Wissam El-Ratal

Characterization of a new luminescent photoelastic coating

The luminescent photoelastic coating (LPC) technique measures the full-field shear strain and its principal direction on the surface of complex three-dimensional components. The measured optical strain response is also dependent on the coating thickness. Achieving uniform coating thickness is difficult, and thus requires thickness correction for accurate quantitative strain measurements. The original formulations of LPC employed a dual-layer coating containing luminescent dyes to transmit both strain and thickness information. This paper will document (theory and experiment) a new strategy: a single-layer coating that incorporates both a luminescent dye and an absorption dye. Dependent on the concentration of the absorption and luminescent dyes, the solution is sprayed onto the object of interest to a minimum threshold thickness that corresponds to a predefined penetration depth. Advantages of the single-layer coating are the elimination of thickness dependency, the elimination of compliance and adhesion issues between multiple layers, simpler data acquisition and post-processing methods, and easier and faster coating preparation and application.

Luminescent photoelastic coatings

In this paper we describe a new technique to measure the surface strain field on complex three-dimensional structural components under static load. It is cost-efficient to implement and suitable to be integrated in the product design cycle in conjunction with finite element analysis tools. The technique employs novel luminescent photoelastic coatings and digital imaging to map the in-plane strain field. The coatings consist of a binder, generally polymeric in nature, and luminescent dyes that are applied to the surface of a test part using conventional aerosol techniques. When excited with circular polarized ultraviolet or blue illumination, the corresponding emission intensity from the coating is measured via a digital camera. The relative change in emission magnitude and phase as measured after passing through an analyzing polarizer is related to the in-plane shear strain and its corresponding principal direction. Several basic test results are presented and discussed, showing quantitative, repeatable, and high spatial resolution measurements.

Luminescent Strain-Sensitive Coatings

The use of novel luminescent coatings and digital imaging to map the in-plane strain field on structural components under static load is described. The technology, referred to as strain-sensitive skin by Visteon Corporation, employs two different approaches: the first uses a luminescent brittle coating (LBC), and the second uses a luminescent photoelastic coating (LPC). A coating consisting of a binder, generally polymeric in nature, and luminescent dye is applied to the surface of a test part by conventional aerosol techniques. The LBC is excited with incoherent ultraviolet or blue illumination, and the corresponding emission is imaged via a digital camera. The relative change in emission intensity is related to the in-plane volumetric strain response for moderate strain levels. The I,PC is excited by the same sources after being conditioned with polarizing and retarding optics to create circularly polarized light. The relative change in emission ellipticity, both in magnitude and phase as measured after passing through an analyzing polarizer, are related to the in-plane shear strain and its corresponding principal direction. These techniques offer quantitative, repeatable, and high spatial resolution measurements. Additionally, they are applicable to complex three-dimensional geometries, cost efficient to implement, and suitable to be integrated in the product design cycle in conjunction with finite element analysis tools. Results from a test conducted on an automobile suspension control arm under static loads are presented and discussed.

Full-field strain measurement using a luminescent coating

In this paper we describe an optical-based technique, called strain sensitive skin (S3), for measuring in-plane strain data on structural members under static load. The technique employs a coating consisting of a luminescent dye and polymer binder that is applied to the surface of a test part via conventional aerosol techniques. Proper illumination stimulates the dye, which in turn emits higher wavelength luminescence. The excitation and emission intensities have different wavelengths; therefore, enabling optical filtering to separate the two signals. The optical strain response is intensity based. A network of randomized microcracks within the binder scatters the waveguided luminescence from the excited dye molecules. The amount of scattered luminescence is related to the changes in the microcrack openings and orientations via mechanical strain. Various calibration tests show the optical strain response to be proportional to the sum of in-plane principal strains. With this new experimental testing tool, full-field high-resolution strain measurements can be acquired. The optical strain response of this new sensor is minimally dependent on viewing and lighting directions, rendering the technique viable to imaging and determining strain fields for three-dimensional complex geometries.

Infrared technology in automotive components research and development

There is increasing pressure in the Automotive Industry to reduce the time it takes to bring new components to production. Typical development times have been shortened from approximately five years to around two years over the last decade. The challenge for the testing community is to meet these time constraints without affecting quality. In order to remain competitive in the automotive industry, it is necessary for the vehicles developed to possess certain properties such as low weight, high stiffness, good fuel efficiency, high reliability, good ride and handling characteristics, good NVH ( Noise, Vibration, and Harshness), as well as good aerodynamical characteristics. It is generally recognized that these objectives cannot be met by developing the components through a series ofmechanical tests, since these methods are both too time consuming and expensive. New testing methods should be introduced in order to meet the aggressive goals associated with shorting the concept-to-customer (CTC) development cycle. These new methods need to be non-destructive (NDT), relatively easy to use and set-up, effective, and able to meet short timing constraints. Test results have to be reliable, repeatable, and accurate. One ofthe new technologies that has been introduced recently at Ford VISTEON, Chassis Systems, Experimental Engineering Department (BE) to meet the short CTC is Infrared.