腐蚀环境下再生混凝土结构耐久性设计研究

为推广耐久性设计在再生混凝土结构工程设计中的应用,在考虑再生粗骨料来源的复杂性和再生混凝土初始损伤的影响基础上,结合近年来我国再生混凝土结构相关研究与应用成果,根据普通混凝土结构耐久性设计原则,分析研究腐蚀环境条件下再生混凝土结构的耐久性设计问题,然后确立腐蚀环境条件下再生混凝土结构耐久性设计的基本方法。结果表明:在再生混凝土与普通混凝土强度等级相同的情况下,当30%再生粗骨料取代率≤50%及再生粗骨料取代率50%时,钢筋保护层厚度应适当分别增加3 mm和5 mm,而再生混凝土养护时间应适当分别延长24 h和48 h。     

锈蚀混凝土梁承载力退化的试验研究

通过试验研究了锈蚀混凝土梁承载力的退化.试验中,共浇铸和试验了58个梁以调查钢筋锈蚀程度、锈蚀电流密度、水灰比和保护层厚度对梁承载力退化的影响.结果表明:当纵向裂缝宽度小于0.01mm时,梁承载力有较小程度的提高,但当纵向裂缝宽度大于0.01mm时,梁承载力随着纵向裂缝宽度的增大而减小.梁承载力退化速率随着锈蚀电流密度和保护层厚度的增大而减小,但随着水灰比的增大而增大.     

锈蚀钢筋混凝土梁的疲劳性能

对8根模拟锈蚀钢筋混凝土梁进行了高周疲劳试验,研究和探讨了模拟锈蚀钢筋混凝土梁的疲劳性能。结果表明,交变荷载作用下试件的斜裂纹出现并迅速发展成主裂缝;模拟锈蚀钢筋混凝土梁多在端部发生剪切疲劳破坏;试件的挠度发展、裂缝分布与破坏形态密切相关;随循环次数增加,锈蚀主筋的最大、最小应力不断增长,应力幅值基本不变;混凝土的最大、最小压应变快速增长,应变幅值平稳增长;试件的疲劳寿命具有较大的离散型;同等条件下,锈蚀钢筋混凝土梁的疲劳寿命往往比锈蚀钢筋的轴向拉伸疲劳寿命长。     

Lab-scale feasibility study on new elastomer comprising chloroprene and acrylonitrile for oil and gas applications

The limited options of suitable elastomers with adequate cost-performance balance drive the necessity to introduce new materials in the oil & gas (O&G) application space. The relevance of a recently developed copolymer of chloroprene and acrylonitrile (referred to as acrylonitrile–chloroprene rubber or NCR) to O&G applications is described in this technical contribution. The new elastomer demonstrates adequate physical properties and reasonably good high and low-temperature capabilities. It offers good resistance to several aqueous and non-aqueous fluids with low volume swelling and retains its physical properties to reasonable extents while exposed to hot test oils. Acrylonitrile–chloroprene rubber has been found to sustain “sour gas” exposure. Good abrasion resistance, high tear strength, and remarkably high flex-fatigue resistance coupled with low heat build-up reflect its durability under dynamic conditions. In addition, acrylonitrile–chloroprene rubber can very well withstand the rapid gas decompression test at 25°C. This unique combination of attributes may allow acrylonitrile–chloroprene rubber to be considered as a candidate material for high-performance O&G applications.     

Creep behavior and failure mechanisms of CVI and PIP SiC/SiC composites at temperatures to 1650 °C in air

Creep properties of 2D woven CVI and PIP SiC/SiC composites with Sylramic™-iBN SiC fibers were measured at temperatures to 1650 °C in air and the data was compared with the literature. Batch-to-batch variations in the tensile and creep properties, and thermal treatment effects on creep, creep parameters, damage mechanisms, and failure modes for these composites were studied. Under the test conditions, the CVI SiC/SiC composites exhibited both matrix and fiber-dominated creep depending on stress, whereas the PIP SiC/SiC composites displayed only fiber-dominated creep. Creep durability in both composite systems is controlled by the most creep resistant phase as well as oxidation of the fibers via cracking matrix. Specimen-to- specimen variations in porosity and stress raisers caused significant differences in creep behavior and durability. The Larson-Miller parameter and Monkman-Grant relationship were used wherever applicable for analyzing and predicting creep durability.     

Microstructures and Properties of Laser-Glazed Plasma-Sprayed ZrO2-YO1.5/Ni-22Cr-10AI-1Y Thermal Barrier Coatings

Thermal barrier coatings (TBCs) consisting of two layers with various yttria contents (ZrO ₂- YO_1.5/Ni-22Cr-10Al- lY) were plasma sprayed, and parts of the various specimens were glazed by using a pulsed CO₂ laser. All the specimens were then subjected to furnace thermal cycling tests at 1100 °C; the effect of laser glazing on the durability and failure mechanism of the TBCs was then evaluated. From these results, two models were developed to show the failure mechanism of as- sprayed and laser- glazed TBCs: model A, which is thermal-stress dominant, and model V, which is oxidation-stress dominant. For top coats containing cubic phase, cubic and monoclinic phases, or tetragonal and a relatively larger amount of monoclinic phases, whose degradation is thermal- stress dominant, laser glazing improved the durability of TBCs by a factor of about two to six. Segmented cracks that occurred during glazing proved beneficial for accommodating thermal stress and raising the tolerance to oxidation, which resulted in a higher durability. Thermal barrier coatings with top coats containing tetragonal phase had the highest durability. Degradation of such TBCs resulted mainly from oxidation of the bond coats. For top coats with a greater amount of monoclinic phase, thermal mismatch stress occurred during cooling and detrimentally affected durability.     

Durability of Titanium/Dicalcium Silicate Composite Coatings in Simulated Body Fluid

Titanium/dicalcium silicate composite coatings with different ratios (weight ratios as Ca₂SiO₄: Ti = 3:7, 5:5, 7:3) were prepared by plasma spraying. Effects of titanium addition on coating properties, such as bonding strength, flexural modulus, and dissolution in simulated physiological environment, were studied. Results showed that the bonding strength between coating and Ti-6Al-4V substrate increased with increase of titanium content in the composite coatings. It was explained by the narrowed dissimilarity of thermal expansion coefficients between the coatings and substrates. Degradation of mechanical properties after immersion in simulated body fluid was also studied. The dissolution of dicalcium silicate in the composite coatings resulted in the decrease of flexural strength and flexural modulus of the coatings in the simulated physiological environment. The higher titanium content in the composite coatings, the stabler are the composite coatings in the physiological environment.     

汽车行李箱盖关闭冲击及耐久性分析

基于LS-DYNA提出一种对汽车行李箱盖进行关闭冲击仿真的建模方法.建立密封条和锁总成的详细模型,并根据仿真结果对行李箱盖进行耐久性预测.仿真结果与试验结果的对比验证该模型的准确性.该方法可有效仿真汽车行李箱盖的关闭冲击及耐久性能,提升设计效率.     

预应力锚索腐蚀耐久性试验方案设计探讨

预应力锚索在岩土工程加固中应用广泛,其腐蚀耐久性对工程运行安全至关重要,而相关的腐蚀变化规律及机理还有待进一步明确。在总结当前预应力锚索腐蚀耐久性研究成果的基础上,对其腐蚀耐久性室内加速试验方案设计进行了探讨。分析了影响腐蚀的主要因素并拟定了各因素的不同影响水平;采用正交设计方法优化试验方案并通过有限元方法对试验模型尺寸和应力分布进行了计算模拟优化和验证;介绍了模型制作等工艺步骤。相关成果可供类似耐久性试验方案设计参考。      

曹娥江大闸结构耐久性设计

本文通过曹娥江大闸耐久性设计介绍,探讨有关措施对提高结构耐久性的作用,为了达到设计寿命100年的目标,主要采取了结构合理分缝、适当加大保护层厚度、高性能混凝土、预应力钢绞线、环氧涂层钢筋、施工期混凝土裂缝控制、水位变动区大块石护砌等措施.