Tensile Strain Measurements Research Articles

Hierarchical porous biomass-derived carbon with rich nitrogen doping for high-performance microwave absorption and tensile strain sensing

Carbon materials with porous structure and heteroatom doping have been proposed as promising microwave absorption materials. The development of materials with the integration of multiple functions is one of the main development directions and challenges of microwave absorbers. Herein, rich nitrogen-doped biomass-derived carbon (NBC) with coexistence of mesopores and macropores is developed from banana peels by hydrothermal and activation-assisted carbonization methods. The NBC exhibits excellent microwave absorption ability with thin thickness, light weight, broadband and strong absorption features. By mixing with paraffin (5 wt% NBC loading), the minimum reflection loss and effective absorption bandwidth of the composite can reach −53 dB and 4.22 GHz at a thin thickness of 1.70 mm. The corresponding specific reflection loss can reach −311.76 dB/cm, which is among the best of most-reported biomass-derived carbon microwave absorbers. On the other hand, through the reinforcement of thermoplastic polyurethane (TPU), the NBC/TPU composite exhibits good cyclic stability in tensile strain measurements. Furthermore, by integrating the strain sensor with an electrochemical metallization memristor and a resistor, a skin-inspired strain-memory which can retain the information after the remove of external stretch was presented as a proof of concept. This work provides a simple and effective method to develop multifunctional materials for microwave absorption and tensile strain sensing.

Composite Mechanical Properties of Coils Made With Nickel-Alloy Laminated Bi-2223 Conductors

High-temperature superconducting magnet coils made with Sumitomo Type HT-NX are complex composite structures composed of Bi-2223 conductor filaments, silver matrix, solder, nickel-alloy laminations, polymer insulation, and epoxy or wax. The mechanical properties of these composites are required inputs to a correct stress analysis. Measurements of the desired properties are performed on representative model test specimens. Mechanical test specimens composed of several layers of insulated conductor are prepared by cutting to length, stacking and epoxy impregnation. Mechanical tests are performed in liquid nitrogen and liquid helium. Elastic constants are found from tensile strain measurements in the conductor longitudinal, or coil hoop, direction and from compressive strain measurements in the conductor transverse, or coil radial and axial directions.

Impact of high UV fluences on the mechanical and sensing properties of polymer optical fibers for high strain measurements.

PMMA-based fibers are widely studied for strain measurements and show repeatable results for Fiber Bragg Gratings (FBGs) inscribed using 325 nm laser and 248 nm laser. However, there is no available material mechanical behavior characterization of the UV source impact on the fiber properties. In this manuscript, fibers are irradiated with high fluence of 325 nm and 248 nm lasers and the fibers properties are investigated using dynamic mechanical analysis and tensile strain for potential use of these fibers past the yield point. It is demonstrated that the UV sources shifted the ultimate tensile strength and changed the strain hardening behavior. Tensile strain measurements show excellent repeatability for gratings inscribed with these two sources with similar sensitivity of 1.305 nm/mɛ for FBG inscribe with 325 nm laser, and 1.345 nm/mɛ for grating written with 248 nm laser in the range 0 to 1.5 % elongation. Furthermore, tests far beyond the yield point (up to 2.8 % elongation) show that grating inscribed with lower UV wavelength exhibit hysteresis. Finally, we demonstrate that 248 nm laser fluence shall be chosen carefully whereas even high 325 nm laser fluence do not critically impact the sensor properties.

Fiber-optic sensor implanted with seven-core helical structure for measurement of tensile strain and extrusion bending

We proposed a fiber-optic sensor implanted with helical seven-core structure based on Mach–Zehnder interference, which can be used for the measurement of tensile strain and extrusion bending. The sensor consisted of a section of seven-core optical fiber with helical structure, which can be described as the SMF-Taper-HSCF-Taper-SMF (HSCF, helical seven-core fiber) sensor. When stretching or bending is applied, the sensor will undergo certain deformation, which will lead to the changes of interference modes in the optical fiber. The tensile strain and extrusion bending can be measured accurately according to the response of transmission spectrum to mode change. The helical seven-core structure can effectively stimulate higher order modes and induced deformation changes. In the experiment, three sensors with different helical periods were fabricated and their spectral characteristics were analyzed. Finally, we selected the sensor with a helical period of 190 μm to conduct a strain and bending test. The results show that the strain sensitivity of the sensor is −21.31 pm / μe in the range of 0 to 500 μe, and the curvature sensitivity of the sensor is −6.36 nm / m − 1 in the range of 0.16 to 1.6 m − 1. This sensor can detect strain and bending and has stable sensing performance and high sensitivity.

Efficiency and safety of genipin collagen crosslinking on rabbit cornea stroma model in vivo

Objective To evaluate the efficiency and safety of genipin collagen crosslinking (G-CXL) on rabbit corneas in vivo. Methods Forty healthy New Zealand white rabbits were randomly divided into 0.20% G-CXL, 0.25% G-CXL, standard UVA-CXL and normal control group.And the right eyes were treated in different grouping.No procedures were performed in the normal control group.The corneal curvature (Km) and central corneal thickness (CCT) of right eyes were evaluated before, 7 days and 14 days after crosslinking treatment.Cornea strips were harvested from the right eyes and tensile strain measurements were performed 7 days and 14 days after crosslinking treatment.The structure of corneal stroma was observed under light microscope (LM) and transmission electron microscope (TEM). Results No statistically significant differences in Km were observed among different groups or different timepoints (Fgroup=0.301, P=0.825; Ftime=1.287, P=0.284). Significant difference in CCTs was noticed among different time pionts (Ftime=3.786, P=0.029). Compared with preoperative, the CCTs of all the groups were significantly increased 7 days after crosslinking (all at P 0.05). Forteen days after crosslinking treatment, Young's modulus at 10% strain was (16.65±3.19), (19.12±2.39), (22.83±4.38) and (12.70±2.72)MPa in 0.20% G-CXL group, 0.25% G-CXL group, UVA-CXL group and normal control group, respectively; stress at 10% strain was (0.83±0.12), (0.97±0.04), (1.23±0.30) and (0.65±0.20)MPa, respectively; the Young's modulus and stress in UVA-CXL group was significantly increased, when compared with 0.20% G-CXL group and normal control group (all at P<0.05). Statistical significance of stress was observed between 0.25% G-CXL group and UVA-CXL group (P=0.046). There is no significant difference in Young's modulus between 0.25% G-CXL and UVA-CXL group (P=0.090). LM showed the reduction of keratocytes existed in superficial stroma of 0.20% and 0.25% G-CXL groups, while the reduction of keratocyte was found in anterior and intermediate stroma of UVA-CXL group.In 0.20% and 0.25% G-CXL groups, the ultrastructure of keratocytes was normal except vacuole in some keratocytes.Keratocytes apoptosis was noticed in UVA-CXL group and keratocytes was normal in deep stroma under TEM. Conclusions 0.25% has a similar biomechanics effect when compared to UVA-CXL.Moreover, histological observation proves a better safety of G-CXL in comparison of UVA-CXL. Key words: Corneal collagen crosslinking; Genipin; Biomechanics; Keratocyte; Transmission electron microscope

Fabrication and characterization of planar Bragg gratings in TOPAS polymer substrates

We report on the fabrication of polymer planar waveguides with inscribed Bragg gratings in TOPAS employing an efficient UV based single writing step technique using excimer laser. Phase shifting Mach–Zehnder interferometry indicates an UV induced increase of the refractive index in TOPAS of 6×10−4 and a modification depth of about 30μm, respectively. The planar Bragg grating structures in the cyclo-olefin copolymer are characterized by a high reflectivity of about 93% and are studied with respect to their potential in optical waveguide sensing, namely temperature and strain sensing. While the Bragg reflection shows almost no cross sensitivity against humidity, it exhibits a spectral blue shift with increasing temperature of −6.5pm/°C after multiple thermal annealing cycles. Compressive and tensile strain measurements reveal a sensitivity of 0.70pm/μɛ.

Simultaneous measurement of strain and temperature by employing fiber Mach-Zehnder interferometer

We demonstrated a novel fiber in-line Mach-Zehnder interferometer (MZI) with a large fringe visibility of up to 17 dB, which was fabricated by misaligned splicing a short section of thin core fiber between two sections of standard single-mode fiber. Such a MZI could be used to realize simultaneous measurement of tensile strain and temperature. Tensile strain was measured with an ultrahigh sensitivity of -0.023 dB/μɛ via the intensity modulation of interference fringes, and temperature was measured with a high sensitivity of 51 pm/°C via the wavelength modulation of interference fringe. That is, the MZI-based sensor overcomes the cross-sensitivity problem between tensile strain and temperature by means of different demodulation methods. Moreover, this proposed sensor exhibits the advantages of low-cost, extremely simple structure, compact size (only about 10 mm), and good repeatability.

Reinforcement Tensile Behavior under Cyclic Moving Wheel Loads

Numerous studies have revealed the benefits of using geogrids in a flexible pavement, especially for reducing permanent deformation. One of the questions that remain about the effectiveness of a geogrid in reinforcing of pavement is the extent to which the geogrid is engaged and mobilized throughout its service. This paper presents results of a laboratory study on various geogrid products embedded in flexible-pavement sections. The laboratory-scale pavement sections were subjected to cyclic moving wheel loads by using reduced-scale accelerated pavement testing (APT). During the APT, strains that developed in the geogrids were measured at intervals of loading applications by strain gauges installed in pairs on the upper and lower surfaces of the geogrid ribs. Permanent deformation of the subgrade was also measured at the same intervals of loading applications. The measurements of geogrid strains throughout the construction process indicated that the construction resulted in a considerable prestressing effect on the geogrids. Measurements from the individual strain gauges in pairs showed that the gauges installed on the upper surfaces of the ribs were in compression while those on the lower surfaces were in tension; the situation suggested a significant effect on the flexural deflection of the ribs on the tensile strain measurements from the strain gauges. Furthermore, it was observed that geogrid ribs in the longitudinal direction of traffic loading were not mobilized, while considerable strains were developed in geogrid ribs in the direction transverse to traffic loading. A clear correlation was found between the reinforcing forces developed in the geogrids and the performance of the reinforced subgrade in relation to resisting permanent deformation.

Mechanical characterisation of flax-based woven fabrics and in situ measurements of tow tensile strain during the shape forming

Forming complex shape composite parts with a good production rate/cost ratio is of particular importance for the automotive industry. The sheet forming of woven reinforcements is a promising technique, especially if complex shapes with singularities such as case corners can be obtained. Due to the more and more important recycling needs, the use of flax fibre based reinforcements may be considered for structural or semi-structural parts. During the sheet forming of a tetrahedron shape, the tows constituting the architecture of the reinforcement material are submitted to tensile strains. When using glass or carbon fibre tows, strains to failure are generally not reached. When flax-based fabrics are considered, the failure/degradation strength of the tows constituting the fabric may be reached. Even if no apparent failure is visible when observing the tows during forming, the strains measured by a mark tracking method indicate that the degradation limit of particular tows of the preform has been reached. This could lead to local lack of fibre density and to possible zones of weakness for the composite part. As a consequence, it is essential to improve the tensile performances of the tows constituting the fabric without losing their good impregnation characteristics and good ability to reach high mechanical properties for the composite part.

A Novel Concept for Strain Sensing Based on the Ferromagnetic Shape Memory Alloy NiMnGa

This paper reports on a novel approach of using magnetic shape memory (MSM) alloys as smart materials in mechanical sensing. The presented concept enables the measurement of tensile strain. The underlying sensor mechanism is based on the reorientation of the martensite variants of the tetragonal unit cell of the MSM alloy (MSMA) which can be induced by either a magnetic field or a mechanical stress. In the novel concept, a magnetic bias field exerts a restoring force opposing the externally applied mechanical stress. The magnetic stray field at the rim of an MSMA sample, measured using a conventional Hall sensor, is used as the sensor signal. The operating principle was experimentally verified using a custom-made tensile test setup. A linear dependence of the magnetic flux density of the stray field on the mechanical strain was observed.

Bending strain analysis considering a shift of the neutral axis for YBCO coated conductorswith and without a Cu stabilizing layer

Bending tolerance is one of the most fundamental mechanical propertiesof YBCO coated conductors for application to a superconductingcoil. In order to reveal the origin of the difference in critical current (Ic) with bending radius among various conductors, it is essential to estimate the bendingstrain at a superconducting layer. In this study, the bending strain was evaluated bothexperimentally and analytically for YBCO coated conductors with and without a Custabilizing layer. The internal tensile and bending strain of YBCO film in a compositeconductor was directly evaluated from the shift of the Bragg peaks of a YBCO film usingsynchrotron radiation. We also present an analytical method to calculate the neutral axisposition by considering its shift due to the progress of plastic deformation of thecomponents such as Cu, Ag and Hastelloy. The validity of our strain analysis wasconfirmed by agreement of the measured and calculated internal bending strains. Thecalculation result shows that yielding of the Cu stabilizing layer has a stronginfluence on the position of the neutral axis and results in a weaker dependence ofIc. A comparison with tensile strain measurements shows that the effect of bending can bepredicted from the tensile strain dependence.

Critical tensile and compressive strains for cracking of Al2O3 films grown by atomic layer deposition

Al2O3 atomic layer deposition (ALD) is a model ALD system and Al2O3 ALD films are excellent gas diffusion barrier on polymers. However, little is known about the response of Al2O3 ALD films to strain and the potential film cracking that would restrict the utility of gas diffusion barrier films. To understand the mechanical limitations of Al2O3 ALD films, the critical strains at which the Al2O3 ALD films will crack were determined for both tensile and compressive strains. The tensile strain measurements were obtained using a fluorescent tagging technique to image the cracks. The results showed that the critical tensile strain is higher for thinner thicknesses of the Al2O3 ALD film on heat-stabilized polyethylene naphthalate (HSPEN) substrates. A low critical tensile strain of 0.52% was measured for a film thickness of 80 nm. The critical tensile strain increased to 2.4% at a film thickness of 5 nm. In accordance with fracture mechanics modeling, the critical tensile strains and the saturation crack densities scaled as (1/h)1/2 where h is the Al2O3 ALD film thickness. The fracture toughness for cracking, KIC, of the Al2O3 ALD film was also determined to be KIC = 2.30 MPa m1/2. Thinner Al2O3 ALD film thicknesses also had higher critical strains for cracking from compressive strains. Field-emission scanning electron microscopy (FE-SEM) images revealed that Al2O3 ALD films with thicknesses of 30–50 nm on Teflon fluorinated ethylene propylene (FEP) substrates cracked at a critical compressive strain of ∼1.0%. The critical compressive strain increased to ∼2.0% at a film thickness of ∼20 nm. A comparison of the critical tensile strains on HSPEN substrates and critical compressive strains on Teflon FEP substrates revealed some similarities. The critical strain was ∼1.0% for film thicknesses of 30–50 nm for both tensile and compressive strains. The critical compressive strain then increased more rapidly than the critical tensile strain for thinner films with thicknesses &amp;lt; 30 nm. The high critical tensile and compressive strains for thin Al2O3 ALD films should be very useful for flexible gas diffusion barriers on polymers.

Strengthening effect of Cr 2O 3 thermally grown on alloy 617 foils at high temperature

Alloy 617 has been selected for the intermediate heat exchanger (IHX) of the very high temperature gas-cooled reactor (VHTR) for the economic production of electricity and hydrogen. In this work, the strengthening effects of Cr 2O 3 thermally grown on alloy 617 foils at 800 and 900 °C were investigated. A micro-tensile test system was used for in situ measurement of tensile strain in the foils and superficial thermally-grown Cr 2O 3. Each foil was heated until the thermally-grown Cr 2O 3 reached a predetermined thickness; then, a load was applied to measure the tensile response. As the Cr 2O 3 layer thickened on the surface of the metal foils, the strengths and stiffnesses of the foils were enhanced. We assumed that there was no interaction between the substrate and the superficial chromia, and the strength of Cr 2O 3 itself was measured. At 800 °C, the Cr 2O 3 was brittle and the strength was governed by crack initiation. At 900 °C, the Cr 2O 3 was much more ductile, and strain hardening was observed for even the smallest thickness. The strength was maintained even after crack initiation was observed on the surface.

Effect of genipin collagen crosslinking on porcine corneas

To evaluate the effect of genipin, a natural crosslinker, on porcine corneas. Department of Ophthalmology, Universidad Nacional de Colombia, Bogota, Colombia. Corneal strips (12.0 mm x 2.3 mm) were harvested from porcine eyes and treated by incubation with genipin at concentrations of 1.00%, 0.25%, and 0.10%. Parallel corneal strips from the same eye were used as untreated controls. After treatment at 20 degrees C for 40 minutes, tensile strain measurements were performed in a biomaterial tester. Porcine button corneas were treated with genipin 0.25% for 15 minutes and then digested by bacterial collagenase. Treated and untreated corneas were evaluated by light microscopy. Young modulus and stiffness in treated corneas increased in a concentration-dependent manner. Genipin increased resistance to corneal collagenase 5-fold in comparison with the controls. A decrease in the interlamellar space in treated corneas was also observed. Corneal collagen crosslinking induced with genipin produced a significant increase in biomechanical strength and resistance to bacterial collagenase. This crosslinker could be useful in treating corneal ectasia and corneal infectious and noninfectious diseases involving corneal melting.

Particulate ionomer films prepared from dispersions of crosslinked polymer colloids: A structure–property study

Polymers with properties that are governed by ionic interactions in discrete regions are termed ionomers. This work presents a comprehensive study of polymer films prepared from dispersions of crosslinked poly(butadiene/methacrylic acid) (poly(Bd/MAA)) particles in water. We showed recently [O. Pinprayoon, R. Groves, B.R. Saunders, J. Colloid Interface Sci. 321 (2008) 315–322] that poly(Bd/MAA) particles could be considered to have a core-shell structure with a MAA-rich shell. The poly(Bd/MAA) dispersions used here contained added ZnO particles which provided a source of Zn 2+. The films were investigated using AFM, FTIR, small-angle X-ray scattering (SAXS), dynamic mechanical thermal analysis (DMTA) and tensile stress vs. strain measurements. The films showed differences and similarities to conventional ionomers which are discussed. The FTIR data revealed that the Zn 2+ ions formed ionic crosslinks with the carboxylate groups (RCOO −). Mechanical property studies were conducted using DMTA and stress vs. strain measurements. The DMTA data revealed evidence of two main phases in the systems: a poly(Bd)-rich phase and a poly(MAA)-rich phase. A third phase was also found; which was ascribed to an interphase between the particle core and shell. The SAXS data showed that the films were composed of distinct poly(Bd/MAA) particles, implying that only partial coalescence occurred across the particle interfaces during formation of these particulate ionomer films. Ionic crosslinking of the particles was suggested to occur in the interfacial region (knit regions). The SAXS data also showed scattering from Zn 2+(RCOO −) ionic-aggregates. These ionic aggregates had an average separation of 2.9 nm, which is much smaller than that for conventional ionomers. Interestingly, the concentration of these aggregates passed through a maximum and decreased as the degree of neutralisation of the MAA groups approached 100%. A conceptual model for the structure of these unconventional ionomers is discussed.

Optical fiber sensor for tensile and compressive strain measurements by white-light Fabry–Perot interferometry

Based on the theory of optical fiber coupling and Fabry–Perot interference, a model of extrinsic Fabry–Perot interferometric (EFPI) optical fiber sensor for measuring strain is analyzed, and the theoretical model is demonstrated. A formula of white-light interfered EFPI optical fiber strain sensor is obtained. The system of the optical fiber sensor is designed using an LED source as light source to obtain reflected spectrum. The experimental results show that it coincides well with the computational simulation of theoretical model, which means the model is accurate.

Tensile strain measurement using mechanical and in situ optical techniques in bi-metallic Ni-base superalloys

The mechanical performance in terms of tensile properties of a nickel-base superalloy bi-material was investigated, to study the tensile strength of the joint. The results of strain measurement and control by means of usual clip-on extensometry, which gives the overall strain, cannot reveal the local deformation. To have more detail about the local strain fields, particularly in the vicinity of the interface which remains the most brittle part of the bi-metal, an in situ image capture and processing technique adapted from particle image velocimetry was used. The two techniques showed a perfect correlation with the peculiarity of a precise assessment of the local strain in the case of the optical method. Tensile curves obtained at constant strain rate showed serrated yielding associated with inhomogeneous plastic flow at high temperatures. This instability of strain rate softening type (strain localization) was well detected by means of the optical technique.

Measurement of Continuous Micro-Tensile Strain Using Micro-ESPI Technique

To determine the micro-mechanical properties for micro/nano materials, it may be essential to measure the strain/deformation during micro-mechanical testing. Therefore, in this study, continuous measurement of in-plane tensile strain in micro-sized specimens of thin film materials was introduced using the micro-ESPI technique. TiN and Au thin films 1 and 0.47µm thick, respectively, were deposited on the silicon wafer and fabricated into the micro-sized tensile specimens by the electromachining process. The micro-tensile loading system and micro-ESPI system were developed to measure the tensile strain during micro-tensile loading. Micro-tensile stress-strain curves for these materials were determined using the algorithm for continuous strain measurement. Furthermore, the new algorithm for enhancing the sensitivity to measurement of in-plane tensile strain was suggested. Using the algorithm, micro-tensile strain data between interfringes were calculated. It is shown that the algorithm for enhancement of the sensitivity suggested in this study makes the sensitivity to the in-plane tensile strain increase.

Study of the stress-assisted two-way memory effect of a Ti–Ni–Cu alloy using resistivity and thermoelectric power techniques

The stress-assisted two-way memory effect has been studied for successive cycles in a Ti–Ni–Cu alloy for two different thermo-mechanical treatments: recovery annealed (TT425) and fully recrystallized. Simultaneous tensile strain and electrical resistance measurements have been performed as a function of temperature and for different applied stresses. The thermoelectric power (TEP) in the stressed martensitic state has also been measured. For the treatment TT425 corresponding to 30% cold drawing followed by 425 °C annealing, a stable reversible strain ε m-β of 4.5% at maximum is found. A relatively low plastic strain ε p occurs for stresses above 125 MPa, which increases with the number of thermal cycles. For the recrystallized treatment, the maximum amplitude of the reversible strain is almost the same but a quite large plastic strain occurs even at 50 MPa and strongly increases with the number of cycles, reaching 12% for 20 cycles at 200 MPa. It is shown that the electrical resistivity change, associated with the reverse transformation, increases linearly with the reversible strain ε m-β. This effect is related to the electrical resistivity anisotropy of the martensite, with the slope being slightly different for the two treatments. In addition, the resistivity is relatively insensitive to the plastic strain. The TEP and the resistivity are sensitive to the orientation of the martensite, but the TEP also strongly depends on the plastic strain.

Properties and performance of sulfide-substituted plasticized poly(vinyl chloride) as a biomaterial.

Plasticized poly(vinyl chloride) (PVC) was surface modified by nucleophilic substitution of the chlorine atoms of PVC by sulfide ions in aqueous media in the presence of a phase-transfer catalyst (PTC) to make it migration resistant. The modified PVC was sterilized by steam autoclaving and gamma radiation and subjected to plasticizer extraction in an extraction medium such as hexane. Virtually no plasticizer migrated out of modified PVC into the medium even after prolonged incubation for 30 d. The properties of the modified surface were evaluated by contact angle measurements, scanning electron microscopy (SEM), cell-culture studies, hemolysis assay, and whole-blood clotting time measurements. The mechanical properties of modified sheets were evaluated by measurements of tensile strength and strain at break after subjecting the specimens to different modes of sterilization. The modified PVC surface showed enhanced wettability and was found to be non-hemolytic and non-cytotoxic. Whole-blood clotting profiles of unmodified and modified PVC were virtually the same. Modification imparted slight yellow color to the material. Surface modification resulted in an 8% decrease in the ultimate stress and 28% decrease in the strain at break values. The sulfide-substituted PVC was found to be blood compatible and would be useful in applications such as tubing for transfusion, dialysis etc., where migration resistance is important.