Fatigue Crack Growth Process in CPVC Pipe Couplings

Transcription

1 e-polymers 2007, no ISSN Ftigue Crck Growth Process in CPVC Pipe Couplings Z. Khn,* N. Merh, F. Sghi Deprtment of Mechnicl Engineering, King Fhd University of Petroleum & Minerls, Dhhrn 31261, Sudi Ari. E. mil: Phone: (Received: 25 My, 2006; pulished: 5 June, 2007) Introduction Astrct: An investigtion of the influence of temperture nd loding frequencies on the morphologicl fetures found on the ftigue frctured surfce of chlorinted polyvinyl chloride (CPVC) hs een conducted. Single edge notched rectngulr coupons otined y flttening schedule 80 CPVC pipe couplings were sujected to ftigue loding t different tempertures of 0, 23, 40, nd 70 o C nd frequencies of 0.1, 1, nd 50 Hz. Crck growth in CPVC, involved comintion of sher yielding nd crzing processes. At the test temperture of 0 o C nd 23 o C, the ftigue crck growth ws noted to occur predominntly y sher yielding while crzing plyed secondry role. On the other hnd t 40 o C nd 70 o C, the ftigue crck growth process ppered to predominntly involve crzing process while sher yielding plyed less significnt role. Filler mteril prticles plyed mjor role s rittle second phse stress-riser prticles nd fcilitted crze initition. i Discontinuous crck growth nds (DGBs) indicting repeted crck rrests were lso noted on the frcture surfce. Key words: CPVC, pipe couplings, ftigue, crck growth, temperture, frequency Understnding of the mcroscopic nd microscopic detils of the frcture surfce morphology in CPVC is of interest ecuse they revel vlule informtion on the mechnism(s) with which the crcks growth occurs under given cyclic stress nd environmentl conditions. Among vrious conditions, temperture nd loding frequency is of the primry interest in pplictions of CPVC s pipe line mteril used for trnsport of potle, sewge, nd se wters s well s other corrosive liquids. Despite of the fct tht the filures of CPVC pipe nd pipe fittings re eing reported t n incresing rte, the investigtions to determine the cuses of such filures nd understnding the mechnism(s) of frcture process in these mterils hve een few nd fr etween. A lrge numer of studies, however, hve een conducted, which ddressed the mechnism(s) of ftigue crck growth in mny other engineering polymers including some on PVC [1-10]. A generl finding of these studies conclude tht under stress sttes where the mximum principl stress is tensile, polymers my, t the eginning of the deformtion, exhiit only smll or even no mcroscopic inelstic deformtion due to sher-yielding. The mechnism of inelstic deformtion then switches to crzing. Crzes form in two step process, first the highly stressed region decys into voids, nd second, fter loclized necking is initited, micro firils form, which ridge the crze gp. The crck growth occurs y frcturing the crze zone, which dvnces the crck tip to the oundry of the crze zone. After this crck tip dvncement, the crck is rrested nd wits for the next crze zone to develop nd crck dvncement y frcturing the crze zone is 1

2 repeted. The frcture thus occurs y sequentil repetitive process of crck tip inelstic deformtion (chrcterized y micro void formtion), crze zone development, nd crze zone frcture leding to crck growth. Crze zone frcture my occur y scission of the crze firils or pull out filure of highly oriented chins in the crze zone. Firil scission is fvored t lower tempertures s well s high strin rte (high frequencies), while chin pull out is expected t high tempertures nd low strin rtes (low frequencies). Although slow crck growth under oth cyclic (ftigue) nd sttic (creep) loding conditions hve een suject of study of lrge numer of investigtors, to our est knowledge, the only work ville in the literture till dte, on the suject of ftigue crck growth in CPVC pipes nd fittings re just few ppers uthored y Merh et l, Khn et l, Sghir et l nd Mezghni et l [11-18]. These uthors hve investigted the effect of tempertures rnging from 10 to 70 o C on the mechnicl properties of CPVC. They found tht the yield strength nd elstic modulus decrese linerly with temperture. Brittle frcture occurred t tempertures elow room temperture while ductile frcture occurred t room temperture nd tempertures ove RT. It is shown tht the crck propgtion in CPVC pipe fittings occurs through crzing process, which involves void formtion nd moleculr orienttion hrdening. The work presented here ims t investigting the mechnism(s) involved in the crck growth process in CPVC pipe fittings sujected to ftigue loding t different tempertures nd test frequencies. Results nd Discussion Ftigue Test Results Figure 1 shows typicl vrition of d/dn with ΔK for different tempertures nd frequencies t stress rnge of 13.3 MP. As reported in erlier work y Merh et l [12] resonle dt sctter is oserved t ll conditions. The effect of frequency on the crck growth rtes t different tempertures is provided in Figure 2 nd the effect of temperture on crck growth rtes t different frequencies is shown in Figure 3. The d/dn vs. ΔK curves shown in figure 2 nd 3 re the verge of two or three tests performed t condition. Results on these figures illustrte two importnt points. First, for given ΔK, the crck growth rte d/dn increses with incresing temperture. For exmple, t the frequency of 1 Hz (Fig. 2-) t ΔK = 2.0 MP m, d/dn of 4, 4.9, 12 nd 27 μm/cycle were oserved for test temperture of 0, 23, 40 nd 70 o C, respectively. A similr result is found t 50 Hz (Fig. 2-c). As explined in erlier work y Merh et l [12], t the frequency of 0.1 Hz however, there is n pprecile enhncement in d/dn when the temperture is incresed from 40 to 70 o C. This decrese in the crck propgtion resistnce t higher tempertures cn e explined y the fct tht due to the temperture induced moleculr virtions the moleculr chin disentnglement in CPVC ecomes much esier nd promotes higher rte of crck growth. On the other hnd t low tempertures the moleculr chins re expected to e more rigidly pcked nd do not undergo esy disentnglement. The crck growth rtes t lower tempertures re expected to e low. 2

3 1.E E-04 R=0.2 Temp=0 0 C Freq=1 Hz Δσ=13.3 MP R= 0.2 Temp=70 0 C Freq=1 Hz Δσ=13.3 MP 1.E-05 1.E-05 d/dn, m/cycle d/dn (m/cycle) 1.E-06 d/dn, m/cycle d/dn (m/cycle) 1.E-06 1.E-07 1.E ΔK (MP m) ΔK, MP m () 1.E ΔK (MP m) ΔK, MP m () Fig. 1. d/dn-δk dt for CPVC () Freq. =1 Hz, Temp = 0 o C, () Temp = 70 o C, Freq. = 1 Hz. d/dn, m/cycle d/dn, m/cycle d/dn, m/cycle ΔK, MP m ΔK, MP m ΔK, MP m () () (c) Fig. 2. Effect of temperture on ftigue crck growth rtes of CPVC t different frequencies: () 0.1 Hz, () 1.0 Hz nd (c) 50 Hz. The effect of frequency on crck growth rte in CPVC presented in Figure 3 (-d) disply the vrition of d/dn with ΔK for different frequencies t the four tempertures of interest (0, 23, 40 nd 70 o C). The results otined revel two importnt points. First, the ftigue crck growth rtes in CPVC re sensitive to frequency chnges t 40 nd 70 o C nd show only negligile sensitivity to the frequency chnges t lower tempertures (T 23 o C). This oservtion is in greement with the result reported in relted work [29, 51]. In this work the uthors show tht the trnsition form sher yielding dominted crck growth to crze dominted crck growth occurred etween 23 nd 50 o C. Second, t higher tempertures the frequency sensitivity ppers to e dependent on the frequency 3

4 level. Higher frequency sensitivity is oserved in the 0.1 to 1 Hz rnge thn in 1 to 50 Hz rnge. d/dn, m/cycle d/dn, m/cycle ΔK, MP m () ΔK, MP m () d/dn, m/cycle d/dn, m/cycle (c) (d) ΔK, MP m (c) ΔK, MP m (d) Fig. 3. Effect of frequency on ftigue crck growth rtes of CPVC t different temperture () 0 C, () 23 C, (c) 40 C nd (d) 70 C. Crck Growth Process -Mcroscopic Frcture Surfce Anlysis Mcro photogrphs of frcture surfce were tken y low power opticl microscope to exmine the frcture process s ffected y the chnges in temperture nd frequency. Representtive frcture surfce mcrogrphs from CPVC smples ftigued t 0, 23, 40 nd 70 0 C nd t different frequencies of 0.1, 1.0, nd 50 Hz re presented in Fig. 4 to 7. 4

5 c Fig. 4. Mcro-frctogrphs of CPVC smples ftigued t 0 o C. () 0.1 Hz, () 1 Hz, (c) 50 Hz; Mgnifiction 2X. c Fig. 5. Mcro-frctogrphs of CPVC smples ftigued t 23 o C. () 0.1 Hz, () 1 Hz, (c) 50 Hz; Mgnifiction 2X. The effect of frequency chnge on the ftigue crck growth process is clerly evident when mcro frctogrphs of smples ftigued t given temperture ut t different frequencies re compred. An exmintion of the frcture surfces of three CPVC smples ftigued t 0 o C t different frequencies of 0.1, 1, nd 50 Hz (Fig. 4) shows much fltter frcture surfce t the frequencies of 0.1 nd 1 Hz s compred to the frcture surfce oserved t 50 Hz. At 50 Hz the frcture surfce ssumes much rougher ppernce especilly from the mid wy to the end of the crck growth process. The flt frcture surfces t 0.1 nd 1 Hz indicte tht t these frequencies the mjor portion of the ftigue crck growth hs occurred under sher yield control process. On the other hnd t the test frequency of 50 Hz, the roughness of the frcture surfce suggests tht the ftigue crck growth must hve occurred minly under crze growth control process. c Fig. 6. Mcro-frctogrphs of CPVC smple ftigued t 40 o C, () 0.1 Hz, () 1 Hz, (c) 50 Hz; mgnifiction 2X. 5

6 c Fig. 7. Mcro-frctogrphs of CPVC smple ftigued t 70 o C. () 0.1 Hz, () 1 Hz, (c) 50 Hz; mgnifiction 2X Similr oservtions cn e mde t ll other test temperture of 23, 40, nd 70 o C, where the frcture surfces re noted to hve lso grdully chnged from flt ppernce t 0.1 Hz to rough ppernce t 50 Hz. It cn thus e sfely ssumed tht t ll four test tempertures of 0, 23, 40, nd 70 o C, n increse in the test frequency from 0.1 to 50 Hz lters the ftigue crck growth process from one which involves growth y sher yielding (t 0.1 nd 1 Hz) to one tht involves growth y predominntly crzing process. It must however e noted tht the frequency effect on the frcture surfce is not s pronounced t 0 nd 23 o C s it is t 40 o C (Fig. 6) nd t 70 o C (Fig. 7). At 40 nd 70 o C, the ppernce of frcture surfce suggests tht t these tempertures only smll portion of the totl crck growth tkes plce under sher yielding nd the ulk of the crck growth occur under crze growth controlled process. Since the crzing process involves pprecile mount of inelstic ehvior in the vicinity of the crck tip region, it is expected tht due to this inelstic condition present t the crck tip, the crze dominnt process should result in lowering the crck growth rtes much more significntly t 40 nd 70 o C thn t 0 nd 23 o C when the test frequency is incresed form 0.1 to 50 Hz. The d/dn versus ΔK curves shown in Fig. 2 (,, c) confirm tht indeed much more pronounced effect of frequency on the crck growth rtes is oserved t 40 nd 70 o C s compred to 0 nd 23 o C. It my e worth noting tht t 0.1 Hz nd 70 o C, where the specimen spend very long time (under very low frequency of 0.1 Hz) t reltively high temperture of 70 o C, the frcture surfce shows very firous morphology (Figure 7-) which my e suggestive of the crck growth occurring perhps under mixed ftigue-creep conditions. The chnge in the test temperture t given frequency lso produces noticele chnge in the frcture surfce morphology in CPVC mteril. A comprison of the frcture surfces of smples tested t 23 nd 40 o C t the test frequencies of 0.1 nd 1 Hz (Fig. 5 nd 6) revel tht the stepwise crck front dvncement t 23 o C seems to occur t slower rte thn t 40 o C, s indicted y the spcing of the crck rrest mrkings present on the respective frcture surfces. It is evident tht the crck front in the cse of 40 o C is dvncing with lrger jump step thn t 23 o C. This mens tht when the crck growth rtes t given frequency re compred one should expect tht t higher test tempertures the crck growth rtes will e higher thn t lower test tempertures. The d/dn versus ΔK dt shown in Figure 2 (,, c) once gin confirm tht the frcture surfce morphology studies re in conformity with the ftigue crck growth test results. At higher tempertures the mteril ecomes less 6

7 resistnt to dvncing crck front nd promotes rpid crze formtion nd crze zone rupture thn it does t lower tempertures. When test temperture is further rised from 40 to 70 o C, the mteril loses much of its structurl integrity nd offers very little resistnce to crck growth process. The crck propgtes rpidly under crze growth dominnt process. The frcture surfce exmintion in Figure 7 provide cler evidence tht the mteril undergoes n pprecile therml degrdtion nd offers mrginl resistnce to ftigue crck growth t test temperture 70 o C. The crck growth rtes re thus expected to e the highest t 70 o C mong ll other test tempertures. The d/dn versus ΔK curves in Figure 2 shows this to e indeed true. SEM Frcture Surfce Anlysis SEM (Scnning Electron Microscopy) nlysis of the frcture surfce reveled the existence of severl chrcteristic fetures such s sher lips, conicl shped ptterns, nd discontinuous crck growth nds (DGBs) on the frcture surfces of the CPVC smples ftigued t different test tempertures nd test frequencies. The frcture surfce morphology indictes the presence of three different crck growth zones. The first zone, in the vicinity of the strter notch indictes tht the erly stges of crck growth occurs under sher yielding process s evidenced y the presence of sher lips (Figure 8). This sher yielding is expected in the vicinity of strter notch root due to the presence of high stress concentrtion, which is expected to exceed the yield strength of the mteril. After this initil crck growth under sher yielding process, the crck growth process chnges to growth y crzing process. This crck growth mode is mrked y the conicl shped ptterns found on the frcture surfce (Figure 9). Fig. 8. Sher yielding t the vicinity of the mchined notch in CPVC. () Smple ftigued t 0 o C nd 50 Hz, () smple ftigued t 23 o C nd 0.1 Hz. These conicl shped fetures result from the frcture of the crzed zone t its mid ri nd dvncement of the crck front. The reminder of the crck propgtion occurs through the primry nd secondry crze formtion nd crze zone firil rupture. Discontinuous crck growth nds (DGBs) indicting repeted crck rrests were lso noted on the frcture surfce. Such DGBs were minly found on the frcture surfce of smples ftigued t the test frequency of 50 Hz. Fig 10 shows the DGBs oserved on the frcture surfce of smples ftigued t 50 Hz t two different tempertures of 0 o C nd 40 o C. 7

8 Fig. 9. Crck growth y crzing process in CPVC. () Smple ftigued t 0 o C t 1 Hz, () smple ftigued t 23 o C t 1 Hz. Fig. 10. Discontinuous growth nds (DGBs) in CPVC smples ftigued t 50 Hz () 0 o C nd () t 40 o C. The existence of DGBs on the frcture surfce is suggestive of locl crck rrest nd results in incresed resistnce to crck propgtion. The density of the DGBs ws noted to increse with increse in tempertures from 23 to 70 o C. The crck propgtion rte is thus expected to decrese with increse in frequency t high tempertures, which confirms the d/dn vs ΔK results discussed erlier. Fig. 11. Ftigue strition in CPVC smple ftigued t () 23 o C nd () 70 o C. 8

9 The crck growth process in CPVC is however found to e different in two wys from other glssy polymers. First the crzing process tkes plce with miniml inelstic deformtion nd without noticele micro void formtion (cvittion) s found in other polymers such s polyethylene [5, 7]. The second difference is tht the frcture surfce in CPVC exhiits typicl ftigue stritions suggesting tht the crck growth in CPVC lso occurs through n incrementl crck growth with ech lod cycle much the sme wy s in metllic mterils. Figure 11 shows such stritions on the frcture surfce of CPVC smple ftigued t 23 nd t 70 o C t frequency of 1 Hz. It ws lso found tht the crck growth in CPVC tkes plce in discontinuous mnner involving repeted crck rrests in much the sme wy s the other glssy polymers. Fig. 12. Additive prticles providing the necessry stress concentrtion for the crze zone initition. () Smple ftigued t 50 o C nd frequency of 0.1 Hz, () smple ftigued t 50 o C nd frequency of 50 Hz. Another interesting nd worth noting oservtion is the role of the propriety dditive mteril prticles (which re usully dded y the mnufcturer to enhnce certin mechnicl properties of the polymeric mterils) in the crck growth process. In the present mteril these dditive mteril prticles plyed role of rittle second phse stress-riser prticles nd fcilitted crze initition. Thus in CPVC micro void formtion (cvittion) s necessry step towrd crze zone formtion ws no longer necessry nd the stress levels required for crze zone initition were provided y the dditive prticles, which cted s stress risers. The initition site of crze zone ssocited with these prticles cn ee seen on the frcture surfce of smple ftigued t 40 o C nd frequency of 0.1 Hz (Fig. 12 nd ). The remnnts of the firil structure of the crze zone points converge t the long needle like dditive prticles which were responsile for the crze zone initition. A chnge in the test temperture did not produce ny significnt chnge in the over ll crck growth mechnism in CPVC, which remined one of comintion of sher yielding nd crzing processes. Evidence of such mixed mode frcture process is provided in Figure 13. The temperture however plyed mjor role in determining the predomintion of one frcture mode over the other. An exmintion of Figure 13 shows tht sher yielding domintes the frcture process in CPVC t test tempertures of 0 o C nd 23 o C, while crzing plys secondry role t these tempertures. On the other hnd t 40 o C nd 70 o C, the ftigue crck growth process predominntly involves crzing process while sher yielding plys less 9

10 significnt role. Figure 13-c shows evidence of crze dominnt frcture process in CPVC smple ftigued t 40 o C. It cn thus e ssumed tht frcture mode trnsition from sher yielding dominnt process to crze formtion nd frcture dominnt process occurs in CPVC t tempertures ove room temperture (23 o C). c Fig. 13. Frcture surfce of smple ftigued t frequency of 1 Hz () t 0 0 C, () t 23 o C, nd (c) t 40 o C. Further hed from the notch re region the effect of temperture is once gin reflected y the difference in the mount of predominnce of one frcture mode over the other with temperture chnge. Figures 14 () nd () provide comprison of the sher deformtion/crze regions for two smples ftigued t the sme frequency (0.1 Hz) ut t two different tempertures of 23 o C nd 70 o C. Fig. 14. Frcture surfce of smple ftigued t () 23 o C nd frequency of 0.1 Hz, () 70 o C nd frequency of 0.1 Hz. 10

11 A comprtive exmintion of the two figures shows tht t 70 o C, the cellulr structure ppers considerly more drwn thn the ones oserved t 23 o C suggesting tht the frcture process t 70 o C is overwhelmingly controlled y the crze growth proly intercting with creep process, while t 23 o C the crze growth plys much less significnt role in the frcture process. Conclusions Ftigue crck growth rte tests for schedule 80 CPVC pipe coupling mteril hve een crried out t different tempertures nd frequencies. The nlysis of the test results leds to following conclusions: -The ftigue crck growth process in CPVC involves mixed mode sher yielding nd crzing processes. The initil frcture occurs through sher yielding, which is then tken over y frcture progress through crzing. -At test tempertures of 0 nd 23 o C, crck growth occurs predominntly under sher yielding, wheres t 40 nd 70 o C, crck growth y crzing is more fvored. -Tempertures ove 23 o C were found to e significntly detrimentl. The ftigue crck growth rtes incresed y fctor of lmost 5 t 40 o C nd y fctor of lmost 10 t 70 o C t 70 o C s compred to the crck growth rtes t room temperture (23 o C). -The frequency sensitivity of the ftigue crck growth ws noticele only t the temperture of 70 o C, where n increse in the frequency from 0.1 to 50 Hz led to decrese in the crck growth rte y lmost fctor of 4. -The crze zone formtion in CPVC is initited t the points of stress concentrtions provided y the dditive prticles. No micro void formtion (cvittion) ws oserved during the crck growth y crzing. Ftigue stritions were oserved in smples ftigued t high frequency of 50 Hz. Experimentl The specimens for monotonic nd ftigue crck growth testing progrms for CPVC were prepred from commercilly ville four inch injection molded couplings. 50- mm wide rings were cut from the couplings nd slit into two equl semicirculr hlves. The couplings were slit in such wy tht it eliminted the weldline from the test mteril. The hlf rings were heted t 105 o C in n electric oven for 20 minutes nd flttened under compression to otin flt pltes. Tensile tests on the smples from the heted nd flttened pltes nd on the ring type specimens from s received couplings were performed to find out whether or not the heting nd flttening process introduced ny chnges in the mteril properties. The results of these tests showed the mteril s tensile properties remined essentilly unchnged nd thus it ws sfely ssumed tht the heting nd flttening process did not lter the mteril in ny note le mnner. Rectngulr coupons hving dimensions of 40 mm x 180 mm x 9.4 mm were mchined from the flttened pltes. A shrp rzor lde ws used to mnully introduce through-thickness 1-mm deep rzor shrp strter notch t one edge of the coupons. It should e pointed out tht the 1-mm depth of the notch cted merely s crck strter notch nd this depth ws kept essentilly constnt in ll test coupons. An Instron mteril testing mchine ws used for ftigue testing. All tests were performed in lod control mode using sinusoidl wveform loding. Two to three tests were conducted t 0, 23, 40 nd 70 o C t three different frequencies of 0.1,

12 σ min nd 50 Hz. A stress rtio R (R= ) of 0.2, nd two stress rnges (Δσ) nd σ mx 11 MP were used. The men stress ws tken to e out 20 % of the yield strength of CPVC in order to keep σ mx elow 50 % of σ ys to minimize plstic yielding. A Questr QM-100 microscope with working rnge of cm nd resolution of 0.1 mm ws used to oserve the crck initition nd growth during the ftigue tests. For the long durtion low tempertures nd low frequencies tests, video recording system ws employed to record the entire crck growth process. Plexigls chmers were used for conducting non-mient temperture tests. The high temperture environmentl chmer ws designed to mintin tempertures up to 150 o C for extended periods of time. The chmer for low temperture testing circulted refrigernt solution through copper tuing plced inside the chmer. A window (30 mm x 60 mm) llowed opticl oservtion nd mesurement of the crck. The frcture surfce morphology of the filed specimens ws studied using Joel JSM scnning electron microscope. Acknowledgements The uthors wish to thnk the University of Petroleum & Minerls nd Sudi Arin Bsic Industry (SABIC) for supporting this reserch through Fst Trck reserch grnt. References [1] Hu, Y.; Summers, J.; Hiltner, A.; Ber, E. J. of Mterils Science, 2003, 38, [2] Kim, H.; Truss, R. W.; Mi, Y.; nd Cotterell, B.; Polymer, 1988, 29, [3] Wei, R.; Wng, X. ANTEC, 1997 Plstics: Plstics Sving Plnet Erth, 3, [4] Phu, S. K.; Lwrence, C. C.; Potter, R. J. of Mterils Science, 1998, 33, [5] Brough, I.; Hwrd, R. N.; Hely, G.; Wood, A. Polymer, 2004, 45, [6] Kim, H. S.; Wng, X. M. J. of Mterils Science, 1994, 29, [7] Prson, M.; Stepnov, A.; Hiltner, A.; Ber, E. J. of mterils Science, 2001,36, [8] Kim, H. S.; Wng, X. M. J. of Applied Polymer Science, 1995, 57, [9] Ferrer-Bls, D.; Mspoch, M., L.; Mi, Y. Polymer, 2002, 43, [10] Beech, S. H.; Mllinson, J. N. Plstics, 1998, 27, [11] Merh, N.; Irfn-ul-hq, M.; Khn, Z. J. of Mterils Processing Technology, 2003, 142-1, [12] Merh, N.; Sghir, F.; Khn, Z. Bzoune, A. Engineering Frcture Mechnics, 2005, 72/11, [13] Sghir, F.; Merh, N.; Khn, Z.; Bzoune, A. Journl of Mterils Processing Technology, 2005, , [14] Merh, N.; Irfn-ul-Hq, M.; Khn, Z. Effect of injection molding weld on ftigue crck resistnce of CPVC t different tempertures. In Proceedings of AMPT2003, Dulin, Irelnd, [15] Merh, N.; Irfn-ul-Hq, M. Khn, Z. Journl of Mterils Processing Technology, 2004, ,

13 [16] Khn, Z.; Merh, N.; Mzghni, K.; Budir, M. O.; Youns, M.; Olisi, O. Ftigue Resistnce of CPVC Pipefittings, Proc. 9 th Middle Estern Corrosion Conference, Fe , 2001, Mnm, Bhrin. [17] Merh Z.; Khn, K.; Mzghni, M.; Budir, O.; Youns, M.; Olisi, O. Ftigue Crck Propgtion in Injection Molded CPVC Pipefittings, Proc. 9 th Middle Estern Corrosion Conference, Fe , 2001, Mnm, Bhrin, [18] Mzghni, K., et. l., Frcture nlysis of crck growth in CPVC pipe fittings t different tempertures, Proc. Polymer Processing Society, June 16-20, 2002, Guimroes, Portugl. 13