Upload
others
View
5
Download
0
Embed Size (px)
Citation preview
Developments in Stress Relaxation and Lifetime estimation test methods
and instruments
Göran Spetz
Stress RelaxationStandardised test methods
Relaxation in compression, ISO 3384
a) measurement at test temperature
b) measurement at room temperature
c) measurement in liquids (rings)
Stress RelaxationStandardised test methods
Relaxation in tension, ISO 6914
a) continuous elongation
b) intermittent elongationthis is not relaxation, but measurement
of the change in modulus
Stress RelaxationWhat happens in the material
• Physical relaxation
• Thermal degradation
• Oxidative degradation
• Continued crosslinking
HistoryThe first relaxation rig
Relaxation rig and amplifier
Relaxation system
Relaxation rigsCompression, Tension, in liquids
Discontinuous relaxation
Discontinuous relaxation
Compression Tester
Control and measurement of:
• Temperature 0,1 °C• Force 0,1 N
• Displacement 0,001 mm
Discontinuous relaxationresults
Method A 168 h at 23 °C; % relaxationMaterial Mean Sr r SR R (R)A 10,9 0.80 2.22 1.21 3.40 31
Method A 168 h at 100 °C; % relaxationMaterial Mean Sr r SR R (R)A 50.5 0.85 2.37 2.15 6.03 11,9
Method B 168 h at 100 °C; % relaxationMaterial Mean Sr r SR R (R)A 67.5 2.07 5.80 8.66 24.3 36
Sr = repeatability standard deviation, measured unitsr = repeatability, in measured units (i.e..%relaxation)SR = reproducibility standard deviation, measured unitsR = reproducibility in measured units (i.e..%relaxation)(R) = reproducibility in %
Table 1 Precision
ITP ISO 3384 Stress relaxation,1998
Stress Relaxation b:9 2007-10-04Elastocon AB
RepeatabilityOne rig different test periods
RepeatabilityTwo rigs the same test period
Important factors
• Keeping a constant deformation
• Keeping a constant temperature
Deformation, mm
Force, N
1,50 1,52 1,54 1,56 1,58 1,60
0
10
20
30
40
45 ° IRH70° IRH
Compression curve
Stress Relaxation b:13 2007-10-04Elastocon AB
Manual compensation
Calculated compensation
Relaxation test in room temperatureInfluence of temperature variations
Relaxation test at elevated temperatureInfluence of room temperature variations
Stress Relaxation systemwith draught hood and room temperature box
Time, h
Relaxation, %
1 5 10 50 100 500 1000 5000 10000
0
20
40
60
80
100
M-ringG-ring
Sealing rings 70 °CRelaxation Test
Stress Relaxation b:20 2007-10-04Elastocon AB
Time, h
Relaxation, %
1 5 10 50 100 500 1000 5000 10000
0
20
40
60
80
100
M-ringG-ring
Sealing rings 70 °CRelaxation Test
Stress Relaxation b:21 2007-10-04Elastocon AB
Time, h
Relaxation index
1 5 10 50 100 500 1000 5000 10000
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
Relaxation - sealing rings
Stress Relaxation b:22 2007-10-04Elastocon AB
70 °C85 °C
100 °C
t1t2t3
Temperature,°C
Ln time, h
0 10 20 30 40 50 60 70 80 90 100 110 120
1e2
5e2
1e3
5e3
1e4
5e4
1e5
5e5
1e6
Arrhenius plot
Stress Relaxation b:23 2007-10-04Elastocon AB
t1
t2
t3
Lifetime
Max temperature of use
1/T
Temperature,1/T
Ln time, h
10
50
100
500
1 k
5 k
10 k
50 k
100 k
500 k
1 M
-3,20e-3 -3,00e-3 -2,80e-3 -2,60e-3 -2,40e-3 -2,20e-3
10
50
100
500
1 k
5 k
10 k
50 k
100 k
500 k
1 M
50 °C 100 °C 150 °C 200 °C
50 % reduction in force
FFKM 545Arrhenius plot
Lifetime estimation - Rubber Materials:33 2005-11-13Elastocon AB
1/T
Temperature,1/T
Ln time, h
100
500
1 k
5 k
10 k
50 k
100 k
500 k
1 M
-3,20e-3 -3,00e-3 -2,80e-3 -2,60e-3 -2,40e-3 -2,20e-3
100
500
1 k
5 k
10 k
50 k
100 k
500 k
1 M
50 °C 100 °C 150 °C 200 °C
Relaxation 50 % reduction in force
Arrhenius plot for FKM
Lifetime estimation - Rubber Materials:31 2005-11-13Elastocon AB
1/T
ISO 3384-1 changes
• Divided into two partsPart 1 at constant temperaturePart 2 at cycling temperatures
• Technical revisions
• Addition of a calibration schedule
ISO 3384-2 Testing with temperature cycling
• Method A, Once a week at low temperature
• Method B, Continuous cycling
Temperature cycle for method A
Temperature cycle for method B
Example of a cycling test
Oven for cycling tests
Automatic Relaxation and Creep Tester
Automatic instrument
Control and measurement of:
• Temperature 0,1 °C• Force 0,1 N
• Displacement 0,001 mm
• Servo motor driven movement ofthe test rig
Relaxation test
Creep test
Stress Relaxation Tests
Stress relaxation tests are very
effective for conducting ageing tests,
as substantial amounts of information
result with little effort, especially
when using the continuous
measurements system