Thermal Response Of Sample Research Articles

Modeling the Thermoelastic Sample Response for Subdiffraction Infrared Spectroscopic Imaging.

There is significant and increasing interest in using the photothermal effect to record infrared (IR) absorption spectra localized to volumes that are considerably smaller than the wavelength of excitation, i.e., subdiffraction imaging. As opposed to conventional IR microscopy, in which absorption and scattering of the illuminating light is measured, subdiffraction imaging can be achieved through detection of the sample's thermal response to IR absorption-induced heating. While this relationship has been examined by a variety of coarse-grained models, a generalized analysis of the dependence of temperature and surface deformation arising from an absorber below the surface has not been reported. Here, we present an analytical model to understand a sample's thermoelastic response in photothermal measurements. The model shows important dependence of the ability to record subdiffraction data on modulation frequency of exciting light, limitations imposed by optical sensing, and the potential to discern location of objects ultimately limited by noise and sharpness of the detecting mechanism. This foundational analysis should allow for better modeling, understanding, and harnessing of the relationship between absorption and sample response that underlies IR photothermal measurements.

High-flux sublimation of a 3D carbon/carbon composite: Surface roughness patterns

3D carbon-fibre reinforced carbon composites (3D Cf/C) are used as thermal protection systems for atmospheric re-entry, where they are exposed to strong ablation. Particularly, sublimation of the carbonaceous material plays an important role during the re entry. To study this, an arc image furnace under controlled Argon flow is used, with heat fluxes of 8 MWm−2 to 10 MWm−2. The furnace and the sample thermal response have been numerically simulated prior to the experiments and match in-situ temperature measurements. Scanning electron microscopy and 3D profilometry with digital optical microscopy were used in order to characterise the epi-macro-structural and the epi-micro-structural roughness of the composite surface, evidencing a faster recession of the fibres as compared to the matrix. Carbon nanotextures have been assessed by using High-Resolution Transmission Electron Microscopy and Polarised Light Optical Microscopy, showing that the matrix is more organised than the fibre. This can explain the “inverse” behaviour under sublimation as compared to oxidation. The results have been qualitatively interpreted using numerical simulation of differential surface recession.

Photopyroelectric Microscopy of Porous Ceramics

Porous ceramics has capital importance in a wide variety of applications as in the case of gas and humidity sensors; in these applications an important fact is that the ceramic structure must insure intercommunication between one side and the other. Several techniques has been used in order to have information about the ceramic structure; among these, photopyroelectric (PPE) spectroscopy is an option to be used in porous ceramic structure characterization. In PPE microscopy, an image of the sample thermal response can be obtained by 2D scanning of a focused beam across a surface, which yields localized information on the possible presence of subsurface features which is an important property of porous ceramics. Recently porous ceramics based on barium titanate mixed with silicon dioxide have been developed to be used as gas and humidity sensors. By the use of PPE microscopy, porous ceramics were analyzed with two different resolutions as a result of the variation of the light modulation frequency. The light modulation frequency is related not only to scanning depth, but also to thermal scale length which gives us the minimum sample length that can be studied and is also related with its thermal diffusion length.

Review and comparison of shearography and pulsed thermography for adhesive bond evaluation

To reduce costs and facilitate automation in the automotive industry, adhesive bonding has gained popularity as a replacement for conventional mechanical fasteners such as bolts, screws, rivets, and welding. Adhesive bonding is particularly useful for bonding parts made of plastics and polymer composites, which are playing an increasing role in reducing vehicle weight. However, the adhesive bonding process is more susceptible to quality variations during manufacturing than tradi- tional joining and fastening methods. Shearography and pulsed ther- mography are full-field, noncontact, nondestructive testing methods that are widely used in the aerospace industry, offering significant potential as practical tools for in-process inspection of adhesive bond quality. The two techniques are often used to address a common set of aerospace applications, e.g., delaminations or skin-to-core disbonds in composite structures. However, they are fundamentally different, based on different flaw detection mechanisms: Shearography measures the sample's me- chanical response to mechanical stresses, while pulsed thermography measures the sample's thermal response to an instantaneous thermal excitation. For the convenience of potential users and readers, the au- thors review shearography and pulsed thermography. The potential of these techniques for inspecting adhesive bonding is demonstrated and compared. 2007 Society of Photo-Optical Instrumentation Engineers. DOI: 10.1117/1.2741277 Subject terms: adhesive bonding; shearography; pulse thermography; optical metrology; nondestructive testing; quality inspection.

Thermal diffusivity measurements of building materials based on 2D models

This paper presents the results and experimental procedure used for obtaining the thermal diffusivity of building materials like cement, sand, expanded polystyrene, silicone and concrete. The determination of this important physical property is based on the solution of the 2D cartesian and cylindrical Fourier equation adapted to high surface conductances. Material samples are shaped as rectangular prisms or cylinders to accomplish these simple geometries. The measurement technique is based on the sample thermal response when it is suddenly submitted to baths of constant temperature. The uncertainty associated with this method is systematically estimated in both cases. Thermal diffusivity is obtained with a precision of about 6% using a simple proving bench. Such precision is good enough taking into account the typical low values of this property for such kind of materials and their strong dependence with temperature.

The thermal conductivity of ribbon-shaped carbon fibers

The thermal conductivity of ribbon-shaped fibers produced at Clemson University and graphitized at 2400 degrees C and of commercial round fibers graphitized at temperatures above 3000 degrees C were measured by two different methods. One instrument, located at BP Amoco in Alpharetta, GA, measures a fiber sample's thermal response to an oscillating heat input. This device was used to measure room-temperature thermal conductivity of the fibers. A second apparatus, located at the University of Louvain-la-Neuve in Belgium, measures a fiber sample's thermal response to a controlled thermal gradient. This device was used to measure the temperature dependence of the thermal conductivity of selected fiber sets. The results will be presented and the accuracy of the two methods compared. (C) 2000 Elsevier Science Ltd. All rights reserved.