Multi-material Design Research Articles

Flexural behaviours and heterogeneous interface fracture in overmoulded multi-material thermoplastic composites

The development of lightweight multi-material composites is imperative to meet the demands of the aerospace and automotive industries. Thermoplastic-based multi-material composites represent a novel approach, wherein two or more distinct composite materials are combined to create a hybrid material with enhanced performance characteristics. However, varying failure modes across multi-scale interfaces in the composites affect their mechanical performance in a complex manner. In this study, multi-material composites were manufactured through overmoulding of virgin polycarbonate (VP) and short-fibre reinforced polycarbonate (SFP) on continuous fibre-reinforced thermoplastic polycarbonate (CFRTP) laminate to assess behaviours of heterogeneous interfaces and structural performance under flexural loading. In the compression overmoulding process, the consolidation of thermoplastics creates interdiffusion of polymer chains across the multi-material interfaces. The multi-material composites successfully demonstrated enhanced flexural properties compared to single material constituent such as VP, SFP, and CFRTP. Benchmarking with CFRTP composite laminates, results revealed that overmoulding SFP on CFRTP results in 319 % higher flexural strength and 36 % higher of flexural modulus. VP/CFRTP composite offered 103 % more flexural strain and 175 % more specific energy absorption during fracture. Strategic optimization of the neutral axis (NA) and integration of high modulus materials in multi-material systems contributed to such performance enhancements. Failure analysis conducted using optical microscope and scanning electron microscopy (SEM) revealed progressive heterogeneous interface fracture and crack propagation in the CFRTP laminate layer. Results indicated that control of interface failure modes need to be considered in multi-material structure design to achieve desired flexural strength.

Experimental Investigation on the Important Factors on Structural Adhesive Joint Strength of Fiber-Reinforced Epoxy Composites

The static strength of fiber-reinforced epoxy composite structural adhesive lap joints was examined experimentally. Surface roughness and geometrical control parameters (adherent and adhesive kinds) were assessed for their effects. To examine load, elongation, and strength at failure, tensile tests were conducted. Cyanoacrylate glue outperformed SHCP 268 resin, and glass fiber-reinforced epoxy composites outperformed sisal fiber-reinforced epoxy composites. The study offers information on how to maximize adhesive bonding for lightweight multi-material design construction.

Characterization of the Anisotropic Electrical Properties of Additively Manufactured Structures Made from Electrically Conductive Composites by Material Extrusion.

Additive manufacturing (AM) of components using material extrusion (MEX) offers the potential for the integration of functions through the use of multi-material design, such as sensors, actuators, energy storage, and electrical connections. However, there is a significant gap in the availability of electrical composite properties, which is essential for informed design of electrical functional structures in the product development process. This study addresses this gap by systematically evaluating the resistivity (DC, direct current) of 14 commercially available filaments as unprocessed filament feedstock, extruded fibers, and fabricated MEX-structures. The analysis of the MEX-structures considers the influence of anisotropic electrical properties induced by the selective material deposition inherent to MEX. The results demonstrate that composites containing fillers with a high aspect ratio, such as carbon nanotubes (CNT) and graphene, significantly enhance conductivity and improve the reproducibility of MEX structures. Notably, the extrusion of filaments into MEX structures generally leads to an increase in resistivity; however, composites with CNT or graphene exhibit less reduction in conductivity and lower variability compared to those containing only carbon black (CB) or graphite. These findings underscore the importance of filler selection and composition in optimizing the electrical performance of MEX structures.

Design of a multi-material acoustic black hole using geometric profile mapping

Since their inception, acoustic black holes (ABHs) have taken on many forms. A wide range of profiles has been investigated for beam termination applications, including power laws and cosine profiles. However, all of these configurations have a common issue - the profiles have an inherent thin section at the end of the beam. This makes the profile susceptible to damage towards the tip, particularly through fatigue. Multi-material ABHs have been proposed as an alternative solution, maintaining a constant external geometry whilst varying the material properties along the length of the ABH termination. Previous work on multi-material ABHs has focused on optimising section lengths of each material based on a cost function, namely kinetic energy in the host beam. This work investigates the performance of multi-material ABH designs with section lengths chosen to approximate the effective impedance change of a range of geometric ABH terminations. The relative performance of each discretised gradient is compared through simulation in addition to comparison to an equivalent continuous gradient.

On the Potential of Manufacturing Multi-Material Components With Micro/Nanocellular Structures Via the Hybrid Process of Electromagnetic Forming Injection Foaming

Abstract Multimaterial design with a combination of solid and foam structures offers a promising avenue for reducing component weight while enhancing their functionalities. However, the complexity of multistage manufacturing processes poses significant challenges to adopting such approaches. To address these challenges, this paper introduces an innovative concept known as Electromagnetic Forming Injection Foaming (EFIF), which integrates injection molding, forming, and foaming processes into a single hybrid process. This process begins with a simultaneous filling-forming phase, followed by supercritical fluid (SCF) assisted foaming controlled by electromagnetic forming. Through a series of experimental and analytical studies, this work investigates the feasibility and effectiveness of EFIF. First, the impact of pressure drop rate and pressure drop on cell size and density is examined through a specialized experimental setup enabling performing injection, forming, and foaming processes in a single operation. The potential influence of electromagnetic forming on foam injection molding is explored through experiments focusing on the effects of a polymer layer between sheet metal blank and the electromagnetic coils. Additionally, an analytical study evaluates the EFIF process by calculating expected pressure drop rates under different processing conditions and their influence on cell nucleation rates. The results showed the possibility of achieving pressure drop rates up to 1.5 × 105 bar/sec, resulting in nucleation rates up to 1.77 × 109 nuclei/cm3sec. Overall, this paper highlights the potential of EFIF to merge existing technologies into a scalable solution for manufacturing multimaterial components with micro- to nanocellular polymer foams.

Advances in elastomeric mount concepts for quasi-zero stiffness isolation

Quasi-zero stiffness (QZS) mounts can exploit geometric nonlinearity to minimize stiffness about an operating point, which isolates vibrations from a supported source or receiver. Previous research on elastomeric QZS mounts featured 3D-printed prototypes but did not consider unique material properties and fabrication artifacts that may impact the static and dynamic behavior of the mounts. Additionally, multi-axis properties and their influence on common box-like systems supported by several mounts lack detailed study. To overcome these limitations and improve the practicality of elastomeric QZS mechanisms, this article discusses nonlinear stiffness, hysteresis, and fabrication issues with elastomeric materials in this context. Multimaterial mount designs that improve strength and stability are considered, and their effectiveness for QZS isolation is experimentally evaluated. System-level dynamics are presented for a box-like load supported by QZS mounts. Comparisons between additive and cast materials in the fabrication of QZS mounts are discussed, and the mounts' dynamic stiffness amplification effect is examined for additive and molded materials.

Crossover Integration: Multimaterial Design and Fabrication Strategies in Advanced Tissue Engineering.

Crossover Integration: Multimaterial Design and Fabrication Strategies in Advanced Tissue Engineering.

Advances in elastomeric mount concepts for quasi-zero stiffness isolation

Quasi-zero stiffness (QZS) mounts can exploit geometric nonlinearity to minimize stiffness about an operating point which isolates vibrations from a supported source or receiver. Previous research on elastomeric QZS mounts featured 3D printed prototypes but did not consider unique material properties and fabrication artifacts that may impact the static and dynamic behavior of the mounts. Additionally, multi-axis properties and their influence on common, box-like systems supported by several mounts lacks detailed study. To overcome these limitations and improve the practicality of elastomeric QZS mechanisms, this paper discusses nonlinear stiffness, hysteresis, and fabrication issues with elastomeric materials in this context. Multi-material mount designs that improve strength and stability are considered, and their effectiveness for QZS isolation is experimentally evaluated. System-level dynamics are presented for a box-like load supported by QZS mounts. Comparisons between additive and cast materials in the fabrication of QZS mounts are discussed, and the mounts' dynamic stiffness amplification effect is examined for additive and molded materials.

Multi-material optimal design of miura origami folds based on genetic algorithm

Multi-material optimal design of miura origami folds based on genetic algorithm

Topology optimization framework for thermoelastic multiphase materials under vibration and stress constraints using extended solid isotropic material penalization

This paper proposes a multiphase material topology optimization (MMTO) method for thermal–mechanical structures that takes into account the effect of the temperature field under stress and frequency constraints. Thermoelastic coupling occurs when an engineering structure is concurrently subjected to thermal and mechanical loads. This work focuses on the following: (1) the derivation of three interpolation schemes that use stress, dynamic, and thermal loads based on the extended solid isotropic material penalization (SIMP) method; (2) the incorporation of stress and dynamic constraints of multi-material thermal-elastic structural designs; and (3) the effective control of the impact of thermal loads on structures based on stress and frequency levels. Numerical experiments show that a clear distinction exists in the final topologies for mechanical and thermal loads among materials. Coupled and uncoupled mechanical and thermal behaviors can be predicted using finite element models based on materials’ coefficients of thermal expansion. We see this method is capable of optimizing a structure’s strength and stability while solving the issue of a thermal environment. In addition, it allows for the precise management of stress and vibration levels when structures are not exposed to a thermal environment.

A comprehensive review of optical fiber technologies in optogenetics and their prospective developments in future clinical therapies

As the incidence of neurological disorders rises, the need for innovative and minimally invasive treatment methods is paramount. This review comprehensively explores the state and the application of optical fiber technologies in optogenetics, highlighting the transformative potential of these advancements for future clinical therapies. Central to our discussion is the exploration of different types of optical fibers in in vivo optogenetics, including their design, fabrication techniques, and applications in neuromodulation. We explore the spectrum of optical fiber varieties, ranging from traditional to biocompatible and biodegradable optical fibers, as well as multifunctional and multimaterial designs. Fabrication methods are discussed, encompassing techniques such as thermal drawing, extrusion, extrusion-based 3D printing, and casting. The review further highlights the vast application landscape of optical fibers, encompassing light transmission and stimulation, fluid delivery, and electrical signal transmission. We delve into the unique properties and functionalities of these optical fibers, highlighting their respective strengths and limitations. By synthesizing current research and outlining key advancements, optical fibers in optogenetics are positioned to make significant contributions to the ongoing efforts in neuroscience to develop more effective and precise treatment modalities for neurological disorders.

Multiphysics modeling and optimization of an innovative shape memory alloy-polymer active composite

Shape memory alloys (SMAs) are a unique class of smart materials capable of recovering significant deformations through temperature variations, making them attractive for adaptive structures and morphing applications. However, integrating SMAs into polymer composites poses significant challenges, such as interfacial delamination and matrix overheating during thermal activation, in addition predicting the stress acting on the SMA during the actuation is pivotal. Addressing these issues is crucial for realizing the full potential of SMA-based active composites in aerospace, automotive, and renewable energy sectors. This study presents a novel multi-material design strategy for SMA-polymer active composites, featuring a rigid PC/ABS layer for mechanical integrity, a soft high-temperature silicone coating for encapsulating SMA wires, and aluminum terminals for wire crimping. A comprehensive multiphysics FEM model was developed to accurately capture the coupled thermo-mechanical response. Extensive experimental characterization and validation were conducted, followed by systematic parametric studies to investigate the effects of critical design parameters on key performance metrics. The developed prototype exhibited remarkable shape morphing capabilities, with a maximum tip deflection of 68 mm (deflection-to-length ratio of 0.4). Excellent agreement between experiments and simulations was achieved, with a maximum error of 1.7 % in tip deflection, validating the accuracy of the multiphysics model. Parametric analyses quantified the trade-offs between geometric parameters, revealing their influence on activation temperature, deflection, SMA wire stress, and fatigue life. Optimal configurations enabling low activation temperatures (<150 °C), low stress levels (<400 MPa), and high predicted fatigue life (>50,000 cycles) were identified. The multi-material design approach effectively addressed common issues in SMA-polymer composites, enabling reliable actuation cycles without damage accumulation. The validated multiphysics model and parametric insights provide a comprehensive framework for optimizing the design and performance of SMA-polymer active composites, paving the way for their widespread adoption in shape morphing applications. Potential implications include the development of adaptive aerodynamic surfaces, deployable structures, and energy-efficient systems across various industries.

Bi-metallic lattice structures manufactured via an intralayer multi-material powder bed fusion method

The laser powder bed fusion technology is widely utilized for manufacturing intricate metallic components, overcoming design limitations inherent in traditional subtractive methods. Recent advancements in powder bed fusion have extended to the creation of metal multi-material structures, allowing for functionally graded and tailored properties within a single component. While functionally graded lattice structures are commonly achieved by spatially varying the relative density and/or topology of the lattice, multi-material lattices are rarely studied particularly via metal additive manufacturing where multi-material methods are a relatively recent development. This study applies an accessible enhancement to a standard powder bed fusion system for multi-material additive manufacturing, and investigates printed and heat-treated bi-metallic lattices containing regions of both 316L and 17–4PH stainless steel. The bi-material interface is examined in lattice and bulk samples, and the compression behaviour of bi-metallic lattices is investigated experimentally and computationally. The material interface is shown to be robust as built and under loading, and the bi-metallic lattices exhibit greater energy absorption than single-material samples. The inclusion of the ductile 316L in bi-metallic lattices also delays the propagation of local failure and shear bands initiated in the more brittle 17–4PH. Finite element analysis simulates the lattice compression which includes strut fracture and as-built diameters informed by computed tomography, enabling further investigation and analysis of multi-material lattice designs. This work demonstrates the benefit of multi-material additive manufacturing by providing improved performance over single-material designs.

Investigation of the Compound Strength of Hybrid Casting Components with Different Variations of Coated and Undercut Sheet Metal

AbstractLightweight design can reduce CO2 emissions and improve energy efficiency, especially in the fuel-intensive transportation sector. Multi-material design approaches can combine specific properties of materials for effective lightweight design. A multi-material component made from two metals used widely in industry could combine the exceptionally lightweight properties of aluminum with the strength and structural integrity of steel. However, joining aluminum and steel is a challenge due to their different thermo-physical properties and the possible formation of brittle intermetallic phases. In hybrid casting, aluminum is cast around a steel sheet insert in a high-pressure die casting process to produce complex parts. In a first approach, a cold gas sprayed aluminum coating on the insert was tested as a bonding agent between the steel substrate and the molten aluminum. The joint was achieved by a combination of metallurgical bonding and micro-clamping. As a second option, surface structures with undercuts were applied to the steel sheet by modified cold rolling, which allowed the molten aluminum to flow into the channels and interlock with the solid steel. Different orientations of the structure on the insert were tested. In addition, the combination of both approaches was used to potentially enhance the positive effect of the pretreatment techniques. Given the critical importance of joint strength, the quality of these approaches was tested by static tensile tests and dynamic fatigue tests. The results show that the joint by coatings is strongly influenced by the process temperature. The improvement of the joint by the surface structure depends on its orientation to the melt flow.

Efficient and Accurate Separable Models for Discretized Material Optimization: A Continuous Perspective Based on Topological Derivatives

Multi-material design optimization problems can, after discretization, be solved by the iterative solution of simpler sub-problems which approximate the original problem at an expansion point to first order. In particular, models constructed from convex separable first order approximations have a long and successful tradition in the design optimization community and have led to powerful optimization tools like the prominently used method of moving asymptotes (MMA). In this paper, we introduce several new separable approximations to a model problem and examine them in terms of accuracy and fast evaluation. The models can, in general, be nonconvex and are based on the Sherman–Morrison–Woodbury matrix identity on the one hand, and on the mathematical concept of topological derivatives on the other hand. We show a surprising relation between two models originating from these two—at a first sight—very different concepts. Numerical experiments show a high level of accuracy for two of our proposed models while also their evaluation can be performed efficiently once enough data has been precomputed in an offline stage. Additionally it is demonstrated that suboptimal decisions can be avoided using our most accurate models.

Electrical Resistance Response to Strain in 3D-Printed Conductive Thermoplastic Polyurethane (TPU)

Additive manufacturing (AM) offers new possibilities in soft robotics as materials can easily be combined in multi-material designs. Proper sensing is essential for the soft actuators to interact with the surroundings successfully. By fabricating sensors through AM, sensors can be embedded directly into the components during manufacturing. This paper investigates NinjaTek Eels electrical resistance response to strain and the feasibility of using the material to create strain sensors. Strain sensors were 3D-printed out of NinjaTek Eel, a soft conductive TPU, and was tested during cyclic loading. A custom resistance–strain test rig was developed for measuring sensor behavior. The rig was calibrated for electric resistance, able to measure electric resistance as a function of strain. A parabolic response curve was observed during cyclic loading, which led to ambiguous readings. A 10-specimen validation test was conducted, evaluating the statistical variation for the first 100 loading cycles. The validation test showed that the sensor is capable of accurate and predictable readings during single load cases and cyclic loading, with the overall root mean square error being 66.9 Ω. Combining two sensors of different cross-sections gave promising results in terms of calibrating. By monitoring load cycles and strain rates, calibration can also be achieved by machine learning models by the microcontroller used to extract data. The presented work in this article explores the potential of using conductive TPUs as sensors embedded in products such as soft robotics, life monitoring of products with structural, and digital twins for live product to user feedback.

A new resistance insert spot welding method for injection-molded FRP–steel component

For weight reduction, multi-material designs comprising metal and fiber-reinforced plastic (FRP) components in vehicle body structures have been increasingly used. However, the commonly used resistance spot welding (RSW) technology for car body assembly cannot be employed to join sheet metal and FRPs, limiting the use of FRPs. To solve this problem, a novel resistance insert spot welding (RISW) technique was developed in this work for RSW of steel parts and FRP structure parts made by injection molding. Small inserts were developed by using finite element method and experiments that may be welded to different micro-alloyed and dual-phase sheet steels using the projection welding method. The usual flange width of original equipment manufacturers could be kept unchanged. Using the developed insert and welding parameters, the maximum temperature in the FRPs surrounding the inserts was limited to 255 °C, minimizing the damage to polyamide 6 (PA6) material (with 40 wt% glass fiber). A weldability range between 2.5 and 7 kA could be achieved. The joining strength of RISW between a micro-alloyed HC340 steel in 0.75 mm and 1.5 mm thickness and a 2.5 mm/3.0 mm PA6-GF40 material is 20 to 80% higher than self-piercing riveting (SPR). For high-speed loading, RISW strength increases by 39 to 56% further. Finally, RISW was successfully applied to an FRP–steel roof-frame sub-assembly that consists of 19 simultaneously integrated inserts, achieving 10% weight reduction.

Investigation of hybrid chalcogenide photonic crystal fiber for MIR supercontinuum generation and optical communication

Abstract This study describes a wideband supercontinuum generation (SCG) in the mid-infrared range using a chalcogenide multi-material microstructured fiber design with significant non-linearity under optical communication. The fiber has a single core of As2Se3 and three rings of As2S5 rods arranged in hexagonal pattern in the AsSe2 cladding region. The reported PCF design has effective area and nonlinear coefficients as 59.4174 μm2 and 219.36 W−1 km−1 respectively at 5.3 μm pump wavelength. Additionally, it has a chromatic dispersion profile that is nearly zero and flattened over a large wavelength range of 5–15 µm, which is advantageous for broadband supercontinuum spectrum in the mid-infrared region. Specifically, with pulse width and pulse peak power of 200 fs and 10 kW, respectively, for a 100 mm fibre length, this research work illustrates the SCG that expands from 1000 nm to over 15,000 nm. These extremely nonlinear PCFs are robust contenders for applications that are nonlinear in nature, such as the generation of slow-light and supercontinuum.

4D Multimaterial Printing of Soft Actuators with Spatial and Temporal Control.

Soft actuators (SAs) are devices which can interact with delicate objects in a manner not achievable with traditional robotics. While it is possible to design a SA whose actuation is triggered via an external stimulus, the use of a single stimulus creates challenges in the spatial and temporal control of the actuation. Herein, a 4D printed multimaterial soft actuator design (MMSA) whose actuation is only initiated by a combination of triggers (i.e., pH and temperature) is presented. Using 3D printing, a multilayered soft actuator with a hydrophilic pH-sensitive layer, and a hydrophobic magnetic and temperature-responsive shape-memory polymer layer, is designed. The hydrogel responds to environmental pH conditions by swelling or shrinking, while the shape-memory polymer can resist the shape deformation of the hydrogel until triggered by temperature or light. The combination of these stimuli-responsive layers allows for a high level of spatiotemporal control of the actuation. The utility of the 4D MMSA is demonstrated via a series of cargo capture and release experiments, validating its ability to demonstrate active spatiotemporal control. The MMSA concept provides a promising research direction to develop multifunctional soft devices with potential applications in biomedical engineering and environmental engineering.

Modeling of a Process Window for Tailored Reinforcements in Overmolding Processes

This study explores cost-effective and customized composite applications by strategically placing carbon fiber-reinforced thermoplastics in multi-material designs. The focus is on developing a model for the simultaneous processing of non-reinforced and reinforced thermoplastic layers, with the aim of identifying essential parameters to minimize insert flow and ensure desired fiber orientation and positional integrity. The analysis involves an analytical solution for two layered power-law fluids in a squeeze flow setup, aiming to model the combined flow behavior of Newtonian and pseudo-plastic fluids, highlighting the impact of the non-Newtonian nature. The behavior reveals a non-linear trend in the radial flow ratio towards the logarithmic consistency index ratio compared to a linear trend for Newtonian fluids. While a plateau regime of consistency index ratios presents challenges in flow reduction for both layers, exceeding this ratio, depending on the height ratio of the layers, enables a viable overmolding process. Therefore, attention is required when selectively placing tailored composites with long-fiber-reinforced thermoplastics or unidirectional reinforcements to avoid operating in the plateau region, which can be managed through appropriate cavity or tool designs.