热作模具钢的发展与应用

用铸造模具钢坯制造模具以其耗能耗材少、生产周期短、制造成本低的特点得到了越来越多的关注、研究与应用。介绍热作模具钢的发展概况及铸造H13钢的具体应用。     

钠钙硅玻璃摩擦磨损性能研究

利用多功能表面性能实验机考察了不同载荷下钠钙硅玻璃与45#钢对摩时的摩擦磨损性能,用体式显微镜和显微硬度计观察和分析磨损表面形貌,并利用双环实验测试了不同加载时间的钠钙硅玻璃残余强度,探讨了材料的磨损机理,结果表明:磨损率随着载荷的增加出现波动,当载荷低于10 N时,摩擦系数随载荷增加而明显增大,而当载荷超过10 N时,摩擦系数随载荷增加而明显降低,在较低载荷下,钠钙硅玻璃的磨损失效主要源于轻微点蚀,在较高载荷下,其磨损失效主要源于表层塑性变形。     

快速镍镀层在含磨粒油润滑条件下的摩擦磨损性能研究

在电刷镀实际操作时,周围环境的污染粒子和磨损过程中产生的磨屑均会成为磨粒。所以,在含磨粒的润滑条件下,研究刷镀层的耐磨性就更有实用意义。本文在接近实际工况下对快速镍镀层摩擦磨损性能做出了切合实际的评价,以期使电刷镀更好地为生产服务。1 试验方法     

天然海水润滑下不锈钢316L与PEEK450CA30的摩擦磨损性能

为了寻找适合于低速大扭矩水液压马达配对副的材料,采用MMU-5G屏显式高温材料端面摩擦磨损试验机考察不同转速、不同载荷下,摩擦副316L-PEEK450CA30在海水中的摩擦磨损性能,并借助OLYMPUS-SZX体式显微镜对试样的磨损表面进行形貌观察。结果表明:在转速和载荷比较低的情况下,摩擦副316L-PEEK450CA30的摩擦系数较小,磨损性能较好;当转速或载荷增大时,摩擦副的摩擦系数和接触面的磨损情况会急剧增大。在转速300r/min、载荷100N和转速100r/min、载荷300N的情况下,摩擦副316L-PEEK450CA30还会发生轻微的黏着磨损。最后得出,当转速为100r/mim、载荷为100N时,对偶副间的摩擦系数最小,耐磨损程度最好,适合作为低速大扭矩水液压马达的对偶副材料。     

粉刷层对混凝土遭受高温作用后抗压性能的影响

本文通过实际案例,对在高温作用后对混凝土构件的抗压性能进行相关的实验研究,并且根据相关的实验结果,粉刷层对混凝土遭受高温作用后抗压性能的影响进行了分析,发现粉刷层在遭受高温作用后,对建筑机构的混凝土构件有着良好的保护作用。     

粉刷层对混凝土遭受高温作用后抗压性能的影响

对27个高温作用后常规混凝土试块和带混合砂浆粉刷层的混凝土试块的抗压性能进行了试验。通过对高温作用后试件损伤形态的分析和高温损伤试件的抗压性能试验,探讨了混合砂浆粉刷层对高温作用后混凝土抗压性能的影响,得到了高温作用后无粉刷层试块和带粉刷层试块的强度折减经验计算公式。试验研究表明,粉刷层对遭受火灾高温作用的混凝土构件有较好的保护作用,在混凝土结构火灾损伤鉴定中应加以考虑。     

含摩擦型消能装置预应力钢柱的耐震性能

针对预应力钢柱基底含摩擦型消能装置的耐震性能进行研究,探讨初始钢绞线预应力与消能装置的影响。通过钢绞线施拉预应力接合钢柱与基础,用来提供钢柱自复位能力;消能装置采用摩擦型消能,提供柱构件与基础接合的滞回消能能力,因此柱构件在受震后拥有自复位与无残余变形特性。研究参数包含初始预应力大小、摩擦消能面积与摩擦型消能装置的位置。通过理论推导建立预应力与消能装置在钢柱与基础接合的性能模式,进而设计试件进行试验来验证其性能。试验结果表明,柱与基础接合面有开启与闭合的现象;提高摩擦型消能装置螺栓的预应力量,能有效提升滞回消能面积;提升初始钢绞线预应力量,能使滞回循环远离原点,确保自复位能力;消能装置安装在柱翼板处比安装在柱腹板处有较好的消能能力,且较为经济。预应力钢柱基底含摩擦型消能装置具有良好的自复位能力,具有滞回消能能力且柱构件无残余变形,理论分析亦能准确预测其性能。     

复合型摩擦消能支撑的滞回模型

根据由试验获得的复合型摩擦消能支撑滞回曲线 ,提出了复合型摩擦消能支撑的滞回模型 ,并用它来拟合试验结果。计算机拟合结果与试验结果的对比表明 ,所制定的滞回模型是合理的     

高温后钢筋混凝土柱的粉刷层抗火性能试验

利用有限元软件对钢筋混凝土柱试验试件进行热—结构耦合仿真模拟分析,分析粉刷层对试件温度场分布的影响,以及粉刷层对火灾后钢筋混凝土框架柱抗震性能的影响,并与试验结果进行了对比。     

采用摩擦和消能装置的加层结构振动台试验研究

本文结合加层结构实际工程,提出采用摩擦阻尼器和砂垫层作为减震装置,进行了增设摩擦和消能装置的加层结构模型模拟地震振动台试验,并引入非经典阻尼分析理论对试验结果进行了分析比较。结果表明采用摩擦和消能装置的加层模型减震效果明显,摩擦和消能装置能有效地吸收地震动输入能量,减小模型结构的地震反应。     

High temperature properties of hot-rolled,structural steels for use in fire engineering design studies

An extensive programme of small-scale tensile tests has been carried out under both steady-state and transient heating conditions to provide elevated temperature data on the behaviour of hot-rolled, structural steels for use in fire engineering design studies.It has been demonstrated that predictions on the behaviour of structural steels at small strains from data derived under steady-state conditions are optimistic and information should preferably be used from transient tests. However, when temperatures and stresses corresponding to strains approaching ‘runaway’ or the ‘limit of deflection’ are compared, then there is negligible difference between the minimum properties derived from either type of test. Tables of data are provided in a form suitable for use in fire engineering calculations.     

二硫化钨改性聚四氟乙烯摩擦摆支座摩擦磨耗性能研究

针对摩擦摆隔震支座聚四氟乙烯PTFE摩擦滑移材料存在磨损率高、冷流性和熔体黏度高等问题,在PTFE材料中添加不同掺量的二硫化钨(WS2)。在对摩擦滑移材料基本物理力学性能进行试验研究的基础上,研究支座的摩擦磨损性能,并分析加载速度、压应力与摩擦系数的关系,进而综合给出PTFE材料中WS2含量的建议值,同时利用ABAQUS软件对摩擦副支座进行有限元分析和试验验证。结果表明：添加纳米级2%、4%WS2对PTFE进行改性,能在确保基本物理力学性能的前提下,显著改善PTFE的耐磨损性能,且摩擦系数与纯PTFE相差不大,是改进桥梁用摩擦摆支座性能的一种较好方法。     

石墨烯复合材料的摩擦磨损研究进展

石墨烯以其优异的性能和独特的二维结构成为材料领域研究热点。石墨烯复合材料的摩擦磨损是石墨烯应用领域中的重要研究方向。本文介绍了石墨烯聚合物复合材料、石墨烯无机陶瓷复合材料和石墨烯金属基复合材料的制备及摩擦磨损性能,同时展望了石墨烯作为高性能润滑材料的研究方向及发展趋势。     

High temperature properties of wax modified binders and asphalt mixtures

The influence of adding two commercial waxes (FT-paraffin and polyethylene wax) to binders of penetration grades 50/70 and 160/220 were investigated for high temperature performance of binders and asphalt concrete mixtures. Binder properties were determined by conventional test methods, dynamic mechanical analysis and bending beam rheometer testing. The high temperature properties of asphalt concrete were investigated using the French rutting tester.The addition of FT-paraffin and polyethylene wax increased the rutting resistance of mixtures for both types of binder. The FT-paraffin modified asphalt mixtures showed the best rutting resistance.Adding polyethylene wax showed the highest stiffening effect in terms of rutting factor by DMA for the binders. However, this could not be verified in asphalt mixture testing. Adding FT-paraffin improved the rutting resistance of asphalt mixtures containing low or high penetration binder, but for the mixture containing high penetration binder the specification limit was exceeded.     

High temperature properties of rubberized binders containing warm asphalt additives

Several studies have been conducted evaluating the properties of warm mix asphalt (WMA), and it is observed that warm asphalt additives work in different ways to either reduce the viscosity of the binder or to allow better workability of the mix at lower temperatures. In terms of rubberized asphalt mixtures, they are compacted at a higher temperature than conventional mixtures, based on the field experience. If the technologies of warm mix asphalt are incorporated, it is expected to reduce the mixing and compaction temperatures of rubberized asphalt mixtures to those of conventional mixtures. This paper presents the high temperature properties of rubberized binders containing warm asphalt additives. Rubberized binders were produced at 10% by binder weight using five binder sources, and the binders with the additives were produced using two (i.e. Aspha-min^® and Sasobit^®) of the available processes and artificially short-term aged through the rolling thin film oven (RTFO) method. Tests were conducted on the binders using the rotational viscometer and the Dynamic Shear Rheometer. The results indicated that the viscosity properties of rubberized binders can be changed significantly through the use of warm asphalt additives. Also, the addition of the additives was found to improve rutting resistance of the rubberized binders.     

重视发动机大修后的冷磨热试

发动机大修以后，为了检查和消除装配中的缺陷，调整各机构，提高配合零件的表面质量，使其能承受应有的载荷，应进行冷磨热试检查，以便延长发动机的使用寿命，得到最好的动力性和经济性。     

轴向柱塞泵摩擦副耐磨可靠性设计

本提出了以摩擦副的（ｐυ）应力模型和应力一强度干涉模型为基础，建立轴向柱塞泵缸体一配流盘这对关键摩擦副可靠性设计模型，并以ＸＢ４０型轴向柱塞泵为实例，作了缸体一配流盘的耐磨可靠性设计。     

Mechanical properties of cold-formed steels at elevated temperatures

Mechanical properties have an important role in the fire safety design of cold-formed steel structures due to the rapid reduction in mechanical properties such as yield strength and elastic modulus under fire conditions and associated reduction to the load carrying capacities. Hence there is a need to fully understand the deterioration characteristics of yield strength and elastic modulus of cold-formed steels at elevated temperatures. Although past research has produced useful experimental data on the mechanical properties of cold-formed steels at elevated temperatures, such data do not yet cover different cold-formed steel grades and thicknesses. Therefore, an experimental study was undertaken to investigate the elevated temperature mechanical properties of two low and high strength steels with two thicknesses that are commonly used in Australia. Tensile coupon tests were undertaken using a steady state test method for temperatures in the range 20–700 °C. Test results were compared with the currently available reduction factors for yield strength and elastic modulus, and stress–strain curves, based on which further improvements were made. For this purpose, test results of many other cold-formed steels were also used based on other similar studies undertaken at the Queensland University of Technology. Improved equations were developed to predict the yield strength and elastic modulus reduction factors and stress–strain curves of a range of cold-formed steel grades and thicknesses used in Australia. This paper presents the results of this experimental study, comparisons with the results of past research and steel design standards, and the new predictive equations.     

Experimental investigation of post-fire mechanical properties of cold-formed steels

Cold-formed steel members are widely used in residential, industrial and commercial buildings as primary load-bearing elements. During fire events, they will be exposed to elevated temperatures. If the general appearance of the structure is satisfactory after a fire event then the question that has to be answered is how the load bearing capacity of cold-formed steel members in these buildings has been affected. Hence after such fire events there is a need to evaluate the residual strength of these members. However, the post-fire behaviour of cold-formed steel members has not been investigated in the past. This means conservative decisions are likely to be made in relation to fire exposed cold-formed steel buildings. Therefore an experimental study was undertaken to investigate the post-fire mechanical properties of cold-formed steels. Tensile coupons taken from cold-formed steel sheets of three different steel grades and thicknesses were exposed to different elevated temperatures up to 800 °C, and were then allowed to cool down to ambient temperature before they were tested to failure. Tensile coupon tests were conducted to obtain their post-fire stress–strain curves and associated mechanical properties (yield stress, Young׳s modulus, ultimate strength and ductility). It was found that the post-fire mechanical properties of cold-formed steels are reduced below the original ambient temperature mechanical properties if they had been exposed to temperatures exceeding 300 °C. Hence a new set of equations is proposed to predict the post-fire mechanical properties of cold-formed steels. Such post-fire mechanical property assessments allow structural and fire engineers to make an accurate prediction of the safety of fire exposed cold-formed steel buildings. This paper presents the details of this experimental study and the results of post-fire mechanical properties of cold-formed steels. It also includes the results of a post-fire evaluation of cold-formed steel walls.     

上行式移动模架作业原理及拼装技术

分析了上行式移动模架的工作原理及作业流程,从主框架组成、模板组成、支腿组成等方面介绍了上行式移动模架的结构组成,探讨了上行式移动模架的拼装及预压,以保证移动模架拼装的工程质量,降低移动模架的施工成本。