PSI - Issue 49

Minghua Cao et al. / Procedia Structural Integrity 49 (2023) 74–80 Minghua Cao et al./ Structural Integrity Procedia 00 (2023) 000 – 000

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minor length of ellipsoidal HA inclusion MMC metal matrix composite PBC periodic boundary condition RVE representative volume element 1. Introduction

Thanks to their combination of mechanical strength and fracture toughness, metals and alloys play a significant role in the repair and replacement of damaged bone tissues as implant materials (Staiger et al,. 2006). Advantages of metal matrix composites (MMCs) used as biomaterials include the adjustable corrosion and mechanical properties (i.e., Young’s modulus and tensile strength) by an appropriate choice of their composition (Witte et al., 2007). Magnesium alloys are one of the suitable materials before the use in biodegradable metal implants. Since the chemical composition of hydroxyapatite (HA) is similar to the apatite in bones, HA attracted research interest as a bioceramic material in implants (Jaiswal et al., 2019). HA was recently applied as a predominant reinforcement material in magnesium-based composites to adjust their degradation behaviour (Dubey et al., 2021). The incorporation of Mg and HA makes magnesium-hydroxyapatite composite (MMC-HA) an important biomaterial for metal implants. The microstructure of MMC-HA is composed of magnesium matrix and hydroxyapatite inclusions of varying shapes and sizes (Fig. 1).

Mg

HA

Fig. 1. Microstructure of MMC-HA (Witte et al., 2007).

In MMCs, bonding strength of the interface between the inclusions and the matrix is easily influenced by service conditions. During manufacturing processes, MMC-HA experiences temperatures that reach 500 °C (Jaiswal et al., 2018). Thermal stresses arise in such MMCs because of the mismatch in coefficients of thermal expansion between HA and Mg. These residual stresses are considered the major factor causing failure of implants (Fogarassy et al., 2005). Interfacial bonding strength and interaction between two phases affected by thermal deformation and stresses are commonly agreed to initiate interfacial debonding of MMCs (Chawla and Chawla, 2013). However, the deformation mechanism of MMC-HA under thermal load at the microscale lacks investigation. In MMCs, the morphology of inclusions plays a significant role in the performance of the composites. The distribution and size of HA inclusions affect the mechanical behaviours of magnesium-based composites (Jaiswal et al., 2020). Mechanical properties of composites can be improved when HA inclusions have a smaller size and interparticle space (Dubey et al., 2021). The morphology of inclusions - together with their properties – is important for thermomechanical behaviours of MMCs. To investigate the performance of MMCs, either phenomenological or micromechanical modelling can be employed. With adjustable mechanical properties, MMC-HA is mainly studied using representative volume elements (RVEs) (Balać et al., 2001; Fritsch et al., 2009) or the mean-field technique (Verma et al., 2021). An RVE-based approach was used in this work to investigate the relationship between the morphology of a single inclusion and the thermomechanical behaviour of MMC-HA. Both the HA inclusion and the Mg matrix were considered isotropic and homogeneous at the microscale. The effect of HA morphology on the thermomechanical behaviour of MMC-HA was studied with three-dimensional numerical models.