涵闸工程施工期混凝土温度监测系统与水化热参数反演

针对涵闸工程混凝土温控防裂需要,研制了全自动化数字测温系统。该系统的硬件部分由数字式温度传感器、采集单元、GPRS DTU组成,软件部分包括中心服务器软件和客户端软件。系统实现了GPRS公用无线网络覆盖范围内无人值守、多测点远程测量和数据实时共享,具有体积小、无需布线、运行稳定、精度高等特点。经过实际工程多次应用,系统运行稳定可靠,达到预期性能。基于以上系统的测量数据,结合三维非稳定温度场数值计算,对特定工程的水化热参数进行了反演。规范给出普硅42.5水泥水化热参数为m=0.69,n=0.56;而根据实测数据反演的结果为m=1.85,n=0.79。根据两组参数分别进行了三维温度应力计算,得到完全不同的计算结果,前者温度应力未超标,后者多处超标需要采用温控防裂措施才能保证结构防裂安全。因此对实际工程进行温度监测和水化热参数反演是非常必要的。     

单向Cf/SiC复合材料的弯曲疲劳性能

对单向Cf/SiC复合材料进行了三点弯曲疲劳性能测试,得到了复合材料的应力－寿命曲线（S－N曲线）,并对其进行线性拟合,得到疲劳最大应力与复合材料疲劳寿命的关系;考察了疲劳过程中刚度下降和疲劳裂纹产生情况。结果表明在疲劳过程中复合材料的弯曲模量有3个变化阶段：首先在疲劳加载初期,弯曲模量的下降速度及幅度都较大;其次在弯曲模量下降到原始弯曲模量的85％（133GPa)后,其变化方式没有明显的规律可循,有时甚至可能上升;最后复合材料发生疲劳断裂时,模量将发生突变。显微结构分析表明：基体横向裂纹群的产生是疲劳断裂的独有特征。它的产生是由于基体SiC的断裂应变小于碳纤维的断裂应变,基体首先开裂并导致应力重新分布的结果。     

Failure load prediction of structural adhesive joints : Part 2: Experimental study

The objective of this study was to determine how the fracture of adhesive joints depends on elastic beam parameters describing the adherends and the applied loads. The basic specimen geometry was the cracked lap shear joint constructed of aluminium alloy with various adherend and bondline thicknesses. Loads were applied in different combinations of bending, tension and shear to generate a failure envelope for each adhesive and specimen geometry. It was found that crack propagation for precracked specimens occured at a critical strain energy release rate but was also a function of the G_I/G_II ratio and the bondline thickness. The experiments also showed that the loads required to propagate a crack in a precracked specimen were always lower than the loads required to break the fillet. Hence, by treating uncracked joints as being cracked, where the fictitious crack tip is assumed to coincide with the location of the fillet, a conservative estimate of the failure load is obtained.     

Slow stable crack growth in high density polyethylenes

The phenomenon of slow stable crack growth in polyethylene is investigated using notched specimens subject to constant load and the concepts of fracture mechanics. The effect of specimen geometry and dimension, the loading and the mode of loading on the applied stress intensity factor versus crack speed ($\text{K}{}_{\mathrm{c}}\text{-}\text{a}\text{?}$) curves has been studied to demonstrate that K_c is the controlling stress parameter for crack growth under suitable conditions. $\text{K}{}_{\mathrm{c}}\text{-}\text{a}\text{?}$ curves are obtained for a high density polyethylene homopolymer in distilled water and in a diluted detergent solution at four different temperatures. Results are also obtained for a much tougher medium density polyethylene copolymer whenever possible. Several mechanisms can be identified from the form of the $\text{K}{}_{\mathrm{c}}\text{-}\text{a}\text{?}$ curves. Two, in particular, have been observed but not explained before: (i) crack growth with a time dependence of 0.25, and (ii) the high $\text{K}{}_{\mathrm{c}}\text{-}\text{a}\text{?}$ slopes for crack growth in a tough copolymer. With the help of scanning electron microscopic studies of the fracture surfaces, (i) is postulated to be due to diffusion controlled void growth process and (ii) is considered to be the result of crack tip blunting effects. From the temperature dependence of crack growth, the activation energy of the diffusion controlled crack growth process is found to coincide with that of the x-relaxation process in polyethylene implying that diffusion controlled crack growth may be related to the motion of main chains in the polymer.     

基于CT扫描的致密砂岩脆性破坏裂纹扩展规律研究

岩石在荷载作用下产生宏观破坏,其破裂面细观形态变化可以直接地反映出结构破坏特征。目前,常采用扫描电镜法、透镜法和CT扫描技术对岩石细观结构进行表征。运用CT扫描技术对典型脆性岩样单轴压缩破坏后破裂面及全断面进行扫描,获取全断面的细观形态,分析和总结了典型脆性岩样破坏细观裂纹扩展的发展规律:每一条独立裂纹都以一恒定曲率半径系数K随层位向试样内部扩展,直至裂纹曲率半径趋近于无穷。此时若无其他因素影响,其曲率半径则不会再随层位继续扩展;并通过分析定义出岩石脆性破坏状态时裂纹的聚集域和非聚集域,同时根据能量守恒定律得出了衍生裂纹及新次生裂纹产生的判据。     

不同泊松比复合材料的裂纹尖端应力场

具有平面负泊松比的碳纤维/环氧树脂非平衡复合材料层板具有很高的断裂韧性和缺口断裂强度。本文用复变函数一变分方法计算了负泊比材料的裂纹尖端应力场，并与常规的平衡复合材料进行了比较。本文重点研究了主应力方向与纤维夹角的关系。结果表明：负泊松比材料独特的裂纹尖端应力场有利于提高缺口断裂强度。     

石墨材料的疲劳

对迄今前人在石墨材料上所开展的疲劳研究工作进行了综述，以不同的疲劳设计方法为线索，一方面通过对石墨寿命评价的S-N曲线来分析石墨的疲劳行为；另一方面从疲劳裂纹扩展的角度来分析在外应力作用下有预制裂纹的石墨的疲劳行为。总结了石墨疲劳研究的主要进展，归纳了石墨疲劳研究中的关键问题，在此基础上对石墨材料的疲劳研究前景进行了展望。     

基于数字图像处理的路面裂缝自动识别与评价系统

公路是完成交通运输和沟通各地区之间联系的重要经络,但是受到自然因素和外力的作用,会对公路的质量造成一定程度的影响,很容易造成路面裂缝,这就提出了一种基于数字图像处理的路面裂缝自动识别与评价系统,以便能够更加快速和准确的确定出路面裂缝的程度,并制定出适当的处理方法。以下,将对此项技术的结构、原理,以及提高系统处理质量和水平的关键技术进行简要的分析。     

Direct Measurement of Transformation Zone Strains in Toughened Zirconia

Residual strains responsible for crack tip shielding have been measured within transformation zones surrounding cracks in Mg-PSZ. Two techniques were used for strain measurement: moiré interferometry and high-resolution image matching. Both methods provide maps of differential in-plane displacements within the specimen surface intersected by the crack, the latter method with the higher resolution. The results are compared with finite-element analysis to assess surface relaxation effects, and the measured strains are used to evaluate the crack tip shielding stress intensity factor. Calculations based on the assumption that the unconstrained transformation strain is hydrostatic dilatation yielded results that were significantly smaller than the measured toughness increases.     

Crack–Tip Toughness of a Soft Lead Zirconate Titanate

Crack–opening displacement (COD) measurements were performed on a commercial lead zirconate titanate (PZT). The intrinsic fracture toughness (or crack–tip toughness) of this material was determined using a new evaluation procedure, which takes into account the near–tip CODs and complete crack profile CODs. The crack–tip toughness K _I0 was determined from an extrapolation of COD data obtained at various loading stages, thus avoiding the complications caused by subcritical crack growth in PZT. Results for plane strain and plane stress condition are presented.