高抗冲PVC管材的研究

研究了一种改性的高抗冲击PVC管材(PVC-M),并对其优异的物理力学性能进行测试、分析、评价.该管材具有相当高的韧性,可在较为恶劣的环境下应用,同时保留了传统PVC-U管材的高设计应力.     

HDPE管材蠕变开裂的测定及其使用寿命的推断

本文参照ISO/TC138N616E“气体燃料供应用埋装聚乙烯管材—规格公制系列”及其附录A中规定的方法对HDPE管材进行在不同温度、不同环应力作用下的蠕变开裂试验。将试验数据进行回归分析,预报出该管材在20℃、50kgf/cm~2环应力作用下,寿命为50年。     

SCG及含内部轴向半椭圆裂纹PE管的寿命

PE管材以其良好的力学性能在工业生产中得到了广泛应用。PE管道的设计寿命一般为50年,在服役过程中,PE管材可能会发生破裂及失效,慢速裂纹增长(SCG)是造成PE管材失效、影响管道服役寿命的重要因素之一。因此,研究PE管材的裂纹扩展行为对保证PE管材的安全使用,保障工业生产的安全稳定运行至关重要。从PE100管材中制取环切圆棒试件(Cracked Round Bar,CRB),根据ISO 18489—2015在不同应力比(R=0.1、0.2、0.3)下进行疲劳实验并得到裂纹扩展规律。采用外推法将实验结果外推得到静载条件下的裂纹扩展规律。对含有内部轴向半椭圆裂纹缺陷的PE管材进行寿命计算,得到了其在50年服役寿命下的最大允许裂纹尺寸和相应的应力强度因子值。     

挤出工艺对聚乙烯管材残余应力分布的影响

通过调整冷却速度制备出具有不同残余应力分布的高密度聚乙烯（PE-HD）管材,考察了挤出工艺对PE-HD管材内外层残余应力和常规物理性能的影响。结果表明,随着冷却速度的增加,管材纵向回缩率逐步增大,且其静液压破坏时间和管材耐慢速裂纹增长（SCG）破坏时间也随之降低;同时管材外层的残余应力随着冷却速度和钻孔深度的增加逐步提高,呈现非均匀分布的情况,而管材内层的残余应力较小,均匀性差异不显著,并通过分层拉伸试验验证了盲孔法测量管材内外层残余应力的适用性。     

聚乙烯管材残余应力的定性和定量评价

研究了冷却速度、挤出速度和拉伸比等不同挤出工艺对管材物理性能及残余应力的影响，结果表明，随着冷却和挤出速度的增加，PE管材纵向回缩率增大，静液压和SCG破坏时间逐渐降低。通过盲孔应变法研究了不同挤出工艺对管材内外层的释放应变和残余应力分布的影响，研究表明，采用理想化的均匀分布模型不适用于残余应力的定量评价，采用非均匀应力分布模型计算得到的管材外层的残余应力随着冷却和挤出速度的增加而增大，而管材内层的残余应力变化较小，由于管材沿壁厚方向冷却速度的不均匀，内外层残余应力分布存在差异。最终，通过对管材内中外层分别进行拉伸、密度和结晶度等物理性能试验，进一步证明了盲孔法定量评价残余应力的有效性。同时试验发现，当挤出拉伸比太高时，分子链取向严重，管材纵向回缩率增大，静液压和耐SCG性能下降，管材外层残余应力的最大值为14.6 MPa,与材料拉伸屈服强度相比，提高了50%。     

缺陷粒子对PVC-U管材强度影响

为探索在试压时低压下即破裂的硬聚氯乙烯(PVC—U)管材的破裂原因，对这些破裂管材的断裂面进行了仔细观察，发现在这些断裂面上均有缺陷粒子存在。通过应力场下的断裂裂缝理论分析，确定这些缺陷粒子在管材中形成的微裂纹在低压下扩展是管材破裂的原因，并进一步指出了各种性质的缺陷粒子的来源，以及在原料采购和生产工艺控制等方面应采取的相应措施。     

NB/T 47012-2010中TP2管材许用应力探讨

通过试验对轧丝后的高效管拉伸试验和硬度进行测试,探讨翅片加工工艺对强度和硬度的影响,讨论了同一根TP2管材不同热处理状态的许用应力选取情况,并提出了铜合金材料的许用应力采用强度极限除以安全系数更加合理的观点。     

PE100级管材专用树脂的性能研究

中沙(天津)石化有限公司生产的管材专用树脂PN049-030-122达到了PE100级管材专用树脂的等级认证。在对其进行结构分析的基础上,评价了管材专用树脂的性能,并与国内相关树脂进行对比。结果表明,PN049-030-122管材专用树脂的应力置信下限值为10.75MPa,其耐慢速裂纹增长性能超过500h,200℃氧化诱导期在173min左右,具有良好的加工性能,且该管材专用树脂的性能完全满足国内生产给水管材的要求。     

不同材质PVC-U管材拉伸性能的评价

通过测定不同材质PVC-U管材的拉伸性能,分析其在拉伸过程中试样截面积和密度的变化及应力-应变曲线的不同,讨论了不同材质PVC-U管材拉伸屈服点判定方法、真应力、拉伸机制的差异。     

布管法生产PVC-O管材的理论计算与实验

针对一种新型PVC-O管材生产方法,从理论上计算扩胀过程管壁内的应力分布,并研究扩胀PVC管坯的最佳工艺参数.讨论两种不同扩胀比下管材与未扩胀管坯的强度变化.按照弹性理论计算,扩胀时管壁内的应力近似为线性分布,其中环向应力近似为均匀分布.扩胀后的PVC-O管材强度和弹性模量都有明显提高,但断裂伸长率降低;且变化的幅度随着扩胀比的提高而增大.通过对PVC管坯扩胀参数的优化,可以获得外观优良,强度提高明显的PVC-O管材.     

Fatigue behavior of continuous glass fiber composites: Effect of the matrix nature

The effect of the matrix morphology on the fatigue behavior of a continuous glass fiber/polypropylene (GF/PP) composite system was studied by means of stress‐life and mode II cyclic delamination tests. The stress‐life behavior of a GF composite is considerably affected by the nature of the matrix. A two‐stage fatigue damage curve was observed in the composite made with a PP matrix, whereas a three‐stage curve was observed in the composite made with a thermoset polyester matrix. For a fatigue stress higher than 50% of the yield stress, the PP matrix composite showed a considerably longer fatigue life than the thermoset polyester matrix composite. Mode II cyclic delamination tests showed that the morphology itself of the PP matrix also played an important role. Higher fatigue delamination growth rates, at given strain energy release rates, and lower strain energy release rates at failure were obtained for a composite showing a coarse spherulitic morphology and well‐marked interspherulitic regions than for a composite showing a finer spherulitic morphology and less‐marked interspherulitic regions. While the fatigue mode of the composite with a coarse spherulitic morphology was interspherulitic, that of the composite with a finer spherulitic morphology was transpherulitic.     

Stress transmission in silica particulate epoxy composite by X-ray diffraction

Stress on particles in silica particulate epoxy composite under constant load was investigated by X-ray diffraction. Microdeformation of the crystal lattice of silica could be detected as a shift of the X-ray diffraction peak induced by the applied stress. When a tensile stress was applied to the particulate composite, incorporated particles were found to be subjected to a stress several times larger than the applied stress. The stress concentration onto particles in particulate composite material, which was considered to result in a mechanical reinforcement of the composite, depends on the volume fraction and size of particles. Quantitative relationships between the stress concentration coefficient, particle diameters and the increment of macroscopic Young's modulus with the incorporation of filler were stated.     

基于温拌沥青技术的苯乙烯-丁二烯-苯乙烯嵌段共聚物/橡胶粉复合改性沥青应力吸收层层间性能

将3种不同的温拌剂添加到苯乙烯-丁二烯-苯乙烯嵌段共聚物（SBS）/橡胶粉复合改性沥青中,并拌和相应的应力吸收层混合料成型后制得复合式试件,通过黏度试验评价了不同温拌剂对SBS/橡胶粉复合改性沥青降黏效果的影响,通过层间拉拔试验、剪切试验和剪切疲劳试验分析了温拌SBS/橡胶粉复合改性沥青混合料应力吸收层层间性能的变化特性。结果表明,温拌剂的降黏效果由优到劣的顺序依次为:Evotherm-3 G、Sasobit-LM、Aspha-min,温拌沥青技术并不影响常温环境下复合改性沥青应力吸收层层间的黏结性能和抗剪性能;高温及水浴环境会导致不同应力吸收层层间力学强度明显降低,且不同温拌剂复合改性沥青应力吸收层的层间拉拔强度和抗剪强度存在差异,其中温拌剂Evotherm-3 G和Sasobit-LM能够增强应力吸收层层间的力学强度;相对于SBS/橡胶粉复合改性沥青的应力吸收层,添加温拌剂会缩短应力吸收层混合料的层间剪切疲劳寿命,Sasobit、Aspha-min和Evotherm-3 G温拌复合改性沥青应力吸收层的层间剪切疲劳寿命分别缩短了约10.0%、17.4%和2.7%。     

Micromechanical analysis of the kink‐band performance at the interface of a thermoplastic composite under tensile deformation

The manufacture of thermoplastic composites normally involves compression molding that generates fiber dislocations known as kink‐bands, which create stress concentrations able to cause the premature compression failure of a composite; nevertheless, the kink‐band influence over the interfacial performance or failure of a composite tested under tension is not fully understood. This work uses Raman spectroscopy as a tool to map the axial stress distribution around a kink‐band in an aramid/low density polyethylene single fiber composite. The stress distribution along the fiber was fitted to a generalized shear‐lag model to calculate the interfacial shear stress; its maximum was found around the kink‐band where the fiber interface was still bonded to the matrix, defining a localized stress concentration. POLYM. COMPOS., 31:1817–1817, 2010. © 2010 Society of Plastics Engineers.     

Interfacial shear strength studies of nicalon fibers in epoxy matrix using single fiber composite test

Interfacial properties of Nicalon (SiC) fiber in epoxy matrices of varying stiffnesses were studied using the single fiber composite test, in conjunction with stress birefringence patterns. Extensive debonding was observed with hard epoxies, but transverse matrix cracks were found in the more flexible epoxies, with the interface remaining intact. Micromechanical modeling and Monte Carlo simulation of the single fiber composite fragmentation process provided a basis to compute the interfacial shear stress from the final fragmentation length distribution. The interfacial shear stress appeared to decrease moderately with increasing matrix ductility. The large diameter Nicalon fibers create transverse cracks in the single fiber composite specimens made with flexible epoxies. Consequently, there is a high possibility of premature failure of the specimen before fiber break saturation is reached. This poses some difficulty in interpreting the results for flexible epoxies. It was also found that the interfacial shear stress values from the single fiber composite tests were always considerably higher than the ultimate shear stress values obtained from bulk epoxy (without fiber) tension tests. This effect is similar to what was seen earlier for single fiber composite tests based on graphite fibers and similar epoxy blends, though the difference between the two values was not as great.     

激光强化电刷镀n-Al2O3/Ni复合镀层残余应力研究

利用Nd3+:YAG激光器对电刷镀过程进行强化,在45钢上制备了n-Al2O3/Ni复合镀层。采用X射线衍射法测定了镀层的轴向残余应力及其随镀层厚度变化情况。结果表明,镀层厚度从10μm增加到200μm,激光强化电刷复合镀层的轴向残余应力由压应力逐渐转变为拉应力。当激光功率为600W时,厚度为200μm的镀层的残余应力为103MPa,比普通电刷镀层降低约255MPa。分析了激光对n-Al2O3/Ni电刷复合镀层轴向残余应力的影响机理。     

橡胶复合材料在循环载荷下的疲劳损伤特性

利用自行建立的疲劳试验系统，以单向聚酯帘线增强橡胶复合材料为对象，研究了循环载荷作用下影响橡胶复合材料疲劳性能的因素。结果表明，应力幅值和加载频率对橡胶复合材料疲劳性能影响较大，而平均应力影响较小。聚酯／橡胶复合材料的疲劳强化现象主要与组分材料本身的特性有关。     

Effects of residual stresses on the fracture properties of non-oxide laminated composites

A layered ceramic composite in the AlN–SiC–MoSi₂ system was prepared with the outer layers under residual compressive stress. The mechanical properties of the constituent layers and of the laminated composite were measured. Due to the residual compressive stress, the fracture strength of the laminated composite was higher than the strength of the outer layer material. The fracture toughness of the laminar composite was evaluated by SEVNB. The resulting values were compared with a fracture mechanics model and a good agreement was found between the experimental measurements and the calculated apparent fracture toughness profile.     

Carbon-Coated-Glass-Fiber-Reinforced Cement Composites: I, Fiber Pushout and Interfacial Properties

Interfacial mechanical properties of carbon-coated-S-glass-fiber-reinforced cement were characterized by a fiber pushout technique. The pushout experiments were conducted on model composites, where the S-glass monofilaments with and without carbon coating were unidirectionally embedded in ordinary portland cement. Interfacial properties, including bonding strength, frictional stress, residual stress, and fracture energy, were extracted from the previously developed progressive debonding model. The composite with a carbon interface exhibited a weaker interfacial bonding strength and frictional stress than did the composite without a carbon interface. The interfacial fracture energy of the composite with a carbon interface was 7.9 J/m², as compared to 47.6 J/m² for the composite without a carbon interface. The composite with the carbon interface exhibited a smaller residual clamping stress (18 MPa), in comparison to that for the composite without a carbon interface (69 MPa). Scanning electron microscopy observations indicated that the filament without a carbon coating was significantly attacked by the alkaline environment and was strongly bonded onto the matrix, whereas the filament with a carbon coating remained intact under the same curing conditions. These studies suggest that carbon coating provides the glass fiber with significantly improved corrosion resistance to alkali in the cement environment.     

Effects of Fiber Volume Fraction on Mechanical Properties of SiC-Fiber/Si3N4-Matrix Composites

The effects of fiber volume fraction on composite mechaniacl properties were examined in SiC-fiber-reinforced Si₃N₄ composites fabricated in our laboratories. Fiber volume fraction was found to have significant effects on important composite properties including failure mode, ultimate strength, matrix-cracking stress, fiber–matrix interfacial shear stress, and work-of-fracture. The composite mechanical properties were improved with increasing fiber volume fraction. However, when the fiber volume fraction was sufficiently large, the composite ultimate strength was degraded. This was related to fiber strength loss as a result of fiber damage from contact with surrounding fibers and abrasive matrix particles during hot pressing.