Investigation of stress fields for non-standard sized glass plates loaded by ring-on-ring

A ring-on-ring (ROR) test is a prevailing test method for evaluating the equi-biaxial strength of glass materials. However, current ROR test standards limit the strength and size of glass to prevent a nonlinear behavior. In this study, the feasibility of ROR testing for non-standard, high-strength glass, such as tempered or ion-exchanged rectangular glass is investigated. To this end, ROR simulation based on theory and experiment is conducted for thirty non-standard glasses with widths of 100–300 mm and aspect ratios of 1.0–2.0. As a result, the maximum measurable stress was about 215.6 MPa for 100 × 200 mm glass and 481.3 MPa for 300 × 600 mm glass with a 3% deviation, which is well above the strength of regular tempered glass. The main purpose of this work is to understand the range of aspect ratio of horizontal and vertical widths of a glass plate that can be evaluated by the standard ROR test.     

A new insight into promotion action of Co2+ in Ni-diamond composite electrodeposition

A new insight into the promotion action of Co²⁺ on both particle and metal deposition in Ni-diamond composite electrodeposition system was analyzed according to electrochemical measurements. The results showed that the addition of Co²⁺ made particles content in deposits increased remarkably. The change of particles content in deposits was related inversely to the change of cathodic zero potential with the increase of the concentration of cobalt sulfate. Zero charge potential of cathode was shifted to much more negative region. The negative shift of the zero potential, combining with positive shift of the zeta potential, increased the electrostatic force between the particle-adsorbed metallic cations and the cathode. It not only benefits to the transportation of particles in solution towards cathode, but also shortens their residence time on cathodic surface. Meanwhile, entry of particles is also promoted. For metals deposition, reduction resistance of metallic cations rises greatly and deposition current at cathodic potentiodynamic polarization decreases after cobalt sulfate has been added into electrolyte. These factors are favorable for increasing particles content in deposits. In addition, physical model of diamond particles deposition state before and after the addition of Co²⁺ has been discussed.     

框架中钢-混凝土组合梁等效弯曲刚度分析

框架体系中钢-混凝土组合梁在竖向荷载作用下的弯矩分布与其端部受到的转动约束条件密切相关,而在不同方向的弯矩作用下钢-混凝土组合梁截面的抗弯刚度又差异显著,要准确计算竖向荷载作用下组合梁的等效弯曲刚度必须充分考虑与其相连的梁柱变形对其端部产生的转动约束刚度。为此,采用分段刚度建立了框架中组合梁在竖向荷载作用下的等效刚度理论模型,以考虑不同梁端转动约束刚度和楼板开裂前后截面特性差异对组合梁等效刚度的影响。基于该理论模型进行大量参数分析,识别了影响组合梁等效弯曲刚度的两个关键参数：转动约束刚度与组合梁开裂后截面线刚度比和梁开裂前后截面刚度比,得到了随梁端转动约束刚度变化的组合梁在竖向荷载作用下等效弯曲刚度的计算式,在框架设计时可方便地用于组合梁的变形和内力计算。对比讨论了建议算式和现有公式的计算精度,并通过结构体系的非线性全过程分析对建议算式的合理性做了进一步的验证。理论分析和设计方法表明,组合梁在竖向均布荷载作用下的负弯矩区长度和等效弯曲刚度随梁端转动约束刚度变化显著,必须在设计中准确考虑。     

Computer-aided robot modeling,programming and simulation

The use of interactive computer graphics for simulation and off line programming provides a powerful tool in implementing robots. This capability essentially became available with the CAD/CAM system.This paper will present the theory of robot modeling and simulation techniques. An overview of CAD/CAM system in robotic application, such as robot off-line programming, simulation and workcell layout will also be represented.     

Effects of hydrogen on the fracture toughness of CrMo and CrMoV steels quenched and tempered at different temperatures

Tempering temperatures ranging between 500 and 720 °C were applied in order to analyse the relationship between steel microstructure and the deleterious effect of hydrogen on the fracture toughness of different CrMo and CrMoV steels. The influence of hydrogen on the fracture behaviour of the steel was investigated by means of fracture toughness tests using CT specimens thermally pre-charged with hydrogen gas.First, the specimens were pre-charged with gaseous hydrogen in a pressurized reactor at 19.5 MPa and 450 °C for 21h and elasto-plastic fracture toughness tests were performed under different displacement rates. The amount of hydrogen accumulated in the steel was subsequently determined in order to justify the fracture toughness results obtained with the different steel grades. Finally, scanning electron microscopy was employed to study both the resulting steel microstructures and the fracture micromechanisms that took place during the fracture tests.According to the results, hydrogen solubility was seen to decrease with increasing tempering temperature, due to the fact that hydrogen microstructural trapping is lower in relaxed martensitic microstructures, the strong effect of the presence of vanadium carbides also being noted in this same respect. Hydrogen embrittlement was also found to be much greater in the grades tempered at the lowest temperatures (with higher yield strength). Moreover, a change in the fracture micromechanism, from ductile (microvoid coalescence, MVC), in the absence of hydrogen, to intermediate (plasticity-related hydrogen induced cracking, PRHIC) and brittle (intergranular fracture, IG), was appreciated with the increase in the embrittlement indexes.     

A viable approach to prepare 3C-SiC coatings by thermal MOCVD using commercial grade precursors

A series of 3 C-SiC coatings were prepared by organometallic chemical vapor deposition (MOCVD) using precursor solution containing a varying proportion of commercial-grade hexamethyldisiloxane (HMDSO) and n-hexane. The phase composition, bonding state, and microstructure of 3 C-SiC coatings were studied in detail by grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The microstructure and mechanical properties of the optimal 3 C-SiC coating were characterized by scanning transmission electron microscopy (STEM) and nanoindentation, respectively. Our results revealed that the amount of undesired graphite phase can be significantly reduced in the 3 C-SiC coating by introducing hydrogen gas in the reaction chamber alongside increasing the ratio of HMDSO/n-hexane in the precursor mixture. The STEM results revealed that the optimal coating was predominantly composed of nano-crystalline 3 C-SiC grains alongside a small amount of amorphous graphite. The hardness and elastic modulus of the optimal coating were 38.19 GPa and 363.2 GPa, respectively.     

Durability of Portland blast-furnace slag cement concrete

This paper summarizes the results of studies carried out at the Building Research Establishment in the UK, on the performance and long-term durability of concrete where ground glassy blast-furnace slag (granulated and pelletized) has been used as a cementitious material. Using data from tests on site structures and laboratory and exposure site studies, comparisons are made of the properties and performances of the slag cement concretes with normal Portland cement concretes of similar mixture proportions. A number of recommendations are given for the effective use of ground glassy blast-furnace slag in concrete. The many technical benefits available to the concrete user, such as reduced heat evolution, lower permeability and higher strength at later ages, decreased chloride ion penetration, increased resistance to sulfate attack and alkali silica reaction were affirmed. However, a cautionary warning of the importance of good early curing is made to ensure that the adverse effects of higher rates of carbonation, surface scaling and frost attack are minimized. The paper is intended to provide guidance for those concerned with the design, specification, application and performance of concrete in practice where slag can also help to reduce costs and energy demands in the production of cement compared with normal Portland cement.     

Atmospheric corrosion of Ni-advanced weathering steels in marine atmospheres of moderate salinity

One conventional and three Ni-advanced weathering steels have been exposed for one year in two marine atmospheres of moderate aggressivity (30 and 75 mg Cl⁻/m² d). The rusts generated have been analysed by polarised light optical microscopy, SEM, XRD, Raman spectroscopy and Mössbauer spectroscopy.The presence of high nickel (1–3% weight) contents in the steel composition leads to higher corrosion resistance in moderate marine atmospheres. The presence of nickel in the weathering steel also raises the proportion of nanophasic (superparamagnetic) goethite in the inner rust layer.     

Influence of strain-induced martensite in the anodic dissolution of austenitic stainless steels in acid medium

The anodic dissolution of austenitic stainless steel bars in an acid medium (0.5 M HCl + 2 M H₂SO₄) under different polarizations is studied. The material comes from bars formed by hot working (HW) and by cold working (CW). UNS S30403 and S31603 grades are considered. The determining effect of alloying elements and working method are proved. The morphology of the attack at different anodic potentials is analyzed. The important influence of the amount and distribution of strain-induced martensite on corrosion is demonstrated. The effect of the martensite on the anodic polarization curves is quantified using specifically designed software.     

A model for a mechanical equation of state under continuously changing conditions of hot deformation

A simple model, which takes into account the combined effects of dislocation climb and glide has been developed. In the extreme case when climb is slower than glide, the model predicts the direct transients observed in pure metals and class II alloys and in the other extreme case, when glide is slower than climb, the inverse transients observed in class I alloys. In the intermediate situation, when the velocity of climb is of the same order of magnitude as the velocity of glide, the model gives very small transients in flow stress even with large changes in strain rate. Under such conditions, the observed occurrence of a mechanical equation of state in two alloys: a ferritic stainless steel and an aluminium 1% magnesium alloy, under continuously changing strain rate conditions can be explained. The model also explains that a practical mechanical equation of state can be followed without the simultaneous existence of a microstructural equation of state, because it predicts that a change in flow stress can occur even without an appreciable change in the microstructure.