Explosive welding can be considered as a kind of hot-pressing. The phenomenon, discovered by Lavrentiev at the end of the WW II [122], is an efficient way to bond together two similar or dissimilar materials. In 70s, the explosive welding was intensively used in attempts to develop an economically effective fabrication route for metal matrix composites. Then the activity started to diminish. There is perhaps a hope to reanimate the interest in using the method because it seems to be an easy way to utilize the explosive after the cold war has ended.
In the process of explosive welding, the impact of two plates is accompanied, as a rule, by a stationary periodic process leading to a characteristic modulating waved interface (see fig. 11.22). All the important events take place in the vicinity of point A, which runs behind the detonation front (see fig. 11.23). Certainly, the conditions for forming the cumulative jet occur periodically here. Processes that occur around point A in the presence of fibres between the plates located either in the direction of the welding front or along normal to the front, are analyzed in [715].
Fig. 11.22. Wave formed at the interface obtained by explosive welding. After Mileiko [419].
Fig. 11.23. A scheme of explosive welding of two plates.
In the first attempts to produce metal matrix composites by explosive welding (see, for example, [108, 281]), the direction of detonation front propagation was chosen to coincide with the fibre direction. In this case some new features were observed and they were associated with the flow of the matrix layer around a more rigid fibre [615]. Many experimental data show that the choice of technological parameters in this case is not a difficult task. The situation is easily reached when the mechanical behaviour of a composite obtained by explosive welding corresponds to that of a composite with an ideal interface bond. Moreover, the very short time of the process excludes the formation of brittle interface layers as well as annealing the reinforcing wires. Another advantage of explosive welding is the possibility of making sheets and plates of large sizes with a high productivity rate.
When making composite tubes and shells with non-axial fibre directions it is not clear a priori what will be the result of the interaction of wave-forming processes at the matrix-matrix interface with a set of the reinforcing fibres lying, for example, along the impact front. A corresponding experiment is described by Mileiko et al. [441, 443]. An assembly before detonation is shown in fig. 11.24, and an example of a structure can be seen in fig. 11.25.
Fig. 11.24. An assembly to fabricate a composite tube with circumferencial reinforcement. 1 – mandrel; 2 and 4 – matrix layers: 3 reinforcement layer; 5 – protective shell; 6 – explosive; 7 – detonator; 8 – cone. After Mileiko and Kondakov [441].
Fig. 11.25. The steel-aluminium composite obtained by explosive welding (Kasperovich and Kondakov).
An interesting situation arises when the wave formation is completely excluded, which is a case, for example, when the reinforcing element is a wire mesh [50]. In this case, the bonding mechanism appears to differ from that described above. In going through the mesh, the matrix surfaces are cleaned and then the physical contact arises and the bond forms.