Effect of boundary conditions and heat source distribution on temperature distribution in friction stir welding

Abstract

Welding experiments on Al-6005A have been carried out using a fully instrumented milling machine. The power input was calculated from the measured torque and forces. The thermal cycles were measured at various locations close to the weld centreline. A finite element pseudo-steady-state uncoupled thermal model was developed, taking into account the influence of the welding parameters on the power input. The distribution of the total power input between surface and volume heat sources was also studied. The measured and predicted thermal cycles are in good agreement when proper contact conditions between the workpiece and the backing plate are introduced.     

开拓电力市场管好电网

电力发展能带动全国经济发展,现在已无争议。目前的问题是如何开拓电力市场和管好电网的问题。要在工业及生活用能源中,扩大用电的比重,就现在低水平的生活情况下,潜力不大。但从这个低生活水平向小康及扶贫前进,却有美好的前景。这需要发展城网 气化。管好电网将成为今后的首要任务必须采用一整套中知交民技术及用户电力技术等。     

Ultrasupercritical power plant development and high temperature materials applications in China

Abstract

The rapid development of Chinese economy demands sustainable growth of power generation to meet industrial and domestic demand. The total installed capacity of electricity and annual overall electricity generation are now both the second highest in the world, close to those of the USA. Forecasts of China's electricity demand over the period 2010–20 are presented. Chinese power plants, like those worldwide, are facing demands to increase thermal efficiency and to decrease the emission of CO₂, SO_X and NO_X. In light of the national resource of coal and electricity market requirements in the next 15 years, power generation – especially ultrasupercritical (USC) power plants with the steam temperature over 600°C – will undergo rapid development. The first 1000 MW USC power unit, with steam parameters 600°C, 26·25 MPa, entered service in November 2006. It is estimated that more than 350 USC power units will be installed in China by 2020. USC power plant designs will adopt a variety of qualified high temperature materials for boiler and turbine manufacturing applications. Among these materials, the modified 9–12%Cr ferritic steels, Ni–Cr austenitic steels and certain nickel base superalloys have received special attention in the Chinese materials market.     

Effects of blending and coating methods on the performance of SIS (styrene-isoprene-styrene)-based pressure-sensitive adhesives

SIS (styrene-isoprene-styrene)-based pressure sensitive adhesives (PSAs) were prepared by melt- or solution-blending. In the coating process, two methods were used: solution coating and melt coating. The performances of the PSAs were found to be different, depending on which of these two blending or coating methods was used. In this study, we investigated the relationship between the viscoelastic properties and the performances of the SIS-based PSAs using different blending and coating methods. Three methods were used: (1) melt-blending and melt-coating, (2) melt-blending and solution-coating and (3) solution-blending and solution-coating. PSAs applied using melt-blending/melt-coating (M—M) have higher peel strength and probe tack than PSAs applied using melt-blending/solution-coating (M—S) and solution blending/solution coating (S—S). However, PSAs applied using M—M blends have lower holding power and SAFT (Shear adhesion failure temperature) than PSAs applied using M—S and S—S blends. The viscoelastic properties and GPC curves of M—S blends were similar to M-M blends, while the peel strength and tack of M—S blends were similar to S—S blends. Therefore, it was concluded that the blending process had more effect on the viscoelastic properties and shear creep of PSAs than the coating process.     

Monitoring of stress corrosion cracking of sensitised 304H stainless steel in nuclear applications by electrochemical methods and acoustic emission

Abstract

A hybrid monitoring technique for stress corrosion cracking (SCC) has been developed that employs simultaneously localised corrosion monitoring, electrochemical noise and acoustic emission (AE) techniques. The application of the hybrid technique for detection of SCC initiation and propagation in sensitised 304H stainless steel in dilute tetrathionate solutions at ambient temperature is reported. Initial result shows that SCC initiation and its early stage propagation can be detected by the localised corrosion monitoring and electrochemical noise methods. The dimensions of the crack can be estimated from the charge values derived from the detected transients. The locations of AE events determined using two sensors are in good agreement with the locations of cracks observed in the specimen. The AE technique is sensitive to rapid crack propagation, but does not appear to be sensitive to SCC initiation and early stage propagation for the present material environment load combination. It is postulated that AE is sensitive to SCC propagation involving a relatively large volume of plastic deformation. On the basis of test results and on information from the literature, it is suggested that in this material environment system SCC cracks initiate via slow anodic dissolution at the chromium depleted grain boundaries. Subsequently, elemental sulphur adsorbed on the surface around the crack tip catalyses the entry of hydrogen atoms produced by the hydrogen reduction reaction into the steel matrix ahead of the crack tip; this hydrogen accumulates gradually over a relatively long period of time and preferentially at carbide/matrix interfaces, eventually causing hydrogen induced brittle fracture along grain boundaries.     

In process monitoring of polymer batch to batch variation in injection moulding

Abstract

Injection moulding studies are reported, during which in process measurements have been used to monitor batch to batch variation of several production grade polymers. Three materials were studied: a polyamide 6, a polyacetal, and a flexible poly(vinyl chloride), all of which were commercial injection moulding polymers supplied by industrial collaborators. Instrumented high precision electric and servohydraulic moulding machines were used to mould parts in house from a number of different material batches. Moulding conditions were kept constant throughout and several process variables were monitored during injection, including melt pressure, melt temperature, and viscosity index –a specific pressure integral calculated from primary injection. Part weights were measured to provide an indication of part quality. Results showed that in each case, variations between batches produced a measurable effect on part quality. These variations were detected by in process measurements, particularly by viscosity index, which tracked significant changes in part weight. Several ‘problem’batches not identified by the compounder's internal quality checks were detected, and the influence of regrind and a development compound were also clearly identified. No simple relationship between viscosity index and part quality was observed for the limited processing range covered. Overall, the studies show the potential of in process measurements to provide a real time, sensitive indication of process variation.     

Very High Force Hydraulic McKibben Artificial Muscle with a p-Phenylene-2,6-benzobisoxazole Cord Sleeve

Small and lightweight actuators that generate high force and high energy are strongly required for realizing powerful robots and tools. By applying ultra-high-strength p-phenylene-2,6-benzobisoxazole fiber sleeves to McKibben artificial muscles, new hydraulic artificial muscles have been developed. While conventional McKibben muscles are driven by a maximum pneumatic pressure of 0.7 MPa, the newly developed muscles are driven by a maximum water hydraulic of pressure of 4 MPa, resulting in very high force capability. This paper presents the materials and structure of the new artificial muscle and the experimental results. The developed muscles are evaluated by four parameters — force density per volume (FDV), force density per mass (FDM), energy density per volume (EDV) and energy density per mass (EDM) — for comparisons with other conventional linear actuators. The prototype artificial muscle, which is 40 mm in diameter and 700 mm in length, can achieve a maximum contracting force of 28 kN, FDV of 32.3 × 10^–3 N/mm³, FDM of 9.44 × 10³ N/kg, EDV of 2600 × 10^–3 J/mm³ and EDM of 762 × 10³ J/kg. These values are 1.7 to 33 times larger than those of the typical conventional actuators. As the result, a high force artificial muscle of 40 mm in diameter that generates 28-kN contracting force has been developed successfully.     

Generation IV material issues

Abstract

Generation IV (GenIV) nuclear power concepts have become an active research topic all over the world during the last five to ten years. There are six concepts accepted for the GenIV international forum (GIF) with the common aim to promote both efficiency and safety of reactor technology. Moreover, the issues of uranium sources and the use of closed fuel cycles are included in the discussion and concepts. Thus, the new concepts will offer attractive features but at the same time bring new and demanding challenges for the materials technology due to increased operating temperatures and irradiation doses as well as more aggressive coolants and/or longer life time expectations than those for plant operated today. In the present paper, an overview of the material issues is given with special emphasis on one of the concepts, namely the supercritical light water reactor.     

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