Additively manufactured (AM)-enabled cellular architectures with tuneable mechanical properties offer new opportunities for design optimisation in orthopaedic implants. In paediatric proximal femoral osteotomy (PFO), conventional implants provide structural integrity and fixation stability, but their high stiffness reduces load transfer to the growing bone (stress shielding). Triply periodic minimal surface (TPMS) lattices exemplify AM-enabled architectures with favourable strength-to-stiffness trade-offs. This study presents a proof-of-concept of a TPMS-integrated Ti-6Al-4V paediatric PFO implant, benchmarked against conventional designs using a patient-specific digital-twin workflow coupling neuromusculoskeletal (NMSK) simulations with finite element analysis (FEA) of bone-implant mechanics. NMSK-derived joint contact and muscle forces were applied to assess von Mises stresses (implant safety), bone-implant micromotion (implant attachment), and cortical mechanical stimulus through strain energy density and microstrain metrics (stress shielding). All implants remained below the relevant material yield-strength range and exhibited micromotion within the accepted threshold. The TPMS-integrated design increased distal cortical strain energy density by 25% relative to the solid plates and reduced the cortical volume falling below the selected microstrain-based disuse threshold. The TPMS implant also generated a more uniform strain distribution near screw interfaces. These engineering metrics suggest that the TPMS design may meet key initial mechanical performance requirements while improving implant-to-bone mechanical compatibility, motivating further fatigue characterisation, experimental validation, and multi-subject studies.

This study investigated regularisation methods in Direct FE2 failure analysis of fused-filament fabricated (FFF) parts modelled as fibre-reinforced composites. Direct FE2 technique offers simplicity with moderate computational cost by incorporating microstructural variations of FFF parts into macroscopic constitutive behaviour. However, similar to conventional FE2 methods, loss of positive-definiteness in tangent stiffness matrix occurs at structural level because of the material-level strain localisation and softening behaviour. Further numerical complexity is added when element deletion technique (EDT) is employed; an aspect which remains unexplored for Direct FE2. To address these issues, three regularisation methods (fracture energy, viscous, and combined schemes) were implemented in Direct FE2 analyses with EDT and their performance was evaluated in predicting the stiffness, strength, and deformation modes of poly(lactic) acid FFF parts with varying ductility. The results of Direct FE2 numerical analyses were compared to regular FE predictions and experimental tensile samples manufactured with different raster angles. It was found that unregularised Direct FE2 simulations suffered from convergence issues and the effectiveness of the regularisation method depended on material ductility, i.e., while some regularisation schemes could alleviate instabilities, others made an unrealistic prediction of failure mechanism. The combined regularisation approach was most effective in predicting ductile (0 degrees) and moderately-ductile (mixed-mode, 45 degrees) behaviour whereas fracture energy approach was best-suited for brittle failures (90 degrees). The viscous regularisation tended to initiate EDT prematurely while combined regularisation provided more realistic depiction of microstructural deterioration.

The intricate geometrical configuration of an auxetic structure enables high energy dissipation capacity at the expense of a highly nonlinear mechanical response. Under external stimuli, complicated deformation mechanisms emerge which dictate the extent of energy dissipation. Recently, the new ‘plastic hinge tracing’ method (Dhari et al., 2021) was introduced to detect such deformation mechanisms for elastoplastic porous materials. This approach is however subjective and cumbersome since it requires monitoring several plastic regions in consecutive deformed configurations. The present study innovatively extends this method by implementing machine learning (ML) techniques for objective detection of deformation modes in auxetics. To this end, a logistic regression ML model was developed to classify the deformation modes of a re-entrant honeycomb structure. The proposed procedure could successfully detect four out of the six deformation modes (‘X’, distorted ‘X’, ‘V’, and ‘V + Z + V’) using the training datasets generated by the finite element analysis and image labels created by K-means clustering algorithm. The success of the proposed automated approach lays the foundation for identifying the deformation mechanisms of other auxetics and porous materials with plastic deformations.

Fracture fixation and limb deformity correction in pediatric orthopedics often use temporary metallic fixation devices. These devices’ higher stiffness compared to cortical bone leads to stress shielding, causing significant bone density reduction, periprosthetic loosening, and bone growth interference. The 3D‐printed triply periodic minimal surface (TPMS) structures present a promising engineering solution to match bone stiffness while ensuring reliable implant strength. In this study, finite‐element modeling and experimental testing are employed to identify optimal multifunctional TPMS‐based lattices that meet the required design constraints of 1) stiffness in the range of cortical bone, 2) strength in the range of cortical bone, 3) minimum osteointegration to facilitate the implant removal after healing, and 4) manufacturability with limited defect sensitivity. Six different types of TPMS structures in Ti–6Al–4V material manufactured via laser powder bed fusion are evaluated for their ability to target the lower and upper bounds of pediatric cortical bone stiffness. Lattices based on the Primitive unit cell design are superior, demonstrating the highest strength/stiffness ratio, best manufacturability, and potentially reduced osteointegration due to larger pore size, smaller surface area, and smallest negative Gaussian curvature compared to other investigated TPMS types.

The rapid development of additive manufacturing (AM) technology and the consequential microstructural variations have brought the simulation aspects into focus. To capture an accurate mechanical response, multiscale methods are used to determine the macroscopic constitutive behaviour. Among these methods, the recently introduced Direct FE2 (DFE2) technique has shown some success in predicting material behaviour via the direct incorporation of representative microstructure volumes into the macroscopic structure. The present study highlights the predictive modelling capabilities of DFE2 linked with an element elimination technique (EET) in investigating the performance of fused filament fabrication (FFF) samples under tension and compression. Parts were manufactured by FFF with various raster angles to vary the failure characteristics. Their mechanical responses and fracture behaviours were simulated by DFE2 and benchmarked against conventional FE, highlighting that the results of DFE2 were competitive against FE. Most importantly, the combination of EET with DFE2 resulted in predictive insights regarding changes in the failure surface for samples with varying raster angles.

This study focuses on large deformation in-plane response of rotating square (RS) auxetics under quasi-static tension with an emphasis on their energy absorption (EA). First, metallic RS samples were fabricated and tested under uniaxial tension and the results were used to establish validated numerical models using ANSYS. Gurson–Tvergaard–Needleman (GTN) model was employed to evaluate the ductile damage and its capability to predict failure of the RS structure was investigated. Numerical analyses were then conducted to compare the large tensile responses of a regular RS (R-RS) and a bio-inspired RS (Bio-RS-0) introduced by Sorrentino et al. (2022). Subsequently, a parametric study evaluated the effect of the size of a circular perforation in the square region of the Bio-RS-0 on the stress distribution, force–deformation response, failure mechanism, and specific energy absorption (SEA) of the structures. Bio-RS-0 enhanced the SEA of R-RS by more than five times due to the increased engagement of the geometry in plastic deformation. Large perforations significantly influenced the response in larger strains and their failure mode. Two failure mechanisms were identified which could be adjusted by perforation size. An optimum perforation size and the corresponding failure mode were identified for maximum SEA. Potential applications for energy absorbing auxetics in tension were discussed at the end.

Determination of the early-age compressive strength of concrete is essential for quality assurance, safety, and economy of construction projects. Due to manual operation on construction site, conventional maturity meters are not efficient for live monitoring of the early-age concrete strength. Higher levels of automated and computerised improvements have been made possible by recent developments in wireless communications, sensor technologies, and data processing methods across the construction industry. For real-time monitoring of the early-stage concrete strength, the current study presents an innovative Internet of Things (IoT)-enabled system developed by concrete data sensors (CDS), an Australian-owned private business. The CDS sensor system (the system) communicates with temperature sensors via long-range wide-area network and is linked to a cloud-based platform for data storage. The suggested system's effectiveness was assessed using three concrete mixtures and developed maturity relationships. It was observed that the predicted early-age compressive strength of the mixes matches well with the actual compressive strength and that the system can effectively automate the characterisation of maturity.

This study challenges the Direct FE2 method to model voids in additively manufactured parts. Two sets of polylactic acid (PLA) tensile coupons—without any voids and with 23% voids—were manufactured using fused deposition modelling (FDM) and assessed under monotonic loading. An in-house Python script was developed to implement the modelling steps of Direct FE2 in ABAQUS commercial package. A homogenised medium was used in conventional finite element (FE) method whereas discrete modelling of voids was adopted in Direct FE2. Despite using the same isotropic elastoplastic material model with progressive damage, the response of Direct FE2 was noticeably softer. Although stress concentration around the voids were illustrated in Direct FE2, high error values demand further refinements in selecting the representative volume. The applications of this approach can be extended to modelling defects in other complex parts such as auxetic/sandwich structures and composites.

A Haar cascade classifier is a machine learning (ML) algorithm used for object detection. In this paper, the Haar algorithm is introduced in the context of a non-destructive evaluation of fibrereinforced composite (FRC) structures. The Haar learning model is used for flaw identification from thermal images. Thermal images are created from cross-ply (CP) carbon fibre-reinforced laminates with flat-bottomed holes (6–10 mm) of different depths from the surface (0.5–1.5 mm). After training is complete, the model successfully detects similar artificial flaws in previously unseen thermal images. In doing so, the feasibility of Haar classifiers for automatic evaluation of FRCs is established.

Auxetics are structures with negative Poisson's ratio which exhibit superior properties such as high energy absorption, shear resistance and fracture toughness.While auxetics are widespread in the aerospace and biomedical sectors, their civil engineering applications have been neglected.Herein, the energy absorption performance of rotating square auxetics was investigated in building applications.Three novel bio-inspired designs that have recently been proposed in the literature were studied for this purpose.It was found that the bio-pattern with a fine-tuned perforation size can significantly enhance the specific energy absorption of the auxetic structures by approximately 10 times.This behavior is a consequence of geometrical manipulation that alleviates stress concentration and develops larger highstress areas in the material.The results were also compared to a flat sheet representing a standard tensile member.The findings point to promising applications of the bio-inspired auxetics as energy dissipator elements in building applications.

The magnetic body force is critical for modelling of convection in ferrofluids. Despite a long history in the development of the theories for ferro-hydrodynamics, literature from the last five years shows that a universal consensus has not been reached concerning the formulation of this term for ferrofluids. We present an updated derivation of the body force directly from the Lorentz force and Maxwell's equations. The derivation requires that the differential volume experiencing the body force only contains complete dipole current loops. This has the effect that an additional surface integral term to account for bound surface current is not needed when modelling situations where the ferrofluid has interfaces with other materials. We compare results from our derived body force with five other formulations from the literature for the case of a single conductor in ferrofluid under static and convection conditions. Most formulations become similar in the limit of small magnetic susceptibility. For a susceptibility of the order of 1, as is typical for ferrofluids, the calculated body force from the formulations differed by a factor of about four, greatly affecting thermomagnetic convection predictions for a heated microwire.

This paper presents an analytical model to investigate the static behaviour of sandwich plates comprised of two isotropic face sheets and a honeycomb core. Through-thickness transverse shear stresses were considered using a unified displacement field with which various plate theories were implemented, i.e., exponential, third-order, hyperbolic, sinusoidal, fifth-order, Mindlin, and the classic plate theory. The equilibrium equations of a simply-supported sandwich panel were derived using the principle of virtual work and Navier solution was obtained under static transverse loading. After validating of the model, various mechanical and geometrical parameters were varied to characterise the behaviour of the structure under regular and auxetic response. It was found that the auxeticity of the core strongly affects the mechanical response, e.g., in controlling deflection, in-plane anisotropy, and Poisson’s ratio. Cell wall angle was found to be most critical parameter that can be used to adjust anisotropy, out-of-plane shear modulus, transverse shear stress distribution, and deflection of the panel. Also the cell aspect ratio controls the sensitivity of the core response to other geometrical variations. In terms of the higher-order theories, the deflection-dependent parameter of the unified formulation seems to have more control of maximum deflection compared to independent rotations. Auxeticity of the core showed some benefits in controlling anisotropy, deflection and providing additional out-of-plane shear rigidity. Overall, since there is not one-to-one relationship between specific values of Poisson’s ratio, anisotropy, and shear rigidity, careful design considerations must be invested to obtain a correct mechanical response.

In the composite industry, wet lay-up and vacuum bagging are widely used, low-cost manufacturing processes. This paper investigates the mechanical performance of wet layup and vacuum bagged carbon fibre-reinforced laminates compressed in a hydraulic press at different compaction pressures. The external compaction pressure is shown to significantly reduce void content, and increase the fibre volume fraction and mechanical performance of tested laminates. The tensile and flexural properties of tested specimens subjected to high levels of external compaction pressure are found to be comparable to those of out-of-autoclave (OOA) prepreg specimens. It is summised that the use of external compaction pressure over wet layup and vacuum bagged composites offers a low-cost (and low-energy) industrial processing route for manufacturing high-performance carbon fibre-reinforced components.

Herein, the effect of anisotropy on the thermal response of two carbon fibre-reinforced composite samples (unidirectional and cross-ply) is studied using step-heating thermography. An objective methodology is developed for qualitative and quantitative analyses of flaws using their aspect ratios and signal-to-noise ratio (SNR). The procedure uses principal component analysis, Gaussian filter, and binarisation for marking the candidate flaw locations. After experimenting on different heating/cooling regimes, single-phase cooling was nominated to further the study. It is found that short thermal excitations reveal surface flaws while increasing the heating period improves the visibility of deeper flaws. Anisotropy, due to fibre alignment, affects the aspect ratio of flaws, distorts their shape, and conjoins clustered flaws. In contrast, SNR values seem to be insensitive to anisotropy. The proposed method offers a quick and simple procedure for post-processing thermal images and highlights the implications of anisotropy therein.

Vacuum bagging and prepreg moulding methods are introduced in this chapter. These advanced moulding techniques address some of the shortcomings of wet layup (hand lamination) but require additional equipment and consumables, as well as higher fabricator skill levels. The requisite equipment and consumables are described in detail. A step-by-step guide to vacuum bagging is offered and the storage and handling requirements of prepregs are considered. The advantages and limitations of these advanced methods are presented alongside their typical fibre volume (and weight) fractions. Finally, fibre volume fractions for wet layup are compared to the higher fractions typically obtained by vacuum bagging and prepreg moulding.

The present study unravels the deformation mechanisms observed during the static inclined compression of re-entrant honeycomb (RH) auxetic structure. A pushover Riks analysis is conducted by facing a rigid plate towards the structure at various angles. A new ‘plastic hinge tracing method’ is introduced to systematically extract the micro deformation mechanisms under inclined loading. The identified modes are related to the macro deformation regime and the overall mechanical response of the RH structure. Moreover, their relation to various measures of efficiency is elaborated. It is shown that a transition stage emerges under inclined loading, which delays achieving the peak energy efficiency. The overall energy dissipation decreases in the inclined cases but interestingly, the performance of the RH structure does not deteriorate. Namely by maintaining a low crushing force under inclined loads, the trade-off of low energy dissipation is balanced and a lower impact is anticipated. Finally, the similarities between the transition stage and the macro modes are highlighted and further directions for investigation are proposed.

This chapter addresses the mechanical properties of a fibre-reinforced composite (FRC). The focus is on calculation of the elastic modulus and strength for unidirectional FRCs using the rule of mixtures expressions, but woven and random fibres are also considered. A unidirectional FRC exhibits anisotropic behaviour. It is stiffest and strongest in the fibre direction but is relatively compliant and weak in the transverse orientation. Woven structures provide similar mechanical properties in their axial (longitudinal) and transverse orientations, whilst random fibre composites simulate in-plane isotropic behaviour. The effect of the fibre and matrix properties on the structural behaviour of a composite is investigated in the context of fibre volume fractions (and weight fractions), assuming no voids and perfect fibre-matrix adhesion.

As an effective lateral resisting system, a steel plate shear wall (SPSW) should provide adequate ductility and dissipate energy while protecting its boundary elements (BEs). Herein, the failure modes of a recently-introduced design for SPSWs (a perforated panel with a web-reduced beam section) was investigated. The aim was to control the failure mechanism of this arrangement by various geometrical modifications. To obtain a high-performing design, the interaction of the structural components was studied in terms of plastic strain distribution, ductility, strength, and stiffness. To this end, a finite element prototype was populated for a range of geometrical parameters. The analyses were carried out by varying the panel and beam perforation sizes; then, one excelling combination was further challenged by altering its panel thickness and the frame aspect ratio. The model successfully distinguished between three common failure modes and provided an interesting insight into the causality of the failure mechanisms. It was found that the size of the perforations in the panel and the beam, and the size of the horizontal boundary elements could be manipulated to obtain the desired mechanism. Therein, the tensile failure of the panel was dominant where a plastic band formed across the panel and protected the vertical BEs and their connections. Moreover, the model outperformed its imperforate counterpart in terms of hysteresis ductility and absorbed energy (by about 250%) due to the increased engagement of the structural members. Finally, the findings were summarised into some practical recommendations for improving the design of the proposed arrangement.

This chapter considers the manufacture of hollow sections. Mandrel lamination (wrapping) and bladder moulding are described and then used to create composite tubes. A step-by-step guide to tube manufacture is presented for prepreg moulding, but the fabrication methods introduced are more widely applicable (and hence, can be adapted for use in wet layup processes). Whilst the focus is on cylindrical tubes, the fabrication process can be simply modified to create square or rectangular hollow sections or more complex tubular structures. A helical spring and a bicycle handlebar are used as more complex examples. Demoulding methods for mandrel wrapped tubes are discussed. A specific focus is given to mechanical extraction and thermal (heating and cooling) mechanisms. The concept of mouldless composite construction is introduced. The importance of a mandrel’s coefficient of thermal expansion is considered in the context of demoulding using thermal methods.