Resistance-type Strain Research Articles

Ground testing of Al-polyurethane shape memory polymer sail material under pulsed light exposure

This article presents a study on design and testing of space sails using Al-polyurethane Shape memory polymer. The properties of the polymer are simulated and tested in the design phase, and the results are compared with the fabricated sail, which is considered nominal. The efficiency of the polyurethane sail is found to be approximately 86.5%. The controllability of the sail is enhanced using a heating system that uses light rays to heat the polymer at specific control spots. The relative deflection at these spots causes a deviation in solar momentum, resulting in a controlled displacement of the sail. This control system is found to be 42% more efficient than conventional vane-type deflection systems. The paper also presents the fabrication of a ground testing apparatus designed to test the sail specimen in laboratory conditions. The apparatus is capable of producing a vacuum chamber pressure up to −400 mm/Hg and includes a magnetic levitation platform with strong permanent magnets to neglect local gravitational effects. The platform provides support for fixing the solar sail frame made from carbon fiber composite material. The testing apparatus consists of a 1000-W halogen light source with intensity ranges of approximately 200,000 lux. Sail material with a reflective surface is exposed to controlled luminance under vacuum conditions to measure the deflection of the sail. Deflection values are recorded by means of a resistance type strain gauge and strain indicator arrangement. Plotting deflections with time period gives the acceleration of the sail inside the test apparatus. A coolant chamber with a ceramic base is also provided to reduce temperature effects inside the vacuum chamber. In conclusion, this study presents a promising approach for the design and testing of solar sails using shape memory polymer and a ground testing apparatus. The results of this research can contribute to the development of more efficient and versatile solar sail technology for fuel-free aerospace propulsion.

A Synthetic Cyclized Antimicrobial Peptide with Potent Effects against Drug-Resistant Skin Pathogens.

Dermal infections requiring treatment are usually treated with conventional antibiotics, but the rise of bacterial resistance to first-line antibiotics warrants alternative therapeutics. Here, we report that a backbone-cyclized antimicrobial peptide, CD4-PP, designed from the human host defense peptide LL-37, has strong direct antibacterial effects on antibiotic sensitive as well as resistant-type strains and clinical isolates of common skin pathogens in the low (<2) μM range. In addition, it influences innate immunity in keratinocytes, and treatment with CD4-PP is able to clear bacterial infections in infected keratinocytes. Additionally, CD4-PP treatment significantly reduces the wound area in a lawn of keratinocytes infected with MRSA. In conclusion, CD4-PP has the potential to serve as a future drug treating wounds infected with antibiotic-resistant bacteria.

Field tests of grouted ground anchors in the sandy soil of Najaf, Iraq

Abstract This article presents test results documentation for four grouted ground anchors embedded in sandy soil. Three anchors were trial, while one was a working anchor. One trial anchor is instrumented with eight resistance-type strain gauges glued on the corrugated pipe and embedded within the grouted body. An acceptance test was made for all anchors to determine the working load. Acceptance criteria suggested by the Post-Tensioning Institute were applied, and the working anchor did not pass the creep criterion, so it was taken out of service. The strain measurements indicated that the compression stresses were generated along the free length, while the tension stresses were generated along the bonded length. The transition point, which is the point with zero axial stress within the grouted body, was located at a distance of 10–12% of the bonded length, measured from the proximal end of the bonded length. The skin friction distribution along the grouted body was nonuniform, and it had a peak at the transition point. The maximum measured value of the skin friction is almost compatible with the estimated one by Fujita’s formula. The skin friction developed along the free length indicates a significant contribution of the free length to the pullout capacity.

Parametric investigation on laser interaction with polyimide for graphene synthesis towards flexible devices

Graphene, is one of the prominent materials in device fabrication due to its high conductive and high flexural strength for electrodes/device applications. The latest technique for graphene synthesis i.e. carbonization of polyimide by laser patterning has received much attention because of its capability to create various functional materials and flexible devices. The requirement of graphene demands larger volume production where laser-induced graphene (LIG) by consideration of pulse overlap could prove to be the solution if a recipe is prepared through appropriate optimization. The present study focused on the CO2 laser (λ = 10.6 µm) interaction with polyimide by generating raster pattern with varying pulse overlap in linear direction. The raster pattern is fabricated at different laser energies and pulse overlap with a constant 30% line overlap between two consecutive lines, in the lateral direction, for synthesizing LIG at relatively low laser power. Various combinations of laser fluences (46 J cm−2, 56 J cm−2, 66 J cm−2) and pulse spot overlap (60%, 70%, and 80%) were used for the polyimide carbonization. Both experimental and numerical simulation (using ComsolTM) results present an insight that optimal control of laser pulse overlap shows significant effect on crystallinity and electrical resistivity of synthesized graphene. The macroscopic quality of the raster pattern is investigated through the optical microscope. Detailed Raman spectro-microscopic analysis is carried out to study the defect to graphenization ratio and its impact on the properties of graphene synthesized. Through Raman analysis, the average in-plane crystallite length of graphene synthesis was observed from 27.732 ± 4–37.132 ± 6 nm. At last, a resistive type strain sensor was fabricated to check the stability of LIG and its reliability for repetitive loading conditions. The pulse overlap photo-thermal model, and its finite element analysis implementation presents better understanding towards optimizing the promising technique towards synthesizing LIG.

Customizable Textile Sensors Based on Helical Core-Spun Yarns for Seamless Smart Garments.

Most of the current sensors cannot meet the needs for seamless integration into the textile substrates of smart clothing and require improvements in terms of comfort and durability. Herein, smart textile-based sensors that have different sensing properties with integrated electronic elements were fabricated by knitting graphene-based helical conductive core-spun yarns. Such graphene-modified core-spun yarns are employed as building blocks of textile strain sensors, which showed high elasticity (ε > 300%), fast response time (120 ms), excellent reproducibility (over 10 000 cycles), wide sensing range (up to 100% strain), and low detection limit (0.3% strain). Thus, resistance-type strain sensors and capacitance-type pressure sensors composed of graphene-based smart fabric could be used to monitor large-scale limb movement and subtle human physiological signals. Such seamless smart textile-based fabric composed of superelastic helical conductive core-spun yarns shows great potential for fabricating an intelligent device to achieve real-time precise medicine and healthcare.

Anisotropy of resistance-type strain sensing networks based on aligned carbon nanofiber membrane

Carbon nanofiber (CNF) is a promising nanomaterial to prepare the strain sensor due to the simple preparation and high controllability. Despite the sensors have been developed based on CNFs, it is still a challenge to detect the full deformation with high sensitivity. In this study, we prepare the aligned semitransparent graphene-reinforced CNF membrane (G-CNFM) by electrospinning. The anisotropy of sensing performance of the ultrathin sensor was demonstrated. The sensor along parallel direction shows high sensitivity in the wide strain range of 0.1–38%. Moreover, the high durability can be obtained for over 1000 cycles at the subtle strain of 0.1% and high strain of 30%. The high linearity was also obtained under the low strain. The low sensitivity was exhibited along perpendicular direction, and the sensor was still working for 1000 cycles at 60% strain. The sensing mechanism was analyzed according to the microstructures of cracks. The thickness, the aligned degree and the width of G-CNFM and the thickness of TPU substrate show effects on the strain levels and sensitivity. The strain sensors can detect the full deformation caused by personal physiological movements and body motions. The sensor made using aligned G-CNFM may be used for various smart wearable electronic applications.

Performance Evaluation of Whitetopping with Improved Design Practices in Texas

Abstract The design method of whitetopping in Texas is a method suggested by the American Concrete Pavement Association (ACPA). However, one of the limitations on this particular design method is that an existing asphalt pavement condition is not considered for slab thickness. Recently, the Texas Department of Transportation developed an improved whitetopping design procedure considering mechanistic-empirical (ME) behavior. In the present study, performance of whitetopping projects constructed by the ACPA design method in Texas were investigated, and improved design details were suggested in order to minimize distresses, such as corner break and slab movement, in transition areas. To evaluate the structural performance of whitetopping, various tests, including the falling weight deflectometer, ground penetration radar, and investigation of concrete coring were conducted on US 90. According to the field survey and tests results, most of the distress was caused by insufficient slab support conditions related to asphalt concrete pavement materials and inadequate slab thickness design. In addition, early-age behavior of whitetopping constructed by the improved ME design method was evaluated and analyzed, and various gage installations, such as vibrating wire strain gage, electric resistance-type strain gages, porous nonstress cylinder, and impervious nonstress cylinder, are discussed.

CHROMagar COL-APSE: a selective bacterial culture medium for the isolation and differentiation of colistin-resistant Gram-negative pathogens.

A selective chromogenic culture medium for the laboratory isolation and differentiation of colistin resistant Acinetobacter, Pseudomonas, Stenotrophomonas and Enterobacteriaceae spp. (CHROMagar COL-APSE) was developed, evaluated and compared to an existing selective bacterial culture medium (SuperPolymyxin). The medium was challenged with 84 isolates, including polymyxin B (POL B)-susceptible and -resistant type strains and colistin (COL)-resistant organisms recovered from human and animal samples. Susceptibility to COL and POL B was determined by agar dilution and broth microtitre dilution. The lower limit for the detection of COL-resistant organisms was also calculated for both CHROMagar COL-APSE and SuperPolymyxin media. The ability to isolate and correctly differentiate COL-resistant organisms within mixed cultures was also assessed and compared using both media. Using CHROMagar COL-APSE, Gram-negative pathogens (n=71) with intrinsic (n=8) or acquired COL (n=63) resistance were recovered with 100 % specificity down to the lower limit of detection of 101 colony-forming units (c.f.u.). The growth on SuperPolymyxin was similar, but notably weaker for COL-resistant non-fermentative bacteria (Acinetobacter, Pseudomonas and Stenotrophomonas). CHROMagar COL-APSE was also more sensitive in supporting the growth of Enterobacteriaceae with COL resistance associated with the carriage of mcr-1. CHROMagar COL-APSE is a sensitive and specific medium for the growth of COL-resistant bacterial pathogens. Due to the low limit of detection (101 c.f.u.), it may be useful as a primary isolation medium in the surveillance and recovery of COL-resistant bacteria from complex human, veterinary and environmental samples, especially those with plasmid-mediated MCR-1 or novel mechanisms of polymyxin resistance.

Design of the Apparatus for Detecting and Transmitting Pressure Signals on the Probe of Electrical Impedance Scanning of Breast

In order to explore the relationship between the impact of detection probe and human contact pressure on its imaging result in the electrical impedance scanning techniques of breast, there is a need to design a set of device to extract pressure signal on EIS detection probe and transmit to the host in a long distance. The design uses Wheatstone full-bridge converter based on the resistance-type strain gauge as an extraction method for the pressure signal. After pre-amplification processing of the extracted signals, the voltage signal is converted into 4-20mA of current signal for long-line transmission via XTR106 chip. By the use of digital potentiometer chip replacing the adjustable resistance in the circuit, and by virtue of MCU chip and ADC chip, the system is characterized by automatic zero set of the full-bridge converter of sensor and adaptive control of amplifier circuit gain, thus realizing high-precision measurement and transmission of pressure signal at four locations of detection probes. The simulation and actual measurement results show that, after the automatic “zero set” operation, the output error of the system is less than ± 0.5%; the amplifier gain is within an adjustable range of 75-500, so that the full-scale output error of the system is less than ± 1%. The test results verify the reliability and validity of the system.

A piezo-resistive graphene strain sensor with a hollow cylindrical geometry

We propose a resistance-type strain sensor consists of hollow tubing graphene fibers (TGFs) with dimethylpolysiloxane (PDMS) coating for millimeters-scale strain/bending detection applications. The TGFs were synthesized via graphene films grown on Ni wire by chemical vapor deposition (CVD). The TGFs are fundamentally folded continuous few-layered graphene films without edges maintained cylindrical tube supported by PDMS coating. Sensing properties were studied comparing with a multi-wall carbon nanotube (MWCNT)/PDMS composites (CNTCs) and the mechanism were discussed. In terms of the gauge factor, the sensor made of TGF is estimated to be in the range of 34.3–48.9 against 8% tensile strain.For a feasibility study, we demonstrate the human finger monitoring by means of bending angle detection on a finger joint.

An improved instrumentation method for PHC piles

This paper describes an instrumentation method to study the behaviour of prestressed high-strength concrete pipe piles (PHC piles) under working static and high-speed-train-induced cyclic loads. The instrumentation method refers to bond resistance-type strain gauges with steel plate inserts that are pre-installed in PHC piles during fabrication. To verify the feasibility of the instrumentation method, three instrumented PHC piles were tested in situ. The test results indicate that the proposed instrumentation method is inexpensive, reliable and promising for cyclic loading. More importantly, the method does not alter the load transfer mechanism of PHC piles. The survival rate of the resistance-type strain gauges installed on the tested piles was found to be higher than 90%. The cumulative settlements induced by high-speed-train-induced cyclic loads were significantly lower than those under working static loads (about 11·5% only), so may be practically neglected when assessing total or post-construction settlement. The unit shaft resistances decreased in clay layers (upper portion of the piles), but increased in sand layers (lower portion of the piles) up to 0·4 million loading cycles. The results from this study provide important technical information for the design of pile foundations supporting high-speed railway bridges.

The strain sensing property of carbon nanofiber/glass microballoon epoxy nanocomposite

This work reports the strain sensing property of a nanocomposite made from a free standing multi-scale structure that consisted of glass microballoons and carbon nanofibers. An epoxy system was infiltrated into the structure in order to fabricate a nanocomposite sensor. The electrical resistance of the sensor when subjected to a tensile strain was investigated. The change in electrical resistance of the sensor versus the applied strain was found to have linear and non-linear regions. In the linear region, the sensor exhibited a similar sensitivity to conventional resistance-type strain gages. A single equation that relates the change in electrical resistance to the applied strain for the linear and non-linear regions was developed.

Ultrasensitive strain sensors made from metal-coated carbon nanofiller/epoxy composites

A set of resistance-type strain sensors has been fabricated from metal-coated carbon nanofiller (CNF)/epoxy composites. Two nanofillers, i.e., multi-walled carbon nanotubes and vapor growth carbon fibers (VGCFs) with nickel, copper and silver coatings were used. The ultrahigh strain sensitivity was observed in these novel sensors as compared to the sensors made from the CNFs without metal-coating, and conventional strain gauges. In terms of gauge factor, the sensor made of VGCFs with silver coating is estimated to be 155, which is around 80 times higher than that in a metal-foil strain gauge. The possible mechanism responsible for the high sensitivity and its dependence with the networks of the CNFs with and without metal-coating and the geometries of the CNFs were thoroughly investigated.

Multi-scale numerical simulations on piezoresistivity of CNT/polymer nanocomposites

In this work, we propose a comprehensive multi-scale three-dimensional (3D) resistor network numerical model to predict the piezoresistivity behavior of a nanocomposite material composed of an insulating polymer matrix and conductive carbon nanotubes (CNTs). This material is expected to be used as highly sensitive resistance-type strain sensors due to its high piezoresistivity defined as the resistance change ratio divided by the mechanical strain. In this multi-scale 3D numerical model, three main working mechanisms, which are well known to induce the piezoresistivity of strain sensors fabricated from nanocomposites, are for the first time considered systematically. They are (a) the change of the internal conductive network formed by the CNTs, (b) the tunneling effect among neighboring CNTs, and (c) the CNTs’ piezoresistivity. Comparisons between the present numerical results and our previous experimental ones were also performed to validate the present numerical model. The influence of the CNTs’ piezoresistivity on the total piezoresistivity of nanocomposite strain sensors is explored in detail and further compared with that of the other two mechanisms. It is found that the first two working mechanisms (i.e., the change of the internal conductive network and the tunneling effect) play a major role on the piezoresistivity of the nanocomposite strain sensors, whereas the contribution from the CNTs’ piezoresistivity is quite small. The present numerical results can provide valuable information for designing highly sensitive resistance-type strain sensors made from various nanocomposites composed of an insulating polymer matrix and conductive nanofillers.

Susceptibility of clinical isolates of Candida species to fluconazole and detection of Candida albicans ERG11 mutations

To investigate fluconazole susceptibility of Candida albicans from non-AIDS patients and to analyse the relationship between mutations in the ERG11 gene of these isolates and fluconazole resistance. Four hundred and twenty-six clinical isolates of Candida species were collected. Fluconazole susceptibility was tested in vitro using microdilution and disc diffusion assays. The ERG11 genes of 23 isolates of C. albicans (8 susceptible and 15 resistant) and 6 type strains (4 susceptible and 2 resistant) were amplified in three overlapping regions of the gene and sequenced. Of the 426 isolates collected, 68.6% were C. albicans; however, only 5.1% were resistant to fluconazole. Eighteen silent mutations and 19 missense mutations were detected. There were six missense mutations only in resistant isolates or resistant type strains: (i) G487T (A114S) and T916C (Y257H) appeared simultaneously in 14 fluconazole-resistant isolates without any other mutation; these may be associated with resistance; (ii) T541C (Y132H) and T1559C (I471T) are known to contribute to fluconazole resistance; and (iii) C1567A (Q474K) or a novel mutation T1493A (F449Y) was identified but correlations with resistance have not been studied. In this survey, C. albicans is the major cause of candidiasis in non-AIDS patients, and some isolates that are resistant to fluconazole have G487T and T916C mutations in ERG11 that are associated with fluconazole resistance.

Processing and modeling of conductive thermoplastic/carbon nanotube films for strain sensing

This paper reports the development of conductive, carbon nanotube (CNT)-filled, polymer composite films that can be used as strain sensors with tailored sensitivity. The films were fabricated via either melt processing or solution casting of poly(methyl methacrylate) (PMMA) matrices containing low concentrations of multi-walled carbon nanotubes (MWNTs). The electrical resistivities of the films were measured in situ using laboratory-designed fixtures and data acquisition system. The measured resistivities were correlated with the applied strains to evaluate the sensitivity of the nanocomposite film sensor. The study suggests that conductive network formation, thus strain sensitivity of the conductive films, can be tailored by controlling nanotube loading, degree of nanotube dispersion, and film fabrication process. The developed sensors exhibited a broad range of sensitivity, the upper limit showing nearly an order of magnitude increase compared to conventional, resistance-type strain gages. A semi-empirical model that shows the relationship between CNT volume fraction and sensitivity is proposed.

Monitoring Fatigue Crack Initiation and Propagation in Cruciform Joints Using Resistance-Type Gages

The monitoring of fatigue crack initiation and propagation in cruciform joints is very complex and time consuming. The amount of technical information generated by a single fatigue test can vary from a terse noting of the cycles to the point till the specimen breaks, to a continuous observation of crack lengths. A wide variety of experimental methods are available to study the changes in bulk properties taking place in a test specimen (with simple geometry) while it is subjected to alternating stresses. However, in many fatigue test situations (for instance, in cruciform joints), it is very difficult to monitor the changes due to multiple possible crack initiation points. In this paper, a method has been developed to monitor the crack initiation for cruciform joints with different geometry by resistance-type strain gages. Also, the application of a relatively new, thin-film bondable transducer, commercially available under the name ‘crack propagation gage,’ was evaluated for fatigue crack propagation tests for cruciform joints at room temperature. Additionally, the strain gage and the crack propagation gage instrumentation system can be used for direct test machine control, permitting completely automated fatigue crack growth testing.

Structure and properties of an amorphous microwire

,Problems of the production, investigation, and use of a microwire with an amorphous vein structure are discussed. It is determined that the magnetic properties of microwires depend heavily on the domain structure. It is established that a domain-free structure, which is characterized by a high coercive force, is also possible in a microwire. The phenomenon of natural ferromagnetic resonance (NFMR) in an amorphous microwire in the range of superhigh frequencies is investigated experimentally. The significance of an internal field of anisotropy, which gives rise to NFMR is examined. Theoretical relationships describe experimental data on NFMR well. The procedure used to produce cast microwire in glass insulation has been developed for some time [1]. Casting is carried out from a molten sample of alloy, which is placed in a glass tube and held in the suspended state by an electromagnetic field. The demagnetized glass tube is drawn into a capillary and wound on a take-in reel. The capillary is filled with metal under certain casting conditions. To achieve a stable casting process, and also to increase the cooling rate, the resulting microwire is passed through a stream of coolant. In industry, microwires of many metals and alloys are fabricated by this method (called the Ulitovskii method). These microwires have come into the most widespread use for the fabrication of resistor components: precision resistors, resistance-type strain gauges, circuit resistance elements, voltage dividers, precision RC filters, etc. Moreover, they are used to fabricate transformer windings, inductance coils, etc. A high cooling rate is called for in the procedure used to produce microwire in glass insulation. The cooling rate of the vein is 105-107 deg/sec. These cooling rates are adequate for the formation of amorphous structures in many traditional amorphous alloys. To stabilize the casting of micrwire, however, it is necessary to introduce additives to certain alloys. An amorphous structure is obtained in cobalt-, iron-, and nickel-base alloys with metalloids (boron, carbon, and silicon). To enhance the adaptability of the casting process to manufacturing, Mn, Cr, Ce, Gd, Cu, and other elements are introduced to the alloys. The adaptability of thermally-stable amorphous alloys to manufacture depends to a large degree on their composition. We used alloys with a compositon close to the eutectic in which a glassy structure is formed comparatively easily. The following phases may form in the alloy, depending on its composition, the cooling rate, the diameter of the microwire vein, and the thickness of the glass insulation; a supersaturated solid solution, a nonequilibrium crystalline phase, and an amorphous phase. A solid solution is produced primarily for type Fe-B-C alloys. Only veins of a small diameter (1-2 #m) contain an amorphous phase. Veins of type Fe-B-Si-C alloys with a diameter of 5-10/~m had both a completely amorphous structure, and a supersaturated solid solution (which has a lower H e value). Veins of type Fe-B-Si alloys with a 15/zm diameter which are close to the eutectic composition contain amorphous components. It should be noted that the positive effect of Carbon additives on the adaptability of the alloys investigated to manufacture is established during the casting of microwires.

A New Metglas Sensor

This paper presents a new type of sensor, one that may be used in the manner of a standard strain gage. The sensor is constructed of a relatively new material, a metallic glass-like substance called Metglas. A change in stress in the magnetoelastic Metglas manifests itself as a change in the magnetic properties of the material. This change in magnetic properties may be measured electronically. The sensor operates on this principal and outputs a dc signal proportional to the stress. The results demonstrate a sensor that does not require the great amplification of a resistance-type strain gage. This is primarily due to a sensitivity almost two orders of magnitude greater than a standard strain gage.

Interaction between a resistance-type strain gauge and the surface of the article being tested

Interaction between a resistance-type strain gauge and the surface of the article being tested