Application
News
No. i272
Precision Universal Testing Machine
Creep Test of Rubber Materials
(JIS K 6273, ISO 2285)
Rubber is an extremely familiar material that has
characteristic mechanical properties such as elasticity and
stretchability and is widely used in a variety of industrial and
consumer products, particularly in applications that require
vibration-proofing or shock-absorbing functions. Synthetic
rubber now accounts for the majority of rubber materials.
Because a diverse range of unique synthetic rubber products
suited to specific applications have been developed,
evaluation of the mechanical properties of these materials is
extremely important.
Creep characteristics can be mentioned as one mechanical
property that requires evaluation. Creep is a phenomenon in
which deformation of a material gradually progresses when
a constant load is applied continuously for an extended time,
and is a cause of malfunction or failure of industrial
products in long-term use in some cases. Thus, in order to
estimate the useful life of a rubber material based on the
intended application or to select a fit-for-purpose material, an
understanding of the creep characteristics of rubber materials
is needed in the development design stage.
This article introduces an example of an evaluation of creep
characteristics by tensile test of chloroprene rubber, which
has excellent weatherability, oil resistance, and heat
resistance and is most widely used as a representative
synthetic rubber.
This test was conducted referring to JIS K 6273, ISO 2285
(Rubber, vulcanized or thermoplastic – Determination of
tension set, elongation and creep) using a Shimadzu
Autograph AGX™-V model Precision Universal Testing
Machine. This material testing system is also suitable for
creep test, as it provides higher test force holding
performance than conventional testing machines.
C. Oya
Test of Tension Set at Constant Load
(JIS K 6273, ISO 2285)
Table 1 shows the equations for calculation of the test items in
JIS K 6273 section 6.5, and Fig. 1 shows the load pattern used in
the creep test. In this test, the gauge lengths at points Ⓐ to
Ⓒ in Fig. 1 were measured, and elongation at constant load,
creep, and tension set at constant load were calculated.
Table 1 Equations for Test Items in JIS K 6273 Section 6.5
Equations for calculation
Elongation at constant load
E2 (%)
E2 = (L3 - L0 ) / L0 ×100
Creep
E3 (%)
E3 = (L4 - L3 ) / (L3 - L0 ) ×100
Tensile set at constant load
E4 (%)
E4 = (L5 - L0 ) / L0 ×100
(Notes)
L0 (mm) : Gauge length before test
L3 (mm) : Gauge length at elapsed time of 30 s (point Ⓐ) from start
of loading
L4 (mm) : Gauge length at elapsed time of 60 min (point Ⓑ) from
start of loading
L5 (mm) : Gauge length at 10 min (point Ⓒ) after specimen is
removed from test device following measurement of
length L4 and is then allowed to contract
Ⓐ: Point at elapsed time of 30 s from start of loading
Ⓑ: Point at elapsed time of 60 min from start of loading
Ⓒ: Point at 10 min after specimen is removed from test device
Fig. 1 Loading Pattern of Test
Specimen
Table 2 shows the specimen material information, Fig. 2 shows
the specimen geometry, and Fig. 3 shows the condition of the
test. The specimen geometry conforms to standard.
Table 2 Specimen Material Information
Material Chloroprene rubber
Specimen dimensions Thickness 2.0 mm, width 4 mm, parallel
length 100 mm
Fig. 2 Geometry of Specimen
Fig. 3 Condition of Test
Stress
Time
30 s
60 min
10 min
A
B
C
Gauge length: 90 mm
Parallel length: 100 mm
Width: 4 mm
