31 creep machines of own construction allowing (alternatively):
- constant tensile load tests
- max. load 8000 N
- max. elongation 0.60 (0.47 true) (at 50 mm gauge length)
- constant tensile stress tests
(Hostinský and Čadek, J. Test. Eval. 4, 1976, p. 26)
- specimen gauge lengths 25, 35 and 50 mm
- max. initial load 8000 N
- max. elongation 0.42 (0.35 true)
- constant compressive stress tests (only 5 machines)
( Dobeš et al., J. Test. Eval. 14, 1986, p. 271)
- specimen gauge lengths 7.5, 12, 15 mm
- max. load 8000 N
- max. elongation 0.32 (0.28 true)
- constant tensile stress (or load) with a possibility of rapid cooling under stress at a predetermined time of creep exposure - see a) or b) - 3 machines
- small punch tests – SPT (3 machine identical with sub d)
ceramic ball penetrated through a thin disk under:
- (i) a given force, central deflection of the disc is measured – analogy with creep tests
- (ii) constant rate of deflection, acting force is measured – analogy with strain–stress
In all tests - possibility of protective atmosphere: purified dry argon, hydrogen, nitrogen
Testing temperatures:
R.T., 70 - 1050 °C, constant within:
- 1 deg for 70 - 600 °C
- 2 deg for 600 - 1050 °C
Temperature gradient along the whole 50 mm gauge length - lower than 2 deg
Elongation detection:
- continuous analog and digital recording
- range of creep rates: 10-10 to 10-2 s-1
- registration of data - PROGRAM CRTES1 (developed in IPM)
Creep curves processing:
- fitting by standard constitutive equations; statistical assessment of long-term properties.
Possibility of recording of creep tests with varying applied stress:
- computer treated creep dip tests, tests with slow applied stress cycling
Possibility to evaluate simple stress–strain (tensile as well as compressive) tests at all temperatures and in protective atmospheres.
Laboratory of Viscous Creep
The laboratory is equipped with two special creep machines for low stress/low strain rate creep tests using helicoid spring specimen technique and one special creep machine for low stress / low strain rates torsion tests of brittle materials (ceramics, intermetallics). Optical measurement of strain eliminates any influence on the stress state and provides high strain sensitivity.
Helicoid spring machines
- Temp. range: 150°C to 1000°C
- Stress range: 0.2MPa to approx. 100MPa
- Strain sensitivity: better than 10-6
- Strain rate range: 10-9 to 10-13 s-1
- Protective atmosphere: purified argon or hydrogen, air
Two methods have been developed to produce the helicoid spring specimens from metallic materials
- (right) Wire drawing, wounding on the threaded bolt and annealing. The method is suitable for pure metals and mild model alloys.
- (left) Machining from tube. The method is suitable for structural materials. The microstructure of the original tube is maintained
Torsion machine
- Temp. range: 300°C to 1200°C
- Stress range: 2MPa to approx. 100MPa
- Strain sensitivity: better than 10-6
- Strain rate range: 10-9 to 10-13 s-1
- Atmosphere: air
