fatigue life of a mining dump truck

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Engineering Failure Analysis 23 (2012) 1826

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Engineering Failure Analysisjournal homepage: www.elsevier.com/locate/engfailanal

Frame fatigue life assessment of a mining dump truck based on nite element method and multibody dynamic analysisChengji Mi a,, Zhengqi Gu a, Qingquan Yang a, Duzhong Nie ba b

State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, Hunan University, China School of Mechatronic Engineering, Xian Technological University, China

a r t i c l e

i n f o

a b s t r a c tAiming at precisely predicting fatigue life for frame of the 220t mining dump truck, a fatigue life analysis method is presented, integrating multibody dynamic analysis and nite element method. The force of main joints at frame are measured from the multibody dynamic model, whose road is restructured based on ISO/TC108/SC2N67. According to GB/T27025-2008, the dynamic stress test of the whole truck is implemented to obtain the peak stress of the mainly forced area, which is compared with the simulated stress. It is found out that the error is allowable so that the accuracy of the nite element model is denitely ensured. The quasi-static stress analysis method is employed to acquire stress inuence coefcient under unit load, which is associated with load histories of the frame to get the dangerous stress area. The fatigue life of the frame is calculated on the basis of PalmgrenMiner damage theory. It is turned out that the minimum life area of the frame is located at the frame joints of suspension, which matches the practice. Crown Copyright 2012 Published by Elsevier Ltd. All rights reserved.

Article history: Received 29 September 2011 Accepted 31 January 2012 Available online 10 February 2012 Keywords: Fatigue life Frame Mining dump truck Multibody dynamic analysis Finite element method

1. Introduction The mining dump truck runs all the year round in the terrible mine road, which is prone to need higher performances than the general highway vehicle, such as stiffness, strength, and fatigue life. As the main part of the mining dump truck, the fatigue life for frame is focused on, especially when it is fully loaded. Actually, dynamic forces caused by the road surface roughness are the foremost factor to lead to fatigue failure of the frame during the mining dump truck services. However, in general, the stress level of the frame does not exceed the fatigue strength of the material except the local stress concentrations. Research on structure fatigue life of mining dump truck is extremely rare by tests because of its hugeness in size and weight. Its special characteristics may lead to obtain fatigue life of the frame based on bench tests impossibly. However, it is difcult to predict exactly the fatigue life of the frame by means of pure computer simulation owing to the differences between real situations and simplied conditions. To increase the accuracy of the predicted fatigue life of the frame, a fatigue life analysis method is presented, which is based on dynamic stress measurement from the practical road surface and combined with multibody dynamic analysis and nite element analysis. Some papers analyzing and predicting fatigue life of vehicles components based on simulations and tests have been published. Shao et al. proposed a new analysis method based on dynamic strain measurement from practical mine road surface conditions combined with nite element analysis, which is applied to drive axle housing failure analysis of a mining dump truck [1]. Topac et al. presented some design enhancement solutions to improve fatigue life of a drive axle housing using

Corresponding author.E-mail address: mcj20112011@hnu.edu.cn (C. Mi). 1350-6307/$ - see front matter Crown Copyright 2012 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.engfailanal.2012.01.014

C. Mi et al. / Engineering Failure Analysis 23 (2012) 1826


nite element and bench tests [2].Combining with multibody dynamic analysis and nite element analysis, Lee et al. successfully estimated the fatigue life of the wheels by comparison of the results from test [3]. It is not hard to see that the fatigue life analysis combined with nite element method, multibody dynamic analysis and tests has become a tendency. First of all, this paper establishes the multibody dynamic model of the mining dump truck, whose road is restructured based on ISO/TC108/SC2N67. Then, the nite element model of the frame is built to analyze the static stress in terms of the simulated force. The comparison between the simulated maximum stress and the tested peak stress implies that the error is acceptable and the nite element model is reliable. Finally, the fatigue life of the frame is calculated on the basis of the quasi-static stress analysis method and PalmgrenMiner damage theory. 2. Multibody dynamic analysis of 220t mining dump truck 2.1. Reconstruction road surface On the basis of ISO/TC108/SC2N67 document, road roughness is considered as vehicle vibration input utilizes power spectrum density of road surface to describe its statistic characteristics, which can be expressed as follows:

W n Gq n Gq n0 n0


where n is spatial frequency, n0 = 0.1/m, W is frequency index. The rational function is used to express the PSD of the road surface, and the expression of the PSD on the road with rational function is as follows:


2aq pa2 n2


where a and q are constants. The time-domain mathematical model of road roughness can be deduced a expression from Eq. (2) [4]:

q h i _ qt 0:111 v qt 40 Gq n0 v w0 t


where v is vehicle speed, w0(t) is unit white noise. In order to simulate the real road surface, standard D-class road is regarded as the road spectrum for dynamic analysis of mining dump truck. According to the Eq. (3), the time-domain mathematical model is built in Matlab/Simulink. After solution, the simulated two-dimensional road roughness is shown in Fig. 1. In addition, the restructured road spectrum PSD is compared with the standard road spectrum as shown in Fig. 2, which indicates that two curves are similar. The data of two-dimensional road roughness can be exported as the road document format in Msc.ADAMS. Then the data can be stretched to be the 3D road model needed in the dynamic analysis.

Fig. 1. 2D Road roughness of D-class.


C. Mi et al. / Engineering Failure Analysis 23 (2012) 1826

Fig. 2. Comparison of PSD between standard road spectrum and restructured road spectrum.

2.2. Nonlinear stiffness and damping characteristics of hydro-pneumatic suspension In order to effectively weaken the impact of road roughness, the hydro-pneumatic suspension system with non-linear stiffness and damping characteristics is used to reduce vibration. The least square method is utilized to t the curve of non-linear stiffness and damping characteristics, which can be expressed as follows:

F k ki0 ki1 Dz ki2 Dz2 ki3 Dz3 _ _ _ F c c 1 Dz c 2 Dz 2 c 3 Dz 3

4 5

_ where Dz; Dz is displacement and speed of suspension, Fk is stiffness force and Fc is damping force. The curves of stiffness force and damping force can be obtained from Matlab as shown in Figs. 3 and 4 and be imported into the dynamic analysis model. 2.3. Multibody dynamic analysis The components of mining dump truck can be dened as parts in Adams and connected with motion pairs. If the couple of parts do not have a motion pair, the relationship between them can be replaced with contact. In addition, the goods

Fig. 3. Rear suspension stiffness force.

C. Mi et al. / Engineering Failure Analysis 23 (2012) 1826


Fig. 4. Suspension damping force.

heap of mining dump truck can be dened according to the SAE standard heap [5]. After nishing the dynamic analysis model as shown in Fig. 5, the initial parameters can be set up like this: the speed of mining dump truck is 30 km/h and the simulated time is 30 s. Then, the forced curve of rear suspension is shown in Fig. 6, which will be the load spectrum of fatigue analysis. 3. Validation of the nite element analysis model of frame 3.1. Static stress analysis The frame consists of different thick sheets which are welded to form the framework. This geometry model is built with SolidWorks and is imported into Hypermesh to build the nite element model with shell elements. In addition, the spring elements are used to simulate the suspension property and the lower node is restricted. At the same time, the weight of the assemblies can be replaced with mass elements. The peak force from the dynamic analysis is considered as the load of the static stress analysis. Finally, the nite analysis model is shown in Fig. 7 with nodes and elements. The frame material is high-strength low-alloy quenched and tempered steel named SUMITEN 610F, whose parameters are shown in Table 1. After solution, the von Mises stress contour is shown in Fig. 8. According to the results, the high stress areas are located at the frame positions of P1 and P2 marked in Fig. 8, which both is around 200 MPa. The high stress of the frame area of P1 mainly is caused by the impact of road roughness, while the abundant goods are dedicated to the high stress of P2.

Fig. 5. Multibody dynamic analysis model.


C. Mi et al. / Engineering Failure Analysis 23 (2012) 1826

Fig. 6. Force curves of rear suspension.

Fig. 7. Finite element model of frame.

Table 1 Physical properties of SUMITEN 610F. Material SUMITEN 610F Density 7800 kg/m3 Elastic modulus 209 GPa Poissons ratio 0.276 Yield strength 480 MPa Ultimate strength 600 MPa

3.2. Dynamic stress test The 46 measuring points with 138 response channels consist of sensors and temperature