Stretchable ionic skins are intriguing in mimicking the versatile sensations of natural skins. However, for their applications in advanced electronics, good elastic recovery, self-healing, and more ...importantly, skin-like nonlinear mechanoresponse (strain-stiffening) are essential but can be rarely met in one material. Here we demonstrate a robust proton-conductive ionic skin design via introducing an entropy-driven supramolecular zwitterionic reorganizable network to the hydrogen-bonded polycarboxylic acid network. The design allows two dynamic networks with distinct interacting strength to sequentially debond with stretch, and the conflict among elasticity, self-healing, and strain-stiffening can be thus defeated. The representative polyacrylic acid/betaine elastomer exhibits high stretchability (1600% elongation), immense strain-stiffening (24-fold modulus enhancement), ~100% self-healing, excellent elasticity (97.9 ± 1.1% recovery ratio, <14% hysteresis), high transparency (99.7 ± 0.1%), moisture-preserving, anti-freezing (elastic at -40 °C), water reprocessibility, as well as easy-to-peel adhesion. The combined advantages make the present ionic elastomer very promising in wearable iontronic sensors for human-machine interfacing.
The present work evaluates the usefulness of “in die” elastic recovery descriptors as an indicator of tabletability. Tablet elastic recovery (“in die” and “out-of-die”) with respect to applied ...compression speed and dwell time were evaluated by applying 2
2-full factorial design with one centre point. Flat tablets of constant true volume were compressed on a compaction simulator at constant pressure. “In die” and “out-of-die” elastic recoveries were calculated by using obtained respective continuous compression profiles and measured tablet dimensions (height and diameter) at a constant humidity. Linear relationship between “in die” and “out-of-die” elasticity descriptors was found. The qualitative and quantitative relationships of “in die” elasticity descriptors with tensile strength (TS) was evaluated by principal component analysis (PCA) and partial least square regression (PLS). These analyses showed that “in die” elasticity descriptors like Heckel yield pressure of elasticity and immediate axial recovery (IAR) have significant negative influence on TS. The present study shows that the experimentally easier accessible “in die” elastic recovery method can be used as an indicator of elasticity of various pharmaceutical tableting materials with respect to tabletability.
The tablet elasticity is important for charactering tablet production problems like capping and lamination. To characterize tablet elasticity, tablet expansion was evaluated form the unloading of upper punch to the 7
days of storage time. The maximum axial tablet elasticity was occurred from the unloading of upper punch to the ejection of tablet from the die.
Display omitted
•An exactly mechanics cutting force model is established in micro end-milling.•Tool trajectory, tool runout, the minimum chip thickness and the material's elastic recovery are considered in the ...determination of IUCT.•A new model to rectify the issue of tool runout effect on the cutting force.•Force coefficients as nonlinear function of the IUCT are extracted by FE simulation of micro orthogonal cutting.
Prediction of cutting force has great significance for controlling the micro-end-milling processes. In this study, a mechanics model for exactly prediction cutting force is comprehensively established by considering the variety of entry and exit angles for each engaged cutting edge and an accurate instantaneous uncut chip thickness (IUCT). The determination of IUCT has considered the combination of the minimum chip thickness, tool run-out, and the material's elastic recovery, which is embedded in the cutting force model. Further, cutting force coefficients as function of uncut chip thickness have been calculated by using finite element method (FEM). To verify the reliability of the presented cutting force model, a series of experiments for cutting force are conducted and experimental results are compared to cutting force predicted. The results demonstrate that the cutting force predicted is well in agreement with that of measured. The effects of elastic recovery and tool run-out on cutting force also are investigated. Some conclusion can be drawn that elastic recovery can more obviously affect the cutting force predicted with smaller the feed per tooth, the errors of experimental and predicted is getting smaller with increasing the cutting depth, the slight change of tool run-out will lead to a great variation in cutting force.
Display omitted
The displacement vector of Cu-Zr atoms under imprinting process after completion unloading stage at temperature of 300 K for different alloy compositions.
Display omitted
•The imprinting force and ...the STZs increase as increasing angle of the punch.•The residual stress rises up in the loading, reduces in the unloading as a larger speed.•The atoms move more disorderly, the RDF peak decreases as increasing temperature.•The atoms movement is denser, the residual stress increases as greater Cu content.•The Cu-Zr MGs formability can be improved by increasing Cu content, and velocity.
Molecular dynamics simulations are employed to study mechanistic characteristics of Cu-Zr metallic glasses films during the imprinting process. The influences of punch geometry, loading velocity, temperature, and alloy composition are exhaustively analyzed in terms of imprinting force, deformation characteristic, residual stress, displacement vector, radial distribution function, and elastic recovery ratio. The results show that the imprinting force and the shear transformation zones (STZs) of the Cu50Zr50 MGs films increase, while the residual stress has slightly changed with increasing angle of the punch. In the case of different imprinting velocities, the imprinting force increases. The residual stress also increases in the loading stage; however, it decreases in the unloading stage. The imprinting force, residual stress, highest peak of the radial distribution function (RDF) decrease and movement of atoms become irregular as increasing of temperature. As increasing Cu proportion, the imprinting force increases, the density of atom movement and residual stress increases, while the highest peak of the RDF decreases. The formality of the Cu-Zr MGs films can be improved by increasing Cu proportion and loading velocity, decreasing temperature due to lower average elastic recovery ratio. The imprinting force values are in the range of 100–185 nN, the residual stress values of the loading stage are from 0.44 to 0.82 GPa and the residual stress values of the unloading stage are from 0.4 to 0.9 GPa, the elastic recovery ratio are in the range of 0.17–20.26%.
The design and synthesis of supramolecular self‐healing polymers with high healing efficiency and excellent integrated mechanical properties is challenging due to conflicting attributes of dynamic ...self‐healing and mechanical properties. Herein, this study introduces a design concept, that is, “dynamic hard domains,” to balance self‐healing performance, mechanical strength, elastic recovery, and at the same time obtain extreme toughness. The essential features of the dynamic hard domains include: (i) a noncrystallized and loose structure, (ii) low binding energy and high mobility, and (iii) sequential dissociation and rapid rearrangement. Based on this strategy, a simple one‐step polycondensation route is reported to synthesize a transparent polyurethane‐urea supramolecular elastomer (PPGTD‐IDA), which successfully combines decent mechanical strength, extreme toughness, outstanding notch‐sensitiveness, self‐recoverability, and room‐temperature self‐healing. Upon rupture, the PPGTD‐IDA completely restores the mechanical properties within 48 h. Furthermore, the results demonstrate repeatable healing of mechanical properties and prominent antiaging healability. Taking advantages of merits of PPGTD‐IDA, it can be utilized for fabricating impact‐resistant materials for protection of aluminum alloys as well as stretchable and self‐healing conductors, which exhibits unique characteristics such as stable conductivity during stretching (even after healing or with notch), and automatic elimination of the notch during stretching/releasing cycles.
A transparent supramolecular elastomer, combining relatively high mechanical strength, extreme toughness, outstanding notch‐insensitiveness, self‐recoverability, and room‐temperature self‐healing properties with complete recovery of mechanical properties is facilely synthesized via the design conception of dynamic hard domains. These well‐balanced properties enable its immediate use in impact‐resistant and energy‐absorbing protective materials as well as stretchable and self‐healing conductors.
The current study aims to analyze the nanomechanical properties of phases formed in different layers of the dissimilar junction created at 1050 °C for 30 min between the two alloys austenitic steel ...(SS-304L) and Zircalloy-4 (Zy-4). Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were employed to observe residual imprints’ morphology to understand the nature of deformation. It was observed that the ε-Zr(Fe,Cr)
2
intermetallic exhibited the highest nanohardness value and elastic recovery rate, while the austenitic steel (SS-304L) displayed the lowest nanohardness value and elastic recovery rate. It is noteworthy that higher phase hardness correlates with reduced maximum and residual indentation penetration depths. The significant pile-up observed in the α-(Fe,Cr) phase of the LI layer indicates considerable plastic flow during the nanoindentation test. The crack was observed only at the extremely fragile phase of the intermetallic compound Zr(Fe,Cr)
2
.
This study focuses on the prediction of cutting forces during micro end milling using a novel approach that takes into account the chip thickness accumulation phenomenon. The proposed original force ...model considers the micro end milling kinematics, geometric errors of the machine tool–toolholder–mill system, elastic and plastic deformations of workpiece correlated with the minimum uncut chip thickness, and flexibility of the slender micro end mill. It also includes a novel analytical approach for the instantaneous area of cut. The chip thickness accumulation phenomenon can be manifested as chip thickness variations in the current tool rotation, resulting from material burnishing and elastic recovery in all previous tool rotations. The predicted forces consider the minimum uncut chip thickness value, which has been estimated directly from the micromilling process of AISI 1045 steel based on an original analytic–experimental approach that applies the identification of a stagnant point in the milling process. The results obtained show that the instantaneous and average micromilling forces determined using the proposed model have considerably better conformity with the experimental forces than those predicted using the commonly used rigid micro end milling model. Moreover, the non-linearity of the cutting forces as a function of feed per tooth is strongly affected by multiple cutting mechanism transitions observed during micromilling with uncut chip thicknesses close to the minimum uncut chip thickness value.
Display omitted
•Novel concept of chip thickness accumulation in burnishing-dominant regime.•Minimum uncut chip thickness model for micromilling considering the stagnant point.•Comprehensive micromilling force model considering effective uncut chip thickness.•High accuracy of predicted forces in cutting- and burnishing-dominant regimes.•Influential effect of chip thickness accumulation on micromilling force variations.
The development of chemically recyclable polymers presents the most appealing solution to address the plastics’ end‐of‐use problem. Despite the recent advancements, it is highly desirable to develop ...chemically recyclable polymers from commercially available monomers to avoid the costly and time‐consuming commercialization. In this contribution, we achieve the controlled ring‐opening polymerization (ROP) of bio‐sourced δ‐caprolactone (δCL) using strong base/urea binary catalysts. The obtained PδCL is capable of chemical recycling to δCL in an almost quantitative yield by thermolysis. Sequential ROP of δCL and l‐lactide (l‐LA) affords well‐defined PLLA‐b‐PδCL‐b‐PLLA triblock copolymers, which behave as thermoplastic elastomers with excellent elastic recovery, tensile strength and ultimate elongation. The upcycling of PLLA‐b‐PδCL‐b‐PLLA to recover ethyl lactate and δCL with high yields is achieved by refluxing with ethanol and then distillation under reduced pressure.
This work presents the controlled ring‐opening polymerization (ROP) of δ‐caprolactone (δCL) to produce high‐molecular‐weight PδCL that was capable to recycle back to pristine monomer with an almost quantitative yield (≈99 %). Well‐defined PLLA‐b‐PδCL‐b‐PLLA triblock copolymers with excellent mechanical properties can be easily prepared by sequential ROP of δCL and l‐lactide.
The self-healing properties and ionic sensing capabilities of the human skin offer inspiring groundwork for the designs of stretchable iontronic skins. However, from electronic to ionic ...mechanosensitive skins, simultaneously achieving autonomously superior self-healing properties, superior elasticity, and effective control of ion dynamics in a homogeneous system is rarely feasible. Here, we report a Cl-functionalized iontronic pressure sensitive material (CLiPS), designed via the introduction of Cl-functionalized groups into a polyurethane matrix, which realizes an ultrafast, autonomous self-healing speed (4.3 µm/min), high self-healing efficiency (91% within 60 min), and mechanosensitive piezo-ionic dynamics. This strategy promotes both an excellent elastic recovery (100%) and effective control of ion dynamics because the Cl groups trap the ions in the system via ion-dipole interactions, resulting in excellent pressure sensitivity (7.36 kPa
) for tactile sensors. The skin-like sensor responds to pressure variations, demonstrating its potential for touch modulation in future wearable electronics and human-machine interfaces.
Soft self‐healing materials are compelling candidates for stretchable devices because of their excellent compliance, extensibility, and self‐restorability. However, most existing soft self‐healing ...polymers suffer from crack propagation and irreversible fatigue failure due to easy breakage of their dynamic amorphous, low‐energy polymer networks. Herein, inspired by distinct structure–property relationship of biological tissues, a supramolecular interfacial assembly strategy of preparing soft self‐healing composites with unprecedented crack propagation resistance is proposed by structurally engineering preferentially aligned lamellar structures within a dynamic and superstretchable poly(urea‐ureathane) matrix (which is elongated to 24 750× its original length). Such a design affords a world‐record fracture energy (501.6 kJ m−2), ultrahigh fatigue threshold (4064.1 J m−2), and outstanding elastic restorability (dimensional recovery from 13 times elongation), and preserving low modulus (1.2 MPa), high stretchability (3200%), and high room‐temperature self‐healing efficiency (97%). Thereby, the resultant composite represents the best of its kind and even surpasses most biological tissues. The lamellar 2D transition‐metal carbide/carbonitride (MXene) structure also leads to a relatively high in‐plane thermal conductivity, enabling composites as stretchable thermoconductive skins applied in joints of robotics to thermal dissipation. The present work illustrates a viable approach how autonomous self‐healing, crack tolerance, and fatigue resistance can be merged in future material design.
Catastrophic failure of soft self‐healing materials often derives from its low‐energy primary network structure susceptible to fatigue crack propagation. In this work, a biomimetic strategy of introducing high‐energy preferentially aligned lamellar structure into highly dynamic and superstretchable poly(urea‐urethane) is proposed, successfully surpassing the notorious trade‐off between soft self‐healing, high fracture toughness, and fatigue resistance.
PDF
