ME 418 LAB D1
FATIGUE TESTING
Unyime (Uy) Bassey Umoh
Email address – ubu610@mail.usask.ca
Office # - 1B70
September 2013
OBJECTIVES
1.
2.
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4.
ME 418 Lab D1 - 2013
3.
To understand the fatigue behaviour of 1018 steel
To understand treatments to improve the fatigue
strength of 1018 steel
To understand the operation of 4 fatigue machines
Krouse
RR. Moore
Budd
Warner-Swasey
To complete 2 fatigue tests on a standard specimen
using a Krouse rotating beam machine


Without treatment
With treatment
2
LABORATORY TIMELINE
Go through concepts of fatigue and equations
 Carry out calculations relevant towards the
Krouse test
 Observe operation of Krouse machine and carry
out test
 Observe operation of 4 fatigue testing machines
 Carry out research challenge
 Record information from Krouse test and sketch
sample identifying crack initiation

ME 418 Lab D1 - 2013
3
LOGBOOK CHECKLIST



ME 418 Lab D1 - 2013

Objectives
Background information
Lab calculations
Information for 4 machines
Sketch of Diagrams
 Method of loading
 Types of stresses produced
 Brief description of operation


Experiment
Number of cycles at failure
 Sketch of failed specimen


Treatment




Procedure
Justification, and
References
Future discussion points
4
THEORY – CONCEPTS

ME 418 Lab D1 - 2013

Fatigue Failure: Progressive Failure process of a
material due to repeated cyclic loading. Loading
induces cyclic stresses, which initiates cracks and
cause them to be propagated until failure occurs
(Collins 43)
Stress-time patterns
Completely reversed (Zero-mean) cyclic stresses*
 Nonzero-mean cyclic stresses
 Random stresses

5
THEORY – CONCEPTS
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ME 418 Lab D1 - 2013
Fatigue (endurance) Limit: The stress level under
which an infinite number of cycles can be
sustained without failure of the material.
Response of Ferrous materials and Titanium
Denoted as Sf for actual machine part and Sf’ for
small polished specimen.
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THEORY – CONCEPTS
ME 418 Lab D1 - 2013
Sf
Figure 1: S-N curves showing response to cyclic loading
http://www.efunda.com/formulae/solid_mechanics/fatigue/images/fatigue_SN_01.gif
7
THEORY – CONCEPTS
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ME 418 Lab D1 - 2013
Fatigue strength: The stress level at which a
material will fail when loaded by N number of
cycles.
Response of Non-ferrous materials
Denoted as SN for actual machine part and SN’ for
small polished specimen
8
THEORY – CONCEPTS
ME 418 Lab D1 - 2013
N
Figure 1: S-N curves showing response to cyclic loading
http://www.efunda.com/formulae/solid_mechanics/fatigue/images/fatigue_SN_01.gif
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THEORY – CONCEPTS
ME 418 Lab D1 - 2013
Figure 1: S-N curves for Ferrous and non-ferrous materials
(Taken without permission from Collins, J. A. Mechanical Design of Machine Elements
and Machines: a Failure Prevention Perspective. New York, NY: Wiley, 2003. Print)
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THEORY – EQUATIONS

SN = 1/6 (S106 - S1).log(N/106) + S106
ME 418 Lab D1 - 2013
*Logarithmic relationship - A straight line
between S1 and S106 on a semi-log plot (i.e. SN vs.
log[N]):
11
THEORY – EQUATIONS

6 (-1/3log[S
SN = S106 . (N/10 )
/S
103
])
106
ME 418 Lab D1 - 2013
*Power relationship – A straight line between
S103 and S106 on a log-log plot (i.e. log[SN] vs
Log[N]):
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THEORY – EQUATIONS
Where:
and,
CL = Load factor
CS = Surface factor
CG = Gradient factor
CT = Temperature factor
CR = Reliability factor
SN’ = Endurance limit for a mirror polished specimen
Z = Endurance ratio (Estimated as 0.5)*
ME 418 Lab D1 - 2013
S1 = SUT
SN’ = ZSUT
*S103 = 0.9SUT
S106 = SN’CLCSCGCT CR
13
LOGBOOK CHECKLIST



Sketch of Diagrams
 Method of loading
 Types of stresses produced
 Brief description of operation


Experiment
ME 418 Lab D1 - 2013

Objectives
Background information
Lab calculations
Information for 4 machines
Number of cycles at failure
 Sketch of failed specimen


Treatment




Procedure
Justification, and
References
Future discussion points
14
CALCULATIONS
(POWER RELATIONSHIP)
ME 418 Lab D1 - 2013
Determine:
1) SN
NGroup = To be Provided,
DGroup = To be Measured,
and:
SUT = 114 ksi
CL = 1
CS = 0.74
CG = 1
CT = 1
CR = 1
Z = 0.5
15
CALCULATIONS
2) Estimated time for test, assuming 5000rpm
ME 418 Lab D1 - 2013
3) Moment, M
16
LOGBOOK CHECKLIST



Sketch of Diagrams
 Method of loading
 Types of stresses produced
 Brief description of operation


Experiment
ME 418 Lab D1 - 2013

Objectives
Background information
Lab calculations
Information for 4 machines
Number of cycles at failure
 Sketch of failed specimen


Treatment




Procedure
Justification, and
References
Future discussion points
17
RESEARCH CHALLENGE

Literature search and Brain storming
Treatment of same specimen to Increase fatigue
strength showing
1. Specimen treatment
 Temperature
 Time
2. Justification
 Mechanical properties
 Micro-structural considerations
3. Note references
ME 418 Lab D1 - 2013

18
AFTER LAB TO DO
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Treatment
Submit treatment procedure within 2 school days
 Complete treatment within 1 week of acceptance
 Submit specimen according to schedule posted in 2C26
 Email Rob peace – rob.peace@usask.ca
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Include all treatment results that will be sent out in
your logbook
Compare strength of heat treated sample with nonheat treated sample
Plot S-N relationship from all groups data
Assuming power relationship, determine
experimental endurance ratio and ultimate strength
of the steel
Compare S-N for theoretical and experimental
ME 418 Lab D1 - 2013

19
LOGBOOK CHECKLIST



Sketch of Diagrams
 Method of loading
 Types of stresses produced
 Brief description of operation


Experiment
ME 418 Lab D1 - 2013

Objectives
Background information
Lab calculations
Information for 4 machines
Number of cycles at failure
 Sketch of failed specimen


Treatment




Procedure
Justification, and
References
Future discussion points
20