Solar Photovoltaic

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NAME: JOHN EBO ANDORFUL COURSE: ME 582 (ENGINEERING RESEARCH METHODS) EXAM NUMBER: PG 1177413 STD REF: 228772! ASSIGNMENT

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EFFECTS OF SOLAR PHOTOVOLTAIC

Transcript of Solar Photovoltaic

NAME: JOHN EBO ANDORFUL

COURSE: ME 582 (ENGINEERING RESEARCH METHODS)

EXAM NUMBER: PG 1177413

STD REF: 20287729

ASSIGNMENT

APPRAISAL OF WELDED LEAF SPRING

BY:ANDORFUL J. E.KWAME NKRUMAH UNIVERSITY OF SCIENCE AND TECHNOLOGYP.O.BOX SK [email protected]

ABSTRACTThe use of repaired fractured leaf springs; either by welding and/or forging rather than a full replacement with a new one has become accepted by the general populace. This repair which is carried out by numerous artisans with years of artisanal experience is without any Science and/or Engineering. This paper seeks to bring to light the effects of welding on the strength and quality of the leaf spring; thereby leading to a change in approach to tackling the issue of fractured leaf springs.

KEYWORDSLeaf spring, Welding, Strength, Hardness

INTRODUCTION The quest to carry more load than required by vehicles plying our roads is leading to frequent breakdowns and in some cases causing accidents on our roads. Key parts like the leaf spring which support the vehicle are thus made to carry more than what they are made to support with most leading to fracturing of this member. This brings into focus such parts of vehicles which are repaired to save cost and time. Repair works include either welding or forging or in some cases a combination of both. This project therefore aims at finding out the effects of welding, on the quality of leaf springs which have been welded after fracturing since welding will in the end affect the original properties of the leaf spring. Specimens from the original and the welded parts of the leaf spring would be acquired, tested and analysed in the materials laboratory. After the analysis, the samples would be appraised and suggestions made as to how best to improve the indigenous technology through the application of materials know-how principles. The laboratory analysis will involve:1. Chemical Composition of the specimens (from the original and the welded leaf springs)2. Hardness test

MATERIALS AND METHODSTwo samples were cut from the un-welded part and two from the welded part for experimentation. The surfaces of the samples were then prepared for experimentation by grinding and polishing. Below are the pictures of the samples before the surface preparation.

Un-welded A B Welded C D

Figure 1Samples before Grinding and Polishing

Grinding and PolishingApparatus Four (4) grades of silicon carbide paper (180,220,240 and 400) for grinding the surfaces of the samples. Rotating wheel with Emory cloth fixed on it.ProcedureEach sample was ground on four different grades of Silicon carbide paper, beginning with the coarsest, which is the 180 grade through to the finest, which is the 400 grade. Only one face of the samples was to undergo the grinding process. Initially, the 180 grade was to remove the much darker scratches on the surfaces of the samples. The samples were then polished on Emory cloth which is fixed on a rotating wheel with a solution of aluminium powder as a lubricant. The polishing was done by holding the specimens face down on the rotating wheel and slowly moving around in opposite direction to the rotation of the wheel. The aluminium powder solution was poured on the rotating wheel at specific times so as to avoid local heating of the sample specimen which would have destroyed the microstructure of the sample specimen. When the surfaces of the samples were mirror bright and showed no scratches they were cleaned in water.Precautions taken were: During grinding, water was poured on the sample intermittently to reduce heat due to friction which would have altered the structure and properties of the sample. The grinding process was done in one particular direction to improve on the sample surface smoothness. During polishing, the solution of aluminium powder was used not only to serve as lubricant, but also to aid polishing. The surface of the sample was lifted up during polishing from time to time to avoid the build up of heat in it.

Below are the pictures of the samples after the surface preparation. Unwelded A B

Welded C D

Figure 2 Samples after Grinding and Polishing

Chemical Composition of SamplesApparatusThermo spectrometerProcedureThe sample was placed in the spark chamber of the thermo spectrometer 4 mm away from a positively charged tungsten electrode. Thus the sample became negatively charged. Heat and polychromatic light were evolved from the sample when the instrument was sparked. The light was diffracted when incident on 775 grooves/mm3 prisms unto the Charged Couple Device (C.C.D). The light energy which varies for each element was then converted into electrical energy with its intensity read as compositional values.ObservationFor accuracies of 0.02 within elemental content values, the Strohlein Apparatus is highly recommended instead of the Thermo spectrometer.The precaution taken was: Due to its extra sensitivity the thermo spectrometer was carefully operated in order to avoid any disturbance which could have affected the values.Hardness (Brinell) Test Apparatus Brinell hardness testerProcedureThe sample was placed on a wheel and the wheel rotated. A load in the form of a ball was then applied to cause indentation during the rotation. A dial gauge attached to the tester measured the indentation in millimetres. This measured value was then used in calculating the Brinell hardness number (BHN) as compared to standard values. Below is the formula for calculating the Brinell hardness number: HB = 2F/ D [D- (D2-d2)] where F= load; D= diameter of the ball in millimetres d= mean diameter of the indentation in millimetresRESULTS AND DISCUSSIONTable 1 shows the elemental analysis of the un-welded and welded samples.Table 1: Results from the Chemical Composition and Hardness Test

SampleIdentificationDate IdC%Mn%Si%S%P%Hardness BHN

WeldedA03/04/060.6960.9420.2910.0170.019341

B03/04/060.7010.9280.2810.0160.022341

Un-weldedC03/04/060.5950.8640.2390.0140.015363

D03/04/060.6000.8590.2390.0140.015363

Table 2: Average chemical compositional values

SamplesC%Mn%Si%S%P%

Welded0.5960.8620.2390.0140.015

Un-welded0.6990.9360.2860.01650.0205

ANALYSISSamples A and B are the samples from the un-welded part and samples C and D are the samples from the welded part.Since the samples were taken from different portions of the leaf spring, a true reflection of the compositional values would be obtained from the average.The average carbon percentages of the un-welded samples (0.699%) fall within the range, 0.6%-0.8% indicates that they are high carbon steels.The average carbon percentages of the welded samples (0.596%) which fall within the range, 0.3%-0.6% indicates that they are medium carbon steels.From the hardness values obtained, it can be deduced that the welded samples have a Brinell hardness value of 363 which is much higher than the Brinell hardness value of 341 for the un-welded samples. However by virtue of their high carbon contents, samples A and B are supposed to be harder than samples C and D, but they have rather been toughened by Tempering to suit their function as leaf springs.This fact is buttressed below by the mechanism behind Tempering.At the tempering temperature, martensite which is the hardest structure promoting hardness in the high carbon steel decomposes into ferrite and the precipitation of fine particles occurs. (Evans, 1971) The fine granular structures formed which are the secondary troosite results in some toughening at the expense of hardness.When the tempering temperature is increased from 100-200C to 450-650C, the carbide particles coalesce to form fewer and larger particles which provide fewer obstacles to dislocation movement. This result in a further decrease in strength and hardness while toughness is further increased. (Davies, 1972)Samples C and D whose strength and hardness increase after welding, with a possibility of non-metallic inclusions due to atmospheric exposure become brittle. This makes them fracture easily and as such unsuitable for applications where toughness is needed.The other elements are in their right percentages therefore their presence is not harmful. CONCLUSION The welded portion out of which samples C and D were obtained, is very brittle because hardness has increased. As such it is highly susceptible to failure upon minimum loading in the form of impact, which leads to vehicular break down resulting in accidents

RECOMMENDATIONThe best thing to do after a leaf spring has failed is to obtain a new piece than weld it because the welding hardens the metal and as such increases brittleness at the expense of ductility, toughness and tensile strength required to withstand impact. In cases where welding have to be carried out, cooling air also referred to as normalising should be employed. (William D. Callister, 1991)In order to obtain accuracies of 0.02 within elemental content values the Strohlein Apparatus is highly recommended for the chemical analysis of metals.An ore microscope should be made available to students to enable them obtain photographs of the material surfaces during microstructure analysis.

REFERENCES

Davies, A. (1972). The Science and Practice of Welding, 6th Edition,. Cambridge, University Press.Evans, D. U. (1971). Fundamentals of Engineering Metallurgy. Edward Arnold Publishers limited.William D. Callister, J. (1991). An Introduction to Materials Science and Engineering Second Edition. John Wiley & Sons Inc., .

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