Elastic Recovery Rate Research Articles

Molecular dynamics analysis on the indentation hardness of nano-twinned nickel

Molecular dynamics simulations were employed to perform the nanoindentation analysis of nanocrystalline nickel with a variety of crystal structures (single-crystal, polycrystalline, and nano-twinned) and twin layer thicknesses under an indenter of spherical shape. To understand the effects of crystal structure and twin spacing on nanoindentation responses, the indentation force, strain, atomic rearrangement, dislocation, temperature, hardness, Young's modulus and elastic recovery rate of the indentation region were analyzed. It was noted that the three types of nanocrystalline nickel's mechanical properties and elastic recovery rate were greatly affected by their crystal structures. The results show that the hardness of the nano-twinned nickel is negatively correlated with the thickness of the twin layer, and the maximum hardness is 18.1 GPa when the thickness of twin layer is 1.2 nm. For the three structures, in the width direction, the elastic recovery ratio of the nano-twin structure is the largest, and the elastic recovery ratio of the nanotwin structure in the depth direction is the smallest. In the single crystal structure, the compression area is concentrated under the indenter and distributed in a ' V ' shape, and in the polycrystalline and twin structures, the compression area is scattered. In the polycrystalline structure, the compression area were distributed below the indenter and at crystal boundaries. In the nano-twinned structure, the compression area were mainly distributed below the indenter.

A Review on Knitted Flexible Strain Sensors for Human Activity Monitoring

AbstractThe recent surge in using wearable personalized devices has made it increasingly important to flexible textile‐based sensors that can be worn comfortably and can sense various body strains. Among them, the knit‐based flexible strain sensors (KFSS) show growing promise for human activity monitoring applications due to its processing flexibility, low cost, wearing comfortability, large strain performance, and high elastic recovery rate. Herein, five sensing mechanisms of knitted flexible strain sensors containing contact resistance, length resistance, tunneling effect, micro‐crack propagation, and disconnection mechanism are summarized, which can be used on different human activity strain conditions, e.g., physiological activities and limb activities. The main fabrication approaches, including knitting techniques, post‐processing techniques, embroidery, and sewing techniques are discussed. Six crucial parameters with corresponding calculation formulas for evaluating sensing performance and review specific applications of KFSS for human limb activity and physiological activity monitoring in healthcare, motion tracking, safety protection, and human–machine interaction are also described. Finally, the tough challenges and prospects of KFSS with the aim of providing meaningful guidance and direction for future research are critically analyzed.

Performance and Mechanism of High-Viscosity and High-Elasticity Bitumen (HVE-MB) Modified with Five Additives

In order to improve the viscoelasticity of bitumen, several modifiers were compounded with it, including SBS, reclaimed rubber powder, tackifier, plasticizer, and oil stabilizer, to produce High-viscosity and High-elastic Modified Bitumen (HVE-MB). The viscoelasticity and various physical and rheological properties of the bitumen were evaluated using a number of factors, such as dynamic viscosity at 60 °C, elastic recovery, penetration, softening point, ductility, and DSR. By comparing different types of modifiers and the content of SBS, it was found that the viscoelasticity of the original bitumen was significantly improved by adding the modifiers. In comparison to the original bitumen, the dynamic viscosity of the HVE-MB increased by more than 110 times, the elastic recovery rate more than doubled, the softening point and ductility improved, and the penetration decreased. As the content of SBS increased, the improvement in the properties became more significant. The workability of HVE-MB satisfies the requirement of less than 2.5 °C by adding the suitable dosage of stabilizer. On the other hand, the content of SBS can be adjusted based on the specific requirements. It is a sustainable and economic way to use the reclaimed rubber powder to improve the technical performance of bitumen.

Rational design for the development of thermoplastic poly(ether-ester) elastomers from bio-based 2,5-furandicarboxylic acid with high elasticity

Development of bio-based thermoplastic poly(ether-ester) elastomer (TPEE) with high performance similar to commercial and petroleum-based TPEE is of great interesting nowadays. Herein, by considering both the hard and soft segments, a rational design strategy is proposed for the synthesis of bio-based TPEE with high elasticity based on a bio-based aromatic monomer 2,5-furandicarboxylic acid (FDCA). The hard segment is poly(neopentyl glycol 2,5-furandicarboxylate) (PNF), a FDCA-based polyester with both high melting temperature and crystallization ability. While the soft segment is poly(tetramethylene glycol) (PTMG), which is widely used for the synthesis of TPEE. By adjusting the molecular weight (Mn) of PTMG soft segment from 650 to 2900 g/mol and its content from 50 to 70 wt%, a series of bio-based TPEEs with excellent performance were synthesized. Our preliminary study of PNF-PTMG multiblock copolymers has shown that the elastic recovery rate is outstanding. The initial elastic recovery ratio at 200 % strain can approach 80 % when the Mn of PTMG is 2000 g/mol and the wt.% of PTMG was 70 %, which is significantly higher than those of the commercial TPEEs. PNF-PTMG displays increasing thermal resistance with Tm up to 194 °C with the increasing of soft segment length. This study suggests a feasible solution for the preparation of bio-based TPEE with ideal performance.

Upcycling of thermoplastic polyurethane into covalent adaptable networks via chain breaking‐crosslinking strategy

AbstractThermoplastic polyurethane (TPU), as one of the most widely used elastomers, has received rapid development, and its recycling becomes increasingly urgent. In this work, a TPU is upcycled to PU covalent adaptable networks (CANs) via chain breaking‐crosslinking strategy of being extruded with polyol and isophorone diisocyanate (IPDI) on a micro twin‐screw extruder. The carbamate exchange between the polyol and TPU breaks the chain of TPU and introduces plenty of reactive hydroxyl groups, which activates the TPU chain. Long‐chain‐branched TPU with hydroxyl groups is obtained during the chain‐breaking step and then crosslinked with IPDI to obtain highly crosslinked networks. PU‐CANs exhibit improved mechanical properties and elastic recovery rate, which is propitious to elastomers. Moreover, the crosslinked network greatly enhances the creep resistance and solvent resistance of the material. PU‐CANs maintain favorable reprocessability, suitable for screw extrusion and hot‐press processing. This work provides a simple and efficient method to upcycle TPU into reprocessable highly‐crosslinked polymers and improve the properties of polymers.

PREPARATION AND PERFORMANCE OF CEMENTING MATERIALS FOR RAPID MAINTENANCE OF PAVEMENT POTHOLES

At present, China has entered the peak stage of large-scale maintenance, but repair materials for asphalt pavement potholes are subjected to problems, such as low construction efficiency and poor durability. Polyurethane modified epoxy acrylic resin was selected in this study to repair pavement potholes rapidly and improve durability further. Meanwhile, the cementing material and aggregate were formed into a mixture for rapid repair. A four-factor and four-level orthogonal experiment was designed, and the optimal mass ratio of each component of the cementing material (EPMY) was determined according to three indexes: tensile strength, elongation at break, and viscosity. The basic properties of the material were evaluated using viscosity, glass transition temperature, thermal stability, and elastic recovery rate tests. Finally, the mechanical properties of EPMY immersed in water, salt, acid, and oil solutions were tested under different environmental stimuli. Results showed that the optimal mass ratio of epoxy resin binder is 100% epoxy acrylic resin:15% diluent:30% toughening agent:60% curing agent:6% accelerant, with a tensile strength of 21.48 MPa and an elongation at break of 48.3% at ?10 °C. Elastic recovery rate is 51.3% at room temperature, glass transition temperature is ?13.6 °C, and mass residual rate of EPMY is 10.06% when the temperature rises to 500 °C. The mechanical properties of EPMY are maximally affected by the acidic solution; and the elongation at break, bending strength, and bending deformation are reduced by 11.63%, 7.52%, and 9.58%, respectively. Moreover, and the elongation at break of EPMY can be maintained above 89%. The cementing material can be used for the rapid repair of pavement potholes, thereby increasing the convenience of maintenance work and improving the maintenance level. Keywords: pavement materials, epoxy resin, polyurethane, material design, mechanical properties

Construction of Stretchable and Large Deformation Green Triboelectric Nanogenerator and Its Application in Technical Action Monitoring of Racket Sports

The rapid development of E-Skin has attracted researchers’ attention to portable wearable devices. However, it is a great challenge to achieve high-output performance and high-environmental protection simultaneously. Polyhydroxybutyrate (PHB) has excellent electron-withdrawing ability and biodegradability, but its stretching ability is poor, which limits its application in portable wearable devices. In this paper, the biocompatible poly(lactide-co-caprolactone) (PLCL) was innovatively selected to modify the properties of the PHB electrospun membranes, and PHB/PLCL composite membranes with different contents of PLCL were constructed. Then, the expanded polytetrafluoroethylene (ePTFE) membranes and PHB/PLCL electrospun membranes were used as the friction layers to construct a flexible triboelectric nanogenerator (TENG). With the increase of PLCL contents, the elastic recovery rate of the composite membranes increased to 68% of tension at 40% strain. The toughness of the composite membrane was increased by 546%, which exhibits ultratoughness and stretchable properties. Based on the ultratoughness and high elasticity electrospun membranes with 50% PLCL, a stretchable and large deformation sensing device was made. The PHB/PLCL-ePTFE TENG could distinguish pingpong and badminton accurately, as well as their various postures such as forehand, backhand, smash poses, etc., which provided a new idea for large deformation monitoring of TENGs.

Dendrimer Based Binders Enable Stable Operation of Silicon Microparticle Anodes in Lithium-Ion Batteries.

High-capacity anode materials (e.g., Si) are highly needed for high energy density battery systems, but they usually suffer from low initial coulombic efficiency (CE), short cycle life, and low-rate capability caused by large volume changes during the charge and discharge process. Here, a novel dendrimer-based binder for boosting the electrochemical performance of Si anodes is developed. The polyamidoamine (PMM) dendrimer not only can be used as binder, but also can be utilized as a crosslinker to construct 3D polyacrylic acid (PAA)-PMM composite binder for high-performance Si microparticles anodes. Benefiting from maximum interface interaction, strong average peeling force, and high elastic recovery rate of PAA-PMM composite, theSi electrode based on PAA-PMM achieves a high specific capacity of 3590 mAh g-1 with an initial CE of 91.12%, long-term cycle stability with 69.80% retention over 200 cycles, and outstanding rate capability (1534.8 mAh g-1 at 3000mA g-1 ). This work opens a new avenue to use dendrimer chemistry for the development of high-performance binders for high-capacity anode materials.

Fabrication of Silane-Grafted Cellulose Nanocrystals and Their Effects on the Structural, Thermal, Mechanical, and Hysteretic Behavior of Thermoplastic Polyurethane.

Reinforcement of polymer nanocomposites can be achieved by the selection of the appropriate fabrication method, surface modification, and orientation of the filler. Herein, we present a nonsolvent-induced phase separation method with ternary solvents to prepare thermoplastic polyurethane (TPU) composite films with excellent mechanical properties using 3-Glycidyloxypropyltrimethoxysilane-modified cellulose nanocrystals (GLCNCs). ATR-IR and SEM analyses of the GLCNCs confirmed that GL was successfully coated on the surface of the nanocrystals. The incorporation of GLCNCs in TPU resulted in the enhancement of the tensile strain and toughness of pure TPU owing to the enhanced interfacial interactions between them. The GLCNC-TPU composite film had tensile strain and toughness values of 1740.42% and 90.01 MJ/m3, respectively. Additionally, GLCNC-TPU exhibited a good elastic recovery rate. CNCs were readily aligned along the fiber axis after the spinning and drawing of the composites into fibers, which further improved the mechanical properties of the composites. The stress, strain, and toughness of the GLCNC-TPU composite fiber increased by 72.60%, 10.25%, and 103.61%, respectively, compared to those of the pure TPU film. This study demonstrates a facile and effective strategy for fabricating mechanically enhanced TPU composites.

Nanoindentation size effects of mechanical and creep performance in Ni-based superalloy

Nanoindentation technique was adopted to study indentation size effects of physical-mechanical and creep performance with various depths (200–2000 nm) in GH901 utilising sharp and spherical tip. Residual impressions of both indenters with pile-up patterns are discussed. Nanohardness, reduced modulus and elastic recovery rates curves versus maximum displacement of two tips are obtained and nanohardness size effects are discussed with different models for Berkovich tip. The data obtained with spherical indentation are analysed separately by establishing stress–strain diagram. The creep results using Berkovich tip indicate that creep strain rate declines while creep stress exponent first decreases and then increases with the increasing depth; the creep stress exponent (n) values, 2.39–7.35, imply the dominant creep deformation mechanism is dislocation control.

Characterization of bulk metallic glasses by microscratch test under Rockwell C diamond indenter and progressive normal load

Microscratch responses of 14 bulk metallic glasses were investigated by Rockwell C diamond indenter under progressive normal load. Effects of mechanical properties on microscratch variables are quantified for bulk metallic glasses. Penetration depth increases linearly with normal force, and a power-law function can be used to express the variation of residual depth with normal force under small loads. Residual depth fluctuates under large loads; and elastic recovery rate, scratch friction coefficient, lateral hardness, and scratch hardness all tend to be stable under large loads. The asymptotic scratch friction coefficient decreases linearly with the increase in scratch hardness. The asymptotic elastic recovery rate is found to be proportional to the ratio of elastic modulus over Knoop hardness, and scaling relationships among hardness values and yield strength are found. Different scratch-based methodologies of assessing fracture toughness are compared and discussed. The successful characterization of fracture toughness by scratch-based methods requires sufficiently large loads, and different methodologies have different scopes of application.

Dual functional low surface energy coating of anti-corrosion / fouling via crosslinking polysilazane preceramic precursor incorporated with fluorine

A dual functional low surface energy coating with polysilazane preceramic precursor is developed to form a silicon-based polymeric film. The result shows that the lowest surface free energy of the fluorinated silicon-based polymeric film is about 28.43 mJ/m2 and its corrosion potential achieves 0.0899 V by the tafel polarization indicating that it has relatively low surface free energy with high corrosion resistance. The water contact angle of the silicon-based polymeric film with polysilazane preceramic precursor diluted in acetone crosslinked at 400 °C can achieve 126.8°. Polysilazane preceramic precursor incorporated with titanium dioxide, TiO2 is able to reduce the surface energy to lower than 30 mJ/m2 for anti-fouling application. Nanoindentation result shows the fluorinated silicon-based polymeric film has the higher elastic recovery rate, 77.3 % representing that fluoride dopant improves its surface toughness. The average hardness and reduced modulus of the silicon-based polymeric film are superior to that of the pure aluminum, showing that this dual functional low surface energy coating provides a relatively high surface strength with high toughness.

Anisotropic elastic recovery behavior of AlN ceramic during nanoindentation and scratching

The anisotropy of the grain orientation of aluminium nitride (AlN) ceramics leads to great differences in elastic recovery of grains which makes it difficult to achieve high machining accuracy. In this study, the anisotropic elastic recovery behavior of AlN ceramic was investigated by nanoindentation and scratch experiments. The results show that as the main Euler angle the grain increases, the elastic recovery rate of the indentation decreases from 39% to 31%, and the elastic recovery of scratch decreases from 47% to 39%. However, there is a local peak in the elastic recovery rate when the main Euler angle is 75° during scratching. Through the analysis of the Schmid factor, it is found that the ease of activating the sliding system of a grain has a great impact on the elastic recovery rate of scratches. Through further analysis, the elastic recovery rate of grains is mainly affected by the combined action of the base slip system and the prismatic slip system during scratching. The prediction models of the elastic recovery rate during nanoindentation and scratching were established and the prediction results are consistent with the experimental results, indicating the reliability of the prediction model.

Influence of poly(ethyleneimine) functionalized multi-walled carbon nanotubes on mechanical and tribological behavior of epoxy resins

Epoxy-based nanocomposites were prepared with the addition of poly(ethyleneimine) (PEI, an amine-riched polymer) functionalized multi-walled carbon nanotubes (MWCNTs), whose microstructure was characterized by TEM and FTIR spectra. Effects of PEI-functionalized MWCNTs (PEI-MWCNTs) on micromechanical properties of nanocomposites were characterized by instrumented indentation with Berkovich indenter and microscratch test with Rockwell C indenter. With the increase in the content of PEI-MWCNTs: both nanoindentation hardness and elastic modulus of nanocomposites increase; scratch normal hardness and elastic recovery rate decrease in an approximately linear way; fracture toughness obtained by scratch-based linear elastic fracture mechanics increase in an approximately linear way.

Swelled Mechanism of Crumb Rubber and Technical Properties of Crumb Rubber Modified Bitumen.

Crumb rubber modified bitumen (CRMB) has excellent high-temperature performance and fatigue resistance, and is widely used in asphalt pavement to cope with increasing traffic axle load and changing climate. Under conventional preparation conditions, the swelling degree of CR can directly impact the comprehensive properties of CRMB; however, physical and chemical properties research on swelling crumb rubber (SCR) and crumb rubber recycled bitumen (CRRB) in CRMB is relatively lacking. In this paper, the working performance of CRMB and CRRB in high-temperature and low-temperature conditions were studied through physical and working performance testing of bitumen. The CR and SCR were tested by scanning electron microscope (SEM), Fourier transform infrared spectrometer (FTIR), gel permeation chromatography (GPC), and particle size distribution (PSD) tests to study the physicochemical behavior and microscopic effects before and after CR swelling. The results showed that CR dosage was in the range of 10%, 15%, and 20%, as well as that CR dosages have a positive effect on the high- and low-temperature performance, storage stability, and elastic recovery of bitumen. The high-temperature PG grades of bitumen were directly improved by four grades, and the elastic recovery rate increased by 339.9%. CR improved the ultra-low temperature crack resistance of bitumen. Due to the absorption of lighter components by CR, the relative content of the heavy component of bitumen increased; however, its low-temperature performance decreased significantly. After swelling, the CR particle size increased and the range became wider, the surface complexity of CR became higher, and the specific surface area was larger. At the same time, CR carried out the transformation process from large and medium molecules to small molecules. During the swelling process, a new benzene ring structure appeared in the CR, and the C-C bond and C-S bond of CR broke, forming part of the C=C bond.

Enhancing elasticity of Eucommia ulmoides gum by branch pendant strategy

Eucommia ulmoides gum (EUG) was usually considered as a hard rubber with poor elasticity at room temperature because of its crystallinity, which limited its applications in rubber materials, and the extraction of EUG from the plant tissues was a challenge task. Biobased EUG was efficiently extracted by acid catalysis in ionic liquid, and modified by Alder-ene reaction via the novel triazolinedione containing different branched alkyl groups, enabling it to become soft rubber with greatly improved properties including excellent elastic recovery rate of 92%, high elongation at break of 1311%, low Young's modulus of 0.44 MPa, and low hardness of 50o, which were comparable to those of natural rubber. Therefore, this sustainable elastomeric material with tunable and enhanced physical and elastic properties would have broadened applications in tires and other rubbery products.

Large-Scale Preparation of Micro-Nanofibrous and Fluffy Propylene-Based Elastomer/Polyurethane@Graphene Nanoplatelet Membranes with Breathable and Flexible Characteristics for Wearable Stretchy Heaters.

Effective personal thermal management is crucial for protecting human health during cold weather. Therefore, wearable heaters based on electric-heating membranes are one of the most promising devices to become essential appliances in our daily lives. The main challenge toward this goal is the development of electric-heating membranes with adequate breathable, flexible, and stretchable characteristics. In the work presented here, micro-nanofibrous fluffy electric-heating membranes were prepared by coating polyurethane/graphene nanoplatelet (PU@GNP) films onto melt-blown propylene-based elastomer (PBE) micro-nanofibrous membranes via a facile, cheap, and large-scale method consisting of a coating-compressing cyclic process. Investigation of the resulting PBE/PU@GNP membranes showed that the PU@GNP films were uniformly deposited onto the PBE micro-nanofiber surfaces, forming fluffy interconnected conducting channels. By applying a voltage of 36 V to the prepared PBE/PU@GNP membranes, the temperature increased to 69.7 °C, confirming excellent electric-heating features. Moreover, the porosity of the fabricated membrane could be tailored readily by adjusting the coating-compressing cycles. Benefiting from the conducting channels, the PBE/PU@GNP membranes exhibited efficiently regulated air permeability ranging from 212 to 60.2 mm/s, a prominent softness score of 53.8, and an excellent elastic recovery rate of 85.5%. These findings demonstrate that PBE/PU@GNP micro-nanofibrous fluffy membranes may well be suitable for application in electric-heating clothing. The cyclic coating-compressing preparation process may be attractive in industrial manufacturing.

Effect of carbon fiber on the properties of polymer cement based building sealant

AbstractThe working property, bond property, and mechanical property of five kinds of polymer cement based building sealant (PCBS) with different carbon fiber content were tested. The effect of carbon fiber on the properties of PCBS was discussed by analyzing the variation of the leveling performance, consistency, low temperature flexibility, surface dry time, elastic recovery rate, tensile mechanical property, and shear mechanical property of PCBS with carbon fiber content. And the modification mechanism of carbon fiber on PCBS was interpreted using scanning electron microscopy and mercury intrusion porosimetry techniques. The results shows that PCBS still has good working property and bonding property with carbon fiber addition. As the carbon fiber content increases, the leveling performance and low temperature flexibility of PCBS are unaltered., the consistency increases, while the surface drying time and elastic recovery rate decrease. The tensile and shear mechanical properties of PCBS can be improved by adding carbon fiber. With the increase of carbon fiber content, the strength performance indexes of PCBS increase, while the energy consumption performance indexes first increased followed by a decrease. When the carbon fiber content is 0.1%, the properties of PCBS is the best. The pore structure of PCBS gradually deteriorates, and the total porosity and the percentage of macropores increase with carbon fiber addition. Carbon fiber primarily exerts cracking resistance and internal deterioration effects in PCBS.

Enhancement of permittivity and energy storage efficiency of poly (vinylidene fluoride-chlorotrifluoroethylene) by uniaxial stretching

Dielectric polymer film capacitors with a high-power density as well as efficient charge and discharge rates have great potential for application to fulfill the miniaturized and lightweight requirements of the electronic and stationary power systems. It was reported that the elastic recovery rate and energy storage density of poly (vinylidene fluoride-chlorotrifluoroethylene) [P(VDF-CTFE)] polymer film can be enhanced through thermostatic uniaxial stretching. But it is unknown about the relationship between the stretching rate and above properties. In this study, we investigated the effect of different stretching rates on the conformation, elastic recovery, dielectric constant, and energy storage density of stretched P(VDF-CTFE) polymer films. It was found that the stretching rate significantly affected the formation of polar [Formula: see text]-crystal phase, causing different dielectric properties. The degrees of elastic recovery of P(VDF-CTFE) film vary with stretching rates. Among them, the elastic recovery rate of the P(VDF-CTFE) 94/6 film is 46.5% at a stretching rate of 15 mm/min, the dielectric constant is 12.25 at 100 Hz, and the energy density reaches 3.95 J/cm3with the energy loss of 39% at 200 MV/m field.

On cutting process damping for small cutters by including the influences of the dead metal zone and elastic recovery

Existing ploughing-based process damping models oriented for the cutting processes did not consider two important factors, i.e. the dead metal zone (DMZ) in front of the rounded cutting edge and the material elastic recovery rate under the clearance face, and thus, they cannot exactly detect the underlying mechanism of process damping in the cutting processes with small cutters. This article systematically investigates the generation mechanism of cutting process damping for small cutters, and proves that the DMZ and the elastic recovery rate have combined contribution to the process damping of small cutters’ cutting. It is theoretically found that in contrast to the full elastic recovery assumed in the macro cutting processes, the material under the cutter’s clearance face is partially recovered in the cutting processes with small cutters, due to the relatively high proportion of plastic deformation. The actual recovery height is numerically calibrated based on the ideal plastic assumption of the stress-strain relationship. Expressions of the statically and dynamically indented areas, which are required for deriving process damping model, are analytically formulated as the functions of the DMZ and the actual recovery height since they greatly change the indentation boundaries between the rounded cutting edge and the clearance face. Above derivations are then utilized to derive the expressions of dynamic cutting forces, and subsequently, the process damping effect is considered to analyze the milling stability. Finally, a series of milling tests with small cutter prove the reasonability of the proposed process damping model.