Compressive Strain Values Research Articles

Usage of shape memory alloy actuators for large force active disassembly applications

Shape memory alloys (SMAs) possess inherent superior properties that make their applications in active disassembly an emerging and interesting field of research. This is because extremely large forces can be generated repeatedly using a small compact-sized element, such as an SMA actuator. To ensure the ability of the SMA actuator to generate a repeated large force or withstand repeated load, several factors should be considered. These include factors that affect the value of the generated recovery forces, such as the amount of strain used, activation temperature, activation time, and cross-sectional area of the SMA element. In general, the compressive strain can be considered as the most influential factor that affects the value of the generated recovery force. The present research investigates the possible use of the SMA actuator in large-force active disassembly applications. To the best of the authors' knowledge, all the studies conducted in this field are concerned with implementing active disassembly in applications requiring small disassembly forces. The present research was conducted in three phases. First, the behaviour of the SMA element upon exposure to different repetitive compressive strains was studied, and the generated recovery force and strain hardening induced in the material were considered to ensure the continuous generation of large recovery forces with the least amount of residual strain induced in the material. Second, the optimum value of the compressive strain required to generate the maximum force with the least amount of residual strain induced in the material was estimated. Third, a practical case study was presented to validate the possible implementation of SMA actuators in large force active disassembly applications. The study successfully estimated the optimum compressive strain value that generated the required recovery force to disassemble the conducted case study using active disassembly technique.

Design of Haul Roads in Open Cast Mines in India—A Mechanistic Design Approach

About 80% of total mining in India is carried out in coal sector through open cast mines where heavy dumpers are plying on the haul roads. Mine haul roads have witnessed an enormous increase in traffic density as well as hauling payloads in the recent past due to increase in coal mining activities. In the Indian scenario, the majority of these large open cast mines are facing the problems of under-performance due to inadequate design of mine haul roads resulting into fast deterioration through rutting and excessive settlement. The present design methodology used in India is broadly based on an empirical CBR (California Bearing Ratio) method. This method seems to have become irrational for optimum and practical design of the haul roads which carry the present-day heavy traffic. Through this paper, an attempt has been made to develop a design based on mechanistic design approach. The main criteria to ensure the structural safety of mine haul roads has been taken as vertical compressive strain over the subgrade which is responsible for rutting failure in a pavement. The critical value of vertical compressive strain has been estimated for the Indian mine conditions. KENPAVE software has been used to design an optimum haul road cross section for existing heavy axle loads and traffic density in open cast coal mines in India. In order to have better appreciation, an example has also been given which compares the design output using conventional and the mechanistic methods.

Behavior of concrete confined with epoxy bonded fiber ropes under axial load

In the past, several experimental and theoretical studies investigated the axial compressive strength and strain of plain concrete (PC) externally confined with natural and synthetic fiber reinforced polymer (FRP) composites. Typical types of synthetic FRP(s) are aramid, glass, carbon, PEN (polyethylene naphthalates) and PET (polyethylene terephthalate), whereas natural FRP(s) include flax, sisal, hemp and jute. In this article, the performance of a novel, low-cost and sustainable strengthening technique i.e., fiber rope reinforced polymer (FRRP) composites to enhance the axial compressive strength, strain and deformability of concrete specimens through external wrapping is explored. The outstanding benefits of the newly proposed FRRP composites are low-cost, wide availability, easy application and more environmentally friendly. In this research, 39 circular plain concrete (PC) cylinders were tested to failure under uniaxial compression. The research parameters covered fiber rope type (such as hemp, cotton and polyester) and number of FRRP layers. Experimental results proved that external confinement by using FRRP is very effective to enhance ultimate strength, strain and deformability of the concrete. Further, based on the test results, the implementation of the existing ultimate compressive strength and strain models established for the synthetic and natural FRP(s) is evaluated to assess their application to the newly proposed FRRP confinement. It is found that more or less all considered models do not accurately predict the tested ultimate compressive strength and strain of the FRRP-confined concrete. In the end, new ultimate strength and strain models are proposed to accurately predict the ultimate compressive strength and strain of concrete specimens confined with fiber rope reinforced polymer composites. The predicted ultimate compressive strength and strain values compare favorably with the experimental results of the present study.

Effect of γ phase on mechanical behavior and detwinning evolution of directionally solidified Ni-Mn-Ga alloys under uniaxial compression

Specimens with single-phase martensite, net-like γ/martensite mixed structure and lamella-like γ/martensite mixed structure were designed to investigate the effect of the γ phase on the mechanical behavior and the detwinning of non-modulated (NM) martensitic variant in Ni-rich Ni-Mn-Ga alloys under uniaxial compression. It can be found the existence of the γ phase significantly enhances the compressive stresses, and the net-like γ phase specimen presents a higher value of compressive strain than that of the lamella-like γ phase specimen. Especially, the detwinning plateau of the lamella-like γ phase specimen is almost invisible due to the martensite colonies with low Schmid factors. Finally, according to the calculation of deformation gradient tensor, we found that the tensors along compression direction (εzz) of net-like γ phase/martensite mixed structure specimen and single-phase martensite specimen are lower than that of the specimen with lamella-like γ phase/martensite mixed structure, which well explained the detwinning strain for these specimens. The present study not only highlights the role of γ phase on the mechanical behavior, but also provides more guidelines for the mechanical training of Ni-Mn-Ga shape memory alloys.

Analysis of Cementing Carbonation During Co2 Sequestration

Effects of global warming are well-known to be caused by emissions of greenhouse gases. As an effort to alleviate the gases production, Capture and Sequestration (CCS) is implied in oil and gas practices where carbon dioxide gas (CO2) is captured from different emission sites and injected into geological formations. However, problems arised in sequestration projects as exposure of CO2 degraded the Portland-based cement in the wellbore. Consecutively, the cement cracked and leakage of CO2 contaminated the underground drinking water. Hence, this paper aims to understand the physical and chemical reaction between CO2 and Class G cement further. Class G cement was obtained from Schlumberger Kemaman Supply Base and tested with water according to American Petroleum Institute (API) standard which water to cement ratio was set to 0:44:1. All of the samples were exposed to CO2 for six, eight and ten days accordingly and analyzed with unconfined compression, Field Emission-Scanning Electron Microscope (FESEM) and X-Ray Diffraction (XRD) testings. Ten days of CO2 exposure towards Class G cement showed the lowest compressive strength as to be compared to other samples. Carbonation reaction between water and CO2 was diagnosed to take place causing the cement to loose its strength. FESEM analysis on the other hand showed that the surface of the sample were uneven with long-shaped crystals with supporting XRD data presented large number of calcium carbonate ((Ca(CO)3). Nevertheless, the unexposed sample showed the opposite result with highest value of compressive strain and large number of calcium hydroxide ((Ca(OH)2).

Strained ultra-thin films of BaO: a molecular dynamics investigation

A recent theoretical work by Bousquet and collaborators have predicted that ferroelectric ordering could be induced in the rocksalt oxides of alkaline earth metals (BaO, MgO, CaO and SrO) by strain. The expected functional properties present in these strained binary oxides, like polarization, dielectric constant and piezoelectric response, would be comparable to those of typical ferroelectric perovskites. Consequently, the strained binary oxides would be promising materials for fabrication of devices like ferroelectric memories and sensors. One possible way to explore the potential underlying these theoretical predictions is to grow thin and ultra-thin films of these binary oxides under epitaxial strain by choosing an adequate substrate. In such systems the interplay between epitaxial strain and the lack of translational symmetry (limited film thickness) may lead to the formation of interesting (anti)ferroelectric phases. Our goal in this work is to explore the potential structural and functional phase diagram of BaO ultra-thin films (thickness of only 8 BaO layers, ≈ 20 nm) obtained for different values of compressive epitaxial strain and temperature by performing a molecular dynamics investigation. A polarized phase (antipolar) is observed at a compressive strain of -9.0%, wich resists till a melting temperature around 1500 K, which is indeed high for such an ultra-thin film.

Structure of materials ultrasonically consolidated from coarse-grained and nanostructured plates of commercially pure copper

Ultrasonic consolidation of commercially pure copper plates with coarse-grained and ultrafine grained structures was carried out. Copper plates in both states were joined by ultrasonic welding using the same route. Consolidated samples were studied in a cross section parallel to the oscillation direction. The compressive strain value and the joint quality in relation to the initial structure of the material were studied. It is shown that the ultrasonic consolidation is a promising method of additive manufacturing using bulk nanostructured materials.

Image-based anatomical reconstruction and pharmaco-mediated bone remodeling model applied to a femur with subtrochanteric fracture: A subject-specific finite element study

Patient-specific finite element (FE) models are constructed in a way that boundary conditions, material and geometric FE models respect the unique characteristics of the patients, offering a more reliable and realistic structural analysis. This study presents an image-based construction process of a patient-specific FE model applied to a femur with a subtrochanteric fracture. Available procedures are systematized and described in greater depth aiming to investigate the difficulties and possibilities in the development of this type of model. A set of image processing techniques (segmentation, labeling, morphological operations and registering) were performed for volumetric reconstruction and registration of femoral fragments by assessing computed tomography (CT) images in a semi supervised procedure. The CT numbers feed the FE mesh with a non-homogeneous distribution of elasticity modulus. A FE analysis and a bone remodeling simulation with pharmacological stimulus based on the dynamics of bone cells populations were also developed for this study. The FE analysis revealed that the principal stresses provided results close to those obtained using a generic homogeneous model, with a difference of about 2%. In contrast, principal strains presented significant differences, up to 12 and 21 % for the maximum tensile and compressive principal strain values, respectively. The critical values of tensile principal strains were located in the superior part of the femoral neck, a typical region of femoral fractures, and maximum principal strains 2 and 3 (compressive) were concentrated in the diaphyseal region, rather close to the actual fracture. These results corroborate previous works indicating that the strain-based failure criterion is more successful in capturing the bone fracture sites when compared to stress-based criteria. The attempt to reconstruct the material state before the failure as implemented here constitutes an innovative way to analyze and reconstruct bone fractures. In the bone remodeling simulation, the inclusion of an antiresorptive agent stimulus produced cortical bone thickening, an increase in the BMD biomarker, and an overall increase in the bone ash density, just as expected in an osteoporosis therapeutic treatment. In conclusion, this study highlights the advantages of subject-specific FE models compared to generic ones in the study of abnormal clinical cases, evaluation of fracture risk, and optimization of surgical intervention. On the other hand, the high level of human intervention and expertise involved in patient-specific FE analyses hinders the incorporation of this technique into clinical practice.

Effect of initial stress/strain state on the L10 phase formation of FePt in FePt/Au/FePt trilayers

The influence of the initial stress/strain state in FePt/Au/FePt thin films on the chemical L10-FePt formation after post-annealing is studied. It is shown that the level of stress/strain depends on the Au interlayer thickness revealing a correspondence in L10 ordering-onset temperature. Compressive strain present in the as-deposited films promotes lowering of the L10-FePt ordering temperature. A reduction of the onset temperature for ordering by 100 °C is observed in films having a 30-nm-thick intermediate Au layer compared to samples revealing lower compressive strain values. During annealing, the strain state caused by the difference in thermal expansion coefficients of FePt, Au, and substrate is relaxed during A1 → L10-FePt phase transformation. It is well known that the coercivity of FePt films rises with increasing fraction of the ordered L10-FePt phase. Furthermore, the insolubility of Au in the L10-FePt lattice results in Au diffusion predominantly along grain boundaries leading to magnetic FePt grain isolation, which in turn gives rise to enhanced coercivity. At an annealing temperature of 900 °C, coercivities as high as 27.5 kOe are achieved for FePt samples with an initial 30-nm-thick Au interlayer.

Mechanical properties of hollow polyester monofilament: Compression and tension behaviors

Comparative analysis has been performed on the mechanical properties of hollow and solid polyester monofilament with identical external diameter. Tensile test of hollow polyester monofilament was conducted to study the influence of hollow core and the manufacturing method on the tensile fracture mechanism of hollow monofilament. The compressive properties of hollow monofilament were determined to provide a bundle-compression method to study the behavior of hollow polyester monofilament under axial compressive loading and compare with solid one. The results show that the tensile property of the hollow monofilament has smaller breaking force and higher breaking elongation than solid monofilament in case of identical external diameter. Under compression loading, the solid monofilament show better compressive properties than hollow one with identical diameter. The hollow core only affects the values of compressive strain and stress, but it has no effect on the compression and deformation mechanism. The study results also show that the polyester monofilament can show better mechanical properties than the solid polyester monofilament for the same weight. This study can help to design the lighter textile materials with the hollow polyester monofilament.

Prediction of Magnetostrictive Properties of Fe-Ga Alloy Based on Internal Energy Model with Magnetomechanical Effect

Fe-Ga alloy is expected as energy harvest material having superior magnetostrictive properties. In this study, we compared angle dependence of amount of magnetostriction with ideal magnetostrictive model using cube-oriented single crystal Fe-18mol%Ga alloy. Magnetostriction in [100] of specimen was measured with changing the direction of statical magnetic field H by strain gauge. As a result, the measured magnetostriction could not fully explaind by traditional energy-based model of magnetostriction. We compared measurement result using strain gauge with calculation result using energy-based model. As a result, there was a large difference in maximum compressive strain value. We established modified energy-based model considering the deviation of magnetic domains so as to match the actual magnetostriction behavior.

High hole mobility in strained In0.25Ga0.75Sb quantum well with high quality Al0.95Ga0.05Sb buffer layer

We have demonstrated high hole mobility in strained In0.25Ga0.75Sb quantum well (QW) structure with a high quality Al0.95Ga0.05Sb buffer layer for future single channel complementary metal-oxide-semiconductor circuits. The Al0.95Ga0.05Sb buffer layer is important to achieve low substrate leakage and guarantee good channel material quality and high hole mobility. We grew buffer layers with various Sb effective flux conditions using molecular beam epitaxy to obtain high crystal quality and proper electrical properties. We systematically evaluated the relationship between the crystal quality and electrical properties using X-ray diffraction, atomic force microscope, Raman, and the Hall effect measurement system. Then, on this optimized buffer layer, we grew the In0.2Al0.8Sb/In0.25Ga0.75Sb/linear-graded Al0.8Ga0.2Sb QW structure to obtain high hole mobility with compressive strain. Moreover, the compressive strain and hole mobility were measured by Raman and Hall effect measurement system. The results show a compressive strain value of 1.1% in In0.25Ga0.75Sb QW channel, which is very close to the theoretical value of 1.1% from lattice mismatch, exhibiting the highest hole mobility of 1170 cm2/V s among reported mobility in In0.25Ga0.75Sb QW. Furthermore, it was able to be fabricated as p-type Fin-FET and shown the excellent electrical characteristics with low Smin and high gm.

Strain and electric field induced metallization in the GaX (X = N, P, As & Sb) monolayer

We investigate the strain and electric field dependent electronic properties of two dimensional Ga-based group III-V monolayer from the first-principles approach within density functional theory. The energy bandgap of GaX monolayer increases upto the certain value of compressive strain and then decreases. On the other hand, the energy bandgap of GaX monolayer is monotonically decreased with increasing tensile strain and become metallic at the higher value. Furthermore, the perpendicular electric field decreases the energy band gap of unstrained GaX monolayer and shows semiconductor to metal transition. These results suggest that the nature of energy bands and value of energy bandgap in GaX monolayer can be tuned by the biaxial mechanical strain or perpendicular electrical field. Additionally, we have also studied the optical response of unstrained GaX monolayer in term of optical conductivity. These findings may provide valuable information to develop the Ga-based optoelectronic devices and further the understanding of the GaX monolayer.

Mechanical properties of fullerite of various composition

Molecular dynamics simulation is used to study the structures of fullerite of various composition as well as their mechanical properties. Fullerites based on fullerene C60 with simple cubic and face-centered packing, fullerene-like molecule C48 and fullerene C240 with simple cubic packing are studied. Compliance and stiffness coefficients are calculated for fullerites C60 and C48. For fullerite C240, C60, and C48, deformation behavior under the effect of hydrostatic compression is also investigated. It is shown that the fullerenes in the fullerite remain almost spherical up to high values of compressive strain, as a result of which the fullerite is an elastic medium up to densities of 2.5 g/cm3. The increasing stiffness and strength under an applied compression is found for all the considered fullerites.

Biomimetic Rotated Lamellar Plywood Motifs by Additive Manufacturing of Metal Alloy Scaffolds for Bone Tissue Engineering.

Additive manufacturing presents opportunities to treat bone defects using biomimetic tissue scaffolds. Past investigations have explored modulating scaffold mechanical properties through varying materials and geometric motifs. Herein, we applied the rotated plywood structure of bone tissue to a 3D printed scaffold with the goal of improving mechanical performance compared to an orthogonal mesh design commonly used in tissue scaffold applications. The scaffolds were subjected to uniaxial compression followed by scanning electron microscopy and microcomputer tomography. The uniaxial compression test was characterized through elastic modulus (mean 1.32 GPa biomimetic, 0.196 GPa orthogonal, p < 0.001), ultimate compressive strength (mean 16.546 MPa biomimetic, 6.309 MPa orthogonal design, p < 0.001), and ultimate compressive strain values (4.867% biomimetic, 9.000% orthogonal, p < 0.005). Correlation of microfracture imaging to bulk scaffold mode of failure suggest that utilizing the biomimetic plywood design not only improved mechanical performance, but also reduced asymmetrtic buckling, plastic deformation, and fracture propagation similar to bone tissue.

Biomechanical analysis of immediately loaded implants according to the “All-on-Four” concept

PurposeThe purpose of this study was to investigate the biomechanical behavior of immediately loaded implants in an edentulous mandible according to the “All-on-Four” concept. MethodsA 3D-finite element model of an edentulous mandible was constructed. Four implants were placed between the bilateral mental foramen according to “All-on-Four” concept. A framework made of titanium or acrylic resin between the bilateral first molars was modeled. Immediate loading and a delayed loading protocol were simulated. A vertical load of 200N was applied at the cantilever or on the abutments region of the distal implants, simulating the absence of a cantilever. ResultsThe peak principal compressive strains in the immediate loading models resulted in 24.0–35.8% and 26.4–39.0% increases compared with the delayed loading models under non-cantilever loading and cantilever loading, respectively. The loading position greatly affected the principal compressive and tensile strain values. The peak principal compressive strains in non-cantilever loading resulted in a 45.3–52.6% reduction compared with those in cantilever loading. The framework material did not influence the peak compressive and tensile strain. The maximum micromotion at the bone–implant interface in the immediate loading models was 7.5–14.4μm. ConclusionsMandibular fixed full-arch prostheses without cantilevers may result in a favorable reduction of the peri-implant bone strain during the healing period, compared with cantilevers. The maximum micromotion was within the acceptable limits for uneventful implant osseointegration in the immediate loading models. Framework material did not play an important role in reducing the peri-implant bone strain and micromotion at the bone–implant interface.

Analysis of Microscopic Strain and Crystalline Structure in Ge/Ge1−X Sn x Fine Structures by Using Synchrotron X-ray Microdiffraction

The strain engineering is a promising technology not only for low-power CMOS but also for optoelectronic applications of germanium (Ge) devices compatible with the conventional silicon (Si) process technology [1]. In terms of CMOS applications, a uniaxial compressive strained Ge has drawn attention as high-mobility channel material in p-MOSFET which is expected to transcend that of conventional strained Si channel [2]. We are focusing on germanium-tin (Ge1−x Sn x ) as a source/drain (S/D) stressors to apply a uniaxial compressive strain into Ge in analogy with Si1−x Ge x S/D for strained Si channel. However, there are few reports of the local epitaxial growth of Ge1−x Sn x on patterned Ge substrate and the local strain technology of the Ge/Ge1−x Sn x heterostructures. Since the recent device dimensions of Si CMOS devices have reached the sub-100 nm scale in accordance with Moore’s law, the investigation of the microscopic crystalline and the strain structures for various next generation semiconductor materials has grown increasingly important. In this study, we experimentally characterized the local strain structure in Ge/Ge1−x Sn x fine heterostructures by using synchrotron x-ray microdiffraction method [3,4]. We prepared Ge stripe structures with various line widths (25–100 nm) sandwiched with Ge1−x Sn x stressors. Patterned Ge(001) substrate with a SiO­ 2 cap layer was formed by anisotropic wet/dry etching as lines parallel along to the <110> direction. The pitch of a Ge stripe is 500 nm. The Ge1−x Sn x layers were grown with solid-source molecular beam epitaxy (MBE) system and metal-organic chemical vapor deposition (MOCVD) system [5]. The Sn content in the Ge1−x Sn x was 2.9–6.5%. The x-ray microdiffraction measurement was performed at the beamline BL13XU in SPring-8 to analyze the local strain distribution and crystalline structure in Ge/Ge1−x Sn x samples. A synchrotron radiation light with an energy of 8 keV (λ=0.155 nm) was used. The cross-section size of an incident x-ray microbeam was estimated to be 0.16×0.20–0.82×0.26 μm2 in preliminary experiments. Transmission electron microscope observations revealed that Ge1−x Sn x were epitaxially grown on both sides of a Ge line, while the crystalline structure of Ge1−x Sn x on SiO2 on the top of Ge line was polycrystalline. We consider that the stressors of locally grown epitaxial Ge1−x Sn x can induce a local strain into the Ge line. In order to directly characterize the in-plane strain status in strained Ge region, we examined two-dimensional reciprocal space mapping (2DRSM) around the Ge1—1—3 asymmetric Bragg reflection with step scans of the microbeam position across the Ge lines with a step of 50 nm. Three diffraction peaks related to the bulk Ge, the epitaxial Ge1−x Sn x stressors, and the strained Ge are clearly observed in 2DRSM results. The intensity of diffraction peak of the strained Ge periodically varied corresponds to the stripe pitches. The diffraction peak position of the strained Ge in 2DRSM indicates an in-plane compressive strain is induced into a Ge line sandwiched with Ge1−x Sn x stressors. From the 2DRSM results for various Ge stripe widths, an in-plane strain value can be estimated from the lattice spacing with respect to that of bulk Ge. The in-plane compressive strain value in the Ge increases with narrowing the Ge line width and increasing the Sn content in the Ge1−x Sn x stressors, which is consistent with the simulated results of finite element method calculations. For the Ge0.943Sn0.057 stressors, the in-plane compressive strains were estimated to be 0.84%, 0.46% and 0.38% for 30, 60, and 100 nm-wide Ge lines, respectively. In summary, the formation of Ge/Ge1−x Sn x fine heterostructures were achieved by MBE and MOCVD, and experimentally characterized the local strain distribution in the Ge/Ge1−x Sn x by synchrotron radiation microdiffraction method. The microdiffraction enables a quantitative analysis of strain and an investigation of local crystalline structure in sub-100 nm-scale Ge lines sandwiched with Ge1−x Sn x stressors. This work was partly supported by the JSPS through the FIRST Program initiated by the CSTP, a Grant-in-Aid for Scientific Research (S) (Grant No. 26220605) and Core-to-Core Program ICRC-ACP4ULSI from the JSPS in Japan. The synchrotron radiation experiments were performed at SPring-8 with the approval of JASRI (Nos. 2012B1783, 2013A1682, 2013B1779, 2015A1874, and 2015B1813/BL13XU). [1] S. Zaima et al., Sci. Technol. Adv. Mater. 16, 043502 (2015). [2] T. Krishnamohan et al., IEDM Proc., 899 (2008). [3] S. Takeda et al., Jpn. J. Appl. Phys. 45, L1054 (2006). [4] Y. Imai et al., AIP Conf. Proc. 1221, 30 (2010). [5] Y. Inuzuka et al., Thin Solid Films 602, 7 (2016).

The microstructures and mechanical properties of Al-15Si-2.5Cu-0.5Mg/(wt%)B4C composites produced through hot pressing technique and subjected to hot extrusion

In this study, B4C (5, 10, and 15 wt%) particle-reinforced Ecka Alumix 231® aluminum matrix composites were produced through the hot pressing technique. Some of these samples were subjected to hot extrusion as a secondary treatment at 4:1 ratio at a temperature of 555 °C. The obtained samples were subjected to density measurement, hardness test, microstructure analysis, and three-point bending test, and their fracture surfaces were examined. A density of over 99% was found in the samples. Al-rich solid solution and primary Si, CuAl2, Al2CuMg, and Mg2Si phases in the microstructure were determined through X-ray diffraction analysis. Grain sizes were found to be 20 μm and 2 μm in the microstructures of the samples produced through hot pressing technique and of those subjected to additional hot extrusion, respectively. High hardness values were obtained in the samples subjected to hot extrusion. In these samples, wt% B4C particle ratio and transverse rupture strength increased considerably. Furthermore, the highest compressive strain value was obtained in the 10 wt% B4C particle-reinforced composites subjected to hot extrusion.

Analysis of Microscopic Strain and Crystalline Structure in Ge/Ge1−X Sn x Fine Structures by Using Synchrotron X-ray Microdiffraction

We examined the formation of locally strained Ge nanostructures sandwiched between Ge1−x Sn x stressors using metal-organic chemical vapor deposition method. We have investigated the microscopic local strain and stress in the Ge/Ge1−x Sn x heterostructures using synchrotron microdiffraction and finite element method calculation. The microdiffraction measurement for an asymmetric lattice plane enables directly quantitative evaluation of the strain value of an individual Ge fine line structure with a few tens of nanometers width. An in-plane compressive strain value of 0.9% is achieved for a 30 nm-width Ge line with Ge1−x Sn x stressors, which corresponds to a compressive stress of 1.2 GPa.

Microstructure and mechanical properties of AZ91 magnesium alloy developed by Spark Plasma Sintering

A gas atomised AZ91 powder has been consolidated by Spark Plasma Sintering (SPS) at different temperatures in the range of 310 °C–500 °C. The influence of the sintering temperature on the Al12Mg17 precipitation and the grain size was investigated through XRD, SEM and EDX analyses. The use of SPS on a metastable powder was demonstrated to be an effective processing route to control the precipitation process while keeping fine grains. Through the estimation of the Hall-Petch and Orowan strengthening, the benefit of this fine microstructure was quantified and the Hall-Petch contribution was revealed predominant. As a consequence for all sintering conditions, the values of resulting hardness (70–90 HV) and Yield Compressive Strength (YCS) (148–230 MPa) were equal or superior to those of the conventional cast AZ91 alloy in its aged T6 condition. The optimum microstructure was obtained for a sintering temperature of 380 °C, for which maximum values of Ultimate Compressive Strength (UCS) and strain at UCS were measured (327 MPa and 13.7%, respectively). These values correspond to an increase by 16% and 11% in comparison to the heat treated cast AZ91-T6 alloy. As for the hardness and YCS at this sintering temperature, they are 8% and 49% higher than those of the cast AZ91-T6 alloy. The study also highlighted that the lack of ductility under tensile testing remains an issue for Mg alloys processed by SPS.