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A nondestructive technique for evaluating the strength of hull elements of submersibles is described. The technique is based on the micromechanical model of temporal dependences of the parameters of acoustic emission that is registered under an original novel technique of loading of a cylindrical hull section. The technique is also suitable for assessing the information value of resource-related acoustic-emission diagnostic indicators.

Expansion of the application domain and heightened requirements for the accuracy of acoustic-emission (AE) testing have necessitated the optimization of AE-based nondestructive strength-testing techniques. Current trends in the development of these techniques are provided and general principles for improving their efficiency are stated. Examples of the implementations of AE testing on various objects are illustrated.

A method for determining the time to the failure of specimens of welded joints on the basis of the automatic determination of the parameters of a micromechanical-destruction model and the time dependences of the number of registered acoustic-emission signals is presented. The possibilities of improving this technique on the basis of the statistical identification of the uniform-destruction stage, which determines the specimen strength, are considered.

The elastoplastic behavior of welded joints would seem to be the result of the joint actions of destruction and plastic-deformation processes. The possibility of modernizing the micromechanical model of acoustic emissions for the purpose of extending its application to the plastic-deformation segment is considered. An example of specimens of butt-welded joints is used to show the possibility of evaluating the residual life of an article on the basis of the obtained model.

Nondestructive testing of the strength of materials and structures is based on the evaluation of representative strength indices that allow forecasting of the instant that destruction will occur. Flaws in a material and complexities in a structure lead to nonuniformities in their structural, stressed-strained, and strength states, to the reduction of the testability of objects, and the necessity of increasing their strength margin. The criteria for determining the kind and nonuniformity of the strength state of structural materials are formulated, a technique for qualitative evaluation of the degree of the strength nonuniformity is considered, and the correlations of different acoustic-emission and geometric strength characteristics, which were obtained by a nondestructive method, are compared to the durability of specimens.

Estimation of the lifetime of a construction consists of forecasting the time remaining before failure and is based on extrapolation of the time dependences of the state parameters of a technical object to their critical values. The use for this purpose of simplified damageability models (e.g., a hypothesis of linear summation of flaws) and the absolute values of acoustic-emission (AE) parameters (e.g., activity, counting rate, duration of pauses) leads to a dependence of the estimate results on a large number of destabilizing factors and, as a result, to low accuracy or laboriousness of these techniques. An earlier suggested micromechanical model of AE parameters makes it possible to find a trade-off between simplicity and accuracy.

Modeling of processes leading to fracture is required for the development of efficient nondestructive methods for monitoring strength. The model used in this study describes acoustic emission at the stage of delocalized microcrack formation that precedes crack formation or crack pop-in, relates fracture and elastic radiation parameters, and shows directions for experimental studies and approaches to the development and modification of diagnostic methods. A model for the coefficient of the similarity of acoustic emission of elastic radiation to fine fracture is considered. The dependence of its parameters on different factors involved in acoustic-emission tests is shown for welded joint samples.