C. Bolis

A comparative study of three adhesion tests (EN 582, similar to ASTM C633, LASAT (LASer Adhesion Test), and bulge and blister test) performed on plasma sprayed copper deposited on aluminium 2017 substrates

The aim of this study was to compare three adhesion tests carried out on plasma-sprayed copper coatings on aluminium substrates. The first test, the bond pull test, designated EN 582 or ASTM C633, involves a uniaxial static stress and is commonly used in the coating industry. The second test, the LASAT (LASer Adhesion Test), is a recently developed technique based on spallation phenomenon due to laser induced shock waves. In this test, the coating delamination results from spallation at the coating/substrate interface due to uniaxial tensile stress. The last test, the bulge and blister test, involves a quasi-static measurement of the crack propagation energy at the coating/substrate interface. These three techniques have been used to evaluate the influences of different process parameters involved in the coating adhesion such as aluminium surface roughness, substrate pre-heating and plasma spray conditions.

Damaging of materials by bi-dimensional dynamic effects

Laser shocks are most often used to produce uniaxial stress and strain into materials by irradiating a spot diameter conventionally admitted at least three times larger than the thickness of the shocked sample. By reducing the laser spot versus the sample thickness, 2D lateral waves are created earlier and their crossing during propagation stages generates traction which can yield to voids into materials (near the front loaded face). This phenomenon has been evidenced by an experimental study, including VISAR measurements which exhibit the signature of the fracture generated by these 2D effects. Numerical simulations with the explicit finite element code RADIOSS clearly evidence the origin of the 2D effects on VISAR measurements. This different mode of damaging materials by laser lateral waves can act simultaneously with the classical laser spallation produced by the uniaxial propagation (shock wave reverberation crossing the unloading). This opens new discussed prospects for the development of 2D damage ...

Use of a macroscopic model for describing the effects of porosity on shock wave propagation

Materials are manufactured by sintering involve porosity. Some material processes, like laser peening, consist in applying shocks onto the surface of a porous material surface to induce permanent densification that will increase its resistance to corrosion and wear. An estimation of the residual compaction and stresses within the material after treatment requires a good knowledge of shock wave propagation in such media. To investigate the effects of porosity on this propagation, we have performed velocity interferometer system for any reflectors measurements on laser shock-loaded samples of sintered steels with 10%−28% porosity. The records do not agree with the predictions of a simple P−α model from the literature. Hence, a formulation of the compaction process is proposed to improve the correlation between experimental and simulated velocity profile.

Embedded optical fibers for PDV measurements in shock-loaded, light and heavy water

In order to study the shock-detonation transition, we propose to characterize the shock loading of a high explosive plane wave generator into a nitromethane cell. To eliminate the reactive behaviour, we replace the nitromethane by an inert liquid compound. Light water (H2O) has been first employed; eventually heavy water (D2O) has been chosen for its better infrared spectral properties. We present the PDV results of different embedded optical fibers which sense the medium with two different approaches: a non intrusive optical observation of phenomena coming in front of them (interface, shock wave, detonation wave) followed by their mechanical interaction with the fiber.

Local Approach to Thermally-Sprayed Coating/Substrate Adhesion through LASAT (Laser Shock Adhesion Test)

Three interface factors may influence thermally-sprayed coatings adhesion: interface morphology (as usual), thermal and chemical features. It was shown that these three aspects of adhesion mechanisms are shown to be dependent and very local. It is especially true for cold spray which is one of the most promising spray processes. As this spraying technique is based on rapid deformation, cold spray coating/substrate interfaces show local morphological, thermal and chemical features, in a way that none of them can be neglected. LASAT is particularly suitable for testing these coatings because it can be applied to small areas (~1 mm²). From this, it has the outstanding advantage to be sensitive to fine-scaled phenomena responsible for coating adhesion.

2D effect during the propagation of schock wave induced by laser plasma : Application for laser adherence test (LASAT)

Using numerical simulations (RADIOSS), 2D mechanical effects induced at laser spot edges have been studied. Results show that during the propagation in material, tensile lateral waves are generated behind the main compressive shock. The main shock wave is attenuated and/or the interface coating-substrate can be debonded by this tensile wave. Experimental validation has be done using pure Al target and Cu thermal spraying coating on Al substrate. Free rear velocity profiles measured by Doppler Velocimetry technique are in rather good agreement in both configurations. New perspectives are open with the 2D-LASAT test for massive target and so, new industrial applications.Using numerical simulations (RADIOSS), 2D mechanical effects induced at laser spot edges have been studied. Results show that during the propagation in material, tensile lateral waves are generated behind the main compressive shock. The main shock wave is attenuated and/or the interface coating-substrate can be debonded by this tensile wave. Experimental validation has be done using pure Al target and Cu thermal spraying coating on Al substrate. Free rear velocity profiles measured by Doppler Velocimetry technique are in rather good agreement in both configurations. New perspectives are open with the 2D-LASAT test for massive target and so, new industrial applications.