Pierre Slangen

Experimental study of hydraulic ram effects on a liquid storage tank: Analysis of overpressure and cavitation induced by a high-speed projectile.

This work is part of a project for evaluating catastrophic tank failures caused by impacts with a high-speed solid body. Previous studies on shock overpressure and drag events have provided analytical predictions, but they are not sufficient to explain ejection of liquid from the tank. This study focuses on the hydrodynamic behavior of the liquid after collision to explain subsequent ejection of liquid. The study is characterized by use of high-velocity projectiles and analysis of projectile dynamics in terms of energy loss to tank contents. New tests were performed at two projectile velocities (963 and 1255 m s(-1)) and over a range of viscosities (from 1 to 23.66 mPa s) of the target liquid. Based on data obtained from a high-speed video recorder, a phenomenological description is proposed for the evolution of intense pressure waves and cavitation in the target liquids.

A 3D effect in the wedge adhesion test: Application of speckle interferometry

The wedge test is of considerable use for evaluating adhesion between two bonded rigid substrates. In its (usual) static form, release of elastic strain energy is equated to effective adhesion energy during crack growth. However, the test is usually treated as two-dimensional. In fact, it is really three-dimensional due to anticlastic bending effects of the bent beam(s) during crack propagation. We studied a composite material/epoxy/aluminium alloy system and observed a curved crack front during propagation. This leads to doubt as to the value of crack length to be inserted in the adhesion energy formula. In addition, by using the highly sensitive technique of speckle interferometry, it was possible to study anticlastic bending effects in a quantitative manner. Far from the crack front, agreement between theory and experimental is good, yet work remains to be done to understand the zone near the fracture zone.

Investigation on cone jetting regimes of liquid droplets subjected to pyroelectric fields induced by laser blasts

Electrical conductivity and viscosity play a major role in the tip jetting behaviour of liquids subjected to electrohydrodynamic (EHD) forces, thus influencing significantly the printing performance. Recently, we developed a nozzle- and electrode-free pyro-EHD system as a versatile alternative to conventional EHD configurations and we demonstrated different applications, including inkjet printing and three-dimensional lithography. However, only dielectric fluids have been used in all of those applications. Here, we present an experimental characterization of the pyro-EHD jetting regimes, induced by laser blasts, of sessile drops in case of dielectric and conductive liquids in order to extend the applicability of the system to a wider variety of fields including biochemistry and biotechnology where conductive aqueous solutions are typically used.

Nematic liquid crystals light valve: application to phase shifting speckle interferometry

Liquid nematic crystals are nowadays more often used to change the polarization and/or phase and amplitude of impinging light wave. Nematic liquid crystals valves (LCLV) are also called SLM (Spatial Light Modulator) or LCVR (Liquid Crystal Variable Retarder). This paper will show the different steps required to get a procedure (optical mounting and computing software) enabling the use of LCLV in the output beam of the laser coupled with a 3D speckle interferometry set-up. This LCLV generates the phase shifts between the reference and object beams. The calibration setup is made of a Mach Zender interferometer with the LCLV in one arm. Interference fringes are obtained and recorded with a CCD camera as LCLV voltage is increased. The fringe processing is achieved with a slice analysis in the Fourier domain. Required phase shifts are then implemented in the phase shifting software. The existing set-up already uses a phase shifter composed by a moving mirror driven by a piezoelectric transducer (PZT). Results of the calibration are compared between piezoelectric device and LCVR. The phase shifting rate and resulting phase error shows the main advantages of the LCVR.

Nematic Liquid Crystals Light Valve Calibration and Application to Phase shifting Speckle Interferometry

Liquid nematic crystals are nowadays more often used to change the polarization and/or phase and amplitude of impinging light wave. Nematic liquid crystals valves (LCLV) are also called SLM (Spatial Light Modulator) or LCVR (Liquid Crystal Variable Retarder). This paper will show the different steps required to get a procedure (optical mounting and computing software) enabling the use of LCLV in the output beam of the laser coupled with a 3D speckle interferometry set-up. This LCLV generates the phase shifts between the reference and object beams. The calibration set-up is made of a Mach Zender interferometer with the LCLV in one arm. Interference fringes are obtained and recorded with a CCD camera as LCLV voltage is increased. The fringe processing is achieved with a slice analysis in the Fourier domain. Required phase shifts are then implemented in the phase shifting software. The existing set-up already uses a phase shifter composed by a moving mirror driven by a piezoelectric transducer (PZT). Results of the calibration are compared between piezoelectric device and LCVR. The phase shifting rate and resulting phase error shows the main advantages of the LCVR. The whole set-up, with LCVR replacing the PZT, is finally applied to the determination of 3D displacement fields of Compact Tension Notch sample.

Overpressure wave interaction with droplets: time resolved measurements by laser shadowscopy

Risk sciences involve increasingly optics applications to perform accurate analysis of critical behavior such as failures, explosions, fires. In this particular context, different area sizes are investigated under high temporal sampling rate up to 10000fps. With the improvement of light sources and optical sensors, it is now possible to cope with high spatial resolution even for time resolved measurement. The paper deals with the study of the interaction between overpressure waves, occurring in case of explosion for example, with a liquid droplet present in the vicinity of the overpressure wave. This is a typical scenario encountered in case of industrial breakdown including liquid leakage and explosions. We designed an experimental setup for the evaluation of the interaction between the overpressure wave and falling liquid droplets. A gas chamber is filled with nitrogen until breakage of the outlet rupture disk at about 4 bar. The droplets fall is controlled by an automatic syringe injector placed in the overpressure wave. The imaging system is based on laser shadowscopy. The laser source is a double cavity 15mJ- 1000Hz Nd YLF laser emitting double pulses of about 10ns at 527nm. To record the double pulse after crossing the falling droplets, the transmitted light is captured by a lasersynchronized double frame camera. Since these measurements are time-synchronized, it is then possible to know accurately the different parameters of the phenomenon, such as overpressure wave velocity, droplets diameter, and Reynolds number. Different experiments have been carried out at about 4000 doubleframe/s. The paper presents the whole experiment, the enhancements of the setup and the results for different liquid products from water to acetone.

Some figures of merit so as to compare digital Fresnel holography and speckle interferometry

This paper presents a detailed analysis of figures of merit to compare digital Fresnel holography and speckle interferometry. The analysis is based on both theoretical and experimental analyses. A theoretical analysis of the influence of the aperture and lens in the case of speckle interferometry is developed. Compared to digital Fresnel holography, this element is a critical point influencing Shannon conditions, spatial resolution, spatial filtering and photometric efficiency. Optimal filtering and image recovering conditions are thus established. The theoretical analysis is validated by experimental results. The influence of the speckle decorrelation is estimated for the measurement of mechanical deformations. The same mechanical loading has been applied for both experimental configurations. The probability density of the noise map is then estimated. Fitting the curves along the theoretical analysis results in an objective comparison of the decorrelation degrees, and gives keys to compare the decorrelation sensitivity of the methods.

Characterization of color texture: CIEL*a*b* calibration of CCD device

A lot of materials used in construction industry are materials showing strong color texture, which may give the product its commercial value. We plan to perform automated appearance sorting using a tri-CCD color video camera as a measurement tool. The aim of the present work is the refinement of a calibration process allowing this tool to deliver for each pixel the same information as a spectroradiometer (CIEL*a*b* coordinates). Analysis of the acquisition tool allows characterization of the card and camera behavior (linearity of RGB gains, spatially varying and fixed pattern noises). Color calibration is performed using measurements with a spectroradiometer.

Glass Ceramic CAD/CAM crowns and severely altered posterior teeth: a three levels study

For many practitioners, longevity of full glass ceramic crowns in the posterior area, molars and premolars, remains a real challenge. The purpose of this article is to identify and evaluate the parameters that can significantly influence their resistance when preparing a tooth. The analysis proposed in this article relies on interrelated studies conducted at three levels: in vitro (mechanical tests), in silico (finite elements simulations) and in vivo (clinical survival rates). The in vitro and the in silico studies proved that an appropriate variation of the geometric design of the preparations enables to increase up to 80% the mechanical strength of ceramic reconstructions. The in vivo clinical study of CAD/CAM full ceramic crowns was performed in accordance with the principles stated within the in vitro and the in silico studies and provided a 98.97% success rate over a 6 years period. The variations of geometric design parameters for dental preparation allows for reconstructions with a mechanical breaking up to 80% higher than that of a non-appropriate combination. These results are confirmed in clinical practice.Graphical Abstract

Behavior of chemicals in the seawater column by shadowscopy

Ninety percent of the Global Movement of Goods transit by ship. The transportation of HNS (Hazardous and Noxious Substances) in bulk highly increases with the tanker traffic. The huge volume capacities induce a major risk of accident involving chemicals. Among the latest accidents, many have led to vessels sinking (Ievoli Sun, 2000 - ECE, 2006). In case of floating substances, liquid release in depth entails an ascending two phase flow. The visualization of that flow is complex. Indeed, liquid chemicals have mostly a refractive index close to water, causing difficulties for the assessment of the two phase medium behavior. Several physics aspects are points of interest: droplets characterization (shape evolution and velocity), dissolution kinetics and hydrodynamic vortices. Previous works, presented in the 2010 Speckle conference in Brazil, employed Dynamic Speckle Interferometry to study Methyl Ethyl Ketone (MEK) dissolution in a 15 cm high and 1 cm thick water column. This paper deals with experiments achieved with the Cedre Experimental Column (CEC - 5 m high and 0.8 m in diameter). As the water thickness has been increased, Dynamic Speckle Interferometry results are improved by shadowscopic measurements. A laser diode is used to generate parallel light while high speed imaging records the products rising. Two measurements systems are placed at the bottom and the top of the CEC. The chemical class of pollutant like floaters, dissolvers (plume, trails or droplets) has been then identified. Physics of the two phase flow is presented and shows up the dependence on chemicals properties such as interfacial tension, viscosity and density. Furthermore, parallel light propagation through this disturbed medium has revealed trailing edges vortices for some substances (e.g. butanol) presenting low refractive index changes.