In this paper, results for SS316 L microtube experiments under combined inflation and axial loading for single and multiloading segment deformation paths are presented along with a plasticity model to predict the associated stress and strain paths. The microtube inflation/tension machine, utilized for these experiments, creates biaxial stress states by applying axial tension or compression and internal pressure simultaneously. Two types of loading paths are considered in this paper, proportional (where a single loading path with a given axial:hoop stress ratio is followed) and corner (where an initial pure loading segment, i.e., axial or hoop, is followed by a secondary loading segment in the transverse direction, i.e., either hoop or axial, respectively). The experiments are designed to produce the same final strain state under different deformation paths, resulting in different final stress states. This difference in stress state can affect the material properties of the final part, which can be varied for the intended application, e.g., biomedical hardware, while maintaining the desired geometry. The experiments are replicated in a reasonable way by a material model that combines the Hill 1948 anisotropic yield function and the Hockett–Sherby hardening law. Discussion of the grain size effects during microforming impacting the ability to achieve consistent deformation path results is included.

The selective light absorption of prestretched thermoplastic polymeric films enables wireless photothermal shape morphing from two-dimensional Euclidean geometry of films to three-dimensional (3D) curvilinear architectures. For a facile origami-inspired programming of 3D folding, black inks are printed on glassy polymers that are used as hinges to generate light-absorption patterns. However, the deformation of unpatterned areas and/or stress convolution of patterned areas hinder the creation of accurate curvilinear structures. In addition, black inks remain in the film, prohibiting the construction of transparent 3D architectures. In this study, we demonstrate the facile preparation of transparent 3D curvilinear structures with the selection of the curvature sign and chirality via the selective light absorption of detachable tapes. The sequential removal of adhesive patterns allowed sequential folding and the control of strain responsivity in a single transparent architecture. The introduction of multiple heterogeneous nonresponsive materials increased the complexity of strain engineering and functionality. External stimuli responsive kirigami-based bridge triggered the multimaterial frame to build the Gaussian curvature. Conductive material casted on the film in a pattern retained the conductivity, despite local deformation. This type of tape patterning system, adopting various materials, can achieve multifunction including transparency and conductivity.

A material-oriented regularization (MOR) methodology is developed to solve manufacturing inverse problem of estimating the manufacture input process parameters for a required output performance, demonstrated by ion beam microprocessing of tungsten components in future fusion reactors. The MOR methodology is explored as following steps: forward problem modeling, identification of characteristic material loading, and solving the inverse problem via the characteristic material loading. A thermodynamic model is established in forward problem scheme by comprehensively incorporating material constraints of tungsten, to simulate the output of residual surface stresses in top layer of several μ m that determines fatigue performance of the microprocessed tungsten component. With the experimentally verified model, all material loading variables, i.e., thermal, elastic strain, and plastic strain energies can be explicitly described under the processing load of thermal energy input. Among the material loading variables, stored elastic strain energy is identified as characteristic material loading with a highest sensitivity in correlation to residual surface stresses, as process signature. The processing load of 2.1–4.2 J/cm 2 is derived for a required residual surface stress in range of 0–1500 MPa within 15 μ m depth, with an upper bound of the relative error of 4.7–11.7% for the inverse problem solution. The MOR enables comprehensive incorporation of material constraints with a self-convergence effect to effectively relax the ill-posedness of manufacturing inverse problems, otherwise in conventional regularizations such constraints have to be empirically adjusted in compromise with data fitting.

Graphene is an ideal reinforcement material for metal matrix composites (MMCs) owing to its high strength, high ductility, light weight, as well as good bonding with metal matrix. In this study, graphene nanoplatelets (GNPs) reinforced Inconel 718 composites are fabricated by selective laser melting (SLM) technique and processed under various postheat treatment schemes. It is found that the fabrication of GNPs-reinforced MMC using the SLM technique is a viable approach. The obtained composite possesses dense microstructure and enhanced tensile strength. Postheat treatments at two levels of solution temperature (980 and 1220 °C) for 1 h followed by two-step aging are carried out. The experimental results indicate that the addition of GNPs into Inconel 718 matrix results in significant strength improvement. Under the as-built condition, the ultimate tensile strengths (UTSs) of SLM Inconel 718 materials are 997 and 1447 MPa, respectively, at 0 and 4.4 vol % GNP content. The strengthening effect of GNPs is most prominent under the as-built condition, and the strength of as-built GNPs-reinforced Inconel 718 is higher than that of unreinforced Inconel 718 under any processing conditions. The formation of γ ′ and γ ″ precipitates is suppressed in the GNPs-reinforced composite under the aging condition due to the formation of metallic carbide (MC) carbide and the depletion of Nb. GNPs effectively inhibits grain growth during postheat treatment. Quantitative investigation of the various strengthening effects demonstrates that load transfer effect is dominating among all contributors.

The continuing trend of device miniaturization brings increasing demand for small metal parts and, consequently, significant interest in microscale metal forming technologies. In this work, the influence of grain size on mechanical response in microscale axisymmetric reverse extrusion of Cu 110 alloy was investigated in detail. A characteristic plastic strain associated with material deformation in the extrusion process was, for the first time to the best of our knowledge, defined, measured, and used to evaluate the material's bulk flow stress at this corresponding strain. This flow stress was then used to scale measured mechanical response in reverse extrusion and help identify deviations from scaling behavior expected in continuum plasticity. A scaling anomaly was indeed observed, indicating a dependence of mechanical response on both the initial grain size and the characteristic dimension of microforming operations. Detailed microstructural examination of grains in extruded Cu parts was conducted, and points to directions for future study to better understand mechanisms behind the observed scaling anomaly.

This paper presents the development of a prototype exfoliation tool and process for the fabrication of thin-film, single crystal silicon, which is a key material for creating high-performance flexible electronics. The process described in this paper is compatible with traditional wafer-based, complementary metal–oxide–semiconductor (CMOS) fabrication techniques, which enables high-performance devices fabricated using CMOS processes to be easily integrated into flexible electronic products like wearable or internet of things devices. The exfoliation method presented in this paper uses an electroplated nickel tensile layer and tension-controlled handle layer to propagate a crack across a wafer while controlling film thickness and reducing the surface roughness of the exfoliated devices as compared with previously reported exfoliation methods. Using this exfoliation tool, thin-film silicon samples are produced with a typical average surface roughness of 75 nm and a thickness that can be set anywhere between 5 μ m and 35 μ m by changing the exfoliation parameters.

In this work, investigations were made for enhancing wear properties of rapid tooling (RT) by reinforcement of fillers (nanoscaled) for grinding applications. The RT has been prepared by using biocompatible composite material (BCCM) feed stock filament (consisting of Nylon 6 as a binder, reinforced with biocompatible nanoscale Al 2 O 3 particles) on fused deposition modeling (FDM) for the development of grinding wheel having customized wear-resistant properties. A comparative study has been conducted under dry sliding conditions in order to understand the tribological characteristics of FDM printed RT of BCCM and commercially used acrylonitrile butadiene styrene (ABS) material. This study also highlights the various wear mechanisms (such as adhesive, fatigue, and abrasive) encountered during experimentation. Finally, the FDM printed RT of proposed BCCM feedstock filament is more suitable for grinding applications especially in clinical dentistry.

Reliability aspects are crucial for the success of every technology in industrial application. Regarding interconnect devices, several methods are applied to evaluate reliability of conductor paths like accelerated environmental tests. Especially, molded interconnect devices (MID), which enable numerous applications with three-dimensional (3D) circuitry on 3D shaped injection-molded thermoplastic parts are often under particular stress, e.g., as component of a housing. In this study, a new test method for evaluating the flexural fatigue strength of conductor paths produced by the laser-based LPKF-LDS ® technology is presented. For characterization of test samples, a test bench for flexural fatigue test was built up. A result of the flexural fatigue test is a characteristic Woehler curve of the metal layer system. Applying this new test method, essential influencing parameters on the reliability of MID under mechanical load can be identified. So, the metal layer system as well as the geometric parameters of the metal layer is crucial for the performance. Furthermore, test specimens are tested under different types of mechanical load, i.e., tensile stress and compressive stress. For a holistic view on reliability of MID, experimental results are discussed and supported by simulations. An important finding of the study is the advantage of nickel-free layer systems in contrast to the Cu/Ni/Au layer system, which is often used in MID technology.

Oscillating microprobes avoid high stress and the sticking effect during contact between microprobe and measured surface. The full performance and application scope of oscillating microprobes can be explored and utilized once the reliable prediction of the microprobe contact behavior is understood. Here, an improved contact model considering adhesion forces, surface roughness, and viscoelastic damping for oscillating microprobes is presented and it is validated by exemplary measurements utilizing a uniaxially oscillating electrostatic microprobe. These results show that the nondestructive identification of material classes seems to be feasible by evaluating the phase shift between the sinusoidal signals of sensor and actuator, respectively.

There is an increasing demand for product miniaturization and parts with features as low as few microns. Micromilling is one of the promising methods to fabricate miniature parts in a wide range of sectors including biomedical, electronic, and aerospace. Due to the large edge radius relative to uncut chip thickness, plowing is a dominant cutting mechanism in micromilling for low feed rates and has adverse effects on the surface quality, and thus, for a given tool path, it is important to be able to predict the amount of plowing. This paper presents a new method to calculate plowing volume for a given tool path in micromilling. For an incremental feed rate movement of a micro end mill along a given tool path, the uncut chip thickness at a given feed rate is determined, and based on the minimum chip thickness value compared to the uncut chip thickness, the areas of plowing and shearing are calculated. The workpiece is represented by a dual-Dexel model, and the simulation properties are initialized with real cutting parameters. During real-time simulation, the plowed volume is calculated using the algorithm developed. The simulated chip area results are qualitatively compared with measured resultant forces for verification of the model and using the model, effects of cutting conditions such as feed rate, edge radius, and radial depth of cut on the amount of shearing and plowing are investigated.

The trend toward miniaturization of metallic microparts results in the need of high-precision production methods. Major challenges are, for example, downsizing of tools and adequate positioning accuracy within blanking. Starting from a novel approach for tool miniaturization and its realization, the aim of this study is showing the assessment of tool sensitivity against process errors. Etched silicon punches were used for blanking copper foils, where outbreaks occurred at the cutting edge. Hence, tool stresses during blanking were analyzed by finite element (FE) method in dependency of defined positioning and process errors and evaluated concerning tool stresses and sheared edge quality.

Conventional material models cannot describe material behaviors precisely in micro/mesoscale due to the size/scale effects. In micro/mesoscale forming process, the reaction force, localized stress concentration, and formability are not only dependent on the strain distribution and strain path but also on the strain gradient and strain gradient path caused by decreased scale. This study presented an analytical model based on the conventional mechanism of strain gradient (CMSG) plasticity. Finite element (FE) simulations were performed to study the effects of the width of microchannel features. Die sets were fabricated and micro/mesoscale sheet forming experiments were conducted. The results indicated that the CMSG plastic theory achieves better agreements compared to the conventional plastic theory. It was also found that the influence of strain gradient on the forming process increases with the decrease of the geometrical parameters of tools. Furthermore, the feature size effects in the forming process were evaluated and quantitated by the similarity difference and the similarity accuracy. Various tool geometrical parameters were designed based on the Taguchi method to explore the influence of the strain gradient caused by the decrease of tool dimension. According to the scale law, the difference and accuracy of similarity were calculated. Greater equivalent strain gradient was revealed with the decrease of tool dimension, which led to the greater maximum reaction force error due to the increasing size effects. The main effect plots for equivalent strain gradient and reaction force indicated that the influence of tools clearance is greater than those of punch radius, die radius, and die width.

This study develops a hybrid micromanufacturing technique to fabricate extremely smooth surface finish, high aspect ratio, and complex microchannel patterns. Milling with coat and uncoated ball-end micromills in minimum quantity lubrication (MQL) is used to remove most materials to define a channel pattern. The milled channels are then electrochemically polished to required finish. Assessment of the fabricated microchannels is performed with optical microscopy, scanning electron microscopy, atomic force microscopy, and white-light interferometry. Theoretical models were derived for surface finish of ball-end milling. The predicted surface finish data agree with experimental data in mesoscale milling, but the calculated data are lower than microscale milling data due to size effects. Built-up-edges, being detrimental in micromilling, can be reduced with optimal coating and milling in MQL. When micromilling and then electrochemical polishing of 304, 316L stainless steels and NiTi alloy, this hybrid technique can repeatedly produce microchannels with average surface finish in the range of 100–300 nm.

The advancement of micro tube hydroforming (THF) technology has been hindered by, among others, the lack of robust microdie systems that could facilitate hydroforming of complex parts that require both expansion and feeding. This paper proposes a new micro-THF die assembly that is based on floating a microdie-assembly in a pressurized chamber. The fluid pressure inside the chamber which surrounds the dies and punches is the same as the pressure required to hydroform the tube. The fluid pressure intensity in the chamber varies in accordance with the predetermined pressure loading path required to successfully hydroform the part. The system was built, and hydroforming experiments were carried out for various micro- and meso-scale shapes, including bulge-shapes, Y-shapes, and T-shapes.

Most end stage renal disease patients receive kidney hemodialysis three to four times per week at central medical facilities. At-home kidney dialysis increases the convenience and frequency of hemodialysis treatments which has been shown to produce better patient outcomes. One limiting factor in realizing home hemodialysis treatments is the cost of the hemodialyzer. Microchannel hemodialyzers produced using compression sealing techniques show promise for reducing the size and cost of hemodialyzers. Challenges include the use of a 25 μm thick elastoviscoplastic (EVP) mass transfer membrane for gasketing. This paper provides a framework for understanding the hermeticity of these compression seals. The mechanical properties of a Gambro AN69ST membrane are determined and used to establish limits on the dimensional tolerances of the polycarbonate (PC) laminae containing sealing bosses used to seal the hemodialyzer. The resulting methods are applied to the fabrication of a hemodialysis device showing constraints on the scaling of this method to larger device sizes. The resulting hemodialysis device is used to perform urea mass transfer experiments without leakage.

During the electrical-assisted forming process, a significant decrease in the flow stress of the metal is beneficial to reduce the required force for the deformation with high-density electrical current introduced through the materials. It is an alternative manufacturing process of traditional hot forming to improve the formability without the undesirable effects caused by elevated temperature, such as surface oxidation. In this study, tension tests and electrical-assisted embossing process (EAEP) experiments were performed to study the electroplastic (EP) effect with high-density pulse current applied to the specimen and demonstrate the advantage of EAEP. In the first section of this study, specimens with various grain sizes were well prepared and an experimental setup was established to study the flow stress of SS316L sheet in the electroplastic tensile test. Extra cooling system was developed and the temperature increase caused by resistive heating was controlled. Thermal influence caused by resistive heating was thereby reduced. The impacts of the pulse current parameters on the flow stress were investigated. It was observed that the flow stress of the SS316L specimens was significantly reduced by the electroplastic effect. In the second section, the EAEP was proposed to fabricate microchannel feature on metal workpiece. Experiments were conducted to demonstrate the feasibility and advantage of the novel process. The protrusion feature height and microstructure of the grain deformation were measured to investigate the effect of the process parameters, such as the current density, the die geometric dimension, and the grain size of the specimen. Larger feature height was measured owing to the higher density current, which meant the electroplastic effects were helpful in EAEP.

The method of roll molding is proposed as an alternative to compression molding for low-cost, high-throughput manufacturing of metal-based microchannel structures. Elemental aluminum- and copper- based microchannel arrays with depths of ∼600 μm and depth:width ratios ≥2:1 were successfully fabricated by roll molding at room temperature. Morphologies of roll molded Al and Cu microchannels were examined in detail. Response of roll molding was characterized by measuring depths of roll molded microchannels as a function of the normal loading force per width. This response of roll molding was further shown to scale with the flow stress of roll molded material. Roll molding offers the potential of fabricating microchannel structures with large footprints in a continuous manner.

Elastic deformation molding method is a newly developed aspheric machining technology which can convert complex aspherical surface machining to simple flat surface machining. The residual stress induced in lapping process of elastic deformation molding method has significant influence on machining precision. In this paper, the influence of residual stress induced lapping process on machining accuracy is analyzed and discussed through experiment. An experiment with elimination of residual stress is carried out. The machining result shows that distortion amount has reduced form 2 μm to 0.8 μm, which means the residual stress can be effectively eliminated. A machining form accuracy of P-V 0.56 μm is obtained.

The microscale drilling performance of a Zr-based bulk metallic glass (BMG) is investigated in this paper. Crystallization, drill temperature, axial force, spindle load (SL), acoustic emissions (AE), chip morphology, hole diameter, and entry burr height are measured and analyzed with varying cutting speed and chip load. The progression of tool wear is assessed using stereo-microscopy techniques. At small chip loads, minimum chip thickness (MCT) is observed to shift cutting mechanics from a shear-dominated to a ploughing-dominated regime. Consequently, evidence of drill instability and larger burr height are observed. As drilling temperatures rise above the glass transition temperature, the BMG thermally softens due to the transition to a super-cooled liquid state and begins to exhibit viscous characteristics. In the tool wear study using tungsten carbide microdrills, rake wear is found to dominate compared to flank wear. This is attributed to a combination of a high rate of diffusion wear on the rake face as well as lower abrasion on the flank due to the decreased hardness from thermal softening-induced viscous flow of BMG.

This paper studies the effects of crystallography on the microscale machining characteristics of polycrystalline brittle materials on a quantitative basis. It is believed that during micromachining of brittle materials, plastic deformation can occur at the tool-workpiece interface due to the presence of high compressive stresses which leads to chip formation as opposed to crack propagation. The process parameters for such a machining process are comparable to the size of the grains, and hence crystallography assumes importance. The crystallographic effects include grain size, grain boundaries (GB), and crystallographic orientation (CO) for polycrystalline materials. The size of grains (crystals), whose distribution is analyzed as a log-normal curve, has an effect on the yield stress of a material as described by the Hall–Petch equation. The effects of grain boundary and orientation have been considered using the principles of dislocation theory. The microstructural anisotropy in a deformed polycrystalline material is influenced by geometrically necessary boundaries (GNB) and incidental dislocation boundaries (IDB). The dislocation theory takes both types of dislocations into account and relates the material flow stress to the dislocation density. The proposed analysis is compared with previously reported experimental data on polycrystalline germanium (p-Ge). This paper aims to provide a deeper physical insight into the microstructural aspects of polycrystalline brittle materials during precision microscale machining.