Prediction of Fatigue Crack Initiation under Variable Amplitude Loading: Literature Review

Metallic materials are widely employed in engineering constructions, and one of the most common failure mechanisms in metals is fatigue failure. Even though metal fatigue has been studied for almost 160 years, many problems remain unsolved. Fatigue in metal occurs when the metallic material is subjected to varying loads, resulting in failure due to damage accumulation. The fatigue process consists of a buildup of damage that leads to crack initiation, followed by a period of crack growth until the critical flaw size is reached. The sum of a start phase and a propagation phase represents the total life. To better understand the fatigue phenomenon at its different stages and predict the fatigue life, various types of prediction models have been developed and reported in the literature. This paper reviewed the different models that include microstructure scale parameters that can be used to predict how fatigue cracks start under variable amplitude loading, including the Modified Tanaka-Mura Model, Acoustic Second Harmonic Generation, and the Probability of Crack Initiation on Defects. For perfect life prediction under variable amplitude loading, a stress-based approach, a strain-based approach, and a continuum damage mechanics approach are reviewed. The purpose of this paper is to get overview of the current state of approaches to the life prediction of fatigue crack initiation with variable amplitude. Finally, gaps in knowledge about the prediction of fatigue crack initiation under variable loading at high temperatures are pointed out.publishedVersio

New Chemical Stabilizer Effect on Plasticity of Lateritic Soil Properties

The lateritic soil that has high content of iron oxides and aluminum hydroxides and low proportion of silica is widespread in the tropical and semi-tropical countries. Lateritic soil as available materials in these areas utilized in different civil engineering applications as roads, canals, earth dams, railways, building, … etc. These applications are depending in a majority on soil classification in design the construction on this soil type. One of the important parameters in classification of soil is an Atterbage’s limits are used in definition of soil type and its strength. Due to increase in population caused an increase in construction to demand the facilities of this growth, therefore the desired soil decrease depend on used and the undesired soil available. Soil stabilization utilized to improve the undesired soil properties by a different technique to achieve the design requirement. Chemical stabilization becomes one of the best solution to soil problems depend on economic and time save. New chemical soil stabilization used is named (NBT II) in this study to exam the effect on plasticity soil properties. Different percentages and different curing time test conducted on lateritic soil to evaluate the range of effect and also examined the effect of plasticity on dry density. The results show decrease in liquid limit with increase in NBT II and then beginning to increase with stabilizer percentage increase the reduction about 11% at 28 days curing, plastic limit increase about 6% at the same time and plasticity index decrease 80%. The results also show the inverse relationship between maximum dry density and plasticity index

Prediction of Fatigue Crack Initiation under Variable Amplitude Loading: Literature Review

Metallic materials are widely employed in engineering constructions, and one of the most common failure mechanisms in metals is fatigue failure. Even though metal fatigue has been studied for almost 160 years, many problems remain unsolved. Fatigue in metal occurs when the metallic material is subjected to varying loads, resulting in failure due to damage accumulation. The fatigue process consists of a buildup of damage that leads to crack initiation, followed by a period of crack growth until the critical flaw size is reached. The sum of a start phase and a propagation phase represents the total life. To better understand the fatigue phenomenon at its different stages and predict the fatigue life, various types of prediction models have been developed and reported in the literature. This paper reviewed the different models that include microstructure scale parameters that can be used to predict how fatigue cracks start under variable amplitude loading, including the Modified Tanaka-Mura Model, Acoustic Second Harmonic Generation, and the Probability of Crack Initiation on Defects. For perfect life prediction under variable amplitude loading, a stress-based approach, a strain-based approach, and a continuum damage mechanics approach are reviewed. The purpose of this paper is to get overview of the current state of approaches to the life prediction of fatigue crack initiation with variable amplitude. Finally, gaps in knowledge about the prediction of fatigue crack initiation under variable loading at high temperatures are pointed out

Effect of Interference Size on Contact Pressure Distribution of Railway Wheel Axle Press Fitting

Mechanical couplings in engineering usually use interference fits to connect the shaft and hub. A railway wheel axle is a press fit that is connected by interference and can be subjected to bending stress. In loaded press fits, a high concentration of contact stresses can be generated in the area of the axle-fillet beam, which in most cases leads to the failure of the axle due to fatigue and fretting fatigues. Therefore, it is crucial to determine the ability of the press-fitted joints to provide sufficient frictional resistance that can withstand the loads and torques by evaluating the safety factor, especially when the mechanical or structural system is loaded. In this paper, the contact pressure and stress distribution along the radius of the wheel axle are studied using the analytical calculation of Lame’s equation, and the numerical method used is by ANSYS software. It was found that interference fits have a great influence on the connection strength of interference fits, which are directly related to the contact pressure. Increasing the interference increases the contact pressure, which allows higher torque and load capacity to be transmitted. The finite element analysis showed good agreement for the highest interference value of 230 µm with a relative error of 1.4%, while this error increased to the maximum relative error of 14.33% for a minimum interference of 100 µm.publishedVersio

Analysis of the negative externalities effects of oil extraction in Iraq for the period (2004-2020)

This study addressed the negative side effects of oil extraction in Iraq and aimed at analyzing the negative side effects of oil extraction on the Iraqi economy for the period 2004-2020. The research problem stems from the fact that Iraq suffers from negative side effects from oil extraction, which are reflected negatively on the Iraqi economy. The most important finding is that the Iraqi economy's dependence on crude oil production as a primary source of financial resources for the country's administration clearly indicates that Iraq is under the influence of the negative side effects of this process and the emergence of the rentier state with a one-sided economy. The study made recommendations, the most important of which was the need to work on the rational and well-planned exploitation of the depleted resources (oil extraction) to reduce the negative consequences of this extraction, which would contribute to the adoption of the proposed remedies waste the resources that the Iraqi economy suffers from, and then start the road towards sustainable developmen

Dexmedetomidine versus labetalol infusions for controlling emergence hypertension in cranial surgeries for supratentorial tumors

Background: Acute hypertension is a common accompaniment during emergence from anesthesia especially in intracranial neurosurgical procedures and may be associated with the development of intracranial hematoma. Although various drugs have been evaluated, management of emergence hypertension in this subset of patients continues to be a challenge for anesthesiologists. Methodology: Seventy-five patients ASA (I-II) scheduled for supratentorial craniotomy under general anesthesia were randomly allocated to one of three groups at the time of dural closure: Group “dex” received dexmedetomidine infusion in a rate of 1 μg/kg/hr, Group “labetalol” received labetalol infusion in a rate of 0.5 mg/kg/hr, and Group “control” a control group where patients received saline infusion at the same rate of dexmedetomidine and labetalol. Hypertensive episodes were managed with nitroglycerin at a dose starting from 1 μg/kg/min if systolic blood pressure exceeded 25% of its preinduction value. Hemodynamic parameters as well as the number of patients, the total dose of nitroglycerin required in each group and the time to extubation were recorded. Results: Dexmedetomidine and labetalol had a significant effect in reducing SBP, MAP, DBP, HR during emergence from anesthesia, with more reduction of the SBP, MAP and DBP in the dexmedetomidine group and of the HR in the labetalol group in comparison with the other two groups. The number of patients needing nitroglycerin was 8 representing 32% of patients in dexmedetomidine group, 5 representing 20% of patients in labetalol group and 22 representing 88% of patients in control group (P value = 0.032). Time to emergence from anesthesia was comparable in the three groups. Conclusion: Both dexmedetomidine and labetalol had favorable effects on hemodynamics at time of emergence from anesthesia in comparison with control group without prolongation of the time of extubation

Clinical observation of the Efficacy of Sufoof Jawahar Mohra (A Unani Formulation) on CD4 Count in A HIV Positive Individual: A Case Study

HIV/AIDS pandemic is emerging as one of the most serious health problems of this century. AIDS was first recognized in the United States in the summer of 1981. The virus causing AIDS was independently identified by a team of French Scientists led by Dr. Luc Montagnier of Pasteur Institute; and American Scientists led by Dr. Robert C. Gello, of National Cancer Institute in 1983-1984. In 1983, Human Immunodeficiency Virus (HIV) was isolated from a patient with lymphadenopathy, and by 1984 it was demonstrated clearly to be the causative agent of AIDS.A 22 year old male HIV positive individual whose CD4 count was 465 (Cells per cumm) was registered in the OPD of Regional Research Institute of Unani Medicine, Mumbai. SufoofJawaharMohra (Unani formulation) was given in the dose of 250 mg orally twice a day.  The CD 4 count done at every 6 month during the treatment. It has been observed that there was a remarkable improvement in the CD4 count. The CD4 count was 465 (Cells per cumm) at base line and at the second follow up it was 571 (Cells per cumm) and in the third follow-up the CD 4 count was 685 (Cells per cumm). There was a remarkable improvement in the CD4 count without complaining of any side effects of drug

NEONATAL BACTERIAL CONJUNCTIVITIS IN TERTIARY HOSPITALS IN SANA'A CITY, YEMEN

Background: Ophthalmia neonatorum (ON) is the most widespread eye infection occurring in the first 28 days of life. Although most of these cases are benign, some may progress to systemic complications or blindness if left untreated. Objectives: The current study was conducted with the aim of revealing the bacteriological causes of conjunctivitis in neonates and the antibiotic sensitivity pattern of these bacteria. Subjects and methods: The study included all neonates at the age of 1 to 28 days presenting at the neonatal nurseries with Neonatal Intensive Care Unit (NICU) and level II care beds in three hospitals; Authority of Al-Thawra General Hospital, Al-Kuwait University Hospital and Al-Sabeen Maternity and Child Hospital in Sana’a city, Yemen. A full history was taken from each nurse and mothers of the neonates included in the study in which the findings were recorded in a predesigned questionnaire including socio demographic, maternal clinical information and therapeutic interventions. To isolate the causative agent, the conjunctival swabs were inoculated on proper media and bacteria were identified by standard microbiological methods and antibiotic resistance was done for the isolates. Results: 203 swabs were collected from newborns with eye discharge over a nine-month period. Positive growth rate was 51.7%, males were more affected (57.1%), 80% of affected neonates had low birth weight, 71.4% of preterm infants were most affected (p <0.01).  There was a significant relationship between invasive and non-invasive mechanical ventilation with neonatal conjunctivitis (p<0.05). Gentamicin showed good in vitro sensitivity to all bacteria isolated, Staphylococcus aureus (83%), Escherichia coli 84.6%, with P. aeruginosa it was 60%. Conclusion: The vast majority of cases of neonatal conjunctivitis were mild with a high level of occurrence, Staphylococcus aureus and Klebsiella pneumoniae were the major bacterial agents, neonatal conjunctivitis most likely to be a hospital-acquired infection. There was a significant association between phototherapy, non-invasive ventilation and incidence of neonatal conjunctivitis . Gentamicin had high activity against the bacteria isolated in this study.                   Peer Review History: Received: 9 November 2021; Revised: 11 December; Accepted: 27 December, Available online: 15 January 2022 Academic Editor: Dr. Sally A. El-Zahaby, Pharos University in Alexandria, Egypt, [email protected] Received file:                Reviewer's Comments: Average Peer review marks at initial stage: 6.0/10 Average Peer review marks at publication stage: 7.0/10 Reviewers: Dr. Bilge Ahsen KARA, Ankara Gazi Mustafa Kemal Hospital, Turkey, [email protected] Dr. Jucimary Vieira dos Santos, Hemonorte Dalton Barbosa Cunha, Brazil, [email protected]  Similar Articles: BACTERIAL CONJUNCTIVITIS OF ADULTS: CAUSES AND OPHTHALMIC ANTIBIOTIC RESISTANCE PATTERNS FOR THE COMMON BACTERIAL ISOLATES BACTERIAL CAUSES AND ANTIMICROBIAL SENSITIVITY PATTERN OF EXTERNAL OCULAR INFECTIONS IN SELECTED OPHTHALMOLOGY CLINICS IN SANA’A CIT