Bond–slip on CFRP/GFRP-to-concrete joints subjected to moisture,salt fog and temperature cycles

Research on bond between composite and concrete on beams externally reinforced with fiber reinforced polymers (ERBs) has generated many publications, but uncertainties remain. The issue of the long term behavior of those joints, especially the effect that severe and prolonged environmental actions may induce, justifies the search for additional data and recommendations to avoid premature debonding and failures.The present paper devotes attention to the effects of environmental aging on the constitutive bond-slip curves. Aging was imposed on an accelerated manner and several actions used to degrade the behavior of the joints evaluated by mechanical testing.Prismatic blocks of reinforced concrete linked on the upper side by a stainless steel hinge and externally bonded by a continuous strip of carbon or glass fiber reinforced polymer (CFRP or GFRP) adherent to the soffit were made so as to fit in commercially available laboratory climatic chambers. After aging, they were tested till failure under four point loading.Aging conditions imposed on the CFRP beams were (i) cycles of high-low relative humidity, (ii) salt fog cycles, and, on the GFRP beams, (iii) salt fog cycles, (iv) dry/wet cycles (water with 5.0% weight of NaCl), (v) total immersion in salt water, and (vi) freeze/thaw cycles.The results of the experimental program enabled the proposal of bond-slip laws that take into account the aging of the beams. They also showed that salt fog cycles were more severe in the case of CFRP, while freeze/thaw cycles were more degrading on bond of GFRP-to-concrete. The salt water effects on the GFRP beams appeared to be beneficial, most likely by improving the tensile strength of concrete. Numerical modeling certified by the obtained experimental data is presented that allows more general estimates of the environmental effects.     

Ship collision risk assessment for the Singapore Strait

The Singapore Strait is considered as the bottleneck and chokepoint of the shipping routes connecting the Indian and the Pacific Ocean. Therefore, the ship collision risk assessment is of significant importance for ships passing through the narrow, shallow, and busy waterway. In this paper, three ship collision risk indices are initially proposed to quantitatively assess the ship collision risks in the Strait: index of speed dispersion, degree of acceleration and deceleration, and number of fuzzy ship domain overlaps. These three risk indices for the Singapore Strait are estimated by using the real-time ship locations and sailing speeds provide by Lloyd's MIU automatic identification system (AIS). Based on estimation of these three risk indices, it can be concluded that Legs 4W, 5W, 11E, and 12E are the most risky legs in the Strait. Therefore, the ship collision risk reduction solutions should be prioritized being implemented in these four legs. This study also finds that around 25% of the vessels sail with a speed in excess of the speed limit, which results in higher potentials of ship collision. Analysis indicates that the safety level would be significantly improved if all the vessels follow the passage guidelines.     

Existence theory for a one-dimensional problem arising from the boundary layer analysis of radiative flows

We consider a simplified system of equations which models the transfer of energy with conductive, convective and radiative effects inside a convex region filled with a compressible fluid whose velocity field is known. The asymptotic analysis for positive but small distance from an optically thick medium leads to a one-dimensional system of differential equation which couples the temperature and the radiative intensity. We show that this system obeys a conservation law and this feature is explored in order to reduce the problem to a single one-dimension transport equation with anisotropic scattering. This equation admits a formulation in terms of integral operators in a suitable function space which allows us to establish the existence of a solution and infer its behavior far from the boundary. We also provide numerical simulations and comparison with the theoretical results which we have shown in order to validate our methodology.     

汽车八自由度模型动态仿真研究

汽车振动系统是一个非常复杂的系统. 为达到准确反映整车振动情况,基于一定假设,在Matlab软件中利用牛顿法建立某汽车八自由度振动模型. 分析整车动态时域响应特性,基于滤波白噪声和二阶Pade算法,建立四轮相关路面模型. 验证路面精确度,并将其作为激励输入整车振动模型,利用Newmark显式积分法进行求解,将各响应量时域信号转化为频域响应信号并与该振动系统的频域仿真对比. 结果证明该模型的可靠性好,求解速度快. 进一步研究车身质心位置、悬架刚度、轮胎刚度和悬架阻尼等因素对驾驶员与车身质心处舒适性的影响,并基于原车参数提出改善整车舒适性的建议.     

A note on the paper: Optimizing web servers using page rank prefetching for clustered accesses

In this short note, we briefly present and discuss an example of page rank algorithm given in [Information Sciences 150 (2003) 165–176].     

The development of a machine vision-assisted,teleoperated pavement crack sealer

Crack sealing is a maintenance technique commonly used to prevent water and debris penetration and reduce future degradation in pavement. The conventional crack sealing operations are, however, dangerous, costly, and labor-intensive. Labor turnover and training are also increasing problems related to crack sealing crews. Automating crack sealing will improve productivity and quality, and offer safety benefits by getting workers off the road. The reduction in crew size and the increase in productivity of the automated sealing process will be translated directly into significant potential cost savings. The main objective of this study is to develop an automated system for sealing cracks in pavement, and to validate the developed system through field trials. A machine vision algorithm, which is composed of noise elimination, crack network mapping and modeling, and path planning, was developed to operate the proposed automated system effectively. Extension of the algorithms and tools presented in the study to other applications is also recommended for future studies.     

Hydrogen gas sensing methods,materials, and approach to achieve parts per billion level detection: A review

Being a clean source of energy, hydrogen gas is in high demand in various industrial and commercial applications. However, the explosive nature of H₂ gas above 4% concentration makes it highly dangerous to store, transport and use. Further, the small size gas molecules of H₂ are prone to leak through the smallest possible holes and cracks. Hence, the detection of H₂ gas becomes essential even at trace levels. This article reviews various gas sensing strategies including methods, materials, and integrated systems available for the sensitive detection of H₂ gas for a bunch of different applications. The article also reviews some approaches which are available in the literature to detect parts per billion (ppb) level of H₂ gas concentrations. This review article aims at explaining the different aspects of H₂ gas sensing technology in a simple yet exhaustive manner.     

The effect of silane coupling agents on radiata pine fibre for use in thermoplastic matrix composites

Gamma-aminopropyltriethoxysilane (GS) and dichlorodiethylsilane (DCS) were employed for surface modification of radiata pine (Pinus radiata) wood fibre. Levels of fibre moisture were carefully controlled to optimise chemical and hydrogen bonding with these silane coupling agents. The effect of pre-treatment using 2% sodium hydroxide, shown to be effective in assisting silane coupling for other natural fibres [Composites, Part B: Engng 30 (1999) 321], was also investigated. X-ray photoelectron spectroscopy and nuclear magnetic resonance (NMR) were used to characterise modification of the wood fibre. Concentrations of up to 3.2 wt% Si were obtained on the fibre surface due to silane coupling, however, pre-treatment was found to dramatically reduce this value. NMR provided evidence that coupling had occurred between the fibre and DCS by reaction producing ether linkages between the hydroxyl groups on the wood fibre and silane. Pre-treatment and treatment were found to have an insignificant effect on fibre strength. Composite sheets were produced by blending fibre (5, 10 and 20 wt%) with polyethylene followed by extrusion. An increase in strength was obtained at fibre contents of 5 wt% for all treatments compared to composites with untreated fibre. This is believed to be mainly due to increased compatibility of the fibre surface to polyethylene. However, there was no such improvement obtained at higher fibre contents. Evidence suggests that the production of voids is limiting composite strength.