Bolt stress inspection by Electromagnetic Acoustic Transducer(EMAT) and PZT

Transcription

1 Bolt tre inpection by Electromagnetic Acoutic Tranducer(EMAT) and PZT Y.P. Shen 1, G.B. Ma 2,3, C. Ma 2, X.X. Zhu 1 and J.H. Zhao 1 More info about thi article: Abtract 1 Phaerie Technology Co., Ltd., Suzhou, China. yp@phaerie.com 2 CGN Inpection Technology Co., Ltd., Suzhou, China 3 Southeat Univerity, Nanjing, China. The paper document a practical method and procedure for bolt tre inpection by electromagnetic acoutic tranducer(emat) and piezoelectric tranducer(pzt). The longitudinal and hear ultraonic wave velocitie of a particular type of bolt are calibrated. The linear coefficient of acouto-elatic effect along bolt axi on both longitudinal and tranvere ultraonic velocitie are calibrated with a tenile machine. With the calibrated parameter, the preload of a bolt with unknown-length are inpected by a portable high power ultraonic equipment PREMAT HS2 and verified by a tenile machine. 2% accuracy or better of tre inpection i achieved for branded bolt. The ource of error are analyzed and dicued. Keyword: Bolt tre; EMAT; high power ultraonic inpection; 1 Backround Bolt preload are traditionally inpected by torque wrench. But in many cae the relationhip between the bolt preload and the torque are far from linearity in practice. Ultraonic inpection of bolt pretenion are tudied by many cientit and engineer. PZT method wa firt developed to inpect the bolt preload by meauring the longitudinal tranition time. Hirao [1] developed EMAT method to meaure the axial tre of a bolt. Jhang [2] and Ding [3] developed mode converted longitudinal wave and mode converted tranvere wave method, repectively, without knowing the initial tate like the length of the bolt. Due to the difficultie of manufacture of acoutic len for longitudinal wave probe and the low efficiency for generating&receiving longitudinal wave in teel by EMAT, the mode-converted method entail weak ignal of converted mode in practical ue. Thi paper employ a PZT tranducer and an EMAT tranducer to get the ultraonic wave tranition time of a preloaded bolt, repectively. PZT probe i eay to generating longitudinal wave, an EMAT get advantage to generate tranvere wave. The trong S/N ratio enure a high accuracy meaurement of the longitudinal wave and hear wave tranition time. [ID29] 1

2 2 Stre-train and acouto-elaticity According to Hook law, the total length of the bolt l under uniformal axial tre i given by, l l( 1 ) 1 l (1) E where l i the original length, E i the Young modulu, i the train. We take the empirical formula of the effective length l eff a the clamping length plu the nominal bolt diameter. Thi empirical etimate i with good accuracy for bolt length greater than 1mm. A illutrated geometry in Figure 1, we have l a b c d (2) l eff b (3) l where i the nominal diameter of the bolt, i the effective length coefficient. Figure 1: Schematic diagram of a bolt Ultraonic hear wave velocity tre. i.e. v along the bolt axi ha been found linearly affected by applied axial v v (1 ) (4) where v i the untreed hear wave velocity and i the acouto-elatic coefficient. The puleecho time of flight TOF for the hear wave i given by, [ID29] 2

3 TOF 2l v 2( l l v eff ) 2l v eff 2( l l) 2l (1 / E) TOF v v (1 ) 1 (1/ E ) (5) Where the ubcript denote the untreed tate. Taylor erie approximation i ued becaue i uppoed very mall compared to unit 1. Equation (5) can be reformed to, TOF TOF 1 1 (6) E The acouto-elaticity coefficient can be calibrated in a tenion machine according to equation (6). We have the longitudinal wave acouto-elatic relationhip a, v l v (1 ) (7) l where ubcript l denote longitudinal wave and i the acouto-elatic coefficient for longitudinal wave along the tre axi. In the ame analyi way we have the calibration equation for a, TOFl TOFl 1 1 (8) E Combining equation (6) and equation(8) lead to the expreion of the tre of a bolt without knowing the original length, TOF v TOF v l l (9) 1/ ETOF l vl 1/ ETOF v Where TOF 2l / v and TOF l 2l / vl are ued. The variable in equation (9) are material property related contant v, v l,, and meaurable parameter, Young modulu can be derived from the longitudinal and hear wave velocitie. TOF and TOF l. The For PZT tranducer, the meaured TOF l include the round trip time of the wedge and couplant. Thi i a tranducer mot-related contant that need to be calibrated and excluded before applying equation (9). [ID29] 3

4 3 Experiment The length of bolt to be calibrated for the velocitie i meaured by a vernier caliper with.1mm -8 accuracy. The round trip time of PZT wedge and couplant i calibrated a by a tandard calibration block with max thickne of 48mm. The tenion machine model i MTS(5KN) a hown in figure 2. The ultraonic equipment for the velocity calibration and tre meaurement i PREMAT- HS2 with ampling rate of 1MSP and 12bit a hown in figure 3. The equipment can be hooked with both EMAT and PZT. The bolt elected are model M according to code GB/T with different length. The compoition of the bolt i alloy type 42CrMo according to the mentioned tandard. One group of bolt i for calibration purpoe and another group i for tre meaurement in treed tate with the tenion machine. The bolt to be inpected are tamped with brand on the bolt head. Figure 2: Tenion machine MTS(5KN) for acouto-elatic contant calibration. [ID29] 4

5 Figure 3: High power ultraonic equipment PREMAT-HS2 for EMAT and PZT meaurement of bolt parameter calibration and tre aement. 4 Reult and dicuion A an example, Figure 2 how the calibration curve of acouto-elatic contant in a tenion machine for an M bolt. The loaded tre i from to 3MPa with tep of 5MPa. The lope of the linear trend line in figure 4 i ued to calibrate the contant according to equation (8). All the calibrated contant are lited in table 1. [ID29] 5

6 TOF(.1u) 15 th Aia Pacific Conference for Non-Detructive Teting (APCNDT217), Singapore y =.1796x R 2 = Stre(MPa) Figure 4: Acouto-elatic contant calibration of longitudinal wave. v (m/) v l (m/) E(GPa) (1-12 Pa -1 ) (1-12 Pa -1 ) Table 1: Calibrated material property related contant. In the ame tenion machine, another elected bolt wa treed from to 3MPa with tep of 5MPa. In every round, a PZT tranducer and an EMAT tranducer were placed on the end of the bolt to record the table time of flight value TOF l and TOF, repectively. The derived tre according to equation (9) were compared to the value from the tenion machine a hown in figure 5. In thee meaurement, the original length of the bolt i not necearily known. The maximum difference between the meaured tre and the et tre i 2% or 2MPa in abolute value. [ID29] 6

7 Figure 5: Stree meaured from utraonic inpection compared to the et value of the tenion machine. Becaue of no couplant and wedge needed for EMAT meaurement, the hear wave time of flight i critical to narrow down the range of the untreed length. From table 1 we know the acouto-elatic contant of longitudinal wave i much larger than that of hear wave. Thi mean the error of the meaured tre i mainly dependent on the meaurement accuracy of longitudinal wave time of flight. A nano-econd TOF mearurement error of a longitudinal wave will reult in the magnitude of 1MPa tre error. A firmly clamp of PZT in meaurement are highly recommended to reduce the uncertainty of the couplant thickne. Xu [4] found the acouto-elaticity of a bolt under tre i not in good linearity in a large range of the applied tre. The non-linearity of the applied tre and the meaured TOF can be alo een from figure 5. Thi may be one of the factor that caue the inpection error. The end of ome bolt are found to be tamped with brand. Thi out-of-flatne cattering will reult in big difficulty on identifying the accurate TOF becaue it hift the phae of the pule echo ignal every round. The tre ditribution of the bolt i another factor that make meaurement error. Different tre ditribution model will reult in different effective length coefficient value in equation (9). For long bolt like greater than 1mm, the effective length coefficient error eem not the major error ource for the final tre meaurement error. 4 Concluion [ID29] 7

8 Thi paper document a practical method and procedure for bolt tre inpection by electromagnetic acoutic tranducer(emat) and piezoelectric tranducer(pzt) with a portable high power ultraonic equipment. The longitudinal and hear ultraonic wave velocitie, a long a the Young modulu, of a particular type of bolt are calibrated. The linear coefficient of acouto-elatic effect along bolt axi on both longitudinal and tranvere ultraonic velocitie are calibrated with a tenile machine. With the calibrated parameter, the preload of a bolt with unknown-length are inpected by a portable high power ultraonic equipment PREMAT HS2 and verified by a tenile machine. In practical tre inpection of branded bolt, 2% accuracy or higher i achieved. The ource of meaurement error are analyzed and dicued. Reference [1] M. Hirao, H. Ogi and H. Yaui, Contactle meaurement of bolt axial tre uing a hearwave electromagnetic acoutic tranducer, NDT & E International, Volume 34, Iue 3, pp , 21 [2] K.Y. Jhang et al., Etimation of clamping force in high-tenion bolt through ultraonic velocity meaurement, Ultraonic, Volume 44, Supplement, pp. e1339-e1342, 26 [3] X. Ding, X. Wu and Y.G. Wang, Bolt axial tre meaurement baed on a mode-converted ultraound method uing an electromagnetic acoutic tranducer, Ultraonic, Volume 54, Iue 3, pp , 214 [4] C.G. Xu et al., Ultraonic inpection method of bolt tenile tre, Journal of Applied Acoutic, Vol. 33, No. 2, Mar., 214 (in Chinee) [ID29] 8