Cooling behavior of fiber reinforced composite samples in a newly designed cryostat for the evaluation of temperature-dependent material properties
Topic(s) : Special Sessions
Co-authors :
Leonard GABELE (GERMANY), Anna TRAUTH , Markus SAUSE (GERMANY)Abstract :
The use of liquified gases in aerospace applications for eco-friendly propulsion requires storage at cryogenic temperatures and typically high pressures. Therefore, the storage systems are subject to thermal and mechanical stresses down to the temperature range of the liquified gases. Understanding the mechanical characteristics of storage systems made from composites is therefore crucial for safe operation, necessitating comprehensive material characterization at cryogenic temperatures.
In composite materials measurement of tensile, compression and shear properties are fundamental to provide data for the design of such structures. Beyond the material properties, testing of joints and evaluation of damage tolerance, as well as the capacity to test cylindrical samples (e.g., filament wound) to study knock-down factors due to manufacturing, are deemed essential for the widespread incorporation of composites in cryogenic storage applications. Our research focuses on devising temperature measurement solutions from 10 K to room temperature without relying on cryogenic liquids as coolant medium. Instead, cooling is achieved through a closed-loop helium-4 Gifford-McMahon cryocooler surrounded by copper shielding in a vacuumed Dewar to minimize radiation heating. This cryostat-system can accommodate various testing concepts for composite materials within the chamber. The load frame inside the cryostat is designed for a capacity of 50 kN according to the requirements of samples designed following the typical test standards. For each setup, specific sample fixtures address low heat capacity and efficient heat conduction. Sample fixtures for quasistatic and fracture mechanic tests have been designed, along with the implementation of optical strain measurement and acoustic emission monitoring.
This study investigates the effects of heat transport in the cryostat to reach lowest sample temperatures in our experimental setup, with a specific focus on the compression fixture (see Fig. 1). A comprehensive analysis and discussion of key factors influencing this temperature is conducted. The primary source is the heat flux through the columns of the load frame, introducing the mechanical load from the test machine to the test fixtures. Another significant contribution is the increased thermal radiation directed at the sample when digital image correlation is implemented, leading to a noticeable rise in sample temperature. Additionally, the integration of acoustic emission sensors introduces a considerable impact on thermal mass and another heat flux. Despite these challenges, the experimental configuration demonstrates the ability to attain test temperatures well below 77 K, underscoring its general suitability in advancing the frontiers of low-temperature experimentation without relying on conventional cryogenic liquid approaches.
In composite materials measurement of tensile, compression and shear properties are fundamental to provide data for the design of such structures. Beyond the material properties, testing of joints and evaluation of damage tolerance, as well as the capacity to test cylindrical samples (e.g., filament wound) to study knock-down factors due to manufacturing, are deemed essential for the widespread incorporation of composites in cryogenic storage applications. Our research focuses on devising temperature measurement solutions from 10 K to room temperature without relying on cryogenic liquids as coolant medium. Instead, cooling is achieved through a closed-loop helium-4 Gifford-McMahon cryocooler surrounded by copper shielding in a vacuumed Dewar to minimize radiation heating. This cryostat-system can accommodate various testing concepts for composite materials within the chamber. The load frame inside the cryostat is designed for a capacity of 50 kN according to the requirements of samples designed following the typical test standards. For each setup, specific sample fixtures address low heat capacity and efficient heat conduction. Sample fixtures for quasistatic and fracture mechanic tests have been designed, along with the implementation of optical strain measurement and acoustic emission monitoring.
This study investigates the effects of heat transport in the cryostat to reach lowest sample temperatures in our experimental setup, with a specific focus on the compression fixture (see Fig. 1). A comprehensive analysis and discussion of key factors influencing this temperature is conducted. The primary source is the heat flux through the columns of the load frame, introducing the mechanical load from the test machine to the test fixtures. Another significant contribution is the increased thermal radiation directed at the sample when digital image correlation is implemented, leading to a noticeable rise in sample temperature. Additionally, the integration of acoustic emission sensors introduces a considerable impact on thermal mass and another heat flux. Despite these challenges, the experimental configuration demonstrates the ability to attain test temperatures well below 77 K, underscoring its general suitability in advancing the frontiers of low-temperature experimentation without relying on conventional cryogenic liquid approaches.