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The creep crack initiation (CCI) location and time of axial surface cracks with different sizes in cracked pipes have been comparatively predicted by finite element calculations based on creep ductility exhaustion model and creep fracture mechanics considering constraint effects by using two new creep constraint parameters ( R ∗ and A c ). The effects of calculation methods of the parameters C ∗ , R ∗ and A c along the crack fronts on the prediction accuracy of CCI time have been analyzed. It has been found that with decreasing crack length, the CCI location changes from the deepest part to near surface part along the crack front, and the composite parameters composed of C ∗ and constraint parameters can predict the CCI location. The CCI time of pipe cracks increases with decreasing crack depth and length due to the decrease of crack-tip constraint level. The excessive conservatism in conventional CCI life assessments using single parameter C ∗ can be significantly reduced by using the two-parameter concept ( C ∗ - R ∗ and C ∗ - A c ) considering constraint effects. When the average values of C ∗ , R ∗ and A c along the crack fronts (instead of the values at the deepest locations of crack fronts) are calculated and used in CCI life predictions of cracked pipes, the prediction accuracy with respect to the finite element calculations based on creep ductility exhaustion model can be significantly improved. The C ∗ values calculated by reference stress method can lead to extra conservatism in CCI life predictions.

The creep crack initiation (CCI) time of six specimen geometries in ASTM E1457 standard has been predicted by using numerical simulations, and the constraint effect on CCI time was analyzed. The results show the specimens with different geometries, size ranges and side-grooves recommended by ASTM-E1457 produce different CCI time data due to different constraint levels. With increasing constraint levels in specimens, the CCI time is reduced. The quantitative correlation formulas of CCI time with creep constraint parameters have been established, and they may be applied in CCI life assessment of high-temperature components for accounting for constraint effect and improving accuracy.

Three-dimensional creep constraint of six specimen geometries in ASTM E1457 standard was characterized by using two constraint parameters, and creep crack growth (CCG) rates in these specimens were predicted by using numerical simulations. The results show that the specimens with different geometries and size ranges recommended by ASTM-E1457 have different constraints, thus produce different CCG rate data. With increasing specimen thickness and side-groove depth, the constraint and CCG rates of all specimens increase. It needs to consider constraint effects on CCG rate when predicting component life using laboratory data. The quantitative correlation formulas of CCG rate with creep constraint have been established.

By using stress dependent creep ductility and strain rate model in a ductility exhaustion based damage model, the creep crack initiation (CCI) behaviour in Cr–Mo–V steel specimens with different geometries and dimensions (different constraints) over a wide range of C* has been predicted by finite element simulations. The predicted creep crack initiation time agree well with the existing experimental data. In low and transition C* regions, the constraint induced by specimen geometries and dimensions has obvious influence on CCI time. With increasing constraint level of specimens, the CCI time decreases due to the increase of stress triaxiality ahead of crack tip. Different CCI trends and constraint effects on CCI behaviour in a wide range of C* result from the interaction of crack-tip stress state and stress dependent creep ductility of the steel. It is suggested that in CCI life assessments of high temperature components, the long-term CCI time data at low C* region should be obtained and used, an...

In this study, monodispersed silica spheres were successfully synthesized by seed-growth method and they can be highly dispersed in the poly(vinyl alcohol)(PVA) solution. PVA/silica composite fibers were fabricated by electrospinning the composite solutions containing different amount of silica. Further investigation showed that the size distribution of silica sphere was monodispersed and the spheres were homogeneously dispersed in the fibers individually. The composite fibers showed an uniform and continuous morphology with a average diameter of 298–345 nm. The as-spun nanofibers were characterized by Field Emission Scanning Electron Microscope (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and thermal gravimetric analysis (TGA). POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers

We study post-stabilization of numerical integrators for an autonomous Hamiltonian system in the form H = H 1 + H 2 , where H 1 and H 2 are two constants of motion. It is better to stabilize the two energies H 1 and H 2 , respectively. As a particular case, the effectiveness of post-stabilization by the total energy is equivalent to one by the two independent energies when the splitting Hamiltonian becomes isotropic.

Refined silicon nanowires have been prepared by a mild etching process and suspended into liquid in order to make them manageable for individual characterization. A transmission electron microscopy (TEM) study has revealed that the etching starts selectively at defect sites on the wires. This implies that the refined wires have many fewer defects than those made of raw materials. Efforts have been made to mount single nanowires onto the desired electrodes by electrophoresis. Compared with the commonly used microactuation method in the field, this is a far more realistic practical use of the wires that has an industrial value.

Nanoparticle amorphous lanthanum borate with a particle size of 20–40 nm was prepared with a Replacing Solvent Dry technique and characterized using TEM and XRD. Its tribological properties as a wear resistance additive of lubricating oil were evaluated with a four-ball tribotester. The wear scar was characterized with XPS. The wear resistance and load carrying capacity of 500 SN base oil was improved by the lanthanum borate. Diboron trioxide and FeB were formed on the wear scar surface. These tribochemical reaction products as well as some depositions formed a wear resistance film on the rubbing surface, which provided the oil with an excellent load carrying capacity.

Variable-temperature ultra high vacuum scanning tunnelling microscopy (VTUHVSTM) has been employed to study the initial stage of Si(111) oxidation. By taking advantage of the in-situ arrangement of the experiment, we are able to constantly monitor the surface structure during the whole oxidation process at elevated temperatures. Ordered structures of oxides from a submonolayer to a full monolayer were observed at atomic level. Our preliminary results may give a clue to one of the fundamental issues of silicon technology: why amorphous silicon dioxide can form a perfect interface with the crystalline silicon substrate.