Micro-sized Specimens Research Articles

A methodology for in-situ micro-compression testing of fiber composites

Abstract A methodology for in-situ micro-compression testing of fiber composites has been developed. The tests were performed on carbon fiber reinforced bismaleimide matrix unidirectional composite, IM7/BMI 5250-4. Micro-size specimens were prepared from the bulk composite plaque through a two-step micro-fabrication process and then tested by using a micro-mechanical testing device placed inside the scanning electron microscope chamber. Results show that the fundamental properties (modulus and strength) of the fiber composites obtained from micro-size specimens are consistent with the theoretical estimations and significantly higher than those from macro-size specimens, which may have revealed the presence of size-scale effects in composite materials. The in-situ testing shows that the overall failure mode of the present composite is caused by “micro-buckling” of fibers in shear-mode. High shear strains are seen to occur at the fiber–matrix interfaces, which lead to the micro-cracking and ultimate failure of the composite.

Pulse Electroplating of Au Films with Ultra High Strength

Au is the most commonly used as contact material for high reliability electrical connectors, circuit boards, and as functional component for micro-electrical-mechanical system (MEMS) devices [1,2]. Electroplating has been applied extensively in fabrication of Au films used for all kinds of devices. Among the electroplating techniques, pulse electroplating is a technique known to control the properties of the deposited films by regulating the pulse amplitude and width. Therefore, morphology, crystal structure and deposition rate of the Au films can be controlled precisely [3]. In this work, grain refinement and surface smoothening of Au films were achieved by pulse electroplating using non-toxic sulfite-based electrolyte. Micrographs obtained by atomic force microscopy (AFM) and X-ray diffraction (XRD) patterns indicate that the surface of the pulse electroplated Au films possess less defect, lower surface roughness, smaller grain size, and denser texture when compared with the Au films prepared by conventional constant-current electroplating. By XRD analysis and Scherrer equation calculation, the estimated grain size of the Au film prepared by pulse electroplating was 10.5 nm, and was much smaller than the grain size of the Au film prepared by constant-current electroplating, which was 22.8 nm. The grain size achieved by the pulse electroplating is even smaller than previous reports [3,4]. This can be attributed to the higher pulse current density which leads to an increase in the nucleation rate during the on-time period. Mechanical strength in micro-scale of the Au films was also evaluated to determine the reliability and lifetime of the components composed of the electroplated Au. After the electroplating, micro-pillars made from the Au films were fabricated by focus ion beam (FIB) milling. Size of the fabricated pillar was fixed at 10 mm ×10 mm×20 mm. The micro-compression test was carried out using a test machine specially designed for micro-sized specimens developed in our laboratory. The pulse electroplated Au micro-pillar acquired a large increase in the compressive strength from 600 to 800 MPa when the grain size approaches 10.4 nm, presumably due to the grain-boundary strengthening known as the Hall-Petch effect [5]. This strength is much higher than that of bulk Au materials, which is only 55~200 MPa. The strength is even higher than that of the micro-pillar fabricated from the constant-current electroplated Au films. These results reveal that the pulse electroplated Au micro-pillar possesses better ductility and malleability than that fabricated by constant-current electroplating and demonstrate that pulse electroplating is a promising technique to fabricated Au functional micro-components especially for the advanced MEMS devices. Reference: [1] N. Togasaki, Y. Okinaka, T. Homma, T. Osaka, Electrochim. Acta, 51 (2005) 822. [2] D. Yamane, T. Konishi, T. Matsushima, K. Machida, H. Toshiyoshi, K. Masu, Appl. Phys. Lett., 104 (2014) 074102. [3] M. S. Chandrasekar, M. Pushpavanam, Electrochim. Acta, 53 (2008) 3313. [4] Y. Lee, S. K. Ahn, Y. Roh, Surf. Coating Tech., 193 (2005) 137. [5] A.H. Chokshi, A. Rosen, J. Karch, H. Gleiter, Scripta Metallurgica, 23 (1989) 1679.

Tensile behavior of micro-sized specimen made of single crystalline nickel

This paper proposed the effect of crystal anisotropy of micro-specimens evaluated by a micro-tensile. The micro-gripper and specimen were fabricated from a commercially available diamond-tip indenter and single crystal Ni disk, respectively, by focused ion beam. The stress–strain curves obtained from the micro-tensile test showed a few load drops, which is similar to serration contributed by occurrence of slip lines observed on surface of the specimens. Moreover, the difference in crystal orientations of 〈111〉 and 〈223〉 along the loading axis on stress–strain behaviors is evaluated. The results indicated the crystal anisotropy by Schmid factor is the same as the deformation behavior of face-centered-cubic bulk metals. Thus, the micro-tensile testing method used in this experiment successfully showed the effect of crystal anisotropy in micro-scale.

Tensile behavior of micro-sized specimen fabricated from nanocrystalline nickel film

This paper reports mechanical properties and tensile behavior of nickel films with average grain size of 8nm. The nickel films were obtained from electroplating with supercritical carbon dioxide emulsion (EP-SCE). Micro-tensile test using a micro-gripper and micro-specimen both fabricated by focused ion beam was conducted to evaluate the mechanical properties, and the tensile behavior was observed by a scanning electron microscope (SEM). The micro-tensile specimen showed a high tensile strength of 3.0GPa, yield strength of 2.4–2.5GPa and plastic strain of 3–5%. SEM observation of the fractured micro-specimen after the micro-tensile test showed typical fractured patterns of ductile materials, which are necking phenomenon, shear lip and dimple pattern. This fractured mode is called cup and corn fracture. The high strength and ductility are suggested to be effects of grain refinement and suppression of grain boundary sliding by carbon contents introduced during the EP-SCE.

Characterization of the influence of specimen thickness on the aging behavior of a polypropylene based model compound

Specimens with varying thickness of different polypropylene random copolymer formulations were oven aged in hot air at 135 °C. Besides macro-sized specimens die-punched from 2 mm thick extruded sheets, 50 μm, 200 μm and 500 μm thick micro-sized specimens, cut edgewise from the sheets by an automated planing procedure, were investigated. The formulations included a base stabilized reference compound and four formulations prepared with systematically varied additional contents of the primary antioxidants Naugard 445 and Irganox 1010 and the secondary antioxidants Irganox PS-800 and Irganox PS-802. Aging characterization was performed by tensile testing, differential scanning calorimetry and high performance liquid chromatography employing strain-at-break, oxidation onset temperature (OOT) and the content in phenolic antioxidants as aging indicators, respectively.Aging characterization revealed a systematic thickness dependence of the embrittlement time and the rate of the reduction in OOT as well as the reduction of phenolic antioxidants. The 50 μm thick specimens exhibited embrittlement times between 50% and 65% of the 2 mm thick macro-sized specimens. For low thicknesses, a high surface to volume ratio is presumably responsible for the fast physical loss of antioxidants, while for thick specimens, physical stabilizer loss is limited by the rate of stabilizer diffusion from the bulk to the surface. Hence, thicker specimens showed longer embrittlement times. Regarding stabilizer loss, Naugard 445 and Irganox PS-800 exhibited significantly higher loss rates than Irganox 1010 and Irganox PS-802.

The Cicero Clay Pits, Onondaga County, New York

For at least fifteen years, concretions in the old clay pits near the village of Cicero in central New York State produced micro-sized specimens of eight common minerals in exquisite crystals. The many habits of calcite and goethite are particularly noteworthy. Material from this locality is familiar to micromounters, and large quantities of specimens were produced. Beyond mention in a few mineral club bulletins, however, nothing about this locality has appeared in the literature. Beginning in 1983, the locality was obliterated by a subdivision of houses. Here we document this interesting locality before the information is lost forever.

Micro-compression test using non-tapered micro-pillar of electrodeposited Cu

We propose a novel method of mechanical test for measuring strength of electrodeposited Cu films using non-tapered micro-pillar. The grain size of each electrodeposited Cu films were changed by controlling current density and investigated by electron back scatter diffraction analysis. The pillars were fabricated by focused ion beam milling. The micro-compression test was carried out twice for each electrodeposition condition using a test machine designed for micro-sized specimen developed in our laboratory. The yield strength increased with increase of current density. The study showed that the influence of orientations on mechanical properties of the micro-sized specimens was magnified with reduction of the number of grains inside a sample.

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.

On an implementation of the strain gradient plasticity with linear finite elements and reduced integration

The size effects exhibited in the structural behaviors of micro-sized loading components cannot be described with classical plasticity theory alone. Thus, strain gradient plasticity together with appropriate experiments has been used to account for this size effect. In previous implementations of strain gradient plasticity into finite element code, low order displacement elements with reduced integration, despite their versatility for solving various structural problems, have been excluded because of their inability to yield the strain gradient inside the element. In this work, a new method of evaluating the plastic strain gradient with linear displacement elements via an isoparametric interpolation of the averaged-at-nodal plastic strain is proposed. Rate-independent yield conditions are satisfied accurately by the Taylor dislocation hardening model with Abaqus UHARD subroutine. To verify the suggested approach, the structural behaviors of micro-sized specimens subjected to bending, twisting, and nano-indentation tests were modeled and analyzed. The predicted size effects are generally in good agreement with previously published experimental results. Computational efforts are minimized and user versatilities are maximized by the proposed implementation.

Fabrication of Micro-Sized Specimen for Axial Compressive Strength Evaluation of Single Fiber Using UV Lithography and Its Testing Method

In this paper, a newly developed process to fabricate micro-sized specimen for axial compressive strength evaluation of single fiber using ultraviolet (UV) lithography was proposed. Technique of UV lithography, which was used in semiconductor production, was adopted to fabricate a test specimen that fiber was partially embedded in a photo-polymer. The photo-polymer SU-8 was used as a resist for high aspect ratio test specimen. A PBO fiber, which has excellent characteristics in tensile strength, tensile modulus and chemical resistance, was used as a test fiber material. Direct axial compression test was performed using the micro-compression testing machine with a flat indenter of 50 μm in diameter and two camera units. Finite element analysis was carried out to compute the internal stress distribution in the fiber under compression and to determine the optimum fiber length. The results showed that the proposed specimen fabrication method using UV lithography was demonstrated to be effective for direct measurement of the compressive strengths of PBO fibers. Finite element analysis revealed that the PBO fiber length in the compression test should be at least 20 μm to avoid the influence of fiber rooting in the resin. The experimental values obtained for the compressive strengths of PBO fibers exhibited Weibull distribution with a mean of 217 MPa, which is lower than the values generally obtained by other test methods such as the loop test or resin embedment test.

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.

Direct Observation of the Change in Microstructure with Deformation in Ferrous Lath Martensite by Using Micro-Sized Specimen

In the present study, the micro-sized cantilever-beam type specimens containing only one block of lath martensite were fabricated, and change in deformation microstructure inside a block with strain was observed directly by scanning electron microscopy and transmission electron microscopy. A number of slip bands appeared in the fixed end of the specimen by deformation. The propagations of slip bands, however, terminate due to the gradient of strain inside the specimen. The direction of slip bands changed during the propagation by the low angle boundaries inside the block. The shear localized region becomes narrow with an increase in strain. Furthermore, the width of laths increases greatly at the large strain region. The increase in width of laths is attributed to the disappearance of some initial lath boundaries by deformation.

204 水銀浸漬したオーステナイト系ステンレス細線の疲労強度評価(OS2-(1)オーガナイズドセッション《材料強度と構造設計》)

Micro-pipe will be used to inject microbubbles into flowing mercury in high power pulsed spallation neutron source. The effect of mercury immersion on the fatigue strength of 316-type stainless steel had been recognized using micro-size specimens. The mercury immersion attach is enhanced on the surface layer contact with mercury. In fact, the hardness of the surface layer was increased by the mercury immersion. Because the micro-pipe will be suffered with the flow induced vibration under flowing mercury and the immersion effect might be enhanced in micro-size range, it is indispensable to evaluate the effects of mercury and size on the fatigue. In the paper, we will show the preliminary results on the tensile fatigue strength of the micro-pipe with mercury immersion and discuss the size effects on the fatigue strength.

519 UVリソグラフィを用いた単繊維圧縮試験片の作製と試験方法の検討(GS8-4 材料力学)

519 UVリソグラフィを用いた単繊維圧縮試験片の作製と試験方法の検討(GS8-4 材料力学)

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.

In-situ Mechanical Testing of Micro-Sized Specimens Fabricated by FIB

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

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.

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.

液体急冷で作製した Nb-TiNi 水素透過合金膜のマイクロ破壊試験

The micromechanical tests have been performed for melt-spun Nb-TiNi ribbons, and the relation between the mechanical properties and microstructural change with heat treatment has been investigated. Micro-cantilever specimens with dimensions of 10(B)×20(W)×50(L)μm3 were prepared by focused ion beam (FIB) machining. Fracture tests were carried out at room temperature in air using a mechanical testing machine developed for micro-sized specimens. The fracture toughness value (KQ) of as-melt spun ribbon which consists of an amorphous phase was 5.3 MPam1/2. In contrast, the KQ of the melt-spun ribbon annealed at 773 K for 3.6 ks decreases to 2.8 MPam1/2. With annealing above 973 K fracture toughness increases again. This is due to the nanocrystallization of the amorphous phase and the formation of aggregates which are composed of B2-TiNi and bcc-Nb(Ti) phase with the cube-on-cube orientation relationship. These results suggest that the high temperature annealing is required for the application to the hydrogen permeation membrane.