Fibre metal laminates (FML) are layered materials consisting of both metal and reinforced composite layers. Due to numerous possibilities of configuration, constituent materials, etc., designing and testing such materials can be time- and cost-consuming. In addition to that, some parameters cannot be obtained directly from the experiment campaign. These problems are often overcome by using numerical simulation. In this article, the authors reviewed different approaches to finite element analysis of fibre metal laminates based on published articles and their own experiences. Many aspects of numerical modelling of FMLs can be similar to approaches used for classic laminates. However, in the case of fibre metal laminates, the interface between the metal and the composite layer is very relevant both in experimental and numerical regard. Approaches to modelling this interface have been widely discussed. Numerical simulations of FMLs are often complementary to experimental campaigns, so an experimental background is presented. Then, the software used in numerical analysis is discussed. In the next two chapters, both static and fatigue failure modelling are discussed including several key aspects like dimensionality of the model, approaches to the material model of constituents and holistic view of the material, level of homogenization, type of used finite elements, use of symmetry, and more. The static failure criteria used for both fibres and matrix are discussed along with different damage models for metal layers. In the chapter dedicated to adhesive interface composite—metal, different modelling strategies are discussed including cohesive element, cohesive surfaces, contact with damage formulation and usage of eXtended Finite Element Method. Also, different ways to assess the failure of this layer are described with particular attention to the Cohesive Zone Model with defined Traction–Separation Law. Furthermore, issues related to mixed-mode loading are presented. In the next chapter other aspects of numerical modelling are described like mesh sensitivity, friction, boundary conditions, steering, user-defined materials, and validation. The authors in this article try to evaluate the quality of the different approaches described based on literature review and own research.

The paper presents an analysis of mixed-mode fatigue crack growth in bridge steel after 100-years operating time. Experiments were carried out under mode I + II configuration on Compact Tension Shear (CTS) specimens and mode I + III on rectangular specimens with lateral stress concentrator under bending and torsion loading type. Due to the lack of accurate Stress Intensity Factor (SIF) solutions, the crack path was modelled with the finite element method according to its experimental observation. As a result, the Kinetic Fatigue Fracture Diagrams (KFFD) were constructed. Due to the change in the tendency of higher fatigue crack growth rates from K_I towards K_III dominance for the samples subjected to bending and torsion, it was decided to analyze this phenomenon in detail using electron-scanning microscopy. The fractographic analysis was carried out for specimens subjected to I + III crack loading mode. The mechanism of crack growth in old bridge steel at complex loads was determined and analyzed.

In this paper, preliminary studies on the failure analysis of hybrid composite materials utilizing acoustic emission and machine learning are presented. The main purpose of this study was to analyze the possibilities of using machine learning techniques as a way to better cluster the data obtained from acoustic emission. In this paper, we focus on data preparation, feature extraction (Laplacian score), determination of cluster number (Caliński–Harabasz, Silhouette, and Davies–Bouldin), and testing three clustering techniques, namely K-means, fuzzy C-means, and spectral clustering. The dataset was obtained by testing fiber metal laminates—composites consisting of metal and composite layers. Two experimental tests were realized on pre-cracked rectangular specimens—one with loading in mode I and one with loading in mode II (DCB—double cantilever beam and ENF—end-notch flexural test). Elastic waves were recorded during these tests via an acoustic emission system. Preliminary studies show that the proposed method can be used successfully to cluster data obtained in this way. The obtained dataset was split into 3 clusters (for the ENF test) and 5 clusters (DCB test). In the next stages of the research campaign, based on the presented results, we intend to change the approach to semi-supervised by running additional single-cause damage tests to enhance the achieved results and enable easier damage recognition.

Fiber metal laminates (FML) are hybrid materials consisting of metal and composite layers. They have great mechanical and fatigue properties. However, interface between metal and composite layers can be critical for their final properties. In this paper, process of determination of some fracture parameters of this interface in unusual FML material is described. Experimental tests following ASTM norm were conducted using Double Cantilever Beam (DCB). However, due to asymmetry, fracture energy cannot be obtained directly from the force–displacement curve. Finite element method simulations were carried out using cohesive elements and cohesive surfaces approach. The cohesive behavior of interface layers were modelled using traction separation law. Key properties of this law were obtained—maximal traction and fracture energy. In this particular case cohesive approach was better in reflecting experimental results. Determined values can be used in later research tasks (like modelling big structures containing this material) as material properties. The presented approach can be used successfully to obtain fracture energy in cases of materials for which standard approach is insufficient.