Design and Characterization of a Fatigue Testing Machine

Transcription

1 Proceeings of the Worl Congress on Engineering an Computer Science 01 Vol I WCECS 01, -5 October, 01, San Francisco, USA Design an Characterization of a Fatigue Testing Machine Gbasouzor Austine Ikechukwu, Member, IAENG, Okeke Ogochukwu Clementina an Chima Lazarus Onyebuchi Abstract Many engineering machines an mechanical components are subjecte to fluctuating stresses, taking place at relatively high frequencies an uner these conitions failure is foun to occur. This is fatigue failure. An this le to the invention of a fatigue testing machine. In view of effective esign that will not fail accientally, this research is conceive. This testing machine will etermine the strength of materials uner the action of fatigue loa. Specimens are subjecte to repeate varying forces or fluctuating loaing of specific magnitue while the cycles or stress reversals are counte to estruction. The first test is mae at a stretch that is somewhat uner the ultimate strength of the material. The secon test is mae at a stress that is less that than that use in the first. The process is continue, an results are plotte. Keywors: Fluctuating stresses, fatigue failure, high frequencies, strength of materials, fatigue loa. I. INTRODUCTION A fatigue is a failure of material or machine ue to the action of repeate or fluctuating stress on a machine member for some number of times. This failure begins with a small crack. The initial crack is so minute that it cannot be etecte by the nake eye an is even quite ifficult to locate in a magniflux or x-ray inspection. The crack will evelop at a point of iscontinuity in the material such as a change in cross section, a keyway, a hole or a notch. Less obvious points at which fatigue failure are likely to begin are inspection or stamp marks, internal cracks or even irregularities cause by machining. Once a crack is initiate the stress concentration effect becomes greater an the crack progresses more rapily. As the stresse area ecreases in size, the stress increases in magnitue until finally, the remaining area fails suenly. A fatigue failure therefore is characterize by two istinct regions. The first of those is ue to the progressive evelopment of crack, while the secon is ue to suen fracture. Unlike other failures, fatigue failure gives no visible warning in avance. It is suen an totally angerous. This suen failure, which is angerous, an can lea to not just minor accient but fatal accient an loss of lives triggere the quest to invent a machine that can test an give or preict the effect of fatigue on various metals such as aluminium, cast-iron, mil steel, etc. Gbasouzor Austin Ikechukwu, MIAENG is a Lecturer in the Department of Mechanical Engineering, Anambra State University, P. M. B. 0 Uli, Nigeria. unconitionalivineventure@yahoo.com Phone: 80758, , Okeke Ogochukwu Clementina is a lecturer in the Department of Computer Science, Anambra State University, P. M. B. 0 Uli, Nigeria Chima Lazarus Onyebuchi is a Researcher in the Department of Mechanical Engineering, Nnami Azikiwe University, P. M. B. 505 Awka, Nigeria In most testing of those properties of materials that relate to the stress-strain iagram, the loa is applie graually to give sufficient time for the strain to fully evelop. Furthermore, the specimen is teste to estruction, an so the stresses are applie only once. Testing of this kin is applicable, then, to what are known as static conitions. Such conitions closely approximate the actual conitions to which many structural an machine members are subjecte. The conition frequently arises, however, in which the stresses vary or they fluctuate between levels. For example, a particular fibre or aluminium on the surface of the rotating shaft subjecte to the action of bening loas unergoes both tension an compression for each revolution of the shaft. Since the shaft is part of an electric motor rotating at 100rev/min, the aluminium metal is stresse in tension an compression 100 times each minute. If in aition, the shaft is also axially loae (as it woul be, for instance, by a helical or worm gear), an axial component of stress is superpose upon the bening component. In this case, some stress is always present in any one metal, but now the level of stress is fluctuating. These an other kins of loaing occurring in machine members prouce stresses that are calle variable, repeate, alternating or fluctuating stresses. Often, machine members are foun to have faile uner the action of repeate or fluctuating stresses; yet the most careful analysis reveals that the actual maximum stresses were below the ultimately strength of the material, an quite frequently even below the yiel strength. The most istinguishing characteristic of these failure is that the stresses have been repeate a very large number of times. Hence, the failure is calle "Fatigue Failure". When machine parts fail statically, they usually evelop a very large eflection, because the stress has exceee the yiel strength an part is replace before fracture actually occurs. Thus, many static failures give visible warning. It is suen an total, an angerous. It is relatively simple to esign against a static failure because our knowlege is comprehensive. Fatigue is a much more complicate phenomenon, only partially unerstoo, an the engineer seeking competence must acquire as much knowlege of the subject as possible. Anyone who lacks the knowlege of fatigue can ouble or triple esigns factors an formulate a esign that will not fail. Design Objectives This aims at esigning an constructing a fatiguetesting machine that is capable of testing the fatigue life of various samples of specimen from metals, such as mil steel, aluminum, brass, etc. Also with the result of each test carrie out with this machine, the fatigue life of various materials can be obtaine an fatigue failure be guare against in an optimum manner. ISBN: ISSN: (Print); ISSN: (Online) WCECS 01

2 Proceeings of the Worl Congress on Engineering an Computer Science 01 Vol I WCECS 01, -5 October, 01, San Francisco, USA II. METHODOLOGY General Description The fatigue-testing machine is of the rotating beam type. The specimen functions as a single beam symmetrically loae at two points. When rotate one-half revolution the stress in the fibres originally above the neutral axis of the specimen are reverse from compression to tension for equal intensity. Upon completing the revolution, the stresses are again reverse, so that uring one complete revolution the test specimen passes through a complete cycle flexural stress. The fatigue testing machine consists of the following components: A. AHP electric motor, B. Bearing an its housing assembly C. Weight hanger assembly D. Dea weight E. Bearing spinling F. Digital counter G. Magnetic cyclic pick up (ynamo) H. Variable spee control I. Switch, J. Specimen K. Drill chunks, L. The metal esk Fig.1: The isometric views of the fatigue-testing machine Bearing an Its Housing Assembly The particular bearing use in this project is the single, row, eep; groove bearing that can take both raial loa an some thrust loa. The bearing is shoulere in a housing mae of cast iron to secure aequate support for the bearing an resist the maximum thrust loa. Weight Hanger Assembly This consists of small bar mae of cast iron, with a spring. The hea of this bar is esigne to be hange on the loaing harness assembly. The spring is esigne to absorb shock preventing any slight vibration of the housings on the ea weight. The choice of cast iron for the material for hanger is ue to the fact that cast iron has the moulus of elasticity E as 60 to 90 mpa an can withstan the maximum weight of which the machine can carry Dea Weight These are loas of ifferent sizes an weight Bearing Spinle (Shaft) The bearing spinle ( are machine from a bar of high grae steel (10 stainless steel) an is thicker than specimen by (5/8 inches) to prevent the machine parts from experiencing fatigue ue to the loaing of the specimen. The stainless steel can withstan averse temperature an corrosive environment, ue to its high carbon content it oes not fail-easily. Two shafts were employe in this work. One is the riving shaft, which is connecte to the motor shaft extension by means of bolting. The other en of this shaft is machine to fit into a rill chuck. The other spinle, the riven shaft is machine to fit into a rill chuck at one en while the other en carries a gear that transmits motion to the ynamo. Both shafts are allowe to pass through the bearing housing which help to check any misalignment an give the shaft rotational support. Digital Counter The igital counter is a terminating evice that gives out the equivalent value of number of revolution of motor in term of cycles. The igital counter registers 1 for each 10 revolution of the motor, so to obtain the number of cycles of stress, counter reaings must be multiplie by 10,000. A total of 1,00,000 revolutions are turne up for each cycle of number. At 1,00 rpm, a complete cycle of numbers takes place in about 166 hours, or 7 ays if operating hours per ay. In a very long test therefore the number of cycle must be recore. The spee reuction unit is lubricate from time to time. This easy-to-rea igital cycle counter is connecte to a magnetic pick up evice (ynamo). Push button control is provie to reset the isplay count at the start of a test. The Cut-Off Switch The cut-off switch is employe to set upon the circuit to the motor when the bearing experiences a angle. Specimens The stanar specimen, a tapere-en specimen has the length of 87.mm. They are machine to match the tapers within the spinles of the machine an hel in place using rill-chuck. Stress as applie to the specimen by irect application of ea weight to ensure precise loaing. Maximum fibre stress in a specimen having a 0.00inches (7.6mm) iameter is. By ecreasing the iameter, the value of the maximum fibre stress can be increase. An easy-touse reference table within the operator's manual makes etermination of the loa weight neee to prouce a particular stress a single circulation. Drill Chucks The metal esk on which the system is assemble on is mae with mm angle iron of mil steel an plain pan mae of mil steel for the top. The length of the esk is 760mm; the with an the height are respectively 10mm an 190mm. The esk is rille at each point where parts are to fit with bolt an nut. A rectangular opening is foun through which the hanger is passe; this is locate at the top of the esk. The length an with of this opening are respectively 1.7mm an 11.8mm. The total weight of the esk is 75kg. A rubber tyre is fixe uner each leg of the esk to amp vibration on the esk an moreso to easy locomotion. Setting Up The Machine The base shoul first of all be set levele so that the weight will hang perpenicularly to the axis of the specimen. Wires in conuct from the power supply are run to the connecting block in the base of the machine an solere to the lugs provie. The machine is equippe to operate from an AC power source at 10volts, 60 cycles, an single phase. Motor an relay equipment to operate from a power source of ifferent rating can be provie on special orer. With mil steel legs, the machine is set on five rubber tyres. The weight hanger is of such length that it will clear the esk since it is mounte on the legs. A shock absorber in the hanger prevents the slight vibration of the housing from ISBN: ISSN: (Print); ISSN: (Online) WCECS 01

3 Proceeings of the Worl Congress on Engineering an Computer Science 01 Vol I WCECS 01, -5 October, 01, San Francisco, USA being impacte to the weight. The base is provie with holes so it can be bolte own if esire. Assemble the housing with a sample of specimen provie in accorance with the irection given below, an start the machine to see if there is any misalignment. This will be inicate by noise an vibration. Examine the housing win for oil. It shoul stan about miway of the winows when the machine is ile. Ajust the spee to 1,00 RPM by means of a rheostat in the base of the machine. The machine shoul now be reay for a test. Spee The normal spee is 1,00RPM. The spee epens on the voltage. If the voltage of the supply line excees the proper amount of sliing rheostat in the base of the machine shoul be ajuste so that the spee cannot excee 1,00RPM uner orinary conitions. Spees in excess of the normal will cause no amage unless continue to long. In ajusting the spee take care that the contraction of the rheostat makes firm contact with the expose potion of the wining. If it esire to run at spee below 1,00 rpm, or graually increase the spee from zero, a variable resistor can be place in the motor lea wires by utilizing the plug type connector. This will be necessary only in exceptional cases where the slight starting torque exerte on the specimen may be objectionable. The inertia of the motor armature is such in comparison with that of the remote half of the spinle that there is sufficient elay in starting for most purposes III. ANALYSIS AND DISCUSSION OF RESULT Specimen Dimension an Machine Capacity For the soli specimen, the iameter of the test specimen is 7.6mm.It is assume that the machine woul at times be require to test some high strength steel at stress levels in the neighborhoo of the yiel stress. Using stainless steel of 10 i.e. 5c steel at temperature of about 15 C, ultimate tensile yiels stress = 700mpa Assuming Tresca's Yiel Criterion, the shear yiel stress is given as 50mpa. The torque require to start yiel at the outer fibres of a specimen of such steel is T y T = 50x π (7.6) 16 = 0,06.5Nmm In this esign, a machine capacity of 0,00Nmm is assume. The torque-transmitting shaft The torque-transmitting shaft, which comprises of the longer shaft, bolts, the chuck an the short shaft passing through bearing housing sustains the same fatigue loa uring a testing program as the specimen unergoing the tests. Where T = torque = 006.5Nmm i.e. = [16 x 006.5/π x 87.5] = 1.09mm In the esign, the minimum shaft iameter use is 5mm. The reason is to make the shaft more rigi an to make it withstan heat an shock for many number of tests without failing easily ue to fatigue. However fig. shows that in some location, circumferential grooves are mae for retaining chucks an rings, thereby reucing the effective ISBN: ISSN: (Print); ISSN: (Online) iameter to approximately 0mm. As state before, the iameters of the gauge length of the shaft epens on the loa range an are thereby esigne accoringly. Check for stress concentration effect. At the position for the chuck, there is a possible or prouct stress raiser. It is the shaft shouler. Shaft Shouler D = 5mm =16.m r = maximum fillet raius = 5m D/ = 5/16. = 1.5mm r/ = 5.0/16. = 0.1m The stress concentration corresponing to the ratio above is 1.17 i.e. kt = 1.17 But the maximum nominal stress in sheer = 16T/π = 16 x 006.5/Ti x (16.) =6.N/m It is esigne that no part of this shafting ever fails in service. With the little knowlege of torsion fatigue, we apply therefore factor of ignorance to some consierations. A stainless steel of 10 or 5c8 steel is recommene for the shafting because of its strength an ability to prevent the machine parts from experiencing fatigue ue to the loaing of the specimen all through the test. This reason of choosing this material can be trace to the avantage of being highly resistance to fatigue owing to its low notch sensitivity, which is itself, a result of its high uctility. 5c8 steel or 10 stainless steel has these parameters; Yiel strength T y =50mpa Ultimate strength S ut = 700mpa Following a generally accepte thumb rule for S ut < Enurance limit Se' = 0.5S ut Enurance limit Se = 0.5 x 700 = 50mpa Using Tresca's Yiel Criterion an assuming the valiity of its application of fatigue loaing, the enurance limit in shear is obtaine as T e = S e / = 175mpa At this point a factor of approximately is applie an T e = T e / = 175/ = 87.5mpa The minimum shaft iameter for the full machine loa is given by the expression = {16T/ πt } l/ Applying the stress concentration factor, T mass = 1.17 x 6. =.616 This value is very much less than the assume enurance limit of 50N/mm an also than the esign shear stress of 87.5N/mm. It is therefore consiere safe. Bolt Design Two bolts are use to hol the shaft to the motor shaft. The bolt iameter is.75mm. They are separate 0mm apart. For a torque of 006.5Nmm Shear force on each bolt = ½ x 006.5/10 = 150.1N Average shear stress = [π/(.75) ] = 85.79N/mm To bear this loa safely, SAE grae bolts are recommene an shear stress of bolt is less than the esign shear stress, which shows that it is safe. WCECS 01

4 Proceeings of the Worl Congress on Engineering an Computer Science 01 Vol I WCECS 01, -5 October, 01, San Francisco, USA Chucks Each chuck consists of two major parts, the hub mae of mil steel an a circular plate of harene meium carbon low alloy steel machine to take the en of the specimen. The two parts are fitte together with two aligning pins an four 5mm iameter SAE grae screws. The hub is shrink-fitte onto the shaft whose iameter is steppe up to 0mm through a gene ales raius as shown in orer to improve the fatigue strength of the joint. Analysis of shrink fit. When cyliner is assemble by shrinkage as shown above, a contact pressure is evelope at the interface. The pressure is a function of the igital interference an for materials of the same moulus E, is given by: P = Eδ/b [(a -b )/b -(b -a )/c -a ] For the case of shrinkage a hub onto a soli shaft, (a = 0) the expression reuces to: P = Eδ/b [l-b /c ] In the esign b = 10mm, c = 16. P =00 x 10 δ / x 10 [1-10/16.] = 10,000[ ] = 80δN/mm An interface of approximately or 7.6 x 10 - mm is recommene. This will result in an interface pressure of P = 80 x 7.6 x 10 - mm = 9.19N/mm. This value of stress is safely below the enurance limit an the esign stress, Total area on which interface pressure acts = π x 0mm = 15.66mm Total effective normal force = x 9.19 = 668.0N Assuming a low value of the coefficient of static friction say μ = 0.08, Limiting tangential force = 0.08 x = 9.N. Where l an are in millimeters. The angular twists of the various segments of the shafting are compute, using the approximate effective length. The results are expresse in the table below. Shaft iameter (mm) Length, l (approx) mm Twist angle (ras) 5 longer shaft x 10-5 short shaft x (gauge length for long 0.8 x (gauge length for short 0.8 x specimen x 10 - From the table, angular twist is obtaine by summing the angular twist of the separate segments. approximate = = 0.11 ras Determination of Bening Stress n moment of inertia I = π /6 = π/6 x (5) = mm Using the relation δ = (M/I) y Where y = 1.5mm M = 006.5Nmm The maximum bening stress is safe for the machine. Deflection uner Peak Loa The eflection is given by δ b = M L /EI Where L is the effective length = 50mm δ b = x (50) x00x 10 x = 0.165mm The corresponing angular isplacement is given by 0.165/50 = x 10 - ras This isplacement is very negligible compare with the relative shaft uner maximum torque 0.1 1ras. Short shaft or riven shaft Determination of bening stress n moment of inertia I = π /6 = π/6 x (5) = mm Using the relation δ b = (M/I) y Where y = 1.5mm M = 006.5Nmm The maximum bening stress is obtaine as = x = 19.8N/mm The maximum bening stress is also safe for the machine. Deflection of riven shaft uner Peak Loa The eflection is given by δ b = M L /EI Where L is the effective length = 150mm δ b = x (150) x00x 10 x = mm 0.06mm Therefore angular isplacement = 0.06/180 =.96 x 10 - ras This isplacement is also negligible compare with the relative isplacement of the ens of the torque-transmitting shaft uner peak loa. The analysis shows that the setting of the ouble eccentric shaft is accurately reflecte by the angular twist of the shafting with negligible error; introuce by the elastic bening of both the torque arm an the crank. Where 1 an are in millimeters. The angular twists of the various segments of the shafting are compute, using the approximate effective length. The results are expresse in the table below. Shaft iameter (mm) Length, l (approx) mm Twist angle (ras) 5 longer shaft x 10-5 short shaft x (gauge length for long 0.8 x (gauge length for short 0.8 x specimen x 10 - From the table, angular twist is obtaine by summing the angular twist of the separate segments. approximate = = 0.11 ras Determination of Bening Stress n moment of inertia I = π /6 = π/6 x (5) = mm Using the relation δ = (M/I) y Where y = 1.5mm M = 006.5Nmm The maximum bening stress is safe for the machine. Deflection uner Peak Loa The eflection is given by δ b = M L /EI Where L is the effective length = 50mm ISBN: ISSN: (Print); ISSN: (Online) WCECS 01

5 Proceeings of the Worl Congress on Engineering an Computer Science 01 Vol I WCECS 01, -5 October, 01, San Francisco, USA δ b = x (50) x00x 10x = x10 10 = 0.165mm The corresponing angular isplacement is given by 0.165/50 = x 10 - ras Maximum torque transmitting capacity = 1.0 x 9. = 9.N/mm This value is far more than the machine shall ever encounter in service. Screws Four 5mm iameter screw in 8.6mm PCD. Shear loa on each screw = 1 x x 8.6 =157.51N Average shear stress = 8.0N/mm 5 Estimation of the angular twist of the entire torque-transmitting shaft uner full capacity loa This exercise is necessary in orer to be certain that the maximum angular isplacement obtainable from the ouble eccentric shafts is aequate for proviing the twist corresponing to maximum loa. The analysis is mae assuming. The use of the use of the largest shaft iameter of (5mm) an that the, specimen steel remains elastic unto the full loa, The general iea is to ensure that aequate allowance is mae for the case of plastic eformation where strains are larger. The angular twist on a length L of a shaft of iameter subjecte to a torque T is given by the expression: T L G Where G is the moulus of rigiity = 80 x 10 N/mm Substituting for T an G, an the expression reuces to L L. 87 ras 80x10 Bearing A total of three bearing are incorporate into the esign. They are of the light series. They are chosen for rigiity an to reuce eflection. The etails are given below: bearings, 5mm bore, single row, eep groove ball bearing, self-aligning for the bearing housing for the three bearings. The bearing in housing No 1 sustains a maximum loa of M = 11.65N. L 50 Hence average shear stress = 0.1N/mm The bearing in housing No. an sustains a loa of M = 0.71N L 150 Also average shear stress = 0.1N/mm 5 Bearing Housing The three main bearing housing Nos 1 - are robust construction an are perfectly mae of cast steel together with the wes as flanges. The casting are then reborne an force rigily onto the horizontal metal plate after which the final counter boring an reaming operators are performe with a high egree of accuracy. This ensures the maintenance of the axial symmetry of the bearing that was mounte in them. Retaining rings are chosen accoring to availability an size, no emphasis is being place on axial loa capacity since in the esign, an there are no axial loas. Analysis of ynamic forces Dynamic force of vary large magnitue are calle into play by the rotation an acceleration of the unbalance masses of the shafts. The effect here is to evelop approximate analytical solution from which maximum ynamic forces are then compute. Design of weight hanger The weight hanger is esigne to carry ea weight that will inuce stress on the specimen. The weight hanger is esigne to gain support from the specimen. This implies that the weight hanger is on the specimen. The weight hanger has these components: Brass buchion: That has a irect contact with the specimen. It is simply on it that the hanger is simply supporte from. It is two in number an separate apart. It is of brass buchion to create room for rotation without loosing its parts. Arms: The hanger has arms that are 00mm long. This arm is extene to a flat pan, which is the base for the weight hanger assembly. The arm is bolte firmly to the flat pan. The spring an leg of hanger: This is the loa carrie. It has a spring to absorb shocks or impact force from getting to the specimen. Even when the machine is switche on there are some vibrations that are generate ue to critical spee of these elements o not have an effect on the weight applie. Analysis of the Design Calculations of the Weight Hanger The weight hanger is esigne uner some assume specifications. The analysis begins from etermining the critical spee. Critical spee of the machine Critical spee is the spee the shaft attains an becomes unstable with eflection increasing without upper bons. When as shaft is turning eccentricity causes a centrifugal force eflection which can be resiste to some extent by the shaft flexural rigiity EL As long as the eflection are small, no harm is one in the cause of the esign, we are etermining the critical spee base on the shaft an ensemble attachments mass. The critical spee of the fatigue testing machine esign is given by: / L c EI g Ay L= 110mm = 0.11m E = 00KN/mm = 00 x 10 N/mm ISBN: ISSN: (Print); ISSN: (Online) WCECS 01

6 Proceeings of the Worl Congress on Engineering an Computer Science 01 Vol I WCECS 01, -5 October, 01, San Francisco, USA I = mm g = 9.8m/s a = area of shaft 5 = 90.9mm γ = p x L = 7850 x 0.11 = 86.5kg/m If ф = Aγ γ = 86.5kgm A = 0.91m ф =.87kg EI g c / L c / = x =.88 ra/s = 157.8ra/mm This is greater than the natural spee of spee of the motor. This now approves the critical spee to be acceptable, to reuce its effect on the machine, the eflection is calculate first before continuing the vibration. With L = 110m, F = 9.N, I = mm = 00 x 10 Static eflection of the shafting is gotten by FL = 0.0mm EI Frequency of the transverse vibration F n =.71Hz 0.0 This is less than the frequency of the rotating spee of the motor. Therefore, the machine is free from much vibration. Determination of spring for amping Vibration Taking Minimum weight to be carrie to 100N Maximum weight to be carrie to 500N Spring inex C = 6, Factor of safety, Fs =1.5, Yiel strength y = 700mPa, Enurance limit, e = 50mpa, Moulus of rigiity G = 80KN /mm, Maximum eflection f = 0mm Determination of size of spring Let = iameter of wire D = mean iameter of spring D = C. We have that Mean loa W m = W max + W min / = / = 00N Variable loa Wr = max - min / = / = 00N Shear stress factor k s = I + ½ c = I + '/ x 6 = 1.08 Wahls stress factor, c k c s We know that menu shear stress m is given by the equation m = k x 8W m x D / π =1.08 x 8 x 00 x 6/π = (96.1/ )N/mm Variable shear stress is gotten from the equation v = k x 8W V x D / π = 1.55 x 8 x 00 x 6/π = (87.6 / ) N/mm Also we know that factor of safety ( F.s) is equal to: 1 /F.s ( m - v / y ) / ( y v / c ) =.95 x 1.5 = 5.mm Diameter of Spring a) Mean iameter D = c. = 6. = 6 x 5. =.5mm b) Outer iameter of the spring D o = D + D o =.5 5. = 7.9mm c) Inner iameter of the spring D i = D + D i =.5 5. = 7.1mm Number of turns of spring Let n = number of turns of spring an eflation of spring 8.W.D.n G n n = n = 15turns. Using square an groune ens of spring, the total number of turns of spring for the weight hanger will be: n1 = n + = 15 + = 17 turns Free length of the spring The free length () of a spring is the length of the spring in the free or unloae conition. It is given by: L f = soli length + maximum compression + clearance between ajacent coils. n 1 +δ max max 17 x (D) = 16. 6mm. Stiffness of spring This is the loa require per unit eflection of the spring. ISBN: ISSN: (Print); ISSN: (Online) WCECS 01

7 Proceeings of the Worl Congress on Engineering an Computer Science 01 Vol I WCECS 01, -5 October, 01, San Francisco, USA W max K = 16.67N/mm Pitch of The Coil Spring P The pitch of a spring coil is efine as the axial istance between ajacent coils in uncompresse state. Freelength P n = 7.915mm Hanger Ro Diameter of the hanger ro will be equal to the internal iameter of the spring minus clearance or allowances. Di =7.1mm Ro iameter = Di Di = (7.1) = =.9mm Hanger Ro Hea (Top) This is a circular shape at the top of the ro to mesh on the top of spring to room for compression of the spring. Diameter of the hanger ro top is equal to outer iameter plus allowance. D o = 7.9mm Ro hea iameter = D o D o = = 1.7 mm At such, fatigue failure is suen an total, hence angerous an leas to major accient characterize by loss of lives, valuable goos an evices. Thus all precautions an measures shoul be taken to checkmate this failure since it cannot be curbe entirely or preicte in-to-to. REFERENCES [1] Braithwaite F. (185), "The fatigue an consequent fracture of metal". Institution of civil engineers minutes of proceeing, [] Joseph. E. Shirgley & Charles R. Mischley, Mechanical Engineering Design. Failure resulting from variable loaing. Sixth eition [] Rankine W. J. M. (19). The causes of unexpecte breakage of the journals of Railway ailes, an on the means of preventing such accients by observing the law of continuity in their construction. Institution of civil engineers minutes of proceeings, [] Schutz W. (1996). A history of fatigue engineering fracture mechanics Test for Brittle Aluminium For a test conucte on the machine using brittle aluminium specimen, the following result on table below was obtaine an when plotte on S - N graph, the graph below was obtaine. Stress (mpa) Life (cycle) Fig. : An S-N graph of a test conucte on the machine using brittle aluminium IV. CONCLUSION When fatigue stress is inuce on a material ue to the action of force reversing an fluctuating, a failure known as fatigue failure takes place. The stuy an test conucte so far shows that fatigue failure cannot be preicte accurately since material failure uner fatigue are affecte not by just reversal loaing alone but also the number of revolution (cycle per minute) an fluctuating stress an other factors such as temperature, atmospheric conition, both internal an external efect on material subjecte uner fatigue stress. Such efect inclues notch, inclusion, stress concentration an non-homogeneity. ISBN: ISSN: (Print); ISSN: (Online) WCECS 01