Ceramic Springs Research Articles

A superelastic SiOC@carbon ceramic spring for multifunctional pressure sensor in wide temperature range

With the flourishing development in space exploration and human motion detection, the wide-temperature flexible pressure sensors are urgently required in various complex application situations. One massive challenge of current available sensors is to enhance the oxidation resistance property, which is crucial for their applications in high-temperature environments. Herein, we fabricated a superelastic silicon oxycarbide @carbon (SiOC@C) ceramic spring, possessing a porous lamellar and spring-like structure. The spring-like structure tends to deform and absorb the energy under the external loads, and then the anisotropic lamellar structure can effectively and uniformly release the stress. The as-prepared SiOC@C spring exhibits excellent superelasticity, high compressibility (60%), and robustness (∼99.0% maximum stress retention after 1000 cycles at 50% compression). Meanwhile, the SiOC@C spring-derived sensor possesses a high sensitivity under low pressure (282.46 kPa−1 at < 1.3 kPa), a low detection limit (< 0.098 Pa) and a short response/recovery time (∼12 ms/4 ms). Moreover, benefiting from the high/low-temperature resistance of SiOC nanolayer coated on the carbon framework, the SiOC@C spring-based sensor can function properly at a wide temperature range from − 196 °C to 500 °C, showing the potential application in various fields of biomedical monitoring, space exploration, and automotive industries.

Manufacturing and deformation behavior of alumina and zirconia helical springs at room temperature

AbstractCeramic helical springs with identical dimensions were produced by hard machining from alumina, alumina toughened zirconia (ATZ), and tetragonal zirconia polycrystals (TZP) stabilized with different oxides. According to the results of the spring constant determination under deformation rates of 3 mm/min, the deformation behavior of all ceramic springs obeys to Hook's law. However, variation of the deformation rate, tests under constant load, and spring recovery behavior revealed differences in the deformation behavior of alumina, TZP, and ATZ springs. Alumina springs exhibited time‐independent deformation in all tests. In contrast, anelastic deformation at room temperature was demonstrated in all springs containing TZP. This deformation is completely reversible over a period of several days. Anelastic behavior is particularly pronounced in Y‐TZP springs, whereas Ce‐TZP springs exhibit comparatively very low but still reliably detectable anelasticity. Oxygen vacancies in the TZP ceramic are considered the most likely explanation for the anelastic behavior of TZP springs at room temperature.

Fiber reinforced SiC ceramic helical spring for high elasticity and large deformation at high temperature

AbstractCeramic spring devices play a significant role in mechanical systems, developing advanced ceramic helical spring with combination of high toughness and good elasticity still remains challenging. Herein, C/SiC composite helical springs with good elastic response to temperatures were fabricated by chemical vapor infiltration method. The C/SiC springs with rectangular and circular coil structures show high densities of 2.04 ± 0.162 and 1.96 ± 0.132 g/cm3, respectively. In contrast, C/SiC spring with circular coil structure can achieve high toughness of 0.92 ± 0.004 N/mm and low energy loss of 9.13 × 10−3 J at room temperature, while also exhibit an ideal spring constant of 0.35 N/mm and low energy loss of 7.82 × 10−2 J at 1000°C, which are highly comparable with those reported traditional ceramic springs. Furthermore, through finite element simulations, the stress distribution shows that both springs generate residual stresses at different temperatures after several cycles. The more uniform stress distribution and small irreversible deformation can be responsible for the superior elasticity of C/SiC spring with circular coil structure. The proposed strategy holds promising potential for developing C/SiC composite helical spring for future elastic devices used in complex and extreme service environments.

Characterization of a silicon nitride ceramic material for ceramic springs

Under extreme working conditions such as high temperature, strong electric and magnetic fields and acidic or basic environments, ceramic springs offer a clear advantage over conventional steel springs. In this study, a tailored grade of silicon nitride ceramic was characterized as spring material. The basic characterization was complemented with component tests. Bend bars, helical springs and conical disk springs were manufactured and tested under various loading scenarios.Manifested by the smallest effective volume of the three tested geometries, helical springs showed the highest fatigue strength. Nevertheless, the complexity involved in manufacturing helical springs pertaining to their geometrical features resulted in a relatively large scatter in fatigue data. The results pointed out the importance of proper design and machining of the contact surface edges in disk springs, which bear the highest stresses.This work demonstrates the potential of producing ceramic springs with broad applicability and sufficient strength and fatigue resistance.

Polymer‐Derived Ceramic Coil Springs

Polymer‐derived ceramic coil springs were manufactured by thermoplastic coiling of extruded filaments. Feedstocks for extrusion were processed from polymethylsilsesquioxane loaded with 34 vol% FeSiCr (reactive filler) and 16 vol% Si3N4 (inert filler). The pyrolytic conversion into a composite residue, the surface reactions, and the mechanical properties were analyzed. Annealing the extruded spring preforms in a reactive nitrogen atmosphere at 1300 °C resulted in the formation of a surface reaction zone with a thickness &lt;10 μm where nitridation reaction products are likely to heal cracks and pores. The as‐pyrolyzed ceramic springs (without surface machining) were loaded in compression. Ceramic coil springs with a filament diameter of 2.5 mm were characterized by a spring constant of 14.3 N mm−1 and attained a fracture stress of 187 ± 40 MPa.

Effect of sintering temperature on microstructure and strength distribution of alumina coil springs

Ceramic coil springs are one of the most widely used components in mechanical systems under harsh chemical conditions and high temperatures. In real applications of ceramic coil springs, knowing the effect of sintering temperature on their microstructure and strength distribution plays a crucial role. In this paper, the microstructure and strength distribution of alumina coil springs sintered at 1550, 1600 and 1650°C are investigated. Strength data of alumina coil springs are fitted by a Weibull distribution and according to the coefficient of determination, the deviation from the Weibull distribution can be determined. It is shown that the Weibull distribution best fits the strength data of alumina coil springs sintered at 1600°C. The probable reasons for deviation from the Weibull distribution are discussed in terms of grain size, porosity, and R curve behaviour.

Current characteristics of quasi-planar vacuum diodes with explosive-emission cathodes made of various materials at a high-voltage pulse duration of a few nanoseconds

The currents of 5-ns pulsed high-current electron beams produced in a planar vacuum diode with explosive-emission cathodes made of various materials with no external magnetic field at an average electric field strength in the gap of about 300 kV/cm have been measured and time-integrated observation of the optical luminescence of the cathode surface have been performed. Cathodes with a ceramic bushing and spring metal contacts, with ceramic plates set in a magnetic iron matrix, with blades made of stamped exfoliated graphite (Graflex), with blades made of foil fiberglass plastic, and a composite cathode made of crystalline boron and copper powders were tested. The current carried by one emission center has been estimated to range between 5 and 20 A for various cathodes. For the metal-dielectric cathode, the velocity of expansion of the cathode plasma over the ceramic surface has been estimated as 2·107 cm/s. The lifetimes of the cathodes at a pulse repetition rate of 50 Hz have been investigated.

Influence of Sintering Temperature on the Mechanical Properties of Alumina Springs

Low‐pressure injection molding (LPIM) was used to produce helical alumina springs. Three sets of springs were sintered at 1550°C, 1600°C and 1650°C to observe the effects on spring constant and fracture stress. Sintered alumina springs were obtained with densities ranging from 94.0% to 97.5% of the theoretical limit. Spring constants were measured from room temperature up to 1100°C. Fracture stress data were analyzed according to Weibull statistics and the method of maximum likelihood. Upon increase of sintering temperature from 1550°C to 1650°C, the spring constant and the Weibull characteristic strength of the alumina springs increases by 15% and 32%, respectively. On the other hand, sintering temperature has a negligible influence on Weibull's modulus. This is because internal bubbles and surface defects introduced in the production stage of the ceramic springs — more than the reduction in porosity with increasing sintering temperature — are critical in determining the reliability of the ceramic springs.

Constante de mola de molas cerâmicas injetadas a baixa pressão

A dificuldade de usinagem de peças cerâmicas já sinterizadas é muito grande, principalmente devido à dureza e fragilidade destes materiais, o que implica em altos custos de produção. Por isso, grandes esforços tem sido feitos no sentido de melhorar os processos de conformação a verde existentes, ou criar novos processos que permitam a obtenção de peças cada vez mais próximas do formato final desejado. Produzir peças cerâmicas com formatos complexos, livres de defeitos, é uma tarefa que implica em grandes dificuldades. Molas cerâmicas possuem formatos extremamente difíceis de serem moldados e, conseqüentemente, atualmente são produzidas comercialmente molas cerâmicas pelo processo de usinagem, geralmente a um custo elevado. Uma alternativa para a produção de molas cerâmicas é a moldagem por injeção em baixa pressão. Para o desenvolvimento de molas cerâmicas para aplicações tecnológicas, é necessário, além de obter peças íntegras e livres de defeitos, aferir algumas de suas propriedades, como a constante de mola. Uma vez que estas molas encontram aplicação em altas temperaturas, torna-se imprescindível realizar a medida da resistência imposta pela mola à deformação elástica em diferentes temperaturas. Para tanto, este trabalho propõem a montagem de um sistema para a medição da constante de mola de molas cerâmicas injetadas a baixa pressão, tanto à temperatura ambiente como em altas temperaturas, usando o método dinâmico da excitação por impulso para medir a frequência de vibração da mola suspensa no interior de um forno. Para ilustrar a aplicação desta técnica são apresentados resultados obtidos para uma mola helicoidal de alumina, da temperatura ambiente até 1100 ºC.

Failure probability of ceramic coil springs

Ceramic springs are commercially available and a detailed reliability analysis of these components would be useful for their introduction in new applications. In this paper an analytical and a numerical analyses of the failure probability for coil springs under compression is presented. Based on analytically derived relationships and numerically calculated results, fitting functions for volume and surface flaws will be introduced which provide the prediction of the failure probability of ceramic coil springs with different spring- and material-parameters. As an example, typical mechanical properties for Si 3N 4 are chosen. It is shown that surface flaws control the strength of the investigated springs.

Low‐Pressure Injection Molding of Ceramic Springs

Injection molding has important advantages over other methods for the production of advanced ceramic parts with complex shapes. In this work, low‐pressure injection molding was used to produce helical ceramic springs using two different kinds of molds. The ceramic powders used were submicrometer‐sized alumina and partially stabilized zirconia. Sintered alumina and zirconia springs were obtained free of defects, with densities from 96% to 99% of the theoretical value. In preliminary mechanical tests, these ceramic springs supported axial deformations up to 10% before failure.

Self‐Crack‐Healing Behavior of Mullite/SiC Particle/SiC Whisker Multi‐Composites and Potential Use for Ceramic Springs

To improve fracture toughness and encourage excellent self‐crack‐healing ability, mullite/SiC particle/SiC whisker multi‐composites and mullite/SiC whisker composites were hot pressed. The crack‐healing abilities and mechanical properties of these sintered composites were investigated. Based on the obtained results, the usefulness of the mullite composite as a material for springs was discussed. The part of mullite/15 vol% SiC whisker/SiC 10 vol% particle containing healed cracks retained high reliability over the whole measured temperature range. When the crack‐healing ability was endowed by SiC whiskers alone, the parts containing the healed pre‐cracks were found to have a heat‐resistance limit temperature. Mullite/15 vol% SiC whisker/10 vol% SiC particle multi‐composite had the best potential as a material for springs used at high temperatures, because it had an adequate crack‐healing ability as well as shear deformation ability almost two times stronger than that of monolithic mullite.

Static Fatigue Limit of Crack-Healed Mullite/ SiC Multi-Composite

Static fatigue behavior of mullite/ 15 vol% SiC whiskers/ 10 vol% SiC particles multi-composite crack-healed was investigated at room temperature and high temperatures from 1000°C to 1200°C. The multi-composite is the most candidate material as ceramic spring, because it has low Young's modulus as well as its reliability is guaranteed by excellent crack-healing ability. For estimating the usefulness of the composite as ceramic spring at high temperature, we must know the static fatigue limit at high temperature. The multi-composite having pre-crack was crack-healed at 1300°C for 2 h in air. The times to failure were investigated when the crack-healed specimens were applied the elevated tensile stress in air at room temperature and high temperatures from 1000°C to 1200°C. From the obtained results, the static fatigue limit was determined. Below 1000°C, the static fatigue limit of the composite crack-healed was found to be almost equal to the corresponding bending strength. Alternatively the static fatigue limit of the composite crack-healed was found to have lower value than the corresponding bending strength above 1100°C. Thus, the heat-resistance limit temperature for static fatigue of the multi-composite was determined to be 1000°C.

Main Features of Designing With Brittle Materials

Brittle material behavior and mode of failure are contrasted with those characteristics of ductile materials. The stochastic nature of brittle fracture, which results from the random occurrence of fracture-initiating microstructural imperfections, necessitates a probabilistic fracture mechanics approach to design with brittle materials. It is also clearly shown which main properties of brittle materials have to be optimized to improve the reliability of mechanically loaded components made of brittle materials. Important features of designing with brittle materials are elucidated and illustrated by an exemplary design calculation of a ceramic disc spring. It is shown how even environmentally induced subcritical crack growth, characteristic of ceramic materials, can be adequately accounted for in the assessment of reliability.

Experimental investigation on the mechanical performance of helical ceramic springs

A series of helical ceramic springs were manufactured from MgO partially stabilized zirconia to investigate their mechanical properties. Nine springs were machined from zirconia tubing, initially one inch in length, with a rectangular pitch of 16, 14, or 12 turns per inch. An experimental apparatus that both supports and equalizes the applied loads on springs was developed. The spring deflection versus applied load was measured using an optical sight mounted on a micrometer. Deflection data on each spring were collected, plotted and successfully modeled using Hooke's Law. A more extensive model was used to calculate the shear modulus of rigidity and shear stress. This model incorporates the spring dimensions, pitch, applied load, and deflection and provides insight into the effects of the materials of construction and manufacturing technique on the effective shear modulus of spring. A specific manufacturing effect was observed in the initial deflection resulting from the mass of the spring as the pitch was increased.

Design of ceramic springs for use in semiconductor crystal growth in microgravity

Segregation studies can be done in microgravity to reduce buoyancy-driven convection and investigate diffusion-controlled growth during the growth of semiconductor crystals. During these experiments, it is necessary to prevent free surface formation in order to avoid surface tension driven convection (Marangoni convection). Semiconductor materials such as gallium arsenide and germanium shrink upon melting, so a spring is necessary to reduce the volume of the growth chamber and prevent the formation of a free surface when the sample melts. A spring used in this application must be able to withstand both the high temperature and the processing atmosphere. During the growth of gallium arsenide crystals during the GTE Labs/USAF/NASA GaAs GAS Program and during the CWRU GaAs programs aboard the First and Second United States Microgravity Laboratories, springs made of pyrolytic boron nitride (PBN) leaves were used. The mechanical properties of these PBN springs have been investigated and springs having spring constants ranging from 0.25 to 25 N/mm were measured. With this improved understanding comes the ability to design springs for more general applications, and guidelines are given for optimizing the design of PBN springs for crystal growth applications.

Forming of Ceramics during Firing without the Application of External Pressure

A method to form thin ceramic bodies is described in which curvature in the component is introduced at high temperature without the application of an external stress. The internal stress that drives the deformation results as a consequence of cation penetration from a coating into a substrate material. This technique has been developed for alumina substrates that are coated with layers of chromia, magnesia, titania, calcia, silica, and iron oxide. Normalized deflections of segment height to sample thickness (A/t) of up to 10 were observed for samples with beam geometry and A/t values of 4 were obtained for disks. The magnitude of the deflection is dependent on the amount of dopant that is applied, as well as the soak temperature and time. An analytical model has been developed to describe the magnitude of the deflections. The best agreement with the experimental data is obtained when the deflections are treated as occurring at high temperature, where the resistance to bending from stiffness effects is reduced. This forming method is shown to be suitable to produce shapes of moderate complexity, such as ceramic wave springs.

Research and Development of Ceramic Gas Turbine (CGT302)

The ongoing Japanese Ceramic Gas Turbine (CGT) project, as a part of the New Sunshine Project funded by the Ministry of International Trade and Industry (MITI), aims to achieve higher efficiency, lower pollutant emission, and multifuel capability for small to medium sized gas turbine engines to be used in cogeneration systems. The final target of this project is to achieve a thermal efficiency over 42 percent at a turbine inlet temperature (TIT) of 1350°C. Under this project, Kawasaki Heavy Industries (KHI) is developing the CGT302 (a regenerative twin-spool CGT). The CGT302 has several unique features: simple-shaped ceramic components, KHI’s original binding system for turbine nozzle segments, stress-free structure using ceramic springs and rings, etc. In addition to these features, a high turbine tip speed and a metal plate fin recuperator were adopted. At the end of the fiscal year 1994, an intermediate appraisal was carried out, and the CGT302 was recognized to have successfully achieved its target. The CGT302 endurance test at the intermediate stage required 20 hours’ operation of the basic ceramic engine. The actual testing accomplished 40 hours at over 1200°C TIT, which included 30 hours of operation without disassembling. The target thermal efficiency of 30 percent at 1200°C has almost been reached, 29.2 percent having been achieved. In 1995 the CGT302 successfully recorded 33.1 percent at 1190°C of TIT with no trouble. We will introduce the current status of R&amp;D of the CGT302 and its unique features in this paper.

On the fabrication of ceramic windings

Components in the form of springs and windings were fabricated from technical ceramics by the extrusion of a polymer-ceramic suspension. Control of thermomechanical properties of the suspension allowed the ceramic to be extruded as a wire and to be plastically worked under gentle heating. The organic component of the blend was removed by pyrolysis before sintering the ceramic powder. This method may be particularly suited to the production of hightemperature ceramic springs, heating elements and ceramic superconductor windings for electrical power applications. Defects produced during removal of the polymer and the methods used to avoid them, shed light on the complex processes taking place in crowded suspensions during extraction of the organic vehicle.

A ceramic spring for high-temperature valves

A ceramic seat preloading spring has been built for use in hightemperature coal gasification valves. The use of a ceramic material avoids many of the problems associated with coal conversion environments, which consist of hot, corrosive gases, mixed with abrasive solids of varying sizes. The design initially relied on conventional spring formulas, and was refined on the basis of testing. The resulting ceramic spring displays essentially linear load-deflection characteristics, and can be used at temperatures up to 900 °C without taking a permanent deflection. The spring will be tested further in an 8 in. valve designed specifically for use on coal gasification plants.