Cyclic plasticity and creep of power plant materials

The thermo-mechanical fatigue (TMF) of power plant components is caused by the cyclic operation of power plant due to startup and shutdown processes and due to the fluctuation of demand in daily operation. Thus, a time-dependent plasticity model is required in order to simulate the component response under cyclic thermo-mechanical loading. The overall aim behind this study is to develop a material constitutive model, which can predict the creep and cyclic loading behaviour at high temperature environment, based on the cyclic loading test data of the P91 and the P92 steels. The tests on all specimens in the study were performed using the Instron 8862 TMF machine system with a temperature uniformity of less than ±10°C within the gauge section of the specimen. For the isothermal tests on the P91 steel, fully-reversed, strain-controlled tests were conducted on a parent material of the steel at 400, 500 and 600˚C. For the P92 steel, the same loading parameters in the isothermal tests were performed on a parent material and a weld metal of the steels at 500, 600 and 675°C. Strain-controlled thermo-mechanical fatigue tests were conducted on the parent materials of the P91 and the P92 steels under temperature ranges of 400-600°C and 500-675°C, respectively, with in-phase (IP) and out-of-phase (OP) loading. In general, the steels exhibit cyclic softening behaviour throughout the cyclic test duration under both isothermal and anisothermal conditions. The cyclic softening behaviour of the P91 steel was further studied by analyzing stress-strain data at 600°C and by performing microstructural investigations. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images were used to investigate microstructural evolution and the crack initiation of the steel at different life fractions of the tests. The TEM images of the interrupted test specimens revealed subgrain coarsening during the cyclic tests. On the other hand, the SEM images showed the initiation of microcracks at the end of the stabilisation period and the cracks were propagated in the third stage of cyclic softening. A unified, Chaboche, viscoplasticity model, which includes combined isotropic softening and kinematic hardening with a viscoplastic flow rule for time-dependent effects, was used to model the TMF behaviour of the steels The constants in the viscoplasticity model were initially determined from the first cycle stress-strain data, the maximum stress evolution during tests and the stress relaxation data. Then, the initial constants were optimized using a least-squares optimization algorithm in order to improve the general fit of the model to experimental data. The prediction of the model was further improved by including the linear nonlinear isotropic hardening in order to obtain better stress-strain behaviour in the stabilisation period. The developed viscoplasticity model was subsequently used in the finite element simulations using the ABAQUS software. The focus of the simulation is to validate the performance of the model under various types of loading. Simulation results have been compared with the isothermal test data with different strain ranges and also the anisothermal cyclic testing data, for both in-phase and out-of-phase loadings. The model’s performance under 3-dimensional stress conditions was investigated by testing and simulating the P91 steel using a notched specimen under stress-controlled conditions. The simulation results show a good comparison to the experimental data

Structural Analysis and Material Characterization of Silver Conductive Ink for Stretchable Electronics

Stretchable electronic systems have become more popular in various applications such as medical, fabric, flexible sensors for personalized health care, etc. There are two major parts of flexible and stretchable circuit boards that are substrate (a plastic material) and conductive ink (formulated polymer with conductive metal). According to electrical measurements, conductive ink plays a very important role in stretchable electronic equipment. The main objective of this paper is to develop a silver (Ag) based conductive ink and characterize its mechanical and electrical properties. Conductive ink is prepared by mixing an epoxy resin, cross – linking agent, additives (adhesion promoter), organic solvent, catalyst and silver flakes all together. ASTM D412 Type C dog bone shaped cutter is used to make three samples of conductive ink. The stress-strain analysis of conductive ink is carried out using universal testing machine (UTM). The conductivity is measured using two-point probe digital multi-meter. Also, the microstructural analysis, morphology and characterization are done by scanning electron microscopy (SEM). The images are taken after curing and tensile testing. The formulated ink possesses high conductivity and stretchability up to 137% strain. The achieved conductivity of the ink is 4.167×104 S/m. The maximum stress before failure, yield stress, Young’s and tangent moduli are calculated as 1.195 MPa, 0.86 MPa, 5.72 MPa and 2.08 MPa, respectively. The SEM analysis indicates that the distribution of silver particles is uniform and in a good density throughout the sample

Multiaxial viscoplasticity modelling of power plant steel

The thermo-mechanical fatigue (TMF) of power plant components is caused by the cyclic operation of power plant. A time-dependent plasticity model can be used to simulate the component response under cyclic thermo-mechanical loading. This paper is concerned with the modelling of thermo-mechanical behaviour of power plant steel under various loading conditions. Fully-reversed, strain-controlled tests were conducted on a parent material of P91 steel at high temperatures in order to determine material constants. A unified, Chaboche viscoplasticity model, was used to model the TMF behaviour of the steel. The multiaxial form of the Chaboche constitutive equations have been implemented in the finite element software and validated by comparing to experimental data. Simulation results have been compared with the results of anisothermal cyclic testing in order to validate the performance of the model in cyclic temperature conditions. The model’s performance under multiaxial stress conditions was investigated by testing and simulating the notched bar specimen under load-controlled conditions

Acute phase protein profiles in calves following infection with whole cell, lipopolysaccharides, and outer membrane protein extracted from Pasteurella multocida type B:2

Acute Phase Protein (APP) investigations of serum or plasma following natural or experimental infection frequently reveal substantial alterations in the APPs, several of which are of veterinary importance in the assessment of herd health. The present study of the experimental nature was conducted to evaluate the acute phase protein responses; haptoglobin, Serum Amyloid A (SAA) and serum albumin in relation to infection with Pasteurella multocida type B and its immunogens; lipopolysaccharide (LPS) and Outer Membrane Protein (OMP) in calves. Eight clinically healthy, non-pregnant and non-lactating Brangus cross calves weighing 150±50 kg were used in this study. The calves (n = 8) were divided into 4 groups of 2 calves in each group. The control group was inoculated with sterile Phosphate Buffered Saline (PBS) whereas group 2 were inoculated with wild-type P. multocida type B:2 and group 3 and 4 were inoculated with LPS and OMP respectively. Blood samples were collected via jugular vein-puncture at 3 h intervals for APPs analysis. APPs were quantified by commercially available ELISA methods. Moribund animals were euthanized while the surviving animals were killed after 48 h. The results revealed that there were statistically significant differences (p0.05) with mean levels of 32.677±1.556 and 36.185±2.239 U L-1, respectively. While P. multocida group (22.193±2.727 U L-1) showed statistically significant difference (p<0.05) than the negative control group (34.233±6.900 U L-1). In conclusion, the findings of this study indicated that APPs; SAA and haptoglobin are sensitive biomarkers to explore host response in relation to Haemorrhagic Septicaemia infections in clinical settings

Ibn Fadlan's role in the Islamisation of Bulghar society

Islam is the oldest established religion among Bulghar entity, the residents along the riverbanks of the Volga-Kama triangle. This valley was famous as the first Islamic country erected in the Eastern European region. The presence of Islam in the region has raised the name of the ruler of Volga Bulgaria and was reinforced by relationship with Baghdad. The Islamisation of the Bulghar society is relevant to the role played by Ahmad ibn Fadlan, the ambassador of the Abbasid government based in Baghdad. Therefore, this article aims to examine the role played by Ibn Fadlan in the Islamization of the Bulghar society. For this study, a qualitative method using historical descriptive approach was employed, which involved compilation and evaluation of the facts of the Risalah Ibn Fadlān. Data for this study were obtained through library research. The data analyses were conducted through texts and document analyses, as well as comparison method. This study finds that Ibn Fadlan plays an important role in the islamisation of the Bulghar society, not just as an ambassador of Abbasid government but as a teacher, preacher and counselor to the Bulghar king and the whole nation

Reliability Assessment Of Self-Alignment Assemblies Of Chip Component After Reflow Soldering Process

Reliability of surface mount components and interconnect are significant issues in electronic manufacturing. Although the reliability of devices has been broadly studied,here we are focusing on the reliability of the solder joint after the self-alignment phenomena during reflow soldering.In this study,the quality of the self-alignment assemblies was analyzed relate to the joint shear strength according to the JIS Z3 198-7 standard and the inspection according to IPC-A-610E standard.The results from reliability study indicate that the shear strength of the misalignment component of solder joints indeed depends on the degree of chip component misalignment.For shift mode configuration in the range of 0-300µm,the resulted chip assembly inspection after the reflow process was in line with the IPC-A-610E standard

Soldering Characteristics And Thermomechanical Properties Of Pb-Free Solder Paste For Reflow Soldering

A deep understanding in thermal characteristics of lead-free solder paste grades is one of the most crucial factors when dealing with reflow soldering process. These temperatures are critical parameters for proper settings of the real reflow process. This report is devoted to discussing the findings obtained during utilization of differential scanning calorimetry (DSC) and calculation using MATLAB to identify the latent heat, solidus and liquidus temperature, and surface tension applicable to numerically simulate the real process of reflow soldering. It can be stated that the equilibrium solidus and liquidus temperatures during solidification process are not a reversal of the melting process, with the solid phase equilibrium occurred at a lower temperature due to the difficulty of ß-Sn nucleation. Amount of heat energy released during solidification differs less than 10% for SAC405 and less than 1% for SAC105 with the latent heat of fusion during the melting process

Polymerase chain reaction detection of Pasteurella multocida type B:2 in mice following oral inoculation

Haemorrhagic Septicaemia (HS) is an acute, fatal, septicaemic disease of cattle and water buffaloes caused by Pasteurella multocida, serotype B:2 in tropical countries. The limitations associated with accurate predictions of mortality, survival levels and the detection of the presence of the organism from various organs of infected animals. Hence, this study used mouse model to evaluate the pattern of mortality and bacterial recovery from organs. Twenty-four mice were randomly divided into two groups. Infected group were inoculated orally with 109 colony forming unit of P. multocida type B, the group 2 were negative controls. The mice were observed for 5 days post-inoculation. At necropsy, visceral organs of dead animals were subjected for the confirmation using Polymerase Chain Reaction (PCR). The results showed that mortality rate was significantly different (p<0.05) between the infected and control groups. Within infected group, highly significant difference (p<0.05) was observed where 12.5% of the mortality rate was recorded within 24 h and 62.5% within 48 h post-infection. The survival rate, in infected group, was found to be around 25%. In diagnosis, P. multocida type B was detected from all organs of animals that did not survive. In contrast, P. multocida type B was neither recovered nor detected from the organs of mice which survived until the end of the experimental period (120 h). The results of this study indicated that manipulation of the organism in experimental animals provided clear information of the incidence of the disease in the field