Sensing delamination

Xiaojun Wang, Chung DDL, Sensing delamination in a carbon fiber pol5mer-matrix composite during fatigue by electrical resistance measurement. Polymer Composites, 18(6), 692-700, 1997. 

Film Delamination Most sensors have a film or membrane used as a sensing layer and/or a biocompatible layer. When this film is not attached properly or degrades, it can fail and delaminated from the electrode surface, causing the sensor to lose function through increased mass transfer resistance, diminished electron transfer, and/or its ability to deter the foreign body reaction.31... 

If, as in the fracture surface type shown in Fig. 3 on the left hand side, the width of the featureless delamination is increasing with delamination length this is also reflected in the R-curve (Fig. 5). There, values are dropping from relatively high cross-ply -values to a value typical of the unidirectional laminate. This could be a hint that energy release rates determined for the cross-ply laminates using the analysis developed for the unidirectional material are valid in the sense that relative proportions are conserved. 

According to the requirements specified in the ISO standard [1] deviation of the delamination propagation from mid-plane invalidates the test. In that sense, any data analysis of the cross-ply laminates, therefore, will yield invalid results. This point was discussed extensively in [4] where the authors also used the Finite-Element method to supplement their analysis and concluded that the corrected beam theory data reduction scheme seemed to remain applicable and that the non-symmetric cross-ply material yielded apparently valid fracture toughness data, even though these were probably affected by transverse cracking. 

Nanoscratch tests have been used to simulate the effect of third-body particulate wear debris on component surface scratching during use. The load at which the co-efficient of friction or friction force suddenly increases is identified as the critical load, and is used to evaluate scratch resistance and adhesion strength. The depth-sensing nanoindenter, usually equipped with a conical indenter, can elucidate the mode of failure, whether elastic/plastic deformation, cracking, or delamination. 

Type A plasma polymers have the characteristic internal stress built in the film, and the plasma polymerization coating acts as the tempered ultrathin layer on the substrate. The internal stress is caused by the wedging effect of the deposition process, and the total stress increases linearly with the thickness. As the thickness increases, the internal stress reaches the critical point beyond which the internal stress becomes greater than the cohesive force or the adhesive force of the plasma polymerized coating. Above the critical thickness, therefore, the coating cracks (not necessarily in macroscopic sense) or delaminates (buckles) from the substrate. Consequently, there exists a thickness limit of plasma polymerization coating. The tighter the structure, the smaller is the thickness limit. 

The multi-sensing technologj-, based on simultaneous high-resolution force and electrical and acoustic measurements, allows for ver> accurate determination of both delamination/ adhesion and scratch resistance of both thin and thick coatings. Using the test tools with higher contact area (or length), like micro-blade or ball, may allow for more repeatable results than those obtained with sharp styluses. 

The nano+micro tester UNMT provides a useful platform for all common types of adhesion and delamination tests, with the complete utilization of all the advantages of the multi-sensing technology. 

In the broad sense, interlaminar adhesion means the adhesion between any laminations of similar or dissimilar materials and hence could be taken to include just about any adhesion test. One particular type for fiber-reinforced plastics, which is known as interlaminar shear strength, is normally considered as a short beam flexural test (sec Chapters 9 and 18). A method peculiar to laminated plastics tube is given in BS 2782, Method 346A [59] and called cohesion between layers of laminated tube. A sample of tube is subjected to compression to induce shear forces between layers and delamination observed by eye,... 

However, SHM applications of the curvature-modes method requires the use of in situ sensing instead of the SLDV approach. Harney et al. [73] describe the use of surface-mounted flexible piezo sensors made of polyvinylidene fluoride placed at 16 locations on a cross-ply CFRP beam. Vibration excitation was done with a piezoceramic wafer mounted at end of the beam energized by a sine signal swept up to 2 kHz. Various damages were applied on separate specimens (saw-cut notches delaminations simulated by Teflon inserts impact). A set of pristine specimens were used to constract a baseline database of curvature modes. Subsequently, data were taken on the damaged beams. Further processing of these experimental results was done in Lestari et al. [74]. The method showed promise although the experimental data suffered from considerable scatter. 

Abot JL, Song Y, Vatsavaya MS, Medikonda S, Kier Z, Jayasinghe C, et al. Delamination detection with carbon nanotube thread in self-sensing composite materials. Compos Sci Technol 2010 70(7) 1113-9. 

Yamada S, Yoshida Y, Saito S, Yamada S and Komiya I (2007), Fibre optic sensing for the delamination behaviour of FRP reinforced steel structures , Asia-Pacific Conference on FRP in Structures (APFIS 2007), 12-14 December, Hong Kong, 587-592. 

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