flexible dynamic analysis of hydraulic excavator’s boom
TRANSCRIPT
Flexible Dynamic Analysis of Hydraulic Excavator’s Boom
De Xin Sun1,2,a, and Xin Hui Liu1,b 1 College of Mechanical Science and Engineering, Jilin University, Changchun, 130022, China
2 Base Department, Changchun Institute of Engineering Technology, Changchun 130117, China
Keywords: Hydraulic Excavator, Dynamic Simulate, RecurDyn, Finite Element Analysis.
Abstract. To study the dynamic response of hydraulic excavator’s boom under different road
condition, this paper set up numerical model of excavator’s working device, then set up the virtual
prototyping simulation model of excavator’s working device and simulated the flexible dynamic
response characteristics of the boom based on multi-body dynamic software, RecurDyn. The results
showed that, modeling and simulating method based on rigid multi-body coupling flexible
multi-body dynamic modeling and analyzing technologies, reproduced the actual working conditions
truly. The dynamic stress’s rule of variation provides an important method for the structure design and
force analysis of hydraulic excavator’s working device.
Introduction
Normally, Excavator’s working device is an open spatial chain mechanism system composed of
boom, dipper stick and bucket, which works under the drive of hydraulic cylinders. The boom plays
an important role.
Currently, researches of excavator’s boom are limited in static analysis by ANSYS and dynamic
analysis by ADAMS. Zou Guo-Hui obtained the working device’s stress and deformation distribution
in extreme conditions through the analysis of ANSYS [1]. Du Lin made static analysis of the
excavator’s boom through ADAMS [2]. Wang Jun, Wang Gui-Xin and Zhang Lin-Yan made
simulation of the hydraulic excavator and obtained the force of the hinge points [3-5].
This paper made flexible multi-body dynamic simulation of the boom with the FFlex module
based on new generation multi-body simulating software RecurDyn, the results showed advantages
when compared with which made in ADAMS.
Modeling
Working device. The excavator’s working device is composed of boom, dipper stick, bucket,
hydraulic cylinders and corresponding lineages, this paper created the model with the
three-dimensional modeling software CATIA. The model was showed in fig. 1. Then the model was
imported to RecurDyn, and added corresponding joints and motions.
Fig. 1 Three-dimensional model of hydraulic excavator Fig. 2 Model of road surface spectrum
Road spectrum. Four independent hydraulic cylinders were added between the rear body and
ground, and the hydraulic cylinders were given different motions to simulate different road
conditions. There were ball joints between cylinders and the rear body, the cylinders on the left side
Advanced Materials Research Vols. 328-330 (2011) pp 2220-2223Online available since 2011/Sep/02 at www.scientific.net© (2011) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.328-330.2220
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were fixed with the ground, while the cylinders on the right side were attached with the ground with
translational joints, the model was shown in fig. 2. After simulation, the excavator showed good
kinematics characters.
Multi-rigid-body dynamic simulation
To simulate the excavation, this paper made dynamic simulation in RecurDyn (fig. 3), and then
calculated forces of key joints. The simulation cycle was 30s:
0-5s, turning, the turning cylinder brought the working device to excavating place.
5s-15s, excavating, finished excavating with the help of the boom cylinder, stick cylinder and
bucket cylinder.
15s-20s, turning, the turning cylinder brought the load to unloading place.
20s-30s, unloading, finished unloading with the help of the boom cylinder, stick cylinder and
bucket cylinder.
Fig. 3 Simulation of model Fig. 4 Grid map of the bucket capacity
Load was applied to the excavator bucket, take the solid as excavating object, take the density of
the solid as 1500 kg/m3, the cross section area was 0.1 m
2 though the calculation of the grids (fig. 4).
Then the capacity was 0.026 m3, and take the 7/6 of the capacity as the excavating volume, the load
was 54.6 kg. Define the mass of the bucket as a function (Eq.1):
m=54.6∗step (time, 8.5, 0, 12, 1)−54.6∗step (time, 20, 0, 23.5, 1) + 88.62663241 (1)
Define a resistance at the bucket tooth, it was a function of time (see Eq.2).
W=K0bh (2)
K0 was excavating ratio coefficient;
b was width of bucket;
h was excavating depth.
Minitype excavator usually works in grade III (common clay, loose wet heavy clay or strong loam)
[6]. Take
K0=1.55×105 N/mm2;
b=0.3m;
h=0.33b=0.1m;
W=1.55×105×0.3×0.1≈5000N;
F=5000∗step (time, 8.5, 0, 9, 1)−5000∗step (time, 10.5, 0, 11, 1).
Due to the connection between the support and the boom was the key points of all of the load and
working device, the two points had the largest forces. The location was shown in fig. 5.
Fig. 5 Connection between support and boom
Advanced Materials Research Vols. 328-330 2221
Force of RevJoint1_2 that was between the support and the boom was shown in fig. 6. Between 5s
and 10s, the excavator was excavating, because of the increasing of the excavating resistance and the
load, there was a peak. Then the dipper stick was back, the excavating radius was decreasing, the force
is decreasing. Around the 25s, the excavating radius was maximum, and the bucket was fully loaded.
Then the force reached the maximum of 32kN. Force of RevJoint1_3 between the support and the
boom cylinder was shown in fig. 7. The maximum of the force was 30kN.
Fig. 6 Force of RevJoint1_2 Fig. 7 Force of RevJoint1_3
Meshing of the boom
After multi-rigid-body dynamic analysis, flexible body finite element simulation of the boom was
taken to obtain the stress changes. Before the simulation, a necessary step was the finite element
mesh.
This paper used Hypermesh meshing software. Hypermesh is a kind of software with perfect finite
element meshing and high efficiency. It has good man-computer interface and comprehensive
meshing tools. Boom finite element was shown in fig. 8.
Fig. 8 Grid figure of boom
Most of the elements was standard hexahedral with high quality. There were 14208 elements and
16772 nodes in the meshing, the element type was soild185, the material was Q345, the yield strength
was σs=345 MPa, elastic modulus was E=2.1×105 MPa, and the Poisson’s ratio was µ=0.3.
Result of flexible dynamic simulation
Importing the model to RecurDyn to take dynamic simulation, and then the stress contour was shown
in fig. 9. It was found in the stress contour that the maximum of the stress has been on the surface
between the hinge axis and the hole, the stress was about 100 MPa, and the remaining stress was
below 50 MPa, so the boom had enough strength. Selecting the node at the hinge, and the stress curve
was shown in fig. 10.
2222 Mechatronics and Materials Processing I
Fig. 9 Stress figure of boom Fig. 10 Stress figure of boom’s hinge joint
According to the data, it can be seen that there were stress peaks when excavating as well as
reaching the maximum radius, which corresponded the fact. The maximum of the stress was 144 MPa,
far less than the allowable stress of the material, and the excavator can withstand shock, vibration and
the other factors.
Conclusion
This paper created the virtual prototyping model of the excavator, and then carried out
multi-rigid-body simulation and flexible body simulation. The force of key joint and the stress figure
of the boom were important for the design of the excavator’s boom.
1. Rigid-flexible multi-body dynamic model was created.
2. Forces and related curves of the joints were obtained.
3. Stress of key point was obtained according to the dynamic stress figure.
References
[1] G.H. Zou and D.C. Song: Development & Innovation of Machinery & Electric Products Vol. 21
(2008), p. 105 (In Chinese)
[2] L. Du: Design and Research Vol. 37 (2010), p. 25 (In Chinese)
[3] J. Wang and S.Y. Li: Modern manufacture engineering Vol. 11 (2009), p. 139 (In Chinese)
[4] G.X. Wang and Y.L. Yang: Journal of Hebei University of Technology Vol. 37 (2008), p. 59 (In
Chinese)
[5] L.Y. Zhang, Z.L. Deng, H.L. Zhang and Y. Fu: Journal of Liaoning University of Petroleum &
Chemical Technology Vol. 28 (2008), p. 46 (In Chinese)
[6] Tongji University: Single-bucket excavator (China-Building Industry Press, China 1986). (In
Chinese)
Advanced Materials Research Vols. 328-330 2223
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