Available online at ScienceDirect. Procedia CIRP 29 (2015 ) The 22nd CIRP conference on Life Cycle Engineering

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1 Available online at ScienceDirect Procedia CRP 29 (2015 ) The 22nd CRP conference on Life Cycle Engineering A Study of Fatigue Remaining Useful Life Assessment for Construction Machinery Part in Remanufacturing Yaozhong Wu a, Weijia Li a, *, Ping Yang a a School of Naval Architecture and Ocean Engineering, Huazhong University of Science and Technology, Wuhan , China * Corresponding author. Tel.: ; address: liweijia@hust.edu.cn Abstract Remanufacturing is the process of returning a worn-out product to an as new condition. For large construction machinery parts with cracks, which are highly value-added, costly, and complexly processed, it is critical to assess the fatigue remaining useful life (RUL) for the following remanufacturing strategy. n this study, a simulation method based on the step-by-step finite element (FE) analysis is presented. The crack life and path are assessed by the linear elastic fracture mechanics theory. Furthermore, the substructure modeling technical is adopted to take account of the influence of structural details and loading shedding during crack growth. For a further step, the method is applied to concrete pump truck boom structure to investigate fatigue crack growth remaining lives and paths The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the nternational Scientific Committee of the Conference 22nd CRP conference on Life Cycle Peer-review Engineering. under responsibility of the scientific committee of The 22nd CRP conference on Life Cycle Engineering Keywords: Remanufacturing; Remaning useful life assessment; Linear elastic fracture mechanics 1. ntroduction Remanufacturing is an important method of processing worn-out electromechanical equipment to realize the development strategy of sustainable economy. And the use of remanufacturing can save resources and reduce environment pollution [1]. n remanufacturing engineering, the parts of worn-out products, which have been served one or more life cycle, are used as remanufacturing blanks. Because the service conditions of remanufactured blanks may be complicated, the remaining useful life (RUL) assessment is more difficult than for the original parts [2]. For example, it is not easy to estimate whether the worn-out parts have RUL and it is even more difficult to see whether the RUL can serve the next life cycle. These above two factors have directly affect the following remanufacturing strategy and the quality of remanufactured products. t is known that large construction machinery such as concrete pump truck, the booms and other parts are typically welded steel plate box girder structures. After these machines served for one or more life cycle, cracks will found at the spot of welding or stress concentration. Thus, fatigue RUL assessment of the parts with cracks which are detected by the non-destructive testing is important for remanufacturing. Recently, several research groups have been reported the development of RUL assessment in remanufacturing. For instance, Mazhar M [3] and Zhang X [4] reported that the RUL is a function of the part s overall life and the actual life. n their report, the Weibull analysis is adopted to estimate the overall life. An artificial neural network (ANN) model is developed to analyze the part s actual life. Hu Y [5] proposed a support vector machine (SVM) model to estimate the RUL of worn-out parts. n her research, the system performance was assumed to follow a Gaussian distribution. And the online sensors are used for updating the performance variables to obtain RUL assessment for current and future time points. By applying non-destructive testing, the fatigue damage can be detected. Dong L [6] used the metal magnetic memory testing (MMMT) to monitor fatigue propagation. This is because that crack can induce spontaneous abnormal magnetic signals in ferromagnetic material. A preliminary relationship between peak-to-peak value H p (y) of magnetic abnormal peak and fatigue crack length was proposed. HUANG H [7] The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the scientific committee of The 22nd CRP conference on Life Cycle Engineering doi: /j.procir

2 Yaozhong Wu et al. / Procedia CRP 29 ( 2015 ) presented the relationship between gradient K max of magnetic memory signals of crack tip and its stress intensity factor K. Physical and mechanical methods can quantitatively feature the behavior of failure mode using physical models of parts. ZHANG G [8] calculated the fatigue life of crankshaft of a six-cylinder engine using a different damage model such as S- N method, normal strain approaches etc. Firstly, the load histories were calculated based on finite element (FE) analysis. Then, the fatigue life can be predicted using different damage models according to the strain-stress histories. n order to help manufacturers make full use of worn-out parts and optimize the remanufacturing process, this study proposes a simulation method for RUL assessment. This simulation method is based on the fracture mechanics theory, and can manage the parts with cracks. Fatigue crack growth is simulated through a step-by-step FE analysis approach. The fatigue RUL can be assessed by taking account of the influence of fatigue load, stress ratio and crack growth rate. A case study on concrete pump truck boom structure is also presented to illustrate the feasibility of this method. t is hopefully to be realized in future remanufacturing domain. 2. Methodology 2.1. Crack growth rate law Based on linear elastic fracture mechanics theory, the fatigue life can be determined by crack growth rate law. n this study, the following crack growth law is used as following equation [9,10], da m m C UKeff Keff (1) dn th where a is the crack length, N is the fatigue crack growth life, C and m are material constants to be found experimentally, and Keff is the threshold range of stress th intensity factor, Keff is equivalent stress intensity factor range, can be obtained by K K K K (2) eff where K, K and K are stress intensity factors for Mode, Mode and Mode, respectively; and U is the effective stress range ratio, which is given by R R R 1 1/ U where R is the stress ratio Calculation of stress intensity factor The assessment fatigue RUL method by crack growth rate law requires an appropriate method to determine the stress intensity factors. n this study, the stress intensity factors are (3) computed using domain forms of the interaction integrals which adopted by ABAQUS [11-13]. n general, the J-integral for a given problem can be written as J B11 K 2K B12 K 2K B13 K 8 (4) terms not involving K where B is the pre-logarithmic energy factor matrix. Define the J -integral for an auxiliary, pure Mode, crack-tip field with stress intensity factor k, as 1 1 Jaux k B11 k (5) 8 Superimposing the auxiliary field onto the actual field yields 1 J K k B K k 2K k B K tot K k B K K k 2 terms not involving or 13 (6) Since the terms not involving K or k in J tot and J are equal, the interaction integral can be defined as k Jint Jtot J Jaux B11 K B12 K B13 K (7) 4 Repeated for Mode and Mode, the interaction integral can be written as k (8) 4 1 Jint B K, no sum on,, f the k are assigned unit values, the solution of the above equations leads to K B J (9) 4 int T where J int Jint, Jint, J int. Similar to the calculation of the J-integral, the interaction integrals J int can be calculated through ABAQUS FE analysis. n most cases, modelling the region close to crack tip with collapsed elements often improves the accuracy of the stress intensity factors because the stresses and strains in the region are singularity. Taking the 4-node isoparametric element as an example, the collapsed quadrilateral elements can be obtained as shown Fig. 1. Collapse one side of an isoparametric element so that all nodes a and b have the same geometric location. The crack tip is modelled with a ring of collapsed quadrilateral elements, as shown in Fig. 2.

3 760 Yaozhong Wu et al. / Procedia CRP 29 ( 2015 ) a b -1-1 h 1 isoparametric space g a, b r physical space Fig. 1. Collapsed 4-node isoparametric element. Crack Crack front node set Collapsed elements [11], and it can be connected to the crack growth domain by the retained degrees of freedom at the retained nodes. n this way, the FE analysis can be achieved with less computing time. 3. Simulation method n this section, a simulation method, which is based on the step-by-step FE analysis, is introduced to give an accurate assessment of the crack growth life in the construction machinery structures. The flow chart of the simulation method is illustrated in Fig. 3. The global FE model is built up using the substructure technique. n each step, the crack growth domain is defined in conjunction with the collapsed elements. The stress intensity factors are computed by ABAQUS. Then, the crack tip is moved to a certain point on the predicted path, which is determined by the maximum circumferential stress criterion. The crack growth life is assessed by computing the equivalent stress-intensity range along the simulated crack path, and the procedure will be repeated until the structure failure. Pre-Processor ABAQUS/CAE Fig. 2. Mesh pattern in the crack tip Definition of the crack growth domain Generation of substructure of surrounding domain 2.3. Crack growth criterion Under general mixed-mode loadings, the direction of crack growth is determined by the crack growth criterion. Several crack growth criterions have been proposed: (1) the maximum energy release rate criterion, (2) the maximum circumferential stress criterion or the maximum principal stress criterion and (3) the minimum strain energy density criterion. n this study, the maximum circumferential stress criterion is used [11]. n polar coordinates r,, the crack will propagate from its tip in a direction so that the circumferential stress is maximum. The can be calculated by 3K K 8K K arccos K 9K (10) where K and K are stress intensity factors for Mode and Mode, respectively. 0 represents the crack propagation in the original direction. 0 if K 0, while 0 if K Substructure n order to simulate realistic fatigue crack growth in largescale structures, the substructure technique is introduced. Thus, the geometrical details and load shedding are taken into considerations. n this study, the analyzed structure is divided into two domains: (1)the crack growth domain and (2)the substructure domain. The substructure can be defined through ABAQUS 4. Case study Mesh generation FE-Analysis Stress intensity factor calculation K eff K C No Structure failure Crack growth analysis Yes Updating crack geometry Crack path prediction Crack growth calculation Crack growth life Fig. 3. Flow-chart of the simulation method Concrete pump truck is a powered mechanical device typically used to pump the concrete to a specify location. The main components of Concrete pump truck consisted of the pump system, the boom system and the truck chassis are shown in Fig.4. The key parts such as boom structures that typically high strength steel plate welded box girder structures, are often highly value-added, costly, complexly processed.

4 Yaozhong Wu et al. / Procedia CRP 29 ( 2015 ) This study takes the boom structure as an example to simulate fatigue crack growth to determine its RUL Problem statement n this study, fatigue cracks initiate at welding spot of the intersection of top plate and side plate close to the cylinder bearing and propagate in the top plate and side plate independently. The cracks are considered to be through-thethickness during the crack growth process. Depending on the non-destructive testing, the initial cracks are set to 5mm in the side and top plate. The properties of the high strength steel and parameters of crack growth law are list in Table 1. The parameters of crack growth law are determined through fatigue experiment. n ABAQUS, the globe FE model of boom structure is built up through substructure technique, as shown in Fig. 5(a). Crack growth domain is defined by shell elements, as shown in Fig. 5(b). can grow sharply when the crack was propagated to a considerable length. When the ranges of stress intensity factor reach the value of fracture toughness, the structures would be failure. n this way, the RUL assessment could be straightforward. Once the RUL of a remanufacturing blank is evaluated, the remanufacturing strategy for a blank can be decided by taking the optimum utilization of the blank s RUL before the process of remanufacturing [14]. For example, when the blank s RUL is longer than the product s service life which was predefined by the manufacturer, the blank can be used without remanufacturing. When the blank s RUL is less than product s service life, the remanufacturing technique like repair and crack arrest is recommended to prolong the blank s RUL. When the blank s RUL is considerably less than product s service life or the blank has no RUL, the best strategy for this blank could be recycling for the available material for reuse Results and analysis Fig. 6 shows the propagation of the fatigue cracks during the simulated process. The two crack tips on the top plate and side plate propagated simultaneously. This would weaken the section strength of boom structures. Fig. 7 shows the calculated ranges of stress intensity factor against the corresponding crack length in top plate and side plate, respectively. t is clear that the ranges of stress intensity factor are increased with the crack length because of the stress concentration at the crack tip. Fig. 8 show the simulated crack growth lives against the corresponding crack length. t is found that the fatigue cracks Table 1. Material properties and parameters for crack growth law. 1.Pump system 2.Truck chassis 3.Boom system Fig. 4. Concrete pump truck Young s modulus 210GPa Poisson s ratio 0.3 Threshold range of stress intensity factor 2.9 MPa m Fracture toughness 121 MPa m Parameters for the crack growth law C= , m=2.42 (stress in MPa, length in m) a Crack area b Crack tips Top plate Side plate Fig. 5. Analysis model of boom structure. (a) global FE model of hull boom structure; (b) crack growth domain

5 762 Yaozhong Wu et al. / Procedia CRP 29 ( 2015 ) a b Fig. 6. llustration of finite element model and crack geometry. (a) step 13; (b) step Top plate Side plate Range of SF(MPam 1 /2) Crack length(mm) Fig. 7. Ranges of stress intensity factor 5. Conclusion A simulation method has been proposed to assess the RUL of concrete pump boom structures for remanufacturing based on fracture mechanics theory. The crack growth process was simulated through a step-by-step FE analysis. The method for calculation the stress intensity factors using forms of interaction integrals through ABAQUS. Furthermore, the

6 Yaozhong Wu et al. / Procedia CRP 29 ( 2015 ) Top plate Side plate Crakc leghth(mm) Number of cycles x 10 6 Fig. 8. Simulated crack growth lives. crack growth paths and lives were predicted by maximum circumferential stress criterion and crack growth rate law, respectively. The substructure technique is integrated in the simulation method to take the influence of structural details and load shedding during growth into account. This study also illustrated a case example on concrete pump truck boom structure using the simulation method for RUL assessment. The crack growth paths and lives under the fatigue loading were simulated using this method. The stress intensity factors were increased with the crack length and the fatigue cracks propagated sharply when the crack length reaches to a considerable length. There are many factors affecting the fatigue crack growth lives of structure. Thus, the fatigue test research would be carried out to investigate the accuracy and efficiency of this simulation method. Acknowledgements The authors would like to thank the support from the National Key Technology R&D Program (Grant No. 2012BAF02B01). The authors express their grateful to engineers Ping Tai and Jianghua Huang in SANY GROUP for their assistance on the simulations. References [1] XU B. Remanufacture and recycling economy. Science Press, Beijing, [2] Li-hong DONG, Bin-shi XU, Shi-yun DONG, Dan WANG. Progress in Life Prediction of Remanufacturing Blanks by Using Metal Magnetic Memory Testing. China Surface Engineering, 2010;23(2): [3] Mazhar M, Kara S, Kaebernick H. Remaining life estimation of used components in consumer products: Life cycle data analysis by Weibull and artificial neural networks. J Oper Manag 2007;25(6): [4] Zhang X, Zhang H, Jiang Z, Wang Y. A decision-making approach for end-of-life strategies selection of used parts. The nternational Journal of Advanced Manufacturing Technology [5] Hu Y, Liu S, Lu H, Zhang H. Remaining Useful Life Assessment and its Application in the Decision for Remanufacturing. Procedia CRP 2014;15: [6] DONG L, XU B, DONG S, CHEN Q, DAN W. Monitoring fatigue crack propagation of ferromagnetic materials with spontaneous abnormal magnetic signals. nt J Fatigue 2008;30(9): [7] Haihong HUANG, Rujun LU, Xi ZHANG, Yan WANG, Zhifeng LU. Magnetic Memory Testing Towards Fatigue Crack Propagation of 510L Steel. Journal of mechanical engineering, 2013;49(1): [8] Zhang G, Wang C, Pu G. Fatigue life prediction of crankshaft repaired by twin arc spraying. J Cent South Univ T 2005;12(2): [9] He W, Liu J, Xie D. Numerical study on fatigue crack growth at a webstiffener of ship structural details by an objected-oriented approach in conjunction with ABAQUS. Marine Structures 2014;35: [10] Okawa T, Sumi Y, Mohri M. Simulation-based fatigue crack management of ship structural details applied to longitudinal and transverse connections. Marine Structures 2006;19(4): [11] ABAQUS 6.11 analysis user s manual. HKS nc. [12] ABAQUS 6.11 theory manual. HKS nc. [13] Moes N, Dolbow J, Belytschko T. A finite element method for crack growth without remeshing. nt J Numer Meth Eng 1999;46(1): [14] Zhang X, Zhang H, Jiang Z, Wang Y. A decision-making approach for end-of-life strategies selection of used parts. The nternational Journal of Advanced Manufacturing Technology 2013.