Characterization and Modelling of the Deformation and Failure of Engineering Metallic Materials

Metallic materials are at the heart of modern industry and infrastructure, valued for their outstanding strength, ductility, and other excellent mechanical properties [1,2]. The deformation and failure in these materials are inherently multiscale and multifactorial phenomena [2,3]. At the atom- or micro-scale, they originate from dislocation motion, twinning, phase transformation, void nucleation, etc. [1,4]. Plastic deformation and failure are strongly shaped by how different microstructural features interact with one another [4,5]. As we push for lighter structures [6,7,8], greater durability in harsh environments [9,10], and longer service lives [11,12,13], understanding how metals deform and fail has become more important—and more challenging—than ever. For this purpose, both advanced characterization techniques and numerical modelling methods have been developed.

Material characterization techniques have advanced quickly in recent decades [14,15], which offers insights into deformation mechanisms at a wide range of length and time scales. At the micro-scale, in situ mechanical testing using electron microscopy allows for the direct observation of dislocation activity [14], phase evolution [16], and crack propagation during loading [15]. Techniques like Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) are widely used to reveal local crystal orientations, microstructural features, and areas of strain, offering a detailed understanding of how materials deform at the grain level [15]. At larger scales, digital image correlation (DIC) techniques offer full-field strain mapping during mechanical tests [17,18], revealing heterogeneity in strain distribution and early signs of localized deformation. Meanwhile, X-ray diffraction, particularly using synchrotron radiation, has enabled the measurement of internal stresses, lattice strains, and phase distributions [19]. Emerging techniques, such as 3D tomography, atom probe tomography (APT), and a focused ion beam (FIB), allow for the three-dimensional reconstruction of microstructures [19,20,21,22].

Numerical modelling techniques have also progressed significantly. The finite element method (FEM) remains a cornerstone of mechanical simulation. The conventional FEM relies on phenomenological constitutive models, which does not consider microstructural factors [23,24,25]. When crystal plasticity models are integrated into finite element simulations, crystal plasticity finite element methods (CPFEMs) can account for the orientation of crystals and the specific slip systems that operate during deformation [26,27,28]. The microstructure in a CPFEM can originate from EBSD data, ensuring more accurate predictions [29,30]. At a lower scale, discrete dislocation dynamics (DDD) simulations capture the collective behaviour of dislocations and their interactions [31], while molecular dynamics (MD) simulations provide atomistic insights into mechanisms such as dislocation nucleation, phase transformation, and grain boundary migration [32,33]. Though computationally intensive, these numerical approaches are invaluable for exploring deformation phenomena that are difficult to observe experimentally. This Special Issue has collected works regarding the recent progress concerning on the above-mentioned topics.

Zhang et al. [34] used cavitation water jet peening (CWJP) to strengthen the surface of the 7075 aluminum alloy. The process increased surface hardness from 109.2 Hv to 144.0 Hv, with the strengthening effect extending up to 600 µm deep. In another study by Ding et al. [35], laser shock peening was also used to improve the fatigue life of 1Cr18Ni9Ti. It was found that the 3J category produced the best result due to the optimal grain refinement and residual compressive stress. Abdi et al. [36] applied twin parallel channel angular extrusion (TPCAE) to an AZ91 cast magnesium alloy to improve its hydrogen storage properties. The TPCAE process was conducted at temperatures from 340 °C to 200 °C, and the hydrogen absorption and desorption tests were measured at 250 °C, 300 °C, and 350 °C. Three TPCAE passes at 250 °C resulted in the best absorption capacity, i.e., 6.1 wt.% within a time span of 2000s. To enhance the welding quality of aluminum and steel, Zhang et al. [37] placed a copper and a nickel coating on the surface of the former and latter, respectively. This interlayer copper–nickel binary coating suppressed the formation of brittle intermetallic compounds, and the welding quality was increased by 56% compared to the uncoated aluminum–steel welding.

Chen et al. [38] conducted dry sliding tribometric tests with different loads to evaluate the mild–severe wear transition of the 2095 Al-Li alloy. The wear rate grew slowly when the load was 2–4N, grew fast at a medium load (8–16N), and grew gradually at loads from 32N to 40N. SEM mapping shows that the abrasion and oxidation were significant during the transition from mild to severe wear, and the tribo-induced plastic deformation of the substrate is the reason for this wear transition. Wang et al. [39] used multiple misorientation parameters, derived from EBSD mapping, to evaluate the plastic damage, including the grain reference orientation deviation (GROD), grain orientation spread (GOS), grain orientation spread over the grain diameter (GOS/D), and the geometrically necessary dislocation (GND). It was found that the GOS/D was a reasonable indicator for the plastic damage in 316 steels. The underlying mechanism for plastic deformation and damage is dislocation movement, and thus understanding the behaviours of dislocation movement is critically important. Chang et al. [40] used an indentation stress relaxation process to study the dislocation velocity and stress exponent in commercial pure aluminum, and this exponent was found to be 2.5 ± 0.5 for ambient temperature.

Shen et al. [30] conducted CPFEM simulations to investigate the influence of ultrafine-grained (UFG) austenite on the mechanical properties of medium-Mn steel by comparing the stress and strain between the samples with and without austenite. The 3D EBSD-scanned microstructure was modelled to ensure high fidelity, where the grain morphology, crystallographic orientation, and phase composition were preserved. The UFG austenite was found to be a main contributor to the ductility and strength of medium-Mn steel. CPFEM simulations were carried out to evaluate the sensitivity of the nanoindentation stress relaxation methodology to the dislocation velocity-stress exponent [40]. Compared to the uniform-field and mean-field methods, the full-field CPFEM requires a large amount of computation time, since homogenization is not theoretically assumed. Liu et al. [41] utilized a Submodel method to exceedingly enhance the mesh resolution in areas of interest, and the CPFEM simulations successfully captured the weak texture components and local deformation. Qin et al. [33] performed molecular dynamics simulations to systemically study the behaviours of crack propagation in the Ni-based superalloy. It was found that high-stress triaxiality promoted brittle cracking, while low-stress triaxiality enhanced the plastic crack; the cracks grow slowly when they are located in the γ and γ’ phase; the γ/γ’ phase interface hinders the crack propagation when the crack is perpendicular to the γ/γ’ interface.

As metal processing techniques continue to evolve, we are seeing the development of more advanced materials with increasingly complex microstructures. These advances call for equally sophisticated tools to understand how structure influences performance. This Special Issue aims to present state-of-the-art developments in this vibrant field, and to deepen our understanding of how metals deform and fail. As Guest Editors, we hope you find this Special Issue helpful and inspiring. Finally, we are deeply grateful to the authors for their publications, to the reviewers for their time and comments, and to the Editorial team for their suggestions and support.