This PDF file contains the front matter associated with SPIE Proceedings Volume 12947, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

It is well known that the buckling of thin-walled cylindrical shells is highly imperfection sensitive - a slight geometric imperfection could lead to a substantially lower load capacity compared to the theoretical buckling load of perfect shells. While the cause of this phenomenon has become qualitatively clear, the accurate assessment of a shell's load capacity is still challenging in that the imperfections are random and that no two shells can be made exactly the same. The current study focuses on the statistical aspects of the imperfection sensitivity with special attention given to the lower tail region (failure risk near one out of one million) of the load capacity distribution, as only the tiny lower tail governs the practical structure design for safety. The results pave the road for developing a physically justified probabilistic buckling knockdown factor that guarantees the failure risk to not exceed one in a million.

[1] Von Karman, Theodore, and Hsue-Shen Tsien. "The buckling of thin cylindrical shells under axial compression." Journal of the Aeronautical Sciences 8, no. 8 (1941): 303-312.

Medical implants have long been designed using traditional methods, relying on multiple parts, rigid components, and sliding surfaces due to their predictability and familiarity. Compliant mechanisms, devices that use mechanical compliance to obtain motion, offer opportunities to reimagine the underlying science behind medical implant design to create systems that are biomimetic, patient-specific, and bio-emulative to improve post-operative recovery. Principles of compliant mechanism design can be extended to the design of deployable and origami-based systems to create multifunctional and environmentally adaptive architectures and devices.

Composite structures widely used in advanced sectors as in the automotive and aeronautical fields, during their useful life are usually subject to dynamic events responsible for apparently invisible failures which, over time, severely compromise their performance. In this regard, a huge amount of experimental results, also validated by theoretical considerations, is available on the behaviour to damage caused by low velocity impacts (LVI) on laminate systems in polymeric composite and on their residual strength. However, until now the research interest has been mainly focused on thin composite laminates (less than 4 mm) and only very few experimental works are available concerning thick laminates (thickness higher than 4 mm) generally used in the skin of airplane wings, stringers, highly loaded components. This study aims to investigate simulated defects in carbon fiber reinforced polymers (CFRP) and of the damage deriving from LVI events, particularly peculiar to structures with higher bending stiffness such as thick ones and, therefore, to fill the current knowledge gap for a more appropriate use of the latter. To this end, thick carbon epoxy resin composite laminates, kindly supplied by Leonardo SpA and impacted at the Department of Industrial Engineering of the University of Naples Federico II, will be systematically investigated with well-established skills on infrared thermography, air coupled ultrasonic tests and shearography at the Institute of Applied Science and Intelligent Systems of the National Research Council. The combined results for both panels with simulated defects and impacted panels provided an accurate description of the different defects present in the thick panels involved in their damage process.

This study employs a phase field modeling framework to understand complex ferroelectric domain structure evolution near a surface that is under contact mechanical loading. Lead titanate is used as a model material to understand how indentation contact deformation leads to ferroelectric domain switching near the stress singularity of the indent. We investigate the evolution of a 180° ferroelectric domain wall using the time-dependent Ginzburg-Landau (TDGL) equation. The phase field method is used to simulate both the ferroelectric domain structures and the evolution of the contact surface. The phase field method is applied to the contact problem to facilitate computing stress concentrations from complex contact interfaces. This research is aimed at formulating a model that can deepen our understanding of ferroelectric material switching under a variety of complex surface loading to enhance fracture toughness and electromechanical material performance through deformation near the surface.

The technique of enhancing the functionality of polymeric materials through compositing microparticles is commonly utilized. For instance, studies have been conducted to manipulate heat transfer characteristics and stiffness while reducing weight through the incorporation of hollow particles. Polymeric materials hold particular significance as shock absorbers, and their dynamic behavior is crucial in defining their mechanical properties. The distinctive approach of dynamic X-ray CT enables the visualization of the internal behavior of polymeric materials under dynamic conditions, allowing the investigation of the relationship between the characteristics of functional materials and the internal behavior of these materials. In this study, dynamic viscoelasticity tests were performed on rubber composites containing particles of different shapes to evaluate the loss factor. Dynamic X-ray CT was also employed to evaluate the local strain within the material and to investigate if the dynamic behavior of the material varies based on the particle shape. Additionally, the generation of voids and their attributes were verified. As a result, it was established that both the amplitude distribution and the phase distribution of local strain changed as the loss factor increased. This result indicates that dynamic behavior alterations due to the incorporation of microparticles can be effectively captured using Dynamics Xray CT.

Multifractal analysis originated from the desire to obtain a deeper understanding of materials that follow random fractal structures. Complex systems display diverse degrees of irregularity and self-similarity on multiple scales that cannot be adequately described by a single fractal dimension due to uncertainties as well as deterministic changes in structure at different length and time scales. The multifractal spectrum measures the distribution of a specific property across different scales or levels within a system using a range of exponents. These properties can encompass anything from turbulence intensity in fluid flow to the distribution of heat flow through a solid. Each exponent in the spectrum corresponds to a particular level of irregularity, and a broad range of exponents indicates more complexity. Multifractal measures have a range of applications, from biology to mechanical engineering, among many others. In multifunctional materials used in adaptive systems, a more accurate description of material properties, such as viscoelasticity, heat transport, phase transformations, often involves considering information about their underlying fractal material structure. This study goes beyond fractals to include randomness in terms of multifractal measures. This involves analysis of the Renyi entropy. We evaluate this approach by examining heat transport in DLA structures which display multifractal properties. Renyi entropy is relevant here due to its entropy order parameter’s close connection to the multifractal spectrum. In fact, the multifractal spectrum can be directly calculated through the generalized Renyi entropy dimension and a box-counting process. We investigate the multifractality of different DLA structures and leverage this insight to better understand heat diffusion processes using fractal-order diffusion equations; however, the methodology is more broadly applicable to a wide range of multiphysics problems involving energy transport over complex media.

Protecting structural components and infrastructures, especially in harsh environments and disaster-prone regions, is a growing challenge, that is exacerbated by the climate crisis. Current solutions often prove costly and complex, limiting their applications especially in developing countries. This research highlights the progress in developing advanced protective systems using traditional elastomers and non-Newtonian polymers (Shear Stiffening Gels -SSG) incorporated into impact-vulnerable structures. By introducing these polymers, it is possible to dynamically enhance the mechanical response of a structure when subjected to external loads, stopping the propagation of internal cracks while also enabling non-structural properties such as damage detection and autonomous healing. This approach is easy to integrate into existing structures making it very versatile for novel civil applications and structural components in the build environment. The adaptability of this approach has great potentiality for swift intervention in disaster-stricken areas.

Printed flexible electronics have received extensive attention due to their significant potential for advancing wearable technologies, such as for monitoring human physiological health and biomechanics. However, current manufacturing techniques (e.g., inkjet printing and screen printing) of these electronics are typically limited by high cost, lengthy fabrication times, and types of print materials. Thus, this study investigates a novel manufacturing technique, namely corona-enabled electrostatic printing (CEP), which leverages high voltage discharged in the air to attract feedstock material particles onto substrates. The CEP technique can potentially fabricate various functional materials in milliseconds, forming binder-free microstructures. This study focuses on optimizing the CEP technique to produce high-performance, flexible, piezoresistive strain sensors. Here, the strain sensors will be fabricated with carbon nanotubes (CNTs) using different discharge voltages. The effect of the discharge voltage (i.e., a critical fabrication parameter) on the sensing performance will be characterized via electromechanical testing. In addition, to better understand the sensing mechanism of the samples, finite element analysis will be performed to investigate the electromechanical response of the CEP-fabricated binder-free CNT networks. Here, computational material models will be established based on microstructures of the CNT networks, which will be acquired from experimental microscopic imaging. Overall, this study will fundamentally advance the CEP manufacturing process for flexible electronics.

In this study, we aim to deepen understanding about the process-structure-property (PSP) relationship of the mechano-optoelectronic thin films where the conjugated poly(3-hexylthiophene) (P3HT) polymers form nano-structured lamellae. The MO thin films are known for the multifunctional capability of the radiant-electrical energy conversion and the direct current (DC)-based strain sensing capability. In the MO thin films, the p-type semiconducting P3HTs form crystalline domains along with n-type semiconducting fullerene derivatives to form p-n bulk heterojunction (BHJ), where holes and electrons are dissociated to generate DC upon the photonic energy introduction at the p-n junctions (i.e., the radiant-electrical energy conversion). In addition, it was shown that the optoelectronic property of the P3HT-based thin film was affected by the amount of the mechanical strain by which the thin film was stretched (i.e., MO property). The MO property has been hypothesized to be attributed to the varying nano-structures of P3HTs resulting from the macro-scale mechanical strain applied onto the P3HT-based thin films. As it is known that the nano-structures of P3HTs are greatly influenced by the manufacturing processes, we plan to study how the P3HTs’ nano-structures are affected by the spin-coating and the air-brushing processes to understand the PSP relationship of the P3HT-based MO thin films.

Liquid crystal elastomers (LCEs) films enable thermally responsive shape change. Mesogenic segments in the elastomeric network can be aligned into crystalline domains via mechanical deformation of the film. If subjected to a second-stage UV cure in the deformed shape, the crystalline domains are retained upon release of the external load. This induces a temporary shape in the LCE. Subsequent heating of the LCE above the nematic-to-isotropic temperature disorders the liquid crystals, and strain energy stored in the elastomer causes the LCE to return to the undeformed. In a reversible manner, the LCE returns to the temporary shape when cooled. In this work, we use thermally responsive LCE films applied to passive thin films, such as mylar and Kapton. The passive film enhances the mechanical strength and stiffness of the film but prevents alignment of the LCE crystalline domains through stretching. Instead, these bilayer films are restricted to folding deformations, wherein the LCE layer is used to induce thermally responsive shape change. We study the effects of layer thickness ratios on the reversibly self-folding bilayer films. The LCE films are synthesized directly on the passive film layer using a two-stage thiol-acrylate Michael addition and photopolymerization (TAMAP) reaction in which the first stage is a thermal cure, and the second stage is a UV cure. We demonstrate the reversible shape change between flat and folded states, and quantify the shape change in terms of the shape fixity and recovered flatness ratios. Potential applications for this system are actuators for deployable structures and soft robotics.

Vibration power generation harnesses weak environmental vibrations and converts them into electrical energy. In this study, a vibration power generator based on a magnetostrictive material (Fe-Ga) was investigated. The generator was designed with a cantilever beam structure, offering advantages in simplicity, robustness, and high-power generation capacity compared with piezoelectric systems. The change in magnetic flux within the coil is attributed to two factors: the change in the magnetoresistance of the magnetostrictive material owing to applied stress, and the variation in air-gap reluctance caused by fluctuations in the air-gap length. In our previous research, we focused on air-gap magnetoresistance variation and proposed a vibro-generator with a narrower air gap. Modifying the air-gap structure increased the generator’s air-gap magnetoresistance variation at the same amplitude, enhancing power generation. In this study, we introduced an auxiliary magnetic circuit to a narrow-gap-type vibration power generator. The main and auxiliary magnetic circuits had opposing flux directions and trends, which maximized the change in flux in the coil. Based on the study’s experimental results, the maximum output power generated by the multiple magnetic circuit vibro-generator was 149% and 46.3% higher than that of conventional vibro-generators and narrow-gap-type vibration generators, respectively. The multiple magnetic-circuit structure can enhance the power generation efficiency of the vibration generator, thereby increasing the application potential of the equipment.

4D printing has gained attention in engineering for its ability to introduce innovative functionalities in printed structures through shape-morphing. However, challenges persist in designing and fabricating intricate structures, mainly due to the complex task of controlling variables affecting morphing characteristics. To overcome these obstacles, the method of multi-material 4D printing is employed to create complex structures through a two-phase morphing process. This research focuses on using acrylonitrile butadiene styrene (ABS) and polycarbonate/acrylonitrile butadiene styrene (PCABS), exploiting the difference in their glass transition temperatures to achieve distinct morphing phases. The study conducts finite element analyses to predict accurate geometric changes in response to temperature changes. Experimental validation is done by fabricating various structures and applying thermal stimulation to realize desired morphing phases. The study results in the design and fabrication of multiple multi-material structures, showcasing both their functionality and intricate geometric complexity.

Traditional design methods for engineering applications aim to achieve optimal performance for specific conditions or moderate performance for a broader range of conditions. However, the optimal performance for a wide spectrum of situations can be facilitated if such systems possess reconfiguration capability. It can be illustrated in the example of structures with steerable joints, which is a popular approach in robotics. By rotating the joints to a different degree, a plethora of resulting configurations can be achieved – configurations that might be specifically suited for the required conditions. Systems based on these principles can be implemented on the macroscopic level in adaptive facades, on the mesoscopic level in mechanical metamechanisms, and at the microscopic level in microelectromechanical devices. In general, adaptive structures often require numerous actuators to facilitate a wide range of reachable configurations, leading to increasing energy demands as the system size increases. This can be seen in the case of robotics when each joint can be independently actively rotated to drive the motion corresponding to the specific degree of freedom. This paper analyzes an alternative situation, when the joins are semi-active and can exist only in either a locked or unlocked state, with only one (last joint) being actively steered. In the ideal case, the energy should be consumed only for switching between states, while maintaining the state should be free with locking achieved via switchable friction. While theoretically improving energy efficiency, such a system makes it much more challenging to control the resulting shape of the structure as compared with its counterpart with actively rotating joints. In this paper, we develop a motion planning algorithm to facilitate the achievement of the desired shape via control over the state of the joints and the position of the last link. In particular, the change of shape is performed by a sequence of single-degree- of-freedom motions determined by a motion planning algorithm based on Rapidly exploring Random Trees and sub-slider-crank systems (RRT-SC). One application of the proposed method is evaluated for reconfigurable building facades and paves the way for the next generation of structures in smart cities.

This paper compares the magnetostrictive properties of Metglas and Galfenol and investigates their potential as substrate materials for diaphragms to tune the performance of piezoelectric diaphragm pumps. These pumps are found in medical, automotive, and aerospace applications. Conventional diaphragm pumps consist of a vibrating diaphragm actuated by a piezoelectric wafer affixed to a rigid substrate; operating in bending mode, the diaphragm propels a specific volume of fluid across a defined space. Pump designs generally represent a trade-off between maximum output pressure and maximum flow rate. In this paper, we propose two well-established magnetostrictive materials, Metglas and Galfenol, as alternatives to conventional passive substrates to actively modulate pump characteristics such as pressure and flow rate. We experimentally characterize the Delta-E effects of Metglas and Galfenol to verify their stiffness tunability in response to magnetic fields. We develop COMSOL finite element models to simulate the performance of a commercial piezoelectric pump with and without the addition of active substrate materials. Finally, we investigate the potential for tuning the performance of diaphragm pumps with magnetostrictive substrates. This concept can enhance the efficiency of pumping mechanisms, allowing for adaptable performance across a range of specifications.

We report a comprehensive design guide for crystalline metamaterials with cubic elasticity - the simplest anisotropic case specified by three elastic constants only. To clarify some popular misconceptions, we first present a discussion about the symmetry requirements. Next, we demonstrate a complete design protocol for periodic structures that are guaranteed to exhibit cubic elastic behaviors, with an emphasis on designs without any four-fold (i.e., 90 degrees) rotational symmetry or mirror symmetry. Further, we show some examples with different extreme anisotropic cases as well as functionalities for wave manipulation.

In this work, a multilayer structure consisted of thin membrane gels, which are formulated by the reaction of PDMS and boron, is proposed to overcome the limitations of contemporary materials employed in sound absorption applications. The membrane gels can autonomously and dynamically respond to an external stimulus, i.e., a sound pressure wave, and activate a phase transition in their polymeric network, with energy absorbed in this phase transition and resulting in high acoustic performance. It was demonstrated that the membrane gels were able to achieve high and dynamic sound absorption individually (≥90%), which dynamically shifted to lower frequencies when the sound amplitudes were increased. The combination of multiple membranes resulted in the occurrence of multiple absorption coefficient peaks (60-85%) over a wider range of frequencies with the same dynamic shift. These results demonstrated that the proposed prototype of thin membrane gels can be used to develop deep subwavelength absorbers with highly tunable acoustic properties, displaying their potential application value in various sound absorption applications.