Search Results (70)

The transition towards sustainable cities requires material selection strategies capable of balancing environmental, economic and social performance while accounting for the emerging functionalities offered by smart materials. This work proposes a sustainability-driven methodology based on normalized multi-dimensional indicators for the objective comparison of functionally equivalent conventional and smart materials in the built environment and demonstrates its application through the parametric design of an urban bench. The quantitative assessment showed substantial differences among the investigated materials: Shape Memory Polymers (SMPs) resulted in a panel mass of 5 kg, CO₂ emissions of 2.4 kg CO₂/kg, and embodied energy of 37 MJ/kg, compared with 32 kg, 13 kg CO₂/kg, and 260 MJ/kg for NiTi, and 40 kg, 15 kg CO₂/kg, and 320 MJ/kg for magnetic Shape Memory Alloys, respectively. Finite element analysis further demonstrated the influence of structural design, with the maximum principal stress decreasing from approximately 0.073 MPa at a panel thickness of 10 mm to 0.015 MPa at 50 mm, corresponding to a reduction of approximately 79%. The results demonstrate that smart materials do not inherently represent more sustainable alternatives than conventional materials; rather, their adoption should be justified when their adaptive functionalities provide measurable benefits capable of compensating for their environmental and economic burdens. The proposed framework provides a practical decision-support tool that shifts material selection from property-driven choices toward function-oriented, sustainability-based design, supporting more informed decisions for next-generation urban infrastructure. Full article

This study presents an analytical model for the long-term bending behavior of simply supported laminated glass (LG) plates with temperature-dependent viscoelastic interlayers. The glass layers are described based on three-dimensional elasticity theory, and the governing stress and displacement equations are formulated using the state-space method. The polymer interlayer is characterized by the generalized Maxwell model and the Williams–Landel–Ferry equation, while its time-dependent response is described through the Boltzmann convolution principle. By combining double Fourier series expansions with the Laplace-transform technique, analytical solutions for the stresses and displacements of multilayer LG plates are derived. The comparison shows that Kirchhoff–Love plate theory gives results close to the present solution for relatively thin LG plates, whereas the discrepancy becomes increasingly pronounced as the plate thickness increases. The finite element results agree well with those obtained from the proposed model; however, for the representative benchmark case, the present solution is approximately 1.13 × 10³ times faster than the FE simulation, and its memory usage is only about 10.88% of that required by the FE model. Parametric studies further reveal the effects of temperature, interlayer thickness, interlayer material, number of glass layers, and aspect ratio on the stress redistribution and deflection development of LG plates. Full article

Glass-transition-driven shape memory polymers are promising materials for 4D printing because their thermally activated transition enables programmed deformation and recovery without relying on melting or crystallization-driven switching. In this study, PDMS-MMA-modified photocurable networks were designed for vat photopolymerization-based 4D printing by varying PDMS-MMA content and switching monomer structure while maintaining a fixed TMPTMA crosslinker content. The resin formulations were prepared using tert-butyl acrylate (tBA) or isobornyl acrylate (IBOA) as switching monomers, PDMS-MMA as a flexible mobility-regulating segment, and TMPTMA as a multifunctional crosslinker. The effects of formulation composition on printability, network formation, thermal stability, thermomechanical transition, mechanical properties, and shape memory behavior were systematically investigated. FT-IR analysis confirmed effective photocuring of the acrylate/methacrylate networks, while rheological evaluation showed that resin viscosity depended on monomer structure and PDMS-MMA content. DMA results revealed thermomechanical transition, although some formulations exhibited broad tan δ responses due to network heterogeneity and distributed segmental relaxation. Based on resin printability, printed-part resolution, and relatively well-defined tan δ transitions, T-15 and I-15 were selected as representative formulations for quantitative shape memory evaluation. Shape memory testing was conducted under force-control mode because stable strain-controlled programming was not achievable for the printed specimens. Both T-15 and I-15 exhibited high shape fixity over two programming–recovery cycles. I-15 showed stable recovery behavior with recovery ratios of 91.51% and 95.87%, whereas T-15 showed apparent over-recovery with recovery ratios exceeding 100%, likely due to residual stress release during reheating. Overall, these results demonstrate that thermally activated shape-memory performance is governed not only by the nominal transition temperature but also by the coupled effects of PDMS-mediated segmental mobility, switching monomer structure, mechanical integrity, and elastic energy storage within a fixed crosslinked network framework. Full article

Thermally responsive shape memory polymer materials are the most widely used type of intelligent materials and have found applications in numerous fields. However, their practical utility is often limited by poor heat conduction. Carbon nanotubes (CNTs), renowned for their exceptional thermo-conductive and photothermal properties, provide a promising solution. In this study, CNTs were integrated into polyurethane prepared by stepwise polymerization method, using hydroxyl terminated polycaprolactone (PCL-diOH), poly(ethylene glycol) (PEG) and hexamethylene diisocyanate (HDI). The resulting polyurethane composite material exhibits remarkable mechanical strength, enhanced thermal conductivity, and superior shape memory performance. Notably, it demonstrates a form of training enhancement phenomenon, which shows higher mechanical properties. And the composite could achieve stress-free two-way shape memory behavior after cyclic stretching process. Additionally, this composite material can exhibit “vitrimer” material properties at higher temperatures (110 °C), allowing for shape reprogramming. The carbon nanotube-reinforced composite material can achieve remote and precise manipulation under light stimulation. By combining the composite material with a metal thermally conductive layer, a multi-layer structure with shape memory properties can be prepared, which can achieve two-way shape memory behavior under electrical and light stimulation, further expanding the application potential of the composite material in the real world. Full article

Shape-memory polymers (SMPs) are gaining significant attention for their ability to recover predefined shapes via external stimuli. Among thermally activated systems, biodegradable blends of polylactic acid (PLA) and polycaprolactone (PCL) are particularly promising for biomedical devices and soft actuators. This study develops a thermo-mechanical theoretical model to investigate the shape-memory behavior of a PLA/PCL composite blend under controlled thermal cycling. The framework integrates transient heat transfer, temperature-dependent elasticity, and viscoelastic dynamics to predict temperature evolution, deformation, and internal stress. The thermal response is computed via Newton’s law of convection, while the mechanical transition is described by a sigmoidal temperature- and crystallinity-dependent Young’s modulus. Beam bending theory is employed to evaluate the spatial distribution of strain and stress. A parametric sensitivity analysis was performed to evaluate the influence of different parameters, including the crystallinity grade, convective heat transfer coefficient, glass transition temperature, and viscoelastic recovery constant. The theoretical study accurately reproduces the shape-memory cycle, quantifying performance through fixation and recovery ratios. This model provides a robust tool for the rational design and optimization of biodegradable smart polymer structures. Full article

Shape memory polymers (SMPs) can undergo reversible shape transformations, yet most conventional one-way SMPs recover only a single programmed shape. Reported bidirectional SMPs frequently rely on complex chemistries or continuous external loads or tolerate pronounced losses in mechanical robustness, largely because microphase separation, crystallization and internal stress are difficult to regulate in an integrated fashion. Here, we propose a UV-programmed internal-stress-locking strategy to construct a crosslinked polyurethane (UV-SMPU) that simultaneously achieves high toughness and stable, stress-free bidirectional actuation. Using polycaprolactone (PCL) as the soft segment, hexamethylene diisocyanate (HDI) as the hard segment and triallyl isocyanurate (TAIC) as a photocrosslinker, in-situ UV curing under pre-stretch fixes a tunable three-dimensional network while “freezing” the microphase-separated morphology and pre-oriented internal stress. Covalent crosslinks stabilize PCL crystallites as reversible actuation domains, whereas hydrogen-bonded hard segments provide elastic restoring force; the coordinated regulation of crosslink density, crystallinity and locked-in internal stress enables efficient CIE/MIC-type transitions without compromising mechanical integrity. The optimized UV-SMPU (3 wt% TAIC, 10 min UV) exhibits excellent thermal stability, a rare strength–ductility balance (26.6 MPa tensile strength; ~1700% elongation) and robust bidirectional actuation, with reversible strain stabilizing at 15.73% after six cycles. This work offers a simple, scalable route to tough bidirectional SMPUs and furnishes mechanistic design principles for next-generation adaptive and soft-actuated materials. Full article

While carbon fiber-reinforced polymer (CFRP) composites are widely utilized in aerospace applications due to their exceptional specific strength and stiffness, they are inevitably subjected to impact loads during service, which can easily induce internal damage such as delamination. To mitigate these issues, this study investigates the low-velocity impact behavior of an SMA-reinforced CFRP U-shaped structure, emphasizing the critical role of curing-induced residual stresses. A numerical model incorporating the thermal-mechanical manufacturing history was developed and validated against experimental data. Results indicate that while embedded superelastic SMA wires effectively suppress crack propagation and enhance energy absorption, neglecting residual stresses leads to a significant overestimation of structural rigidity and peak loads. Due to the coefficient of thermal expansion mismatch between the SMA wires and the resin matrix, the SMA-CFRP system exhibits higher sensitivity to initial internal stresses than pure CFRP. By accounting for the residual stress field, the relative error in predicted peak force and absorbed energy for the SMA-CFRP model was reduced from 9.3% to 3.5% and 18.9% to 7.8%, respectively. These findings demonstrate that residual stress lowers the failure threshold and is essential for capturing the synergistic effects of SMA phase transformation and matrix damage, providing a more accurate reconstruction of the structural energy balance. Full article

Carbon Fiber Reinforced Polymer (CFRP)-strengthened steel plate systems demonstrate remarkable advantages in civil engineering structural rehabilitation, with their overall performance critically reliant on the interfacial bond behavior between CFRP and steel plates. This paper systematically reviews the typical failure modes, key factors influencing interfacial bond performance, and corresponding testing methodologies. Research indicates that interfacial shear stress dominates the failure process. Enhanced strengthening efficacy can be achieved by employing CFRP plates with optimized adhesive layer thickness (recommended 0.5–1.5 mm) and double-sided bonding configurations. Concurrently, substrate surface treatment and environmental factors (temperature–humidity, corrosion, etc.) significantly affect interfacial bond performance. Current research primarily focuses on the single-factor and strength failure performance of standard specimens, lacking a systematic understanding of the long-term durability and failure mechanisms of complex structures under multi-field coupling effects. This review further summarizes the distinctive features and application scenarios of innovative strengthening systems—including prestressed, unbonded, and shape memory alloy composite systems—to provide guidance for engineering selection and standardized design. Full article

A refined mathematical framework is developed to investigate the ability of shape memory alloy (SMA) nanofibers to control the shear instability of a hybrid small-scale plate made of three layers containing nanofibers. The middle layer is reinforced by SMA nanofibers, while typical nanofibers are utilized to reinforce other layers. Using the Brinson theory, the nonlocal theory and the principle of virtual work, the scale-dependent coupled equations of the reinforced ultrasmall plate are presented. A differential quadrature technique is then applied as a solution procedure for different edge conditions. The influences of various factors, including the coefficients of the polymer matrix, the recovery stress, orientation and volume fraction of SMA nanofibers on the control ability are studied. It is concluded that the shear instability capacity of small-scale plates can be reasonably controlled by using SMA nanofibers. Particularly, higher recovery stresses result in higher critical shear loads. As the SMA volume fraction increases, the shear instability load remarkably increases. Full article

This study explores the development of 4D-printed smart structures based on PLA/PETG (75/25) polymer blends reinforced with nanocellulose (0–3 wt%), processed using fused filament fabrication (FFF). Both conventional U-shaped specimens and anti-tri-chiral auxetic architectures were fabricated to evaluate the effects of nanocellulose on mechanical performance and shape memory behavior. Tensile tests demonstrated that nanocellulose reinforcement enhanced both strength and stiffness, with the highest values observed at 2 wt% (tensile strength of 56 MPa and Young’s modulus of 3.3 GPa). In standard U-shaped samples, all compositions showed excellent shape fixity and recovery (100%). For auxetic structures, shape memory behavior and deformation response varied with nanocellulose content. Notably, 2 wt% nanocellulose yielded the highest shape recovery ratio (90.8%) and fixity (99.8%), indicating improved elasticity and structural responsiveness. Meanwhile, 1 wt% nanocellulose resulted in the highest energy absorption and more controlled deformation under compression, suggesting enhanced energy dissipation and stress distribution. A slight decrease in performance at 3 wt% is attributed to nanocellulose agglomeration and reduced polymer chain mobility. These findings highlight nanocellulose as a multifunctional additive that enables fine-tuning of mechanical and functional properties in 4D-printed structures. Depending on the intended application whether focused on energy absorption, mechanical strength, or shape recovery nanocellulose content can be strategically adjusted. This approach opens pathways for designing responsive materials suited for biomedical engineering, adaptive devices, and advanced environmental technologies. Full article

High-Bandwidth Memory (HBM) enables the bandwidth required by modern AI and high-performance computing, yet its three dimensional stack traps heat and amplifies thermo mechanical stress. We first review how conventional solutions such as heat spreaders, microchannels, high density Through-Silicon Vias (TSVs), and Mass Reflow Molded Underfill (MR MUF) underfills lower but do not eliminate the internal thermal resistance that rises sharply beyond 12layer stacks. We then synthesize recent hybrid bonding studies, showing that an optimized Cu pad density, interface characteristic, and mechanical treatments can cut junction-to-junction thermal resistance by between 22.8% and 47%, raise vertical thermal conductivity by up to three times, and shrink the stack height by more than 15%. A meta-analysis identifies design thresholds such as at least 20% Cu coverage that balances heat flow, interfacial stress, and reliability. The review next traces the chain from Coefficient of Thermal Expansion (CTE) mismatch to Cu protrusion, delamination, and warpage and classifies mitigation strategies into (i) material selection including SiCN dielectrics, nano twinned Cu, and polymer composites, (ii) process technologies such as sub-200 °C plasma-activated bonding and Chemical Mechanical Polishing (CMP) anneal co-optimization, and (iii) the structural design, including staggered stack and filleted corners. Integrating these levers suppresses stress hotspots and extends fatigue life in more than 16layer stacks. Finally, we outline a research roadmap combining a multiscale simulation with high layer prototyping to co-optimize thermal, mechanical, and electrical metrics for next-generation 20-layer HBM. Full article

The present work deals with the mixing of two green polymers at several definite ratios that led to the receiving of biodegradable polylactic acid (PLA)/polycaprolactone (PCL) blends possessing well-expressed macromechanical and shape memory properties. Four non-compatibilized polymer compositions were prepared by using a twin-screw melt extrusion technique, allowing for a homogeneous dispersion of the PCL droplets in the PLA matrix and higher interfacial adhesion between the two phases. The mechanical behavior of the specimens was estimated by tensile experiments conducted at three particular crosshead velocities. It was established that the addition of PCL as a soft segment redounded to an increment of the toughness and elongation at ultimate strength of the polymer composite at the expense of the maximum tensile stress and Young’s modulus. These latter two parameters were found to be more sensitive, in terms of reaching high values, to the content of PLA as a hard segment in the polymer blend. Performing thermoresponsive shape memory tests disclosed an overwhelming reversibility between the temporary and permanent states of the composite materials, including significant shape fixation ($R_f$) and shape recovery ($R_r$) rates. SEM analysis of the PLA/PCL compositions revealed a distinct phase-separated microstructure, confirming the immiscibility of the two polymers in the blend. Full article

Shape-memory polymer nanocomposites (SMPNCs) have emerged as a transformative class of smart materials, combining the versatility of shape-memory polymers (SMPs) with the enhanced properties imparted by nanostructures. Integrating these nanofillers, this review explores the pivotal role of SMPNCs in addressing critical limitations of traditional SMPs, including low tensile strength, restricted actuation modes, and limited recovery stress. It comprehensively examines the integration of nanofillers, such as nanoparticles, nanotubes, and nanofibers, which augment mechanical robustness, thermal conductivity, and shape-recovery performance. It also consolidates foundational knowledge of SMPNCs, covering the principles of the shape-memory phenomenon, fabrication techniques, shape-recovery mechanisms, modeling approaches, and actuation methods, with an emphasis on the structural parameters of nanofillers and their interactions with polymer matrices. Additionally, the transformative real-world applications of SMPNCs are also highlighted, including their roles in minimally invasive medical devices, adaptive automotive systems, 4D printing, wearable electronics, and soft robotics. By providing a systematic overview of SMPNC development and applications, this review aims to serve as a comprehensive resource for scientists, engineers, and practitioners, offering a detailed roadmap for advancing smart materials and unlocking the vast potential of SMPNCs across various industries in the future. Full article

Using 3D-printed (3DPd) polymers and their composites as shape memory materials in various smart engineering applications has raised the demand for such functionally graded sustainable materials. This study aims to investigate the viscoelastic, shape memory, and fracture toughness properties of the epoxy-based ultraviolet (UV)-curable resin. A UV-based DLP (Digital Light Processing) printer was employed for the 3D printing (3DPg) epoxy-based structures. The effect of the hydrothermal accelerated ageing on the various properties of the 3DPd components was examined. The viscoelastic performance in terms of glass transition temperature (T_g), storage modulus, and loss modulus was evaluated. The shape memory polymer (SMP) performance with respect to shape recovery and shape fixity (programming the shape) were calculated through dynamic mechanical thermal analysis (DMTA). DMTA is used to reveal the molecular mobility performance through three different regions, i.e., glass region, glass transition region, and rubbery region. The shape-changing region (within the glass transition region) between the T_g value from the loss modulus and the T_g value from the tan(δ) was analysed. The temperature memory behaviour was investigated for flat and circular 3DPd structures to achieve sequential deployment. The critical stress intensity factor values of the single-edge notch bending (SENB) specimens have been explored for different crack inclination angles to investigate mode I (opening) and mixed-mode I/III (opening and tearing) fracture toughness. This study can contribute to the development of highly complex shape memory 3DPd structures that can be reshaped several times with large deformation. Full article

This article presents a study of the viscoelastic behavior of an epoxy polymer and a glass-reinforced composite based on it under cyclic thermomechanical loading. The goal is to model and explain the experimentally observed stress state formation, including the accumulation of residual stresses under various initial mechanical stress levels and heating/cooling cycle durations. An improved material model, implemented as a Python script, is used, allowing for the consideration of memory effects on thermomechanical loading depending on the level and nature (mechanical or thermal) of the initial stresses. A Python script was developed to determine the viscoelastic parameters (elastic modulus E₁, elastic parameter E₂, and viscosity) for the three-element Kelvin–Voigt model. These parameters were determined at different temperatures for both the polymer and the glass-reinforced composite used in the modeling. The accumulation of stresses under different ratios of mechanical and thermal stresses was also investigated. Experiments showed that high levels of residual stress could form in the pure epoxy polymer. The initial stress state significantly influences residual stress accumulation in the pure epoxy polymer. Low initial tensile stresses (0–1.5 MPa) resulted in substantial residual stress accumulation, exceeding the initial stresses by up to 2.7 times and reaching values of up to 2.1 MPa. Conversely, high initial stresses (around 4 MPa) suppressed residual stress accumulation due to the dominance of relaxation processes. This highlights the critical role of the initial loading conditions in predicting long-term material behavior. In the glass-reinforced plastic, the effect of residual stress accumulation was significantly weaker, possibly due to the reinforcement and high residual stiffness, even at elevated temperatures (the studies were conducted from 30 to 180 °C for the composite and from 30 to 90 °C for the polymer). The modeling results show satisfactory qualitative and quantitative agreement with the experimental data, offering a plausible explanation for the observed effects. The proposed approach and tools can be used to predict the stress–strain state of polymer composite structures operating under cyclic thermomechanical loads. Full article