Influence of loading rate on bond behaviour of reinforcing steel and prestressing strands

Pull-out tests with short embedment length were carried out within a wide range of loading rates. The highest loading rate which could be achieved on a Split-Hopkinson-bar equipment was about 500,000 times the loading rate in a static test. The test variables were the steel type, the concrete quality and the loading rates. It turned out that plain reinforcing bars and prestressing strands were insensitive to variations in the loading rate, whereas deformed bars showed a significantly higher bond resistance with increasing loading rate. This influence is more pronounced according as the concrete quality is lower and the bar displacements are smaller. An explanation of the phenomena is suggested.     

Experimental parameters affecting hypercoulometric response in gas-phase coulometry

The response of an electron-capture detector designed for coulometric response was examined as a function of solute, pulse interval, carrier-gas type, solute amount, carrier-gas flow rate, and chromatographic-peak profile. For CCl3F, it was shown that the average numbers of electrons absorbed per molecule ranged from 1.0 to 4.1, varying primarily with pulse interval but also displaying a complex dependence on sample amount. Comparison of these results with theoretical expectations leads to the conclusion that a 1:1 "coulometric response" may not be observed under certain operating conditions. Because the specific conditions required depend on many variables, including, to some extent, sample amount, true coulometric operation of an electron-capture detector is difficult to establish and maintain. Effects which may contribute to the production of hypercoulometric response are critically discussed.     

Experimental studies of the biological response to a new bone cement

As part of the assessment of the biological properties of a new bone cement (London Hospital cement) which contains poly(ethylmethacrylate) and n-butylmethacrylate, the monomer (n-butylmethacrylate) has been compared in toxicity studies with methylmethacrylate monomer, as used in conventional bone cement. N-butylmethacrylate monomer had an LD₅₀ of 1.0 to 1.2 ml kg^–1 and was therefore only slightly more toxic than methylmethacrylate monomer (LD₅₀ 1.2 ml kg^–1) when injected intraperitoneally into mice. It did not have any more significant cardiorespiratory depressive effect on intravenous infusion into rabbits, either in single or cumulative doses, when compared with methyl monomer (repeated infusions in 12 rabbits). Both monomers caused a transient bradycardia, tachypnoea, raised central venous pressure and arterial hypotension in low doses with rapid recovery, though the effects were sustained at higher cumulative doses of 60 mg kg^–1 and above. These results demonstrate that n-butylmethacrylate monomer does not differ significantly in toxicity from the monomer used in conventional cement and can therefore be used as a component in the new material.     

游离磨料多股线线锯切割实验研究

游离磨料线锯切割是将磨浆中的磨粒通过一定速度的细钢丝线带入切割区域,达到去除工件材料的目的。多股线由多根细金属线绕制而成,表面具有很多凹槽,与钢丝线光滑表面相比,可以输送更多的磨粒进入切割区域,从而提高切割效率。应用0.25 mm的多股线和0.25 mm的钢丝线对光学玻璃K9进行切割对比实验,结果表明,在相同工艺条件下,多股线的切割效率和表面粗糙度均优于钢丝线,但切缝宽度大于钢丝线。     

On the parameters influencing the deposition of polystyrene colloidal crystals

Colloidal crystals of polystyrene particles of 1.0, 1.4 and 2.8 μm diameter have been prepared by vertical deposition. The influence of parameters such as temperature, particle size and concentration as well as dispersion medium has been studied. The size of domain and the crystalline structure of the particle arrays have been analyzed by optical microscopy. The quality of the crystals has been improved (minimizing cracks) by controlling sedimentation (density matching), evaporation (volatility of the medium) and drying (co-solvents).     

扇区水泥胶结测井仪实验研究

扇区水泥胶结图像是通过扇区水泥胶结测井仪器（Scan Bound Tool,SBT）获得的。仪器的底端是发射探头,在距离发射探头0.6m处安装了一个接收探头。接收探头用一个压电圆管,分成8个等间隔的扇区极化,每个扇区接收到一个波形,一共8个波形。用实验的方法研究了激发脉冲宽度和幅度对波形幅度和频率的影响。取出每个波形的首波幅度得到8条曲线,描述圆周8个扇区的水泥胶结情况。将每个深度点对应的8个幅值用颜色表示出来,得到整个圆周的水泥胶结图像。由于圆周方向只有8个扇区,分辨率比较低,图像边缘不清晰。对观测到的8个扇区的幅度值用高斯函数进行插值处理后,图像边缘得到了一定改善。分别用线性插值,二次插值处理后,图像连续、边缘清晰,对比度明显增强,整个圆周不同扇区水泥胶结的差异显示明显,为进一步分析扇区水泥胶结提供了基础。     

Comparative study of the parameters influencing the machinability of leaded brasses

One of the main applications of brasses is the manufacture of fluid carrying systems. The shape of the final product is usually made by means of machining the rolled or extruded standard bars, so that effective and low cost machining operations are required. Leaded brasses are extensively used when a good machinability is required.Two leaded brasses bars (CuZn39Pb3 alloy) with the same geometry but with different behaviour in saw cutting operations have been characterized in this work. Chemical composition, mechanical and microstructural properties have been studied in order to clarify the observed differences during saw cutting machining.Significant differences have been found with respect to the size and distribution of lead globules and phase volume fractions (α + β′), that have been explained due to the existence of different solidification and cooling patterns in both products; being the lead distribution the most important characteristic relative to the leaded brass cutting performance.     

Experimental investigation of bond stress distribution and bond strength in unconfined UHPFRC lap splices under direct tension

Several studies on tension lap splices have shown the improvement of bond strength using Ultra-high performance Fibre Reinforced Concrete (UHPFRC). The bridging effect of fibres on cracks improves the bond splitting strength substantially in comparison to normal concrete. This paper investigates the influence of fibre content on the strength of tension lap splice of reinforcing bars in UHPFRC without additional transverse reinforcement. Different splice lengths and UHPFRC mixes were tested. Internal strain measurements were used to capture the force transfer mechanism and the evolution of longitudinal strain distribution and associated bond stresses. The bond performance is clearly related to the pre- and post-cracking tensile capacity of UHPFRC. At a distance exceeding 2 d_b from bar extremities, bond stress distribution at failure displayed a quasi-constant value regardless of the lap splice length up 10 d_b. This reveals for short lap splices that the bearing action of all ribs along the splice length contributes equally in resisting the applied force. This experimental program provides experimental results for understanding the local force transfer mechanism in UHPFRC lap splice and contribute for further developments on bond in UHPFRC.     

Experimental investigations on bond strength between coconut fibre and concrete

Effect of fibre embedment lengths, diameters, pretreatment conditions and concrete mix design ratios on the bond strength between single coconut fibre and concrete is investigated. Fibres are prepared and categorised manually. Fibre diameters are measured by a stereomicroscope. Fibre and concrete properties are also determined experimentally. The simplified equations are proposed for estimating the fibre tensile stress, elastic modulus and toughness. Single fibre pull-out tests are carried out to determine load–slippage curves with the help of an Instron tensile machine having load cell. Bond strength and energy required for fibre pullout are calculated from the experimental data. The results show that fibres have the maximum bond strength with concrete when (i) embedment length is 30 mm, (ii) fibres are thick, (iii) treated with boiling water, and (iv) concrete mix design ratio is 1:3:3. Similar effects are observed for energy required for fibre pullout. With the obtained knowledge, empirical equations are also developed to determine the bond strength and energy required for fibre pullout.     

Experimental analysis on bond between PBO-FRCM strengthening materials and concrete

The effectiveness of externally bonded strengthening for reinforced concrete (RC) elements strongly depends on the bond between the strengthening material and the concrete and on the mechanical properties of the concrete cover. In this paper the bond between fiber reinforced cementitious matrix (FRCM) materials made out of a poliparafenilenbenzobisoxazole (PBO) net embedded in a cement based matrix and the concrete is experimentally analyzed. Experimental results of double shear tests involving different bond lengths and fibers cross sections are presented. The results allow to estimate the effective anchorage length and evidence that the debonding occurs at the fibers/matrix interface after a considerable fibers/matrix slip. They also confirms the effectiveness of the FRCM materials as external reinforcements for concrete. The obtained experimental results can be used to calibrate a local bond-slip relation to be used in the design of the external reinforcement.     

Influence of interface-related parameters on some heat stable salts in the corrosion studies of carbon steel for post-combustion CO2 capture

The effect of flow and temperature on the corrosion behavior of carbon steel in an aqueous methyldiethanolamine solution containing different heat stable salts, such as sodium sulfate, sodium sulfite and sodium thiosulfate, has been studied. The introduction of flow and increase in temperature generally caused an increase in the corrosion rate of carbon steel but the presence of the heat stable salts affected the corrosion behavior to different extents. Sulfate increased the corrosivity of the aqueous methyldiethanolamine solution, thus showed accelerated corrosion behavior in the presence of flow and with increase in temperature when compared with the solution without heat stable salts. The presence of sulfite reduced the corrosivity of the methyldiethanolamine solution due to its oxygen scavenging ability. Although flow and temperature stimulated an increase in the corrosion rate of carbon steel, the corrosion inhibiting effects of sulfite ions increased with the salt concentration. Also, the presence of sodium thiosulfate caused a reduction in carbon steel corrosion. Its inhibition ability is largely the result of the formation of FeS product layer resulting from its disproportionation reaction. This layer offered a slight resistance to the influence of flow and increase in temperature when compared with the system without heat stable salts.     

Review Processes and influencing parameters of the solid particle erosion of polymers and their composites

The solid particle erosion behaviour of polymers and polymeric composites has been reviewed. Attention was paid to the effects of testing variables (e.g., erodent type, size and flux, impact angle) and target material characteristics (e.g., crystallinity, crosslink density, reinforcement content and arrangement). The occurring failure mechanisms were classified and discussed. Various predictions and models proposed to describe the erosion rate (ER) were listed and their suitability was checked. Recommendations were given how to solve some open questions related to the structure—erosion resistance relationships for polymers and polymeric composites.     

An evaluation of some additional factors influencing the effectiveness of warning letters

The primary objectives of the study were to determine the effectiveness of two types of warning letters and an informational pamphlet in reducing the subsequent collision and conviction records of pre-negligent drivers. An additional study objective was to determine the effectiveness of a follow-up reinforcement letter sent to collision and conviction free drivers. The results six months subsequent to treatment showed no significant treatment effects on convictions, but a positive pamphlet effect on collisions. The follow-up reinforcement analysis for collision and conviction free drivers showed no significant treatment effects on collisions. On convictions, however, there was a main effect attributable to type of warning letter as well as an interaction between type of warning letter, pamphlet condition, and follow-up reinforcement. No treatment conditions were significantly influenced by subject characteristics.     

Experimental and analytical investigation on bond between Carbon-FRCM materials and masonry

Historical masonry constructions often need to be strengthened and upgraded to satisfy current seismic code requirements. Recently many interventions have been done bonding composite materials to the surface of existing masonry elements. The effectiveness of these interventions strongly depends on the bond between the strengthening material and the masonry and on the mechanical properties of the masonry substrate. In this paper the bond between fiber reinforced cementitious matrix (FRCM) materials made out of a Carbon net embedded in a cement based matrix and the masonry is experimentally and analytically investigated. Experimental results of double shear tests involving different bond lengths are presented. The results evidence that the debonding occurs at the fibers/matrix interface after a considerable fibers/matrix slip. They also confirms the effectiveness of the Carbon-FRCM materials as external reinforcements for masonry structures. The obtained experimental results are used to calibrate a local bond-slip relation that is essential in the modeling of the structural behavior of masonry elements strengthened with Carbon-FRCM.     

Experimental studies of the fibre pull-out problem

The fibre pull-out problem was studied experimentally using a method which enabled direct measurement of the energy release rate of de-bond and also observation of the fracture process involved. Preliminary test results indicated that the process was a twostage one, with de-bond initiating at the fibre tip, followed later by de-bond initiating at the free surface end. If a flaw of sufficient size was present then a stage-two de-bond would occur. Results showed reasonable agreement between experimental results and computer measurements.