Statistical models in engineering , Statistical models in engineering , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Statistical Models in Engineering

Some studies on evaluation of degradation in composite adhesive joints using ultrasonic techniques.

This article discusses the use of pulse-echo ultrasonic testing for the inspection of adhesive bonds between thin metal sheets (0.8 mm). The method is based on the measurement of the reflection coefficient at the metal/adhesive interface. After describing briefly the physical aspects of the phenomenon, an index is defined to detect defective zones of the joint (both for the lack of adhesive and for insufficient adhesion); the influence of the experimental variables (transducer frequency, coupling medium and contact force) on the measurement is discussed. The analysis shows that coupling medium and transducer frequency do not influence the results and that the method is robust with respect to the variation of contact force. By means of a control experiment it is shown that the statistical distribution of the index corresponding to good and defective adhesion zones are sufficiently separate to be distinguished. Finally, a procedure based on the statistical theory of decisions is proposed to evaluate the integrity of the joint under test.

Ultrasonic testing of adhesive bonds of thin metal sheets

Presents different approaches to discrimination and classification problems from a statistical perspective. Provides computer projects concentrating on the most widely used and important algorithms, numerical examples, and theoretical questions reinforce to further develop the ideas introduced in the text.

Discrimination and Classification.

Correlation between the amount of artificial defects in bonded region and the acousto-ultrasonic parameters (AUPs) including the signal amplitude in adhesively bonded joints of carbon-fiber reinforced plastic (CFRP) laminates and Al6061 plates was investigated The effect of the frequency content and the bandwidth of input signals were studied using 200 kHz, 650 kHz, 1 MHz, 2 MHz pulses and 1 MHz tone-burst signals With increasing fraction of defects, the signal amplitude and AUP1 were decreased but AUP2 was increased This result was attributed to the energy transfer characteristics of bonded joints with delamination-type defects and the change of spectral content as a result of the defects Considering the highly attenuative nature of composite laminates, a pulse signal with major frequency content at or around the third harmonic of thickness mode resonance, 600∽700 kHz for the dimension of specimens used in this study, was found optimal for acousto-ultrasonic testing of CFRP-aluminum joints

Acousto-ultrasonic evaluation of adhesively bonded CFRP-aluminum 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.

Ultrasonic feature-based classification of the interfacial condition in composite 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 joint's components and surface condition of the adherends. This leads to a method for selecting the optimal probe frequency for carrying out the ultrasonic inspection.

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

A novel method for evaluating nondestructively the quality of bonded assemblies is presented. It is shown that a combination of HOC (higher order crossing) analysis and another frequency domain parameter can distinguish between different surface treatments, as well as predicting cohesive or adhesive failure of bonds. It is believed that this method will open the way to predict the durability of bonded structures at the manufacturing or inservice stages.

A novel method of processing pulse echo data in adhesive bond inspection

Acoustic Resonance Methods for Measuring Dynamic Elastic Modulus of Adhesive Bonds

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.

P. A. Dickstein

Papers

Ultrasonic feature-based classification of the interfacial condition in composite adhesive joints

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

A novel method of processing pulse echo data in adhesive bond inspection

Acoustic Resonance Methods for Measuring Dynamic Elastic Modulus of Adhesive Bonds

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