analysis of connecting rod in ansys
TRANSCRIPT
APPLICATION OF Design and Analysis of a Connecting Rod
CADmantra Technologies Pvt. Ltd.
: OVERVIEW
• Product of ANSYS Inc., Pennsylvania, US founded in 1970
• Over 40,000 customers (96 of top 100 in the FORTUNE 500 list)
• Acquisitions : CFD Engineering, Airbus, CFX, Century Dynamics, Harvard Thermal, Fluent Inc. (2006), Apache Design Solutions (2011), etc.
• Static and Dynamic Analysis, Steady-state and Transient Thermal, Fluid Flow and Modal Analysis
• Extensive array of solvers
• Accurate prediction according to theoretical models
DESIGN OF A CONNECTING ROD
• Connection between piston (gudgeon) pin and crank pin
• Converts linear motion to rotary motion
• Subjected to alternating compressive load
• Designed as a short strut against buckling using Rankine’s Formula
According to Rankine’s formula :
• Wcr about x-axis = ߪ𝑐×𝐴
[ݔݔܭ/ܮ]ܽ+12
• Wcr about y-axis = ߪ𝑐×𝐴
[yyܭ2/ܮ]ܽ+12
• For a connecting rod equally strong about both axes, the buckling loads must be equal. i.e.,
Ixx = 4 x Iyy [∴ 𝐼 = 𝐴×2ܭ ]
Generally, Ixx = 3 to 3.5 times Iyy, and the connecting rod is designed to buckle in X direction.
X
X’
Y
Y’ In this case, we get :
Ixx = 3.2 x Iyy
- SECTION
PROBLEM SPECIFICATION
Honda 250 cc Specifications:
• Liquid cooled, 4-stroke, single cylinder, DOHC
• Displacement : 249.67 cc
• Bore x Stroke : 76mm x 55 mm
• Maximum Power : 28.6 BHP@9000 rpm
• Maximum Torque : 23 NM@7500 rpm
STEPS IN AN ANALYSIS
Pre -processing
• Material Assignment
• Creating/Importing CAD Model
• Meshing
• Applying Loads and Fixtures
Solving
• Choosing a solver
• Setting Analysis Parameters (if any)
Post-processing
• Viewing results
• Interpreting results
MATERIAL ASSIGNMENT Mechanical Properties of Forged Steel
CAD MODELLING
Section of the Connecting Rod :
• – Section • B x H = 12 x 15 mm
• Thickness of web and flange = 3 mm
Piston End Crank End
Inner Diameter = 16 mm Inner Diameter = 24 mm
Outer Diameter = 24 mm Outer Diameter = 32 mm
Length of the connecting Rod = (2 x stroke length) = 110 mm
LOADS AND FIXTURES
According to the formula :
Power = ½ 𝑃𝑚𝑒𝑝×𝐿𝐴𝑁
60
• Mean Effective Pressure = 1.14 Mpa
• Considering Maximum Gas Pressure (Pmax) = 2 MPa,
• Buckling Load = Maximum Gas Force (Pmax×Apiston) = 9 kN
• Thickness of Web and Flange is taken 3 mm
MESH GENERATION • Model is divided into ‘Finite Elements’
• Calculations are done at the nodes
Meshing
1-D
• Beams
• Pipes
• Columns
2-D
• Sheet Metal
• Instrument Panel
3-D
• Engine block
• Crankshaft
Tetra Penta Brick(Hex) Pyramid
MESHING
• Tetra-meshing
• Max. size = 1.8 mm
• Fine Mesh : • High Accuracy
• More Time
• Coarse Mesh : • Low Accuracy
• Less Time
STRESSES AND DEFORMATION
LINEAR BUCKLING
• The connecting rod buckles along X-X direction as expected.
FATIGUE TESTS
• S-N Diagram is constructed according to the formula :
Sa = σf ’ (2Nf) b
= 1131 (Nf) -0.0711 (MPa)
• Alternating Loading is tested according to Goodman’s Theory
• Min. Safety Factor = 2.44
• Min. Life = 108 cycles
RESULTS
Sl. No. Test Value
1. Equivalent Stress (von Mises) 252.2 MPa
2. Max. Principal Stress 97.73 MPa
3. Normal Stress (X-axis) -60.26 MPa
4. Normal Stress (Y-axis) -222.36 MPa
5. Normal Stress (Z-axis) 97.73 MPa
6. Total Deformation 0.05 mm
7. Fatigue Test : Safety Factor 2.44
8. Linear Buckling : Load Multiplier 5.598