Damage mechanism in weldment of 2.25Cr-1Mo steel under creep-fatigue loading

The purpose of this study is to clarify damage process of “Type IV cracking” in weldment of a 2.25Cr-1Mo steel and to propose a micro damage prediction method. From continuous observation under a creep-fatigue test, it was found that spherical shape voids initiated and grew on grain boundaries in fine grain region and these voids grow continuously by changing their shape to crack-like. Both spherical and crack-like void growth rate equations were derived from the proposed void growth model. It was indicated that measured void growth rate under the creep-fatigue loading was well predicted by the growth rate equations.     

Morphology and properties of nylon6 and high density polyethylene blends in absence and presence of nanoclay

The morphology and properties of nylon6/HDPE blends without and with nanoclay has been reported. Scanning electron microscopy study of the (70/30 w/w) nylon6/HDPE blends with small amount (0.1 phr) of nanoclay indicated a reduction in the average domain sizes (D) of dispersed HDPE phase and hence better extent of mixing compared to the blend without any nanoclay. X‐ray diffraction study and transmission electron microscopy revealed that nanoclay layers were mostly located in nylon6 matrix of the (70/30 w/w) nylon6/HDPE blend. However, the same effect of nanoclay on the morphology was not observed in (30/70 w/w) nylon6/HDPE blend where HDPE became the matrix. In (30/70 w/w) nylon6/HDPE blend, addition of nanoclay increased the D of dispersed nylon6 domains by preferential location of the clays in side the nylon6 domains. Thus, the clay platelets in the matrix phase acted as barrier that restricted the coalescence of dispersed domains during melt‐mixing. Addition of PE‐g‐MA in both the compositions of nylon6/HDPE blend effectively reduced the D of dispersed phases. Storage modulus and thermal stability of the blend were improved in presence of small amount of clay, whereas addition of PE‐g‐MA lowered the mechanical and thermal properties of the blends. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of Solid Fat Content on Structure in Ice Creams Containing Palm Kernel Oil and High-Oleic Sunflower Oil

ABSTRACT: The development of a structural fat network in ice cream as influenced by the solid:liquid fat ratio at the time of freezing/whipping was investigated. The solid fat content was varied with blends of a hard fraction of palm kernel oil (PKO) and high-oleic sunflower oil ranging from 40% to 100% PKO. Fat globule size and adsorbed protein levels in mix and overrun, fat destabilization, meltdown resistance, and air bubble size in ice cream were measured. It was found that blends comprising 60% to 80% solid fat produced the highest rates of fat destabilization that could be described as partial coalescence (as opposed to coalescence), lowest rates of meltdown, and smallest air bubble sizes. Lower levels of solid fat produced fat destabilization that was better characterized as coalescence, leading to loss of structural integrity, whereas higher levels of solid fat led to lower levels of fat network formation and thus also to reduced structural integrity. Practical Application: Blends of highly saturated palm kernel oil and monounsaturated high-oleic sunflower oil were used to modify the solid:liquid ratio of fat blends used for ice cream manufacture. Blends that contained 60% to 80% solid fat at freezing/whipping temperatures produced optimal structures leading to low rates of meltdown. This provides a useful reference for manufacturers to help in the selection of appropriate fat blends for nondairy-fat ice cream.     

Formation mechanisms of high quality diffusion bonded martensitic stainless steel joints

Abstract

Diffusion bonding of martensitic stainless steel was conducted at different times. Based on the interface characteristic and shear strength, bonding mechanisms were discussed. Results showed that the bonding quality was controlled by void shrinkage and interface grain boundary migration. Large voids with scraggly edges changed to small voids with smooth edges, leading to an increase in interface bonding ratio. Two cases of interface grain boundary migration were revealed: interface grain boundary migration at the triple junction induced by the reduction in grain boundary energy and strain induced interface grain boundary migration resulted from the stored energy. Owing to the void shrinkage and interface grain boundary migration, the shear strength of the joint matched that of the base material.     

Continuum and atomistic modeling of electromechanically-induced failure of ductile metallic thin films

A multiscale modeling approach is presented for the analysis of electromechanically-induced void morphological evolution and failure in ductile metallic thin films, which are used for device interconnections in integrated circuits. Self-consistent mesoscopic simulations of surface morphological evolution are combined with atomistic calculations of surface properties and molecular-dynamics (MD) simulations of plastic deformation mechanisms in the vicinity of void surfaces. Results are presented that demonstrate a coupled mode of surface instability that leads to formation of electromigration-induced slit-like features and stress-induced crack-like features on void surfaces. In addition, MD results are presented for the dislocation-mediated mechanism and the kinetics of void growth in ductile metallic systems subject to hydrostatic and biaxial tensile strains. The incorporation of MD-derived constitutive information for plastic deformation into the mesoscopic analysis and simulation framework also is discussed.     

冷轧 Al-Li 合金的再结晶

对 Al-Li 合金的再结晶温度和再结晶形核机制进行了研究。结果表明:所研究的 Al-Li 合金的再结晶开始温度为250℃,终了温度为400℃。再结晶形核有亚晶聚合和亚晶长大两种机制。     

Study of EM void nucleation and mechanic relaxation effects

In this paper the void formation during electromigration is characterized with the single standard via (SSV) and the innovative local sense structure (LSS). LSS allows the measurement of small resistance change before the final void formation. This has allowed to define a time nucleation for the void. The SSV has been used to study: side effect in the first phase (i.e. the “plateau”), the time to failure (TTF) and the void growth. The comprehension of all these phenomena will be fundamental for the future of interconnects reliability physics and lifetime prediction.     

Enhanced meta-modelling technique for analysis of mode crossing, mode veering and mode coalescence in structural dynamics

In this paper, an enhanced meta-modelling procedure for the approximation of structural eigenfrequencies and eigenvectors is introduced. The procedure allows for correct prediction of the modal parameters in case of mode crossing, veering, and coalescence phenomena that can be observed when variations of the structural parameters occur. The procedure overcomes the erroneous approximation of these phenomena which results from a direct approximation of the modal parameters. The methodology is based on the response surface approximation of the structural matrices and on the concept of modal reduction. A comparison with a direct response surface approximation of the eigenfrequencies shows a considerable improvement in the accuracy as it is presented for a finite element frame structure.     

Online monitoring of transit-time ultrasonic flowmeters based on fusion of optical observation

It is well-known that transit-time ultrasonic flowmeters (TTUF) are unsuitable for bubble-contained flows. This paper presents a new online monitoring method based on optical observation, which monitors the functionality of the TTUF in the presence of bubbles in the fluid. The method avoids the unnecessary Emergency Shutdowns (ESD) due to bubble presence in the fluid by bubble detection. The proposed method accomplishes bubble identification through a combination of image processing and wavelet analysis. In addition, a new method is proposed which estimates single bubble size in horizontal pipes using a data fusion approach.