Tension fractures

In tension, fracture occurs before the stress reaches G/10. 

Figure 14.8 Stress-strain curves for polycarbonate at T = 11 K determined under tension and uniaxial compression. The nominal stress curves, cs , correspond to the dashed lines, and those for the true stress, o- correspond to solid lines. The material tested under tension fractures immediately after reaching yield, unlike the situation that occurs under compression. (From Ref. 12.)...

Subsurface tension fractures will form when the minimum effective stress (CTj) reduces to the tensile strength of the rock (-C,). This will occur when the minimum total stress (S3) is reduced by tectonic dilation, or pore fluid pressure is increased (Watts, 1987). These failure conditions can be summarised as follows ... 

Tectonic breaching within the GEA is mostly related to Cretaceous to Tertiary compressional or tran-spressional deformation and is manifested by two processes. Firstly, extension occurs above the neutral surface of inversion folds (Fig. 8a), thereby creating a pattern of radial tension fractures, extending upwards from the seal into the overlying section. Radial fractures will not form below the neutral surface of the fold limb which is in compression. As a consequence, reservoir objectives lying above or close to the neu-... 

The miniature Compact Tension fracture specimen is new, and as such, needs thorough evaluation before the resulting data can be considered to be intrinsic material behavior. 

The calcite veins were formed at crustal depths of at least 1 km (Nemcok et al. 1995). Therefore, so they are unlikely to have formed as tension fractures (with <7j negative) but rather as hydrofractures, as is also indicated by their aspect ratios and inferred fluid overpressure. 

Figure 4.3 SEM photograph of the compact tension fracture surface of 4 phr (parts per hundred grams of resin) ETBN-modified VE resin showing cavitated particles.

Figure 4.4 SEM photographs of the compact tension fracture surface of 4 phr VTBN-modified VE resin showing a) transition from fast fracture to crack-initiation region and b) close-up of one particle. Propagation was from left to right. The specimen was stained with osmic acid. Reprinted with permission from J.S. Ullett, and R.P.Chartoff, Polymer Engineering and Science, 1995, 35, 13, 1086 1995, John Wiley and Sons Publishers...

Drop weight, standard and precracked Charpy impact, tensile test, and compact tension fracture toughness specimens are provided for unirradiated tests. Drop weight tests will be conducted in accordance with ASTM E-208. Charpy impact tests will be conducted in accordance with AGTM E-23. Tensile tests are conducted in accordance with ASTM E-8 and E-21. Correlation of drop weight and Charpy impact tests to establish will be made in accordance with NB2300 of the ASME Code, Section III. Charpy impact and tensile test specimens are provided for post-irradiation tests. 

Unfortunately, the elastic response of rabber in flow is the least well-understood facet of the viscoelastic nature of mbber. A good example of elasticity in flow is the behavior of chewing gum when pulled to break. After chewing and softening, if one pulls the chewing gum to tension fracture, the broken ends of the gum retract The flow of the gum is the extension while pulling and the elasticity is represented by the recovery of the broken ends. Whether in compression, transfer, or injection molding, the flow of the mbber compound is also accompanied by elastic rebound. 

Tension fractures (extension fractures) originated from tension stress perpendicular to the created fracture. On a big scale, this type corresponds to joints. 

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