Pressure-sensitive Materials Research Articles

3D hybrid porous Mxene-sponge network and its application in piezoresistive sensor

High-performance pressure sensors attract widespread attention due to the potential applications in human-machine interaction and wearable electronics. However, most of flexible pressure sensors need elaborate nanostructure design, and thus their manufacture is consuming and complicated. Therefore, a large-scale and low-cost technology is highly desirable to fabricate flexible pressure sensitive materials with high sensitivity in broad pressure range. Here, an MXene-sponge was fabricated by a simple and efficient dipping-coating process method and was applied in the piezoresistive sensor with insulating Polyvinyl Alcohol (PVA) nanowires as a spacer. The sensor based on MXene-sponge presents high sensitivity for a broad pressure range (147 kPa−1 for less than 5.37 kPa region and 442 kPa−1 for 5.37–18.56 kPa region), a low detection limit of 9 Pa, a rapid response time of 138 ms, and an excellent durability over 10,000 cycles. Human physiological signal (such as respiration, joint movement and pulses) can be real-time monitored by the MXene-sponge sensor. The potential applications of the sensor in measuring pressure distribution and human-machine interaction are also explored.

Study on hot melt pressure sensitive coil material for removing surface nuclear pollution dust

A new method for removing surface nuclear pollution by using hot melt pressure sensitive membrane was presented. The hot melt pressure sensitive membrane was designed and prepared by screening hot melt pressure sensitive adhesive and substrate. The simulated decontamination test of the hot melt pressure sensitive membrane was performed by using 100 mesh and 20 mesh standard sieve dust for simulation of nuclear explosion fall ash and radioactive contaminated particles, respectively. It was found that the single decontamination rate of simulated fall ash and contaminated particles were both above 80% under pressure conditions of 25kPa or more at 140°C. And the maximum single decontamination rate was 92.5%. The influence of heating temperature and pressure on the decontamination rate of the membrane was investigated at the same time. The results showed that higher heating temperature could increase the decontamination rate by increasing the viscosity of the adhesive. When the adhesive amount of the adhesive layer reached saturation, a higher pressure could increase the single decontamination rate also.

Graphene-coated polymer foams as tuneable impact sensors

The use of graphene-based nanocomposites as electromechanical sensors has been broadly explored in recent times with a number of papers describing porous, foam-like composites. However, there are no reported foam-based materials that are capable of large dynamic compressive load measurements and very few studies on composite impact sensing. In this work, we describe a simple method of infusing commercially-available foams with pristine graphene to form conductive composites, which we refer to as G-foam. Displaying a strain-dependent electrical response, G-foam was found to be a reasonably effective pressure sensing material. More interestingly, G-foam is a sensitive impact-sensing material. Through the addition of various amounts of polymer filler, the mechanical properties of the composites can be tuned leading to the controllable variation of the impact sensing range. We have developed a simple model which quantitatively explains all our impact sensing data.

Deviatoric section shape functions for materials exhibiting dependence on shear-to-axial yield stress ratio

Proposal of a class of smooth functions describing shape of the deviatoric section of the failure surface of isotropic materials is given. Their convexity is investigated and the resultant restrictions to the free parameters are derived. Applications to pressure sensitive or insensitive materials as yield criteria are shown. Discussion of calibration of material parameters is carried out and dependence of the failure surface on the shear-to-axial yield stress ratio is demonstrated.

Shockwave-Loading-Induced Enhancement of Tc in Superconducting Bi2Sr2CaCu2O8+\u03b4

We report a shockwave method for altering the properties of the superconductor material Bi2Sr2CaCu2O8+δ (Bi2212). We find that the superconducting transition temperature (Tc) increases from 84 K for the pristine sample to 94 K for the sample treated at a temperature and pressure of ~1200 K and ~31 GPa, respectively. X-ray diffraction and transmission electron microscopy characterizations indicate that this Tc enhancement arises from a phase transition from pristine Bi2212 to a mixture of superconducting Bi2212 and semiconducting Bi2Sr2CuO6+δ (Bi2201) during the shockwave treatment. The shockwave-treated sample exhibits n-type semiconductor properties (with an on-off ratio ~5), in contrast to the pure metallic pristine sample. Our study offers an alternative route for modifying the superconducting properties via a shockwave treatment. Furthermore, this method may provide a new approach for studying other temperature- and pressure-sensitive materials.

Nonlinear elastoplastic analysis of pressure sensitive materials

When structures undergo extreme loading conditions, the materials pass the elastic limits. Therefore, to preserve economy as well as safety, it is essential to perform a realistic elastoplastic analysis using the constitutive equations in plasticity. On the other hand, computing the stress alongside its associated variables on Gauss points is a delicate process and virtually the most important part of these analyses. In this study, an efficient stress-updating technique is presented for the constitutive rate equations of the pressure sensitive materials such as concrete, rock, soil and some kind of metals. Accordingly, the Drucker–Prager plasticity is utilized to consider the hydrostatic pressure in addition to the J 2-invariant of the deviatoric stress. Moreover, the isotropic and kinematic hardenings are used to take into account more realistic behavior of the materials. Finally, a wide range of numerical tests is carried out to show the performance of the presented method together with the application of the suggested formulations in elastoplastic analysis of a gravity dam.

Pressure-sensitive behaviors, mechanisms and model of field assisted quantum tunneling composites

Field assisted quantum tunneling composite (FAQTC) is a unique pressure-sensitive material with the advantages of large resistance change range under external force, easy preparation and excellent mechanical properties. In this paper, with attentions to the pressure-sensitivity of the FAQTCs, the effects of silicon rubber matrix, diameter and dosage of nickel particles as well as magnetic field treatment are systematically investigated. The reproducibility of the pressure-sensitivity of the FAQTCs under cyclic load is explored. Based on Cotton's equation and Burger's model, the descriptions of stress relaxation behavior and electrical resistance relaxation behavior of the composites under static compressive loading are given respectively. The results show that external magnetic field during curing process allows better adjustment of the pressure-sensitivity of the FAQTCs with fewer nickel particles. The increase of the dosage of nickel particles can improve the stability and reproducibility of the pressure-sensitivity of the composites. Electrical resistance relaxation behavior of the composites is partly controlled by the stress relaxation behavior. Moreover, based on the theory of percolation conduction, the mechanism of the pressure-sensitivity of the FAQTCs under uniaxial load is discussed and further qualitatively explained by adopting effective conducting path model. Finally, on the basis of this model combined with quantum tunneling effect, a mathematical model describing the pressure-sensitivity of the composites is established, which can well describe the pressure-sensitivity of the composites.

The use of Knoop indentation for the assessment of the plastic properties of mortars and natural stones

The present work investigates the Knoop hardness of rocks and other pressure sensitive materials. We tested ten different types of rocks, a cement paste, and PMMA. We also analyzed existing experimental results for Mg-PSZ (magnesia-partially stabilized zirconia) and Pb40Ni40P20 metal glass. We performed finite element indentation analysis for three types of material models: Mohr-Coulomb (associative), Drucker Prager (associative and non-associative), and foam-type. The material models assumed isotropic elasticity (with low elastic strains) and no strain-hardening effects. We compared our analytical results with our experimental results using material data from the literature. We found that different materials can be best described by either the Mohr-Coulomb or Drucker-Prager models. Highly porous materials showed unreasonably high Knoop hardness, raising questions on how their surface can be prepared for indentation tests. Materials with known model types such as cement, PMMA, Mg-PSZ and metal glass, verified our analytical results.

SHPB tests and dynamic constitutive model of artificial frozen sandy clay under confining pressure and temperature state

The dynamic stress-strain curves of frozen sandy clay are obtained with the spilt Hopkinson pressure bar (SHPB) under different confining pressures (i.e., 0.5, 1.0 and 1.5MPa) at the freezing temperature of −5°C and −15°C with the strain rate from 160s−1 to 265s−1. The experimental results show that the frozen sandy clay is a rate-dependent and temperature sensitive and confining pressure sensitive material and its dynamic peak stress increases with the increase of the strain rate and the confining pressure and the decrease of the freezing temperature. A dynamic constitutive model is proposed based on the test results. The theoretical and the experimental results are very close and the given dynamic constitutive model is feasible. The effect of confining pressure, strain rate and freezing temperature on the dynamic mechanical behavior of frozen sandy clay are well considered in the model.

Model of the Mechanical Behavior of Cementitious Matrices Reinforced with Nanomaterials

CNTs and CNFs have been introduced as a nanoscale reinforcing material to cementitious composites, for stiffening and strengthening the microstructure. This technology is motivated by the need to control crack initiation in the cementitious gel before it propagates into visible crack formations. Experimental evidence supports this concept; however, testing at the nanoscale may only be conducted through nanoindentation, which has a limited range only providing localized results that cannot be extrapolated to general stress states. To evaluate the restraining action of nanomaterials in the gel microstructure, a computational mechanistic model has been developed where the material phases (gel, nanotubes, and pores) are modeled explicitly allowing for natural randomness in their distribution and orientation. Repeated analysis with identical input data reproduces the statistical scatter observed in laboratory tests on identical material samples. The formulation uses a discrete element approach; the gel structure is represented by a random network of hydrates and successfully reproduces the known trends in mechanical behavior of cementitious materials (pressure and restraint sensitive material behavior) and the small ratio of tensile to compressive strength. Simulations illustrate that it is possible to computationally reproduce the measured properties and behavior of fiber-reinforced cement composites using information from simple laboratory tests.

Nanoporous materials with a general isotropic plastic matrix: Exact limit state under isotropic loadings

In this paper, hydrostatic strength properties of nanoporous materials are investigated by addressing the limit state of a hollow sphere undergoing isotropic loading conditions. Void-size effects are modelled by treating the cavity boundary as a coherent-imperfect homogeneous interface. The hollow sphere is assumed to be comprised of a rigid-ideal-plastic material obeying to a general isotropic yield criterion. The latter is defined by considering a simplified form of the yield function proposed by Bigoni and Piccolroaz in [Int J Solids Struct; 41: 2855–2878], resulting able to account for a broad class of pressure-sensitive materials whose plastic response is also affected by the stress Lode angle. The corresponding support function is consistently derived and discussed. The exact solution of the limit-state problem is fully determined, providing a closed-form description of stress, strain-rate and velocity fields, as well as the macroscopic hydrostatic strength of nanoporous media. Proposed approach allows to consistently generalise available analytical solutions for porous and nanoporous materials, by accounting for a general plastic response of the solid matrix and for void-size effects. Finally, present exact solution, as well as the identification of the support function for the adopted general strength criterion, open towards novel kinematic limit-analysis approaches for describing macroscale strength properties of nanoporous materials under arbitrary triaxial loadings.

Chemistry and Technology of Samarium Monosulfide

<p class="Pa10">Samarium monosulfide SmS (Fm3m, а = 5.967 Å, ΔЕ = 0.23 V, n = 10<sup>20</sup> cm<sup>–1</sup>, <em>σ</em><em> </em>= 500 Ω<sup>–1</sup> cm<sup>–1</sup>, <em>α</em><em> </em>= 350 μВ/K) is a thermoelectric material (Z>1) and, at the same time, a pressure-sensitive material (K≥40–50). Samarium monosulfide is a daltonide phase with a solid solution whose extent is mostly in the range of cationic vacancies: Sm<sub>1+x </sub>S<sub>1-x</sub>□<sub>2x</sub> (<em>x </em>= 0–0.035; 1750 K). The congruent melting temperature of SmS is 2475 K. In the Sm–S system, Sm<sub>3</sub>S<sub>4</sub> crystallizes from melt without change in composition. Samarium monosulfide thermally dissociates to Sm<sub>3</sub>S<sub>4</sub> and Sm. Large-scale SmS lots are produced from samarium and sulfur. Synthesis is carried out in sealed-off silica glass ampoules at 500–1350 K followed by heat treatment in tantalum crucibles at 1500–2400 K. The reaction of metal samarium with sulfur results in the formation of sulfide phases that coat the samarium surface in the following order: SmS, Sm<sub>3</sub>S<sub>4</sub>, Sm<sub>2</sub>S<sub>3</sub>, and SmS<sub>2</sub>. Subsequent annealing at 1500–1800 K provides SmS yields up to 96–97 mol %. Equilibrium minor phases for SmS are Sm<sub>3</sub>S<sub>4</sub>, Sm<sub>2</sub>О<sub>2</sub>S, and Sm. X-ray amorphous SmS was prepared by reacting organic samarium compounds with sulfur or H2S. The samarium (+2) oxidation state determines the chemical specifics of SmS. 90–120 μm SmS powders are thermally hydrolyzed starting at 600 K with Н<sub>2</sub> evolution and oxidize starting at 520 K to yield Sm<sub>3</sub>S<sub>4</sub> and then Sm<sub>2</sub>О<sub>2</sub>S phases. A 90–120 μm SmS fraction for film deposition by flash evaporation is prepared by milling annealed SmS samples. Tablets 75 mm in diameter for use in magnetron sputtering are pressed from a <60-μm fraction.</p>

Study of Pressure-Sensitive Materials for Floor Sensor Networks

This paper presents a comparative study of pressure-sensitive sensor materials being suitable for monitoring purposes in pressure mapping sensor networks. Four sensor materials working on piezoresistive, piezoelectric, quasi-piezoelectric and capacitive principle have been discussed including the built-up, the working principle, the manufacturing and the most important properties. Additionally, the electromechanical models of the sensor elements have been introduced and verified by comparing the modelled and measured sensor characteristics. The studied materials were compared and evaluated using a decision matrix with respect to the applicability as a thin and flexible pressure sensor unit in a competitive large-area floor sensor network.

Effects of Non-Associated Flow on Residual Stress Distributions in Crankshaft Sections Modeled as Pressure-Sensitive Materials under Fillet Rolling

Effects of Non-Associated Flow on Residual Stress Distributions in Crankshaft Sections Modeled as Pressure-Sensitive Materials under Fillet Rolling

General transmission conditions for thin elasto-plastic pressure-dependent interphase between dissimilar materials

We consider a thin soft adhesive interphase between dissimilar elastic media. The material of the intermediate layer is modelled by elasto-plastic pressure-sensitive constitutive law. An asymptotic procedure, together with a novel formulation of the deformation theory of plasticity for pressure-sensitive materials, is used in order to derive nonlinear transmission conditions for the corresponding imperfect zero-thickness interface. A FEM analysis of the original three-phase structure is performed to validate the transmission conditions for the simplified bimaterial structure.

Relationship between activation volume and polymer matrix effects on photochromic performance: bridging molecular parameter to macroscale effect.

Photochromic compounds have attracted attention as ophthalmic lenses because of their reversible color modulation upon irradiation with light. However, the efficiency of the photochromism is strongly affected by their surrounding because of the structural changes concomitant with the photochromism, which causes the decrease in the photochromic performance in the polymer matrix. Therefore, the clarification of the degree of the structural changes is necessary to apply to the ophthalmic lenses. Bridged imidazole dimers are one of the fast photoswitch molecules possessing high photochromic quantum yield and durability. Although the enhancement of the photochromic properties of bridged imidazole dimers has been vigorously studied, the quantitative information about the structural changes has not been revealed in detail. In this study, we investigated the pressure effects on the photochromic properties of bridged imidazole dimers. The activation volume for the thermal back-reaction of the photogenerated biradical species becomes an effective measure to predict the degree of the structural change during the photochromic reaction. We revealed that the smaller activation volume is suitable for keeping the efficient photochromic reaction in the polymer matrix because the photochromic reaction is not affected by the surroundings. These fundamental insights into the molecular dynamics provide valuable information to develop fast photochromic compounds that are suitable for the use in the polymer matrix and pressure sensitive photochromic materials.

Research on the Piezoresistive Properties of Conductive Silicone Rubber under Water Pressure

The conductive silicon rubber samples have been prepared in different filler ingredients, the platform is builded for testing the piezoresistive characteristics of conductive silicon rubber when the material is under water pressure and the test methods are designed, the body piezoresistive properties and surface piezoresistive properties under the water pressure within a certain range are studied respectively. The results show that, the sample of 6% acetylene black/2% nanoSiO2 blends exhibit the best piezoresistive performance when the samples are under water pressure, the piezoresistive properties of the material can be improved with the increase of the thickness of the materials (2mm-4mm), and the conductive silicon rubber used for the pressure-sensitive materials of piezoresistive gauge is feasible.

적층조형과 직접주사방식을 결합한 광경화성 수지 기반의 신축성 촉각센서의 제작

Many kinds of robots and machines have been developed to replace human laborin industrial and medical fields, as well as domestic life. In these applications, the device sneed to obtain environmental data using diverse sensors. Among such sensors, the tactile sensor is important because of its ability to get information regarding surface texture and force through the use of mechanical contact. In this research, a simple tactile sensor was developed using the direct writing of pressure sensitive material and layered fabrication of photocurable material. The body of the sensor was fabricated using layered fabrication, and pressure sensitive materials were dispensed between the layers using direct writing. We examined the line fabrication characteristics of the pressure sensitive material according to nozzle dispensing conditions. A simple array flexible tactile sensor was successfully fabricated using the proposed process.

Application of Pressure-Sensitive Materials in Cement-Based Composites for Self-Assessment of Structural Degradation

Application of Pressure-Sensitive Materials in Cement-Based Composites for Self-Assessment of Structural Degradation

An exact semi-analytic solution for residual stresses and strains within a thin hollow disc of pressure-sensitive material subject to thermal loading

There is considerable current interest in the development of constitutive equations for pressure-dependent plastic materials. In particular, in contrast to classical plasticity there is no commonly accepted relation to connect stress and strain or strain rate for such materials. Analytic and semi-analytic solutions are convenient to compare qualitative features of boundary value problems solved for different models. Such comparative studies can be useful to choose this or that model for specific applications. Analytic and semi-analytic solutions are also necessary to verify numerical codes. In the present paper, a new semi-analytic solution for a thin hollow disc subject to thermal loading is developed. A numerical method is only necessary to solve transcendental equations. The constitutive equations for connecting the plastic portion of the strain rate tensor and the stress tensor consist of the Drucker-Prager yield criterion and its associated flow rule. Therefore, the main distinguished feature of the solution is that the material is plastically compressible.