Interferometry based high-precision dilatometry for dimensional characterization of highly stable materials

Abstract

We present an optical dilatometer for high-accuracy and high-resolution absolute measurement of the linear coefficient of thermal expansion (CTEl). Based on a highly symmetric differential heterodyne interferometer, dimensional changes of a tubular shaped specimen under controlled thermal conditions can be characterized. Our measurement facility is located in vacuum where the test specimen can be temperature controlled in a temperature range between 20 °C and 60 °C. A thermally stable support and two identical isostatic mirror clamps were specifically designed to fix a reference and a measurement mirror inside the tube enabling a measurement, where no load in the axial direction was applied to the device under test (DUT). We measured the linear CTE of two carbon-fibre reinforced plastic (CFRP) tubes with different predicted linear CTEs at room temperature: −0.647 × 10−6 K−1 and 0 ± 2.5 × 10−9 K−1, respectively. Currently, we are investigating the manufacture limitations of the CFRP and the limitations of our apparatus in terms of measurement accuracy. In the next step, we will characterize a specifically manufactured zero-class Zerodur™ tube with a CTEl value <10 × 10−9 K−1. Due to its high thermal stability and non-directional structural isotropy this material has been chosen for macroscopic calibration of the metrology system. The results of these measurements will thus provide the resolution limitations of our facility and can be taken as an absolute accuracy reference.

Coefficient of Thermal Expansion of Rubberwood (Hevea Brasiliensis) in Convective Drying Process

“…It is a well-known fact that most materials change their dimensions as a function of temperature which is called thermal expansion (Cordero et al 2009). The fractional change in dimensions of a material per unit rise in temperature is often characterised by the coefficient of thermal expansion (CTE) which is recognised as a fundamental parameter in mechanical and structural design applications of materials (Zeisig et al 2002).…”

Measurement of thermal elongation induced strain of a composite material using a polarization maintaining photonic crystal fiber sensor

“…In order to very accurately measure the linear thermal expansion coefficient of precision items such as gauge blocks, optical interferometer based wavelength measurements [8], and interferometric dilatometetry [9], have been used to obtain deformation values. A displacement measuring interferometeric system using a heterodyne scheme [10], is another technique that provides high accuracy. However, all of the interferometeric systems are very sensitive to their external environment, involve a difficult alignment process and can be physically too large for many applications.…”

Dimensional stability validation and sensor calibration with sub-nanometer accuracy

“…Advanced materials and connections demand validation of medium to long-term, if not life-time, stability to the picometer level, e.g. C/SiC, CFRP and diffusion bonded junctions [1,2]. Highest level position sensing and control require displacement sensors that not only do provide picometer-level sensitivity (resolution) and precision (stability) but also accuracy.…”