Ultrasonic welding offers ability to weld thin layers of malleable metals at low temperature and low power consumption. During ultrasonic welding, intensive material interactions occur due to the severe plastic deformation (SPD) and frictional heat generation, which leads to the microstructural change. Different grain microstructures have been observed after different ultrasonic welding conditions. Theory of the microstructural evolution was for the first time hypothesized as three regimes, namely SPD, dynamic recrystallization (DRX) and grain growth according to the material thermomechanical loading conditions. A novel metallo-thermo-mechanically coupled model was developed to model the temperature-dependent mechanical deformation and microstructural evolution during the ultrasonic spot welding process. The numerical analysis was carried out with a three-dimensional (3D) finite element model using DEFORM 11.0. The material constitutive model considered cyclic plasticity, thermal softening, and acoustic softening. Dynamic recrystallization and grain growth kinetics laws were applied to simulate the microstructural evolution under different welding time durations. The simulation results demonstrated that the essential characteristics of the deformation field and microstructure evolution during ultrasonic welding were well captured by the metallo-thermo-mechanically coupled model. The numerical framework developed in this study has been shown to be a powerful tool to optimize the ultrasonic welding process for its mechanical properties and microstructures.

This paper presents an experimental study on the mechanical characteristics of carbon steels used for pipeline applications. The considered materials are: X65 micro-alloyed and F22 low-alloyed steel. C(T) specimens are extracted directly from the pipes, and fatigue crack growth tests are carried out considering three parameters affecting crack growth rates in mechanical components: absence or presence of hydrogen, low temperature and test frequency. This work is dedicated to the description of the setup used in the experimental tests and to the discussion of obtained results. Experimental results show an evident effect of the hydrogen presence on the fatigue crack growth. Fracture surface examination confirms the results of mechanical testing.

A series of ANb 2 O 6 ( A = Ca , Mg, Cu, Ni) columbites and 50% Ni doped with CaNb 2 O 6 ,MgNb 2 O 6 and CuNb 2 O 6 has been prepared using sol-gel technique. The samples were sintered at 900°C for 6 hours. Structural characterization of the prepared samples has been done using X-ray diffraction (XRD) method. To study their applicability in low temperature confired ceramic (LTCC) technology, dielectric have been characterized. Microwave dielectric properties like dielectric constant over Ku-band for all the compositions have been measured. Dielectric constant was found to fall between 4.8 to 10.

In any item of structural or pressure equipment there is a need to avoid the occurrence of brittle fracture. As we saw in API 571, brittle fracture is a catastrophic failure mechanism caused by the combination of low temperature and a material that has a low resistance to crack propagation at these temperatures. Under these conditions a material is described as having low toughness (or impact strength) — i.e. it is brittle. Impact strength is measured using a Charpy or Izod test in which a machined specimen is impacted by a swinging hammer.

For the understanding of cycle thermodynamics and of the technology of construction, the period from the mid-1960s to the mid-1980s was essentially one of consolidation. Rapid advances in computing capacity encouraged the development of ambitious simulations of the gas process cycle. With the notable exception of a contribution by Miyabe et al. (1982), however, study of the regenerator continued in isolation and without impact on Stirling engine design. The era saw a number of new embodiments. The free-piston variant was invented (Finkelstein 1963a, b, 1964). West (1970) proposed the liquid-piston or Fluidyne engine. Bradley (1974) demonstrated an engine operating from a low-temperature source, possibly the first of a type to become known as the ‘Low Δ T ’ genre.

A new environmental friendly polyurethane(PU) foam with blowing agent of HFC-245fa was developed in order to substitute for traditional foam with blowing agent of CFCs, which has been phased out according to Montreal protocol and subsequent treaties. But the coefficient of thermal conductivity of the new foam is not available at present when it is used for cryogenic storage tanks and pipes. In this paper, the mechanism of heat transfer in the foams was analyzed and a layered insulation model used at low temperatures was described accordingly. The mean apparent thermal conductivity under low temperature of the new PU foam, which has zero ODP, was investigated. The relationship between density and the thermal conductivity was experimentally studied. The results proved that the newly developed material had a better performance in thermal insulating system and provided a reference data when use the material under low temperatures.

Air conditioning system based on liquid desiccant is a potential alternative to conventional vapor air conditioning system due to its advantages such as utilization of low temperature heat source, independently humidity and temperature control strategy and high energy storage capacity. In this paper, the technologies of two-stage liquid desiccant dehumidification which adopting LiCl solution and CaCl 2 solution as the desiccant solution, is analyzed and applied in a new air conditioning system in Shanghai summer condition. The two-stage liquid desiccant dehumidification subsystem shows the advantages of easier regeneration and lower cost due to the application of CaCl 2 compared with the LiCl alone dehumidification. A mathematical model is build to simulate its performance. It is found that the regeneration heat is reduced compared with LiCl alone dehumidification. The Tcop of the two-stage dehumidification applied in a hybrid system reaches 0.68. Two-stage liquid desiccant dehumidification is a feasible solution for dehumidification in Shanghai in China.

Despite significant improvements in recent years, the Core Damage Frequency at the Surry Power Station still has a substantial contribution from catastrophic flooding. Having exhausted all realistic means of prevention, the Dominion staff has begun to evaluate means of preventing core damage in the event of an unrecoverable station blackout due to flooding. The staff has developed a strategy for taking a unit from full power conditions at the time of the blackout to a low-risk state of low temperature and pressure, with successful decay heat removal, without any emergency AC or DC electrical power and with almost no plant control. This recovery procedure has been successfully tested on the plant simulator but still awaits verification on an engineering simulator. Results to date indicate that the core remains covered and cooled for at least 12–24 hours. This recovery strategy is applicable in any long-term station blackout, whether due to flood, fire or any other cause.

Tribochemistry is defined as the branch of chemistry dealing with chemical and physiochemical changes of matter due to the influence of mechanical energy [1]. It was suggested in [2] that the high pressures and high temperatures at the interface between two surfaces can cause chemical reactions, which under normal conditions would proceed very slowly or not at all. Tribochemical reactions always occur in dynamic and complex situations, which make them difficult to describe with a mathematical model. Several physical, chemical and mechanical factors can affect tribochemical reactions and thus influence the production of different reaction products in various situations. Further, most of these factors influence one another via a number of feedback loops. For example, mechanical contact stresses depend on the topography of surfaces, which are determined by the deformation of asperities and by wear processes, which in turn depend on contact stresses. Chemical reactions are also activated by a number of mechanisms [1, 2] and influence mechanical processes by modifying the surface topography and the materials' properties. In accordance with these findings, it was recognized that each tribochemical reaction must be considered a simultaneous function of mechanical and chemical phenomena. Therefore, it is clear that it is extremely difficult to come to a conclusion about the most influential factors in tribochemical reactions that can result in tribochemical changes at the interface, since mechanical and thermal effects act simultaneously and both influence the result. An indicative and interesting example is that of sliding at very low sliding speeds, for example, in fretting, since at low sliding speeds contact temperatures should be low and, therefore, tribochemical reactions should be a consequence of the broadly prevailing mechanical factors. We know that tribochemical reactions determine the sliding behavior of silicon nitride ceramics, and this also applies to low-speed sliding and fretting [3, 4, 5, 6, 7, 8, 9]. In the literature, low temperatures and negligible thermal effects on tribochemical reactions are typically assumed for low-speed sliding. Even in some of the rare attempts to measure the contact temperature at very low sliding velocities, for example, in fretting [10], rather low temperature increases were determined, which also agreed well with the theoretical calculations. On the other hand, evidence for phase transformations in materials that are typical of high temperatures was also obtained several times in low-speed sliding experiments [5, 9, 11, 12, 13, 14, 15]. However, since these processes occur within a “closed” contact where any exact measurements are impossible, we have to rely on the indirect evidence of a subsequent surface analysis, or theoretical calculations, and this is bound to introduce an element of uncertainty. Therefore, different, and sometimes contradictory, assessments of the importance of thermal and mechanical effects on tribochemical reactions are reported in the literature.