Dynamic Fatigue of High Performance Synthetic Ropes

Dynamic Fatigue of High
Performance Synthetic Ropes
Phil Roberts, Paul Smeets*, Danielle Stenvers and Rafael Chou
Samson Rope Technologies, Inc. USA
* DSM High Performance Fibers, The Netherlands
Goal
™ To provide data and support for retiring HMPE fiber
tug ropes in a economic, but safe manner.
™ On-going project to inspect and analyze and catalog
residual strength of used Samson Amsteel-Blue rope.
Approach
™ Investigate and understand forces of vessel and
machinery dynamics on Amsteel-Blue
™ Create a testing method to catalog and analyze visual
changes to Amsteel-Blue and residual strength from
used ropes and new ropes under laboratory
conditions
The Application for the Study –
Tractor Tug Winch Line
64 mm diameter Amsteel-Blue winch line on Crowley Marine
Services Inc. Harbor-Class tractor tug, “MASTER”, in
Long Beach harbor, California
Rope Strength
After Dynamic Fatigue
R e s id u a l S tre n g th s
% P ublished Minimum S trength
100%
90%
80%
70%
60%
50%
40%
Jobs
E n d s o f M a in T o w lin e s
P e n d a n ts
M id s e c tio n s o f M a in T o w lin e s
Data Analysis
Jobs Line Fit Plot - M idsections
Residual
Strength
Residual Strength
100%
95%
Predicted
Residual
Strength
90%
85%
80%
75%
70%
65%
60%
0
500
1,000
N umber of Jobs
1,500
2,000
Possible Mechanisms of Strength Loss of
Amsteel-Blue Rope after Dynamic Fatigue
ƒ Abrasion and cutting damage
ƒ Fiber Fatigue
ƒ Compression of rope on the winch
drum
– Deformation of rope construction
ƒ Line twist during application
ƒ Shock loading
Identifying the Relative Significance of
Contributing Factors
Abrasion and cutting damage
Cutting damage on test samples was cataloged and analyzed to see if a
percentage loss of rope strength can be calculated by severity or
number of strand and yarn cuts in rope working section
Fiber Fatigue
Fiber samples from different portion of the fatigued ropes were tested
and analyzed for their residual strength
Compression of rope on the winch drum
Ropes samples from different compression conditions
were tested and analyzed to study the compression effect
Line twist during application
Lab simulation tests on small diameter ropes with artificial twists were
conducted
Shock loading
Shock load simulation tests were conducted to study the
effect of shock load on rope strength
Conclusions
™ Fatigue behavior should be studied as a
function of number of jobs, not hours
™ Abrasion and cutting damage has
averaged 5-10% wear – leading to an
estimated of same strength loss
™ Fiber fatigue is not a major contributing
factor of the strength loss of ropes
™ Drum compression is estimated to
account for strength loss of 10-15%
™ Line twist of 1 to 1.5 turns per foot
equates to a 15-20% strength reduction
™ Shock load does not weaken the rope