Simulating and Testing Ice Screw
Performance in the Laboratory
Final
Presentation
04/28/03
Stefano A. Alziati
Warren L. M. Bennett
Advisors: Dr. Kim Blair
Dave Custer
Slide 1
Introduction
•
•
•
•
•
•
Project Motivation
Statement of Problem
Description of Experiment
Results & Discussion
Conclusion
Questions
Ice screw being pulled from Specimen
Slide 2
Project Motivation
• The attraction of extreme sports is aiding its rapidly
increasing popularity.
• Present safety equipment ineffective
more accidents
• Project will be first step towards safer ice protection
• Very little published research available:
– Harmston & Luebben Study, 1997
Slide 3
Primary Hypothesis & Objectives
• Primary Hypothesis:
The structure and morphology of different types of ice
formations can be characterized and simulated in a lab to
provide a “test bed” useful for assessment of ice screws.
• Primary Objective:
To develop a repeatable means of reproducing ice in a lab
and to characterize this ice using rheological data.
• Success Criteria:
a) If hypothesis 1 is true, then success is characterizing the
critical properties of ice.
b) If hypothesis 1 is false, then success is identifying why ice
cannot be made successfully.
Slide 4
Secondary Hypothesis and
Objective
• Secondary Hypothesis:
If the first hypothesis is true, using the simulated ice, the
variables affecting screw placement safety can be
determined.
• Secondary Objective:
To use laboratory created ice to test simulated falls on ice
screws in a manner useful to climbers.
• Success Criteria:
If hypothesis 2 is true, then success is the development of a
test for ice screw safety that produces consistent and
repeatable data for differing ice types.
Slide 5
Description of Experiment
Stage 1: The characterization of ice
• Produced different types of ice using different methods.
• Ice types chosen on ease of production and difference in
characteristics
Slide 6
Experiment (cont’d)
Apparatus setup for stage 1
Slide 7
Preparing specimen for test
Experiment (cont’d)
Stage 2: Testing of ice screws in ice
• Produced the two ice types on a larger scale.
• Placed ice screws at different angles into each specimen
and pulled at different load rates.
Slide 8
Experiment (cont’d)
Stage 2 Test Rig
Slide 9
Close-up of Ice Screw/MTS interface
Results – Stage 1
Compressive Tests:
• ABS 1:
– Compressive strength:
2203 lbs
– Std Dev: 638 lbs
0
-500
0
5
10
Time (s )
15
20
25
-1000
-1500
-2000
-2500
-3000
• ABS 2:
– Compressive strength:
1802 lbs
– Std Dev: 618 lbs
-3500
Compressive load on ABS#1
0
-500
0
5
10
Time (s )
15
-1000
-1500
-2000
• F-Stat: 9% chance of ABS1
being different to ABS2
Slide 10
-2500
-3000
-3500
Compressive load on ABS#2
20
25
Results – Stage 1 (cont’d)
• Density:
– ABS1: 913 kg m-3
– ABS2: 804 kg m-3
– F-Stat: 97% chance of ABS1 being different to
ABS2.
Slide 11
Discussion – Stage 1
• Compressive Test:
– Means are different, however this is not statistically significant
0
-500
– Qualitatively different after testing
• ABS1 still sticks to fingers
• ABS2 feels wet to touch
0
• ABS1 peaks sharper
• ABS2 peaks more rounded
10
Time (s )
15
25
-1500
-2000
-2500
-3000
Compressive load on ABS#1
0
-500
0
5
10
Time (s )
15
-1000
-1500
-2000
-2500
-3000
-3500
Slide 12
20
-1000
-3500
– Graphs are different:
5
Compressive load on ABS#2
20
25
Discussion – Stage 1
• Density:
– Shows definite difference between ABS1 and ABS2.
• Differentiated appearance between ABS1 and ABS2
• Relation to Hypothesis 1:
– Valid hypothesis. Structure and morphology of different ice
types were simulated and characterized in the lab
successfully.
Slide 13
Results – Stage 2
• Typical ice screw test data set.
Slide 14
Results – Stage 2
Load
ABS1 (low rate)
ABS1 (high rate)
ABS2 (low rate)
ABS2 (high rate)
- ve
Previous study’s claim.
Slide 15
0
+ ve
Screw
angle
Results – Stage 2
Peak Mean Failure Load vs. Screw Placement angle
3000
ABS 1
ABS 1
ABS 2
ABS 2
2500
(low rate)
(high rate)
(low rate)
(high rate)
Failure Load (lbs)
2000
1500
1000
500
0
-30
-20
-10
0
Angle
Results from the experiment.
Slide 16
10
20
30
Discussion – Stage 2
• Loading rate:
– Loading rate more significant than screw placement angle or ice
type.
• Very useful for climbers.
• loading rate can be controlled, using ropes that can stretch more and/or
using a friction device for slowing fall.
– No ice screw broken. Possibly due to:
•
•
•
•
Slide 17
development in ice screws over last six years
the length of screw
Temperature of the ice Screws
Loading rate of MTS machine not sufficient for breakage
Discussion – Stage 2
• Screw placement:
– Not much of an influence on the load taken. In general, zero angle is
the one that will hold the most.
Peak Mean Failure Load vs. Screw Placement angle
3000
ABS 1 (low rate)
ABS 1 (high rate)
ABS 2 (low rate)
ABS 2 (high rate)
2500
Failure Load (lbs)
2000
1500
1000
500
0
-30
-20
-10
0
Angle
Slide 18
10
20
30
Discussion – Stage 2
• Relation to Hypothesis:
– Hypothesis proved.
• Variables affecting screw placement safety identified
and tested.
• Ice type, loading rate and screw placement angle all
affect safety.
Slide 19
Conclusion
• Compressive Testing is not necessarily a valid test to
differentiate between ice types.
• Fall Rate significantly affects failure load
• Screws safest at zero degrees
– Previous work not supported by study
Slide 20
Further work
• A test for assessing ice screw performance has
been developed. Further improvements and
developments possible:
– Research on methods for making more different ice types.
– Determination of other tests that can characterize ice
– Research on the effect of screw length on load.
Slide 21
Acknowledgements
• Advisors Kim Blair & Dave Custer
• 622 Faculty Staff
– Earl Murman, Ed Greitzer & Jennifer Pixley.
• Lab staff:
– Dick Perdichizzi, John Kane, Don Wiener, Dave
Robertson & Paul Bauer.
Slide 22
Questions
?
Slide 23
Results – Stage 2
Ice Type
Slide 24
Rate
Angle
Mean
Std. Dev.
SD/ mean
ABS1
0.01
-30
1394
309
22%
ABS1
0.01
0
1660
294
18%
ABS1
0.01
+30
1329
322
24%
ABS2
0.01
-30
1220
410
34%
ABS2
0.01
0
2375
75
3%
ABS2
0.01
+30
810
243
30%
ABS1
1.0
-30
229.75
47
21%
ABS1
1.0
0
446
142
32%
ABS1
1.0
+30
708
481
68%
ABS2
1.0
-30
211
142
68%
ABS2
1.0
0
697
25
4%
ABS2
1.0
+30
547
276
51%