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ISSN : 1598-6721(Print)
ISSN : 2288-0771(Online)
The Korean Society of Manufacturing Process Engineers Vol.18 No.3 pp.26-32

Stress Analysis of Tractor Front-End Loader against Impact Load Using Flexible Multi-Body Dynamic Simulation

Chang-Seop Shin*, Beom-Soo Kim**, Hyun-Woo Han**, Woo-Jin Chung**, Seung-Je Cho**, Young-Jun Park**,***#
*Upland-field Machinery Research Center, Kyungpook National University
**Department of Biosystems & Biomaterials Science and Engineering, Seoul National University
***Department Research Institute of Agriculture and Life Sciences, Seoul National University
Corresponding Author : Tel: +82-2-880-4612, Fax: +82-2-873-2049
31/01/2019 03/02/2019 28/02/2019


This study was conducted to analyze the stresses by impact loads on front-end loaders attached to tractors using flexible multi-body dynamics. The model was designed and validated by comparing previous experimental data with the simulation data obtained in this study. Nine sets of conditions were designed using three weights (500, 300, and 100 kg) loaded inside a bucket and three heights (1700, 1350, and 1000 mm) of the bucket from ground level. A parametric study was carried out at five locations for two types of parts of a front-end loader. All the safety factors for the five locations under all conditions were calculated and were greater than 1. Thus, the designs of the front-end loaders were structurally safe. Based on this study, front-end loaders attached to tractors can be designed effectively in terms of cost and safety.

유연 다물체 동역학 해석을 이용한 충격 하중에 따른 트랙터 프론트 로더의 응력 분석

신 창섭*, 김 범수**, 한 현우**, 정 우진**, 조 승제**, 박 영준**,***#
*경북대학교 밭농업기계개발연구센터
**서울대학교 바이오시스템·소재학부
***서울대학교 농업생명과학연구원


    Korea Institute of Planning and Evaluation for Technology in Food, Agriculture, Forestry and Fisheries

    Ministry of Agriculture, Food and Rural Affairs

    © The Korean Society of Manufacturing Process Engineers. All rights reserved.

    This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

    1. Introduction

    Although there are self-propelled agricultural machines, such as combine harvesters, most agricultural machinery is attached to the rear end of tractors through a power take-off (PTO) shaft. In addition, front-end loaders are attached to the front ends of tractors and use hydraulic cylinders as power sources.

    Based on annual operation times, rotary tillage (45%), plow tillage (29%) and loader work (19%) constitute the majority of farm work involving tractors[1]. As heavy soil is moved up and down by a loader, free fall occurs and creates an impact load on the loader while loading and unloading soil. Accordingly, it is necessary to analyse the stresses on the front-end loader, which is subjected to various impact loads from different heights.

    Park et al.[2] conducted an experimental study to measure the stresses on tractor front-end loaders and analysed the structural safety. However, the analysis was limited to impact loads of uniform magnitudes falling from the same height. Thus, variable load and height conditions were not considered.

    In one study, a flexible multi-body dynamics analysis program for wheel loaders was developed[3]. In another study, the safety of the seat and belt of a two-wheeler was examined using Recurdyn, which is commercial software[4]. In addition, the development of a dynamic model of a wheel-loader using the transmission, hydraulic, and vehicle dynamic modules of Recurdyn was reported[5]. Flexible multi-body dynamics simulations have been applied to ships[6-9] and in other fields. However, this method has not been applied to front-end loaders for tractors.

    Based on existing experimental data for impact loads acting on front-end loaders for agricultural tractors, a multi-body dynamic simulation was conducted in this study to identify the stresses and strains at five points under three different load magnitudes at three different heights. After validating the simulations, a parametric study was performed.

    2. Impact load test

    The work in this section was based on the study by Park et al.[2].

    2.1 Equipment for test

    For the impact load test conducted by Park et al.[2], a steel structure was loaded to a total load of 500 kg in the tractor front-end loader bucket.

    The front-end loader used in the test was the Taesung KTS-763 model, which is a parallel-type loader with two booms and bucket cylinders. The loader was mounted on a TYM 4100 tractor manufactured by Tongyang Moolsan. Fig. 1 shows the shape of the front-end loader, parts for measuring the strain, and strain measurement locations of each part. Three types of strain gauges (Kyowa’s uni-, bi-, and triaxial strain gauges) were used. Data were acquired using a data collector from Dewetron.

    2.2 Impact load test

    A 500 kg steel structure, which corresponds to the maximum permissible load, was loaded in the front-end loader bucket. The bucket was lifted 20 times to a height of 1350 mm and was subsequently subjected to free fall to a height of 500 mm above the ground, where measured strains at 23 locations on the front-end loader (Fig. 1(b)).

    3. Modeling and Validation

    Before the parametric study, the Von-Mises stress values of the flexible multi-body dynamic simulations of this study were compared with the stress data obtained from existing experiments to validate the simulation model.

    3.1 Tractor Model

    Based on the ratio of the two weight loads applied to the front and rear wheels of the tractor (0.44:0.56), as illustrated in Fig. 2 below, the center of mass (CM) for modelling the tractor body with a loader was determined at a point 1015.62 mm horizontally from the center of the front wheel and 450 mm vertically from the ground. The tire was modeled as a bushing element with stiffness and damping coefficients only in the y-direction.

    3.2 Loader Model

    The hydraulic cylinder of the loader was modelled as a spring-damper. The wheels and the body were connected through a dummy element of the tractor chassis.

    As shown in Fig. 3, rigid body modeling was conducted for most components, including the bucket and load. Flexible body modeling was performed to form meshes for Arm LH, which was necessary for the stress analysis, and PIN was connected to it as shown in Fig. 4.

    3.3 Simulation Condition

    After 4 s stabilizing process, the bushing element, which restrained the rotation between the tractor body and the arm, was deactivated to allow the arm to fall due to gravity.

    3.4 Von-Mises Stress

    As shown in Fig. 5, the Von Mises stress values at five locations obtained from the simulation ranged from 50.732 (L20) to 285.89 (L2). As presented in Table 1, the stresses of the simulation were similar to those of the existing experiments, with a lowest difference of 2.9% (L2).

    4. Parametric study

    4.1 Parameter conditions

    As illustrated in Fig. 6, the height conditions of the loader bucket wer 1700, 1350, and 1000 mm. For the load in the bucket, weight conditions of 500, 300, and 100 kg were applied. The nine analysis conditions used in the study are presented in Table 2.

    4.2 Stresses by 9 conditions

    Fig. 7 shows the results obtained for the nine conditions. The safety factors at each location were calculated by dividing the yield strength of SS400, which was used as the material, by the peak stress obtained by the analysis.

    As presented at Table 3-7, the minimum value of the stresses and safety factors was 1.4. Accordingly, all the cases were safe, with safety factors over 1. The loader underwent larger loads when bucket loads of 500 or 300 kg fell from a height of 1350 mm than when they fell from 1700 mm. However, there was not a significant difference between the two cases. Accordingly, free fall from any heights between 1700 and 1350 mm did not cause significantly differently loads on the loader. Table 4, 5, 6

    5. Summary and Conclusions

    To determine the structural safety for each component of the tractor-mounted loader, a parametric study was conducted by using a commercial flexible multi-body dynamics simulation program. The findings of this study can be summarized as follows.

    1. When the simulation results were compared with the existing experimental data, the error rates were 2.9% (L2), 4.05% (L17), 20.02% (L20), 15.24% (L21), and 5.27% (L23), demonstrating the high accuracy of the model.

    2. When the bucket was loaded with 500 or 300 kg, the free fall from a height of 1350 mm caused a larger stress than that from a height of 1700 mm.

    3. Safety factors were calculated based on stresses generated by free falls from heights of 1700, 1350, and 1000 mm, and weights of 100, 300, 500 kg were used, where 500 kg was the maximum permissible load. All the safety factors obtained exceeded 1. The results of these flexible multi-body dynamics simulations will be useful for the design of tractor-mounted loaders.


    "This study was supported by the Korea Institute of Planning and Evaluation for Technology in Food, Agriculture and Forestry (iPET) through Agriculture, Food and Rural Affairs Research Center Support Program, funded by Ministry of Agriculture, Food and Rural Affairs (MAFRA) (No. 716001-07)."


    Equipment for impact test
    Modelling of tractor body with tire
    Modelling of loader attached to the tractor
    Mesh of 5 points for stress analysis
    Stresses on 5 locations after free fall
    Height Conditions for parametric study
    Stresses by study conditions


    Error between test and simulation results
    9 Cases for analysis by weight and height
    Stresses (MPa) and safety factor for 9 cases on L2 location
    Stresses (MPa) for 9 cases on L17 location
    Stresses (MPa) for 9 cases on L20 location
    Stresses (MPa) for 9 cases on L21 location
    Stresses (MPa) for 9 cases on L23 location


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