Tension crack

It is important to note material such as those plastics or wood that are weak in either tension or compression will also be basically weak in shear. For example, concrete is weak in shear because of its lack of strength in tension. Reinforced bars in the concrete are incorporated to prevent diagonal tension cracking and strengthen concrete beams. Similar action occurs with RPs using fiber filament structures. 

Figure 24. Cross section showing spherical pore and tension cracks concentric with sulfur- urea interface in an improperly cooled sulfur coating...

With increase of the roadway depth, the left side and the right side of the roadway are subjected to tensile, shear, or combined stress state. Thus, tension crack, shear crack or mixed mode crack are existed in these locations. 

Under the increase of loads, there are three independent tension cracks firstly arise on the left side wall. As further increase of the loading, cracks continually propagate, converge and coalesce leading to the penetrating cracks on both sidewalls and the floor until complete failure of the roadway. 

Figure 7.21 SEM observations of the healed crack (a) SMPFs without pre-tension (crack narrowed to 60 pm) and (b) SMPFs with 100% pre-tension (crack narrowed to 20 pm). Source [21] Reproduced with permisson from Elsevier...

Rotational slides usually develop from tension scars in the upper part of a slope, the movement being more or less rotational about an axis located above the slope (Fig. 3.10). The tension cracks at the head of a rotational slide are generally concentric and parallel to the main scar. When the scar at the head of a rotational slide is almost vertical and unsupported, then further failure will usually occur, it is just a matter of time. As a consequence, successive rotational slides occur until the slope is stabilized. These are retrogressive slides, and they develop in a headward direction. All multiple retrogressive slides have a common basal shear surface in which the individual planes of failure are combined. 

Earth fssure in south central Arizona. The fissure results from erosional enlargement of tension cracks caused by differential subsidence. The subsidence is caused by declining groundwater levels. Courtesy of Dr T.L Holzer. 

You may also want to know how to spot tension cracks, or fissm-ed materials in an excavation. These could be indications of potentially hazardous situations. 

This approach combines LTCC microsystems technology and piezo technology and allows for a tremendous improve of functional integration, e.g. sensing, actuation, buried electronic circuits, and strain- stress transformation. Tlie challenge exists in avoiding tension cracks at shrinking of... 

In summary, the seismic geo-hazards characteristics in the low mountains and hilly topography areas is mainly tension crack and small collapse which is usually focus on the top and along the ridge. In the middle and high mountains areas, seismic geo-hazards more often occur in the middle and upper parts of slope than those at the top of the hill. Types of geo-hazards were usually above medium-size landslides or rockfalls. In the canyon areas, the seismic geo-hazards density of the V-shaped canyon was higher than that of the U-shaped canyon areas. Therefore, it has reason to infer that the canyon morphological characteristics has a certain impact on the ground motion response on both sides of the slopes. 

Field investigation of Weigan hill after Wenchuan earthquake showed that the hilltop had unusually stronger ground motion response than the lower part of the slope, the seismic tension cracks were extending as NWW direction along the ridge. 

Slopes are likely to fail if they have failed on a previous occasion and are not reinforced by proper remedial works. Tension cracks, leaning trees, and deformed ground and structures in the slope all indicate that a slope has a high probability of failure. The stability of slopes with otherwise high probabilities of failure is significantly increased if proper remedial works have been carried out. Therefore, failure history and failure indications, as well as the condition (status)... 

Model N-1 was an unreinforced slope. During the process of loading centrifugal acceleration from 0 g to 25 g, the displacement of the slope was quite small, just a small amount of settlement at the top and unconspicuous bulge at the slope surface. When the centrifugal acceleration reached 35 g, the lower third of the slope bulged further with local damage occurred, and many cracks appeared after a while, which were able to form a circular potential slip surface. At the same time, a tension crack about 5 cm deep appeared on top of the slope. With the development of cracks, a clod of soil about 3.5 cm far from the slope surface collapsed abruptly. Then the slope came into a new state of equilibrium after the collapse. The test was stopped at the acceleration of 100 g (See Fig. 2). 

It was found from the failure pattern that the unreinforced slope was prone to collapse suddenly, while reinforced slopes were able to maintain their integrities. As far as the reinforced slope is concerned, cracks mainly occurred in three places (1) the zone near the surface, from toe to half of the slope (2) top of the slope and (3) the interface between each layer of reinforcement and the soil. The cracks occurred first near the slope surface. The cracks on top of the slope were mainly tension cracks. The largest crack on the top mainly located in the unreinforced region. In the reinforced... 

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