## 1 Introduction  
Currently, the electric drive system, as the core component of the electrification of new energy vehicles, is developing towards high power density, high efficiency, high reliability, and safety, among other characteristics [1]. Due to their efficient performance, permanent magnet synchronous motors are widely used in electric drive systems. As a critical component in permanent magnet synchronous motors, the rotor is subjected to multiple physical loads, such as electromagnetic force, thermal stress, and centrifugal force, during its operation. There are numerous failure modes, such as magnetic bridge fatigue [2], winding aging [3, 4], and permanent magnet demagnetization [5, 6]. In addition, the risk of rotor magnetic bridge failure is further exacerbated by the increased intensity of the actual complex alternating loads. It is essential to consider the failure of rotor magnetic bridges under multiple physical fields and to build a magnetic bridge accelerated test load spectrum that reflects actual user conditions to verify product reliability levels and support high-quality development. In recent years, many scholars have researched the failure load and reliability of the permanent magnet synchronous motor rotor. [PERSON] et al. [7] used a finite element simulation to analyze the stress distribution in the rotor under rated speed conditions. They concluded that the centrifugal force on the rotor structure is proportional to the square of the speed. The higher the speed, the greater the centrifugal force. This method only considers the centrifugal forces on the magnetic bridge under alternating speeds. However, they ignore the effect on the life of the magnetic bridge due to thermal stresses caused by alternating temperatures, such as thermal conduction and thermal concomitant, as well as the electromagnetic forces generated by torque fluctuations during actual operation. [PERSON] et al. [8] pointed out that the external forces on the rotor during the process mainly include centrifugal force, electromagnetic force, and thermal stress caused by the temperature rise in the rotor. The simulation analysis shows that the electromagnetic forces are small compared to the centrifugal forces and thermal stresses and can be neglected at high motor speeds. However, they only considered the steady-state condition in the simulation analysis process. Meanwhile, the load on the rotor is complex and dynamic in the actual process, and a transient condition analysis should be further considered. In addition, the damage contribution to the magnetic bridges under different stresses can be further analyzed in terms of damage or lifetime in conjunction with their physical failure model when defining the proportion of different physical loads. [PERSON] et al. [9; 10] evaluated the lifetime of a motor rotor based on transient operating conditions, taking into account electromagnetic-thermomechanical stresses. However, they only studied the rotor structure of the in-line design, and the conclusion of the dominant failure load was not convincing. Most importantly, the effect of temperature on the S-N curve of the material was ignored when the lifetime assessment was performed. In addition, the rotor magnetic bridge is influenced by multiple sources of load and can experience various failure modes, such as fatigue and aging. Currently, scholars have conducted many studies on the development of accelerated test load profiles [11; 12], which mainly involve load data acquisition, condition construction, target definition, and cycle number determination. [PERSON] et al. [1] studied the construction of accelerated test cycle conditions for mechanical components of electric drive systems based on user data and mainly considered fatigue failure. [PERSON] et al. [13] analyzed the failure mechanism of the power device IGBT and accelerated the assessment of its thermal aging failure through power cycle conditions.