Solution conductivity dependent crack size effect in stress corrosion cracking and corrosion fatigue

The chemical crack size effect on environmentally assisted crack growth was first demonstrated experimentally by Gangloff [1] and supported on a more robust theoretical framework by Turnbull et al. [2,3]. It is probably better dubbed the electrochemical crack size effect since the potential drop in the crack was a critical factor in determining the solution chemistry and the sensitivity to crack size. In recent experimental studies [4] we have focused on the growth rate of small and long stress corrosion and corrosion fatigue cracks in 12Cr steam turbine blade steels in low conductivity water containing 35 ppm Cl- (simulating upset steam condensate chemistry). A large effect of crack size on growth rate was observed for the same mechanical driving force. However, the crack-size effect disappeared in lower conductivity solution, 300 ppb Cl- and 300 ppb SO42- (corresponding to normal steam condensate chemistry). Furthermore, corrosion fatigue long crack growth rates were the same in aerated and in deaerated solutions for the two environments but stress corrosion cracks arrested in deaerated solution. An explanation for these varied results will be presented based on the concept of the solution conductivity dependent crack size effect and its impact on potential drop and the crack-tip potential. To underpin this conceptual idea and to explore further the scale of this effect for varied crack size and solution conductivity combinations, modelling of crack electrochemistry is being undertaken and the preliminary results will be discussed. R.P. Gangloff, The criticality of crack size in aqueous corrosion fatigue, Res. Mech. Let., 1981, 1, 299-306. A. Turnbull and J.G.N. Thomas, A model of crack electrochemistry for steels in the active state based on mass transport by diffusion and ion migration , J Electrochemical Society, 129 (7), 1412-1422, 1982. A. Turnbull and D.H. Ferriss, Mathematical modelling of the electrochemistry in corrosion fatigue cracks in steel corroding in sea water . Corrosion Science, 27 (12), 1323-1350, 1987. S. Zhou, M. Lukaszewicz and A. Turnbull, Small and short crack growth and the solution-conductivity dependent electrochemical crack size effect, Corros. Sci., 97 (2015) 25-37

Do corrosion pits eliminate the benefit of shot-peening?

Shot peening is used in many industrial applications, e.g. steam turbine blades, to induce near-surface compressive residual stresses and reduce the likelihood of failure by fatigue, corrosion fatigue and stress corrosion cracking. On the whole, shot peening has proven to be very successful in increasing the life of structures and components. However, the depth of the compressive stress layer is typically only about 250 µm and this poses the question as to the retained benefit when corrosion pits develop to varying depth. In the first stage to addressing this issue we show that the fatigue limit of a 12 Cr martensitic stainless steel turbine blade material tested in air at varying pit depths, ranging from 50 µm to 320 µm, was still significantly enhanced by shot peening even for the maximum depth studied. Complementary measurement of the crack propagation rate from a corrosion pit showed that the propagation rate was retarded by the near-surface compressive stress for crack depths up to 0.9 mm, well beyond the depth of the compressive layer. Serial sectioning to identify the loci of crack initiation sites yielded the unexpected result that crack development occurred preferentially away from the pit base, especially for the smaller pit depths. Finite element analysis to predict the stress and strain around a corrosion pit and to estimate the stress intensity factor will be described as a basis for rationalising the experimental observations. Please click Additional Files below to see the full abstract

The Application of Approximate Entropy Theory in Defects Detecting of IGBT Module

Defect is one of the key factors in reducing the reliability of the insulated gate bipolar transistor (IGBT) module, so developing the diagnostic method for defects inside the IGBT module is an important measure to avoid catastrophic failure and improves the reliability of power electronic converters. For this reason, a novel diagnostic method based on the approximate entropy (ApEn) theory is presented in this paper, which can provide statistical diagnosis and allow the operator to replace defective IGBT modules timely. The proposed method is achieved by analyzing the cross ApEn of the gate voltages before and after the occurring of defects. Due to the local damage caused by aging, the intrinsic parasitic parameters of packaging materials or silicon chips inside the IGBT module such as parasitic inductances and capacitances may change over time, which will make remarkable variation in the gate voltage. That is to say the gate voltage is close coupled with the defects. Therefore, the variation is quantified and used as a precursor parameter to evaluate the health status of the IGBT module. Experimental results validate the correctness of the proposed method

Investigating behavior inhibition in obsessive‐compulsive disorder: Evidence from eye movements

We investigated the role of inhibition failure in Obsessive Compulsive Disorder (OCD) through an eye tracking experiment. Twenty‐five subjects with OCD were recruited, as well as 25 with Generalized Anxiety Disorder (GAD) and 25 healthy controls. A 3 (group: OCD group, GAD group and control group) × 2 (target eccentricity: far and near) × 2 (saccade task: prosaccade and antisaccade) mixed design was used, with all participants completing two sets of tasks involving both prosaccade (eye movement towards a target) and antisaccade (eye movement away from a target). The main outcome was the eye movement index, including the saccade latency (the time interval from the onset of the target screen to the first saccade) and the error rate of saccade direction. The antisaccade latency and antisaccade error rates for OCDs were much higher than those for GADs and healthy controls. OCDs had longer latency and error rates for antisaccades than for prosaccades, and for far‐eccentricity rather than near‐eccentricity stimuli. These results suggest that OCDs experience difficulty with behavior inhibition, and that they have higher visual sensitivity to peripheral stimuli. In particular, they show greatest difficulty in inhibiting behavior directed towards peripheral stimuli

The influence of model quality on self-other mate choice copying

We explored, through two experiments, the influence of model quality and gender on mate choice copying (MCC) behavior for oneself and for others. In the first experiment, we used a 3 (decision-making role: self, stranger, close friend) × 2 (gender: male, female) between-subjects design. The phenomenon of MCC was only found in females. There was no significant difference between making decisions for oneself and for close friends, but there was a significant difference between making decisions for oneself and for strangers. In the second experiment, we used a 2 (model quality: higher, lower) × 3 (decision-making role: self, stranger, close friend) × 2 (gender: male, female) mixed experimental design. Results showed an MCC effect under the condition of high-quality models for both males and females, but no MCC effect for low quality models, either for males or females. Again, there was no significant difference between making decisions for oneself and for close friends, but there was a significant difference between making decisions for oneself and for strangers. These results reveal that context is important for the manifestation of MCC behavior: both women and men are influenced by the choices of high quality models, but ignore the behavior of low quality models

Quantum critical point in SmO1−xFxFeAs and oxygen vacancy induced by high fluorine dopant

The local lattice and electronic structure of the high-T(c) superconductor SmO(1-x)F(x)FeAs as a function of F-doping have been investigated by Sm L(3)-edge X-ray absorption near-edge structure and multiple-scattering calculations. Experiments performed at the L(3)-edge show that the white line (WL) is very sensitive to F-doping. In the under-doped region (x ≤ 0.12) the WL intensity increases with doping and then it suddenly starts decreasing at x = 0.15. Meanwhile, the trend of the WL linewidth versus F-doping levels is just contrary to that of the intensity. The phenomenon is almost coincident with the quantum critical point occurring in SmO(1-x)F(x)FeAs at x ≃ 0.14. In the under-doped region the increase of the intensity is related to the localization of Sm-5d states, while theoretical calculations show that both the decreasing intensity and the consequent broadening of linewidth at high F-doping are associated with the content and distribution of oxygen vacancies

A laboratory study of the expiratory airflow and particle dispersion in the stratified indoor environment

Understanding the role of human expiratory flows on respiratory infection in ventilated environments is useful for taking appropriate interventions to minimize the infection risk. Some studies have predicted the lock-up phenomenon of exhaled flows in stratified environments; however, there is a lack of high-quality experimental data to validate the theoretical models. In addition, how thermal stratification affects the transport of exhaled particles has not been explored so far. In this study, a water tank experiment was conducted according to the similarity protocols to mimic how the expiratory airflow and particles behaved in both uniform and stratified environments. The lock-up phenomenon was visualized and compared with the predicted results by an integral model. Results showed that our previously developed theoretical model of a respiratory airflow was effective to predict the airflow dispersion in stratified environments. Stratification frequency (N) of the background fluid and the Froude Number 〖"Fr" 〗_"0" of the thermal flow jointly determined the lock-up layer in a power law. For the particle dispersion, it indicated that small particles such as fine droplets and droplet nuclei would be ‘locked’ by indoor thermal stratification, and disperse with the thermal flow over a long distance, potentially increasing the long-range airborne infection risk. Large particles such as large droplets can deposit within a short distance, hardly affected by thermal stratification, however, droplet infection could happen to the susceptible people at a close contact with the infector. This study could give some guidance in view of cross-infection control indoors for stratified environment

Causative agent distribution and antibiotic therapy assessment among adult patients with community acquired pneumonia in Chinese urban population

<p>Abstract</p> <p>Background</p> <p>Knowledge of predominant microbial patterns in community-acquired pneumonia (CAP) constitutes the basis for initial decisions about empirical antimicrobial treatment, so a prospective study was performed during 2003–2004 among CAP of adult Chinese urban populations.</p> <p>Methods</p> <p>Qualified patients were enrolled and screened for bacterial, atypical, and viral pathogens by sputum and/or blood culturing, and by antibody seroconversion test. Antibiotic treatment and patient outcome were also assessed.</p> <p>Results</p> <p>Non-viral pathogens were found in 324/610 (53.1%) patients among whom <it>M. pneumoniae </it>was the most prevalent (126/610, 20.7%). Atypical pathogens were identified in 62/195 (31.8%) patients carrying bacterial pathogens. Respiratory viruses were identified in 35 (19%) of 184 randomly selected patients with adenovirus being the most common (16/184, 8.7%). The nonsusceptibility of <it>S. pneumoniae </it>to penicillin and azithromycin was 22.2% (Resistance (R): 3.2%, Intermediate (I): 19.0%) and 79.4% (R: 79.4%, I: 0%), respectively. Of patients (312) from whom causative pathogens were identified and antibiotic treatments were recorded, clinical cure rate with β-lactam antibiotics alone and with combination of a β-lactam plus a macrolide or with fluoroquinolones was 63.7% (79/124) and 67%(126/188), respectively. For patients having mixed <it>M. pneumoniae </it>and/or <it>C. pneumoniae </it>infections, a better cure rate was observed with regimens that are active against atypical pathogens (e.g. a β-lactam plus a macrolide, or a fluoroquinolone) than with β-lactam alone (75.8% vs. 42.9%, <it>p </it>= 0.045).</p> <p>Conclusion</p> <p>In Chinese adult CAP patients, <it>M. pneumoniae </it>was the most prevalent with mixed infections containing atypical pathogens being frequently observed. With <it>S. pneumoniae</it>, the prevalence of macrolide resistance was high and penicillin resistance low compared with data reported in other regions.</p