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

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

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

Islam and Ethnicity: The Case Study of Ombatse Crisis 2011-2015 in Nasarawa State, Nigeria

This paper examines the activities of the Ombatse cult group and the violent conflicts that occurred as a result of their activities which took place in some parts of Nasarawa State from 2011 – 2015. The aim of the study is to portray how Islam is against ethnic bigotry. It also intends solutions based on Islamic teachings on how to resolve disputes especially which is ethnically related. It also discussed its effects on Islam and Muslims in the State. The paper found out that peace is one of the basic tools for the development of any society, as Islam encourages peaceful co-existence among/between Muslims and non- Muslims as well as co-existence among other ethnic nationalities as Islam prohibits ethnicity and nationalism. Therefore, the paper further revealed that the major actors who participated in the crises were predominately Muslim youths from the ethnic groups involved in the violent conflict. The research also unveils the context and undertone which precipitated establishment and those who financed activities of Ombatse group in the areas studied. Regarding methodology, this study utilizes a qualitative technique. In-Depth Interviews (IDI) were conducted to obtain data for the study. The study concludes that some Muslim who are ignorant of the basic tenets of Islam were easily brainwashed to show allegiance to their ethnic identity than Islam. The Ombatse mobilized support along ethnic consciousness in order to achieve hidden political motives of those who initiated the cult group

Bridge Collapse in Nigeria: A Case Study of Tatabu Bridge in Mokwa Local Government Area of Niger State

Large parts of Niger State are located in low terrain and have proximity to River Niger: the largest river in Nigeria; coupled with the presence of three hydro Electric power stations in the state. Niger State has been confronted annually by flood disaster that has destroyed many lives and properties. The focus of this paper is to investigate the causes behind Tatabu bridge collapse. In this investigation, soil strength and index test, hydrological data, nature of the terrain, concrete strength test and evaluation of flood impact on the bridge and its embankments using ANSYS Finite Element Method were conducted. The results of the investigations revealed that the collapsed bridge was positioned within a valley as well as steady increase in precipitation from 2015 to 2017 which directly increased the stream flow rate and also runoff.  It was also observed that the debris settlement within the cell of the collapsed bridge contributed to reduction of the cross sectional area of single cell. The compressive strength test of the bridge members revealed that the strength are within acceptable limit. The authors recommended that there is the need for embankment protection either covers vegetation, stone pitch, slope stabilizer, or concrete interlocking is required for future consideration. Due to increase in water balance, the new bridge capacity should be increased to accommodate the high volume of water.  The new bridge should be reconstructed above the valley or repositioned away from the valley. it is also recommended that a complete replacement of the underlain material forming the adjacent slope to the bridge retain wall with a better compacted engineering soil to avoid future pavement failure of the kind. Keywords: Bridge, Flood, ANSYS, Collapse, Terrai

Analysis of Fuelwood Consumption in Pampaida (Millenium Village) of Kaduna State, Nigeria

This study examined fuelwood utilisation in Pampaida, a village in Ikara Local Government Area of Kaduna State, Nigeria. Finding of the study revealed that fuelwood is the dominant primary energy used in the area. Majority of the people (90%) preferred fuelwood because it is easily accessible, affordable to them in the area. Most of the fuelwood is obtained freely from the forest, and farmlands. In addition, results showed that the level of fuelwood consumption in the area is very high because close to two-third of the respondents use up between 1-3 bundles of fuelwood daily; and one-third of them require between 4-6 bundles/cords per day. Moreover, it was found that a large part of household expenditure goes to fuelwood. However, majority of the respondents (85%) are unaware of the environmental effects of fuelwood consumption. The study therefore recommended the need for conscious efforts in providing alternative cheap and accessible renewable energy sources for use in Pampaida

Analysis of Fuelwood Consumption in Pampaida (Millenium Village) of Kaduna State, Nigeria

This study examined fuelwood utilisation in Pampaida, a village in Ikara Local Government Area of Kaduna State, Nigeria. Finding of the study revealed that fuelwood is the dominant primary energy used in the area. Majority of the people (90%) preferred fuelwood because it is easily accessible, affordable to them in the area. Most of the fuelwood is obtained freely from the forest, and farmlands. In addition, results showed that the level of fuelwood consumption in the area is very high because close to two-third of the respondents use up between 1-3 bundles of fuelwood daily; and one-third of them require between 4-6 bundles/cords per day. Moreover, it was found that a large part of household expenditure goes to fuelwood. However, majority of the respondents (85%) are unaware of the environmental effects of fuelwood consumption. The study therefore recommended the need for conscious efforts in providing alternative cheap and accessible renewable energy sources for use in Pampaida

Assessment of Automobiles and Pedestrians Control Techniques Within Markets in Kaduna State, Nigeria

The Assessment of automobile and pedestrian control techniques within the market environment cannot be overemphasized as it is one of the most important ways in curtailing poor market environment in terms of traffic congestion. Automobile and pedestrian congestion is a situation that arises when the road networks are incapable of accommodating the traffic generated. Automobile and pedestrians control techniques in market refers to regulation, adoption, or maintenance of automobile and pedestrian functions or feature either by design or new construction within the market. The sustainable design encompasses standard layout, adequate parking, standard road network system, provision of signs and markings, proper zoning etc. This research aimed at assessing pedestrian and automobile control technique adopted within markets in Kaduna with the view of designing a more improved circulation pattern and sustainable markets in terms of automobile and pedestrian control within the study area. With this regard, an observation method of research was adopted. The daily markets were randomly selected out of the numerous markets within Kaduna metropolis and its environs. The result shows that the proper automobiles and pedestrians control techniques was not properly observed or  adopted in over 90% of the market. The study further revealed that the selected markets within Kaduna share similar features and characteristics. Therefore to curtail these, recommendations were made on various practical methods for integration/adoption in market design so as to archive an effective automobile control within the markets in Kaduna metropolis. Keywords: Automobiles, Control Techniques, Market Congestion, Pedestria

Stress engineering of multi-pass weld metal to enhance structural integrity

In multi-pass welding, the weld metal and the associated heat-affected zone are subjected to repeated thermal cycling from successive deposition of filler metals. The thermal straining results into multi-mode deformation of the weld metal which causes a variably distributed residual stress field through the thickness and across the weld of a multi-pass weldment. In addition to this, the as-welded fusion zone microstructure shows dendritic formation of grains and segregation of alloying element. This may result in formation of micro-corrosion cells and the problem would aggravate in case of highly alloyed materials. Local mechanical tensioning is an effective way of elimination of the weld tensile residual stress. It has been shown that application of cold rolling is capable not only of removing the residual stress, but depending on its magnitude it may also form beneficial compressive stress state. Multi-pass structural steel welds used as structural alloy in general engineering and structural applications. Such alloys are subjected to severe in-service degradation mechanisms e.g., corrosion and stress corrosion cracking. Welds and the locked-in residual stress in the welded area often initiate the defect which finally results in failure. In the present study, a multi-pass structural steel weld metal was first subjected to post-weld cold rolling which was followed by controlled heating by a fiber laser. Cold straining resulted in redistribution of the internal stress through the thickness and controlled laser processing helps in reforming of the grain structure. However, even with controlled laser, processing the residual stress is reinstated. Therefore, a strategy has been adopted to roll the metal post-laser processing so as to obtain a complete stress-free and recrystallized microstructure