As a key component to withstand extreme working conditions such as high pressure, high temperature and corrosive media, the fracture toughness of petrochemical forgings is a measure of its ability to maintain integrity in the presence of cracks, and is an important indicator to ensure the safe operation of equipment. In order to accurately evaluate the fracture toughness of petrochemical forgings, it is necessary to adopt appropriate testing methods. In this paper, the commonly used fracture toughness test methods for petrochemical forgings are introduced, including sample preparation, test principle and application range.
The test of fracture toughness requires the preparation of samples that meet the standards. Commonly used sample types include compact tensile (CT) sample, three-point bending (3PB) sample, and standard impact (Charpy) sample. The preparation of the sample should be carried out in accordance with relevant standards to ensure that the geometric size, processing accuracy and surface quality of the sample meet the test requirements. In the preparation process, it is also necessary to pay attention to the sampling direction of the sample to ensure that the test results can truly reflect the performance of the forging.
Linear elastic fracture mechanics (LEFM) principle is usually used to test the fracture toughness of petrochemical forgings. LEFM theory holds that when the energy required per unit length of crack propagation reaches the critical energy of the material to resist crack propagation, crack propagation will occur. Therefore, the fracture toughness of the material can be assessed by measuring the critical energy required during crack propagation. In the actual test, J-integral, KIC and other parameters are usually used to characterize the fracture toughness of materials.
The fracture toughness test method of petrochemical forgings is mainly suitable for evaluating the fracture resistance of forgings in the presence of cracks. The fracture toughness indexes of forgings under different temperatures, strain rates and corrosive media can be obtained through testing, which provides a basis for material selection, structural design, manufacturing process optimization and safe operation of equipment. In addition, the fracture toughness test method can also be used to study the aging, damage tolerance and fracture mechanism of materials, and provide guidance for the improvement of material properties and the development of new materials.
Common fracture toughness test method
Compact tensile (CT) test specimen: CT specimen is a commonly used test specimen for fracture toughness, which has the advantage of high test accuracy and reliability. The fracture toughness of the material can be evaluated by measuring parameters such as J-integral or KIC during crack propagation by preforming cracks on the specimen and applying tensile loads. This method is suitable for forging test of various materials and thickness ranges.
Three-point bending (3PB) test specimen: 3PB test specimen is another commonly used test specimen for fracture toughness, which is characterized by simple preparation and low cost. The critical load and crack propagation length during crack propagation can be measured to evaluate the fracture toughness of the material by preforming cracks on the specimen and applying three-point bending loads. This method is suitable for the measurement of forgings with large thickness and brittle materials.
Standard Impact (Charpy) test specimen: The Charpy test specimen is a standard specimen used to measure the impact toughness of a material and can also be used to assess the fracture toughness of a material. By applying an impact load to the specimen, the energy absorbed during crack initiation and propagation can be measured to evaluate the fracture toughness of the material. This method is suitable for rapid screening of materials and comparison of fracture toughness of different materials.
The test method of fracture toughness of petrochemical forgings is one of the important means to ensure its safety, stability and long period operation. The fracture toughness of forgings can be evaluated effectively by preparing samples in line with the standard, adopting the appropriate test principle and application range and selecting the appropriate test method, which provides the basis for material selection, structural design, manufacturing process optimization and safe operation of equipment. In the future, with the continuous innovation and development of test technology, the fracture toughness test method of petrochemical forgings will be more perfect and reliable to provide a strong guarantee for the development of the petrochemical industry.
