PHOTONIC SENSORS / Vol. 4, No. 3, 2014: 236 241 Long-Term Mechanical Propertie of Smart Cable Baed on Deenitized Encapulation Senor Sheng LI 1* and Min ZHOU 2 1 National Engineering Laboratory for Fiber Optic Sening Technology, Wuhan Univerity of Technology, Wuhan, 430070, China 2 Wuhan WUTOS Limited Company, Wuhan, 430223, China * Correponding author: Sheng LI E-mail: liheng@whut.edu.cn Abtract: In order to enure the teting range and long-term reliability of the fiber Bragg grating () ued for the mart cable, a mart cable embedded with train enor baed on the deenitized encapulation tructure wa deigned. For a mart cable pecimen, the fatigue loading experiment with the cycle from 100 thouand to 2 million and 0.95 time nominal breaking cable force (P b ) were carried out, which teted the long-erving effect of the mart cable. The tet reult of the tatic tenion loading and unloading during the tepwie fatigue cycle proce howed that the encapulated train enor had the good linearity and repeatability. Alo all enor urvived after 2 million time fatigue cycle. 0.95P b tatic tenion tet howed that the encapulated train enor embedded inide the cable reached 4.5% teting accuracy in the 0.86P b working range. After 0.95P b tatic tenion tet, the diection tet wa carried out by breaking the force tenion. The reult howed that the appearance of the encapulated enor were good, and the deign tructure were not changed and damaged. Keyword: Smart cable, fatigue experiment, fiber Bragg grating, force monitoring, bridge engineering Citation: Sheng LI and Min ZHOU, Long-Term Mechanical Propertie of Smart Cable Baed on Deenitized Encapulation Senor, Photonic Senor, 2014, 4(3): 236 241. 1. Introduction Forming a mart cable by embedding optical fiber enor inide a cable in the fabricating tage ha been widely reearched. The fiber Bragg grating () enor [1, 2] i a mainly ening mean for the mart cable [3 5]. Alo there are ome tudie on the mart cable by the Brillouin ening technique [6]. The difficultie in the -baed mart cable are to increae the reliable train range which require for 5000 με [7], cloe to the rupture limit train of the naked [8], and the compatibility proce requirement hould conform to the conventional cable manufacturing procee. The exiting reearch on the mart cable mainly focue on the hort-term property performance by the tatic loading tet and i lack of the conideration of the long-term propertie. In order to meet the large train working range of the cable in the over tenioning tage and the maximum combined load in the operational tage, an deenitized encapulation enor wa tudied for olving the range problem effectively. In addition, baed on Chinee code [9] about the fatigue requirement for the teel wire of the cable, 2 million time fatigue cycle experiment and Received: 2 April 2014 / Revied verion: 22 May 2014 The Author() 2014. Thi article i publihed with open acce at Springerlink.com DOI: 10.1007/13320-014-0191-2 Article type: Regular
Sheng LI et al.: Long-Term Mechanical Propertie of Smart Cable Baed on Deenitized Encapulation Senor 237 0.95 time nominal breaking cable force (P b ) loading experiment were carried out for a pecimen mart cable. 2. Structure of the mart cable 2.1 Sening principle For the traditional ingle teel tube encapulation tructure, the cooperative deformation between the teel tube and the teting object occur prior to the deformation of the driven by the encapulated teel tube. So when ubjected to the large tre, the train tranfer proce uually cannot totally finih due to the reaon that enor pedetal fatened to the teel wire may break off the encapulation tructure. So a hown in Fig. 1, the i mainly encapulated by three-egment teel tube. The boundary of the teel tube in the middle only faten one ide, and the other ide i completely free. The train tranfer pathway of the encapulation tructure can be expreed a: teel wire of the cable adheive pedetal fiber optical fixed-point at the end. In eence, the middle teel tube only protect the from the lateral load and the impact of the hear force. And after the tranfer through the pedetal, the directly bear the tenile train. Set that L delegate the ditance between two pedetal and the ditance between two optical fiber fixing point, repectively. When the teel wire tenile deformation occur, the deformation coordination relationhip between the teel wire train ε and the optical fiber train ε f can be expreed a εl = ε L. (1) f Thu, the train enor enitivity can be adjuted by etting different ratio of L. When L > L, the train enitivity of the wavelength drift decreae compared to the teel wire train, which achieve the enor deenitization. Chooing the proper ratio of L can enure the reliable tet range requirement of the enor under the ervice load of the cable. 2.2 Deenitized tet Three pecimen of the propoed enor with different ratio of L were ued for the tenion tet baed on the ingle teel wire in the laboratory. A hown in Table 1, the experimental reult of the three pecimen howed that the actual value calculated from the tenion tet were a little bigger than the theoretical value due to the tranmiion force influence of the adheive between the pedetal and teting teel wire. However, three pecimen all achieved the aim of deenitization. The actual train enitivity coefficient were all le than the theoretical value of the naked, namely le than 1 pm/με. Taking the bet deenitized effect of the 3rd length for example a Fig. 2, three pecimen all had the good repeatability. And the fitting linear correlation all exceeded 0.99. Tabl e 1 Strain enitivity coefficient of different tructure dimenion enor (unit: pm/με). Strain enitivity coefficient 1t pecimen 2nd pecimen 3rd pecimen Theoritical value 0.679 0.593 0.519 Actual value 0.724 0.654 0.559 Fig. 1 Layout of train enor. Fig. 2 Load veru wavelength relationhip curve of the 3rd pecimen.
238 Photonic Senor 2.3 Fabrication cheme The fabrication cheme of the mart cable mainly contained eight tep, which were depicted in Fig. 3. To avoid the effect of the high temperature epoxy tuffing on the fiber, the fifth tep wa arranged after the fourth tep. In the fifth tep, the enor were fatened to the periphery teel wire of the cable in the connection pipe region. The layout of the enor in the mart cable i hown in Fig. 4. The reerved channel in the firt tep provided the through pace for teel tube which gave the protective meaure to the output optical fiber. The calibration tet of the mart cable wa the lat tep, which utilized the over tenioning tet procedure for every cable. with the help of Jiangu FASTEN Group Company (teel wire nominal trength σ b =1670 MP a ). The mart cable embedded five deigned train enor and one temperature enor ued for the temperature compenation. The main purpoe of the tet wa to check the long-term mechanical propertie of the mart cable baed on Chinee code about fatigue requirement for the teel wire of the cable. Fig. 3 Fabrication cheme of mart cable with enor. Fig. 4 Layout of the enor in one mart cable. 3. Mechanical property teting 3.1 Object and purpoe A hown in Fig. 5, a 3.5-meter-length mart cable with the 85φ7 mart cable wa fabricated Fig. 5 Smart cable tet pecimen. 3.2 Method and tep The whole tet proce i hown in Fig. 6, and before the fatigue tet, the force enitivity coefficient reference wa etablihed by the two-cycle loading and unloading tenion tet with 300 kn load interval from 300 kn to 2100 kn. Due to different actual intallation location, the force enitivitie to the teel wire train of five enor were different, a hown in Table 2. However, both the linear correlation and repeatability of all enor were good. Figure 7 preent the load veru wavelength relationhip curve of 1# enor. According to the code, the upper limit of the fatigue tre wa et at 668 MPa (0.40σ b ), and the tre range Δσ wa et at 200 MPa. The tatic loading tenion tet with 0.4P b range were carried out after every tage fatigue cycle experiment adopted by ine wave load with the 2-Hz frequency, which ued for tracking the tability of the mart cable output ignal and analyzing the force enitive coefficient time varying trend. In addition, after 2 million time
Sheng LI et al.: Long-Term Mechanical Propertie of Smart Cable Baed on Deenitized Encapulation Senor 239 fatigue cycle, 0.95P b range tatic tenion and breaking force tenion tet were carried out for checking the maximum working range of the mart cable and the appearance tate of the deigned enor inide the cable. tep output cable force under 0.4P b range tatic loading tenion tet were hown in Table 3 and 4. The maximum force error between the loading and teting did not beyond 50 kn and 200 kn before and after the fatigue experiment. Tabl e 3 Force of the mart cable before fatigue (unit: kn). Cae 1t loading 1t unloading 2nd loading 2nd unloading 600 620.1 599.5 648.6 590.6 900 938.2 889.3 948.9 887.0 1200 1228.1 1175.1 1240.6 1167.7 1500 1517.6 1466.2 1524.8 1478.0 1800 1804.5 1772.9 1814.1 1777.8 2100 2109.3 2109.3 2107.5 2107.5 Fig. 6 Teting proce for mart cable. Tabl e 2 Force enitivity coefficient reference of each enor (unit: kn/pm). Senor 1# 2# 3# 4# 5# Force enitivity coefficient 1.947 1.363 1.174 1.622 1.656 Tabl e 4 Force of the mart cable after fatigue (unit: kn). Cae 1t loading 1t unloading 2nd loading 2nd unloading 600 465.9 448.2 458.2 454.1 900 842.1 826.4 837.5 806.7 1200 1210.6 1191.7 1214.9 1186.9 1500 1589.6 1559.5 1586.6 1564.5 1800 1923.0 1941.9 1935.0 1927.1 2100 2276.7 2298.1 2285.6 2299.7 The force error were caued by the change in the force enitivity coefficient during the fatigue cycle proce. Figure 8 how the development trend of the enor force enitive coefficient calculated from the relationhip between the teting load and enor wavelength. Fig. 7 Load veru wavelength relationhip curve of 1# enor. 3.3 Reult and analyi All deigned enor urvived after 2 million time fatigue cycle. The force of the mart cable wa delegated by the cable force output average of five deigned train enor which conidered the temperature compenation and took the tatic tenion train enitivity coefficient before the fatigue experiment a the calculation bai. Before and after 2 million time fatigue, the reult of every Fig. 8 Development trend of enor force enitive coefficient. After 2 million time fatigue cycle, 0.95P b tatic tenion tet wa carried out. Table 5 how the maximum working range of five deigned
240 Photonic Senor enor. During the tatic tenion proce, 1# 3# enor all urvived, while 4# enor wa failure at 0.8627P b (a hown in Fig. 9) and 5# enor wa failure at 0.89P b. So the maximum working range of the mart cable could be et at 0.86P b. The cable force teting accuracy change during the fatigue cycle proce i hown in Fig. 10 baed on (2). With an increae in the fatigue cycle, the teting accuracy decreaed gradually. After 2 million time fatigue cycle, the accuracy till reached 4.5%. Accuracy = m axim um error / range 100%. (2) Table 5 Senor teting range. Senor No. 1# 2# 3# 4# 5# P b (%) 0.95 0.95 0.95 0.86 0.89 Fig. 9 Wavelength drift of 4# enor during the tenion loading proce. Fig. 10 Cable force teting accuracy change during the fatigue cycle proce. There wa no break of the mart cable after 0.95P b tatic tenion tet. The appearance inpection reult after unloading howed that the anchorage and cable were both in good condition. According to the breaking force tenion, the diection for the mart cable wa finihed. A hown in Fig. 11, by appearance checking, the encapulated enor under the protective hield were good, and the deigned tructure were not changed and damaged compared to the intallation tage. Fig. 11 Senor appearance contrat between the intallation and diection tate. 4. Concluion The -baed mart cable i a meaningful mart tructure. The deenitized encapulation olve the large train meaurement problem when uing the enor. The propoed cable fabricating cheme can enure a high urvival rate for the enor. The fatigue experiment reult howed that after long-term loading the mart cable had 4.5% teting accuracy in the 0.86P b working range. The breaking force tenion and diection experiment verified the long-term effectivene of the deigned enor and intallation tructure. The propoed tudy plan baed on fatigue code requirement for the teel wire of cable can provide a reference for tudying the long-term mechanical propertie of other type of the mart cable tructure. Acknowledgment The reearch work reported in thi paper wa jointly upported by the National Engineering Laboratory for Fiber Optic Sening Technology, Wuhan Univerity of Technology, China and FASTEN Group Company. Thank to the upport of Wuhan City Building Reearch Fund (201310), the Fundamental Reearch Fund for the Central Univeritie (WUT: 2014-IV-090), and the National Natural Science Foundation of China (Major Program: 61290310). Open Acce Thi article i ditributed under the term of the Creative Common Attribution Licene which permit any ue, ditribution, and reproduction in any medium, provided the original author() and ource are credited.
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