The possibility of nondestructively characterizing the microstruc ture, morphology or mechanical properties of materials is certainly a fascinating subject. In principle, such techniques can be used at all stages of a material's life - from the early stages of processing, to the end of a structural component's useful life. Interest in the subject thus arises not only from a purely scientific point of view but is also strongly motivated by economic pressures to improve productivity and quality in manufacturing, to insure the reliability and extend the life of existing structures. The present volume represents the edited papers presented at the Second International Symposium on the Nondestructive Characterization of Materials, held in Montreal, Canada, July 21-23, 1986. The Proceedings are divided into eight sections, which reflect the multidisciplinary nature of characterizing materials nondestructively: Polymers and Composites, Ceramics and Powder Metallurgy, Metals, Layered Structures/Adhesive Bonds/Welding, Degradation/Aging, Texture/ Anisotropy, Stress, and New Techniques. Invited papers by R. Hadcock of Grumman Aircraft Systems, R. Cannon of Rutgers University, H. Yada of Nippon Steel and R. Bridenbaugh of Alcoa review respectively the processing of polymer matrix composites, ceramics, steel and aluminum, emphasizing the need for material property sensors to improve process and quality control. Two other invited papers, one by A. Wedgwood of Harwell and the other by P. Holler of the IzFP in Saarbrucken review state of the art techniques to characterize particulate matter and metals respectively.

Engineering structures for reliable function and safety have to be designed such that operational mechanical loads are compensated for by stresses in the components bearable by the materials used. Vhat is "bearable"? First of all it depends on the properties of the chosen materials as well as on several other parameters, e.g. temperature, corrosivity of the environment, elapsed or remaining serviceable life, unexpected deterioration of materials, whatever the source and nature of such deterioration may be: defects, loss of strength, embrittlement, wastage, etc. DEFECTS and PROPERTIES of materials currently determine loadability. Therefore in addition to nondestructive testing for defects there is also a need for nondestructive testing of properties. The third type of information to be supplied by nondestructive measurement pertains to STRESS STATES under OPERATIONAL LOADS, i.e. LOAD-INDUCED plus RESIDUAL STRESSES. Residual stresses normally cannot be calculated; they have to be measured nondestructively; well-approved elastomechanical finite element codes are available and used for calculating load-induced stresses; for redundancy and reliability, engineers, however, need procedures and instrumentation for experimental checks.