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KR-102963812-B1 - Apparatus and Method for 4K Cryogenic Impact Testing Using Liquid Helium

KR102963812B1KR 102963812 B1KR102963812 B1KR 102963812B1KR-102963812-B1

Abstract

The apparatus and method for a 4K cryogenic impact test using liquid helium according to the present invention comprises an impact tester, a test specimen case that accommodates a test specimen and supplies liquid helium, a cooling time measuring unit that can check the cooling time including a simulated test specimen, and a liquid helium supply unit. According to the apparatus, liquid helium is directly sprayed onto the test specimen to cool it to approximately 4K, and the impact test is performed during the spraying operation of liquid helium without a separate movement process, thereby minimizing the influence of temperature changes and external factors and improving the accuracy of material toughness evaluation.

Inventors

  • 오승준
  • 온한용
  • 윤정환

Assignees

  • 동아대학교 산학협력단

Dates

Publication Date
20260511
Application Date
20250901

Claims (10)

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  7. An impact testing machine for measuring the toughness of a specimen, comprising a support on which a test specimen is mounted and a hammer for fracturing the test specimen; A test specimen case capable of being seated on a stand of the impact testing machine, having a space formed inside for accommodating a test specimen, and a liquid helium inlet provided to supply liquid helium into the space; A cooling time measuring unit configured to be seatable on a stand of the impact testing machine and including a simulated test specimen equipped with a temperature sensor, thereby enabling verification of the cooling time required for the simulated test specimen to cool to a target temperature; and A liquid helium supply unit that includes a liquid helium tank and directly injects liquid helium into the test specimen case and cooling time measuring unit; The hammer of the above impact tester operates simultaneously while liquid helium is supplied into the test specimen case through the liquid helium supply unit, and The above cooling time measuring unit is, A simulated test specimen case configured to be seated on a stand of an impact testing machine, a simulated test specimen accommodated inside the case, and a temperature sensor mounted on the simulated test specimen, wherein A 4K cryogenic shock test apparatus using liquid helium, characterized in that the temperature sensor is configured to be inserted into one or more insertion grooves formed in the center of the simulated test specimen case to measure the deep surface temperature of the simulated test specimen.
  8. A method for performing an impact test on a specimen in a cryogenic environment of 4K using liquid helium, A first step in which a cooling time measuring unit including a simulated test specimen equipped with a temperature sensor is mounted on a stand of an impact tester; A second step in which liquid helium is supplied into the cooling time measuring unit, and the simulated test specimen is cooled to the target temperature; A third step in which the cooling time required for the simulated test specimen to reach the target temperature is measured in the second step above; A fourth step in which the above cooling time measuring unit is removed from the stand of the impact tester; A fifth step in which a test specimen case containing a test specimen is placed on the stand of the impact testing machine; A sixth step in which liquid helium is supplied into the test specimen case in the fifth step above and liquid helium is directly sprayed onto the test specimen; and A 4K cryogenic impact test method using liquid helium, characterized by including: a seventh step in which, after the cooling time measured in the third step has elapsed in the sixth step, the hammer of the impact tester is operated while liquid helium is being sprayed to measure the impact absorption energy required for the fracture of the test specimen.
  9. In Paragraph 8, In the above Step 2 and Step 6, A 4K cryogenic impact test method using liquid helium, characterized in that the liquid helium is not sprayed directly onto the simulated test specimen and the test specimen, but is sprayed directly into the test specimen case containing them, thereby allowing the simulated test specimen and the test specimen to be uniformly cooled.
  10. In Paragraph 8, In the above 7th step, A 4K cryogenic impact test method using liquid helium, characterized in that when the hammer of the impact tester operates, the test specimen case fractures together with the test specimen.

Description

Apparatus and Method for 4K Cryogenic Impact Testing Using Liquid Helium The present invention relates to an apparatus and method for a 4K cryogenic impact test using liquid helium, and more specifically, to an apparatus and method for a 4K cryogenic impact test using liquid helium in which liquid helium is directly sprayed onto a test specimen to cool the test specimen to a cryogenic temperature of 4K, and a Charpy impact test is performed while the liquid helium is being sprayed. Recently, businesses utilizing ultra-low temperature eco-friendly energies such as liquid helium and liquid hydrogen have been gaining attention. However, eco-friendly energy businesses operating in such ultra-low temperature environments require extensive verification regarding stability. Since structures constructed for the handling of ultra-low temperature liquids are inevitably affected by temperature, consideration of thermal aspects is essential; in particular, a thorough review of the low-temperature properties of the materials is absolutely necessary. For example, key facilities for the storage and transport of cryogenic liquefied materials, such as liquid hydrogen, are directly exposed to ultra-low temperature environments. In such conditions, materials exhibit a characteristic of rapidly shifting from ductile to brittle behavior as the temperature decreases. Since this change in material properties can cause structural deformation or failure, potentially leading to unexpected accidents, it is crucial to predict this in advance and establish appropriate countermeasures starting from the design phase. Therefore, structural designs must be carried out by considering the unique ductile-brittle transition temperature (DBTT) of each material, and various studies are continuously being conducted to ensure the stability against brittle fracture of facilities and structures operating in low-temperature environments. At temperatures below DBTT, the material suddenly loses its ductility and becomes brittle, exhibiting brittle fracture characteristics where it breaks easily even with slight impact. The property of resisting such brittle fracture is called toughness. Measuring the toughness of materials is essential to predict the likelihood of brittle fracture in materials applied in low-temperature environments. Material toughness is an inherent property of a material that allows it to resist brittle fracture without plastic deformation when subjected to tensile stress. While there are various methods to determine material toughness, the Charpy impact test is the most commonly used, considering factors such as the simplicity of evaluation and the time required. The Charpy impact test is performed by measuring the amount of energy absorbed by a material while the specimen is fractured. Here, absorbed energy refers to the energy required for the fracture of the specimen, and generally, the absorbed energy of the material tends to decrease as the temperature decreases. However, it is technically difficult to create a low-temperature environment at the target temperature within a chamber for Charpy impact testing. Accordingly, most current Charpy impact tests adopt a method in which the test specimen is immersed in liquid nitrogen to cool it to the target temperature, and then rapidly transferred to an impact testing machine to perform the test. In addition, according to ASTM E23, which specifies low-temperature testing procedures, it is recommended to perform an impact test within 5 seconds after removing the test specimen immersed in liquid nitrogen in order to prevent the problem of temperature rise occurring after the test specimen cooled to a low temperature reaches the target temperature. However, when the test specimen is cooled to cryogenic temperatures, there is a limitation in that it is difficult to accurately evaluate the toughness of the material because such a temperature rise proceeds more rapidly upon contact with the external environment. FIG. 1 is a configuration diagram of a 4K cryogenic shock test apparatus using liquid helium according to the present invention. Figure 2 is a photograph of an impact tester according to the present invention. Figure 3 is a photograph of a test specimen case mounted on a stand of an impact tester according to the present invention. FIG. 4 is a photograph of a test specimen case containing a test specimen according to the present invention. FIG. 5 is a front view illustrating the internal structure of a test specimen case containing a test specimen according to the present invention. FIG. 6 is a side view illustrating the internal structure of a test specimen case according to the present invention. Figure 7 is a photograph of a simulated test specimen and a temperature sensor of a cooling time measuring unit according to the present invention. The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments desc