DURABILITY AND OPTIMIZATION OF CONNECTING RODS/media/Files/Autosteel/Great Designs in...
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DURABILITY AND OPTIMIZATION OF CONNECTING RODS
Adila Afzal and Pravardhan ShenoyGraduate Research Assistants
and Ali Fatemi, ProfessorThe University of Toledo
Funded by:
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OVERALL OBJECTIVES
• Evaluate and compare fatigue performance of forged steel and powder metal connecting rods.
• Perform life predictions of connecting rods and validate by experiments.
• Perform dynamic load analysis and optimization
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PROJECT OUTLINE
• Literature Survey on Connecting Rods– Load and Stress Analyses– Durability and Optimization Aspects– Manufacturing Processes and Economic Costs– Comparative Studies of Forged Steel & PM Connecting Rods
• Experimental Work– Specimen Testing (Material Evaluation)
• Forged steel• Powder metal• C-70 steel
– Testing of Forged Steel and Powder Metal Connecting Rods • Manufacturing fixtures• Load-control fatigue testing
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PROJECT OUTLINE
• Analytical Evaluations– Digitizing Connecting Rod Geometry– Stress (FEA) Analysis– Durability (Fatigue) Analysis and Life Predictions– Dynamic Load and Stress (FEA) Analysis – Optimization Analysis
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PUBLICATIONS AND PRESENTATIONS
• Durability and Optimization of Connecting Rods, Great Designs in Steel Seminar 2004, Livonia, MI (February 18th
2:30 PM).
• A Comparative Study of Fatigue Behavior and Life Predictions of Forged Steel and PM Connecting Rods, SAE Technical paper 2004-01-1529, SAE World Congress 2004, Innovations in Steel Bar Products and Processing Session (M2), Detroit, MI (March 11th,11:00 AM).
• Dynamic Load and Optimization Aspects, to be published.
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CONNECTING ROD NOMENCLATURE
From “Tension and Compression in Connecting Rods, Schreier 1999”
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LOADING OF CONNECTING ROD
Connecting Rods Are Subjected to:• Inertia forces due to mass• Forces generated from the combustion process• Forces due to wearing of forging flashes
These Forces Produce:• Cyclic axial force and stress• Cyclic bending moment and stress
(perpendicular to the crankshaft axis)• Cyclic bending moment and stress
(parallel to the crankshaft axis)
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LOADING OF CONNECTING ROD (SONSINO, 1996)
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Conventional forged steel
• Sedan, 150 HP @ 5700 RPM
• Weight: 0.93 lb
Powder metal
• Minivan, 150 HP @ 5200 RPM
• Weight: 1.2 lb
CONNECTING RODS
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Specimen TestingStrain-controlled tensile tests
Strain-controlled fatigue tests
Based on ASTM standards and recommended practices
Flat specimens from forged steel and powder metal connecting rods
Instron closed-loop servo-controlled hydraulic axial load
frame and digital servo controller are utilized for the tests.
SPECIMEN TESTING
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2.54
76
6.985
9.53
2.5
24.5
R12.
7
Flat plate specimen configuration and dimensions
according to ASTM Standard E606
(All dimensions in mm)
SPECIMEN GEOMETRY
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COMPARISON OF MATERIAL MECHANICAL PROPERTIES
Forged Steel Powder Metal
YS (MPa) 700 588YS Ratio 1 0.84UTS (MPa) 938 866UTS Ratio 1 0.92YS’ (MPa) 620 609YS’ Ratio 1 0.98Sf (at Nf = 106) 423 334Sf Ratio 1 0.79
* Base of comparison is Forged Steel.
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MATERIAL CYCLIC & MONOTONIC STRESS-STRAIN BEHAVIORS
0
100
200
300
400
500
600
700
800
900
1000
0.0% 0.5% 1.0% 1.5% 2.0%
True Strain (%)
Tru
e St
ress
(M
Pa)
FS mo no to nic curveFS cyclic curveP M mo no to nic curveP M cyclic curve
Monotonic
Monotonic
Cyclic
Cyclic
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MATERIALSTRESS-LIFE COMPARISON
Better overall S-N fatigue resistance of the forged steel
Long-life fatigue life of forged steel more than an order of magnitude longer than powder metal
O Forged steelX Powder metal
1E+4 1E+5 1E+6 1E+7
200
1000
1E+3
Tru
e St
ress
Am
plitu
de, Δ
σ/2
(MPa
)
Reversals to Failure, 2Nf
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MATERIALTOTAL STRAIN-LIFE COMPARISON
For a connecting rod, subjected to many millions of cycles, high cycle regime is of primary interest
In the high cycle regime, forged steel results in about a factor of seven longer life than the powder metal material. 0.10%
1.00%
1E+3 1E+4 1E+5 1E+6 1E+7 1E+8Reversals to Failure, 2Nf
Tru
e St
rain
Am
plitu
de, Δ
ε/2,
%
O Forged steelX Powder metal
1E+4 1E+5 1E+6 E+7
0.10%
1.00%
1E+3
Reversals to Failure, 2Nf
1E+8
Tru
e St
rain
Am
plitu
de, Δε/
2, %
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DIGITIZED MODEL OF FS CONNECTING ROD
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BOUNDARY CONDITIONSFOR STRESS (FEA) ANALYSIS
Tension and compression loads applied as pressure on bearing surfaces.
In tension cosine function over 180 deg, in compression uniform distribution over 120 deg (Webster 1983).
Four cases considered:
Crank end Pin endtension restrainedcompression restrainedrestrained tensionrestrained compression
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MESH DETAILS
7.77 mm2.54 mm
1.52 mm 1.27 mm (used)80,000 elements130,000 nodes
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CONTOURS OF VM STRESS FOR FS CONNECTING ROD (Pmax = 26.7 kN or 6 kip)
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CONNECTING ROD TEST FIXTURES
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CONNECTING ROD TEST CONDITIONS
Load-controlled axial tests
Load ratio Pmin/ Pmax = - 1.25
Test frequency 2-5 Hz
Life range 4 X 104 – 4 X 106 Cycles
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COMPONENT TEST RESULTS& STRESS-LIFE COMPARISONS
Forged steel connecting rod fatigue strength is 387 MPa, while for PM connecting rod it is 282 MPa.
About two orders of magnitude longer life for the forged steel connecting rod.
Sa = 852 (Nf)-0.0572
Sa = 971 (Nf)-0.0895
O Forged steelX Powder metal
R = - 1.25
(2)
1E+4
(2)
1E+5 1E+6 1E+7
200
600
Cycles, Nf
Stre
ss A
mpl
itude
(Sa),
MPa
(MPa
)
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FRACTURE SURFACES
FORGEDSTEEL
PM
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FS FRACTURE SURFACES
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Sponsored by: American Iron and Steel Institute