P.A. Dickstein

Ultrasonic Feature-Based Classification of the Interfacial Condition in Composite Adhesive Joints

The sensitivity of ultrasonic features to the condition of the adherend-adhesive interface in composite joints was studied. The inspected specimens represent different bonding characteristics due to the variety of surface pretreatments to the composite adherends. Each signal obtained from ultrasonic inspection of a specimen was characterized by a feature vector, consisting of features derived from both the time and frequency domain representations of the signal. Some of the features were found to be significantly sensitive to the interfacial characteristics of the joints. The sensitivity was verified by means of conventional statistical tests. The sensitivity of the features enabled the application of basic pattern recognition techniques for the classification of the joints according to the surface preparation of the adherends.

Statistical Pattern Recognition Techniques: A Sample Problem of Ultrasonic Determination of Interfacial Weakness in Adhesive Joints

A pattern recognition approach was applied to the analysis of ultrasonic echo signals from two classes of aluminum-to-aluminum adhesive bonds. The two classes differed in the surface preparation of the adherends prior to bonding, resulting in different interfacial properties of the joints. These properties have a crucial effect on the long-term adhesive properties of the specimens. Application of advanced signal processing and pattern recognition techniques enabled the classification of the joints according to the surface preparation of the adherends, based on features extracted from the ultrasonic signals. The statistics yielded an upper bound for the probability of mis-classification of the specimens. The sensitivity of certain features, extracted from the ultrasonic signal, to the interfacial characteristics of the specimens is explained by means of the natural frequencies of a joints components and surface condition of the adherends. This leads to a method for selecting the optimal probe frequency for carrying out the ultrasonic inspection.

ULTRASONIC EVALUATION OF THE DEGRADATION OF COMPOSITE ADHESIVE JOINTS

Abstract An investigation into the nondestructive monitoring of the environmental degradation of composite adhesive joints is presented. Three classes of joints, representing a variety of interfacial properties due to different pretreatments, were exposed to circulating hot water. Periodically thereafter specimens were weighed, subjected to an ultrasonic A-scan, and destructively tested to assess the breaking-loads and modes of failure. Statistical feature based analysis was conducted to correlate ultrasonic features to the amount of water soaked by the joints and the corresponding changes in their initial breaking-loads. The sensitivity of the ultrasonic features to the quality of the pretreatment provided to the joints was statistically tested as well.

Characterization of an ultrasonic measurement system by means of its instrument function

Abstract Measurement systems can be regarded as input-output systems represented by a characteristic instrument transfer function. This characterization of the experimental set-up enables a quantitative evaluation of its sensitivity and resolution, and a comparison of relative performance among several such systems. Three alternative methods for the quantitative characterization of a measurement system through its instrument function are presented, each based on a phenomenological and semi-empirical approach. The three methods are described theoretically and then applied to the analysis of an ultrasonic experimental set-up. The features of the instrument function, obtained independently by the three methods, are compared, and the relative advantages and disadvantages of each method are evaluated.

Non Linear Correlation between Statistically Sensitive Ultrasonic Features and the Strength of Composite Adhesive Joints

The motivation for the increasing use of fiber-reinforced materials as structural components in the aeronautical and automobile industries is their improved strength to weight ratio. The most widely used technique for the joining of composite components is adhesive bonding. However, the use of bonded composite joints has been hampered by the lack of a reliable nondestructive testing (NDT) technique for the evaluation of the interfacial condition of the joints, which has an essential role in establishing the joint strength.