Wide-opened crack

The CTH approach is able to control the crack width, which can be closed by controlling the compression pre-strain level. A simple equation has been established by Li et al. [54] to correlate the crack width to be closed and the pre-strain level during compression programming. Cracks with different opening widths can be closed based on the level of compression programming (of course it is limited by the maximum allowed compression pre-strain level). In the unconstrained shape recovery approach such as the SMASH approach, it has not been demonstrated that it can close a wide-opened crack with constrained boundary. Also, it cannot control the crack width that can be closed because it depends on the external load to perform programming and relies on the shape recovery ratio and boundary condition of specimens to perform crack closing. 

We will now find out what is the ideal shape memory (SM) material for narrowing wide-opened cracks. For this reason, let us discuss an ideal model, as shown in Figure 7.3. 

Therefore, we aim to answer the following questions in this study (1) a proper coating agent to enhance the shape fixity and dispersion ability of the strain hardened short SMPFs (2) the ability for strain hardened SMPU fibers to repeatedly heal wide-opened cracks and (3) the effect of fiber length on the healing efficiency. 

The films deposited in 4 h on untreated and on CISCM I-activated PMR-15 were both 230 nm thick (Table 1), consisting of densely packed particles -50-100 nm in diameter that are likely agglomerates of 10 nm crystals (based on the XRD data). A few agglomerates of -500 nm could also be seen. Open cracks -50 nm wide were evident in both films, as compared to 270 nm thick Method 2 films on silicon that showed only closed cracks.12... 

Figure 9.38 is a BF image of a healed fracture that is about 4 / m wide. The fracture walls are straight and separated by a band of new quartz, which has grown in the open crack. The bands of electron-beam damage centers (Section 8.13.1) parallel to the fracture walls probably mark the positions of trace impurity concentrations formed at incremental growth... 

Figures 4.26 and 4.27 show the retrofitting of one of the masonry towers of the ancient VerceUi castle in Italy by applying CFRP rods bonded into the space between the bricks. One of the four towers showed wide vertical cracks. Reinforcement of the outer side of the masonry wall was necessary. This was achieved by wrapping horizontal CFRP rods around the tower to prevent further opening of the cracks. The rods were bonded using epoxy resin. The strengthening was completed in May 2004.

In the following, we would like to present a proof-of-concept study to validate this CTH scheme for healing wide-opened structural-length scale cracks [33,34]. 

Clearly these two models are consistent with each other and merge when the crack is looked at over a wide range of scales as in Fig. 7.14. At macroscopic resolution, the crack seems to be in equilibrium at a particular loading (Fig 7.14(a)). There does not seem to be any motion at the crack tip. However, when viewed at the atomistic level (Fig 7.14(b)) the crack tip is seen to be in rapid thermal Brownian motion. The reacted molecules form the adhered region to the left of the crack tip, whereas the unreacted molecules lie to the right at the open crack surface. The crack tip is not a static point in this model. It is wandering kinetically from right to left as the molecules spontaneously break and then rebond. 

Among these cracks, the widest cracks with 1 m opening occurred in Shuanghe Village. The cracks changed with seismic process. Firstly, the ground surface was ruptured under tensile force with wide opening and certain vertical displacements. After the... 

Cutting operations should be performed in wide-open areas so sparks and slag will not become lodged in crevices or cracks. 

The corrosion of steel fibres in cement matrix was a subject of concern in the first period of appUcation of SERC, but later it was proved that only short sections 2-3 mm long that stretch out of the concrete surface corrode and disappear in a short time. Cracked specimens maintained during 18 months in four different environments proved that no decrease of strength could be found in the non-cracked concrete and rusty fibres were found only in the immediate surface in the carbonated zone (Nemeeger et al. 2003). The test carried on by Granju and Balouch (2005) have confirmed that even fibres which bridged open cracks of 0.5 mm wide and maintained a year in a marine environment exhibited only minor traces of corrosion that did not progress inside the concrete matrix. 

The correct way to start up a centrifugal pump is with the discharge valve barely cracked open. If the operator starts the pump with the discharge valve wide open, or if he suddenly opens the discharge after initiating flow, the pump will cavitate. Why does this happen ... 

Vein Deposits. The vein deposits of uranium are those in which uranium minerals fill cavities such as cracks, fissures, pore spaces, breccias, and stockworks. The dimensions of the openings have a wide range, from the narrow pitchblende-fiHed cracks, faults, and fissures in some of the ore bodies in Europe, Canada, and AustraHa to the massive veins of pitchblende at Jachymov, Czech RepubHc (15). 

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