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

ultrasound through a boundary with varying degrees of adhesion has been developed. The aim of this work is to deduce adhesion informations from the phase velocity of waves guided in a multilayer structure (global characterization) or from the reflection coefficient of bulk waves at a boundary (local characterization). 49173 Dickstein, P.A.," Girshovich. S.; Sternherg, Y.: Sinclair, A.N.; Leibovitch. tt. U l t r a s o n i c f e a t u r e - b a s e d classification of the interracial condition in composite adhesive joints Research in Nondestructive Evaluation, Vol. 2, No. 4, pp. 207-224 (1990). The sensitivity of uhrasonic features to the condition of the adherend-adhesive interface in composite joints was studied. The inspected specimens repremnt 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 from both the time and frequency domain representation 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 mnsitivity 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.

Lipatov, Y.S.; Todosijchuk, T.T.; Grishachev, V.F.; Cherednichenko, S.P. Acoustic e m i s s i o n a t f r a c t u r e of adhesion contacts in rigid polymeric composites 49063

Journal of Adhesion, Vol. 35, No. 3, pp. 217-227 (1991) The possibility of using the acoustic emission (AE) method for the characterization of the process of fracture of adhesion joints in strained rigid polymeric composites is discussed. Recorded as main informational parameters are the total count of AE signals, the count rate, the amplitude distribution of the signals and their frequency characteristics as well as the dependence of these quantities on the stress applied to the sample and on the straining time. Increase in the adhesion bond strength is shown to result in raising the total AE over the whole filler concentration range. The effect of the filler dispersity on the above-listed parameters has been ascertained. A technique for calculating the adhesion joint strength on the basis of the maximum of the AE signal count rate, fracturing stress, and amplitude characteristics of AE signals with allowance for the stress concentration in the formation of a polymeric sample is suggested. 48933 Papadakis, E.P.; Chapman, G.B. Q u a n t i t a t i v e nondestructive evaluation of adhesive lap joints in sheet

molding compound by adaptation of a commercial bond tester International Advances in Nondestructive Testing. Vol. 16. Edited by W.J. McGonagle. pp. 291-330. Gordon and Breach Science Publishers (1991) A method has been devised to obtain quantitative NDE measurements from a commercial adhesive bond tester designed for GO/NO-GO qualitative sorting. The method requires the connection of one electric meter across two points in the alarm circuit of the instrument. Further. the method requires the choice of proper referencing specimens as standards by a statistical method, The principle is that the reference specimens must he only marginally better than the barely acceptable adhesive bond. The instrument can be used to measurements which correlate with adhesive bond strength even in the premnce of bonds which fail partly by substrate delamination. Measurements can be made to define a probability of detection (POD) for disbonds versus disbond size. With this POD in hand, one can define a Specification for an adhesive lap joint in terms of an acceptable percentage of bonded area. This Specification is in use. The bond test instrument is in use on adhesive bonds in SMC and continues to be cost-effective according to the Doming Inspection Criterion.

Hsu, D.K.; Dayal, V. Ultrasonic Newton's rings

48932

Applied Physics Letters, Vol. 60, No. 10, pp. 1169-1171. (9 Mar. 1992) Interference fringes due to bondlioe thickness variation were observed in ultrasonic scans of the reflected echo amplitude from the bondline adhesively joined aluminium skins. To demonstrate that full-field interference panems are observable in point-bypoint ultrasonic scans, an optical setup for Newton's rings was ~anned ultrasonically in a water immersion tank. The ultrasonic scan showed distinct Newton's rings whose radii were in excellent agreement with the prediction. 48908 lyer. V.R.; Kinra, V.K. C h a r a c t e r i z a t i o n of a sub-half-wavelength adhesive layer using ult r a s o n i c spectroscopy Enhancing Analysis Techniques for Composite Materials, Atlanta, Georgia (United States), 1-6 Dec. 1991. pp. 35-41. Edited by L. Schwer, J.N. Reddy and A. Mal. NDE-Vol. 10. A S M E (1991) An ultrasonic spectroscopy technique in through-transmission is umd to determine the acoustical propenies of an adhesive layer in an adhesively-bonded joint. The joint is modeled as a thin adhesive layer "immersed" in a solid medium. It is assumed that the adherend is sufficiently thick, so that h/lambda > 5; h is the adherend thickness and lambda the wavelength. The problem of ultrasonic NDE is pored in one of the following ways: given thickness determine wavespeed; given wavespeod determine thickness, from the measured phase, amplitude or complex spectrum. An inversion scheme based upon the method of least squares is used to determine the unknown parameter, wavespeed or thickness, from the measured spectrum.

ttigo. Y.; Kazama, S.; Handa, K. Evaluation of adhesive joint tensile strength by elastic-wave transfer function m e t h o d 48880

Nondestructive Characterization of Materials IV. Edited by C.O. Ruud, J.F. Bussiere and R.E. Green. pp. 197-203. Plenum Press (1991).

96

New nondestructive evaluation method of ETFuM (Elastic-wave Transfer Function Method) was developed and applied to evaluate adhesive joint strength. Two kinds of specimen with smooth and rough surface for bonding, and three kinds of epoxy adhesive (clear, with ceramic and with rubber compound) were used. Good correlation was seen between adhesive tensile strength and the evaluation Ha, the parameter of ETFuM, within the range of measurement made in this work. It is therefore, concluded that the method presented here is u~ful to a certain extent in making evaluations of adhesive joints intended for use in actual products.

YousseJ~Y.; Fahr. A.; Roy, C. NDE of adhesively bonded joints using acousto-ultrasonics and pattern recognition

48873

Nondestructive Characterization of Materials IV. Edited by C.O. Ruud, J.F. Bussiere and R.E. Green. pp. 345-353. Plenum Press (1991). The acousto-ultrasonic technique along with pattern recognition analysis can be used for the evaluation of the integrity of adhesively bonded joints. Experimental measurements of AU signals on single-lap joint specimens and their classifications using the SAS pattero recognition routines indicated that it was possible to separate defective samples from well-bonded specimens with excellent recognition rates. Also, classification of AU signals by failure load regardless to pro-treatment of samples or defect resulted in positive recognition. Further investigations are required to establish the applicability of these techniques on large and complex bonded structures,

Wang. W.; Rokhlin, S.I. Characterization of interphasial properties in adhesive joints using angle-beam reflection ultrasonic spectroscopy 48872

Nondestructive Characterization of Materials IV. Edited by C.O. Ruud, J.F. Bussiere and R.E. Green. pp. 355-362. Plenum Press (1991). In this work samples with good-bond interpham at one side and controlled interphasial properties at the other side of the adhesive layer were investigated. The experiment uses an obliquely incident transverse wave and measures the spectrum of the signal reflected from the interpbams. By using a nonlinear least square optimization for curve fitting the loci of minimum reflection coefficient we determine the viscoelastic properties and the thickness of the inteq~base.

Fitch, C.E. Pulsed low-frequency ultrasonic bond and thickness testing summary

48670

Nondestructive Characterization for Advanced Technologies, Oakland, California (United States), 18-22 Mar. 1991. pp. 129-131. ASNT (1991). The following material discusses a pulmd, low-frequency pitch and catch sonic-ultrasonic contact test concept. The novel pitch and catch test probe requires no couplant. The instrument concept can be umd for disbond and thickness evaluation in many interesting applications. The low-frequency (5-100 kHz) acoustic waves having relatively large bulk longitudinal and shear wavelengths interact in complex ways producing quasi-resonant behavior in small samples. In many thin ~,~u-nples,extensional and fiexural lamb modes are developed to provide sensitive detection capabilities. Low attenuation at the.~ frequencies permits detection of many effects not easily detectable at higher frequencies even though wavelengths are large, A short theory, existing applications, and possible future developments are discussed in the following material.

Achenbach, J.D.; Parikh, O.K. Ultrasonic detection of nonlinear mechanical behavior of adhesive bonds

48429

Review of Progress in Quantitative Nondestructive Evaluation, La Jolla, California (United States), 15-20 Jul. 1990. Vol. 10B, pp. 1837-1844. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1991). ISBN 0-306-43903-4 In this paper the interest is focusmd on adhesive failure. It is assumed that adhesive failure is preceded by nonlinear behavior in the thin boundary layers at the adhesive/adherent interfaces. The extent to which such nonlinear behavior affects the reflection and transmission of ultrasonic wave motion is investigated on the basis of analytical and numerical results. Three models of increasing complexity are considered for the adhesive layer: (I) a nonlinear relation between tractions and gross displacements across a repremntative adhesive thickness parameter; (2) rome .as under (I), but with a correction for the inertial of the adhesive layer; and (3) a nonlinear continuum. For them three models the reflection and transmission for normal incidence has been investigated, and the relative accuracy of the simple models has been determined. For given nonlinear behaviors of the boundary and interior layers, the overall relation between traction and adhesive-layer extension has been determined. Conversely, if the overall relation is unknown, it is shown how it can be obtained from the reflection data. Knowledge of this relation allows an extrapolation to the failure load of the adhesive bond. It is also shown that the nonlinear behavior gives rim to the development of higher harmonics, which are related to the nonlinear parameters of the boundary layers.

McGowan, P.; Adler, L. Higher order nonlinearity measurement techniques in thin adhesive layer 48428

Review of Progress in Quantitative Nondestructive Evaluation, La Jolla, California (United States), 15-20 Jul. 1990. Vol. 10B, pp, 1845-1852. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1991). ISBN 0-306-43903-4 In a recent paper a nonlinear method was suggested to evaluate adhesive joint quality and it was pointed out that nonlinear measurements are more directly correlated to mechanical strengths than linear ones. In that paper a new dynamic acousto-elastic measurement technique was introduced and shown to he sensitive enough to measure both first and second order nonlinearities at load levels of 15% of the ultimate strength. The objective of this paper is to introduce a more sensitive measurement technique to

N DT & E International Volume 25 Number 2 1992