## 1 Introduction
Since the performances of vehicle system are also deteriorated when the mortar damage develops to a certain extent, the vehicle responses are considered when studying the effect of CA mortar disengagement. The studies usually [16, 17, 18, 19, 20, 21] established a vertical vehicle-slab track model and discussed the effect of CA mortar disengagement with different lengths and heights on the dynamic performances of vehicle and track structures. Studies based on the experimental results were also carried out to explore the effects of mortar disengagement on the responses of vehicle and track systems. [PERSON] et al. [22,23] analyzed the vibration characteristics of the  
Figure 1: Diagram of the mortar disengagement [9]. vehicle and CRTS I slab track under different mortar disengagement conditions through field test and theoretical analysis. [PERSON] et al. [24] investigated the influence of mortar damage on the track system by numerical and experimental results to recommend values for criteria of mortar disengagement. Both the mortar disengagement in ballastless slab track and unsupported sleepers in ballasted track are local instabilities, which exert similar influence on the vibration responses of vehicle and track structures. [PERSON] et al. [25; 26] comprehensively studied the effects of unsupported sleepers on the interaction behaviors in the void and neighbor zones via numerical simulation and experimental measurements. According to the literature review, the existing investigations mainly focus on the damage mechanism of CA mortar and the influences of mortar disengagement on the track carry capacities of CRTS I slab track. However, compared with the mortar in CRTS I slab track, the elastic modulus of mortar in CRTS II slab track is much larger. The equivalent stiffness of mortar in CRTS II slab track is much greater than that in CRTS I slab track, which leads to more significant influences on vehicle and track systems due to mortar disengagement [5]. Meanwhile, the longitudinal stress of slab and compressive stress of mortar layer in the past investigations are seldom mentioned, which are adversely affected by local mortar disengagement seriously [27]. Most investigations simulated the mortar layer as spring-damper elements, leading to the difficulty in obtaining the stress of mortar layer [20; 28]. Additionally, the research technology mostly relies on experiments or theoretical methods. Disadvantages of experiments are the long test cycle, high cost and tendency to be affected by environment [29; 30]. Moreover, it is not feasible to set up mortar disengagement with different lengths and heights in the field experiment. Theoretical analysis introduces considerable equilibrium equations, which usually need an iterative producer and small integration step of time to obtain converged solutions. Moreover, the algorithm for compiling the programmer is merely detailed in references [31]. Therefore, both experiments and theoretical analysis have great limitations. As a professional multi-body simulation (MBS) software package for railway vehicle, the efficiency of vehicle modeling is greatly improved through the SIMPACK platform [32]. SIMPACK cannot directly formulated the flexible track, which is initially established in a finite element (FE) analysis software ANSYS. With the help of ANSYS, the flexible track structures are conveniently established, and the calculation time is shortened through substructure analysis. By employing mature software packages, the modeling efficiency is evidently improved, and the visualization of the simulation model is realized as well. This paper is dedicated to exploring the influences of mortar disengagement on the dynamic performances of vehicle system and carrying capacities of track structures, utilizing a rigid vehicle-flexible track model established in SIMPACK with the help of the ANSYS platform. The simulation model is performed with different mortar disengagement conditions.