Environmental stress cracking

If a material in air below its yield strength mechanically loaded, so you can after a certain period, which can be very long, stress cracks. Cause may be internal or external, or a combination of both types of stress. The simultaneous stress by a chemical medium can lead to a drastic reduction in time to rupture. This phenomenon is called environmental stress cracking ( ESC environmental stress cracking = ) referred.

Mechanism

Measurement methodology

The determination of the ESC is complicated because it is influenced by many parameters. This can be, inter alia, of the test specimen (orientation, structure, residual stresses ) and manufacturing, thermal history of the specimen, chemicals.

Object is to determine the relative effect of the load by chemical media ( vicinity) of each plastics ( test specimen and finished parts ). However, it is often not possible to establish a link between the results of ESC short-term measurements on test specimens and actual usage behavior of finished parts.

Full Notch Creep Test

The Full Notch Creep Test ( FNCT ) is one of the test methods for determining the slow crack growth behavior of polyethylene under the action of a wetting agent, which is used to accelerate the test. The FNCT is in the standard ISO 16770 regulated internationally and also on German as Plastics " Plastics - Full -notch creep test ( FNCT ) - Determination of environmental stress cracking (ESC ) of polyethylene " - Determination of environmental stress cracking resistance of polyethylene under the influence of media (ESC ) - creep test on specimens with a circumferential notch ( FNCT ) available. The current status on 1 February 2004.

Experimental principle

When samples are rectangular -made, preferably in the size 10 × 10 × 100 mm ³, samples of pressed plates or finished products (eg from a pipe wall ) are used. These are (Full notch ) provided with a circumferential groove which is used for crack initiation. The acceleration test is tested at elevated temperature ( 50-95 ° C) and under the effect of a wetting agent ( ARKOPAL N100 and ARKOPAL N110 ). The test specimens are subjected under these environmental conditions of a constant load, and detects the time up to fracture. These masses are chosen so that normally stress 4-5 MPa act in the remaining cross section of the notched sample and slow crack growth - slow crack growth (SCG) takes place. Since the test takes place in a network means you count him also to environmental stress cracking.