预应力混凝土空心叠合板试验研究

针对现有的一般预应力空心叠合板楼盖板厚较大,自重较大等缺点,提出了一种新形式的预应力混凝土空心叠合板,通过对3块简支板,3块简支叠合板和1块两跨连续叠合板进行静力荷载试验,分析了这种板在静力荷载作用下的裂缝、承载力、挠度等特点,研究了其开裂荷载和极限承载力较高的原因。试验结果表明这种预应力空心叠合板具有良好的抗裂性能和较高的极限承载能力,建立了开裂弯矩、极限承载力、挠度的计算方法,为这种叠合板的设计和工程应用提供了依据。     

某固体火箭发动机点火器药柱断裂分析与改进

针对某固体火箭发动机点火器加速老化后,在低温动力环境试验中部分产品的B/KNO 3点火药柱断裂现象,采用故障树法对断裂的原因进行了排查,并通过压力试验、强度仿真等方法对其进行分析。结果表明：药柱支撑体与装药管体间较大的间隙和药柱支撑体排列的不合理,导致药柱在振动过程中出现应力集中区域,从而产生断裂。因此,提出了消除间隙、增加支撑体、优化支撑位置等改进措施,验证试验表明改进措施消除了药柱断裂现象。     

Fatigue crack sizing in steel bridge decks using ultrasonic guided waves

A baseline-free quantitative sizing methodology utilizing ultrasonic guided waves for fatigue cracks under welded stiffeners in steel bridge decks has been developed. An inverse wavefield extrapolation-based formulation for obtaining the crack reflectivity and depth profile has been presented in the kernel of which, the presence of welded orthogonal stiffeners has been accounted for. Having conducted experiments on a test bridge deck subject to fatigue loading, it has been demonstrated that the crack profile can be estimated from the reflection coefficients obtained. In comparison with the reference measurements, the maximum crack depth estimation error turned out to be about 20%.     

Estimating the orientation of Stage I crack paths through the direction of maximum variance of the resolved shear stress

Our formalisation of the Shear Stress-Maximum Variance Method takes as a starting point the hypothesis that, in ductile materials subjected to fatigue loading, the crack initiation planes, i.e. the so-called Stage I planes, are those containing the direction experiencing the maximum variance of the resolved shear stress. From a computational point of view, the most remarkable implication of the above assumption is that, as soon as the variance and covariance terms characterising the considered load history are known, the effective time needed to estimate the orientation of the critical plane does not depend on the length of the load history itself. Further, such a computational efficiency is seen to be associated with an high-level of accuracy in estimating fatigue lifetime of both plain and notched engineering components, this holding true under constant as well as under variable amplitude uniaxial/multiaxial fatigue loading. In this scenario, by assuming that the orientation of Stage I planes can directly be determined through the orientation of Stage II crack paths, the present paper investigates whether, independently from the degree of multiaxiality and non-proportionality of the applied loading history, the direction of maximum variance of the resolved shear stress is also capable of accurately estimating the orientation of Stage I crack paths.     

Simulation Charpy impact energy of functionally graded steels by modified stress-strain curve through mechanism-based strain gradient plasticity theory

In the present work, Charpy impact energy of functionally graded steels produced by electroslag remelting composed of graded ferritic or austenitic layers in both crack divider and crack arrester configurations has been modeled by finite element method. The yield stress of each layer was related to the density of the statistically stored dislocations of that layer and assuming by Holloman relation for the corresponding stress-strain curves, tensile strengths of the constituent layers were determined via numerical method. By using load-displacement curves acquired from instrumented Charpy impact tests on primary specimens, the obtained stress-strain curves from uniaxial tensile tests were modified. The data used for each layer in finite element modeling were predicted modified stress-strain curves obtained from strain gradient plasticity theory. A relatively good agreement between experimental results and those obtained from simulation was observed.     

循环甲醇冷却器接管锥壳裂纹分析及防范措施

循环甲醇冷却器使用一段时间后,其接管锥壳出现了3个裂纹:1个纵向裂纹,2个横向裂纹。从材料化学成分、制作内应力方面进行了分析,找出出现裂纹的原因,并提出了防范措施。     

Fiber reinforced mortar affected by alkali-silica reaction: A study by synchrotron microtomography

Alkali-Silica reaction (ASR) is a physicochemical process that can deteriorate concrete and is a recurring engineering problem. In this study three different cylindrical samples affected by ASR were prepared: a plain mortar and two composite mortars containing fibers (polypropylene and a polymer hybrid), which were analyzed at the microtomography (μCT) beamline 8.3.2 at the Advanced Light Source (ALS). In general, three different features were observed during the 136 day observation period: (1) aggregate dissolution, (2) crack propagation from inside the aggregate, through the cement matrix, and at the ITZ, and (3) the alkali-silica gel filling cracks and voids. In addition, accelerated mortar bar tests were utilized to observe ASR's expansive effect in the plain and composite mortars, and the fibers' ability to restrain expansion due to ASR.     

Electrical disintegration and micro-focus X-ray CT observations of cement paste samples with dispersed mineral particles

Electrical disintegration is an effective liberation technique in mineral processing where the liberation ratio depends on the mineralogical properties of the mineral grains. However elucidation of the liberation behavior is difficult since the fragments after the electrical disintegration are fine and complex. This study applies electrical disintegration to cement paste samples with various dispersed mineral particles (calcite, quartz, albite, and pyrite) and the disintegrated products are observed with a micro-focus X-ray CT scanner. Current channels and crack extension behavior from the channels are identified by cross sectional CT and three dimensional reconstructed images. A classification of the crack patterns was carried out and compared with the results of liberation ratio measurements of the products.     

闭式双点压力机曲轴断裂失效分析研究

本文为分析曲轴产生断裂失效的原因,采用对失效件进行详细分析,找到导致零件失效的原因,并分析这些影响因素的作用机理,得出基本合理的科学理论。通过后续的实际生产检验,证实分析和改进措施的有效性。     

Heating characterization of the thickness-through fatigue crack in metal plate using sonic IR imaging

In sonic IR imaging, a major problem is exploring the heating characteristics of crack vicinity to guide the optimization of the test conditions. In this paper, the crack's heating characteristics of the metallic plate with an artificial fatigue crack has been studied. Experimental results showed that the during ultrasonic excitation the temperature rise of crack vicinity at the plate's excitation side is higher than that at its opposite side, whereas the total heating efficiency of the crack face appears to be stable. Through the profile mapping of the crack face, the frictional heating is mainly concentrated near the excitation side. Based on this phenomenon, we built a mathematical heat transfer model to calculate the temperature distribution of the crack vicinity and investigated the heating features of crack faces. Additionally, the mathematical model gives a quantitative relation between the depth of the heat source and the ratio of the temperature distribution of the crack vicinity at opposite side to that at the front side. This study aims to provide a quantitative evaluation method for locating the frictional heating areas in sonic IR imaging.