Matthew R Jones

Active thermography techniques are of interest for quality assurance of additive manufacturing processes. However, accurate measurements of thermophysical properties of materials are required to successfully implement active thermography. In particular, the spectral absorption coefficient of materials commonly used in additive manufacturing must be known to accurately predict the spatial distribution of thermal energy generated from absorption of power emitted by a laser or pulsed flash lamp. Accurate measurements of these optical properties are also needed to develop greater understanding of additive manufacturing processes that rely on radiative heat transfer to fuse powders. This paper presents spectral absorption coefficient measurements and uncertainty estimates of fully and partially dense ABS, PLA, and Polyamide 12 samples.

Surface temperature and apparent radiative surface properties (emissivity, absorptivity) may be controlled by varying surface topology through a phenomenon known as the cavity effect. Cavities created by origami folds offer the potential to achieve dynamic control of apparent radiative surface properties through actuation. To illustrate this phenomenon, a thin (0.0254 mm) stainless-steel, specularly reflecting surface (emissivity, ε = 0.117) was resistively heated (6.74 W). Accordion-shaped folds (1.27 cm panels) were used to create V-shaped grooves that transition from 29° at the center to 180° near the edges. Thermocouples were attached to the center of each cavity panel (Figure (a)). An IR image of the surface (Figure (b)) reveals that the apparent temperature increases as the cavity angle decreases and is not necessarily indicative of the actual surface temperature. This increase is due to an increase in the number of specular reflections associated with the cavity effect. A sim...

Thermal management systems for space equipment commonly use static solutions that do not adapt to environmental changes. Dynamic control of radiative surface properties is one way to respond to environmental changes and to increase the capabilities of spacecraft thermal management systems. This paper documents an investigation of the extent to which origami-inspired surfaces may be used to control the apparent absorptivity of a reflective material. Models relating the apparent absorptivity of a radiation shield to time-dependent surface temperatures are presented. Results show that the apparent absorptivity increases with increasing fold density and indicate that origami-inspired designs may be used to control the apparent radiative properties of surfaces in thermal management systems.

ABSTRACT This paper presents the solution to a nonlinear model of a circular foil heat flux gauge that is exposed to a blackbody source in a vacuum environment. This is the scenario typically used to calibrate a circular foil heat flux gauge. The nonlinear model is solved using a Green's function approach. This approach results in an integral equation for the steady-state temperature profile in the gauge, which is solved using the method of successive approximations. A relationship between the incident radiative heat flux and the temperature profile is developed using this model. This relationship is compared to relationships that were derived using linear models. The first and simplest linear model neglects emission from the foil. The second linear model is obtained by linearizing the emissive power of the gauge. It is shown that these linear models only produce accurate results when the gauge design and operating conditions result in a nearly uniform foil temperature. A procedure based on the nonlinear model is proposed for optimizing the design of a circular foil heat flux gauge. A calibration procedure based on the nonlinear model is also proposed.