow behaviour through rheometer. Homogeneity of the feedstock was verified by using TGA and scanning electron microscopy. Then, hot embossing was done, and it was found that the feedstock having solid loading up to 68 vol.% were successfully embossed, and components were without physical defects. The polymeric part was driven off by thermal debinding using a thermal cycle designed on the basis of a thermogravimetric study of the binder. Finally, the vacuum sintering of the parts allows high quality parts to be obtained.     

TiH2粉注射成形用新型粘结剂的研制及其性能

研发了一种适合TiH2粉注射成形用新型石蜡基粘结剂,对粘结剂组元间的相容性进行了计算,并分析了该粘结剂的流变性能和脱脂性能。结果表明:该新型粘结剂各组元相容性好,能够与TiH2粉实现良好混合,装载量(体积分数)达到70%以上;粘结剂流变性能佳且稳定,在注射温度为160℃和剪切速率为125s-1的条件下,黏度为0.081Pa.s,粘流活化能为36.85kJ.mol-1;与常规石蜡基粘接剂相比,在同样工艺条件下使用正庚烷脱脂时相同时间下脱脂率提高20%～30%;脱脂坯缺陷少、保形性好;与原料粉相比,经过热脱脂后坯样的碳含量仅增加了0.02%,氧和氮含量均降低。     

Hybrid Fabric/Molybdic Acid-Modified Phenolic Resin Composites with Improved Antiwear Properties

Molybdic acid–modified phenolic resin (Mo-PF) had been synthesized and was used to prepare fabric composites. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) indicated that the thermal properties were improved when the phenolic resin was modified by molybdic acid. The tribological properties of the fabric composites were evaluated by a pin-on-disk tribometer. Compared to the unmodified ones, the result showed that the fabric composites made by Mo-PF displayed a lower wear rate under all tested conditions. The optimal content of molybdic acid to modify the phenolic resin was obtained, as the correspondingly produced fabric composite displayed improved tribological properties. The effect of applied load, sliding speed, and environment temperature on tribological properties of the fabric composites and the related mechanisms were also discussed.     

水基流延法制备低温共烧陶瓷生带材料新工艺

为实现硼硅酸盐玻璃陶瓷基低温共烧陶瓷生带材料的低成本、安全无毒化生产,采用以水性乳胶作为粘结剂的水基流延工艺进行制备;采用数字旋转黏度计分别对分散剂、固相、粘结剂含量对浆料黏度的影响进行了研究,利用扫描电镜对烧结前后生带材料的微观形貌进行了分析.结果表明:利用硼硅酸盐玻璃+Al<,2>O<,3>粉体作为固相,苯丙乳液作为粘结剂,苯丙烯酸铵作为分散剂,甘油作为增塑剂,成功制备出了固含量高、稳定性好、干燥快的水基流延浆料;制备的生带材料表面光滑、强度高,容易在室温下叠层,经过850℃×30 min烧结,其致密度可以达到96.45%.     

紫外光接枝丙烯酸改性废胶粉工艺优化及其复合材料的力学性能

以丙烯酸为接枝单体,二苯甲酮为光敏剂,在紫外光的引发下对废胶粉进行表面接枝,用正交方法对改性工艺进行了优化,制备了改性废胶粉/天然橡胶复合材料,表征了改性前后废胶粉的表面形貌和结构,考察了其加入量对复合材料力学性能的影响。结果表明:当丙烯酸和二苯甲酮与废胶粉的质量比分别为10%和9%,废胶粉粒径为150μm和光照时间为4min时,为最佳工艺条件,此时接枝率最高,达3.38%;接枝改性后的废胶粉表面粗糙度增加;随改性废胶粉含量的增加,复合材料的拉伸强度和邵氏A硬度先增大后降低,并在质量分数10%时达到最大值,分别为27.28MPa和69.2HSA。     

Effect of the Abrasive Size on the Friction Effectiveness and Instability of Brake Friction Materials: A Case Study with Zircon

The friction-induced vibration triggered at the sliding interface between the gray iron disk and brake friction material was studied by changing the size of the zircon particles in the friction material. The friction tests were performed using a reduced brake dynamometer and the friction characteristics of the friction materials containing zircon particles with sizes of 3, 50, and 100 μm were analyzed. Our results show that the properties of the sliding surface were strongly affected by the entrenchment of the abrasive particles in the friction layers during sliding. The friction effectiveness was inversely proportional to the size of the abrasive, while friction instability was pronounced when smaller zircon particles were used. The smaller zircon particles produced larger plateaus on the sliding surface with low contact stiffness. However, the contact plateaus with the low contact stiffness showed higher amplitudes of the friction oscillations, suggesting a surface with low stiffness also can produce high propensity of friction instability during sliding. Based on the friction stability diagram and surface properties, such as contact stiffness and surface roughness, it was suggested that the static coefficient of friction, which was changed as a function of dwell time, was crucial to understand the cause of friction-induced force oscillations and propensity of friction instability of brake friction materials.     

Ion microprobe studies of reactions in squeeze-cast aluminium alloy matrix composites

An ion microprobe with high lateral resolution has been used to study the chemical reactions at the fibre/matrix interface of metal–matrix composites. During the squeeze-casting process, the Al–Si–Mg matrix reacts with the preform made of Saffil fibres (96% Al₂O₃, 4% SiO₂). The reaction occurs mainly between the silica binder and Mg from the matrix according to SiO₂ + 2Mg = 2MgO + Si. A continuous layer of MgO was formed around the fibres, even on surfaces that were not covered by the silica binder. Possible reasons are discussed for the formation of MgO in areas where binder coating was missing. In such areas, Mg reduces SiO₂ that is contained in the fibre. However, the fibres (A1₂O₃) are not attacked by Mg. In the isolated case of fibres that were completely uncoated, no reaction products were observed at the interface. The presence of silica binder seems to be an essential requirement for this reaction to occur. When squeeze-casting is performed with sufficiently high melt temperature, Al from the matrix also reduces silica.