Dekker Mechanical Engineering
The subject of Specifications and Standards, which is an Important factor in the over-all consideration of nondestructive evaluation, is being dealt with In a separate supplementary report. These sections have been paged separately, each with its own table of contents, and have been set apart by colored divider sheets. PREFACE The past two decades, particularly, have seen what has been popularly described as the "materials explosion," a burgeoning not only of improved materials of construction,
... ls of construction, but new concepts for materials (dispersion strengthening, composite reinforcement, cermets and ceramics, pyrolytic graphite, sandwiches, etc.)i accompanied by improved and novel fabrication and joining techniques. The simultaneous increased complexity of equipment and vehicle systems to meet the everdemanding requirements of defense and space exploration has forced designers to attempt to exploit these new materials and techniques with greater sophistication and efficiency in their design approaches. In so doing, the designers have availed themselves of every possible technical contribution: new design concepts, materials at maximum strength with minimum flaws, the understanding of crack initiation and propagation, etc. Understandably, the ultimate users, desiring the best of all worlds, have compounded the problems by adding to their exacting functional and design requirements more stringent reliability constraints, to assure safety of personnel and mission. Inherent in the above scheme of development and optimization must be assurance, at every stage, of rigorous attainment of the pre-established quality upon which the design has been based with m.^imum safety factors to maximize design efficiency. It is obvious also that as the criticality of application has increased, the trend toward requiring 100% quality assurance has also increased, obviating the possibility of destructive testing (e. g., through sampling inspection) and, to a significant degree, the use of proof testing for both technical and economy reasons. Thus, the net result of designing with relatively new materials, concepts and fabrication techniques, combined with more exacting requirements and increased reliability, has been the growth of an urgent need for more effective and more comprehensive approaches for nondestructive testing and evaluation.