Effect of high-pressure rolling followed by laser processing on mechanical properties, microstructure and residual stress distribution in multi-pass welds of 304L stainless steel

Multi-pass fusion welding by a filler material (wire) is normally carried out to join thick steel sections used in most engineering applications. Multiple thermal cycles from a multi-pass weld resulted in a variable distribution of residual stress field across the weld and through the thickness. Presence of tensile residual stresses can be detrimental to the integrity and the service behaviour of the welded joint. In addition to a complex distribution of residual stress state, multi-pass welds also form dendritic grain structure, which are repeatedly heated, resulting in segregation of alloying elements. In this research, microstructural refinement with modification of residual stress state was attempted by applying post-weld cold rolling followed by laser processing and then cold rolling. The residual stress was determined non-destructively by using neutron diffraction. Post-weld cold rolling followed by laser processing was carried out to induce recrystallization of the cold rolled grains. Microstructural characterisation indicates a significant grain refinement near the capping pass. However, post-weld cold rolling followed by laser processing reinstates the lock-in stress. In this study, it was demonstrated that a complete recrystallized microstructure with compressive state of stress can be formed when a further cold rolling is applied on the laser processed, recrystallized microstructure

Ethno-religious mobilisation and the sapping of democracy in Nigeria: on the legacy of the transition programme

Paper presented at the Wits History Workshop: Democracy, Popular Precedents, Practice and Culture, 13-15 July, 1994

Application of local mechanical tensioning and laser processing to improve structural integrity of multi-pass welds

Multi-pass fusion welding by a filler wire (welding electrode) is normally carried out to join thick steel sections used in most engineering applications. Welded joints in an installation, is the area of critical importance, since they are likely to contain a higher density of defects than the parent metal and their physical properties can differ significantly from the parent metal. Fusion arc welding process relies on intense local heating at a joint where a certain amount of the parent metal is melted and fused with additional metal from the filler wire. The intense local heating causes severe transient thermal gradients in the welded component and the resulting uneven cooling that follows produces a variably distributed residual stress field. In multi-pass welds, multiple thermal cycles resulted in a variably distribution of residual stress field across the weld and through the thickness. These complex thermal stresses generated in welds are undesirable but inevitable during fusion welding. Presence of such tensile residual stresses can be detrimental to the service integrity of a welded structure. In addition to a complex distribution of residual stress state, multi-pass welds also forms dendritic grain structure, which are repeatedly heated, resulting in segregation of alloying elements. Dendritic grain structure is weaker and segregation of alloying elements would result in formation of corrosion microcells as well as reduction in overall corrosion prevention due to depletion of alloying elements

Conditioned

Once there lived in a little town in a little college, a tiny little man who solved many of the eternal problems by ignoring them..

The Corrupter

HELLO, Blue Eyes. Hello. Do you know me? A man knows his property. You are mine. Yours!!? Yes, mine . . At least, you will be. But I do not know you. I never saw you before. ..

Synthesis and Evaluation of the Antidiabetic Potentials of Chitosan Combinations with Metformin and Momordica Balsamina Leaf Extract in Alloxan-Induced Diabetic Rats

Chitosan, a carbohydrate biopolymer, is medically gaining attention as a dietary supplement and a drug beneficial for improving blood glycemia, impaired glucose tolerance and altered lipid metabolism. Largely obtained from crustaceans, chitosan is also a promising vehicle used to deliver anti-diabetic drugs in implantable as well as injectable and oral routes. The present study is therefore aimed to synthesize chitosan and evaluate its antidiabetic potentials in combination with metformin and/or methanolic leaf extract of Momordica balsamina (MBM) in alloxan-induced diabetic rats. Chitosan was synthesized from crayfish shell through demineralization, deproteinization, deacetylation, and decolouration of the produced chitin. In the present study, a simple and an inexpensive acid-base titrimetric method was used for the determination of degree of deacetylation while the physicochemical properties; moisture content and ash content were determined using standard procedures.The efficacy of the drug binary systems of chitosan-metformin and chitosan-MBM were evaluated on the glucose tolerance of Wistar Albino rats made diabetic by a single interperitoneal injection of alloxan monohydrate (150 mg/kg body weight). The oral administration of both drug binary systems and chitosan exerted a significant (p<0.05) improvement on carbohydrate metabolism via glucose tolerance test when compared to the untreated diabetic rats. The blood glucose level of the chitosan group returned to near normal level 2 hours post-porandially, while chitosan-MBM, chitosanmetformin and metformin groups returned to their initial values only after 4 hours. Our findings are suggestive of the fact that chitosan-based drug binary systems possess anti-hyperglycemic activities and thus the potential to improve the pharmacokinetic and pharmacological profile of oral hypoglycemic drugs/herbs. Our findings could serve as basis for the development of novel antidiabetic drug systems. Keywords: Antidiabetic, Chitosan, Metformin, Methanolic extract, Momordica balsamin

Western Exploitations and the Nexus of African Underdevelopment

This paper examines Walter Rodney’s argument of How Europe Underdeveloped Africa and its justification years after political independence. The paper has   adapted Dependency Theory. The paper has reveals that widening gap between Developed and Underdeveloped States is as a result of both external and internal factors especially the colonial integration of African economies in the World Capitalist System and its exploitative institutions and programmes and internal factors of both systemic and institutional corruption, political instability, colonial mentality of consumption and other factors are responsible for underdevelopment of Africa with attendant effects of poverty, inequality, unemployment, disease and infrastructural decay etc. on basis of conclusion. The paper recommended that visionary and purposeful leadership that surrounds itself with experts will initiate and sustain revolutionary development in Africa. Also proper planning and continuity in developmental policies and programmes and united front against corruption be strictly adhered to for the continent to develop. Keywords: Development, Underdevelopment, Exploitations and Good Governance. DOI: 10.7176/JAAS/64-06 Publication date:May 31st 202

Trump Administration and the Politics of Visa Denial to Nigerian Citizens

President Trump on January 31st 2020 has added six countries to his list of nations facing stringent travel restrictions, a move that will virtually block immigration from Africa’s most populous nation, Nigeria, and from Myanmar, where the Muslim minority is fleeing genocide. Beside Nigeria, three other African countries, Eritrea, Sudan and Tanzania, will face varying degrees of restrictions, as will one former Soviet state, Kyrgyzstan,  Myanmar’s.  All six countries have substantial Muslim populations. The total number of countries now on the restricted travel list stands at 13. Immigrant visas, issued to those seeking to live in the United States, will be banned from Nigeria, Myanmar, Eritrea and Kyrgyzstan. The ban will also prevent immigrants from Sudan and Tanzania from moving to the United States through the diversity visa lottery, which grants green cards to as many as 50,000 people a year. The paper would uses secondary source of data from relevant publications. The researcher was of the view that most of these countries with US Visa restriction have issues of security problems and are mainly Muslim countries. The paper was of the view that   if these countries need to have respect and international recognition the government of these countries must take the issue of insecurity and fighting terrorism as a priority agenda so that they cannot be isolated as unsecured countries among countries of the world. Keywords: Immigrant, Visa, Terrorism and Insecurity. DOI: 10.7176/JLPG/97-11 Publication date:May 31st 202

John Locke’s Political Philosophy and It’s Relevance to the Sustenance of Peace and Good Governance in Nigeria

Philosophers are the mirror of the society where they use their glass to critically view and analyses certain human problems in order to propose a certain solution to that problem. The political philosophy of John Locke on the sustenance of peace and the conduct of good governance have given direction to any true democratic leaders who are in power to serve humanity and making lives better for his peoples. This paper was of the opinion that leaders in Nigeria since the return to democracy in 1999 in to the country the system has fail to meets the desired dividend for peaceful society and provision of functional government; this led to emerging problems of insecurity and pockets of conflicts in different parts of the country. This paper has uses secondary data source through reviewing relevant secondary information on the subject matter. This paper was of views that if leaders in Nigeria would be serious on the process of operating good governance they should provide   an enabling environment that would promote peace and security among the citizens by ensuring welfare and the need of the peoples are the priority agenda that can drive the nation out of these menace of insecurity and conflicts through respecting rule of law, fighting corruption, separation of power and tolerance. Keywords: Peace, Good Governance. Philosophy and Human needs. DOI: 10.7176/PPAR/10-5-06 Publication date:May 31st 202

Comparative study of evolution of residual stress state by local mechanical tensioning and laser processing of ferritic and austenitic structural steel welds.

Complex thermal stresses generated in welded structures are undesirable but inevitable in fusion welding. The presence of residual stresses can be detrimental to the integrity of a welded joint. In this research, redistribution of residual stress magnitude and profile was studied and compared in two multi-pass welded structural alloys (API X100 and 304L stainless steel) after cold rolling and laser processing. The residual stress field was studied by neutron diffraction using the SALSA strain scanner at their reactor neutron source at ILL, Grenoble. In addition to a complex distribution of residual stress state, multi-pass welds also forms dendritic grain structure, which are repeatedly heated, resulting in segregation of alloying elements. Dendritic grain structure is weaker and segregation of alloying elements may result in formation of corrosion microcells as well as reduction in overall corrosion prevention due to depletion of alloying elements in certain areas. The modification of as-welded residual stress state was done by cold rolling which was followed by laser processing to create a recrystallized microstructure to minimise segregation. The main objective of this study is to understand the suitability of this novel manufacturing technique to create a stress free weldment with recrystallised grain structure. Hardness evolution in the welded structures was scanned following welding, post weld cold rolling and cold rolling followed by laser processing. Hardness distribution in both the structural alloys showed a significant evidence of plastic deformation near the cap pass of the weld metal. Residual stress redistribution was observed up to 4 mm from the capping pass for ferritic steel, while in austenitic steel weld, post weld cold rolling was effective in modifying the residual stress redistribution throughout the entire thickness. Laser processing in both cases reinstated the as-welded residual stress distribution and resulted in softening of the strained area