Micro-sized Cantilever Research Articles

A single micro-LED manipulation system based on micro-gripper

Micro-LEDs (μLEDs) have advantages in terms of brightness, power consumption, and response speed. In addition, they can also be used as micro-sensors implanted in the body via flexible electronic skin. One of the key techniques involved in the fabrication of μLED-based devices is transfer printing. Although numerous methods have been proposed for transfer printing, improving the yield of μLED arrays is still a formidable task. In this paper, we propose a novel method for improving the yield of μLED arrays transferred by the stamping method, using an innovative design of piezoelectrically driven asymmetric micro-gripper. Traditional grippers are too large to manipulate μLEDs, and therefore two micro-sized cantilevers are added at the gripper tips. A μLED manipulation system is constructed based on the micro-gripper together with a three-dimensional positioning system. Experimental results using this system show that it can be used successfully to manipulate μLED arrays.

Micromechanical testing for quantitative characterization of apparent slip system: Extinction of persistence of slip in carbon bearing Fe-3% Si

The effect of carbon on the persistence of the slip in Fe–3 mass% Si was investigated. We applied micro-sized cantilever bending tests to obtain ψ–χ relationships that enable quantitative analysis of the persistence of the slip. It was demonstrated that the result from decarburized specimens using this method is consistent with those obtained in previous studies from bulk-sized tensile test specimens. This novel method eliminates the difficulty of preparing bulk-sized single-crystal specimens for investigating the persistence of the slip. The persistence of the slip weakened in aged specimens containing 0.016 mass% C and disappeared in quenched specimens with the same carbon content, where wavy slip bands were observed. The reason for these changes in the macroscopically apparent slip plane is explained by the assumption that the frequency of nucleating kink-pair in the competitive {110} planes is a function of the resolved shear stress.

Fracture behavior and deformation-induced structure changes of a Ti-based metallic glass using micro-sized cantilevers

Micro-cantilever bending tests are performed to quantify the fracture toughness and reveal the deformation mechanism of a Ti-based metallic glass. Plastic deformation is localized in shear bands initiating from the roots of the notches of the cantilevers. Although the load-displacement curves show considerable ductile failure characteristics, the notch fracture toughness values that obtained from the bending tests are extremely low (∼4.7 MPa m). Size dependent fracture is thought to be observed, where the fracture toughness increases with decreasing the uncracked ligament size of the cantilevers. TEM bright field images show that the shear bands with the width of 4–7 nm present brighter contrast. The regions in vicinity of the shear bands show dark zones (ranging from 3 to 5 nm in size) surrounded by continues bright zones. Cu nanocrystals are found not only inside the shear bands, but also around them. The free volume theory together with the simulation results is applied to explain the formation of shear bands in this Ti-based metallic glass during the bending deformation. The observed Cu nanocrystals are thought to be formed as a consequence of plastic-deformation-assisted crystallization. It is suggested that local atomic rearrangements lead to shifting of Cu nanocrystals towards more stable positions and cause the formation of Cu nanocrystals in regions subjected to high shear stress field.

Effect of Surface and Interfacial Tension on the Resonance Frequency of Microfluidic Channel Cantilever.

The bending resonance of micro-sized resonators has been utilized to study adsorption of analyte molecules in complex fluids of picogram quantity. Traditionally, the analysis to characterize the resonance frequency has focused solely on the mass change, whereas the effect of interfacial tension of the fluid has been largely neglected. By observing forced vibrations of a microfluidic cantilever filled with a series of alkanes using a laser Doppler vibrometer (LDV), we studied the effect of surface and interfacial tension on the resonance frequency. Here, we incorporated the Young–Laplace equation into the Euler–Bernoulli beam theory to consider extra stress that surface and interface tension exerts on the vibration of the cantilever. Based on the hypothesis that the near-surface region of a continuum is subject to the extra stress, thin surface and interface layers are introduced to our model. The thin layer is subject to an axial force exerted by the extra stress, which in turn affects the transverse vibration of the cantilever. We tested the analytical model by varying the interfacial tension between the silicon nitride microchannel cantilever and the filled alkanes, whose interfacial tension varies with chain length. Compared with the conventional Euler–Bernoulli model, our enhanced model provides a better agreement to the experimental results, shedding light on precision measurements using micro-sized cantilever resonators.

Investigation of failure mechanisms of nacre at macro and nano scales

Nacre is a natural composite featuring exceptional mechanical properties such as high strength and high toughness. Its unique structure is now universally applied in engineering bioinspired materials. On the other hand, it is still a technical challenge to investigate its interfacial strength and fracture mechanisms at micro or nano-scale. In this work, the interfacial strength and fracture mechanism of the ‘brick-mortar’ structure in nacre are investigated using micro-sized cantilever beam and bend samples. As compared to previous works, a high aragonite/biopolymer interfacial strength is observed (~298 MPa). The crack propagation path is investigated via experiment and finite element modelling and compared with the fracture mechanics analysis. It is confirmed that crack deflection to the aragonite/biopolymer interface contributes to a high overall toughness. This work provides a better understanding of the toughening mechanism in nacre and other bioinspired composites.

Fracture toughness testing at the micro-scale − The effect of the unloading compliance method

Fracture mechanical testing of micro-sized cantilevers was conducted in order to quantify the fracture toughness and behaviour of the (1 0 0)[0 1¯ 1] crack system in α-iron at 37.5 K, 133 K and room temperature. The cantilevers are outside the range of validity for linear-elastic fracture mechanics due to the small sample size, rendering the cantilevers out of bounds in relation to linear-elastic fracture mechanics and classical fracture mechanics. Elastic-plastic fracture mechanics has therefore been applied to determine the conditional fracture parameters KQC and JQC. A comparison between cantilevers continuously loaded with corrected dynamic stiffness measurements and another data set of cantilevers tested with the unloading compliance method has been made. A distinct difference in determined fracture toughness and crack behaviour was identified, indicating potential concerns when applying the unloading compliance method at the micro-scale on ductile materials.

Crack arrest testing at the micro-scale

Crack arrest testing of micro-sized cantilever beams (≈8 × 4 × 6 μm, length, width and height, respectively) was conducted in order to evaluate the suitability of a new method to quantify local crack arrest properties. Chevron notched cantilevers were milled to match the (1 0 0)[0 1¯ 1] crack system in α-iron, where earlier attempts to obtain brittle or rapidly propagating fracture proved difficult. Brittle crack initiation and propagation was achieved by means of the deposition of a layer of SiOX on the surface, acting as a brittle starter. All tests were performed at −75 °C, using an in-house designed cooling system. The cracks arrested after propagation into the iron cantilever. A finite element model was developed to determine the appropriate dimensionless shape factor and provide a rigorous computer analysis of these complexly shaped cantilevers. KQC and KQa, at initiation and arrest respectively, were determined and evaluated. The cantilevers were later displaced further at 40 K to allow evaluation of crack jump lengths and to obtain a more complete analysis of the fracture surfaces. The average fracture toughness was determined to be 3.89 ± 1.00 MPam, and the average arrest toughness to be 2.6 ± 0.86 MPam. The finite element model highlights the effect of small variations in geometry which was larger than anticipated and strongly affects the shape factor, up to a 25% difference in f(a/W). As small variations in geometry are inevitable when milling with FIB, the need for individual models tailored to every cantilever is discussed.

Fracture mechanical testing of single crystal notched α-iron micro-cantilevers

Fracture mechanical testing of micro-sized cantilevers was conducted in order to quantify the fracture toughness and modes of fracture for the (100)[01¯1] and (101¯)[101] crack systems in α-iron. The testing was performed at both room temperature and at −75°C. Previous molecular dynamics analysis has indicated brittle behavior for the (100)[01¯1] and ductile behavior for the (101¯)[101] orientation, giving rise to the question; could this be achieved with testing at the micro-level. Elastic-plastic fracture mechanics was applied due to the small sample size, rendering the cantilevers out of bounds in relation to linear-elastic fracture mechanics boundaries. Conditional fracture parameters, KQ and JQ, were determined through the load-displacement curves where the change in unloading stiffness was used to determine crack growth. The crack growth was corrected to fit micrograph measurements. By normalizing the JQ vs. crack growth curves with its critical values, a new characterization tool was deemed applicable and proved promising in characterizing fracture behavior.

Fracture Toughness of Granite Measured Using Micro to Macro Scale Specimens

The objective of this study is to examine any variation from micro to macro scale mode-I fracture toughness of granite using micro-sized specimen and semi-circular specimen. The rock used in the tests is Iksan granite (Korea) which is composed of minerals, such as plagioclase and alkali feldspar, quartz. In order to investigate micro scale fracture toughness, a mechanical testing machine was used. This machine is an original one and developed by ourselves. In the test, a micro-sized cantilever beam type specimen was used. Its dimension is 10 × 10 × 50μm. On the other hand, in order to examine macro scale fracture toughness, Semi-Circular Bend (SCB) test is adopted. This is one of ISRM-suggested methods for estimation of the mode-I fracture toughness of rocks. The semi-circular specimens are prepared with a radius of 12.5mm to 50mm. Based on the fracture toughness obtained from both tests, the size effect of granite is discussed in the range from micro to macroscale.

Effects of chemical components on the bending properties of micro-sized cantilevers in three types of SU-8

Bending tests were performed using micro-sized cantilever specimens in three different types of epoxy-based photoresist, SU-8 (i.e. SU-8, SU-8 2000, abd SU-8 3000) to clarify the effects of the chemical components on the bending properties, especially focused on the solvents and/or the additive. Gamma-butyrolactone (@c-BL) is contained as solvent in SU-8; in contrast, cyclopentanone is used in both SU-8 2000 and SU-8 3000. The additive is contained in SU-8 3000 only. The bending properties such as Young's modulus, Yield stress, and bend strength are similar between SU-8 and SU-8 2000; although the solvents are different between the resists. The result shows that the effects of these solvents on the bending properties are little. On the other hand, the Yield stress and the bend strength in SU-8 3000 are lower than those in the others. In addition, the micro-sized cantilevers in SU-8 3000 behaved in a ductile manner during the bending tests, although the other SU-8s behaved in brittle manner. It is suggested that SU-8 should be made softer by the additive, which is a kinds of aliphatic compound.

Accelerated myotube formation using bioprinting technology for biosensor applications

Muscle-powered, biological, microelectro-mechanical system is promising for actuator and biosensor applications. Functional conjugation between the cells, tissues, and biomolecules to the microdevice is crucial for this application. Bioprinting as an enabling technology possesses the advantages of high throughput, digital control, and highly accurate delivery of various biological factors to the desired locations for numerous applications such as 3D tissue fabrication. We have now evaluated the feasibility of the precise placement of mouse myoblasts onto micro-sized cantilevers. The evenly aligned printed cells fused with each other and formed mature myotubes after only 4days. In contrast, it took more than 14days for randomly deposited cells to do so. The printed myotubes were functional and responded to the electrical stimulation synchronously. Furthermore, the integrated Bio-MEMS device responded to the chemical stimulation spontaneously which demonstrated the potential as a functional biosensor. The contractility of the system was recovered quickly after the removal of the chemical stimulation, which indicated the flexibility of this system and the recycling potential.

Evaluation of anisotropic structure in electrodeposited Ni film using micro-sized cantilever

► We propose a mechanical test of electroplated Ni film using micro-sized cantilever. ► Two micro-sized cantilevers are fabricated. ► The beam directions are parallel or vertical to crystal growth direction. ► The bending tests are conducted with test machine designed for micro-sized specimens. ► Cantilever with beam direction parallel to growth direction is stronger than another. We propose a method of mechanical test for measuring strength of electrodeposited Ni film using micro-sized cantilever. Two cantilevers were fabricated for each beam direction parallel and vertical to grain growth direction. Bending tests were carried out with a test machine designed for micro-sized specimens. Bending tests of the two cantilever specimens showed that strength of the cantilever which beam direction is parallel to grain growth direction is higher than that of vertical to grain growth direction. EBSD analysis of the specimens after the bending test implies that difference in strength was caused by deformation twin.

Strengthening effect of twin boundaries in bcc crystal evaluated through a micro-bending test

ABSTRACTIn the present study, the strengthening effect of nano-scale twins in body-centered cubic (bcc) crystal was evaluated using micro-sized cantilever type specimen which contained the nanotwinned region (midrib) in ferrous lenticular martensite. The SEM observations of the micro-sized specimen after bending deformation indicated that midrib can act as barriers against dislocations, resulting in slip localization and non-localization across midrib. The load-displacement curve obtained by bending test showed that twin boundaries significantly enhance the critical resolved shear stress of bcc.

Microfracture Test of Mg12ZnY Intermetallic Compound in Mg-Zn-Y Alloys

ABSTRACTA Mg-Zn-Y alloy including a Mg12ZnY intermetallic compound exhibits excellent mechanical properties as compared to conventional magnesium alloys. The superior mechanical properties of this alloy seem to originate from the Mg12ZnY intermetallic compound; however, the mechanical properties of Mg12ZnY itself have not yet been fully investigated owing to the small size of this compound. In this study, a microfracture test was performed to investigate the fracture properties of the Mg12ZnY intermetallic compound. The material used in this test was a Mg88Zn5Y7 alloy. Micro-sized cantilever specimens composed of Mg12ZnY, with dimensions of 10 × 20 × 50 μm3, were prepared selectively isolated from the Mg88Zn5Y7 alloy using focused ion beam (FIB) machining. Notches with a width of 0.5 μm and a depth of 5 μm were also introduced into the micro-sized specimens. Microfracture tests were performed using a mechanical testing machine for microscale materials. The fracture toughness values (KQ) of Mg12ZnY were 1.2−3.0 MPam1/2. TEM observations indicated that the KQ values were dependent on the crack orientation in Mg12ZnY, with the higher KQ values correlating with cracks propagating parallel to the c-axis of Mg12ZnY. This suggests that the fracture toughness of Mg-Zn-Y alloys can be improved by controlling the orientation of the Mg12ZnY compound.

1501 マイクロ試験によるFe-Sn合金の粒界強度評価(OS15-1 ナノ・マイクロの視点からの変形と破壊の力学)

Bending tests were performed for a micro-sized cantilever specimen that made at Fe-2wt%Sn alloy by using focused ion beam and the root of the specimen was set to a grain boundary to investigate strength for grain boundary fracture by using an atomic force microscope with ultramicro hardness tester. The alloy was heated at 600℃ for 5 h in argon gas atmosphere to cause grain boundary segregation of Sn. Three specimens were prepared for a random grain boundaiy and each specimen had a notch with different depth from 0.7μm to 2.3μm on the grain boundary. The three specimens were fractured at the grain boundary in the bending tests. The J integrals evaluated around the notch tips of three specimens by finite element analysis were between 158 J/m^2 and 171 J/m^2. The J integrals were equal within 5% independent the notch depth, indicating that the quantitative evaluation for the strength of grain boundaries as J integral can be attained by adopting this experimental method.

T0301-1-1 マイクロ試験による粒界強度評価手法の開発(マイクロ・ナノ構造体の強度・力学特性)

Bending test was performed for a micro-sized cantilever specimen that made at Fe-2wt%Sn alloy and the root of the specimen was set to a grain boundary to investigate a condition for grain boundary fracture as a preliminary test for evaluation of grain boundary strength by using an ultramicro hardness tester. The alloy was heated at 600℃ for 5h to cause grain boundary segregation of Sn. The grain boundary was fractured in the bending test for the specimen made at large angle grain boundary; whereas the specimen made at small angle grain boundary was not. This result indicates the possibility that quantitative evaluation for the strength of embrittled grain boundaries can be attained by adopting this experimental method.

Micromechanical Testing of Nanostructured NbTiNi Hydrogen Permeation Membranes

AbstractNb-Ti-Ni alloy is one of the candidates for hydrogen permeation membranes. The hydrogen permeability of a membrane depends on its thickness, and mechanical properties such as the fracture toughness of the membrane are important to ensure reliability and durability. In the present work, micro-mechanical tests have been carried out for melt-spun Nb-Ti-Ni thin films consisting of amorphous and nano-crystalline phases. The relationship between the mechanical properties of the melt-spun films and the microstructural changes occurring in the films due to heat treatment has been also discussed. The Nb-Ti-Ni alloy thin films were prepared by the melt-spun technique and then heat-treated at 873-1173 K. Micro-sized cantilever specimens with dimensions of 10 × 10 × 50 μm3 were prepared by focused ion beam (FIB) machining. Fracture tests were carried out using a mechanical testing machine for the micro-sized specimens; the testing machine was developed by us. In addition, microstructures were observed by transmission electron microscopy (TEM). The fracture toughness (KQ) value decreased up to 823 K, and it increased above 1173 K. The specimen heat-treated above 1173 K showed ductile fracture. The fracture morphology of the specimen heat-treated up to 1023 K showed grain boundary fracture characteristics, and that of the specimen heat-treated at 1173 K changed to transgranular fracture.

パルス通電焼結法で作製されたＳＵＳ／ＷＣ表面硬化材料の微細領域における機械的性質の評価

In order to improve wear properties of austenite stainless steel, we applied powder composite process to obtain thick hard layer on stainless steel. The raw alloy powder was prepared by planetary ball milled tungsten carbide (WC) powder and SUS316L stainless steel powder. Sintering process was performed by pulsed current sintering (PCS) method. Wear properties were evaluated by pin-on-disk wear testing machine, and a remarkable improvement was confirmed in wear resistance property. In this investigation, we applied micro-sized testing technique to evaluate mechanical properties of WC layer and Stainless interface of layer. Micro-sized cantilever specimens with a size of 10×20×50μm3 were prepared by focused ion beam machining system. Micro-sized bending tests were successfully completed using a mechanical testing machine for micro-sized specimens. The maximum bending stresses were different for stainless matrix, interface layer, and SUS/WC composite. Ductile rapture surface was observed at stainless matrix, and brittle rapture surfaces at interface of WC layer and Stainless layer and SUS/WC composite layer.

Microscale Fracture Toughness Testing of TiAl PST Crystals

AbstractA microscale fracture testing technique has been applied to examine the fracture properties of lamellar in TiAl PST crystals. Micro-sized cantilever specimens with a size ˜ 10×20×50 μm3 were prepared from Ti-48Al two-phase single crystals (PST) lamellar by focused ion beam (FIB) machining. Notches with a width of 0.5 μm and a depth of 5 μm were also introduced into the specimens by FIB. Two types of notch directions (interlamellar and translamellar) were selected when introducing the notches. Fracture tests were successfully completed using a mechanical testing machine for micro-sized specimens at room temperature. The fracture toughness (KQ) values of the interlamellar type specimens were obtained in the range 1.5–3.6 MPam1/2, while those of the translamellar specimens were 5.0–8.1 MPam1/2. These fracture toughness values are lower than those having been previously reported in conventional TiAl PST samples. For macro-sized specimens, extrinsic toughening mechanisms, including shear ligament bridging, act in the crack wake, and the crack growth resistance increases rapidly with increasing length of crack wake for lamellar structured TiAl alloys. In contrast, the crack length in microsized specimens is only 2–3 μm. This indicates that extrinsic toughening mechanisms are not activated in micro-sized specimens. This also indicates that intrinsic fracture toughness can be evaluated using microscale fracture toughness testing.

Fe-3 mass%Si 合金単結晶の微小試験片における破壊挙動とその試験片寸法効果

Fracture tests have been performed for both macro- and micro-sized specimens prepared from an Fe-3%Si alloy single crystal, and the size effects on fracture behavior have been considered. Micro-sized cantilever beam specimens with dimensions of 10 μm×10 μm×50 μm were prepared by focused ion beam machining. Notches with a depth of 5 μm were introduced into the micro-sized specimens and fatigue pre-crack was also introduced ahead of the notch. Macro-sized three-point bending specimens with dimensions of 2 mm×2 mm×10 mm were also cut from same Fe-3%Si alloy single crystal. Notches with a depth of 1 mm were introduced into the macro-sized specimens, and fatigue pre-crack was also introduced. Notch plane was set to be (100), which is a cleavage plane of this material, and notch direction was set to be [010] for both type of specimens. For macro-sized specimens, cleavage fracture occurred during introducing fatigue pre-crack. In constant, the micro-sized specimens were fractured by ductile manner. A plastic zone was clearly observed on the specimen surface near the crack tip and dimples were found on the fracture surface. The plastic zone size of this material is calculated to be 90 μm. This size is small enough to satisfy small scale yielding for macro-sized specimens, although this size corresponds to large scale yielding in micro-sized specimens. This may cause the size effect on the fracture behavior of this material. The results obtained in this investigation provide important information for designing actual MEMS devices.