Assessment of Surface Treatment on Fatigue Life of Cylinder Block for Linear Engine using Frequency Response Approach

Transcription

1 Aerican Journal of Applied ciences 6 (4): 75-75, 9 IN cience Pulications Assessent of urface Treatent on Fatigue Life of Cylinder Block for Linear Engine using Frequency Response Approach M.M. Rahan, A.K. Ariffin,. Adullah, M.M. Noor, Rosli A. Bakar and 3 M. A. Maleque Autootive Excellence Center, Faculty of Mechanical Engineering, University Malaysia Pahang, Tun Adul Razak Highway, 63 Gaang, Kuantan, Pahang, Malaysia Departent of Mechanical and Materials Engineering, Faculty of Engineering, University Keangsaan Malaysia, 436 UKM, Bangi, elangor, Malaysia 3 Faculty of Engineering and Technology, Multiedia University, Jalan Ayer Keroh Laa, 7545 Bukit Beruang, Melaka, Malaysia Astract: Ojectives: This study was focused on the finite eleent techniques to investigate the effect of surface treatent on the fatigue life of the virating cylinder lock for new two-stroke free piston engine using rando loading conditions. Motivation: An understanding of the effects related to the rando loading is necessary to iprove the aility of designers to accurately predict the fatigue ehavior of the coponents in service. An internal coustion engine cylinder lock is a high volue production coponent sujected to rando loading. Prole stateent: Proper optiization of this coponent that is critical to the engine fuel efficiency and ore roustly pursued y the autootive industry in recent years. A detailed understanding of the applied loads and resulting stresses under inservice conditions is deanded. Approach: The finite eleent odeling and analysis were perfored utilizing the coputer aided design and finite eleent analysis codes respectively. In addition, the fatigue life prediction was carried out using finite eleent ased fatigue analysis code. Aluinu alloys were considered as typical aterials in this study. Results: The frequency response approach was applied to predict the fatigue life of cylinder lock using different load histories. Based on the finite eleent results, it was oserved that the fatigue life was significantly influenced for the nitriding treatent. The otained results were indicated that the nitrided treatent produces longest life for all loading conditions. Conclusion: The nitriding process is one of the proising surface treatents to increase the fatigue life for aluinu alloys linear engine cylinder lock. Key words: urface treatents, cylinder lock, rando loading, finite eleent ethod, fatigue life, frequency response INTRODUCTION Due to arket pressures for iproveents in productivity, reliaility, ductility, wear resistance as well as the profitaility of echanical systes, anufacturers are placing increasing deands on availale aterials. In order to enhance the surface properties of today s aterials, producers of coponents are turning to different surface treatents [-]. There are several techniques availale for echanically iproving the surface properties of the coponents, such as polished, ground, achined, hot rolled, forged, cast, etc. oe of these techniques produce an iprove surface y plastic deforation of surface irregularities [3]. Various ethods have so far een eployed in order to iprove fatigue strength, including optiization of geoetric design, stronger, aterials and surface processing such as nitriding, cold rolled, shot peening, aong the shot peening has long een widely used as a low cost and siple ethod for increasing the fatigue strength of the coponent. Light etals have een utilized for autootive parts to reduce the weight of autooiles, aiing at the significant reduction of CO eission and environental urdens [4-5]. The use of aluinu (Al) instead of steel for lightening of vehicle coponents or achine parts has recently increased. Al and its alloys have advantages over non etallic aterials, aluinu alloys have a high elting point, a good corrosion resistant, a good workaility and have a good theral conductivity. However, the hardness and wear resistance of Al alloys are respectively lower and inferior to those of steel, therefore, there is a liit in their application to oving parts. Hence, research has een carried out in surface odification technology to Corresponding Author: M.M. Rahan, Autootive Excellence Center, Faculty of Mechanical Engineering, University Malaysia Pahang, Tun Adul Razak Highway, 63 Gaang, Kuantan, Pahang, Malaysia 75

2 A. J. Appl. ci., 6 (4): 75-75, 9 increase the applicaility of Al alloys as oving parts. urface odification technologies for Al alloys can e classified into three ain groups. Alloying is the first ethod and this fors a hard fil on the Al surface [6]. The nd group is coating ethod, which covers the Al surface with hard aterials [7]. The third is a heat treating process, such as nitriding [8].The ojective of the current study is specifically to investigate into the effect of surface treatents on the fatigue life iproveent of the cylinder lock of linear engine. Nuerical investigates are perfored to characterize copletely the different induced effects efore and after surface treatents. The nuerical results were discussed and analyzed. Their influences on HCF ehavior of the virating coponent ade fro AA 66-T6. MATERIAL AND METHOD Theoretical asis of frequency doain: The equation of otion of a linear structural syste is expressed in atrix forat in Eq.. The syste of tie doain differential equations can e solved directly in the physical coordinate syste: { } + { } + { } = { } M x(t) C x(t) K x(t) P(t) () where, {x(t)} is a syste displaceent vector, [M], [C] and [K] are gloal ass, daping and stiffness atrices, respectively, {P(t)}is an applied load vector. When loads are in rando in nature, a atrix of the loading power spectral density functions [ p (ω)] can e generated y eploying Fourier transfor of load vector {P(t)}: ( ω) ( ω) ω = p ( ω) ( ω) () where, is the nuer of input loads. The diagonal ter ii (ω) is the auto-correlation function of load P i (t)and the off-diagonal ter ij (ω) is the crosscorrelation function etween loads P i (t) and P j (t). Fro the properties of the cross PDs, it can e shown that the ultiple input PD atrix [ p (ω)] is a Heritian atrix. The syste of tie doain differential equation of otion of the structure in Eq., is then reduced to a syste of frequency doain algera equation: ( ω ) = ( ω) ( ω) ( ω) T x H H n n n p (3) n where, n is the nuer of output response variales. The T denotes the transpose of a atrix. [H(ω)] is the transfer function atrix etween the input loadings and output response variales: ( ω ) = ( ω + ω + ) H M i C K (4) The response variales [ p (ω)] such as displaceent, acceleration and stress response in ters of PD functions are otained y solving the syste of the linear algera equations in Eq. 3. Classical FE analysis results in a vector of 6 coponent stresses at each node. This is shown in Fig.. The coponent stresses consist of 3 noral and 3 shear stress coponents along the gloal coordinate or the eleent coordinate axis and are expressed atheatically in Eq. 5: Noral: xx ( ω), yy ( ω), zz ( ω ) hear:,, ω ω ω (5) xy yz xz For the purpose of fatigue analysis a single PD is required for each node showing soe stress equivalent such as von Mises, Tresca or the asolute axiu principal stress. These are otained y aking the eigen values of the stress tensor atrix given y Eq. 6 as follows: principal Direction ( ω ) eigenvalues σ ω = ω ( ω ) = eigenvectors (6) where, σ principal (ω) is a vector of the three principal stresses, direction (ω) is a atrix of the direction cosines for the three principal axes noralized to yield three unit colun vectors, the nth colun referring to the nth eigen value. (ω) is 3 3 atrix of the coponent stresses defined as: ( ω) ( ω) ( ω) ( ω) ( ω) ( ω) xx xy xz ( ω ) = xy ω yy ω yz ω xz yz zz 3 xz yz zz (7) σ ω xx ω xy ω xz ω σ ω = eigenvelues xy ω yy ω yz ω (8) σ ω ω ω ω The desired stress invariant could e otained fro Eq. 8. The odulus sign is necessary due to the principal stresses returned y Eq. 8 are coplex. 76

3 A. J. Appl. ci., 6 (4): 75-75, 9 y called Narrow and solution. This expression was defined solely in ters of the spectral oents up to 4. z Inp ut I G lo al co ordin ate axis x 6 coponent stresses at node xx xx x x xy yz x z N o ral stresses hear stresses Fig. : Transfer function calculated as 6 coponent stresses Proaility density function p () d p( i ) Maxiu principal stress: ax,, σ ω = σ ω σ ω σ ω (9) ax 3 Von Mises stress: () ( σ ( ω) σ ( ω ) + σ ( ω) σ3 ( ω ) + σ3 ( ω) σ ( ω) ) σ ω = von Mises. Tresca: σ ( ω) σ ( ω), 3, Tresca ax σ ω σ ω σ ω σ ω σ ω = () 3 where, σ xxx (ω) is the transfer function with respect to frequency (ω) rad/sec expressed as a stress invariant. Frequency can also e expressed in ters of Hz after using the appropriate conversion. Frequency response ethods: This research was descried variety of approaches for coputing fatigue life or daage directly fro the PD of stress as opposed to a tie history. The stress power spectra density represents the frequency doain approach input into the fatigue [9]. This is a scalar function that descries how the power of the tie signal is distriuted aong frequencies. Matheatically this function can e otained y using a Fourier Transfor of the stress tie history auto-correlation function and its area represents the signals standard deviation. It is clear that PD is the ost coplete and concise representation of a rando process. Bendat presented the theoretical asis for the first of these of these frequency doain fatigue odels, so tress range() Fig. : Proaility density functions However, the fact that this solution was suitale only for a specific class of response conditions was an unhelpful liitation for the practical engineer. Bendat showed that the proaility density function of peaks for a narrow and signal tended towards Rayleigh distriutions as the andwidth reduced. To coplete his solution ethod, Bendat used a series of equations derived y Rice [] to estiate the expected nuer of peaks using oents of area eneath the PD. The ost convenient way of storing stress range histogra inforation is in the for of a Proaility Density Function (PDF) of stress ranges. A typical representation of this function is shown in Fig.. It is easily to transfor fro a stress range histogra to a PDF, or ack to tie histories. The in widths used and the total nuer of cycles recorded in the histogra are the only additional inforation required. To get a PDF fro a rainflow histogra each in in the rainflow count has to e ultiplied y t xd, where t is the total nuer of cycles in histogra and d is the interval width. The proaility of the stress range occurring etween i -d/ and i +d/ is given y p( i )d. The actual counted nuer of cycles, n i = p() d t : k The allowale nuer of cycles: N( i) = () Assue p() is the Rayleigh distriution which s represented y a narrow and process and stress aplitude,, can e treated as a continuous rando variale. 8 p = f ( ) NB = e (3) 4 77

4 A. J. Appl. ci., 6 (4): 75-75, 9 The expected total fatigue daage for narrow and gaussian process: ni t E D = = p() d i N( i) K E P T (4) 8 = e d K 4 where, N( i ) is the nuer of cycles of stress range occurring in T sec, n i is the actual counted nuer of cycle, t is the total nuer of cycles equals to E [P] T. Failure occurs, D.. In order to copute fatigue daage over the lifetie of the structure in secpnd, the for of aterials -N data ust also e defined using the aterial paraeters k and. The typical -N curve for high cycle fatigue is as shown in Fig. 3. Figure 3 shows that, under constant aplitude cyclic loading, a linear relationship exists etween cycles to failure (N) and applied stress range () when plotted on log-log study. There are two alternative ways of defining this relationship, as given in Eq. 5: N = k, where = and k = (RI) (5) A ethod for coputing PD oents is descried y Rahan. oe very iportant statistical paraeters can e coputed fro these oents. These paraeters are Root Mean quare (RM), nuer of Zero crossing with positive slope (E[]), nuer of peaks per second (E[P]). The forulas in Eq. 6 highlight these properties of the spectral oents: RM = ; E = ; E P = 4 (6) where,,, and 4 are the zero, st, nd and 4th order oent of area of the PD respectively. Another iportant property of spectral oents is the fact that it is possile to express the irregularity factor as a function of the zero, nd and 4th order spectral oents, as expressed in Eq. 7: E γ = = E P 4 (7) Figure 4 shows how to calculate the irregularity factor. When irregularity factor is equal to, there are an infinite nuer of peaks for every zero up crossing. This is considered a wide and rando process. The value of irregularity factor is equal to corresponds to one peak per one zero up crossing and it represents a narrow-and rando process. Alternatively, a narrowand process can e defined y the width of its spectru. For this reason, the spectral width paraeter, λ, is introduced as Eq. 8: λ = γ (8) That eans λ = represents a narrow-and rando process. The irregularity factor γ is an iportant paraeter that can e used to evaluate the concentration of the process near a central frequency. Therefore, the irregularity factor can e used to deterinate whether the process is narrow and or wide and. Irregularity factor varies etween and. A narrow and process (γ ) is characterized y only one predoinant central frequency indicating that the nuer of peaks per second is very siilar to the nuer of zero crossings of the signal. This assuption leads to the fact that the PDF of the fatigue cycles range is the sae as the PDF of the peaks in the signal. In this case fatigue life is easy to estiate. Upcrossing E[] 3 Irregularityfactor = = = =.5 Peak E[p] 6 Peak tress Upward crossing tress range,log High cycle fatigue Meanvalue Tie Life to failure (Cycles),log N sec. Fig. 3: Typical -N curve for high cycle fatigue 78 Fig. 4: Calculation of the irregular factor, γ

5 A. J. Appl. ci., 6 (4): 75-75, 9 Many expressions have een proposed to correct the conservatis associated with this solution. The solutions of Wirsching and Light [], Tunna [], Chaudhury and Dover [3], teinerg [4], and Hancock [5] were all derived using this approach. They are all expressed in ters of the spectral oents up to 4. Tunna solution: p() Wirsching solution: Where: Wirsching T 8 = e γ 4γ (9) c NB () E[D] = E[D] a + [ a]( ε) ε = γ where, ε is a spectral andwidth paraeter which is an alternative version of the irregularity factorand a and c are est fitting paraeters expressed as: a = ; c = () where, is the slope of the -N curves which is defined in Eq. 5. This solution is given in the for of an equivalent stress range paraeter eq, Where: Hancock equivalent stress: eq = p() d () ( eq) Hancock = γ Γ + Chaudhury and dover equivalent stress: (3) erf ( γ ) =.3γ +.496γ +.98γ * 3.354γ 3.337γ γ.7846γ teinerg olution: ( ) ( ) ( ).683 = eq teinerg (5) The fatigue daage can then easily e otained y sustituting this into the general daage equation used when deriving the narrow and solution: E[P] T E[D] = eq (6) k Proaly the ost faous epirical forula for approxiating the rain flow aplitude distriution is that proposed y Dirlik, which uses a coination of an exponential and two Rayleigh densities. In the Dirlik odel, approxiate closed-for expression for the proaility density function of rain flow ranges, which was otained using Monte Carlo technique. The Dirlik solution is expressed y the Eq. 7 and details the specific literature reported in the refs [6-7] : N() = E[P] T p() (7) where, N() is the nuer of stress cycles of range (N/ ) expected in T seconds, E [P] is the expected nuer of peaks and p() is the proaility density function: Z Z Z Q D Z R e + e + D 3Z e D p() = Q R (8) where, p() is the proaility density function, is the stress aplitude, is the zeroth order spectral oent and: = eq C & D Where: + ε + γ + Γ + Γ π * γ + + erf ( γ) Γ (4) =, D γ =, x 4 4 γ x D R =, γ D + D Z =, D (x γ ) = + γ γ D + D = R.5( γ D3 D R) D3 = D D, Q = D 79

6 A. J. Appl. ci., 6 (4): 75-75, 9 where, x, D, D, D 3, Q, Z and R paraeters depending on the,, and 4, Z is a noralized variale.,, and 4 are the zeroth, st, nd and 4th order spectral oents, respectively. It should e Pressure (MPa) Pressure (MPa) sec. Narrow and signals sec. Pressure (Mpa) Biodal ( peaks) signals Triodal (3 peaks) signals sec. Fig. 5: Tie-loading histories of narrow and, iodal and triodal signals. Pressure (Mpa /Hz) Narrow and signal Hz Pressure (Mpa /Hz).664 Biodal signal Pressure (MPa /Hz) Hz.47 Triodal signal Hz Fig. 6: Power spectral density functions of the narrow and, iodal and triodal signals.543 Pro. Dens.() Narrow and signal MPa.745 Pro. Dens.() Biodal ( peaks) signal MPa.876 Pro. Dens.() Triodal (3 peaks) signal MPa Fig. 7: Proaility density functions of the narrow and, iodal and triodal signals noted that, if copared to the Wirsching-Light odel, this approach gives an aplitude distriution (and thus a rain flow daage) depending on just four spectral oents (i.e.,, and 4), including in particular a dependence on oent. All of aove discussed ethods are deterining fatigue life fro PDs stress. Loading inforation: Figure 5 shows the tie-load histories signals of the narrow and ( peak) and two wide and of iodal ( peaks) and triodal (3 peaks) loading histories [8]. Figure 6 and 7 also show the power spectral density function and corresponding proaility density function of those signals. REULT AND DICUION A geoetric odel of the cylinder lock of the free piston engine is considered in this study. Threediensional odel geoetry was developed in CATIA software. ince the tetrahedral is found to e the est eshing technique, the 4 nodes tetrahedral (TET4) eleent version of the cylinder lock was used for the initial analysis. In addition, the TET4 copared to the nodes tetrahedral (TET) eleent esh using the sae gloal esh length for the highest loading conditions (7. MPa) in the coustion chaer. The investigating the results, it can e found that the TET esh predicted higher von Mises stresses than that the TET4 esh. The TET esh is presued to represent a ore accurate solution since TET4 eshes are known to e dreadfully stiff [9]. TET4 eployed a linear order interpolation function while TET used quadratic order interpolation function. For the sae eleent size, the TET is expected to e ale to capture the high stress concentration associated with the olt holes. A TET was then finally used for the solid esh. Mesh study is perfored on the FE odel to ensure sufficiently fine sizes are eployed for accuracy of calculated results ut at copetitive cost (CPU tie). In the process, specific field variale is selected and its convergence is onitored and evaluated. ensitivity analysis was perfored to otain the optiu eleent size. The analysis was perfored iteratively at different eleent lengths until the solution otained appropriate accuracy. Convergence of the stresses was oserved, as the esh size was successively refined. The eleent size of. was finally considered. A total of 3545 eleents and 669 nodes were generated with. eleent length. Copressive loads were applied as pressure (7 MPa) acting on the surface of the coustion chaer and preloads were applied as pressure (.3 MPa) acting on 7

7 A. J. Appl. ci., 6 (4): 75-75, 9 the olt-hole surfaces. In addition, preload was also applied on the gasket surface generating pressure of.3 MPa. The loading and constraints on the cylinder lock are shown in Fig. 8. The constraints were applied on the olt-hole for all six degree of freedos. response analyses were perfored using the finite eleent analysis code. The frequency response analysis used the daping ratio of (5%) of critical. The daping ratio is the ratio of the actual daping in the syste to the critical daping. Most of the experiental odal Fig. 8: Loading and constraints on the cylinder lock Fig. 9: Maxiu principal stresses distriution for the Pseudo-static linear analysis The finite eleent results of tie doain (Pseudostatic ethod) i.e., the axiu principal stresses distriution is shown in Fig. 9. The fatigue life of tie doain histories are perfored using the stress-life ethod eployed rain flow cycle counting technique [-]. Tie doain fatigue approach consists of a nuer of steps. The first is to count the nuer of stress cycles in the response tie history. This is perfored through a process of rain flow cycle counting. Daage fro each cycle is deterined, typically fro an -N curve. The daage is then sued over all cycles using linear daage suation techniques to deterine the total life. The frequency 7 Fig. : Maxiu principal stresses distriution for the frequency response analysis with zero Hz reported that the odal daping in ters of nondiensional critical daping ratio expressed as a percentage [-3]. In fact, ost structures have critical daping values in the range of (-%), with values of (-5%) as the typical range. Zero daping ratio indicates that the ode is un daped. Daping ratio of one represents the critically daped ode. The result of the frequency response finite eleent analysis with zero Hz i.e. the axiu principal stresses distriution of the cylinder lock is shown in Fig.. Fro the results, the axiu and iniu principal stresses of 38. and MPa for the Pseudo static analysis and 38. and MPa for the frequency response analysis for zero Hz were otained respectively. These two axiu principal stresses contour plots are alost identical. The variation of the axiu principal stresses with the frequency is shown in Fig.. It can e seen that the axiu principal stress varies with the higher frequencies. This variation is due to the dynaic influences of the first ode shape. It is also oserved that the axiu principal stress occurs at a frequency of 3 Hz. The axiu principal stresses of the cylinder lock for 3 Hz is shown in Fig.. Fro the results, the axiu and iniu principal stresses of 56. and -7. MPa were otained at node 4936 and 4778 respectively.

8 A. J. Appl. ci., 6 (4): 75-75, 9 The results of the fatigue life contour for the narrow and loading histories at ost critical locations for Pseudo-static analysis and frequency response approach with 3 Hz are shown in Figure 3 and 4 respectively. The iniu life prediction for Pseudostatic analysis and frequency response approach with 3 Hz are otained 7.67 and 9.44 sec respectively. Maxiu Principal stress (MPa) MPa 3 Hz shown in Fig. 5. The dotted straight line on the Fig. 5 shows the perfect correlation etween the Pseudo-static and frequency response approach. It can e seen that the predicted results are well correlated etween these approaches. Predicted iniu life is 7.67 seconds at node 4936 Log of Life (econds) Fig. 3: Predicted fatigue life contours plotted for Pseudo-static analysis Fig. : Maxiu principal stresses plotted against frequency Predicted iniu life is seconds at node 4936 Log of Li fe (econ ds) Fig. 4: Predicted fatigue life contours plotted for the frequency response analysis with 3 Hz. E+ Fig. : Maxiu principal stresses contour for the frequency response analysis with 3 Hz It would e expected that the condition of lower stress would correspond to longer life and vice versa. However, the results indicates the opposite ecause the frequency resolution of the transfer function are selected the sall value then the result show the nonconservative prediction. Fro Figure 3 and 4, it can e seen that the fatigue life contours are different and ost daage was found at frequency of 3 Hz. The predicted fatigue life on log-log coordinates using the Pseudo-static and the frequency response analysis is Viration fatigue life in sec..e+9.e+8.e+7.e+6.e+5.e+4.e+3.e+.e+.e+.e+.e+.e+.e+3.e+4.e+5.e+6.e+7 Pseudostatic fatigue life in sec. Fig. 5: Coparison etween the fatigue life of the Pseudo-static and the frequency response analysis.e+8.e+9.e+ 7

9 A. J. Appl. ci., 6 (4): 75-75, 9 Effect of frequency resolution: Frequency resolution of the transfer function is significant to capture the input PD. The significances of the frequency resolutions of AEBKT loading histories are also shown in Fig. 6 and 7. Two types of Fast Fourier Transfor (FFT) uffer size width naely 89:.64 Hz and 6384:.35 Hz were used in Fig. 6 and 7. The FFT uffer size defines the resolution of the power spectru. The uffer ust e a power of and of course the longer the uffer, the higher the resolution of the spectral lines. To calculate the resolution divide the Nyquist frequency y half the FFT uffer size. If the Nyquist frequency is 5 Hz and the FFT uffer size selected is 89, then the spectral lines are 5/(89/) =.64 Hz apart. Another use of a saller uffer size is for short data files as these cannot e adequately analyzed with a ig uffer, since there ay not e enough data to give a good spectral average. Using a saller uffer size could give a etter spectral average at the expense of spectral line width. The total area under each input PD curve is deterined to e identical. However, the 6384:.35 Hz width has twice as any points copares to the 89:.64 Hz. Tale is shown the coparison etween the narrow and ( peak) and wide and of iodal ( peaks) and triodal (3 peaks) loading histories with the tie doain fro all the frequency doain approach ethods. Fro the results, it can e seen that the Dirlik ethod gives the est results for all three loading conditions (narrow and and wide and signals). The narrow and gives good results fro the narrow and signal ( peak), ut ecoes too conservative when the signal is iodal and triodal signals ( and 3 peaks). Tunna reaks down copletely for a wide and signal. Wirsching is non conservative and then too conservative as is teinerg. Hancock, Chaudhury and Dover do reasonaly well ut not as well as Dirlik odel. When the signal is wide and (iodal and triodal), the narrow and tends to turn any signal into a narrow and signal aking the resulting prediction fatigue life extreely and soeties overly conservative. The Dirlik ethod found to gives the est results when copared with the corresponding tie doain result and others. Fro the aove discussions, it is concluded that the Dirlik ethod is recoended for general usage. Effect of surface treatents: The investigation of the effect of surface treatents on the fatigue life of coponent sujected to rando loading conditions. The aterial used in this study is AA66-T6. Power spectral density with FFT uffer size 6384:.35 Hz width are consider in this analysis. A high proportion of all fatigue failures nucleate at the surface of coponents and thus surface conditions ecoe an extreely iportant factor influencing fatigue strength..6 RM Power (Mpa Hz ) Fig. 6: Power spectral density when using the FFT uffer size of 89:.64 Hz width. -.6 RM Power (MPa Hz ) Fig. 7: Power spectral density when using the FFT uffer size of 6384:.35 Hz width Tale : Predicted fatigue life at critical location (Node 4936) for various frequency response approaches using the narrow and wide and signal Predicted Fatigue life at critical location in sec ( 6 ) Load-tie histories Tie Narrow Chaudhury signals doain and Dirlik Tunna Wirsching Hancock and dover teinerg Narrow and Biodal Triodal

10 A. J. Appl. ci., 6 (4): 75-75, 9 Tale : The effect of the surface finish and treatents on the fatigue life at critical location (node 4936) for 3 peaks loading conditions urface Predicted viration fatigue life in years finish processes Untreated hot peened Cold rolled Nitrided Polished Ground Good achined Poor achined Forged Cast urface effects are caused y differences in surface roughness, icrostructure, cheical coposition and residual stress. The correction factor for surface finish is soeties used a qualitative description of surface finish such as polished or achined. The surface factors as a function of ultiate tensile strength involving different surface finish conditions such as grinding, achining, hot rolling and as-forged. The correction factors for surface treatent and finish are otained fro the epirical data and are related to the ultiate strength of the aterial. The coparison etween the surface treatents with various surface finish processes using the 3 peaks wide and signal tie-loading histories are shown in Tale. It can e seen that the fatigue life for nitriding surface treatents is surprisingly increases than those other surface treatent processes due to the developent of copressive residual stresses and the increase of hardness near the surface. It can e shown in Tale that there are no effect on ground, forged and cast surface finish condition with the cold rolled surface treatents. Forging can cause surface decarurization and the loss of caron atos fro the surface aterial causes it to have a lower strength and ay also produce residual tensile stresses. Both of these factors are especially detriental to fatigue strength. urface treatents including nitriding, cold rolling and shot peening that produced copressive residual surface stresses can prolong the fatigue life. These surface treatents cause the axiu tensile stress to occur elow the surface of the aterials. However, the tensile residual surface stresses are found to e especially detriental and can proote corrosion fatigue. In addition, urface treatents can also increase the endurance liit of the aterial used. A diffusion process such as nitriding is found to e a dreadfully eneficial for increasing the fatigue strength. This process is capale of increasing the strength of the aterial on the surface as well as causing the voluetric changes, which produce the residual copressive surface stresses. Thus the nitriding could e applied to the fatigue critical area of the suject to iprove the fatigue life and also iprove the fretting resistance, since the cylinder lock is in contact with other coponents. CONCLUION This study was conveyed the iportant findings on the influence of the surface treatent process paraeter on the fatigue lives. Frequency doain fatigue analysis was applied to a typical cylinder lock of two-stroke free piston engine. The results show that all surface treatent processes can e applied to increase the fatigue life of the aluinu alloys coponent. The surface copressive residual stress was the greatest effect on the fatigue life. According to the results, it was concluded that the polished and nitriding coinations found the great influences on the fatigue life iproveent. Nitriding treatent was to produce copressive forces in the outer layers of the coponent. The copressive residual stresses and the tensile residual stresses found to e eneficial and detriental to the fatigue life respectively. The nitriding process has the coined effect of producing a higher aterial strength on the surface and causing the voluetric changes which produce the residual copressive stresses. In addition, the viration fatigue analysis e capale of iprove understanding of the syste ehaviors in ters of frequency characteristics of oth structures and loads and their couplings. ACKNOWLEDGEMENT The researchers would like to thank the Departent of Mechanical and Materials Engineering, Faculty of Engineering, Universiti Keangsaan Malaysia to provided the laoratory facilities. The authors would like to express their especial thanks to Universiti Malaysia Pahang for provided financial support. REFERENCE. Rahan, M.M., A.K. Ariffin,. Adullah and A.B. Rosli, 7. Effect of nitriding treatent on fatigue life for free piston linear engine coponent using frequency response ethod: A finite eleent approach. truct. Durail. Hu. Monitor., 3: issue=v3n4&no=5. Rahan, M.M., A.K. Ariffin, N. Jaaludin and C.H.C. Haron, 6. Influence of surface treatents on fatigue life of a free piston linear generator engine coponent using rando loading. J. Zhejiang Univ. ci. A., 7: DOI:.63/jzus.6.A89 74

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