INTRODUCTION
The connecting rod is an important driving part of diesel engine. It is loaded
in compression and in tension. Its main motions are shown in Fig.
1.
The finite element analysis is an effective analysis method, used widely in
the design of connecting rod. In 2000s, some studies tried to carry out the
shape optimization using the special strategies, such as topology and genetic
optimization, bounded constraints of the stress and fatigue life of connecting
rod (Yuan and Zhang, 2012; Sun
et al., 2012; Haiba et al., 2005).
Xu and Yu (2007) studied the failure investigation
of a diesel engine connecting rod. The fatigue cracks initiated from the axial
grooves by the alternative load so that the multipleorigin fatigue fracture
took place on the connecting rod. Griza et al. (2009)
evaluated the relation between tightening force and fatigue crack propagation
in connecting rod bolts with an analytical fracture mechanics approach. Baldizzone
et al. (2012) studied the spalling phenomena of the crankpin surface.

Fig. 1: 
Main motions of the pistonconnecting rod system (Vertical
arrow: Oscillating, Circular motion: Rotating) 
The nonmetallic inclusions underneath the surface was considered the cause
of the damage and the varieties and contents of nonmetallic inclusions were
identified. Bo et al. (2010) studied the method
of fatigue life prediction based on the material SN curve is able to predict
the critical position and fatigue life in connecting rod fatigue test.
There is great significance to predict remanufacturing remaining fatigue life
of connecting rod. Remanufacturing blanks has undergone many service cycle.
Whether the parts have residual service life or its remaining useful life is
able to sustain the next life cycle which is a important technology of the remanufacturing
and is the primary problem before remanufacturing process.
Based on the traditional theory and methods of the fatigue life analysis, the
engine connecting rod fatigue life is predicted by finite element analysis method
and dynamic simulation method (Chen et al., 2006).
The timeload spectrum of engine connecting rod is obtained using Dynamics simulation
by ADAMS software. The rod local stressstrain distribution is received by ANSYS
finite element analysis. The limit fatigue strength of rod is calculated (Milan
et al., 2004). Based on the rod stress and Miner fatigue damage theory,
the Goodman fatigue method is used to calculate the fatigue strength of the
rod and to predict its fatigue life.
To predict the fatigue life of the connecting rod, the timeload spectrum analysis
of the rod of a diesel engine is performed, the finite element analysis software
ADAMS is used to simulate the real force of the actual situation. The stress
distribution of connecting rod was calculated by ANSYS. Goodman fatigue theory
was used to get fatigue strength and to estimate total fatigue life of the rod,
then its residual fatigue life was predicted combing with its historical service
time.
DYNAMICS SIMULATION METHODOLOGY
Setting parameters of dynamics simulation:
Materials:
Crankshaft: 
42CrMoA 
Piston: 
ZLl09 (ZAlSil2CulMglNil) 
Connecting rod: 
45Cr 
Methodology: The three dimensional model of the connecting rod is established
by PROE software. The timeload spectrum of the connecting rod is calculated
by ADAMS software using dynamic simulation method.
PROE model of the rod is imported into ADAMS software.

Fig. 2: 
Result of PROE model of the rod imported into ADAMS software 
The material properties of piston, connecting rod and crankshaft are defined
and the mass of them are calculated, respectively. The result of PROE model
of the rod imported into ADAMS software is shown in Fig. 2.
Rated speed of crankshaft is 2400 r min^{1}, so the crank every turn
around time is 0.025 sec. For sixcylinder fourstroke engine, the time of load
cycle analysis of connecting rod should be twocircle, i.e., 0.05 sec. The corresponding
rotation angle is 720°. Pressure is 13.5 Mpa when the fuel exploded. The
piston diameter is 124 mm. The pressure F is 16, 3000 N. The explosion force
working angle is 120° in a sixcylinder engine. The explosive power at this
time is assumed to be constant.
Analysis results of dynamics simulation: When the crankshaft turns 0.003
sec, i.e., turns 43.2 degrees, cylinder explodes after avoiding dead center.
The impact force is 163,000 N. The instantaneous compression load of connecting
rod is 99, 071 N; The crankshaft turned 0.003 sec, i.e., turned 43.2 degree,
it escapes the dead point. At that time the cylinder explosion produce the impact
force of 163,000 N and the connecting rod is instantaneous subjected to a compressive
load of 99,071 N.
At 0.004 sec, i.e., 57.6 degree, the compression load reduced to 16,001 N.
Due to increasing angular acceleration in 0.007 sec, i.e., 100.8 degree, the
maximum compression load rating is 24,800 N. At 0.0125 sec, i.e., 180 degree,
the compression load reduced to 16,001 N. At 0.019 sec, i.e., 273.6 degree,
the maximum tension load is 12771 N. At 0.025 sec, i.e., 360 degree, the tension
load is 7542 N. The load time history from 0.0290.05 sec and from 0.0040.025
sec is same. The cycle load simulation results of the connecting rod big end
are shown in Fig. 3.

Fig. 3: 
Timeload spectrum of the connecting rod in a load cycl 
CONNECTING ROD FINITE ELEMENT ANALYSIS OF CONTACT FATIGUE
Finite element model:
• 
Material property: 45Cr, E = 2.06x10^{11},
= 0.3 
• 
Unit type: Solid brick 8 nodes 185 
• 
Boundary conditions: According to the actual working condition
of the connecting rod, the big and small ends are respectively fixed to
analysis its stress and strain 
• 
Meshing: There is more fillet on the connecting rod. So, it is
difficult to divide mesh of the connecting rod, automatic grid method is
used to mesh model. Figure 4 shows the mesh of the connecting
rod. It contained about 8956 elements 
RESULTS ANALYSIS
Using ANSYS, stress distribution of connecting rod is obtained. As shown in
Fig. 58. Figure 5 shows
that the maximum stress occurs in the bar of the connecting rod near the small
end when the big end loaded under compressive load. The maximum stress is about
26.6 Mpa in 0.004 sec and the maximum stress is about 41.2 Mpa in 0.007 sec.
Figure 6 shows that the maximum stress occurs in the small
end when the big end loaded under compressive load. The maximum stress is about
22.5 Mpa in 0.004 sec and the maximum stress is about 25.3 Mpa in 0.007 sec.
Figure 7 show that when the big end loaded under tension load,
the maximum stress is about 8.5 Mpa in 0.0125 sec, 49.2 Mpa in 0.019 sec and
24.5 Mpa in 0.025 sec, respectively.

Fig. 4: 
Finite element model of connecting rod 
Figure 8 show that when the small end loaded under tension
load, the maximum stress is about 8.4 Mpa in 0.0125 sec, 58.5 Mpa in 0.019 sec
and 24 Mpa in 0.025 sec, respectively.
Received in the connecting rod the maximum tension 12771 N in 0.019 sec rod
small end of a point receives the maximum tensile stress is 57.547 Mpa while
the big end received the maximum tensile stress 49.338 Mpa, so statistics stress
results way in accordance with the large end fixed to the small end of the stress
value statistics. In 0.019 sec, the maximum tension load of the connecting rod
is 12771 N, rod small end of a point receives the maximum tensile stress of
the small end is 57.547 Mpa, the maximum tensile stress of the big end is 49.338
Mpa. So, the stress results statistics method. Stress results of statistical
way is according to the big end being fixed, the small end being forced.
Abscissa 110 represent the ten force point on the crankshaft from 0.0040.05
sec, the ordinate represents the stress value of the point A (i.e., the maximum
stress points on the small end at the maximum tensile force effecting). Statistical
results are shown in Fig. 9.

Fig. 5(ab): 
Stress distribution of big end under compression load, (a)
Stress distribution at 0.004 sec and (b) Stress distribution at 0.007 sec 

Fig. 6(ab): 
Stress distribution of small end under compression load, (a)
Stress distribution at 0.004 sec and (b) Stress distribution at 0.007 sec 
CONNECTING ROD LIFE CALCULATION
Connecting rod fatigue limitation calculation: The connecting rod materials
is 45Cr. Fatigue limit is σ_{1} = 241.8 Mpa, the conditional fatigue
limit of The connecting rod is σ_{1D} = 91.59 Mpa, after taking
into account the factor of safety, the conditional fatigue limit is:
Prediction service life of connecting rod based on the miner fatigue damage
theory: Based on the finite element analysis results it can be concluded
that the maximum stress is 57.55 Mpa. At the rated load, the maximum stress
is less than fatigue limit, so the life of rob can be considered infinite.
In rated loading cyclic, the curve of the stress changes in a fourstroke cycle
is drawn with the simulation, as shown in the Fig. 10. The
connecting rod is endured a fatigue damage while crankshaft runs each lap. As
the red line section shown in the figure, during this time the connecting rod
bearing the maximum tension force.

Fig. 7(ac): 
Stress distribution of big end under tension load, (a) Stress
distribution at 0.0125 sec (b) Stress distribution at 0.019 sec and (c)
Stress distribution at 0.025 sec 

Fig. 8(ac): 
Stress distribution of small end under tension load, (a) Stress
distribution at 0.0125 sec (b) Stress distribution at 0.019 sec and (c)
Stress distribution at 0.025 sec 

Fig. 9: 
Curve of the maximum stress (A point) on the connecting rod
changing with time 

Fig. 10: 
Variety of stress in a fourstroke cycle 
Table 1: 
Calculation parameters of Equivalent symmetric cyclic stresses
σ_{i} 

I: Level i, σ_{min}: Minimum stress, σ_{max}:
Maximum stress, σ_{m}: Average stress, σ_{a}:
Stress amplitude 
Other times the stress of the rod is less than the conditional fatigue limit
50.88 Mpa.
To predict Fatigue life, Goodman fatigue calculation method takes into account
the fatigue stress amplitude, mean stress and material mechanical performance
parameters. σ_{i} is calculated according to Goodman fatigue limit
diagram. The calculation results of Equivalent symmetric cyclic stresses σ_{i}
are shown in Table 1.
The calculated σ_{1 }is 50.9 Mpa, σ_{2 }is 24.75
Mpa.
The equivalent symmetric cyclic stress σ_{1 } and σ_{2}
corresponding to material fatigue failure limit cycles were, respectively:
The cycle number of the connecting rod under rated load is obtained:
The vehicles speed is Assumed to be 80 km h^{1}, Crankshaft rated
speed is 2400 r min^{1}, so crankshaft rotation 1800 rpm km^{1}
is calculated. The vehicle can safely travel 3,514,000 km. Assuming the engine
to work 12 h a day and uninterrupted work 300 days a year, it can be calculated
motor vehicle safe and reliable working time is about 12 years and 2 months.
Remaining fatigue life calculation of the connecting rod: The vehicle
mileage specified in “Motor vehicle
standard specifies mandatory retirement”
is generally not more than 600,000 km. while the rated speed of the crankshaft
is 2400 r min^{1}, the traveling speed is 80 km h^{1}, so
the equivalent life N_{0} is equal to 1.08x10^{9}. Rated load
rod work cycles 6.325x10^{9} minus the rod remaining work cycles 5.245x10^{9}
and then the rod remaining safe use mileage of 2.8 million km is calculated.
It can meet the requirements of the next life cycle of the connecting rod.
CONCLUSION
The breaking down of an engine connecting rod is analyzed with the remaining
fatigue life analysis process. Firstly, the threedimensional solid model of
the connecting rod is established by Pro/E software. Then, the timeload spectrum
of the rod is calculated by ADAMS software. Import threedimensional model into
ANSYS, to analysis contact fatigue of the connecting rod, the stressstrain
distribution is calculated. The conditions limit fatigue strength of the connecting
rod is investigated by traditional fatigue analysis methods. And then based
on the rod stress the Miner fatigue theory is used in analysis. The rod fatigue
strength and life prediction are researched with the Goodman fatigue Law. The
results showed that the remaining fatigue life of the rod is able to meet the
next life cycle.
ACKNOWLEDGMENTS
The present investigation has been sponsored by the National Science Foundation
of China (51279095), the National 973 Project (2011CB013403), the Science Foundation
of Shandong Province of China (ZR2010EM032), Independent Innovation Foundation
of Shandong University (IIFSDU2012ZD033) and the Special Funding of Postdoctoral
Innovation Projects of Shandong Province (201102011).