The Flash Method

The Flash Method is employed to determine the thermal diffusivity of various materials. In this method, a sample undergoes exposure to a brief, intense radiant energy pulse, facilitated by a high-power source such as a laser or flash lamp. The specimen absorbs and subsequently re-emits this energy on its surface, leading to a temperature increase. This temperature rise is then captured and recorded using an infrared (IR) detector.

The schematic representation of the measurement setup and procedure is illustrated in the figure below.

Laser Flash Method scheme

The detector signal provides information about the measurement duration and the normalized temperature rise on the surface of the sample, precisely at the location of the light pulse. To calculate the thermal diffusivity, it is essential to establish the baseline and determine the maximum temperature rise. This is achieved through a fitting model, which also identifies the time at which half of the maximum temperature rise is attained.

The formula used for this calculation is derived from a physical model representing the thermal behavior of an adiabatic slab of material with a constant thickness, subjected to a short energy pulse at a constant temperature. Various assumptions are made in this model, addressing deviations from reality. The fitting models take these deviations into account, including factors such as the finite pulse length of the power source and heat loss of the sample to its surroundings.

With knowledge of the density and specific heat capacity of the sample, the thermal conductivity can be determined using the equation:

It’s crucial to note that these parameters are temperature-dependent. Therefore, a comprehensive characterization of the material involves measuring these properties at various temperatures.

The Flash Method offers several advantages, including rapid and non-destructive measurements applicable to samples with low to high thermal conductivity. Additionally, the method accommodates simple specimen geometries, allowing for the investigation of small samples with easy preparation.

Which properties are determined with Flash method?

The Flash Method is employed to measure the thermal diffusivity of materials. By using a suitable reference material, it becomes possible to conduct a comparative method for measuring the specific heat capacity. With the obtained values for thermal diffusivity, specific heat capacity, and density, it is then feasible to calculate the thermal conductivity.

Key Material Properties:

  • Thermal diffusivity
  • Specific heat capacity
  • Density

Which norms count for the Flash Method?

Relevant Standards:

  • ASTM E1461 – Standard Test Method for Thermal Diffusivity by the Flash Method
  • ASTM E2585 – 09(2015) Standard Practice for Thermal Diffusivity by the Flash Method

These standards provide guidelines for conducting precise measurements of thermal diffusivity using the Flash Method, contributing to accurate assessments of thermal properties in materials.

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