Electromechanical Testing Research Articles

Fracture de la malléole médiale. Étude biomécanique des méthodes de fixation par cerclage métallique sous tension

BackgroundThis study compared the biomechanical properties of three different fixation methods of tension band wirings, used in the treatment of medial malleolus fractures. The first method used an innovative “handmade bent pin” for cerclage fixation. The second method used a U-shaped K-wire to attach the cerclage to the medial tibial cortex. These two novel fixation techniques were compared with the traditional tension band wiring technique, which is fixated to the bone by a screw. HypothesisNovel fixation techniques of tension band wiring provide stable fixation. Material and MethodsIn this study 27 artificial bone models, which medial malleolus fractures were simulated on, were used. Using an electromechanical test device, the force required to pull out each implant was assessed and compared. ResultsThis study found that; while handmade bent pinning resulted averagely 840.25 N (range: 647–1066,±118.72) and U-shaped K-wire fixation was 381.71 N (range: 176–651±150.2) pull out strength, traditional tension band wiring indicated 871.33 N (range: 549–1008,±137.74) pull out strength. DiscussionHandmade bent pinning method provides similar results with traditional tension band wiring. Therefore, in suitable cases, it may be an acceptable alternative to traditional tension band wiring techniques when treating malleolar fractures. Although the outcomes of U-shaped K wire fixation indicated lower than other two groups, the outcomes were comparable with the literature. So, while performing tension band wiring, both handmade fixation systems may be used in certain cases. For orthopaedic surgeons, it is better to know and think about these alternative handmade pinning systems created from simple K-wires during the surgery if needed. Level of evidenceIV, Biomechanical trial.

Influence of seawater ageing on the mechanical and damage self-sensing capability of glass fiber-MWCNT/epoxy laminates subjected to flexural loading by means of the electrical resistance approach

The self-sensing capability of multiscale composite laminates exposed to seawater ageing was investigated under monotonic and cyclic flexural loading. To this end, glass fiber fabrics were coated with multiwalled carbon nanotubes (MWCNTs) using different contents and then infused with epoxy resin under vacuum pressure. Dynamic mechanical analysis and three-point bending tests showed that the thermo-mechanical and flexural properties of composites were significantly affected due to seawater ageing as a consequence of plasticization of the matrix. However, the composites with 0.75 wt% MWCNTs help the composite to retain mayor part of its strength and strain to failure compared to the neat composite. Electromechanical tests of dry and wet composites under monotonic and cyclic flexural loading revealed that seawater ageing reduces the piezoresistive sensitivity, although the still were able to detect matrix cracking, fiber/matrix failure, delamination and fiber breakage. Cumulative counts of the residual change in resistance after each cycle were associated with plastic deformation for composites exposed to seawater ageing. Thus, the results demonstrated that electrical networks produced by spray-coated MWCNTs has good self-sensing capabilities for in situ damage detection and strain monitoring of composite laminates even after their exposition to seawater ageing, providing a feasible real-time monitoring technique of marine structures.

The capability of organic compounds to swell acrylonitrile butadiene O-rings and their effects on O-ring mechanical properties

As interest in replacing petroleum-derived aviation fuels with resilient, alternative fuels increases, the ability to derive correlations between the chemical compositions of aviation fuels and their properties and performance becomes more important. In this work, correlations between the exact chemical structures of organic compounds and their ability to increase the volume and decrease the tensile strength of Buna-N o-ring seals were explored. Buna-N o-ring seals are a representative group of essential seals in the hydraulic and pneumatic components of aircraft fuel delivery systems. They are utilized to prevent fuel leakage within the pumps, metering devices, and connectors. To measure the volume swell percent of o-ring seals caused by various organic compounds, a test rig was assembled that suspended o-ring seals in neat Sasol IPK (isoparaffinic kerosene) or in Sasol IPK doped individually with an organic compound at 8% by volume. Of the aromatic compounds tested, ethylbenzene and indane swelled o-ring seals most effectively, with volume swell percent values of 3.1 ± 0.2% and 2.8 ± 0.1%, respectively. In comparison, the approved aviation fuel Jet A/HEFA has volume swell percent value of 2.2 ± 0.2%. Alkylbenzenes with a smaller number of alkyl groups, less branching in the alkyl groups, and shorter alkyl chains caused greater swelling and greater decrease in the tensile strength for o-ring seals. Naphthene-containing aromatic compounds (i.e., indane and tetralin) swelled o-ring seals more effectively than alkylbenzenes with the same number of carbons (i.e., n-propylbenzene and n-butylbenzene). Therefore, steric hindrance seems to have an important impact on the ability of these compounds to swell o-rings. Nonaromatic unsaturated hydrocarbons, such as cyclohexene, were also found to swell o-ring seals to some extent. On the other hand, saturated hydrocarbons, such as cyclohexane, contributed to minimum or no swelling. Tensile strengths of intact o-rings were measured using an MTS Insight Electromechanical Testing Instrument. Aromatic compounds that facilitated greater swelling of o-ring seals also caused greater decrease in the tensile strength. For example, ethylbenzene and sec-butylbenzene, with volume swell percent values of 3.1 ± 0.2% and 0.9 ± 0.1%, respectively, reduced the o-ring tensile strength from 15.4 MPa to 13.6 MPa and 14.9 MPa, respectively. Additional experiments demonstrated that volume swell and tensile strength of o-ring seals are reversible properties. Hence, a decrease in tensile strength for o-ring seals does not imply irreversible damage. Overall, the extent of volume swelling and the lowering of tensile strength for o-ring seals was found to depend on the exact chemical structure of the organic compound.

Efficient energy-saving and multifunctional insulation coating

In order to improve the insulation property of walls, hollow ceramic microspheres are applied to produce insulation coating. The thermal conductivity meter and electro-mechanical universal testing machine controlled by the microcomputer are employed to do research on the impacts that different proportions of ingredients have on the thermal conductivity, tensile and bonding strength and waterproof performance. According to the experimental results, with the increase of hollow ceramic microspheres and the decrease of waterproof performance become worse. As a result, under the premise of ensuring the tensile strength and waterproof performance conform to the national standards, it is rational to increase the proportion of hollow ceramic microspheres as much as possible to achieve a betterthermal insulation performance.

Electromechanical Model-Based Design and Testing of Fiber Scanners for Endoscopy

Forward-viewing catheters and scopes for diagnosing disease and guiding interventions in small ducts (less than 3 mm diameter) require wide-field high-quality imaging since scope tip bending is difficult and ineffective. A high-fidelity electromechanically coupled finite element (FE) model of a piezoelectric actuated resonant fiber scanner is presented, which enables improvement on the general design of fiber-optic scanner geometry to increase scan frequency and field of view (FOV). Using the proposed model, parametric sweeps on the specific design variables achieved by acid etching of glass fiber are analyzed to identify their effect on scanner performance and to choose improved designs. The resulting complex fiber scanner design requires development of unique microfabrication techniques. Comparison of three model simulations and their experimental testing show that our proposed coupled model has prediction error of ≤12% with respect to experimental data, while other uncoupled models have up to 39% error. The model and microfabrication techniques presented in this paper have significance for fiber scanning-based systems in that they demonstrate reliability for model-driven design and also flexibility for fiber scanner design of complex geometries, allowing for improvement on medical imaging performance.

Fabrication of Dielectric Elastomer Composites by Locking a Pre-Stretched Fibrous TPU Network in EVA.

Dielectric elastomer (DE) composites with high electrical breakdown strength and large voltage-induced deformation were developed by retaining pre-stretched thermoplastic polyurethane (TPU) fibers in ethylene vinyl acetate copolymer (EVA). The microstructure of the candidate E-TPU fiber membrane and EVA coated E-TPU (E-TPU/EVA) film were characterized by scanning electron microscopy (SEM). The quasi-static and dynamic mechanical property, and the electromechanical properties, including the dielectric constant, dielectric loss tangent, and electromechanical sensitivity, of the DE composites were evaluated. Initially, tensile tests demonstrated that the DE composites based on E-TPU/EVAs had a higher elongation at break of above 1000% but a low elastic modulus of approximately 1.7 MPa. Furthermore, dielectric spectroscopy showed that the E-TPU/EVA had a dielectric constant of 4.5 at the frequency of 1000 Hz, which was 1.2 times higher than that of pure EVA film. Finally, it was found from electromechanical test that the voltage induced strain of E-TPU/EVA rose to 6%, nearly 3 times higher than that of pure TPU film, indicating an excellent electromechanical property. The DE composites developed have demonstrated the potential to be good candidate materials in the fields of artificial intelligence, biomimicry and renewable energy.

Tensile and compressive behaviour of S355 mild steel in a wide range of strain rates

This paper presents a comparison between mechanical compressive and tensile properties of S355 structural (mild) steel in a wide range of strain rates. A split Hopkinson pressure bar apparatus is used to investigate the dynamic compressive behaviour at high strain rates (740–5880 s−1). A hydro-pneumatic machine (5–25 s−1) and a modified split Hopkinson tensile bar apparatus (300–850 s−1) are used to study the strain rate sensitivity under dynamic tension. Quasi-static tensile and compressive tests are conducted on a universal electromechanical testing machine. The model parameters of two commonly used constitutive equations (Johnson–Cook and Cowper–Symonds) are also compared, separately for each model during compression and tension deformations.

Medial malleolus fractures: A biomechanical comparison of tension band wiring fixation methods

BackgroundThis study compared the biomechanical properties of three different fixation methods of tension band wirings, used in the treatment of medial malleolus fractures. The first method used an innovative “handmade bent pin” for cerclage fixation. The second method used a U-shaped K-wire to attach the cerclage to the medial tibial cortex. These two novel fixation techniques were compared with the traditional tension band wiring technique which is fixated to the bone by a screw. HypothesisNovel fixation techniques of tension band wiring provide stable fixation. Material and methodsIn this study 27 artificial bone models, which medial malleolus fractures were simulated on, were used. Using an electromechanical test device, the force required to pull out each implant was assessed and compared. ResultsThis study found that; while handmade bent pinning resulted averagely 840.25N (range: 647–1066±118.72) and U-shaped K-wire fixation was 381.71N (range: 176–651±150.2) pull out strength, traditional tension band wiring indicated 871.33N (range: 549–1008±137.74) pull out strength. DiscussionHandmade bent pinning method provide similar results with traditional tension band wiring. Therefore, in suitable cases, it may be an acceptable alternative to traditional tension band wiring techniques when treating malleolar fractures. Although the outcomes of U-shaped K-wire fixation indicated lower than other two groups, the outcomes were comparable with the literature. So while performing tension band wiring, both handmade fixation systems may be used in certain cases. For Orthopaedic surgeons, it is better to know and think about these alternative handmade pinning systems created from simple K-wires during the surgery if needed. Level of evidenceIV, Biomechanical trial.

Stainless Steel Microfibers for Strain-Sensing Smart Clay Bricks

Life cycle monitoring of structural health of civil constructions is crucial to guarantee users’ safety. An optimal structural health monitoring system allows to automatically detect, locate, and quantify any damage in structural elements, thus anticipating major risks of local or global failures. Critical issues affecting traditional monitoring systems are sensors’ placement, hardware durability, and long-term reliability of the measurements. Indeed, sensors’ deployment is crucial for an effective investigation of the static and dynamic characteristics of the structural system, whereby durability and long-term stability of sensing systems are necessary for long-term monitoring. A very attractive solution to some of these challenges is developing sensors made of the same, or similar, material of the structure being monitored, allowing a spatially distributed and long-term reliable monitoring system, by the use of self-sensing construction materials. Within this context, the authors have recently proposed new “smart clay bricks” that are strain-sensing clay bricks aimed at embedding intelligent monitoring capabilities within structural masonry buildings. While previous work focused on smart bricks doped with titanium dioxide and using embedded point electrodes, this work proposes an enhanced version of smart bricks based on the addition of conductive micro stainless steel fibers that possess higher electrical conductivity and a more suitable fiber-like aspect ratio for the intended application, as well as plate copper electrodes deployed on top and bottom surfaces of the bricks. The paper thus presents preparation and experimental characterization of the new smart bricks. The influence of different amounts of fibers is investigated, allowing the identification of their optimal content to maximize the gauge factor of the bricks. Both electrical and electromechanical experimental tests were performed. Overall, the presented results demonstrate that the new smart bricks proposed in this paper possess enhanced strain-sensing capabilities and could be effectively utilized as sensors within structural masonry buildings.

Mechanism of fracture of NiTi superelastic endodontic rotary instruments.

The aim is to investigate the premature catastrophic fracture produced for different periods during clinical endodontic treatment of two brands of NiTi endodontic rotary instruments. 3 samples as-received, 6 samples used with patients for 2 and 7 h and 5 samples fractured were studied for each brand of endodontic NiTi rotary instruments. Transformation temperatures (Ms, Mf, As and Af) and enthalpies of transformation were determined by calorimetry. Critical stresses until fracture (σβ→SIM, σSIM→β) were obtained using an electromechanical testing machine. The samples were also visualized by Scanning Electron Microscopy. Calorimetric studies have shown an increase of the Ms and As transformation temperatures with time of use as well as a decrease of their stress transformations. Moreover, reverse transformation enthalpies decreased along the time. The enthalpies of transformation decreased because martensitic plates were anchored, which prevented their transformation to austenite; thus losing its superelastic effect. The stabilisation of the martensitic plates induced the collapse of the structure and so the main cause for the fracture. The heat treatment proposed has been increased the life in service of NiTi superelastic endodontic instruments recovering theirs superelastic effect.

Shear-deformed fabric sensor made of P(VDF-TrFE) for damage detection of draped composite structures: A feasibility study

For the damage detection of complex-shaped composite structures fabricated by vacuum bag degassing molding with a draping process, a fabric sensor made of poly(vinylidene fluoride-trifluoroethylene), was constructed. Characterization of the fabric sensor by picture frame tests and an electromechanical test was carried out. The locking angle of the fabric sensor was around 30°, and the static sensitivity of the sensor increased with the shear angles owing to an overlapping effect. Subsequently, low-velocity impact tests were performed by using a drop-weight impact machine (2.35–7.06 J) to confirm the feasibility of the P(VDF-TrFE) fabric sensor for the damage characterization of the composite dome structures. As the first step of health monitoring method with a new type of sensor an estimation technique for the potential failure of the composite structures was suggested by considering the relationships between the impact energy and voltage signals from the fabric sensors.

Correlation between Electrical Transport and Nanoscale Strain in InAs/In0.6Ga0.4As Core-Shell Nanowires.

Free-standing semiconductor nanowires constitute an ideal material system for the direct manipulation of electrical and optical properties by strain engineering. In this study, we present a direct quantitative correlation between electrical conductivity and nanoscale lattice strain of individual InAs nanowires passivated with a thin epitaxial In0.6Ga0.4As shell. With an in situ electron microscopy electromechanical testing technique, we show that the piezoresistive response of the nanowires is greatly enhanced compared to bulk InAs, and that uniaxial elastic strain leads to increased conductivity, which can be explained by a strain-induced reduction in the band gap. In addition, we observe inhomogeneity in strain distribution, which could have a reverse effect on the conductivity by increasing the scattering of charge carriers. These results provide a direct correlation of nanoscale mechanical strain and electrical transport properties in free-standing nanostructures.

Determination of the crack resistance curve for intralaminar fiber tensile failure mode in polymer composites under high rate loading

This paper presents the determination of the crack resistance curve of the unidirectional carbon-epoxy composite material IM7-8552 for intralaminar fiber tensile failure under dynamic loading. The methodology, proposed by Catalanotti et al. (2014) for quasi-static loading conditions, was enhanced to high rate loading in the order of about 60 s−1. Dynamic tests were performed using a split-Hopkinson tension bar, while quasi-static reference tests were conducted on a standard electromechanical testing machine. Double-edge notched tension specimens of different sizes were tested to obtain the size effect law, which in combination with the concepts of the energy release rate is used to measure the entire crack resistance curve for the fiber tensile failure mode. Digital image correlation is applied to further verify the validity of the experiments performed at both static and dynamic loading. The data reduction methodology applied in this paper is suitable for intralaminar fiber failure modes without significant delamination. Sufficient proof is given that quasi-static fracture mechanics theory can also be used for the data reduction of the dynamic tests. It is shown, that the intralaminar fracture toughness for fiber tensile failure of UD IM7-8552 increases with increasing rate of loading.

Detection of Vertical Root Fractures Using Cone-Beam Computed Tomography in the Presence and Absence of Gutta-Percha.

Background Vertical root fractures (VRFs) can significantly reduce dental prognosis. Cone-beam computed tomography (CBCT) offers better visualization of VRF than conventional radiography. However, gutta-percha creates artifacts in cone-beam CT (CBCT) images and reduces the diagnosis quality. The purpose of this study was to evaluate the accuracy of CBCT in detection of VRF in presence and absence of gutta-percha in canals. Materials and Methods In this cross-sectional study, 50 extracted mandibular premolars were selected. After preparing the access cavity, canals were instrumented using step-back method, and gutta-percha #40 was placed afterwards. The fractures were created using electromechanical universal testing machine on 25 teeth. The teeth were randomly placed in dry mandibular dental sockets, and the first CBCTs were taken. Then the gutta-percha was removed, and the second CBCTs were taken. Results The results of Kappa coefficient between two observers in roots with and without gutta-percha were 0.644 and 0.830, respectively (p value ≤ 0.001). The sensitivity and specificity of VRF diagnosis in assessing gutta-percha filled canals were 32% and 68% for the first observer, respectively (Kappa < 0.000, p value = 1.000), and 40% and 68% for the second observer, respectively (Kappa = 0.080, p value = 0.556). The sensitivity and specificity of VRF diagnosis in assessing the empty canals (without gutta-percha) were 72% and 96% for the first observer, respectively (Kappa = 0.680, p value ≤ 0/001), and 72% and 96% for the second observer, respectively (Kappa = 0.680, p value ≤ 0/001). Conclusion The intracanal filling materials such as gutta-percha reduce the diagnostic ability of vertical root fractures. Hence, it is recommended to remove those materials from root canals before imaging to improve the diagnostic potential of CBCT.

Cracking effects in squashable and stretchable thin metal films on PDMS for flexible microsystems and electronics

Here, we study cracking of nanometre and sub-nanometre-thick metal lines (titanium, nickel, chromium, and gold) evaporated onto commercial polydimethylsiloxane (PDMS) substrates. Mechanical and electromechanical testing reveals potentially technologically useful effects by harnessing cracking. When the thin film metal lines are subjected to uniaxial longitudinal stretching, strain-induced cracks develop in the film. The regularity of the cracking is seen to depend on the applied longitudinal strain and film thickness—the findings suggest ordering and the possibility of creating metal mesas on flexible substrates without the necessity of lithography and etching. When the metal lines are aligned transversally to the direction of the applied strain, a Poisson effect-induced electrical ‘self-healing’ can be observed in the films. The Poisson effect causes process-induced cracks to short circuit, resulting in the lines being electrically conducting up to very high strains (~40%). Finally, cracking results in the observation of an enhanced transversal gauge factor which is ~50 times larger than the geometric gauge factor for continuous metal films—suggesting the possibility of high-sensitivity thin-film metal strain gauge flexible technology working up to high strains.

The Electromechanical Behavior of Dielectric Elastomer Actuator Stiffened by Fiber

Dielectric elastomer is functional material that can convert electrical energy to mechanical energy. In this paper, a cylindrical dielectric elastomer actuator was designed and fabricated by using fiber stiffening to improve its electromechanical performance. the effects of pre-straining, rate of applied voltage and fiber stiffening on the electromechanical behavior were investigated by the experiments. It was found that the best applied load for pre-straining was 524g based on the electromechanical tests at the applied voltage rate of 10V/s. The maximum actuated strain decreased with an increase in rate of applied voltage. When the fibers were embedded in the dielectric elastomer actuator, the maximum actuated strain was 27.5%, doubled the value of 14% without fiber stiffening at the applied voltage rate of 20V/s.

Carbon nanofiber-filled conductive silicone elastomers as soft, dry bioelectronic interfaces.

Soft and pliable conductive polymer composites hold promise for application as bioelectronic interfaces such as for electroencephalography (EEG). In clinical, laboratory, and real-world EEG there is a desire for dry, soft, and comfortable interfaces to the scalp that are capable of relaying the μV-level scalp potentials to signal processing electronics. A key challenge is that most material approaches are sensitive to deformation-induced shifts in electrical impedance associated with decreased signal-to-noise ratio. This is a particular concern in real-world environments where human motion is present. The entire set of brain information outside of tightly controlled laboratory or clinical settings are currently unobtainable due to this challenge. Here we explore the performance of an elastomeric material solution purposefully designed for dry, soft, comfortable scalp contact electrodes for EEG that is specifically targeted to have flat electrical impedance response to deformation to enable utilization in real world environments. A conductive carbon nanofiber filled polydimethylsiloxane (CNF-PDMS) elastomer was evaluated at three fill ratios (3, 4 and 7 volume percent). Electromechanical testing data is presented showing the influence of large compressive deformations on electrical impedance as well as the impact of filler loading on the elastomer stiffness. To evaluate usability for EEG, pre-recorded human EEG signals were replayed through the contact electrodes subjected to quasi-static compressive strains between zero and 35%. These tests show that conductive filler ratios well above the electrical percolation threshold are desirable in order to maximize signal-to-noise ratio and signal correlation with an ideal baseline. Increasing fill ratios yield increasingly flat electrical impedance response to large applied compressive deformations with a trade in increased material stiffness, and with nominal electrical impedance tunable over greater than 4 orders of magnitude. EEG performance was independent of filler loading above 4 vol % CNF (< 103 ohms).

Printed Wheatstone bridge with embedded polymer based piezoresistive sensors for strain sensing applications

Printed sensors find an increasing interest essentially due to their characteristics of flexibility and low cost per unit area. In this work a screen printed Wheatstone bridge is presented, suitable for strain sensing applications. A piezoresistive ink composite based on biocompatible thermoplastic elastomer styrene-ethylene/butylene-styrene (SEBS) as matrix and multi-walled carbon nanotubes (MWCNT) as nanofillers was used as a piezoresistive sensing material. Different deposition techniques, such as, screen printing, spray painting and drop casting were evaluated in order to optimize the resistance variation related to the piezoresistive effect. Several Wheatstone bridges with one and two sensors were designed to obtain an output sensitivity as a function of the strain submitted to the sensors. Further, different sensor geometries were evaluated to maximize the strain output sensitivity. Electro-mechanical bending tests showed a good linearity and a sensitivity up to 18 mV/V in the all screen printed half Wheatstone bridge output with two MWCNT/SEBS sensors.

Electro-mechanical endurance tests on smart fabrics under controlled axial and friction forces

The design, building and validation of machine for endurance tests on fabrics are described in this paper. The system is addressed to the reliability testing of smart fabrics with electrical conductivity. The development of e-textiles, in fact, requires innovative test benches for the evaluation of performances decay with load cycles accumulation; the proposed system is able to monitor the electro-mechanical parameters of fabric sample in the same time in order to support industrial development and predict failures on final applications.

Relationship between micro-structure and mechanical properties of dissimilar aluminum alloy plates by friction stir welding

Friction stir welding can be applied to weld dissimilar aluminum alloys which have different chemical and mechanical properties without causing any weld defects under a wide range of welding conditions. In this study, AA2024-T3 and AA6063-T6 aluminum alloys were selected and successfully welded in butt position together using by friction stir welding. The welding trials were conducted using different rotational speed and traverse speed conditions also investigating their effect on mechanical and micro-structural behavior of friction stir welding joints. The micro-structural evolution of the material was analyzed by optical observations and scanning electron microscopy inspections of the weld cross-sections. Tension and fatigue studies were also employed to the study. On the other hand, the fracture characterizations of samples were examined by scanning electron microscopy. Fatigue tests were performed by using a resonant electro-mechanical fatigue testing machine by axial bending fatigue test procedure. The fatigue strength has been analyzed drawing S-N curves. Experimental results indicate that micro-structural and mechanical properties are significantly affected by changing welding parameters within the chosen range of welding conditions.