High Modulus Materials Research Articles

"Dissolve-on-Demand" 3D Printed Materials: Polymerizable Eutectics for Generating High Modulus, Thermoresponsive and Photoswitchable Eutectogels.

Solvent-free photopolymerization of vinyl monomers to produce high modulus materials with applications in 3D printing and photoswitchable materials is demonstrated. Polymerizable eutectic (PE) mixtures are prepared by simply heating and stirring various molar ratios of N-isopropylacrylamide (NIPAM), acrylamide (AAm) and 2-hydroxyethyl methacrylate (HEMA). The structural and thermal properties of the resulting mixtures are evaluated by 1D and 2D NMR spectroscopy as well as differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). UV photocuring kinetics of the PE mixtures is evaluated via in situ photo-DSC and photorheology measurements. The PE mixtures cure rapidly and display storage moduli that are orders of magnitude greater than equivalent copolymers cured in an aqueous medium. The versatility of these PE systems is demonstrated through the addition of a photoswitchable spiropyran acrylate monomer, as well as applying the PE formulation as a stereolithography (SLA)-based 3D printing resin. Due to the hydrogen-bonding network in PE systems, 3D printing of the eutectic resin is possible in the absence of crosslinkers. The addition of a RAFT agent to reduce average polymer chain length enables 3D printing of materials which retain their shape and can be dissolved on demand in appropriate solvents.

Biomimetic nanofiber-iongel composites for flexible pressure sensors with broad range and ultra-high sensitivity

To achieve high-performance flexible pressure sensors, it is imperative to develop biomimetic devices that mimic the functional structure and sensing mechanism of human skin. Nevertheless, the creation of skin-like sensors with both ultra-high sensitivity and broad response range poses a formidable challenge. Drawing inspiration from the tactile sensing mechanisms and hierarchical structure of human skin, we engineered a nanofiber-iongel (NFIG) composite with internally graded stiffness characteristics and surface semi-embedded microstructures through the application of electrostatic spinning and droplet injection methods. The gel mimics the layered nanofiber structure of human skin, along with its ion-sensing mechanism, and comprises an ion gel infused with highly elastic PVDF-HFP nanofibers. This study explores the impact of Young's modulus and external pressure on unit capacitance, and it establishes a fiber-gel composite model to assess how the fibers influence sensor performance, encompassing ion fluxes, displacements, and alterations in electric potential. These findings reveal that the utilization of high-modulus materials enhances ion mobility, decreases the double electrical layer thickness, and augments pressure resistance. Based on these discoveries, we engineered the NFIG sensor, which exhibits ultra-high sensitivity (>10,000 kPa−1), a wide pressure range (∼1000 kPa), and exceptional stability (over 5000 cycles). Furthermore, this sensor is versatile, finding utility in a range of human monitoring contexts, array configurations, and even skateboard monitoring, thereby substantiating its promise in the fields of human-computer interaction and sports health.

Analysis of fracture state and fatigue life of high modulus carbon fiber wrapped composite barrel

High-modulus Carbon Fiber-reinforced Polymer composites are widely used in critical industries due to their exceptional mechanical properties. However, the fatigue and fracture of high modulus carbon fiber materials are currently poorly studied. For this purpose, the NOL ring fatigue tensile testing is referenced and improved to investigate the performance and service life of high-modulus carbon fiber wound barrels. NOL ring specimens, made of M40 carbon fiber material, are subjected to quasi-static tensile and fatigue tests. The fracture state and characteristics of high modulus materials during fatigue are analyzed. Two-parameter Weibull distribution function is used to analysis statistically the fatigue life results of composite samples. Then, the life curve is drawn for different stress amplitudes. Additionally, the fiber fracture surface is observed under a high-power microscope. The fiber fracture model under brittle fracture is established. The results indicate that the fracture characteristics and mechanisms of high-modulus materials differ from those of high-strength materials, necessitating different fatigue life assessment methods. The fatigue failure of high modulus fibers exhibits brittle fracture similar to quasi-static loss, with flat fracture surfaces and minimal cumulative damage. The failure mechanism is accompanied by brittle fractures with a small amount of fiber pulled out.

Marginal Adaptation of In Vitro Class II Restorations Made Out of Bulk or Conventional Composite Using Single- or Multi-Layered Techniques.

Objective: Testing the influence of various restorative materials (conventional or bulkfill composites) and filling techniques (single- or multi-layered techniques) on the in vitro marginal adaptation of large class II direct composites with supra and sub-gingival margins subjected to thermomechanical loading (TML). Methods: A total of 40 prepared teeth were attributed randomly to five experimental groups. In Group 1, restorations were made of multi-layered high-viscosity conventional composite (Tetric EvoCeram); in Groups 2 and 3, restorations were made of a high viscosity bulkfill composite (Tetric EvoCeram Bulk Fill) applied in one (Group 2) or three layers (Group 3); in Groups 4 and 5, restorations were made of a flowable bulkfill composite (SDR flow) applied in one (Group 4) or two layers (Group 5), covered with a layer of high-viscosity conventional composite (Ceram-X Universal). A single adhesive (OptiBond FL) was used in all groups. All specimens were submitted to a staged TML comprising three phases (2 × 500,000 and 1,000,000 cycles) at 50 N with 3350 thermal cycles (5 to 55 °C) every 500,000 cycles. The tooth-restoration interfaces on proximal surfaces were evaluated quantitatively by scanning electron microscopy, before and after each TML phase, hence at three timepoints (T0, T1, T2 and T3). The following segments were considered for evaluation: proximal, vertical enamel margins (assessed individually on both restoration sides), cervical enamel (restoration side above CEJ) and cervical dentin margin (restoration side below the CEJ). Results: TML induced a significant reduction in continuous adaptation at both enamel and dentin margins in all groups, with percentages of continuous margins ranging from 75.2 to 91.8% at T0, and decreasing to values ranging from 21.3 to 73.9% at T3. Both composite systems and layering protocols had a significant influence on marginal adaptation of the restorations, with statistical associations depending on the restoration group and the timepoint considered. Defective margins in enamel were all of a cohesive nature with micro-fractures, while in dentin, interfacial gaps were the main defect observed. Conclusions/Clinical significance: The present results highlighted significant degradation of marginal adaption after long-term in vitro fatigue test using materials even with high-viscosity conventional resin composites, applied with a proper layering approach in medium-large sub-gingival cavities. While no significant differences were observed at the dentin cervical margins, there was a tendency for better adaptation at the enamel margin when using a higher modulus material with a multi-layered technique.

Sunlight-powered self-excited oscillators for sustainable autonomous soft robotics

As the field of soft robotics advances, full autonomy becomes highly sought after, especially if robot motion can be powered by environmental energy. This would present a self-sustained approach in terms of both energy supply and motion control. Now, autonomous movement can be realized by leveraging out-of-equilibrium oscillatory motion of stimuli-responsive polymers under a constant light source. It would be more advantageous if environmental energy could be scavenged to power robots. However, generating oscillation becomes challenging under the limited power density of available environmental energy sources. Here, we developed fully autonomous soft robots with self-sustainability based on self-excited oscillation. Aided by modeling, we have successfully reduced the required input power density to around one-Sun level through a liquid crystal elastomer (LCE)-based bilayer structure. The autonomous motion of the low-intensity LCE/elastomer bilayer oscillator "LiLBot" under low energy supply was achieved by high photothermal conversion, low modulus, and high material responsiveness simultaneously. The LiLBot features tunable peak-to-peak amplitudes from 4 to 72 degrees and frequencies from 0.3 to 11 hertz. The oscillation approach offers a strategy for designing autonomous, untethered, and sustainable small-scale soft robots, such as a sailboat, walker, roller, and synchronized flapping wings.

Orthotropic vs quasi-isotropic: How the tape orientation influence the performance of disentangled polyethylene laminates

Disentangled ultrahigh molecular weight polyethylene (DPE) is a high-tenacity and high-modulus material having great potential for impact resistance applications. This research presents a comprehensive experimental study on the effect of orientation on the tensile and low-velocity impact performance of laminates produced from DPE tapes. The laminates were constructed by laying the DPE tape at different orientations followed by compression moulding. Quasi-isotropic laminate showed good tenacity in all directions whereas cross-ply orthotropic laminate showed the maximum tenacity in both the principal directions (0° and 90°). The impact energy absorption by the orthotropic laminate was 61.1% higher compared to that of quasi-isotropic laminate. The results imply that cross-ply laminate is the most suitable one for ballistic applications.

Investigation of butadiene-elastomer-based high modulus materials reinforced by basalt, glass, and carbon fabrics

A relevant task in improving the properties of elastomers is to increase their strength and stiffness, which affect the reliability and durability of rubber products. The paper presents a technology for manufacturing high-modulus materials based on SKD-V butadiene rubber and reinforcing layers of fabrics from basalt, glass, and carbon fibers. The results of studying elastic strength properties reveal a significant increase in the ultimate strength of reinforced samples in comparison with an unmodified elastomer. The increase in tensile strength varies from 1.7 to 2.8 times. The addition of reinforcing layers reduced the elongation value by 25 to 47 times compared to rubber without reinforcement. High tensile strength and low elongation increase shear resistance. The wear resistance testing of elastomers coated with reinforcing fabrics shows a decrease in abrasion resistance reduced by a factor of 5.8. Abrasion wear and interaction between the reinforcing filler and the polymer are studied by electron microscopy. The study of the microstructure shows a weak contact between the fiber and the elastomeric matrix. Lack of contact during the abrasion process causes destruction of the fibers on the abrasive surface and their further separation. Due to the combination of high tensile strength and low elongation, the reinforced materials obtain high modulus properties combined with lateral mobility.

Метод изопах в неполяризованном свете

An isopachic method with unpolarized light using a Mach-Zehnder interferometer is proposed. In the case of unpolarized light, isopachics are observed not only due to a change in the thickness of the model but also due to induced birefringence. In contrast to the existing methods, the proposed method allows you to study sections of three-dimensional models or flat stressed samples with no thickness variation. A brief theoretical consideration based on the formalism of the coherence matrix is given, as well as the experimentally obtained isopachic field for a model made from high-modulus material. The method is convenient and simple in technical implementation.

Isopachic method with unpolarized light

An isopachic method with unpolarized light using a Mach-Zehnder interferometer is proposed. In the case of unpolarized light, isopachics are observed not only due to a change in the thickness of the model but also due to induced birefringence. In contrast to the existing methods, the proposed method allows you to study sections of three-dimensional models or flat stressed samples with no thickness variation. A brief theoretical consideration based on the formalism of the coherence matrix is given, as well as the experimentally obtained isopachic field for a model made from high-modulus material. The method is convenient and simple in technical implementation. Keywords: photoelasticity, interferometry, stresses, isopachic, isochrome, isocline.

Active particle tracking microrheology using artificial thermal noise

Passive particle-tracking microrheology (PTM) uses inherent Brownian motion of colloidal probe particles to characterize the mechanical properties of materials at micrometer and submicrometer length scales. In higher modulus materials (G* > 101 Pa), the particle experiences restricted Brownian motion such that its displacements during reasonable observation time scales drop below the spatial resolution of a typical optical microscope (∼10 nm). Thus, the passive PTM technique is generally limited to low modulus materials (G* ∼ 100 Pa). To overcome this, we have developed a form of active microrheology using electromagnetic tweezers that induce an artificial thermal noise on a superparamagnetic particle in the form of a random white noise signal. This signal imparts stochastic forces that drive resolvable displacements, which are greater than what is observed from thermal energy (kT) alone. The main advantage of this technique over traditional active microrheological methods is that the induced random motion of the particle allows one to use hydrodynamic models to obtain material functions without needing to measure a defined strain field. We implement the artificial thermal noise approach with a 35.1 Pa s Newtonian fluid and measure viscosities that are an order of magnitude higher than the typical passive PTM limit (100 Pa s).

Suggested Modifications of the ASTM D2344-16 Short-Beam Shear Test Method to Be Applied to Fiber Metal Laminates

Abstract ASTM D2344/D2344M-16, Standard Test Method for Short-Beam Strength of Polymer Matrix Composite Materials and Their Laminates, is used to test fiber-metal laminates (FMLs), although its scope is limited to high-modulus fiber-reinforced composite materials. These two groups of materials have differences in their mechanical behavior, and it is possible that this standard cannot be employed in FMLs in its current status. To verify this, short-beam shear (SBS) tests were performed in aramid aluminum laminate (ARALL) 3 4/3 specimens employing two sets of rollers diameters. One set was in accordance with ASTM D2344/D2344M-16, whereas the other made use of smaller diameters. The options to stop the tests presented in the standard were not adequate for the ARALL specimens using the normalized rollers diameters. Modifications to the standard in order to include FML specimens are suggested as follows: to include a test rig with reduced roller diameters, to observe of delamination at one side of a specimen as a new option to stop the test, and to define the short-beam strengths (Fsbs) as that corresponding to the maximum load value observed previous to a total load drop-off of 30 %. The difference between the means of Fsbs obtained with both set of rollers was not significant when using these modifications.

Effects of different aligner materials and attachments on orthodontic behavior

Background/purposeThe orthodontic aligner becomes popular worldwide in orthodontic therapy as an esthetic alternative to fixed labial braces. This study evaluated orthodontic tooth movement behavior using different aligner materials and attachment shapes for the movement of a single tooth. Materials and methodsFirst bicuspid extracted resin typodont models were printed with a 3D printer. Three type of attachments, an ellipsoid shape (thick and thin) and a bar, were designed to fit the canine crown surface. Three types of aligner materials, Polyethylene Terephthalate enhanced with glycol (BIOSTAR) Polyethylene Terephthalate (BenQ), and Thermoplastic polyurethanes (TPU) were used to fabricate different aligners. The typodonts with aligners were sunk in a water bath to simulate canine distal movement in vivo. The canine crown, root movement, and long axis angle changes in each step were calculated and recorded. The data were analysed using a oneway ANOVA statistical method. ResultsComparing the three aligners, the changes the long axis of the canine showed that the BENQ group had a smaller change in the long axis angle. The BENQ group canine involved bodily movement, but the canine movement of the BIOSTAR and TPU group involved tipping. Comparing the three attachments, the bar type attachment had more canine crown tipping in the BIOSTAR and TPU groups. The thick and thin ellipsoid-shaped attachments showed no statistical differences in tooth movement. ConclusionAttachment shape or size had little influence on the bodily movement of the tooth. A high modulus material may thus be suitable for clinical applications.

Data-Driven Discovery and Understanding of Ultrahigh-Modulus Crystals

High-modulus materials that yield small elastic deformation under mechanical loads hold great promise for use in a wide range of engineering applications. However, the discovery and understanding o...

Modeling a Dynamic Response at Resonant Vibrations of an Elongated Plate with an Integral Damping Coating

Classical methods of surface damping using free and constraining damping layers are discussed. The structure of a perspective integrated version of a damping coating is presented. This integral damping coating consists of two layers of a material with pronounced viscoelastic properties, between which there is a thin reinforcing layer of a high modulus material. A generalization of the Thompson-Kelvin-Voigt model is given for the description of viscoelastic properties of the material under tension-compression in the case of a complex stress state. A finite-element method was developed to determine the dynamic response of an elongated plate with the integral damping coating. This method is based on a four-layer finite element with 14 degrees of freedom: the main material is within the Kirchhoff-Love's model, the damping layers are in a flat stress state, the reinforcing layer perceives tension and compression. This model allows us to take into account the effect of transverse compression of the damping layers of the plate, which significantly increases its damping properties at high vibration frequencies. The stiffness matrices, the damping matrices, and the mass matrices of the constituent layers aim at obtaining similar complete matrices of a finite element. A system of resolving equations was obtained on the basis of the Lagrange equations of the second kind with respect to the vector of nodal displacements of the finite element model of the plate with an arbitrary dynamic load. In the case of a harmonic load with a frequency that coincides with one of the frequencies of free vibrations of the plate, a transition to a modal equation with respect to the normal coordinate corresponding to the given frequency is possible. Numerical experiments were carried out to test the developed finite element method using the example of a hingedly supported elongated plate with an integral damping coating. The numerical experiments showed a qualitative change in the composition of stresses in the damping layers of the plate at high vibration frequencies, which significantly affects its damping properties.

Highly filled resins for DLP-based printing of low density, high modulus materials

Digital Light Processing (DLP)-based 3D printing enables the fabrication of complex structures from a broad range of neat and filled resin formulations, yet mass sensitive applications in the automotive, aerospace, and electronics industries are hindered by the lack of low-density resins. This paper investigates the formulation of a resin suitable for DLP-based fabrication of low density, high modulus structures with fine resolution of negative and positive features. An acrylate-based resin is loaded with a high-volume fraction (50 vol%) of hollow glass microspheres achieving adequate cured depth to fabricate 25 µm layer thicknesses. The suspension stability over typical multi-hour DLP print durations is verified. The filled resin exhibited a viscosity less than 5 Pa-s, which is below the upper limit of viscosity to recoat the Polydimethylsiloxane (PDMS) window between layers. The printed material possesses a uniform density distribution of 0.81 g cm−3 investigated using thermogravimetric analysis (TGA) and micro-Computed Tomography (micro-CT) imaging. The minimum feature sizes for the formulation are demonstrated as 400 µm for internal cavities (negative features) and 250 µm for protruding features (positive features). An example of a structure with an intricate geometry is created by printing a repeating mechanical metamaterial unit cell.

COMPLEX EIGENFREQUENCIES AND DAMPING PROPERTIES OF AN ELONGATED PLATE WITH AN INTEGRAL DAMPING COATING

This paper considers the classical methods of surface damping of bending vibrations of thin-walled structures and a promising integral version of a damping coating consisting of two layers of a material with pronounced viscoelastic properties separated by a thin reinforcing layer of a high modulus material. A finite element with 14 degrees of freedom for modeling an elongated plate with the specified damping coating has been developed with consideration of the transverse compression of damping layers under high-frequency vibrations of the plate. The generalized problem of complex eigenvalues in the lower part of the spectrum of complex modes and frequencies of free vibrations of a damped plate is solved by the subspace iteration method taking into account the frequency dependence of the dynamic elastic moduli of the material. The damping properties of the plate are determined from the imaginary parts of the complex eigenfrequencies and the relative energy dissipation at resonance.

Mechanically Robust, Softening Shape Memory Polymer Probes for Intracortical Recording.

While intracortical microelectrode arrays (MEAs) may be useful in a variety of basic and clinical scenarios, their implementation is hindered by a variety of factors, many of which are related to the stiff material composition of the device. MEAs are often fabricated from high modulus materials such as silicon, leaving devices vulnerable to brittle fracture and thus complicating device fabrication and handling. For this reason, polymer-based devices are being heavily investigated; however, their implementation is often difficult due to mechanical instability that requires insertion aids during implantation. In this study, we design and fabricate intracortical MEAs from a shape memory polymer (SMP) substrate that remains stiff at room temperature but softens to 20 MPa after implantation, therefore allowing the device to be implanted without aids. We demonstrate chronic recordings and electrochemical measurements for 16 weeks in rat cortex and show that the devices are robust to physical deformation, therefore making them advantageous for surgical implementation.

Quantitative mapping of high modulus materials at the nanoscale: comparative study between atomic force microscopy and nanoindentation.

Local mechanical properties of submicron features are of particular interest due to their influence on macroscopic material performance and behaviour. This study is focused on local nanomechanical measurements, based on the latest Atomic Force Microscopy (AFM) mode, where the peak force set point is finely controlled at each pixel. After probe calibration, we evaluate the impact of spring constant of two AFM hand-crafted natural full diamond tips with steel cantilevers, used for mapping. Based on the fast capture of the cantilever deflection at each pixel and real time force curve analysis in the elastic region, AFM local measured contact moduli mappings of the silica beads (>50GPa) incorporated in an epoxy resin matrix, are compared with those determined using classical instrumented nanoindentation tests. Our analyses show that with the two AFM probes, without local residual deformation, the high moduli of the silica beads measured with this advanced AFM mode are within the standard deviation of the values determined by classical nanoindentation. LAY DESCRIPTION: The knowledge of material properties at the nanometer scale is a key parameter for well understanding and determining the behavior of material at macroscopic scale. In this paper, we compare two methods (an advanced mode and a classical one) based on the analysis of probes in interaction with the surface of studied material. We focus on a latest developed mode for determining local mechanical properties with a very high spatial resolution. For the advanced mode, we also consider two different hand-crafted probes. Our analyses show that with the high spatial resolution advanced mode, local mechanical properties are well determined. We also highlight the impact of the properties of the used probes for this advanced mode. In a final step, the power of the presented investigation lies in the fact that it does not modify the topography of the surface.

Mussel-inspired, self-healing polymer blends

Reversible dynamic covalent and noncovalent interactions are widely used to generate intrinsically self-healing polymers. However, nearly all approaches require sophisticated design and multi-stepped, tedious synthesis limited to weak hydrogels and rubbers, and pre-assume that high-modulus materials are more difficult to heal than low-modulus ones. Inspired by mussel foot proteins with the special amino acid unit of 3, 4-dihydroxy-l-phenylalanine, we develop a paradigm for achieving self-mendable polymer blends, composed of polyurethane (PU) as the matrix and poly(dopamine methacrylamide) (PDMA) as the dispersed phase. Healing efficiency increases from 24 to 32% for neat PU to 80–90% for the blends with increased moduli. This paradigm provides new insights into the role of mechanical properties in determining self-healing: high mechanical properties do not necessarily weaken self-repairability. The proof-of-concept enables easy modification of soft materials by solution mixing them with a polymer containing catechol groups, and thus opens up new applications in coatings, adhesives, antifouling, and biological engineering.

Numerical Modeling of Resonant Vibrations of an Elongate Plate with an Integral Damping Coating

The classical methods of surface damping of bending vibrations of thin-walled structures and a promising integrated version with a damping coating consisting of two layers of a material with pronounced viscoelastic properties and an intermediate thin reinforcing layer of a high-modulus material are discussed. A four-layer finite element for an elongate plate with an integral damping coating is developed taking into account the lateral compression of the damping layers. A system of governing equations of the finite-element method is constructed for analyzing the dynamic response of the plate during its resonant vibrations. Iterative algorithms have been developed to take into account the amplitude dependence of the logarithmic decrements of vibrations of material of the damping layers when determining the damping properties of the plate and determining its vibration eigenmodes and eigenfrequencies with consideration of frequency dependence of the dynamic elastic moduli of the material. Numerical experiments were carried out to test the finite element developed and the iterative algorithms mentioned. The influence of aerodynamic resistance forces on the overall damping level of a cantilever plate with an integral damping coating is assessed.