Search Results (13)

Cutting force measurement plays a fundamental role in machining research and industrial applications, but existing dynamometers present important trade-offs between cost, stiffness, and dynamic bandwidth. Strain gauge devices are inexpensive but too flexible for high-speed operations, whereas piezoelectric systems provide excellent accuracy and bandwidth at prohibitive costs. This work presents the design, construction, and validation of a novel plate dynamometer based on polyvinylidene fluoride (PVDF) sensors, aimed at providing an effective alternative having an intermediate cost and suitable for advanced milling applications. The device integrates eight symmetrically arranged PVDF films in a stiff steel structure, complemented by four accelerometers for inertial compensation. A finite-element analysis confirmed favorable stress distribution at the PVDF contact surfaces and high resonance frequencies (under ideal clamping conditions). Modal tests demonstrated that uncompensated PVDF signals offer limited bandwidth, but the application of the Universal Inverse Filter (UIF) extended the usable bandwidth to 5 kHz along direct directions and up to 0.3–4 kHz along cross directions, approaching the performance of piezoelectric reference devices. Milling tests under diverse cutting conditions further validated the new device. Overall, the proposed device bridges the gap between low-cost strain gauge and high-performance piezoelectric dynamometers, offering a versatile and promising solution for both laboratory research and industrial applications. Full article

Graphene nanocomposites are a promising class of advanced materials for sensing applications; yet, their commercialization is hindered due to impurity incorporation during fabrication and high costs. The aim of this work is to prepare graphene–polysulfone (G−PSU) and graphene–polyvinylidene fluoride (G−PVDF) nanocomposites that perform as multifunctional sensors and are formed using a one-step, in situ exfoliation process whereby graphite is exfoliated into graphene nanoflakes (GNFs) directly within the polymer. This low-cost method creates a nanocomposite while avoiding impurity exposure since the raw materials used in the in situ shear exfoliation process are graphite and polymers. The morphology, structure, thermal properties, and flexural properties were determined for G−PSU and G−PVDF nanocomposites, as well as the electromechanical sensor capability during cyclic flexural loading, temperature sensor testing while heating and cooling, and electrochemical sensor capability to detect dopamine while sensing data wirelessly. G−PSU and G−PVDF nanocomposites show superior mechanical characteristics (gauge factor around 27 and significantly enhanced modulus), thermal characteristics (stability up to 500 °C and 170 °C for G−PSU and G−PVDF, respectively), electrical characteristics (0.1 S/m and 1 S/m conductivity for G−PSU and G−PVDF, respectively), and distinguished resonant peaks for wireless sensing (~212 MHz and ~429 MHz). These uniquely formed G−PMC nanocomposites are promising candidates as strain sensors for structural health monitoring, as temperature sensors for use in automobiles and aerospace applications, and as electrochemical sensors for health care and disease diagnostics. Full article

The novel conductive polyvinylidene fluoride (PVDF) fibrous membrane with high conductivity and sensitivity was successfully prepared via electrostatic spinning and efficient silver reduction technology. Based on the selective dissolution of porogen of polyvinylpyrrolidone (PVP), the porous PVDF fibrous membrane with excellent adsorbability and mechanical strength was obtained, providing a structure base for the preparation of conductive PVDF fibrous membrane with silver nanoparticles (AgNPs-PVDF). The Ag⁺ in the AgNO₃ mixed solution with PVP was absorbed and maintained in the inner parts and surface of the porous structure. After the reducing action of ascorbic acid-mixed solution with PVP, silver nanoparticles were obtained tightly in an original porous PVDF fibrous membrane, realizing the maximum conductivity of 2500 S/m. With combined excellent conductivity and mechanical strength, the AgNPs-PVDF fibrous membrane effectively and sensitively detected strain signals of throat vocalization, elbow, wrist, finger, and knee (gauge factor of 23). The electrospun conductive AgNPs-PVDF combined the characteristics of low resistance, high mechanical strength, and soft breathability, which provided a new and effective preparation method of conductive fibers for practical application in wearable devices. Full article

Typical extension flow occurs in electrospinning process of Poly(vinylidene fluoride) (PVDF) solutions such that researchers focus on extensional rheological behaviors of PVDF solutions. The extensional viscosity of PVDF solutions is measured to know the fluidic deformation in extension flows. The solutions are prepared by dissolving PVDF powder into N,N-dimethylformamide (DMF) solvent. A homemade extensional viscometric device is used to produce uniaxial extension flows and the feasibility of the viscometric device is verified by applying the glycerol as a test fluid. Experimental results show that PVDF/DMF solutions are extension shinning as well as shear shinning. The Trouton ratio of thinning PVDF/DMF solution is close to three at very low strain rate and then reaches a peak value until it drops to a small value at high strain rate. Furthermore, an exponential model may be used to fit the measured values of uniaxial extensional viscosity at various extension rates, while traditional power-law model is applicable to steady shear viscosity. For 10~14% PVDF/DMF solution, the zero-extension viscosity by fitting reaches 31.88~157.53 Pa·s and the peak Trouton ratio is 4.17~5.16 at applied extension rate of less than 34 s⁻¹. Characteristic relaxation time is λ~100 ms and corresponding critical extension rate is ${\dot{\epsilon }}_c$~5 s⁻¹. The extensional viscosity of very dilute PVDF/DMF solution at very high extension rate is beyond the limit of our homemade extensional viscometric device. This case needs a higher sensitive tensile gauge and a higher-accelerated motion mechanism for test. Full article

Lead azide (LA) is a commonly used primary explosive, the detonation growth of which is difficult to study because it is so sensitive and usually has a small charge size in applications. We used photon Doppler velocimetry (PDV) and calibrated polyvinylidene fluoride (PVDF) gauges to reveal the detonation growth in LA, which was pressed in the confinements with controlled heights. The particle-velocity profiles, output pressure, unsteady detonation velocity, reaction time, and reaction-zone width were obtained and analyzed. Three phases of detonation propagation of LA microcharges are discussed. The volume reactions occur at the beginning of detonation in LA microcharges without forming complete shock profiles. Then the shock front is fast with a slow chemistry reaction zone, which is compressed continuously between the height of 0.8 mm and 2.5 mm. Finally, the steady detonation is built at a height of 2.5 mm. The stable detonation velocity and CJ pressure are 4726 ± 8 m/s and 17.12 ± 0.22 GPa. Additionally, the stable reaction zone time and width are 44 ± 7 ns and 148 ± 11 μm. The detailed detonation process has not previously been quantified in such a small geometry. Full article

The success of surgical procedures is strictly related to the biomechanical properties of the suture. Mechanical comparisons are scarcely reported in the literature, so the purpose of the present study was to evaluate and compare the mechanical behavior of different sutures commonly used in oral surgery in terms of traction resistance. Sutures made of eight different materials were analyzed: silk (S), polyglycolide-co-caprolactone (PGCL), polypropylene (PP), rapid polyglycolide (rPGA), standard polyglycolide (PGA), polyamide (PA), polyester (PE), and polyvinylidene fluoride (PVDF). For each material, three different sizes were tested: 3-0, 4-0, and 5-0. The breaking force of each suture was assessed with a uniaxial testing machine after being immersed in artificial saliva at 37 °C. The outcomes analyzed were the breaking force, the needle–thread detachment breaking-point and the node response after forward–reverse–forward (FRF) tying when subjected to a tensile force. The 3-0 rPGA provided the maximum resistance, while the lowest value was recorded for the 5-0 PGCL. In general, 3-0 and 4-0 gauges showed non-statistically significant differences in terms of needle–thread detachment. The highest needle–thread detachment was found for the 3-0 PGA, whereas the lowest value was observed for the 5-0 PGCL. After tying the knot with an FRF configuration, the thread that showed the highest resistance to tension was the 3/0 silk, while the thread with the lowest resistance was the 5/0 silk. These data should be considered so that the operator is aware of as many aspects as possible on the behavior of various materials to ensure successful healing. Full article

In this work, new highly sensitive graphene-based flexible strain sensors are produced. In particular, polyvinylidene fluoride (PVDF) nanocomposite films filled with different amounts of graphene nanoplatelets (GNPs) are produced and their application as wearable sensors for strain and movement detection is assessed. The produced nanocomposite films are morphologically characterized and their waterproofness, electrical and mechanical properties are measured. Furthermore, their electromechanical features are investigated, under both stationary and dynamic conditions. In particular, the strain sensors show a consistent and reproducible response to the applied deformation and a Gauge factor around 30 is measured for the 1% wt loaded PVDF/GNP nanocomposite film when a deformation of 1.5% is applied. The produced specimens are then integrated in commercial gloves, in order to realize sensorized gloves able to detect even small proximal interphalangeal joint movements of the index finger. Full article

High explosive hydro forming (HEHF) is a suitable technique for large metal plate forming. Manufacturing stages of such a part requires an adapted design of explosive charge configurations to define the mechanical loading exerted on the part. This mechanical loading remains challenging to be experimentally determined but necessary for predictive numerical simulation in the design of parts to form. Providing that the actual mechanical impulse would allow the neglecting of the modelling of the detonation stage, this considerably increases the computational time. The present work proposes an experimental method for obtaining the exerted mechanical loading by HEHF on the part to form. It relies on the development of low-cost sensor based on a polyvinyliden fluorid (PVDF) gauge. In addition to it, an analytical approach based on shock physics is proposed for the sensor signal interpretation. The method considers the multi-layer aspect of the sensor and its intrusiveness with respect to waves propagation. Measurements were repeated to assess their relevance and the reproducibility by using steel and aluminium anvils in HEHF. Numerical modelling in 2D plane geometry of the experiments was performed with two commercial hydrocodes. The comparison of mechanical impulses shows an agreement in terms of chronology but a noticeable difference in terms of amplitude, explained by mesh size and numerical diffusion. Full article

Pavement structures are designed to withstand continuous damage during their design life. Damage starts as soon as the pavement is open to traffic and increases with time. If maintenance activities are not considered in the initial design or considered but not applied during the service life, damage will grow to a point where rehabilitation may be the only and most expensive option left. In order to monitor the evolution of damage and its severity in pavement structures, a novel data compression approach based on cumulative measurements from a piezoelectric sensor is presented in this paper. Specifically, the piezoelectric sensor uses a thin film of polyvinylidene fluoride to sense the energy produced by the micro deformation generated due to the application of traffic loads. Epoxy solution has been used to encapsulate the membrane providing hardness and flexibility to withstand the high-loads and the high-temperatures during construction of the asphalt layer. The piezoelectric sensors have been exposed to three months of loading (approximately 1.0 million loads of 65 kN) at the French Institute of Science and Technology for Transport, Development and Networks (IFSTTAR) fatigue carrousel. Notably, the sensors survived the construction and testing. Reference measurements were made with a commercial conventional strain gauge specifically designed for measurements in hot mix asphalt layers. Results from the carrousel successfully demonstrate that the novel approach can be considered as a good indicator of damage progression, thus alleviating the need to measure strains in pavement for the purpose of damage tracking. Full article

A major contributor to longitudinal vibration in marine propulsion systems is propeller induced excitation. This constitutes a key source of underwater acoustical radiation through excitation of the hull. Understanding this hydrodynamic force at the interface of the thrust bearing is important in order to develop an accurate vibrational model of the propulsion system and in determining potential control mechanisms. In order to investigate the thrust force during operation of a propulsion system, Polyvinylidene Fluoride (PVDF) was embedded into the stationery collar inside a custom thrust bearing in a scaled model of a typical propulsion system. The number of blades of the propeller and its rotational speed were altered to obtain an understanding of the characteristic vibrations of the shaft propulsion system. The rig comprised of the propeller, shaft, journal bearings and a thrust bearing. A two and three blade propeller and a four, five and six pad bearing were tested. A strain gauge and accelerometer were used to infer the propeller force and enable comparison with the PVDF signals. As a result of the asymmetrical flow around the propeller, the blade passing frequencies (BPF) are clearly observed. This frequency contribution was present at all speeds tested. The PVDF signal also showed significant pad passing frequency (PPF) and BPF and modulation of both. Full article

It’s difficult to directly measure the pressure on the surface of the material in the impact process. PVDF (Polyvinylidene Fluoride) gauges may help to solve this problem. In this paper, some split Hopkinson pressure bar (SHPB) experiments were carried out with the PVDF gauges as specimens, with the strain gauges pasted on the bars being used as the measurement method. By comparing the results of the strain gauges and the PVDF gauges, it is proved that there is a stress concentration when the PVDF gauges were sandwiched directly in the solid interface. Then, two methods to eliminate the stress concentration are verified by experiments. The first method is adding a cushion, such as electrical tape. The second method is using 502 glue, which is evenly coated on the interface. Full article

Fatigue, a hot scientific research topic for centuries, can trigger sudden failure of critical structures such as aircraft and railway systems, resulting in enormous casualties as well as economic losses. The fatigue life of certain structures is intrinsically random and few monitoring techniques are capable of tracking the full life-cycle fatigue damage. In this paper, a novel in-situ wireless real-time fatigue monitoring system using a bio-inspired tree ring data tracking technique is proposed. The general framework, methodology, and verification of this intelligent system are discussed in details. The rain-flow counting (RFC) method is adopted as the core algorithm which quantifies fatigue damages, and Digital Signal Processing (DSP) is introduced as the core module for data collection and analysis. Laboratory test results based on strain gauges and polyvinylidene fluoride (PVDF) sensors have shown that the developed intelligent system can provide a reliable quick feedback and early warning of fatigue failure. With the merits of low cost, high accuracy and great reliability, the developed wireless fatigue sensing system can be further applied to mechanical engineering, civil infrastructures, transportation systems, aerospace engineering, etc. Full article

Due to advantages such as light weight, flexibility, and low cost, polyvinylidene fluoride (PVDF) films have been widely used in engineering applications as sensors for detecting strain, pressure, or micro-force. However, it is known that PVDF strain sensors have strain cross-sensitivity in mutually orthogonal directions. Furthermore, the size of the PVDF film sensor would also affect the dynamic strain sensing performance. In this paper, to investigate the cross-sensitivity and size effects experimentally, we employ PVDF film sensors to perform dynamic measurements on a cantilever beam. Since the vibrations of the cantilever beam are excited by impacts of a steel ball, the induced highly repeatable transient responses contain a wide range of resonant frequencies and thus can be used to investigate both the size and cross-sensitivity effects of the PVDF film sensors in a dynamic sensing environment. Based on the experimental results of the identified resonant frequencies compared with results obtained from a strain gauge, finite element calculations, and theoretical predictions, suggestions for the use of the PVDF strain sensor in modal testing are given in this paper. Full article