Holographic Evaluation of Edge Delamination in Bars Bonded to a Rigid Support With Foam-Adhesive

When a bar having one end bonded to a rigid support with foam-adhesive is loaded, the high peeling stresses at the bonded edge foster edge delamination along the interface of bonding. Upon inspection by double exposure holography, with an incremental point load applied at the free end of the bar between exposures, the indistinct fringe perturbation and the unknown resilience of the foam-adhesive (quantified by its foundation modulus) impede unambiguous evaluation of the condition of adhesion. This paper describes a simple method for rapid detection and assessment of artificially created edge delamination in such bar structures. The theoretical analysis elucidates the suitability of modelling the bar as partially clamped, and having an equivalent slope at its support related to the foundation modulus. Two dimensionless parameters are defined, which have between them a linear relationship for a nondelaminated bonding but a nonlinear relationship for a delaminated one. Finally, a simple iterative procedure is described for estimating the delaminated length without having to predetermine the elasticity of the support.

Holographic Inspection of Plates Containing Areas of Localized Thickness Variation

Circular plates, under unknown clamping conditions and containing simulated defects in the form of circular localized thinning or thickening, are inspected by double-exposure holography. With an incremental uniform pressure applied between exposures, eccentric defects are readily revealed from the distinct irregular fringe patterns. In the case of central circular defects, however, the absence of distinct irregular fringe patterns does not enable easy visual detection of the defects. The simple method of analysis described in this paper, based on the fact that the displacement in a defective plate differs from that in a defect-free plate, allows easy deduction of central and eccentric defects from the fringe patterns. Furthermore, this method enables identification of the type of defect (localized thinning or thickening), the extent of thickness variation, as well as an accurate estimation of the location and size of the defect.

Shock tube study of the drag coefficient of a sphere in a non-stationary flow

A review of previous attempts to study the drag coefficient of a sphere in a non-stationary flow, experimentally, is given. Thereafter, a detailed account of the present study is presented. A shock tube facility was used for inducing relatively high acceleration in small spheres laid on the shock tube floor. The spheres acceleration resulted from the drag force imposed by the post shock wave flow. Using double exposure holography, the spheres trajectory could be constructed accurately. Based upon such trajectories, the spheres drag coefficient was evaluated for a relatively wide range of Reynolds number (6000 < Re <101000). It was found that the obtained values for the sphere drag coefficient were significantly larger than those obtained in a similar steady flow case.