fe simulation of engine head block for structural durability
TRANSCRIPT
By PRADEEP PAWAR.
GuideProf. N. S. Hanamapure
INTRODUCTIONWhat is Durability?
Simply it describes overall life requirementExperimental Durability Tests and their
limitationsDevelopment of CAE toolsEver increasing power density requires …
highly optimized coolant flow (minimized volume)detail knowledge about material behavior and
modelingunderstanding failure mechanismadvanced and robust simulation processes
Durability analysis of Engine Head block
Mechanical BC’sMechanical BC’s Stress / strain analysis(durability testing, duty cycle)Stress / strain analysis(durability testing, duty cycle)
Stresses /StrainsStresses /Strains
Gasket pressureGasket pressure
Durability(HCF, LCF, TMF)Durability(HCF, LCF, TMF) OK?OK?
no
Heat transfer analysis(nucleate boiling)Heat transfer analysis(nucleate boiling)
Temperature fieldHeat fluxTemperature fieldHeat flux OK?OK?
Simulation variant
noSimulation variant
Material- filling & solidification- behavior, modeling- testing- process
Material- filling & solidification- behavior, modeling- testing- process
yes
yes Design Release(Durability)Design Release(Durability)
Deformations(liner, …)Deformations(liner, …)
Heat transfer BC’sHeat transfer BC’s
CFD simulationInner cylinder flow, coolant flowCFD simulationInner cylinder flow, coolant flow
Flow field(HTC, combustion)Flow field(HTC, combustion) OK?OK?
yes
noSimulation variant
CAE Models(FE-Model, complete engine), (CFD models coolant jacket, combustion chamber & ports)CAE Models(FE-Model, complete engine), (CFD models coolant jacket, combustion chamber & ports)
Flow BC’sFlow BC’s
Multidisciplinary Simulation Approach
Thermodynamic Analysis Thermodynamic 1D calculationsCFD simulationIn-cylinder combustion simulation Coolant flow simulationThermal or Heat Transfer Analysis
Conjugate heat transfer analysis Inputs – Surface heat flux, under-hood HTC and T Outputs – Solid temperatures
Thermo-structural Analysiscarried out to account for the different operating
conditions of the engine as per the real world usage
pattern. This includes the following,
Cold assembly
Cold firing
Warm-up
Warm-up with peak firing load
FE Model - first activity
Material Data - elasto-plastic curves
Fatigue AnalysisFatigue analysis always begin at a crackStages of Fatigue Failure
Crack initiation(life till crack of 2mm is detected)
Crack propagationSudden fracture due to unstable crack growth
S-N or ε-N curves are base Modes of failure
HCF – Endurance factor of safety
LCF – Damage
High Cycle Fatigue
Low Cycle Fatigue
105 2*105
Endurance strength
No. of cycles
Alternating stress
Various Approaches for Fatigue Analysis
Stress Life approachOld MethodStress or S-N diagram is baseUsed for HCF applications (i.e. assembly expected
to last for 100000 cycles)
Strain Life approachStrain or ε-N diagram is baseUsed for LCF applications
Fracture Mechanics approachUsed for calculation of remaining life i.e. crack
propagation life
Case StudyEvaluation of strength of engine cylinder
head and crankcase assemblytwo cylinder four stroke engineThem0-dynamic AnalysisCFD simulations
Coolant flow simulationIn-cylinder – HTC & Fluid temperature
Under-hood- HTC & Air temperature
Conjugate Heat transfer approach is used
Thermo-structural AnalysisLoad cases
Assembly Load case Cold Firing Load case Engine Warm-up Hot firing load case
FE ModelConsist two cylinders
Fatigue AnalysisHCF analysis is carried out to calculate
fatigue safety factorStress life approach is used
Design ModificationLow safety factors were observed in some of
the regions. Modifications were suggested to improve the safety factors in those regions.
Case StudyEngine discussed hear is a diesel enginedue to increased power output, cylinder head
is susceptible to High cycle Fatigue (HCF) cracks as well as Low Cycle Fatigue (LCF) cracks at weaker areas like water bracket area, valve bridge on fire deck, fuel line boss, intake port bridge, etc.
FE ModelTwo complete cylinders (#5 and #6)
Boundary Conditions Symmetric BC are applied at cutting planes AA and BB.
The full speed full load durability test on diesel engine developed showed that cylinder head shows more cracks in head bolt boss area and intake port bridge due to HCF.
The stress analysis under assembly loads, thermal loads and high cycle firing loads is carried out in ABAQUS.
FEMFAT Version 4.6b is used for calculations of fatigue factor of safety. Safety Factor is less than 1 in some areas is observed therefore some design modifications are required.
The supplementary rib is provided at intake port bridge and augmented thickness is added at head bolt boss area
This design modification increases bending stiffness at crack location. The modified design at intake port bridge and head bolt boss is effective to improve the durability (increase of about 13% in safety factor).
ConclusionSuccessful mechanical development of
today's increasingly high loaded engine designs demands new sophisticated simulation techniques.
Cracks can be investigated by FE analysis and optimization design can be obtained.
It is possibly increasing to replace the classic durability test in engine development .
CAE is essential method in rapid development process.