PSI - Issue 54

Ela Marković et al. / Procedia Structural Integrity 54 (2024) 156 – 163

157

2

Ela Markovi ć et al. / Structural Integrity Procedia 00 (2023) 000–000

1. Introduction A number of engineering components used in various applications may experience high and usually very localized, static, and dynamic stresses and strains requiring different material properties in different regions. For example, gears must have high toughness on the interior to resist fracture and high hardness on the exterior to prevent wear, El-Galy et al. (2019). Materials, possessing gradually varying material properties are also known as functionally graded materials (FGMs). The aim of such materials is to improve the structural integrity of components in an optimal, targeted manner, Abali et al. (2012). Various types of heat treatments can be adopted to achieve material properties that vary over the cross-section of a component. Surface hardening enhances the surface hardness and strength while preserving the core's softness and ductility, leading to a more durable surface that can withstand wear and a tough core that can endure high impact loads, Dossett and Totten (2013). There are various surface hardening processes available, most of which result in high compressive residual stresses on the surface that reduce the probability of crack initiation and slow down crack propagation at the interface between the harder surface and softer core, Dossett and Totten (2013). This paper explores the stress-strain response of unnotched and notched specimens made from homogeneous and functionally graded low-alloy steel 42CrMo4 subjected to static loading using finite element analysis.

Nomenclature E

Young’s modulus

HV Vickers value of hardness HV core Vickers value of core hardness HV surface Vickers value of surface hardness K Strength coefficient n Strain hardening exponent R e Yield strength R ht Normalized case hardening depth x*

Depth at which the hardness reaches 80% of hardness at the surface

Distance from surface

x ε

True strain Elastic strain Plastic strain True stress

ε e ε p

σ

2. Numerical model In this study, stress-strain response of two specimen geometries (tension strips with and without opposite semicircular edge notches) and material structures with homogeneous elasto-plastic properties throughout, and with functionally graded material properties along a single dimension were investigated. Figure 1 illustrates the considered material structures with their dimensions.

Fig. 1. Unnotched and notched specimen dimensions.