Building forgings are widely used in the construction industry, such as Bridges, high-rise buildings, large-scale water conservancy projects and so on. Due to the complexity of service environment, these forgings often have fatigue cracks, which affect the structural safety. Therefore, the research on fatigue crack propagation and crack arrest technology of building forgings is of great significance to ensure the safety and stability of buildings.
At present, the research on fatigue crack propagation and crack arrest technology of building forgings at home and abroad mainly focuses on material properties, fatigue crack generation and crack propagation mechanism, life prediction and crack arrest methods. In terms of fatigue crack propagation, researchers pay more attention to the factors affecting crack initiation, propagation rate and propagation path. In the aspect of crack stop technology, the principle, process and effect of crack stop are mainly studied.
Fatigue crack generation and propagation mechanism: Under the action of cyclic load, weak links such as dislocation and grain boundary in the microstructure of building forgings are easy to produce micro-cracks. With the increase of the number of cycles, microcracks gradually expand and converge to form macroscopic cracks. During crack propagation, the stress distribution inside the material changes, which leads to the uncertainty of the crack propagation direction.
Crack stop principle: The crack stop technology mainly applies resistance on the crack growth path, such as the use of polymer materials, metal materials filled, etc., to slow down or prevent the crack growth. At the same time, the fatigue resistance of forgings can be improved by optimizing the structure design of forgings and selecting high-strength materials, so as to prolong its service life.
Preparatory treatment: Surface treatment of forgings with fatigue cracks, including cleaning, drying, etc., to improve the adhesion of filling materials.
Crack arrest treatment: according to the shape and location of the fatigue crack, choose the appropriate filling material and process method. Commonly used filling materials include epoxy resin, polyurethane and other polymer materials, as well as metal powder, alloy and other metal materials. The filling process includes coating, injection, extrusion, etc. The appropriate method can be selected according to the actual situation.
Final treatment: After filling is completed, the forgings are cured, trimmed, etc., to ensure the quality and safety of the forgings.
Taking the derrick forging of a large bridge as an example, obvious fatigue cracks appear in the process of use. In order to ensure the safety of the bridge, the fatigue crack propagation and crack arrest technology described in this paper is used to repair the bridge. The specific repair process is as follows:
Detailed surface treatment of cracked boom forgings, including removal of surface dirt and degreasing treatment, is carried out to improve the adhesion of filling materials.
The metal powder filling method is used to fill the metal powder to the crack, and supplemented by appropriate pressure to achieve the tight filling of the metal material.
After filling the forgings, the high temperature curing treatment is carried out to make the filling material and the forgings body form a whole and improve the overall strength.
Quality inspection of cured forgings is carried out to ensure that they meet relevant standards and operational requirements.
After the repair treatment, the boom forging successfully inhibited the crack propagation and significantly improved its fatigue resistance. In the actual use process, the service life of the forging has been significantly extended to ensure the safe and stable operation of the bridge.
Fatigue crack propagation and crack arrest technology of building forgings is of great significance to ensure the safety and stability of buildings. This paper introduces the principle, process flow and a practical application case of this technology. Practice has proved that this technology has remarkable effect in suppressing crack propagation and prolonging the service life of forging parts. However, this technology still has some shortcomings, such as the high performance requirements of filling materials, the process implementation may cause certain damage to the forging. Therefore, the future research direction should include optimizing the performance of the filling material, improving the process method, and further reducing the operating cost to better promote and apply the technology.
