Invited Speakers

Abstract: The unique feature to respond to small changes in its environment has made the stimuli-responsive polymers very promising in the generation of smart-materials for medical and engineering applications. Very appealing seems to be their combination with plasmonic nanoparticles to yield nanocomposites which combine and/or modify the intriguing properties of the individual components, or exhibit novel properties. Within this presentation, we will highlight some of our recent progress in their successful integration through a series of strategies based on the intervention of methacrylic monomers with a hidden thiol group, to accomplish highly desirable features of hydrodynamic size compression, amphiphilic, pH-/thermo-responsiveness, and enhanced optical properties for biological and technological applications of our functional nanocomposites. Actually, our polymer-stabilized NPs in organic and aqueous solvents offer a great chemical playground for directed self-assembly, by simply changing composition of the solvent, hydrophobicity of monomers; which expands their potential applications. A modulation of the optical and swelling properties of the materials will be exposed. Additionally, development of smart substrates for antibacterial uses, via innovative in situ reactive and reduction pathway, will be considered.

Keywords: Plasmonic nanomaterials, smart nanocomposites, nanogels, eccentric/Janus morphologies, optical-swelling properties, surface coatings

Acknowledgements: The grant "TED2021-129959B-C22" from MCIN/AEI/10.13039/501100011033 and the European Union “NextGeneration EU”/PRTR», and PID2022-1377QNB-I00 of Spain.

Abstract: The temperature influence and carbon black reinforcement effect on the mechanical behavior of uncured rubber were investigated through cyclic tensile tests at different strain rates. Experimentally, the stress-strain responses under different loading scenarios were achieved. These results indicate the distinct deformation characteristics of uncured rubber (initial modulus, stress level at a certain stretch, hysteresis and Mullins effect) are significantly dependent on carbon black content and temperature. An interpretation of the underlying physical mechanism of uncured carbon black filled rubber is proposed, which is similar to that of vulcanized rubber. Based on this interpretation, a microscopic thermo-mechanical constitutive model is developed to characterize the complex nonlinear mechanics of uncured rubber material. The prediction ability of this new model was evaluated by comparison with data issued from different cases of carbon black contents and strain rates. This work would be beneficial for gaining a more comprehensive understanding on the service property or manufacturing performance of various rubber products.

Abstract: Dielectrics elastomers (DEs), one category of soft electroactive polymers, are characterized with softness, high energy density, rapid response, lightweight, and particularly large deformation capability under electrical stimuli. With such distinguished properties, DEs have extensive applications as soft robots, artificial muscles, stretchable electronics, actuators, oscillators and energy harvesters. When DEs in these applications are designed to undergo cyclic loading for a long period of time, a critical issue is to ensure their mechanical durability by predicting the fatigue life. However, the evaluation of the fatigue life of soft dielectrics is very challenging due to the modelling complexity when electromechanical coupling, finite deformation and material viscoelasticity are involved. Therefore, this work aims to develop a novel fatigue predictor to assess the fatigue life of soft DEs under various loading conditions to reveal the fatigue mechanisms. Stemming from the crack nucleation approach, a configurational stress tensor for DEs with the consideration of both electromechanical coupling and material viscoelasticity is formulated as the basis to define a fatigue predictor. As all energetic properties of defect evolution in the material are included in the configurational stress tensor, the developed fatigue predictor is capable of capturing all the factors that govern the fatigue damage of DEs which have been demonstrated by the simulation results. It is concluded that the electrical part and the viscous part of the configurational stress do not lead to fatigue damage of DEs, while the strain-softening behavior of elastomers exerts a significant effect on the fatigue life of DEs. This modeling work is anticipated to help better understand the fatigue mechanisms of DEs and can be extended as a general platform for the fatigue analysis of other materials subjected to coupled field. As the predictor is capable of adopting most of the strain energy density functions for rubber-like materials and the thermodynamics evolution laws for viscoelastic solids, it is feasible to implement this modeling framework in finite element analysis for DEs with more complicated deformation.

Keywords: Dielectric elastomers, fatigue, configurational stress tensor, electromechanical coupling.

Acknowledgements: This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC).

Abstract: High-throughput experimental technology has drastically transformed the landscape of material development by substantially reducing both the development time and associated costs. This is particularly evident in development of new materials for aeroengines. Creep behaviour is one of the key mechanical properties for performance of aeroengines, especially the blades. Tensile creep testing was the traditional method to evaluate creep behaviour, but this is both time-consuming and expensive. This study introduces a novel approach of a high throughput compression creep test, which facilitates simultaneous testing of eight samples, thus significantly reduces the time and cost compared to traditional methods. This novel testing method has been successfully employed for rapidly screening creep properties during development of new materials and offers the capability to screen roles of chemical composition for engineering materials. In addition, this study has also successfully utilized the compression creep data to establish a quantitative correlation with tensile creep data, leading to accurate predictions of stress rupture life very quickly. Thus, the high throughput compression creep technique represents a significant advance in the field, offering a novel technique for the rapid evaluation of high-temperature performance of superalloys.

Abstract: While laser powder bed fusion (LPBF) has revolutionized the processing technologies of metal components, the persistent challenge of porosity defects, including cracks, lack-of-fusion, and gas pores, continues to impose critical limitations on the structural integrity and mechanical performance of printed alloys. Here, we propose a novel liquid-induced healing (LIH) post-process that employs an intergranular liquid via localized partial remelting at grain boundaries, enabling capillary-driven defect backfilling while establishing interconnected channels for gas evacuation. Employing LPBF-fabricated IN738LC and IN718 superalloys as model systems, we comprehensively evaluate the LIH process’s effectiveness in defect elimination and its influence on key mechanical properties, including tensile strength, fatigue resistance, and creep performance. Our findings demonstrate that the LIH treatment achieves near-complete porosity eradication and significantly enhances mechanical properties through a cost-effective methodology, thereby alleviating current limitations in metal additive manufacturing for engineering applications.

Abstract: Various types of wear mechanisms (three-body wear, delamination, pitting, abrasion, etc.) can occur between the polymer-metal interface of total knee arthroplasties. In most cases, the mechanism of these types of wear has only been experimentally verified or approximately described. It must be noted that analytical description is not yet available for the majority of wear types. An exception to these mechanisms is abrasive wear, for which a number of analytical studies have been developed. This type of wear can be approximated mathematically by the so-called Archard equation. It should be noted that, due to the complex motion of the knee joint, the original Archard equation must be extended by several parameters in order to adequately describe the wear process. Such parameters are the cross shear ratio, the coefficient of friction or the sliding rolling ratio. The present study gives a broad overview of the analytical wear models, currently available from the relevant literature, and also provides further suggestions on how to bring these models closer to reality.

Keywords: Analytical models, wear, cross-shear ratio, slide-roll ratio, coefficient of friction.

Acknowledgements: The author would like to thank the Department of Materials Science and Technology, AUDI Hungaria Faculty of Automotive Engineering, Széchenyi István University and the Bolyai János Research Grant (BO/00047/21/6) of the Hungarian Academy of Sciences.

Abstract: To address the challenges in the forming of traditional fiber-reinforced composites (such as difficult processing and limited design freedom) and meet the urgent demands in aerospace, automotive, and rail transportation (including lightweight structures, complex geometries, and integrated molding), additive manufacturing of continuous fiber-reinforced composites has become a research hotspot in advanced manufacturing worldwide. This report focuses on the fused deposition additive manufacturing technology for continuous fiber-reinforced polymer matrix composites, discussing the current technological limitations of additive manufacturing processes and corresponding improvement strategies. The presenter introduces a series of advanced manufacturing techniques, including the preparation of printing filaments, the development of a rotating print head, and fiber optimization strategies. A complete mechanical characterization and damage failure simulation were conducted for composites with localized anisotropy. By increasing fiber content, reducing manufacturing defects, and optimizing fiber orientation, this study leverages the design flexibility of additive manufacturing to achieve the rapid fabrication of ultra-lightweight carbon fiber composites. Furthermore, the proposed finite element simulation method for in-plane localized anisotropy serves as an effective tool for the design and analysis of continuous fiber composites. Considering the current state of research both domestically and internationally, this report also explores the future development trends of continuous fiber-reinforced composites in advanced additive manufacturing, including multi-material integration, large-scale production, and intelligent digitalization.

Abstract: Accurate impact force identification is crucial for ensuring the structural integrity and safety of engineering systems, yet the inverse problem remains a formidable challenge due to its ill-posed nature. Traditional regularization techniques, such as Tikhonov regularization and singular value decomposition, have long been employed to stabilize solutions and mitigate uncertainties. However, recent advancements in machine learning, particularly hybrid neural network frameworks, are revolutionizing the field by offering robust and data-driven alternatives.

This talk will provide a comprehensive journey through impact force identification methodologies, from classical inverse problem-solving approaches to state-of-the-art hybrid deep learning techniques. We will explore how dynamic response data from piezoelectric sensors can be leveraged to reconstruct unknown impact forces and discuss the transition from deterministic mathematical frameworks to data-driven neural architectures. Case studies involving composite structures, including carbon-fiber epoxy honeycomb panels, will illustrate the efficacy of these approaches.

By bridging the gap between physics-based modeling and artificial intelligence, this talk will highlight the advantages, challenges, and prospects of hybrid methodologies in structural health monitoring. Insights will be gained into how these techniques enhance precision, reduce computational costs, and open new frontiers for real-time impact force reconstruction in complex engineering systems.

Abstract: The growing demand for lightweight multifunctional composites with integrated structural and sensory capabilities has driven innovations in advanced protective materials. This work pioneers the development of polyborosiloxane (PBS) and PBS-enhanced carbon fiber composites, systematically investigating their impact resistance and real-time force-sensing functionality. Two distinct PBS formulations with tailored crosslinking densities were synthesized, followed by comprehensive characterization of their strain-rate-dependent viscoelastic behavior and impact energy dissipation mechanisms. Crucially, our findings reveal that under dynamic high-strain-rate compression, PBS transitions sequentially through three distinct phases: (1) initial viscoelastic deformation, (2) shear-induced yielding plateau, and (3) strain-hardening densification. Compared to traditional epoxy/carbon laminates, PBS/Carbon composites exhibited superior impact energy absorption, withstanding up to seven repeated impacts due to the brittle cracking of PBS and its stiffening transition and the self-healing function. Moreover, the addition of carbon nanotubes to the PBS matrix enabled the development of a force-sensing composite, which could detect and measure impact forces. The PBS/Carbon laminates also exhibited enhanced flexibility, making them suitable for advanced protective applications requiring repeated impact resistance and real-time force monitoring.

Abstract: Plant fibers, derived from nature, grow organically and are biodegradable. Plant fibers possess distinct specific mechanical properties comparable to those of synthetic fibers and exhibit superior damping and sound-absorbing and noise-reduction performances. Plant fibers hold promise as a green alternative to the advanced fiber reinforcement currently in widespread use. The applicant has addressed the challenges and difficulties associated with the application of plant fibers as natural materials in continuous fiber reinforced composite structures. A series of innovative results are achieved: 1) The identification of a novel‘hierarchical interface’ damage and fracture mechanism in plant fiber reinforced composites confers exceptional sound absorption and damping properties. It has led to the formulation of the ‘hierarchical interface’ theory for composite materials and the creation of an innovative design methodology for regulating the performance of the ‘hierarchical interface’. 2) The elucidation of a new mechanism underlying the formation of process-induced defects in plant fiber reinforced composites, coupled with the proposal of a precise optimization method for low-defect molding process parameters, has successfully addressed the challenge of achieving high-quality manufacturing.

Abstract: During the fabrication of aerospace composite structures with complex geometries, hybrid manufacturing defects such as fiber wrinkles, resin-rich areas, and voids inevitably occur at regions of abrupt feature transitions. These defects lead to significant variations in the internal microstructure of composite materials, posing potential risks of structural failure. Therefore, the development of reliable nondestructive testing (NDT) techniques is crucial for accurately assessing hybrid manufacturing defects in composites. To address the challenges of defect characterization and the lack of detection benchmarks, an ultrasonic wave propagation analysis model is established for composite structures containing fiber wrinkles and void defects. The study quantitatively correlates porosity/delamination with the frequency dependence of ultrasonic reflections and links fiber wrinkles with the non-reciprocal ultrasonic transmission time-of-flight. This enables reliable decoupling of hybrid defect detection features. Additionally, a multi-frequency ultrasonic imaging method for hybrid defect identification without the need for benchmark comparisons and a wrinkle imaging technique for composite structures without requiring wave velocity input are proposed.

Abstract: At present, the theoretical model of composite material forming process has limitations, and the mechanism of complex multi-scale defect generation is not yet clear, and the research on the mechanical properties of composite materials with defects is not yet systematic, and urgent need to broaden the research on biomimetic structure design of composite materials. She researches in the areas of fiber-reinforced composite material forming, damage, structural design, and provides theoretical models, simulation methods, and experimental means for the application of composite materials in advanced aerospace equipment.

Abstract: Structural lightweight design is a critical technical indicator in the aerospace and new energy power equipment industries. The adoption of new materials, innovative structural configurations, and advanced manufacturing processes serves as the primary approach to achieving structural lightweighting. Fiber-reinforced composites, with their exceptional material properties and designable microstructures, have become an ideal material and structural form for lightweighting and functionalization in these fields. In particular, the rapid development of continuous fiber additive manufacturing technology in recent years has enabled the practical realization of multi-scale optimization designs for fiber-reinforced composites. Building on the rapid progress in structural and multidisciplinary optimization theories and methods, significant advancements have been made in composite optimization and engineering applications. However, the multi-scale optimization design of continuous fiber-reinforced composites, which holds greater potential for lightweighting and functionalization, still faces numerous challenges, especially when considering the integrated "material-structure-manufacturing" design. These challenges include the "curse of dimensionality" in discrete design variables, "reduction of design space," "uncertainty in feasible domains," "dependence on initial trajectory assumptions," and "difficulties in the concurrent characterization of structural topology and fiber trajectories." This report systematically presents recent research progress by our team in the field of multi-scale optimization design for fiber-reinforced composites, including multi-scale variable stiffness optimization design for discrete fiber composites, multi-material multi-scale variable stiffness optimization design for fiber-reinforced composites, stress-constrained multi-scale topology optimization design for composites, and multi-scale optimization design incorporating multi-point shape-preserving constraints. These contributions aim to provide innovative methodologies for the lightweight design of advanced composite structures in aerospace applications.

Abstract: Rare-earth barium copper oxide (REBCO) coated conductor (CC) tapes demonstrate significant promise for high-energy and high-field applications. In impregnated REBCO superconducting windings, the weak c-axis strength of REBCO CC tapes renders delamination - induced by thermal mismatch stress and Lorentz forces - a critical threat to operational stability. While impregnated REBCO superconducting magnets comprise multi-layer components with distinct material properties, their constituent materials exhibit markedly different stress states under combined cryogenic temperatures and intense electromagnetic fields. Current numerical modelling approaches primarily employ two methodologies: homogenized models and refined models. Whereas homogenized models enable efficient computation of global physical fields at the expense of local interfacial delamination details, refined models achieve high-resolution analysis while demanding substantial computational resources. To address this efficiency-accuracy dilemma, this study develops a two-dimensional axisymmetric concurrent multiscale model incorporating bilinear cohesive zone model (CZM) for investigating the mechanical properties and interfacial failure behaviours of REBCO superconducting coils under cryogenic electromagnetic conditions. The proposed framework follows a three-stage implementation: First, macro-scale electromagnetic-thermal-mechanical properties are estimated through composite homogenization theory to establish the homogenized superconducting coil model. Subsequently, potential failure zones are identified at the macro-scale using quadratic failure criteria and replaced with CZM-defined refined submodels capturing delamination mechanisms. Finally, multiscale coupling is achieved through interface connectivity. Validation through comparative analysis with fully refined models confirms the computational efficiency of concurrent multiscale model while maintaining accuracy in simulating delamination behaviours during both cooling and electromagnetic excitation processes.

Abstract: A bistable composite tape-spring (CTS) structure is stable in both extended and coiled configurations, which can be fully coiled or folded following the positive Gaussian curvature deformation mechanics. Both the structural coiling and folding mechanics are dependent on tape geometries. This presentation will deliver our continuous research on deployable mechanics of the bistable CTS structure, covering mainly on the following: (i) a typical CTS folding process consists of linear bending, torsional buckling, localisation and then folding at large displacements, the folded tape shape is dominated by axial shear strains and transverse curvature changes; (ii) the deployable mechanics of a CTS is dependent on its internal stress level, which can be tailored by applying fibre prestressing, where the prestressed fibres generate compressive stresses to alter the internal stress, and thus controlling the structural bistability and deployable mechanics, as well as improving its load-carrying capabilities; (iii) smart driving of a CTS can be achieved under thermal energy, as well as magnetic field, there is a minimum energy constraint to initiate the shape morphing process, and the critical shape driving boundaries are dependent on scale effects; (iv) the bistable principle of the CTS can be extended to produce bistable torsional structures, as well as multistable hinge structures with tailorable stabilities. These are expected to further enrich the diversities of functional structures to benefit novel requirements for various deployable applications, and enable customised design, as well as smart driving for flexible and multifunctional space explorations.

Keywords: Bistable, composite, tape-spring, smart driving, morphing mechanics.

Acknowledgements: The authors are grateful for financial support from the National Natural Science Foundation of China (52475152, 52005108), as well as the start-up Funding from Education Department of Fujian Province and Fuzhou University (XRC-20066). We also thank the technical staff and aegis of the Fuzhou University International Joint Laboratory of Precision Instruments and Intelligent Measurement & Control.

Abstract: Impact damage mechanisms of natural plant fiber reinforced composites are essential for their structural design and practical applications. This study reports quasi-static and dynamic compressive behaviors of three-dimensional braided ramie fiber reinforced composites (3DRFRC) and the comparison with carbon fiber reinforced composites (3DCFRC). The results show that the 3DRFRC has a long yield stage under the quasi-static compression owing to ramie fiber bend. The 3DRFRC exhibits higher in-plane dynamic compressive properties than those of the 3DCFRC, and the energy absorption rate (EAR) of the former is 27% more than that of the latter at 30J impact energy. EAR of the four-directional in the 3DRFRC exceeds 90% under dynamic compression and is higher than that of the five-directional owing to more accessible deformations. The FEA results show that the resin damage in yarn was the leading cause of yarn damage under dynamic compression. The ramie fiber bend and lumen collapse are micro-scale damage mechanisms of the 3DRFRC under in-plane and out-of-plane dynamic compression, respectively.

Keywords: 3-Dimensional reinforcement, impact behavior, finite element analysis (FEA), damage mechanics, braiding.