Multi-material Systems Research Articles

Development of a Numerical Model of the Hot Air Staking Process Based on Experimental Data

Intelligent light weight concepts are increasingly designed as multi-material systems in order to achieve optimized properties through a targeted combination of materials. For these applications, the market demands joining technologies that make it possible to join foreign materials reliably (e.g., incompatible thermoplastics, thermoplastic-metal and thermoplastic-thermoset). In view of these industrial challenges, thermoplastic staking is an established forming process. At present, computer-aided development and precise FE-simulation (finite element-simulation) of these processes are not state-of-the-art. Accordingly, the previous design is based on subjective empirical values and empirical tests of the component. Within the framework of the paper, these gaps are to be closed by the development of numerical models for the heating and forming behavior of thermal plastic rivets (hot air staking) and the associated experimental validation. This requires the experimental development of the cause-effect relationships between melt formation and the resulting forming behavior. Finally, the numerical simulation shows a high conformity to the experimental data and allows an evaluation of the minimum heating time as well as initial approaches to evaluating the resulting structures by the simulation.

Artificial Evolution and Design for Multi-Material Additive Manufacturing.

Limitations of the traditional manufacturing methods often force engineered components to be made of single material systems. However, this is going through changes due to the advent of additive manufacturing (AM) methods, as the point-by-point consolidation allows for a possible change of the material constitution within a given part domain. This will give rise to a plethora of new material and property options for the designers, where just human perception may fail to realize the full benefits. Automated design tools integrating material choice, dispersion, analysis, and optimization algorithms need to be developed to assist in finding the optimal multi-material dispersion solutions achieving given performance criteria sets. Considering the fact that the multi-material manufacturing systems are only recently coming into use, design solutions targeting optimal placement of multiple materials are not common. This article addresses this gap, evaluating a numerical model integrated with different optimization schemes to find the optimal material solutions achieving certain preset performance criteria such as combinations of natural frequencies in different degrees of freedom. A case study of three different metaheuristic optimization schemes based on genetic algorithms indicates, first, that it is possible to create a beam with six uniformly spaced natural frequencies and to change these frequencies without modifying the structural geometry; and second that the basic genetic algorithm generally outperforms neural net-based alternatives for this problem. This tailoring of the structural resonance spectrum demonstrates that evolutionary computing combined with multi-material AM can be used to unlock previously unavailable structural functionality.

Electrohydraulic Tentacle Actuators: Rapid 3D Printing of Electrohydraulic (HASEL) Tentacle Actuators (Adv. Funct. Mater. 40/2020)

In article number 2005244, Robert F. Shepherd and co-workers introduce a comprehensive multi-material system and fabrication route for the design and manufacture of soft, electrohydraulic actuators. The actuation and self-sensing capabilities of the capacitive modules are demonstrated. Moreover, they employ 3D printing to pattern dense arrays of these capacitive actuators to form a synthetic muscular hydrostat capable of multi-dimensional motion.

Multi-material microstereolithography using a palette with multicolor photocurable resins

A multi-material microstereolithography system in which multiple photocurable resins are stored on a single glass palette was developed to produce multicolor three-dimensional (3D) models. Multiple photocurable resins with different colors are replaced by moving a linear translational X-stage that supports the glass palette. A Z-stage moves radially to remove the air bubbles that adhere around the 3D model when replacing the resins. The uncurable resin was washed out by sequentially immersing the 3D structure in two tanks containing a cleaning solvent. This makes it possible to produce multicolor 3D models without contaminating the resins and air bubbles.

Verification of numerical homogenization approach in predicting thermal conductivities of fiber reinforced composites with voids and randomly distributed fibers

The aim of this paper is to establish the homogenization approach that eliminates the difficulties encountered by the conventional numerical methods in analyzing thermal behavior of the multi-material component systems with minimum computational resources. Analysis of problems with intricacies or larger domains can be made simpler through finite element assisted homogenization approach. In this paper, applicability of homogenization approach is verified by considering two cases (i) composite with voids and (ii) composite with fibers distributed randomly. Fiber randomness case is investigated by Digital Image-Based (DIB) modeling technique in association with MATLAB’S image processing module. Also effect of transverse fiber crack on the effective thermal conductivity of the composite is studied. Results of homogenization approach compared with micro-mechanics approach yielded maximum percentage deviation of 1.72% for voids case and 1.49% for fiber randomness case.

Adaptive multi-material topology optimization with hyperelastic materials under large deformations: A virtual element approach

We introduce a general multi-material topology optimization framework for large deformation problems that effectively handles an arbitrary number of candidate hyperelastic materials and addresses three major associated challenges: material interpolation, excessive distortion of low-density elements, and computational efficiency. To account for many nonlinear elastic materials, we propose a material interpolation scheme that, instead of interpolating multiple material parameters (such as Young’s modulus), interpolates multiple nonlinear stored-energy functions. To circumvent convergence difficulties caused by excessive distortions of low-density elements under large deformations, an energy interpolation scheme is revisited to account for multiple candidate hyperelastic materials. Computational efficiency is addressed from both structural analysis and optimization perspectives. To solve the nonlinear state equations efficiently, we employ the lower-order Virtual Element Method in conjunction with tailored adaptive mesh refinement and coarsening strategies. To efficiently update the design variables of the multi-material system, we exploit the separable nature and improve the ZPR (Zhang–Paulino–Ramos) update scheme to account for positive sensitivities and update the design variables associated with each volume constraint in parallel. Four design examples with three types of nonlinear material models demonstrate the efficiency and effectiveness of the proposed framework.

In situ fabrication of carbon fibre–reinforced polymer composites with embedded piezoelectrics for inspection and energy harvesting applications

Current in situ damage detection of fibre-reinforced composites typically uses sensors which are attached to the structure. This may make periodic inspection difficult for complex part geometries or in locations which are difficult to reach. To overcome these limitations, we examine the use of piezoelectric materials in the form of macro-fibre composites that are embedded into carbon fibre–reinforced polymer composites. Such a multi-material system can provide an in situ ability for damage detection, sensing or energy harvesting. In this work, the piezoelectric devices are embedded between the carbon fibre prepreg, and heat treated at elevated temperatures, enabling complete integration of the piezoelectric element into the structure. The impact of processing temperature on the properties of the macro-fibre composites are assessed, in particular with respect to the Curie temperature of the embedded ferroelectric. The mechanical properties of the carbon fibre–reinforced polymer composites are evaluated to assess the impact of the piezoelectric on tensile strength. The performance of the embedded piezoelectric devices to transmit and receive ultrasonic signals is evaluated, along with the potential to harvest power from mechanical strain for self-powered systems. Such an approach provides a route to create multi-functional materials.

Preface

Welcome to the 2020 11th International Conference on Mechatronics and Manufacturing (ICMM 2020), which was held at Tama Campus, Chuo University, Tokyo, Japan during January 10-12, 2020.The ICMM 2020 had provided a forum for scientific and technological advances in the theory and practice of mechatronics and manufacturing. In recent years, the development of sensors and actuators promoted many new and challenging research fields of mechatronics, such and robotics, MEMS, IT and so on. Furthermore, new research trends are developing in the field of manufacturing, such as ultra-precision machining, additive manufacturing, multi-material systems and so on. Consequently, holding a highly-professional meeting, in which many academic researchers and industrial engineers could exchange their knowledge and experiences, is getting more and more important.ICMM is growing with the numbers of participants and increasing in its quality. The latest ICMM 2020 aimed to be one of the leading international conferences in the world, and it provided an exciting environment for researchers and engineers to present and discuss the latest technologies and applications in the field of mechatronics and manufacturing.In the present conference, a number of academic and industrial works have been submitted and selected after a peer review process by experts among the technical committee members and other international reviewers in the related fields of expertise. We hope all the attendants had experienced a remarkable opportunity for the academic and industrial communities to address new challenges and share solutions, and discuss future research directions.Finally, we thank all participants who had come to Tama and joined the conference.Conference Chair of ICMM 2020Yoshihiko UEMATSUGifu University, JAPAN

Multimaterial Fiber Detector for Real‐Time and Remote X‐Ray Monitoring

AbstractX‐ray radiation is a leading cause of cancer, and thus a device that offers effective and real‐time radiation monitoring is of significant interest. The configuration design, fiber drawing, and device construction are introduced for a multimaterial fiber detector system that allows real‐time and remote X‐ray monitoring. A fiber detector embedded with metal–semiconductor–insulator ladder‐like configuration is designed and successfully constructed on the basis of Plateau–Rayleigh instability. The multimaterial design affords the detector robust radiation‐harvesting ability, enabling the collection of up to ≈88.13% of total X‐ray energy. The unique ladder‐like configuration allows the efficient generation and collection of free charges. Moreover, the detector exhibits excellent mechanical flexibility and can be woven into a complex configuration and even wearable fabrics. Finally, the application of the micro‐detector in real‐time wireless X‐ray monitoring is demonstrated. This research not only presents a flexible radiation detection strategy for various ionizing radiation types, such as X‐ray, gamma ray, and neutrons radiation, but also has potential uses in remote radiation monitoring in case a conventional rigid device is inapplicable.

Stress propagation and debonding effects in impedance-graded multi-metallic systems under impact loading

This article investigates the performance of an impedance-graded multi-metallic system. Material combinations of steel–titanium, steel–aluminium and steel–titanium–aluminium are compared against a monolithic steel configuration. The experiments were carried out using a single-stage gas gun, where the target specimens consisted of these material configurations. The targets were subjected to the impact of an aluminium flyer at a velocity of 180 m/s, where elastic waves were expected to propagate through the target. The free surface velocity of the final material in the target was measured and these readings were used to quantify the stresses in the materials. These stress results were compared with the output from two-dimensional axisymmetric numerical models and theoretical equations. The findings of this study indicated that a target configuration with gradual impedance reduction could minimize the magnitudes of both compressive and tensile stresses in the materials, where the latter is critical towards preventing debonding in a multi-material system.

The virtual core - modelling and optimization of core manufacturing and application

Development and manufacturing of high quality cast parts with tight dimensional requirements depend to a large extent on the stability and application of the sand cores. The core-sand is based on a complex granular multi-material system, where curing of an organic or inorganic system bond the grains into a porous core. The chosen combination of sand and binder determines the thermo-mechanical properties of the core. The paper provides an overview of current modelling capabilities along the life cycle of sand cores. A detailed analysis of the production steps is presented as well as the resulting properties linked to the application in the casting process. Several questions and some answers are given to the understanding of core related defects and how simulation can bridge the gap between core production and application of cores in the casting process. Today, process simulation of sand core production is an accepted tool for core box design and prediction of robust production conditions. The first modelling step is core shooting where expanding air is the driving force for sand flow from a core shooting machine into the core box. Coupled two phase flow modelling of air and granular material is required to represent the process sufficiently. The final process step in core manufacturing is core curing and moisture transport where porous media gas flow modelling is applied. Phase transformations as well as the relevant transport phenomena and the complete heat balance in case of thermally controlled processes need to be considered. During casting the deformation of the bonded sand material is generally governed by thermal expansion, phase transformation and the location of core prints. For long thin walled cores, buoyancy forces due to density differences between the cast material and the bonded sand material can play an important role due to creep effects in the organic binder systems. For inorganic systems moisture content and moisture transport during casting are affecting the mechanical behaviour, such as bending strength. The paper presents a detailed overview of a recent implemented soil plasticity model which is calibrated for different binder systems and sand types. The data are based on comprehensive mechanical tests to provide temperature, moisture and time dependent input data for the shown examples. This includes new steps and future challenges in modelling the anisotropy of printed sand cores and digitalization of the foundry in general.

Potential of Joining Dissimilar Materials by Cold Formed Pin-Structures

• Basic research on the joining of dissimilar metals via cold formed pin-structures. • Cold formed pin-structures are suitable to join dissimilar metals. • Caulking enables higher joint strengths compared to direct pin-pressing. • Significant increase of joint strength by using multi-pin-structures. • Inhomogeneous material flow complicates the forming of multi-pin-structures. Joining dissimilar materials brings established joining techniques to their limits due to different thermal expansion, unequal stiffness/strength and chemical incompatibilities. The use of pin-structures has proven an appropriate strategy to join multi-material-systems in laboratory scale. At present, the industrial application of this joining technology is limited due to the time-consuming pin manufacturing process and the inadequately researched achievable joint strengths. In this study, extrusion of the pin-structures from sheet metal is used to investigate an approach that can be directly integrated into existing production processes and does not require auxiliary joining elements. With direct-pin-pressing and caulking, two different joining strategies are analysed to join multi-material systems of sheet steel (DC04, t 0 = 2 mm) and aluminium (EN AW 6016-T4, t 0 = 2 mm). The basic feasibility of the joining technique is experimentally proven by using single-pin-structures. The joint strength is analysed by tensile shear tests, micro sections and failure patterns. Based on the experimental results, a failure criterion for the joint is defined. Parallel to the experiments, numerical finite element models (FE-models) for the single-pin-joint are developed and validated. In a further step, numerical investigations for multi-pin-structures are carried out in order to derive predictions on achievable joint strengths with this joining technique. It is shown that the form-fit is crucial for the joint strength. Thus, 93 % higher shear strength is achieved for caulked joints. By multi-pin-structures the strength can be increased considerably. For a 5 × 3 pin-structure, shear strength of 9.9 kN can be achieved.

Experimental, numerical and analytical study on the shock wave propagation through impedance-graded multi-metallic systems

The behaviour of multi-material systems subjected to dynamic loads is currently a topic of interest. This paper aims to study the performance of an impedance-graded multi-metallic (IGMM) system in mitigating the effects of stress waves generated during a high-velocity impact event. The IGMM system was designed by placing different metals in their reducing order of impedance. The experimental work was carried out using a single-stage light gas gun with a steel flyer fired at a velocity of 350 m/s. Armour-grade steel, titanium and aluminium were chosen as the materials and were used to design monolithic, bi-metallic and tri-metallic impedance graded targets. The free surface velocity of the final material in the target was measured using PDV probes and the generated velocity profile was used to quantify the Hugoniot Elastic Limit and the magnitude of the transmitted shock waves. A two-dimensional axisymmetric numerical model was used to simulate this impact event, which was carried out using the non-linear finite element code LS-DYNA. An analytical model was developed based on the shock wave propagation theories, using Matlab, to quantify the magnitude of the stresses within the different materials in the target. The output from the numerical and analytical models were in good agreement with the experimental results. The main findings from this study highlighted the potential of the IGMM system in reducing transmitted compressive stresses as well as prevention of spalling during impact loading events.

Study on application of adhesives for Carbon Fiber Composites connection in High-speed Rail

At present, the high-speed train mainly made up of carbon fiber composites adopts a new flame-retardant multi-material system. It is necessary to select adhesives for the Adhesive bonding structures of different materials in order to meet the overall technical and performance requirements of high-speed trains. Through this research, mechanical performance data of several structural adhesives and sealant adhesives are obtained when they are bonded to the high-speed trains with carbon fiber composite material as the main body. Finally, the optimum adhesives for bonding different material systems in the high-speed trains are determined under different operational aging environments, which also provides data support for the formulation of connection specifications for carbon fiber reinforced composites in the field of high-speed railway. In addition, a multi-dimensional data reduction method is proposed for the analysis of sealant performance data, which is very helpful for the future analysis of big data of adhesives.

Interfacial fracture toughness measurement in both steady state and transient regimes using four-point bending test

The paper describes some extensions of four-point bending tests for determining the interfacial fracture toughness $$\Gamma $$, in both steady-state and transient regimes, as a function of the fracture mode mixity. Two sets of multimaterial systems were studied: (i) Aluminum alloy (ASTM 2017)/epoxy/PMMA polymer and, (ii) Aluminum alloy (ASTM 2017)/stainless steel (ASTM 301) obtained by bonding and thermal spray coating techniques respectively. The interfacial fracture toughness was investigated by means of analytical and Finite Element Analysis using ABAQUS software. The numerical trend solution of both interfacial fracture toughnesses as function of crack length, and friction coefficient has been obtained and compared to an analytical one. We will propose a method on (i) how both reversed notch position in multimaterial systems and crack delamination beyond the inner loading points (transient regime) are explored to extend the measurement of interfacial fracture toughness, (ii) how the numerical analysis is used to determine the interfacial fracture toughness through an experimental compliance measurement in transient regime, and (iii) we attempt to reveal why the interfacial toughness has strong phase angle dependence.

Modelling the combined effects of hydrogen traps and surface films on hydrogen permeation in ferritic steels

PurposeThe purpose of this study is to develop a model extending Oriani’s formula by introducing a normalised concentration to simulate hydrogen diffusion in a multi-material system such as coated steels, under the presence of traps.Design/methodology/approachImplemented through the finite element method based on the analogy between mass diffusion and heat transfer, the governing equation was applied to investigate the combined effects of hydrogen traps and surface oxide films on hydrogen permeation in ferritic steels.FindingsThis study shows that the effective diffusivity varies over several orders of magnitude depending on the traps and films. This explains the divergence of measured hydrogen diffusivities in steels. It is revealed that hydrogen permeation in steels with Pd or Ni film is a trapping-dominant transport process, while hydrogen permeation in steel with oxide film is a process controlled by both trapping effect and retarding effect of oxide film. The oxide film enhances total hydrogen concentration within the steel substrate and is therefore detrimental. The Pd or Ni film has a little influence on total hydrogen concentration distribution depending on trapping energy.Originality/valueHydrogen flux curves and transient hydrogen concentration distributions can be directly obtained through the developed model. The proposed approach can also be extended to investigate other interstitial (i.e. carbon, oxygen and nitrogen) diffusion with traps revisited in complex systems.

Computer modelling and simulation of a novel printing head for complex tissue engineering constructs

In tissue engineering, three-dimensional functional scaffolds with tailored biological properties are needed to be able to mimic the hierarchical structure of biological tissues. Recent developments in additive biomanufacturing allow to extrude multiple materials enabling the fabrication of more sophisticated tissue constructs. These multi-material biomanufacturing systems comprise multiple printing heads through which individual materials are sequentially printed. Nevertheless, as more printing heads are added the fabrication process significantly decreases, since it requires mechanical switching among the physically separated printheads to enable printing multiple materials. In addition, this approach is not able to create biomimetic tissue constructs with property gradients. To address these limitations, this paper presents a novel static mixing extrusion printing head to enable the fabrication of multi-material, functionally graded structures using a single nozzle. Computational fluid dynamics (CFD) was used to numerically analyze the influence of Reynolds number on the flow pattern of biomaterials and mixing efficiency considering different miscible materials.

Development of a multi-material microstereolithography system using resin pallets

Development of a multi-material microstereolithography system using resin pallets

A novel printing channel design for multi-material extrusion additive manufacturing

Additive manufacturing has a great potential in terms of its capability to produce components with complex geometries and to make multi-material and composite products by combining different materials in a single manufacturing platform. Current trends for the multi-material extrusion additive manufacturing process are categorized by multi-nozzle systems and multi-material inlet systems. In the case of multiple nozzle system, materials are deposited from different nozzles in sequence. On the other hand, in the case of multi-material inlet system, different materials are sent into a mixing tube and deposited as a mixture of materials. In this case, functionally graded parts can be fabricated by changing the volume fraction of two or more materials. Hence, the fabrication of parts with a continuous material supply by varying ratios for the extrusion technologies requires the development of printing heads with suitable printing channels, capable of varying the mixing ratio of different materials. To evaluate the effect of different printing channel designs on the material’s flow pattern and the functionally graded material printability, this paper presents a three-dimensional transient computational fluid dynamics (CFD) simulation of the two miscible liquid-liquid system in a printing channel. Different geometries and materials are considered

Additive Manufacturing of Silicone Composites for Soft Actuation

Elastomer composites have proven to be promising functional materials for soft actuators. Direct manufacturing of these materials is a practical prerequisite for Soft Robotics applications, where form and function are intricately entangled. In this article we show a multimaterial printer and associated processes for in situ fabrication of silicones and silicone-based elastomer composites for soft actuators. We discuss the fabrication process for both the silicone/ethanol composite material and encapsulating silicone skin using an inline passive mixing system, followed by characterization of the rheological and mechanical properties of the printed materials for various print modalities. Rheological study revealed the conditions, allowing continuous 3D printing of both small and big items out of silicone rubber and silicone/ethanol composite. Anisotropic mechanical properties allow for the design of functional characteristics of soft actuators by choosing print design modalities. We demonstrate a single-print-job additive manufacturing of functional multimaterial systems for soft actuation, and suggest that the developed processes will allow us to design soft robots with a broad range of actuation characteristics.