Continuum damage mechanics analyses of type IV creep failure in ferritic steel crossweld specimens

A major high temperature failure mechanism for weldments in ferritic steel steam pipework is circumferential creep cracking within the region of the heat affected zone, adjacent to the parent material, that experiences the lowest temperatures during the welding process. This is commonly known as type IV cracking. In recent years a number of experimental studies have investigated the occurrence of type IV failure in laboratory test pieces, however, there have been few attempts at theoretical modelling of type IV failure to assist in the formulation of design and assessment procedures. This report discusses the use of the creep continuum damage mechanics method for the analysis of the deformation and failure of weldments that are known to fail within the type IV region.The creep behaviour of each of the material regions of a weldment is described with a set of physically based constitutive equations, which incorporate a number of state variables. The finite element creep continuum damage mechanics method is used, with the physically based constitutive equations, to analyse the deformation and failure of the welded testpieces. The computations are shown to be in good agreement with the experimental results. The implications of the analyses are discussed with reference to the assessment of weldments that are susceptible to type IV failure.     

Isotope and chemical studies for a geothermal assessment of the island of Nisyros (Greece)

Two distinct hydrothermal aquifers occur beneath the volcanic crater The deeper one is characterised by temperatures above 330°C and a chemical and isotopic composition in agreement with a thermal modification of seawater by water/rock interaction and boiling processes at depth The shallow aquifer has temperatures below 170°C and salt content and isotopic composition between those of seawater and local groundwaters The steam produced at the caldera rim (Kaminakia group) has a δD and δ¹⁸O of −42‰ and −61‰ respectively whereas the steam produced inside the caldera (Stephanos and Polybotes group) exhibits average δ values of −11‰ and +25‰ for D and ¹⁸O respectively Such values are indicative of different parent waters for the above two aquifers The isotope geothermometers based on the pairs (CH₄–H₂) (H₂O–H₂) and (CH₄–CO₂) from the same fumaroles yield values consistently within the 100–350°C range.     

Static and dynamic testing of a quasi-isotropic composite with embedded optical fibres

An efficient use of composite materials in loaded structures requires NDT techniques that can reliably monitor the damage state of these materials in situ and continuously during service. A promising solution to this problem is the incorporation of optical fibres into the composite structure during manufacture. However, because optical fibres are always an order of magnitude bigger than material fibres, stress concentrations will inevitably be created which can lead to premature damage initiation and thus to a reduction in the mechanical properties. Therefore the first step in the development of a damage detection system based on optical fibre technology always has to be an investigation of the mechanical properties of the resulting structures. In this paper, optical fibres were incorporated in the different interfaces of a quasi-isotropic composite laminate. Both static and dynamic mechanical tests were carried out to determine the influence of the optical fibres on the mechanical properties of the resulting composite structures. Differences in behaviour between the different configurations were correlated with differences in damage propagation.     

Modeling and experimental study of grinding forces in surface grinding

Grinding forces are composed of chip formation force and sliding force. A new mathematical model of grinding forces in surface grinding is developed in this paper. Effectiveness of this model is proved by comparison of the experimental results and the model calculation results. Chip formation energy can be divided into static chip formation energy and dynamic chip formation energy which is mainly influenced by shear strain, shear strain rate and heat in the metal removal process. A formula for calculating the chip formation force is proposed by analyzing the relationship between specific chip formation energy and chip formation force. Combined with the achievements of other researchers, a new formula for calculating sliding force considering the influence of processing parameters on friction coefficient is obtained.     

Radiation driven evaporation for polydisperse water sprays

This study concerns the prediction of radiation heat transfer in evaporating water sprays for a 1D planar media. The spray evolution is described by a Lagrangian sectional approach with the initial diameter size classes defined by normal and log–normal distributions. The spray and the gas-phase radiative properties are recast in terms of cumulative distribution functions (CDF) for use with a correlated-k approach to solve the radiative transfer equation (RTE). The spectral properties required for constructing the CDFs for the droplets and gas are determined using Mie theory and the HITEMP databases, respectively. Cases are conducted to explore the sensitivity of radiative energy attenuation to time evolving droplet size distributions as a function of initial distribution, distance to the energy source, volume fraction and temperature. Results from this study show that the PDFs generate a positive skewness due to the size dependent absorption properties of the droplet. These findings suggest that the droplet size distribution can be adequately described by prescribed, non-symmetrical PDFs that are parameterized by lower order moments.     

超声波实时测量技术在固体火箭发动机中的应用

利用超声波对固体推进剂燃速进行实时测量是先进的燃速测量方法之一。针对超声波技术在固体火箭发动机试车中的应用,对典型固体火箭发动机材料进行测试研究,获得了发动机材料的超声波信号特征。将超声波探头直接安装在发动机壳体外侧部位,测量了固体推进剂在常压燃烧时的厚度变化。针对动态燃速测试,提出了超声波数据处理方法,对固体装药在常压燃烧下的回波进行处理,获得了装药的厚度变化过程和燃速,并分析了燃面附近温度分布对燃速测量的影响。结果表明：用超声波测量金属壳体固体发动机的燃速必须在壳体上开窗使超声波透过壳体和绝热层界面,而对复合材料壳体发动机可将超声波探头直接安装在壳体外侧;燃烧引起的装药表面温度变化对测量的影响可以忽略;该数据处理方法可以有效获得装药厚度变化。     

Recent advances in justifying CIM technologies

The difficulties of justifying new computer-integrated manufacturing (CIM) technologies to top management are well known, and are common to many firms. Typically, the frustrations of the ‘justification exercise’ are as maddening to top managers as they are to the proposers. The latest research on this topic is reviewed here, and conclusions based on two surveys and numerous field studies are presented. An example of what one firm is doing to address the problem of CIM's intangible benefits concludes the paper.     

A study on the beta and omega phases in a Ti-Al-Cr alloy

The β phase obtained in the Ti-42Al-3Cr alloy has an ordered B.C.C. structure with a₀=0.3197nm, which is rich in chromium. The omega phase precipitated from the β phase in this alloy has an ordered hexagonal structure with a₀=0.452nm and c₀=0.577nm. The orientation relationship between the omega phase and the parent β phase yields the usual orientation relationship: [111]_c∥[0001]_b and {110}_c∥{1120}_b.