Kurt Munson HBM Prenscia - nCode · HBM Prenscia: Public © 2016 HBM Fatigue Analysis of Powertrain Components Including Gray Cast Iron Kurt Munson HBM Prenscia User Group Meeting

HBM Prenscia: Public

© 2016 HBM

Fatigue Analysis of Powertrain ComponentsIncluding Gray Cast Iron

Kurt MunsonHBM Prenscia

2016 nCode User Group Meeting

© 2016 HBM October 5-6, 2016 www.ncode.com


© 2016 HBM

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1. Durability challenges in powertrain components2. Methods of analyzing powertrain component durability

Vibration fatigueSafety factor analysisStress gradient approach for castingsTemperature’s effect on fatigueSpecialized methods for gray cast iron

3. Summary

Agenda




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• Powertrain engineering covers a wide range of components that require differing methods for durability assessment.

Powertrain Durability Challenges

Images copyright Beaudaniels.com




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Designing Around Endurance Limit


Pistons, crankshafts, valve springs, etc. may be assessed using a safety factor analysis.




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5Safety Factors in Design: Simple to Complex

UTS‐basedsafety factorUTS‐basedsafety factorUTS‐basedsafety factor

Fatigue limit safetyfactor



Cumulative damage

Cumulative damage

Cumulative damage

Fatigue limitwith mean stresssafety factor



Stress‐Life, Strain‐Life, etc.

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• Many parts are designed according to a safety factor.• What is the ratio of strength to stress?• The safety factor can be calculated many ways:




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Designing Around Vibration


Electronics and other under‐hood mounted components are signed off with vibration tests.




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7Vibration Fatigue from Harmonic Stresses

• The response PSD: . | | • Derive the statistical cycle distribution based on work by S. O. Rice

SNAnalysis Fatigue ResultsFRF

H1

PSDL1

Response PSD and Statistical Cycle Distribution

SN Curve

[σA] = [H1]².L1




© 2016 HBM

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Frequency (Hz)

PSDL2

Vibration Fatigue from Harmonic Stresses

SNAnalysis Fatigue Results

PSDL1

Response PSD and Statistical Cycle Distribution

SN Curve

[σA] = [H1]².L1 + [H2]².L2 + [H1]*.[H2].L12 + [H1].[H2]*.L21

Gain Phase

Frequency (Hz)

CSDL12

Frequency (Hz)

FRFH2

FRFH1




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Designing Around Heat


Turbochargers and exhaust systems require thermo‐mechanical fatigue analysis.




© 2016 HBM

10Which Temperature Dependent Fatigue Method is Best?

Is stress caused by

temperature

YesNo

Isothermal fatigue

Start

Chaboche Transient & Creep RuptureChaboche Transient

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Is T > 50% of Tmelt (K)?

YesNo




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Designing with Castings


Engine block and other castings require specialized material modelling and fatigue algorithms




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FKM Guideline “Analytical Strength Assessment of Components in Mechanical Engineering” 5th edition, 2003, English version, Tr. E. Haibach published by VDMA, Frankfurt. ISBN 3-8163-0425-7

z

dzd

n = Kt/Kf

Notch Sensitivity and Fatigue of Cast Materials




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• Cast iron with graphite flakes for improved manufacturability and damping• Often used in engine blocks, pump housings, and disk brake rotors• Graphite flakes are weak and act as voids when loaded• Leads to higher strength and stiffness in compression than tension

Gray Iron

By Hb tuw ‐ Own work, CC BY‐SA 4.0, https://commons.wikimedia.org/w/index.php?curid=45350398




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• Hysteresis loop is no longer symmetric• Shape changes in loading vs. unloading, and tension vs. compression• Strain life methodology used with modified plasticity model and Smith Watson

Topper damage parameter• Available in nCode 12.1

Fatigue of Gray Iron




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• 9 gray irons are included in the standard nCode material database

Gray Iron Materials Data in nCode




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16Software Demonstration




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Methods of analyzing powertrain component durability• Vibration fatigue• Safety factor analysis• Stress gradient approach for castings• Temperature’s effect on fatigue• Specialized methods for gray cast iron – new in nCode 12.1

Summary




© 2016 HBM

www.hbmprenscia.com

Kurt Munson

Principal consulting engineer

[email protected]

Thank you!



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Kurt Munson HBM Prenscia - nCode · HBM Prenscia: Public © 2016 HBM Fatigue Analysis of Powertrain Components Including Gray Cast Iron Kurt Munson HBM Prenscia User Group Meeting