Modelling the fatigue crack growth in friction stir welded joint of 2024-T351 Al alloy

In this work the fatigue crack propagation within the friction stir welded (FSW) joint of 2024-T351 Al alloy is studied as well as fatigue lifetime of the joint using Walker and Nicholls models. The FSW joint is characterised in terms of the residual stress (using the hole drilling technique), material, and cyclic properties. The material surface is polished in order to avoid any surface irregularities. The crack initiation is detected applying scanning electron microscopy (SEM), however plastic replication technique is used to monitor the crack propagation. The concepts of crack closure, residual stress and stress relaxation are incorporated into both models. Finally the results are validated and compared together regarding to the experiments

An optimized direct control method applied to multilevel inverter for microgrid power quality enhancement

Multifunctional DGs and active power filters have become a mature technology in recent years, so in this paper, an optimized current control method for a multilevel converter is proposed. The control method will overcome harmonic current tracking inefficiency of previous control methods in online harmonic compensation applications in microgrids. This control method is applicable for grid-connected inverter-based multi-functional Distributed Generation (DG) converters. It could also be used in active power filter applications which need high-speed reference tracking ability. Having the advantages of current control methods like hysteresis band control, proportional-integral (PI) and proportional-resonant (PR) control methods, the proposed approach overcomes disadvantages of these methods especially in harmonic reference tracking as it will be discussed in detail. The main advantages of this method are the simplicity of implementation, calculation delay compensation and its fast response to changes. The power electronic circuit, operating principles, two-horizon predicted switching states of multilevel inverter, experimental results and applications of this control method will be discussed in the paper. For studying the feasibility of the control method, an experimental prototype is tested in a microgrid platform

Computational investigation of crack behavior in friction stir welding

The aim of the present work is to predict the fatigue life of a friction stir welded (FSW) joint in the 2024-T351 aluminum alloy using the finite element method in the framework of Fracture Analysis Code for Two Dimensions (FRANC2D/L). The simulation is conducted using linear elastic fracture mechanics based on Paris' model, and the maximum tensile stress and displacement correlation methods are applied to calculate the crack direction and stress intensity factor, respectively. Several strategies are applied in order to predict the crack propagations through various welded zones regarding the corresponding parameters and Paris constants for each zone. The entire crack growth process is investigated step by step through all of the FSW zones, and the fatigue lifetimes of the FSW joint under various loading conditions are predicted by implementing the same procedure. The numerical results are validated with experimental and analytical work

Simulation of fatigue crack growth in friction stir welded joints in 2024-T351 al alloy

The aim of the present work is to predict the fatigue life of friction stir welded joints in 2024-T351 Al alloy using the finite element method in the framework of fracture analysis code for two-dimensions (FRANC2D/L). The simulation was conducted under linear elastic fracture mechanics, based on Paris' model and maximum tensile stress and displacement correlation methods were applied to calculate the crack direction and stress intensity factor, respectively. One strategy has been presented, how crack propagation was investigated based on the corresponding Paris constants for each FSW zone. Numeri-cal results were validated with experimental and analytical work

Strength investigation of thick welded T-Joint using finite element modelling

The paper discusses the computation of finite element modelling (FEM) of a thick welded joint as a high load transfer joint. The FEM utilises MSC PATRAN/NASTRAN software programs to predict and simulate the critical area of a welded joint. The elasticity limit for the specimen was determined and stress distribution was achieved in the joint to indicate critical parts of a welded T-joint and predict the critical locations for crack initiation in this kind of joint. Simulation and experimental results show good in agreement and the sources of some differences in these results are discussed

Implementation of a System for Monitoring Overall Equipment Effectiveness (OEE) and Exploring Correlation Between OEE and Process Capability

An effective process equipment monitoring tool widely accepted in manufacturing units today is overall equipment effectiveness (OEE). OEE began its debut as a pillar of the total productive maintenance (TPM) system, where the goals are to increase the reliability and availability of equipment so that resource waste is reduced and product quality is enhanced. Interest by a manufacturing company in North Carolina in evaluating OEE in terms of appropriateness in its application, along with a desire to explore other quality performance metrics that can be easily tracked to predict OEE, was the motivation behind this study. The goals of this study were:  1) To recommend to the manufacturing company definite steps that they should undertake to implement a robust OEE based equipment performance evaluation system  2) To demonstrate on a pilot basis how the implementation should be carried out, and   3) Study whether process capability which can be used as a leading quality indicator has any correlation to OEE which is a lagging indicator.   A framework was established for the implementation of OEE in a pilot area of the manufacturing unit. A systematic plan was proposed and implemented which demonstrated that it is possible to reverse the effects of an ineffective OEE measurement process and create an effective system to pursue continuous improvement. Success in this endeavor can be attributed to pursuing training at various levels. Another key factor in establishing the system was using an appropriate calculation method for OEE compatible to the understanding power of the company's workforce. Providing clear definitions that were easy to understand and interpret for all terms involved in the OEE calculation also played a key role in the success of the implementation. Recommendations on how to go about changing the company's culture to embrace the concept of OEE were provided and pursued. Use of OEE values for conducting personnel annual evaluations was stopped.   For exploring the correlation between process capability and OEE, the null hypothesis that there is no relation between process capability index and OEE, and between process capability index and each of OEE's three elements which are availability, performance and quality, was chosen. Calculating p-values for hypothesis testing, using non-linear regression analysis it was found that at a significance level of 0.05, the null hypothesis cannot be rejected for any of the four sub-hypothesis.   Limitations to the study included a short time period for the study and a lack of good available data. Another limitation was the fact that the final decision whether a part is good or bad was made by attempting to assemble the part in the final assembly operation. Further future work to this study would be to explore correlation between process capability and OEE in a controlled lab environment with more machines and parts and definite part specification limits.  M.S

Implementation of a System for Monitoring Overall Equipment Effectiveness (OEE) and Exploring Correlation Between OEE and Process Capability

An effective process equipment monitoring tool widely accepted in manufacturing units today is overall equipment effectiveness (OEE). OEE began its debut as a pillar of the total productive maintenance (TPM) system where the goals are to increase the reliability and availability of equipment so that resource waste is reduced and product quality is enhanced. Interest by a manufacturing company in North Carolina in evaluating OEE in terms of appropriateness in its application along with a desire to explore other quality performance metrics that can be easily tracked to predict OEE was the motivation behind this study. The goals of this study were: 1) To recommend to the manufacturing company definite steps that they should undertake to implement a robust OEE based equipment performance evaluation system 2) To demonstrate on a pilot basis how the implementation should be carried out and 3) Study whether process capability which can be used as a leading quality indicator has any correlation to OEE which is a lagging indicator. A framework was established for the implementation of OEE in a pilot area of the manufacturing unit. A systematic plan was proposed and implemented which demonstrated that it is possible to reverse the effects of an ineffective OEE measurement process and create an effective system to pursue continuous improvement. Success in this endeavor can be attributed to pursuing training at various levels. Another key factor in establishing the system was using an appropriate calculation method for OEE compatible to the understanding power of the company's workforce. Providing clear definitions that were easy to understand and interpret for all terms involved in the OEE calculation also played a key role in the success of the implementation. Recommendations on how to go about changing the company's culture to embrace the concept of OEE were provided and pursued. Use of OEE values for conducting personnel annual evaluations was stopped. For exploring the correlation between process capability and OEE the null hypothesis that there is no relation between process capability index and OEE and between process capability index and each of OEE's three elements which are availability performance and quality was chosen. Calculating p-values for hypothesis testing using non-linear regression analysis it was found that at a significance level of 0.05 the null hypothesis cannot be rejected for any of the four sub-hypothesis. Limitations to the study included a short time period for the study and a lack of good available data. Another limitation was the fact that the final decision whether a part is good or bad was made by attempting to assemble the part in the final assembly operation. Further future work to this study would be to explore correlation between process capability and OEE in a controlled lab environment with more machines and parts and definite part specification limits.

Fingerprinting techniques investigation to detect petroleum hydrocarbon origin in coastal sediments of Persian Gulf

Persian Gulf coasts are subjected to different sources of petroleum pollution. This paper enhanced fingerprinting method of applying biomarkers polycyclic aromatic hydrocarbons (PAHs) and n-alkanes in identifying the distribution of oil spills and petroleum products. A total of 18 samples were collected from the northern coasts of Persian Gulf. PAH concentrations in the coastal sediments ranged from 184.49 to 2771.88 ng g−1. Distribution of three-ring PAHs was much higher than the others. PAHs concentration can be categorized as low to moderate comparing the global scale. Applying principal component analysis and data clustering revealed two major groups. The first group, including alkylated phenanthrenes, belongs to the low molecular weight PAHs with two and three rings, which are abundant in petrogenic sources mostly caused by petroleum spills. The second group consists of four- and five-ring PAHs. This group is frequently detected in pyrogenic source, such as combustion of coal, wood, vehicle fuel, and waste tire

Association between vitamin D receptor gene polymorphisms (Fok1 and Bsm1) and osteoporosis: a systematic review

International audienceOsteoporosis is a health concern characterized by reduced bone mineral density (BMD) and increased risk of fragility fractures. Many studies have investigated the association between genetic variants and osteoporosis. Polymorphism and allelic variations in the vitamin D receptor gene (VDR) have been found to be associated with bone mineral density. However, many studies have not been able to find this association. Literature review was conducted in several databases, including MEDLINE/Pubmed, Scopus, EMBASE, Ebsco, Science Citation Index Expanded, Ovid, Google Scholar, Iran Medex, Magiran and Scientific Information Database (SID) for papers published between 2000 and 2013 describing the association between Fok1 and Bsm1 polymorphisms of the VDR gene and osteoporosis risk. The majority of the revealed papers were conducted on postmenopausal women. Also, more than 50% studies reported significant relation between Fok1, Bsm1 and osteoporosis. Larger and more rigorous analytical studies with consideration of gene-gene and gene-environment interactions are needed to further dissect the mechanisms by which VDR polymorphisms influence osteoporosis