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Articoli di riviste sul tema "PRISTINE LFP"
1
Sahoo, Prangya P., Martin Kemeny, Boris Hudec, Miroslav Mikolasek, Matej Mičušík, Peter Siffalovic, Andrea Strakova Fedorkova e Karol Frohlich. "Enhanced Performance of LiFePO4 Cathodes Protected By Atomic Layer Deposited Ultrathin Alumina Films". ECS Meeting Abstracts MA2022-02, n. 3 (9 ottobre 2022): 306. http://dx.doi.org/10.1149/ma2022-023306mtgabs.
Testo completoAbstract (sommario):
The LiFePO4 (LFP) cathode has a theoretical specific capacity of 170 mAh/g. This material is stable, safe, and environmentally benign. Li-ion batteries with LFP cathodes have a long cycle life with excellent charging/discharging performance. In our contribution, we show that the surface modification of the LFP cathode using ultrathin alumina films grown by atomic layer deposition (ALD) can improve Li-ions charge transfer and rate performance of the Li-ion in half-cell configuration with the LFP cathode. We used two types of LFP cathodes in our study with Li-metal as an anode in a half cell configuration. The first LFP electrode had a thickness of 25 μm and consisted of particles of 0.5 - 1 μm in size [1], while the second one (commercial NANOMYTE BE-60E (NEI Corp.)) had a thickness of 70 μm and the average LFP particle size was 2 μm. Ultrathin Al2O3 films were grown on LFP cathodes by ALD at 100 °C using trimethylaluminum (TMA) and water vapors. Due to the self-saturation surface-limited nature of the ALD reaction, even substrates of highly complex morphology can be uniformly coated, where the limitation is the reach of the precursor vapor molecules. The thickness of the ALD layers depends linearly on the number of ALD cycles and ranges from 0.5 to 2 nm for 5 to 20 cycles. Galvanostatic charging/discharging experiments were performed to evaluate the rate capability of the electrodes. Pristine and Al2O3 coated LFP electrodes were laser cut to 18 mm diameter circular electrodes, inserted in the electrochemical test cells PAT-Cell (EL-CELL), and tested using PAT-Tester-x-8 analyzer. LFP with Al2O3 protecting layers was compared to the pristine LFP electrode. For the LFP cathode with the thickness of 25 μm the pristine sample saturates at the specific capacity of 32 mAh/g at 1.8 c-rate, while for the electrode treated with 5 and 20 cycles of Al2O3 the specific capacity dropped to 80 and 60 mAh/g, respectively. The electrodes protected by Al2O3 film always exhibited better rate capability than the pristine sample. A more detailed analysis of the performance was accomplished for the NANOMYTE electrodes. A specific discharge capacity of 160 mAh/g at a c-rate of 0.2 was achieved for both pristine and Al2O3-protected electrodes. Two supercycles with the c-rate 0.2, 0.5, and 1 were applied to the samples. The specific capacity of the pristine LFP electrode dropped from 160 mAh/g for the c-rate 0.2 to about 90 mAh/g at the c-rate 1, while the electrode which was protected by 5 cycles of Al2O3 exhibited a capacity of 120 mAh/g. Investigation of the rate capability fading using electrochemical impedance spectroscopy revealed a gradual increase of the Nyquist plot semicircle diameter as a function of cycles. According to the equivalent circuit model, the semicircle diameter corresponds to the charge transfer at the solid/electrolyte interface. The charge transfer resistance at the solid/electrolyte interface increases with charge/discharge cycling. The charge transfer resistance of the pristine electrode increased more steeply than that of the electrode with 5 cycles of Al2O3. Improvement of the charge transfer resistance of the LFP electrode covered by thin Al2O3 film can be explained by the formation of the Li3.4Al2O3 phase upon lithiation. The diffusivity of the Li ions in the Li3.4Al2O3 phase is several orders of magnitude higher than that of in the Al2O3 film [2]. The results obtained by electrochemical characterization are compared to the X-ray photoelectron spectroscopy performed on samples before and after galvanostatic charging/discharging measurements. [1] A. Fedorkova et al., J. Power Sources 195 (2010) 3907. [2] S. C. Jung et al., J. Phys. Chem. Lett. 4 (2013) 2681.
2
Frąckiewicz, Justyna E., Tomasz K. Pietrzak, Maciej Boczar, Dominika A. Buchberger, Marek Wasiucionek, Andrzej Czerwiński e Jerzy E. Garbarczyk. "Electrochemical Properties of Pristine and Vanadium Doped LiFePO4 Nanocrystallized Glasses". Energies 14, n. 23 (1 dicembre 2021): 8042. http://dx.doi.org/10.3390/en14238042.
Testo completoAbstract (sommario):
In our recent papers, it was shown that the thermal nanocrystallization of glassy analogs of selected cathode materials led to a substantial increase in electrical conductivity. The advantage of this technique is the lack of carbon additive during synthesis. In this paper, the electrochemical performance of nanocrystalline LiFePO4 (LFP) and LiFe0.88V0.08PO4 (LFVP) cathode materials was studied and compared with commercially purchased high-performance LiFePO4 (C-LFP). The structure of the nanocrystalline materials was confirmed using X-ray diffractometry. The laboratory cells were tested at a wide variety of loads ranging from 0.1 to 3 C-rate. Their performance is discussed with reference to their microstructure and electrical conductivity. LFP exhibited a modest electrochemical performance, while the gravimetric capacity of LFVP reached ca. 100 mAh/g. This value is lower than the theoretical capacity, probably due to the residual glassy matrix in which the nanocrystallites are embedded, and thus does not play a significant role in the electrochemistry of the material. The relative capacity fade at high loads was, however, comparable to that of the commercially purchased high-performance LFP. Further optimization of the crystallites-to-matrix ratio could possibly result in further improvement of the electrochemical performance of nanocrystallized LFVP glasses.
3
Fu, Yanqing, Qiliang Wei, Gaixia Zhang, Yu Zhong, Nima Moghimian, Xin Tong e Shuhui Sun. "LiFePO4-Graphene Composites as High-Performance Cathodes for Lithium-Ion Batteries: The Impact of Size and Morphology of Graphene". Materials 12, n. 6 (13 marzo 2019): 842. http://dx.doi.org/10.3390/ma12060842.
Testo completoAbstract (sommario):
In this work, we investigated three types of graphene (i.e., home-made G, G V4, and G V20) with different size and morphology, as additives to a lithium iron phosphate (LFP) cathode for the lithium-ion battery. Both the LFP and the two types of graphene (G V4 and G V20) were sourced from industrial, large-volume manufacturers, enabling cathode production at low cost. The use of wrinkled and/or large pieces of a graphene matrix shows promising electrochemical performance when used as an additive to the LFP, which indicates that the features of large and curved graphene pieces enable construction of a more effective conducting network to realize the full potential of the active materials. Specifically, compared to pristine LFP, the LFP/G, LFP/G V20, and LFP/G V4 show up to a 9.2%, 6.9%, and 4.6% increase, respectively, in a capacity at 1 C. Furthermore, the LFP combined with graphene exhibits a better rate performance than tested with two different charge/discharge modes. Moreover, from the economic and electrochemical performance view point, we also demonstrated that 1% of graphene content is optimized no matter the capacity calculated, based on the LFP/graphene composite or pure LFP.
4
Sahoo, Prangya Parimita, Alper Güneren, Boris Hudec, Matej Mičušík, Zoltán Lenčéš, Peter Siffalovic e Karol Frohlich. "Improved Properties of Li-Ion Battery Electrodes Protected By Al2O3 and ZnO Ultrathin Layers Prepared By Atomic Layer Deposition". ECS Meeting Abstracts MA2022-02, n. 31 (9 ottobre 2022): 1136. http://dx.doi.org/10.1149/ma2022-02311136mtgabs.
Testo completoAbstract (sommario):
Surface modification using thin layers grown by atomic layer deposition (ALD) is an effective strategy for performance improvement of Li-ion batteries. Ultrathin Al2O3 layers are the most studied coating material. In our contribution we compare properties of Al2O3 and ZnO ultrathin layers prepared by ALD on lithium-iron-phosphate (LFP) cathodes and Si-graphite anodes. Ultrathin Al2O3 and ZnO films were grown at 100 °C using trimethylaluminum (TMA) and diethylzinc (DEZ) precursors, respectively, with water vapors as reactant. The growth rates of the Al2O3 and ZnO films were about 0.1 nm/cycle on control flat Si substrates. ALD layers thickness in this study ranged from 5 to 20 cycles. A modified deposition recipe utilizing a prolonged precursor dwell time in the reactor chamber for coverage of the highly porous battery electrodes has been utilized. As TMA, DEZ and H2O all have rather high vapor pressures, we assume that significant part of the electrodes were coated. Porous LFP cathodes (NANOMYTE BE-60E, NEI Corp.) with the thickness of 70 μm were used as a substrate. The average particle size of the LFP substrate was ~ 2 μm with the specific surface area of 15 m2/g and active material loading of 7.3 mg/cm2. Experimental capacity C of the LFP electrode is 170 mAh/g in the voltage range 2.5 - 4.1 V using 0.1 charging/discharging c-rate. As an anode material porous silicon-graphite composite electrode sheets NANOMYTE BE-150E (NEI Corp) with the thickness of 65 μm and composition of active material 20% Si and 65 % graphite were used. The nominal capacity C of the silicon-graphite anode is 750mAh/g in the voltage range 0.05 - 1V using 0.05 charging/discharging c-rate. In our contribution we present specific discharge capacity of the electrodes as a function of charging/discharging cycles. For both pristine and Al2O3 protected LFP cathode sheets specific discharge capacity of 160 mAh/g was achieved at the c-rate of 0.2. The specific capacity of the pristine LFP electrode dropped from 160 mAh/g at the c-rate 0.2 to about 90 mAh/g for the c-rate 1, while the electrode protected by 0.5 nm of Al2O3 saturated at 120 mAh/g. Properties of ZnO- protected LFP cathodes are compared to that covered by Al2O3. Electrochemical properties of the silicon-graphite anode were studied using low c-rate of 0.05. During the first cycles the specific capacity is relatively low due to the formation of the solid-electrolyte interface layer at the surface. After several cycles the capacity increased to the nominal value of 750 mAh/g. In our study we compare the charging/discharging capability of the pristine silicon-graphite anode and that of the electrodes covered by 5 -20 ALD cycles of Al2O3 and ZnO films during the first charging/discharging cycles. We discuss the effect of ALD protecting layers on the rate capability of the silicon-graphite anode. Finally, the results of the electrochemical measurements are compared to those obtained by X-ray photoelectron spectroscopy.
5
Pattammattel, A., R. Tappero, M. Ge, Y. S. Chu, X. Huang, Y. Gao e H. Yan. "High-sensitivity nanoscale chemical imaging with hard x-ray nano-XANES". Science Advances 6, n. 37 (settembre 2020): eabb3615. http://dx.doi.org/10.1126/sciadv.abb3615.
Testo completoAbstract (sommario):
Resolving chemical species at the nanoscale is of paramount importance to many scientific and technological developments across a broad spectrum of disciplines. Hard x-rays with excellent penetration power and high chemical sensitivity are suitable for speciation of heterogeneous (thick) materials. Here, we report nanoscale chemical speciation by combining scanning nanoprobe and fluorescence-yield x-ray absorption near-edge structure (nano-XANES). First, the resolving power of nano-XANES was demonstrated by mapping Fe(0) and Fe(III) states of a reference sample composed of stainless steel and hematite nanoparticles with 50-nm scanning steps. Nano-XANES was then used to study the trace secondary phases in lithium iron phosphate (LFP) particles. We observed individual Fe-phosphide nanoparticles in pristine LFP, whereas partially (de)lithiated particles showed Fe-phosphide nanonetworks. These findings shed light on the contradictory reports on Fe-phosphide morphology in the literature. Nano-XANES bridges the capability gap of spectromicroscopy methods and provides exciting research opportunities across multiple disciplines.
6
Ni, Jie, Yike Lei, Yongkang Han, Yingchuan Zhang, Cunman Zhang, Zhen Geng e Qiangfeng Xiao. "Prefabrication of a Lithium Fluoride Interfacial Layer to Enable Dendrite-Free Lithium Deposition". Batteries 9, n. 5 (22 maggio 2023): 283. http://dx.doi.org/10.3390/batteries9050283.
Testo completoAbstract (sommario):
Lithium metal is one of the most attractive anode materials for rechargeable batteries. However, its high reactivity with electrolytes, huge volume change, and dendrite growth upon charge or discharge lead to a low CE and the cycle instability of batteries. Due to the low surface diffusion resistance, LiF is conducive to guiding Li+ deposition rapidly and is an ideal component for the surface coating of lithium metal. In the current study, a fluorinated layer was prepared on a lithium metal anode surface by means of chemical vapor deposition (CVD). In the carbonate-based electrolyte, smooth Li deposits were observed for these LiF-coated lithium anodes after cycling, providing excellent electrochemical stability for the lithium metal anode in the liquid organic electrolyte. The CE of Li|Cu batteries increases from 83% for pristine Li to 92% for LiF-coated ones. Moreover, LiF-Li|LFP exhibits a decent rate and cycling performance. After 120 cycles, the capacity retention of 99% at 1C is obtained, and the specific capacity is maintained above 149 mAh/g. Our investigation provides a simple and low-cost method to improve the performance of rechargeable Li-metal batteries.
7
Ramirez-Meyers, Katrina, e Jay Whitacre. "Characterization of Used A123 LiFePO4 Cells from a Hybrid-Bus Battery Pack". ECS Meeting Abstracts MA2022-01, n. 5 (7 luglio 2022): 596. http://dx.doi.org/10.1149/ma2022-015596mtgabs.
Testo completoAbstract (sommario):
As the battery market grows, developing a battery waste management economy becomes imperative. After primary use, the main options for discarded batteries are recycling, refurbishment, reuse, or disposal. Recycling involves extracting valuables materials from ground-up battery cells, while reuse and refurbishment involve direct use of packs or their components, with or without maintenance adjustments. Recycling and disposal are the most common battery waste pathways, while reuse and refurbishment practices require further understanding of battery degradation before being implemented on a large scale. Furthermore, relatively high recycling costs are motivation to pursue more cost-efficient recycling methods like direct recycling. This work expands on previous studies on the statistical distribution of the state-of-health (SOH) of used LiFePO4 (LFP) cells extracted from a hybrid-bus battery pack.1 We characterize samples from used and pristine A123 M1-A and M1-B 26650 cells using XRD and SEM. We will compare the cell materials’ morphologies and structure to their electrochemical performance in two diagnostic tests: a constant-current cycling test and an electrochemical impedance spectroscopy test. Preliminary data have been collected from used M1-A cells that demonstrated starkly different states-of-health during electrochemical testing—ranging in residual capacities from 2.2 Ah to 0.30 Ah. The low-SOH M1-A cell had severe anode delamination and morphological cracks in the center of the cylinder cross-section. Cathode delamination in the cell also increased towards the center of the cylinder. The high-SOH M1-A cell’s electrodes had a consistent morphology throughout the cell, but delamination was worst at the center of the cylinder’s cross-section. In this presentation, we will summarize our x-ray diffraction and scanning electron microscopy data for the cells described in Table 1. We will also discuss technical pathways for direct recycling of active materials from LFP battery waste. Ramirez-Meyers and J. Whitacre. “(Invited) Statistical Distribution and Feasibility for Re-Use of A123 LiFePO4 Cells from a Hybrid-Bus Battery Pack.” ECS Meeting Abstracts, no. 6, p. 1052. IOP Publishing, 2020. Figure 1
8
Kang, Seok Hyeon, Hwan Yeop Jeong, Sang Jun Yoon, Soonyong So, Jaewon Choi, Tae-Ho Kim e Duk Man Yu. "Hydrocarbon-Based Composite Membrane Using LCP-Nonwoven Fabrics for Durable Proton Exchange Membrane Water Electrolysis". Polymers 15, n. 9 (28 aprile 2023): 2109. http://dx.doi.org/10.3390/polym15092109.
Testo completoAbstract (sommario):
A new hydrocarbon-based (HC) composite membrane was developed using liquid crystal polymer (LCP)-nonwoven fabrics for application in proton exchange membrane water electrolysis (PEMWE). A copolymer of sulfonated poly(arylene ether sulfone) with a sulfonation degree of 50 mol% (SPAES50) was utilized as an ionomer for the HC membranes and impregnated into the LCP-nonwoven fabrics without any surface treatment of the LCP. The physical interlocking structure between the SPAES50 and LCP-nonwoven fabrics was investigated, validating the outstanding mechanical properties and dimensional stability of the composite membrane in comparison to the pristine membrane. In addition, the through-plane proton conductivity of the composite membrane at 80 °C was only 15% lower than that of the pristine membrane because of the defect-free impregnation state, minimizing the decrease in the proton conductivity caused by the non-proton conductive LCP. During the electrochemical evaluation, the superior cell performance of the composite membrane was evident, with a current density of 5.41 A/cm2 at 1.9 V, compared to 4.65 A/cm2 for the pristine membrane, which can be attributed to the smaller membrane resistance of the composite membrane. From the results of the degradation rates, the prepared composite membrane also showed enhanced cell efficiency and durability during the PEMWE operations.
9
Wu, Mi, Zhengyi Han, Wen Liu, Jinrong Yao, Bingjiao Zhao, Zhengzhong Shao e Xin Chen. "Silk-based hybrid microfibrous mats as guided bone regeneration membranes". Journal of Materials Chemistry B 9, n. 8 (2021): 2025–32. http://dx.doi.org/10.1039/d0tb02687e.
Testo completoAbstract (sommario):
LAPONITE® (LAP) nanoplatelets were incorporated within a regenerated silk fibroin (RSF) microfibrous mat via electrospinning, which exhibited better cell adhesion and proliferation of bone marrow mesenchymal stem cells (BMSCs) than the pristine RSF ones.
10
Silva, Jhonatan M., Fernando E. Maturi, Hernane S. Barud, Vera R. L. Constantino e Sidney J. L. Ribeiro. "New organic-inorganic hybrid composites based on cellulose nanofibers and modified Laponite". Advanced Optical Technologies 7, n. 5 (25 ottobre 2018): 327–34. http://dx.doi.org/10.1515/aot-2018-0030.
Testo completoAbstract (sommario):
Abstract The combination of cellulosic materials and clays, such as Laponite, can provide composites with superior optical and mechanical properties compared to pristine cellulose. Synthetic clays can also be used as a host matrix for the immobilization of luminescent complexes, as the incorporated complexes may present enhanced emission quantum efficiency, photo and thermostability compared to the non-immobilized ones. In this way, we, herein, report the preparation of luminescent composites through the incorporation of a Eu(III) complex [Eu3+(tta)n] containing Laponite (Lap) into cellulose nanofibers (CNF). The thermogravimetry results show that the obtained CNF/Lap@[Eu3+(tta)n] films present higher thermal resistance than the CNF film. The Eu3+(tta)n species were found in the composite structure with preserved luminescence characteristics, and no leaching or degradation of the organic ligand was observed with the preparation of the composites.
Tesi sul tema "PRISTINE LFP"
1
KHARB, SACHIN. "THEORETICAL MODELLING AND SIMULATION OF PRISTINE LFP AND Ni DOPED LFP AS CATHODE MATERIAL OF LITHIUM ION BATTERY". Thesis, 2019. http://dspace.dtu.ac.in:8080/jspui/handle/repository/16716.
Testo completoAbstract (sommario):
A simulation model for electrochemical impedance spectroscopy (EIS) of pristine LiFePO4 (LFP), doped with various concentrations of Ni such as LiNi.03Fe0.97PO4 (LFNP3), LiNi.05Fe0.95PO4 (LFNP5) and LiNi.07Fe0.93PO4 (LFNP7) in place of Fe has been developed in COMSOL Multiphysics. The model was studied under constant frequency domain perturbation using AC current impulses of 5-10 mA in frequency range 10kHz-10mHz. The simulated model parameters, which depict ideal conditions were varied one at a time, and then, two at a time to bring them close to experimental performance as extracted from experimental data. Among all the undoped and Ni doped LFP samples, lithium iron phosphate doped with 3% Ni i.e. LiNi.03Fe0.97PO4 comes close to 92% of the theoretical predicted yield [55], which translates to a maximum electrode state of charge of 0.9-0.92. The dielectric constant of pristine LFP, LFNP3, LFNP5 and LFNP7 is dependent on frequency of operation and affects the capacitance of electrode as the frequency domain perturbation is investigated. At low level of doping, the electrochemical performance improves, but on increasing the doping content of Ni more than 5 %, the resistances increase beyond that of pristine LPF.
2
MANISH e PINKI. "STRUCTURAL AND ELECTROCHEMICAL STUDY OF OLIVINE TYPE LIFEPO4 AS CATHODE MATERIAL". Thesis, 2023. http://dspace.dtu.ac.in:8080/jspui/handle/repository/20117.
Testo completoAbstract (sommario):
This study is intended to synthesize the olivine-type pristine LiFePO4 (LFP) using the solid-state ball
milling method. The structural, electrical, and electrochemical properties of as synthesized pristine
LiFePO4 has been analyzed. The synthesized sample was characterized using X-ray diffraction (XRD)
to confirm the single/mixed phase formation of the olivine type LFP as a cathode material. Hence, the
Rietveld refinement analysis of the observed XRD pattern indicates that olivine type orthorhombic
single phase with the space group, Pnma is formed without any impurity. Fourier Transform Infrared
Spectroscopy (FTIR) is also performed to see the groups developed, bond strength and bond
stretching and bond vibrations in the LFP. The dc conductivity and activation energy were estimated
by the source measurement unit using Arrhenius equation. The electrochemical performance of LFP
has been carried using Cyclic Voltammetry (CV), Electrochemical impedance spectroscopy (EIS)
and Galvanostatic charge/discharge (GCD) methods. Here, it is found that the 1st cycle of pristine LFP
delivers a specific discharge capacity of 52(±5) mAh g-1
at 0.5C rate and after 50 charge/discharge
cycles a noticeable retention in the capacity is observed which implies that, the electrochemical Li+
insertion/extraction process is extremely reversible and that the structure of pristine LiFePO4
is quite stable and also the pristine LFP has a coulombic efficiency of greater than 99 %.
Atti di convegni sul tema "PRISTINE LFP"
1
San Andre´s, Luis, e Keun Ryu. "Flexure Pivot Tilting Pad Hybrid Gas Bearings: Operation With Worn Clearances and Two Load-Pad Configurations". In ASME Turbo Expo 2007: Power for Land, Sea, and Air. ASMEDC, 2007. http://dx.doi.org/10.1115/gt2007-27127.
Testo completoAbstract (sommario):
Gas film bearings enable the successful deployment of high-speed micro-turbomachinery. Foil bearings are in use; however, cost and lack of calibrated predictive tools prevent their widespread application. Other types of bearing configurations, simpler to manufacture and fully engineered, are favored by commercial turbomachinery manufacturers. Externally pressurized tilting pad bearings offer a sound solution for stable rotor support. This paper reports measurements of the rotordynamic response of a rigid rotor, 0.825 kg and 28.6 mm in diameter, supported on flexure pivot tilting pad hybrid gas bearings. The tests are performed for various imbalances, increasing supply pressures, and under load-on-pad (LOP) and load-between-pad (LBP) configurations. Presently, the initial condition of the test bearings shows sustained wear and dissimilar pad clearances after extensive testing reported earlier, see Ref. [1]. In the current measurements, there are no noticeable differences in rotor responses for both LOP and LBP configurations due to the light-weight rotor, i.e. small static load acting on each bearing. External pressurization into the bearings increases their direct stiffnesses and reduces their damping, while raising the system critical speeds with a notable reduction in modal damping ratios. The rotor supported on the worn bearings shows a ∼10% drop in first critical speeds and roughly similar modal damping than when tested with pristine bearings. Pressurization into the bearings leads to large times for rotor deceleration, thus demonstrating the little viscous drag typical of gas bearings. Rotor deceleration tests with manually controlled supply pressures eliminate the passage through critical speeds, thus paving a path for rotordynamic performance without large amplitude motions over extended regions of shaft speed. The rotordynamic analysis shows critical speeds and peak amplitudes of motion agreeing very well with the measurements. The synchronous rotor responses for increasing imbalances demonstrate the test system linearity. Superior stability and predictable performance of pressurized flexure pivot gas bearings can further their implementation in high performance oil-free microturbomachinery. More importantly, the measurements show the reliable performance of the worn bearings even when operating with enlarged and uneven clearances.
2
Niutta, Carlo Boursier, Raffaele Ciardiello, Giovanni Belingardi e Alessandro Scattina. "Experimental and Numerical Analysis of a Pristine and a Nano-Modified Thermoplastic Adhesive". In ASME 2018 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/pvp2018-84728.
Testo completoAbstract (sommario):
In this work, the mechanical properties of two different adhesives compositions have been investigated both experimentally and numerically. The studied thermoplastic adhesives are Hot-Melt Adhesive (HMA). In particular, a pristine and a nanomodified adhesive with 10% in weight of iron oxide have been considered. The adhesives have been subjected to a series of single lap joint (SLJ) tests using adherends made of polypropylene copolymer. As it is well-known, the structural-mechanical behavior of adhesive joints is mostly influenced by the bonding process: thickness of adhesive as well as its application procedures and the surface preparation of adherends are among the most influencing factors. In addition, the mechanical behavior of SLJ test is particularly influenced by the correct alignment of adherends and applied load. These aspects have been investigated, analyzing the experimental results. Moreover, the experimental results have been used to develop a numerical model of the two adhesives. The numerical analysis has been carried out using the commercial software LS-DYNA. Transient nonlinear finite element analysis has been performed to simulate the mechanical behavior of the thermoplastic adhesives. In particular, the cohesive formulations of the elements have been taken into consideration after a careful literature review. In order to set-up and to validate the mechanical properties of the adhesives, the experimental SLJ tests have been simulated. The developed finite element models enable to investigate more complex joint structures where these types of adhesives are used, such as plastic piping systems and automotive applications. Further, the numerical models allow to investigate with higher accuracy and lower time different aspects such as manufacturing and non-linear effects.
3
Albakri, Mohammad I., Sriram Malladi e Pablo A. Tarazaga. "Non-Linear Impedance-Based Structural Health Monitoring for Damage Detection and Identification". In ASME 2015 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/smasis2015-8964.
Testo completoAbstract (sommario):
Impedance-based structural health monitoring (SHM) is a non-destructive, active technique for real-time structural damage assessment. Conventional impedance-based SHM practices apply a sinusoidal signal of fixed amplitude to excite the piezoceramic patch and obtain the impedance signature over a certain frequency range. Damage is then detected by comparing the measured impedance signature to a baseline measurement taken at the pristine state. In this work, the amplitude of the driving signal, which is directly related to the magnitude of the excitation force acting on the structure, is introduced as an additional variable, and sweeps over both frequencies and amplitudes are performed. Several structural defects, such as cracks and loose joints, are nonlinear in nature. Therefore, changing the excitation force will allow the detection of such damage induced nonlinearities and track their evolution. Numerical simulations are carried out to study the effects of nonlinearities on the impedance signature using a single mode model. Several types of structural nonlinearities, such as hardening, softening, and nonlinear damping are studied with the assumption that the piezoelectric actuator stays in its linear regime. Experiments are conducted on a single beam and a lap joint, and impedance signatures in the range of 12–15 KHz are measured at different levels of excitation. Nonlinear damping and softening behavior are detected experimentally by examining the measured impedance signatures. Numerical and experimental findings suggest the possibility of detecting and tracking structural nonlinearities using impedance measurements.