Francesco Semprucci

Delamination in fibre-reinforced polymer composites is a critical failure mechanism that can ultimately lead to a catastrophic failure. To characterise in-plane shear delamination (Mode II), several test setups have been proposed in the literature, with the End-Loaded Split (ELS) test being the most suitable for applications that require stable crack propagation (ISO 15114). This manuscript focuses on studying Mode II fatigue delamination in unidirectional carbon fibre-reinforced laminates using the ELS configuration. Experimental tests with varying displacement ratios and different initial energy levels were conducted to capture a wide range of stable crack propagation scenarios. To complement these experimental efforts, a numerical model based on cohesive zone models (CZM) was implemented in Abaqus, utilising a user-defined material subroutine (UMAT). The numerical results closely align with the experimental data, validating the model’s predictive capabilities. This combined approach deepens the understanding of Mode II fatigue delamination and provides a strong framework for designing and analysing composite structures.

In recent years, sandwich composite panels have gained significant attention due to their high strength-to-weight ratio, excellent energy absorption capability, and structural efficiency under impact and crash conditions. These panels, which consist of lightweight cores enclosed between stiff face sheets, are widely used in aerospace, automotive, and marine applications. Previous research on energy absorption mechanisms, failure modes, and the influence of core materials on crash performance has highlighted the advantages of various core configurations in improving Specific Energy Absorption (SEA). Among these, 3D-printed cores stand out for their design flexibility, efficient manufacturing process, and ability to customise mechanical properties through geometric optimisation. The present study investigates the crash behaviour of sandwich composite panels with 3D-printed polylactic acid (PLA) cores by examining different core geometries and configurations through an experimental campaign.

Crashworthiness refers to a structure’s ability to absorb and dissipate impact energy through controlled deformation, thereby enhancing protection of vehicle occupants and onboard equipment. Composite materials possess significant potential in crashworthy airborne and ground vehicle structures due to their favourable specific energy absorption. However, their performance depends on several design factors such as materials, stacking sequences, and geometry. To reduce development costs and time to market, numerical simulations have become a necessary tool for optimising these factors. A challenge in this approach is the calibration of models, which is decisive for ensuring reliable and predictive simulations. Among other approaches, Non-local Damage Models have demonstrated reliability in simulating crashworthy composite structures. This work presents the intralaminar fracture energy calibration of fabric ply within a Waas–Pineda model, as implemented in ESI Virtual Performance Solutions, using Compact Tension and Compact Compression tests.

Composite materials are increasingly used in industrial applications, particularly in the aeronautic sector. However, their susceptibility to impact damage remains a critical concern, making damage tolerance a key focus for design and manufacturing. One approach to improving damage tolerance involves interleaving elastomeric films within polymeric composites, though this introduces experimental and numerical complexities. In particular, numerical simulations require reliable modelling techniques to predict the structural effects of hybridisation. This paper tested two different stacking sequences, differing in the number and placement of the elastomeric layers, under quasi-static indentation conditions. A numerical analysis was carried out using two distinct formulations of Hashin’s failure criteria and a continuum damage model, implemented through specifically developed User Material Subroutines. The experimental and numerical results were then compared, and the advantages and drawbacks of each modelling technique were discussed and compared.

Crashworthiness is a critical property that enables aerospace structures to minimise injuries and equipment damage during impact scenarios. This review examines the current state of crashworthiness research, with a focus on regulatory frameworks, experimental testing, and numerical modelling techniques. Stringent safety standards set by the Federal Aviation Administration (FAA) and the European Union Aviation Safety Agency (EASA) guide the design and certification protocols for aeronautical structures. Experimental crash testing, which includes both full-scale and subscale impact tests, provides essential data for validating material behaviour and energy absorption capabilities under both quasi-static and dynamic loading conditions. Advanced numerical modelling tools offer significant insights into crash behaviour, enabling optimisation of structural designs whilst reducing reliance on costly physical testing. This review highlights the integration of regulations, empirical data, and computational tools in advancing crashworthiness research, with an emphasis on developing safer, more efficient, and sustainable aerospace designs. Future directions should prioritise the use of sustainable materials and optimise crashworthy designs through artificial intelligence (AI) and advanced numerical models to enhance structural performance and safety.