# Damage Analysis of Rolling Stock Automatic Coupler under Cyclic Loads
## 1 Introduction
The parameters \(\overline{S}_{T},\ A_{1},\ A_{2},\ \beta\) (see Section 3) for damage summation were obtained from experimental \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \(T\), kN & 150 & 350 & 550 & 750 & 950 & 1150 & 1350 & 1550 \\ Number of loads & 3078 & 4668 & 2785 & 2107 & 1344 & 784 & 395 & 139 \\ \hline \(T\), kN & 1750 & 1950 & 2150 & 2350 & 2550 & 2750 & 2950 & 3150 \\ Number of loads & 104 & 59 & 34 & 23 & 13 & 8 & 5 & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Traction force \(T\). \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \(\mathbf{C}\) & \(\mathbf{Mn}\) & \(\mathbf{S}\) & \(\mathbf{P}\) & \(\mathbf{Si}\) & \(\mathbf{Cu}\) & \(\mathbf{Cr}\) & \(\mathbf{Ni}\) & \(\mathbf{Mo}\) & \(\mathbf{V}\) \\ \hline
0.31 & 1.70 & 0.01 & 0.03 & 0.37 & 0.17 & 0.16 & 0.07 & 0.04 & \(<\)0.03 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Chemical composition of the steel of an automatic coupler. diagrams of elastic-plastic cyclic deformation (Table 3). Alteration of the mechanical characteristics of the material is viewed as the key factor for increasing the durability of an automatic coupler. Structural modifications that could reduce stress concentration are not employed in the literature reviewed. All the steels investigated were found to belong to the class of cyclically stable materials with weakly anisotropic properties in the normal state and to the class of cyclically softening anisotropic materials after quenching and tempering. A comparison of the low-cycle fatigue curves has demonstrated that an increase in the mechanical strength characteristics of steel results in a significant enhancement in durability. The durability of heat-treated (20 GL--quenched and tempered) steel specimens increases almost tenfold compared to normalization alone. One paper [18] describes a method for assessing the service life of automatic couplers according to the vulnerability deformation criteria of metal structures. The proposed method is based on a combination of software packages for the simulation of longitudinal dynamics and the assessment of static and dynamic stresses--in this case, those occurring in the couplings. The analysis of the coupling life, based on the results of these study phases, was carried out by means of methods and programs for the assessment of fatigue vulnerability and the determination of the safe life. The study presented in ref. [19] evaluates the remaining service life of cast steel heavy-duty railway truck couplings with initial defects. A test program was carried out to determine high-cycle fatigue strength, fatigue crack growth rate, threshold, and fracture toughness. A numerical model of the damaged heavy-duty tractor coupling was developed, taking full account of the assembly gap and the complex non-linear contact. The remaining life was then determined using fracture mechanics methods for the actual load spectrum. In many research papers, the strength and reliability of automatic couplers have been addressed by stress-strain state computations using the finite element method. However, the strength of the automatic coupler is assessed by calculation using a linear damage summation according to the fatigue curve, without distinguishing between the low-cycle quasi-static fatigue as well as high-cycle damage. This kind of calculation fails to account for changes in the stress and strain state or offer a quantitative evaluation of different types of damage. In addition, the investigations reviewed used the Goodman diagram for durability assessment, while the former is only applicable to the high-cycle fatigue region. Hence, the application of the Goodman diagram to the low-cycle fatigue region is questionable, particularly in the presence of quasi-static damage.