Citation: Shangguan, Y.; Wang, W.;
Yang, C.; He, A. Fatigue Strength
Assessment of an Aluminium Alloy
Car Body Using Multiaxial Criteria
and Cumulative Fatigue Damage
Theory. Appl. Sci. 2023, 13, 215.
https://doi.org/10.3390/
app13010215
Academic Editors: Alberto
Campagnolo and Alberto Sapora
Received: 28 November 2022
Revised: 18 December 2022
Accepted: 21 December 2022
Published: 24 December 2022
Copyright: © 2022 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Article
Fatigue Strength Assessment of an Aluminium Alloy Car Body
Using Multiaxial Criteria and Cumulative Fatigue
Damage Theory
Yiming Shangguan
1,2
, Wenjing Wang
2,
*, Chao Yang
2
and Anrui He
1
1
National Engineering Technology Research Center of Flat Rolling Equipment, University of Science and
Technology Beijing, Beijing 100083, China
2
School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University, Beijing 100044, China
* Correspondence: wjwang@bjtu.edu.cn
Abstract:
With the rapid development of urban rail transit, metro vehicles have become preferred
choices for urban transportation. It is important to accurately evaluate the fatigue strength of a car
body to ensure subway safety. A new method based on multiaxial stress criteria and cumulative
fatigue damage theory was proposed for the fatigue strength assessment of welded joints of an
aluminium alloy head car body subjected to variable cyclic loads. A local coordinate system was
established, according to the geometrical characteristics of the weld. Local stresses perpendicular
and parallel to the weld seam were obtained to calculate the stress ratio, stress range, and allowable
stress value corresponding to the stress component. Then, the fatigue strength utilization of the joints
was estimated to determine whether the fatigue strength of the weld met the design requirements.
Moreover, the estimated fatigue life of the car body was predicted with cumulative fatigue damage
theory. This method considers both the material utilization degree in multiple stress states and the
estimated body fatigue life of the car body. The research results provide a reference and a more
comprehensive guarantee for the fatigue strength evaluation of a subway car body’s welded structure
to ensure vehicle safety.
Keywords:
fatigue strength assessment; aluminium alloy car body; multiaxial criteria; cumulative
fatigue damage theory; welded joints
1. Introduction
Fatigue has been researched for decades as one of the most common failure modes of
mechanical structures. The fatigue damage assessment approaches of welded structures
include the hot spot stress method, effective notch stress method, etc. The hot spot stress
is related to the overall geometry and load conditions of the welded structure, but does
not include the stress concentration caused by local factors, such as weld size and welding
defects [
1
,
2
]. W J Wang et al. [
3
] used the hot spot stress method to calculate the hot spot
stress value at the welding toe, and a modified S–N curve, considering the thickness effect
of the main board, was proposed to predict the fatigue life of the sample. B J Wang et al. [
4
]
compared the hot spot stress calculation result with the nominal stress from shell elements
in a welded bogie frame, and their results showed that the hot spot stress is higher than the
nominal stress. Z Y Zhou et al. [
5
] clarified the limitations of the hot spot stress method.
These researchers proposed that the hot spot stress method could effectively evaluate
toe failure based on the geometric discontinuity of the welding structure, but could not
appraise the fatigue failure caused by defects on the weld root and inside the weld. This
method is suitable for the fatigue analysis of the toe of nonstandard structural details and
complex welding joints. The effective notch stress method uses a specific radius to replace
the notch at the weld root and toe and calculates the effective notch stress at the weld toe
and weld root by the finite element method (FEM). This approach avoids the occurrence of
Appl. Sci. 2023, 13, 215. https://doi.org/10.3390/app13010215 https://www.mdpi.com/journal/applsci
