Welding and crack healing

Equation (10.48) is particularly useful for studies of crack healing, welding time in molding operations, and film formation from latexes (21). Alternately, equations (10.47) and (10.48) can be cast in the form. 

Diffusion in polymer-polymer systems is important in many practical applications, such as crack healing, polymer blending, welding, adhesion, elastomer tack, polymer fusion, and many others. However, diffusion coefficient data is lacking due to the complexity of the polymer diffusion process. Typical techniques employed are infrared spectroscopy, spectroscopic ellipsometry, and optical schlieren. Only a few studies of interdiffusion in polymer pairs are reported. Depending on the temperature and other physical parameters of the system, Fickian and Case II diffusions (see Section 4.3) can be observed with varying relative importance (Jabbari and Peppas, 1993). 

Total interpenetration of chains (X approaches Rg) is not necessary to achieve complete strength when M > M and x < 7). However, a word of caution while complete strength may be obtained in terms of critical fracture measures such as G c and A lc, the durability, measured in sub-critical fracture terms, such as the fatigue crack propagation rate da/AN, may be very far from its fully healed state at r. We have shown that while the weld toughness A lc increases linearly with interdiffusion depth X as K f. X, the fatigue crack propagation behavior of partially healed welds behaves as [1]... 

A total of 37 leaks was experienced in PFR SG units in the period 1974 to 1984 with 33 of these occurring in evaporators, 3 in superheaters and 1 in a reheater. All the leaks originated at the welds between the tubes and the tube plates associated with cracking of the tube-to-tube plate welds. These were hard and had high residual stresses beeause there was no post-weld heal treatment. The type of direct tube-to-tube plate weld (the butt/fillef weld adopted initially at PFR, which could not be heat treated after manufacture, are being avoided in future fast reactor SGs. 

Through diffusion, the cracks in a polymer can be healed, and two different parts of a polymer can be rejoined or welded together. In the following, we shall discuss briefly the application of the reptation model for the study of the healing and welding processes. 

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