Cracks dormant

Stress Crack Resistance. Failure caused by environmental stress cracking may be attributed to stored stresses acquired in the molding or exlrnding operation. These dormant stresses may release themselves by cracking under the combined influence of an adverse environment and polyaxial stretching dunng use. Polyethylene of narrow molecular weight distribution tends to crack less under environmental stress. 

Cracks are either dormant or active. Dormant cracks can be repaired without experiencing additional cracking. Active or working cracks will most often crack again, even when repaired. The method and material for repair can influence the effectiveness of the repair. 

Cracks can be described as active or dormant. An active crack will open and close with changes in temperature and with cyclic movement of the structure. Dormant cracks may not go through such movement, but they can still leak, collect dirt, interfere with traffic, and so on. A structural crack usually can be attributed to inadequate structural design, insufficient strength (material composition), or poorly designed joints. If joints are not provided in concrete slabs, the concrete wiU create its own joints by cracking, and these cracks will continue to develop until the concrete member comes to equihbrium. 

Active cracks may be sealed with an elastomeric sealant. Dormant cracks may be sealed with a fluid epoxy sealer that can be pumped into the crack or allowed to flow in by gravity. An epoxy sealer of 100 percent sohd content will seal the crack without shrinkage and will join the crack faces to re-form a monolithic structure.This seal will be strong enough to resist further cracking. However, should stress stiU occur, cracking will take place somewhere else in the structure. 

JQ Wang, A Atrens, Analysis of service stress corrosion cracking in a natural gas transmission pipeline, active or dormant . Engineering Eailure Analysis, 2004, 11, 3. 

Fig. 7.20 Dormant crack at the notch root 1.3 mm depth in a mild steel after 24-10 cycles [27]...

---