a) To find out the critical stress regions and stress values due to the application of tensile and compressive load by using bolt-pretension.
b) To find out maximum deformation under tensile and compressive loading.
c) To calculate the factor of safety for highly stressed zone.
The 1/3rd mass of the con-rod corresponding to the segment between c.g and small end is lumped on small end as it behaves like reciprocating mass along with the piston, ring and pin. The total reciprocating mass is the sum of masses of 1/3rd of connecting rod and complete piston assembly.
1) Specification : AISI4140H
2) Hardness (Normalized) : 277-321 Brinell Hardness
3) Poisson’s Ratio : 0.293
4) Young’s Modulus : 2.1165e5 Mpa
5) Yield Stress : 417.1 Mpa
6) Density : 7.85 e-6 Kg/mm3
INPUTS REQUIRED FROM ENGINE ASSEMBLY FOR STRESS ANALYSIS
TOTAL RECIPROCATING MASS =2.5KG (PISTON+RINGS+PIN)
CRANK RADIUS = 80 mm
MAXIMUM RPM OF ENGINE = 2400
RATED RPM OF ENGINE = 2000
DIAMETER OF PISTON = 125mm
MAXIMUM GAS PRESSURE = 12.7 N/mm2
STROKE = 125mm
MESHED MODEL OF CONNECTING ROD
SYMMETRY BOUNDARY CONDITIONS APPLIED)
PROCEDURE FOR ANALYSIS OF BOLT PRETENSION
Thus spring element substitutes for the presence of tightened bolt in assembled condition.
The results of step1 & step2 are matched in terms of stresses by taking deflections for contact element by trial & error.
Equivalent Stiffness (k) = F/(d3+d4)
where, F= Pretension load
d3= Deflection in bearing cap due to compression
d4= Deflection in first thread of connecting rod due to compression in member between thread & constrained face.
These values of d3 & d4 are read from the analysis of step1&2.
ANALYSIS OF CONNECTING ROD WITH BOLT PRETENSION
Deflection in capside bolt = d1
Deflection in bearing cap = d3
Deflection in connecting rod bolt = d2
Deflection in first thread of connecting rod =d4
Pretension F=70000 N
(RATED TIGHTENING AXIAL LOAD)
Pretension in the step1 is now replaced by gap elements (Contact Elements) to verify stresses in bolt as shown in Fig.2.
Stiffness k= AE/L
where A= p /4*d2= p /4*(10.6)2= 88.26 mm2, E= 2E5 & L=89.77 mm
k = 1.97E5 N/mm
Total deflection=d1+d2=0.034814+0.202E-7=0.03481402 mm
MAXIMUM DEFLECTIONS IN CONNECTING ROD THREAD AND BOLT
MAXIMUM STRESS IN CONNECTING ROD THREAD AND BOLT
VON MISES STRESS PATTERN TO VERIFY STRESSES IN BOLT