The fracture site of the hook rod happens to be at the groove, which is the most stressed area due to its small radius. Therefore, the stress concentration at the edge of the groove is the mechanical reason for the fracture of the hook rod.

　　From the perspective of material properties, the decrease in strength is prone to plastic deformation at this location, resulting in subtle cracks. Therefore, insufficient strength is the internal reason for the fracture of the hook rod. The hook rod mainly bears tensile load during operation and is intermittent, which can be considered as low cycle fatigue.

　　The process of damage and fracture is as follows: under the action of lifting force, the stress concentration at the groove causes significant stress, and due to the low strength level of the material, local plastic deformation is easily generated; Plastic deformation will lead to the initiation of fatigue cracks. As lifting progresses, the hook rod continuously undergoes low cycle fatigue, and microcracks continue to form, grow, and connect to form macroscopic cracks. When the crack extends to a certain size, the remaining area is insufficient to withstand the load of the heavy object, ultimately leading to the overall fracture of the suspension rod.

　　The fracture of the hook rod is a typical brittle fracture. The stress concentration at the groove, coupled with improper material selection and low strength level, are the main reasons for the fracture of the hook. Given the above analysis, the fracture of the hook rod is related to the strength of the material used, lifting method, load size, and frequency of use.

　　Therefore, it is recommended that:

　　(1) Overloading of the hook during operation is strictly prohibited;

　　(2) The lifting should be slow to avoid generating impact loads;

　　(3) Pay attention to strengthening the maintenance of the hook rod in daily life. Before use or after a period of use, conduct local non-destructive testing (such as dye penetrant testing or magnetic particle testing) on key parts;

　　(4) It is recommended to use special materials for hooks with higher strength levels, such as DG20Mn, or increase the rated lifting level of the hook (from 5t to 10t).