Tribological approach to study polishing of road surface under traffic

Abstract

The polishing phenomenon of road pavements under the vehicle traffic constitutes the main mechanism inherent to the loss of skid resistance over time. A better understanding of this phenomenon would allow an improvement of road safety. This study comprises a review of laboratory test and a model simulating the polishing of road surfaces. The laboratory test uses a polishing machine so called 'Wehner–Schulze' which can reproduce the evolution of the road texture from specimens taken directly from road or made in laboratory. The model is based on contact mechanics considerations and considers that the local polishing rate is controlled by the pressure distribution between the car tyre and the road surface. The model evaluates the pressure distribution by taking into account the surface roughness, the applied load and the mechanical properties of the bodies in contact. From the pressure distribution and a proposed wear law, the local roughness evolution of the surface pavement can be readily evaluated. The removal material is proportional to the contact pressure and to the aggregate properties used in roads mix design. The results show that the predicted road profile evolution is consistent with those given by experiments.     

大型地网接地电阻测量用变频电源的研制

介绍了变频法测量地网接地电阻的优点及变频电源的设计要求、原理框图和SPWM脉冲实现方法 ,给出了其驱动电路和保护电路的设计及变频电源的主要技术指标 ,其输出频率为 30～ 70Hz(可调 ) ,测量仪精度可达到 5级     

21—THE WIRA SHOWER TESTER: A NEW INSTRUMENT FOR THE QUALITY CONTROL OF FABRICS

A new instrument for measuring the absorption and penetration-resistance of fabrics is described. It is based on a novel method of drop propagation, and it is shown that the dynamical properties of the drops lie within the wide range of values provided by natural rain. The test procedure, which is intended to form the basis of a draft British Standard method of test, is described. Results of tests on a variety of apparel fabrics are given, and these include comparative tests on unproofed and treated cloth and tests on fabrics of known wear performance.     

Optimisation of work roll shifting and bending to roll thinner gauge HR coils using genetic algorithm

Abstract

Rolling of thin gauge hot rolled (HR) coils demands stringent flatness tolerance. Thin HR coils (≤3 mm) are rolled towards the end of any rolling campaign. The profile and flatness of the strip depend on the profile of the loaded roll gap in the mill stands. There are five key factors that influence the loaded roll gap: initial roll surface profile, roll thermal expansion, wear of roll, deflection of roll stack and shifting of work rolls. This paper deals with all these factors individually for the formulation of an objective function in order to minimise the flatness error. The shifting and bending of rolls are the controllable parameters that require optimising. This has been accomplished using a genetic algorithm (GA) optimisation technique.     

Melting speed of mould powders: determination and application in casting practice

Abstract

Controlled melting of mould powder on top of the meniscus is essential for efficient mould flux performance. This paper presents two complementary methods to determine the melting speed of a mould powder. One method measures the displacement of a prepressed cylinder of mould powder at a fixed temperature. This method yields qualitative, but reproducible, results which can be related to flux composition. In the second method, a sample of mould powder is melted on top of a steel bath. The data are interpreted with the help of an improved theoretical melting model, resulting in quantitative values of melting speed and thickness of the molten flux layer. The results of both methods agree well with measured plant data.     

Surface self-densification in boron alloyed austenitic stainless steel and its effect on corrosion and impact resistance

Abstract

A boron alloyed AISI 316L, sintered in pure hydrogen at 1250°C, was investigated to study the effect of the microstructure, with particular reference to the near full dense and boride free surface layers, on corrosion resistance and impact properties. The near full dense and homogeneous austenitic surface layer results from the flow of the liquid towards the bulk of the specimens during sintering. It significantly improves the corrosion resistance, while impact properties are strongly influenced by the bulk microstructure, where the boride network creates favourable conditions for both nucleation and propagation of crack.     

Durable adhesives for large laminated timber

Large laminated timber (LT) made of hardwood is widely used as the main constitutional element of goods such as furniture, pianos and doors. A high durability of LT is essential to these products. This study focused on finding as to what adhesives were acceptable as highly durable adhesives for LT. Twelve different adhesives such as resorcinol-formaldehyde resin, aqueous emulsion-type isocyanate resin, poly(vinyl acetate) emulsion, epoxy resin, etc. were used. The durability of LT, i.e., the percentage of delamination length of LT under tests such as humidity and temperature cycling tests, and outdoor tests, was discussed in relation to the adhesive shear strength of a lap joint (LJ). The results showed that the percentage of delamination length under both low ?20°C for 16 h and high-temperature 50°C for 8 h cycling tests (temperature-resistance) on LT indicated a strong trend with the adhesive shear strength of the LJ exposed to dry air at 100°C for 24 h. In addition, the percentage of delamination length under outdoor exposure test for three months (outdoor-resistance) of the LT showed a trend with the adhesive shear strength of the LJ exposed to dry air at 100°C for 24 h, as well as with the adhesive shear strength of the LJ immersed in water at 60°C for 3 h. These trends pointed out that the thermal stability of the adhesive from ?20°C for 16 h up to 50°C for 8 h was an important parameter in order to improve adhesive durability for the LT.     

8—THE DRY WEAR OF STEEL,IN RELATION TO SPINNING-TRAVELLER WEAR

An account is given of a study of the wear of steel under conditions related to the wear of spinning travellers, and it is shown that there is a critical bulk temperature near 100°C above which traveller wear is likely to increase rapidly with increasing load. It is believed that the high wear rates are due to thermal softening of the metal near the rubbing surfaces, and oxides on the rubbing surfaces appear to be the principal agents of wear. The results obtained are compared with the observations of other workers that are reported in the literature.     

Fundamental Definitions and Concepts

Thin films of Ni-Fe alloys of various compositions have been deposited potentiostatically from an alkaline sulfate bath solution containing the sodium salt of ethylene diamine tetraacetic acid (EDTA) and triammonium citrate (TAC). The complex nature of the bath solution was analyzed by cyclic potentiometric and spectrophotometric studies. The composition of the alloy was found to vary with the plating bath composition (Ni/Fe), plating potential and the concentration of complexing agent (EDTA). XRD studies showed that alloys are solid solutions of Fe in Ni (γ-Phase) with fcc structure, free from oxides/hydroxides and pore free. The surface analysis by SEM revealed the nucleation by crystallites giving smooth deposit. The magnetic properties (Hc, Ms and squareness ratio) were evaluated from the parallel (in-plane) and perpendicular hysteresis loops. Plating conditions were optimized to plate good quality thin films of Ni-Fe alloy with 80% Ni(Permalloy) with tailor made magnetic properties which suit electronic industries.     

Annual General Meeting

The authors have shown that special formulations are required to give complete covering of steel surface (with no swelling, break away, cracks, etc) with flame sprayed film coating of epoxy resin. For this purpose, there should be minimum stress in the film, and it was concluded that treatments effective for this purpose involve adding adequate filler to reduce the thermal expansion coefficient, controlling the degree of cure, holding small closed pores in the film and semi-curing immediately after spray to keep the required tensile strength.