Finite Size and Speciment Thickness Influence in Acousto-Ultrasonic NDE

Acousto-ultrasonics (AU) uses a pair of transducers to characterize distributed damage in composite plates. A transducer placed normal to the surface creates resonances which propagate as plate waves. Once the receiving transducer picks up the signal, simple analysis techniques, such as the zeroth or first moment of the power spectrum, are applied to create a Stress Wave Factor (SWF). The SWF is then used to quantify the damage state of the composite once the system has been properly trained

Lamb Wave Mode Selection for Increased Sensitivity ot Interfacial Weaknesses of Adhesive Bonds

Interface quality between layers in a layered structure is critical in fracture and fatigue analysis. A theoretical and quantitative solution to the problem from a NDE point of view would be desirable in both manufacturing and for in-service investigation of a variety of different structures. For example a great need exists to develop a reliable and efficient inspection program of adhesive bond delamination and interfacial weakness detection in aging aircraft noting that the bond degradation generally preceeds cracking in the aluminum skin, starting at the rivet holes

One Sided Inspection for Elastic Constant Determination of Advanced Materials

Knowledge of mechanical properties of a composite material is prerequisite to good engineering design. The problem of theoretically predicting the mechanical properties of a composite material as a function of the properties of its constituents has been thoroughly investigated by many authors [1–2]. In one general class of techniques, termed “effective modulus” theories, the composite is viewed as a homogeneous anisotropic material with “effective” elastic constants that are determined by the elastic constants of the constituent materials. All of these theories remove the microstructure of the composite from consideration and, as a result, cannot be expected to predict accurately the properties of the composite material over a wide range of deformation scales. One limitation which comes about from this “smearing” of the microstructure into a homogeneous continuum is that the effective modulus theories, and hence materials which are assumed to have “effective elastic constants”, are incapable of predicting frequency dispersion of waves, which is sometimes very pronounced in composite materials [3]

Poisson's ratio from polarization of acoustic zero-group velocity Lamb mode.

Poisson's ratio of an isotropic and free elastic plate is estimated from the polarization of the first symmetric acoustic zero-group velocity Lamb mode. This polarization is interpreted as the ratio of the absolute amplitudes of the surface normal and surface in-plane components of the acoustic mode. Results from the evaluation of simulated datasets indicate that the presented relation, which links the polarization and Poisson's ratio, can be extended to incorporate plates with material damping. Furthermore, the proposed application of the polarization is demonstrated in a practical field case, where an increased accuracy of estimated nominal thickness is obtained

Lamb Wave Mode Selection for Increased Sensitivity ot Interfacial Weaknesses of Adhesive Bonds

Interface quality between layers in a layered structure is critical in fracture and fatigue analysis. A theoretical and quantitative solution to the problem from a NDE point of view would be desirable in both manufacturing and for in-service investigation of a variety of different structures. For example a great need exists to develop a reliable and efficient inspection program of adhesive bond delamination and interfacial weakness detection in aging aircraft noting that the bond degradation generally preceeds cracking in the aluminum skin, starting at the rivet holes.</p