吸水率对尼龙66力学性能的影响研究

通过实验研究了吸水率对尼龙(PA)66和改性PA66的弯曲强度、拉伸强度、缺口冲击强度等力学性能的影响规律.结果表明,弯曲强度、拉伸强度随吸水率增大而下降;缺口冲击强度随吸水率增大而提高.其中,弯曲强度随吸水率的变化最大,缺口冲击强度次之,拉伸强度变化最小.改性PA66的力学性能受吸水率的影响程度明显大于未改性的.还对吸水性改变PA66力学性能的机理进行了探讨.     

不同类型增韧剂对超低聚合度PVC树脂性能的影响

分别考察了CPE、MBS对超低聚合度PVC树脂冲击强度、拉伸强度、弯曲强度和热变形温度的影响。结果表明:与CPE相比,采用MBS可使超低聚合度PVC树脂获得非常高的冲击强度,更高的热变形温度,但拉伸强度和弯曲强度略有降低。     

有机硅密封剂高温力学性能研究

在温度25~250℃对3类硫化体系的5种有机硅密封剂的拉伸强度、180o剥离强度和剪切强度的研究表明:随着温度的升高,5种有机硅密封剂的拉伸强度、180o剥离强度和剪切强度均不断下降,其中拉伸强度和剪切强度降低的速率递减。有机硅密封剂的高温性能变化与硫化体系类型密切相关,脱氢硫化体系HM321密封剂在25~150℃拉伸强度、剪切强度和180o剥离强度均最高,但在25~250℃拉伸强度、剪切强度和180o剥离强度保持率均最低。脱氨硫化体系XY-602S有机硅胶粘剂在232~250℃的拉伸强度和剪切强度最高,25~250℃的拉伸强度保持率也最高。     

单层芯DPP芳纶输送带指形接头的研究

对DPP芳纶输送带指形接头进行试验研究,考察指长、指宽、接头芯胶粘合强度、加强织物层、硫化工艺和操作过程对DPP芳纶输送带静态接头强度的影响。结果表明：指形接头强度与指形自身的强度有关,指形自身强度取决于其指长与指宽;提高接头芯胶的粘合强度可提高接头强度;覆盖胶和芯胶强度越高、老化性能越好,接头越不容易开裂。     

可再分散乳胶粉对瓷砖粘结剂粘附性能的影响

可再分散乳胶粉具有极突出的粘结强度,可提高砂浆的柔韧性,赋予砂浆优良的耐碱性、防水性、可塑性、耐磨性和施工性。本文研究了可再分散乳胶粉对水泥砂浆拉拔强度、热循环后拉拔强度、冻融循环后拉拔强度、浸水后拉拔强度以及破坏方式的影响。结果表明:可再分散乳胶粉对水泥砂浆在不同处理条件下的拉伸强度和粘附强度有明显的改善效果。     

关于金刚石微粉强度问题探讨

拉曼光谱通过测定金刚石微粉颗粒的晶体结构及内部缺陷和杂质含量评价微粉强度品级,是一种科学、有效、能快速检测金刚石微粉强度品级的方法.根据拉曼光谱测定金刚石微粉强度品级,研究了金刚石微粉强度与金刚石单晶原料强度、金刚石原材料的合成时间、微粉生产工艺和微粉表面处理工艺之间的关系.结果表明,金刚石微粉的强度虽然与原材料强度品...     

氯化聚乙烯对ABS/PVC合金性能的影响

以氯化聚乙烯(CPE)为增韧剂,用双螺杆挤出机共混制备丙烯腈-丁二烯-苯乙烯塑料(ABS)/聚氯乙烯(PVC)合金。研究了PVC及CPE用量对ABS/PVC合金的拉伸强度、弯曲强度、缺口冲击强度、维卡软化温度、氧指数和熔体流动性的影响。结果表明,随着PVC用量的增加,ABS/PVC合金的拉伸强度略有增加,弯曲强度基本不变,冲击强度呈现先略增加然后显著降低的趋势,维卡软化温度降低,氧指数增加;随着CPE用量增加,ABS/PVC合金的缺口冲击强度增加,拉伸强度和弯曲强度降低,氧指数和维卡软化温度变化很小,当ABS/PVC/CPE为40/60/15时,合金的拉伸强度为39.8 MPa、弯曲强度为60.8 MPa、缺口冲击强度为18.3 kJ/m2,氧指数为29.7%。     

聚丙烯/滑石粉复合材料的制备及其力学性能北大核心

用经偶联剂改性的滑石粉(Talc)与聚丙烯(PP)共混制备PP/Talc复合材料,测试了复合材料的拉伸强度、弯曲强度和冲击强度等,并探讨了Talc含量对复合材料力学性能的影响机理。结果表明:Talc含量对复合材料力学性能有明显影响,复合材料的拉伸强度、弯曲强度和冲击强度均随Talc含量的增加而增大,但均会出现拐点,即当Talc含量分别超过18%,20%,8%时,复合材料的拉伸强度、弯曲强度和冲击强度却随Talc含量的增加而逐步降低。     

干馏用低变质粉煤成型技术研究

选用有机粘结剂,将低变质粉煤冷压成型煤,经中温干馏制备兰炭,研究了不同粘结剂对型煤、兰炭的落下强度和抗碎强度的影响;单一聚酰胺树脂、两种以及三种粘结剂复配的用量分别为14%、13%、12%时,兰炭的两种强度接近,粘结剂用量均为12%时,三种粘结剂复配的兰炭落下强度为94.6%、抗碎强度为54.2%,优于单一和两种粘结剂复配的强度;不同粘结剂对型煤的落下强度、抗碎强度影响较小,随着粘结剂用量的增加,型煤的两种强度均在增大,当粘结剂用量超过12%后,两种强度的增幅不明显。     

气相二氧化硅在胶衣树脂中的应用研究

本文研究了德国N20、国产A200及A380二氧化硅对剪切拉伸强度及模量、弯曲强度及模量、冲击强度、粘度、触变性的影响,试验发现,加入气相二氧化硅能进一步提高力学强度.     

Direct tensile tests on prismatic concrete specimens

A new type of clamping grips for direct tensile tests on concrete is presented. The grips make it possible to use prismatic specimens without inducing stress concentrations of too high a magnitude and this significantly simplifies the manufacturing of specimens and the performance of direct tensile tests.Test results of the direct tensile strength determined by the new clamping grips are presented for a number of concrete types. These results are compared with test results of the flexural tensile strength and the ratio flexural tensile strength/tensile strength seems to agree well with the theoretical estimations.     

Determination of the impact tensile strength of structural adhesive butt joints with a modified split Hopkinson pressure bar

The impact tensile strength of structural adhesive butt joints was determined with a modified split Hopkinson pressure bar using hat-shaped specimens. A typical two-part structural epoxy adhesive (Scotch weld^® DP-460) and two different adherend materials (Al alloy 7075-T6 and commercially pure titanium) were used in the adhesion tests. The impact tensile strength of adhesive butt joints with similar adherends was evaluated from the peak value of the applied tensile stress history. The corresponding static tensile strengths were measured on an Instron testing machine using joint specimens of the same geometry as those used in the impact tests. An axisymmetric finite element analysis was performed to investigate the static elastic stress distributions in the adhesive layer of the joint specimens. The effects of loading rate, adherend material and adhesive thickness on the joint tensile strength were examined. The joint tensile strength was clearly observed to increase with the loading rate up to an order of 10⁶ MPa/s, and decrease gradually with the adhesive thickness up to nearly 180 μm, depending on the adherend materials used. The loading rate dependence of the tensile strength was herein discussed in terms of the dominant failure modes in the joint specimens after static and impact testing.     

The effect of sorption on the tensile creep and strength reduction of desiccated concrete

The influence of sorption of fluids of differing molecular size on the strength and tensile creep of desiccated concrete and mortar are investigated. It is shown that the desiccated tensile strength is significantly reduced by sorption in accordance with the molecular sieve concept; compressive and splitting tensile strengths are also reduced but to lesser extent. For specimens subjected to a constant applied tensile load, strength reduction increases the effective stress-strength ratio thereby contributing to creep. In some cases, the concomitant effect of strength reduction and sorption induced deformations results in specimen fracture.     

Comparative study of weld-line strength for unfilled and glass-filled thermoplastic polyamide-6 materials

The injection molding process is widely accepted for the processing of engineering thermoplastics due to the ease of manufacturing complex designs. Weld-line is a defect occurring in injection molded parts when two flow fronts join each other. At weld-line locations, parts exhibit lower mechanical strength mainly due to inadequate intermolecular diffusion and fiber orientation anisotropy. The present work is aimed at investigating and comparing weld-line strength for unfilled and glass-filled polyamide-6 materials. To achieve this, polyamide-6 unfilled, 30% glass-filled, and 50% glass-filled materials are used to manufacture plaques. The special-purpose mold is designed to obtain plaques with and without weld-lines with help of Moldflow simulations. The specimens for tensile tests are then cut from molded plaques and experimental testing is conducted to evaluate tensile properties. Fractured surfaces of specimens are examined using a scanning electron microscope. The results demonstrated a significant drop in tensile strength and modulus for glass-filled material weld-line specimens when compared to specimens of no weld-line. However, for unfilled specimens, tensile strength and modulus are almost the same for samples with and without weld-line. A reduction in tensile strength of 13%, 49%, and 57% is observed for unfilled, 30% glass-filled, and 50% glass-filled polyamide-6 material respectively.     

Uniaxial tensile strength and fracture analysis of a hot-pressed boron carbide

Tensile specimens with three different gage dimensions were used to determine the tensile strength of a hot-pressed boron carbide. The strength-limiting flaw population and information on the fracture behavior under an applied tensile stress were also determined. The material follows traditional strength size-scaling for advanced ceramics, and flexure strength data for the same boron carbide was an excellent fit with the uniaxial tensile strength data. The strength-limiting flaw in all specimens was a carbon-based inclusion or agglomerate. The size of the fracture mirror around the origin and the fracture toughness value estimated from the measured strength-limiting flaw size are in excellent agreement with previously reported data. This information shows that standard four-point flexure strength tests can be used to confidently predict the uniaxial tensile strength of this hot-pressed boron carbide.     

Experimental Investigation of Aluminum/Epoxy Interfacial Properties in Shear and Tension

This paper presents the results of comprehensive testing to characterize the effect of several different surface treatments on shear and tensile bond strength between 7075-T6 aluminum and two epoxy systems: EPON 815/V40 and EPON 828/Z. A rod pull-out test was used to determine interfacial shear strength, modeled after similar tests on reinforced concrete. The tensile bond strength was characterized using a tension test fixture designed in this study. Overall, the interfacial shear strengths were higher than the tension strengths. Surface knurling gave the highest interfacial shear strength, representing a 72% increase over untreated specimens. Phosphoric acid anodization (PAA) was also quite effective in shear. In tension, the highest strength was obtained from specimens treated with the PAA process along with a silane coupling agent. These specimens showed an increase in interfacial tensile strength by a factor of 5.6.     

Tensile behavior of composite patched cracked metallic structures

Composite patches of epoxy-based unidirectional carbon and woven glass prepregs were adhesively bonded on uncracked and center cracked standard specimens of aluminum sheet, and patched specimens were evaluated by tensile testing. The effect of various surface treatments, patch length, and number of plies on the tensile strength was studied. Surface preparation of the specimens by sandblasting had a pronounced effect on strength improvement compared to other physical or chemical treatments. The strength of the cracked specimens increased up to 79% for unidirectional carbon patched specimens and 75% for woven glass patched specimens. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 2063–2068, 1998     

Creep rupture of the joint between a glass-ceramic sealant and lanthanum strontium manganite-coated ferritic stainless steel interconnect for solid oxide fuel cells

Creep rupture is investigated at 800?°C of a joint between a glass-ceramic sealant and a ferritic stainless steel interconnect coated with lanthanum strontium manganite for solid oxide fuel cell application. Results reveal the shear and tensile creep strength of the as-joined, non-aged joint at a rupture time of 1000?h is about 42% and 3% of the average shear and tensile bonding strength, respectively. A thermal aging of 1000?h at 800?°C enhances the creep strength. For both non-aged shear and tensile specimens with a short creep rupture time, fracture mainly takes place in an oxyapatite interlayer which is formed in the joining process. For a medium creep rupture time, fracture site changes to a mixed BaCrO₄/oxyapatite layer. Oxyapatite and BaCrO₄ dominate the creep failure mechanism for 1000?h-aged shear specimens, while (Cr,Mn)₃O₄ spinel plays a role in the creep failure of 1000?h-aged tensile specimens.     

环氧树脂胶粘剂工程应用研究

采用某种型号的环氧树脂(EP)胶粘剂胶接LY12-CZ铝合金试片,在110～170℃范围内加热4 h后测定胶接件的剪切强度,并对该胶接件的不同加载速率与拉伸剪切强度的关系进行了研究。结果表明:短时高温加热对该胶粘剂的剪切强度没有影响,这有利于飞机组件的整体修复;拉伸剪切强度随着加载速率的增加而增大,这又为探讨加载速率对不同胶粘剂性能的影响提供了试验依据。     

Effect of process conditions on the weld‐line strength and microstructure of microcellular injection molded parts

This study was aimed at understanding how the process conditions affect the weld‐line strength and microstructure of injection molded microcellular parts. A design of experiments (DOE) was performed and polycarbonate tensile test specimens were produced for tensile tests and microscopic analysis. Injection molding trials were performed by systematically adjusting four process parameters (i.e., melt temperature, shot size, supercritical fluid (SCF) level, and injection speed). For comparison, conventional solid specimens were also produced. The tensile strength was measured at the weld line and away from the weld line. The weld‐line strength of injecton molded microcellular parts was lower than that of its solid counterparts. It increased with increasing shot size, melt temperature, and injection speed, and was weakly dependent on the supercritical fluid level. The microstructure of the molded specimens at various cross sections were examined using scanning electron microscope (SEM) and a light microscope to study the variation of cell size and density with different process conditions.