Maximum Service Temperature Research Articles

The Effect of a Thermotropic Material on the Optical Efficiency and Stagnation Temperature of a Polymer Flat Plate Solar Collector

Solar hot water and space heating systems constructed of commodity polymers have the potential to reduce the initial cost of solar thermal systems. However, a polymer absorber must be prevented from exceeding its maximum service temperature during stagnation. Here, the addition of a thermotropic material to the surface of the absorber is considered. The thermotropic layer provides passive overheat protection by switching from high transmittance during normal operation to high reflectance if the temperature of the absorber becomes too high. A one dimensional model of a glazed, flat-plate collector with a polymer absorber and thermotropic material is used to determine the effects of the optical properties of the thermotropic material on the optical efficiency and the stagnation temperature of a collector. A key result is identification of the reflectance in the translucent state required to provide overheat protection for potential polymer absorber materials. For example, a thermotropic material in its translucent state should have a solar-weighted reflectance greater than or equal to 52% to protect a polypropylene absorber which has a maximum service temperature of 115 °C.

Study of tensile behaviour of thermally aged alloy D9 wrapper tubes of fast breeder reactor using acoustic emission

BACKGROUND: Hexagonal wrapper tubes in fast breeder reactor (FBR) contain smaller circular tubes called fuel pins made of austenitic 15Cr–15Ni–Ti modified stainless steel (alloy D9). This is used in 20% cold worked condition. At maximum service temperature of fuel clad (around 973 K), prolonged exposure to high temperature could remove the effect of cold work. Thermal ageing of cold worked alloy D9 at 823–1123 K results in carbide precipitation which affect the subsequent deformation behaviour. OBJECTIVE: The tensile behaviour of alloy D9 after ageing at 823–1123 K for 10–10,000 h has been studied using acoustic emission (AE). METHODS: Tensile tests along with AE monitoring were conducted at room temperature at nominal strain rate of 1.33 × 10 −3 s −1 . RESULTS: Strength decreased and elongation increased with ageing temperature. Till 1000 h ageing time, AE parameters (up to yield) decreased with ageing temperature. But for 5000 and 10,000 h, they increased first and then decreased with a peak at around 973 K. This coincides with a trough in elongation at around 973 K. CONCLUSIONS: The trough in elongation has been attributed to increasing difficulty of plastic deformation by pinning of dislocations. A correlation exists among tensile, Larson–Miller (LMP) parameter and AE parameters.

Durability of polydicyclopentadiene under high temperature, high pressure and seawater (offshore oil production conditions)

In the offshore industry polymer coatings are widely used to ensure thermal insulation of steel pipes, and to avoid over-cooling of the hot oil inside. Because of very severe service conditions (i.e. high temperature, high pressure and presence of seawater) and an expected life time of 20 years, durability of these coatings is a major issue for this industry. Polypropylene and polyurethane are often used for this application, nevertheless these polymers have some limitations in terms of processing time for polypropylene and maximum service temperature for polyurethane. Polycyclopentadiene (pDCPD) shows good processing characteristics and low thermal conductivity, so this polymer could be a good alternative coating in the offshore industry, but the durability of this polymer under offshore conditions is unknown. This paper present results from an accelerated ageing study of pDCPD in seawater at temperatures from 90 °C to 180 °C for 18 months. Polymer evolution during ageing is characterized using both mechanical (tensile test and DMA) and chemical (FTIR, NMR) analyses. For ageing at temperatures below Tg (i.e. 155 °C) the only degradation mechanism is oxidation, whereas for ageing temperatures above Tg secondary polymerization process of the material is observed.

Complex Characterization of a New Low Ni Maraging Steel with Enhance Service Stability

A new low Ni maraging steel, based on 18Ni (300) type has been developed. The optimized chemical composition (complex alloyed with Al-Si-Ti or Si-Zr-Nb) in accordance with optimum heat treatment was found (solution: 970 °C/1h/air and ageing: 550 °C/3h/air), in order to obtain maximum service temperature of over 600 0C and ensured the good combination of strength and toughness properties. The precipitates, such as Ni3(Mo, Ti), were well controlled in lath martensite (Rm=2090N/mm2 and Rp0,2=1930N/mm2)and the presence of Si, Zr and Nb enhance structure stability at high temperature (for example the ultimate tensile strength at 5500C is about 1440N/mm2). Therefore, this new type of maraging steel was the subject of a national patent: “Maraging steel for high temperature service and heat treatment technology” – PATENT No.120356/30.08.2010.

High temperature tensile properties of in situ TiBw/Ti6Al4V composites with a novel network reinforcement architecture

Abstract TiB whisker reinforced Ti6Al4V (TiBw/Ti64) composites with a novel network reinforcement architecture have emerged due to their superior combination of superior room temperature tensile properties. In the present study, their superior high temperature tensile properties and special strengthening mechanisms were further investigated. At 500 °C, the tensile strength of the as-sintered 5 vol.%, 8.5 vol.% and 12 vol.% TiBw/Ti64 composites increased by 36.9%, 40.5% and 44.8% compared with that of the monolithic Ti64 alloy. Moreover, the tensile elongations are close to 10% at 500 °C and 20% at 700 °C. The maximum service temperature of the TiBw/Ti64 composites can be increased to 600 °C while retaining the strength of the monolithic Ti64 alloy the alloy at 400 °C. This is attributed to the network boundary strengthening mechanism as elucidated by the microstructure–property–fractographic analysis.

A review of the processing, composition, and temperature-dependent mechanical and thermal properties of dielectric technical ceramics

The current review uses the material requirements of a new space propulsion device, the Variable Specific Impulse Magnetoplasma Rocket (VASIMR®) as a basis for presenting the temperature-dependent properties of a range of dielectric ceramics, but data presented could be used in the engineering design of any ceramic component with complementary material requirements. A material is required for the gas containment tube (GCT) of VASIMR® to allow it to operate at higher power levels. The GCT’s operating conditions place severe constraints on the choice of material. An electrically-insulating material is required with a high-thermal conductivity, low-dielectric loss factor, and high-thermal shock resistance. There is a lack of a representative set of temperature-dependent material property data for materials considered for this application and these are required for accurate thermo-structural modelling. This modelling would facilitate the selection of an optimum material for this component. The goal of this article is to determine the best material property data values for use in the materials selection and design of such components. A review of both experimentally and theoretically determined temperature-dependent and room temperature properties of several materials has been undertaken. Data extracted are presented by property. Properties reviewed are density, Young’s, bulk and shear moduli, Poisson’s ratio, tensile, flexural and compressive strength, thermal conductivity, specific heat capacity, thermal expansion coefficient, and the factors affecting maximum service temperature. Materials reviewed are alumina, aluminium nitride, beryllia, fused quartz, sialon, and silicon nitride.

Beyond Ni-based superalloys: Development of CoRe-based alloys for gas turbine applications at very high temperatures

Abstract High temperature material development is mainly driven by gas turbine needs. Today, Ni-based superalloys are the dominant material class in the hot section of turbines. Material development will continue to push the maximum service temperature of Ni-superalloys upwards. However, this approach has a fundamental limit and cannot be sustained indefinitely, as the Ni-superalloys are already used very close to their melting point. Within the framework of a DFG Forschergruppe program (FOR 727) – “Beyond Ni-base Superalloys” – CoRe based alloys are being developed at the Technische Universität Braunschweig as a new generation of high temperature materials that can be used at + 100 °C above single crystal Ni-superalloys. Two main strengthening concepts, namely precipitation hardening by MC carbides and composite hardening by Co2Re3-type σ phase are being explored in CoRe alloy development. Selected results of microstructural characterizations, including in-situ measurements by synchrotron and neutron scattering are presented.

Post‐protection effect of heat‐resistant insulations on timber‐frame members exposed to fire

SUMMARYIn lightweight walls and floors, the load‐bearing timber members are protected by cladding on the sides to form a divider between two fire compartments or to provide appropriate fire protection to the load‐bearing members. The spaces between the timber members can be void or filled with insulation materials. Although a huge number of different insulation materials exist, the most commonly used material is mineral wool insulation.The existing design model for glass wool‐insulated timber‐frame constructions, given in European standard 1995‐1‐2, assumes collapse of the glass wool after failure of the cladding. However, a new form of glass wool insulation, suitable for use at high maximum service temperatures, is now available in the market. The charring phase after the cladding's failure is known as the post‐protection phase. The behaviour of the new heat‐resistant glass wool in the post‐protection phase is similar to that of stone wool and considerably better than that of traditional glass wool. The protective properties of stone wool have changed over the last decades.Charring is one of the main parameters needed to calculate the resistance of a structure to fire. Based on experimental investigations, this paper describes the analysis of the effect of the insulation with regard to its ability to protect timber members against charring during the post‐protection phase. Copyright © 2011 John Wiley & Sons, Ltd.

Shear-mode piezoelectric properties of ternary Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystals

A systematic study of the optimized orientation and temperature dependence of shear-mode piezoelectric properties for ternary Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT or PIMNT) piezocrystals was carried out. It was found that [111]-poled samples presented the best shear piezoelectric properties when driving along [11¯0] (the thickness direction). The electromechanical coupling coefficient k15 and piezoelectric coefficient d15 and g15 were found to be 96.4%, 5966 pC/N, and 0.047 Vm/N, respectively, for optimum-cut samples with platinum (Pt) electrode. Besides, the maximum service temperature for shear mode is around 105 °C, which is much higher than PMNT single crystals.

Annealing Ni nanocrystalline on WC–Co

The effects of annealing temperature on nanocrystalline sputter-deposited Ni thin films (500 nm) deposited on WC–Co (4 wt.%) were investigated. Special attention was focused on quantitative evaluation of residual stress and Ni diffusion into the WC–Co, after heat treatment, from 873 to 1273 K. The estimated level of residual stress, as measured by X-ray diffraction, is around −1.3 ± 0.1 GPa for the as-deposited film, whereas after annealing at 1273 K it decreases significantly. Atomic force microscopy shows that high annealing temperature results into an exponential increase of the roughness. An intermixing between the nanocrystalline Ni and the Co from WC substrate occurs, as it is revealed by quantitative depth-resolved Rutherford backscattering spectrometry analysis and also supported by X-ray photoelectron spectroscopy. We ascribe a significant stress relief with the increasing annealing temperature to the diffusion process. The understanding of this process is particularly important in WC–Co parts with the surface treated with Ni in order to improve the maximum surface service temperature.

The Processing and Performance of High Temperature Polymers for Automotive Fluid Handling Applications

One of the main focuses on automotive engine design in the last number of years has been a move towards engine compactness in an effort to increase cabin space. This has lead to a dramatic increase in temperature around the engine compartment from around 120dC to 200dC. This exceeds the maximum service temperature of many of the polymer materials currently used in fluid delivery systems. Already some of these components are now of necessity being replaced with metals. These metallic systems although heat resistant, are heavier, difficult to form and prone to fatigue failure. This present work investigates the melt degradation properties at elevated temperatures and the effect of immersion in standard automotive fluids (an extension of SAE J2027) on the mechanical performance of a range of polymers that are potential candidate materials for use in such “under bonnet” high temperature applications. The materials that were investigated included nylons, polypropyleneoxide/polyamide blends (PPO/PA), and polyetherimide (PEI). The rheological characteristics of nylon 4.6, PPO/PA and PEI were investigated and the results showed significant decrease in shear viscosity at dwell times in excess of three minutes for nylon 4.6, and PPO/PA. Injection moulded samples of the nylon 4.6, impact modified nylon 4.6, nylon 12, PPO/PA and PEI were immersed in the standard automotive test fluids, Fuel C, zinc chloride solution and aggressive water. Subsequent mechanical analysis of the various specimens showed only slight decrease in the tensile modulus of the nylon 4.6 after immersion in Fuel C, however significant weight gain and deterioration in tensile modulus were recorded after immersion in aggressive water. Dynamic Mechanical Thermal Analysis on the nylon 4.6 showed only slight decrease in storage modulus (Log E') and Tg, after immersion in Fuel C. However a significant decrease in Tg, by up to 80dC was recorded for samples immersed in aggressive water.

An experimental study on the failure of carbon/epoxy single lap riveted joints after thermal exposure

Abstract The bearing strength of a blind riveted single lap joint of a carbon/epoxy composite after thermal exposure was studied. Considering the maximum service temperature based on material specifications and glass transition temperature, six types of specimens were prepared and tested in accordance with ASTM D5961. Failure loads of specimens exposed to a 177 °C environment were above 90% compared to sound specimens. Failure loads of 77% were obtained for specimens exposed to a 232 °C environment for 4 h. Bearing and rivet pulling-through failure modes were observed in all specimens. Delamination caused by degradation of the matrix property was found in specimens exposed to temperature higher than 204 °C.

Performance and applications of a small PM generator

AbstractThis paper presents a high‐speed low‐power small permanent magnet (PM) generator for aerospace applications where environmental requirements are very severe. Since Alnico magnet material has a low temperature coefficient of remanent flux density and maximum service temperature, it is suitable for the application. Furthermore, the main disadvantage of PM generators is the difficulty of output voltage regulation to compensate for speed and load variation, due to the lack of a simple means of field control. Hence, a circuit is used to connect to the generator to provide a fixed dc voltage to the load. The steady‐state performance is analyzed by the finite element (FE) method. Experimental tests are conducted to verify the FEM predictions. Agreement between FE analysis work and testing results is good. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A Constitutive Creep Equation for 9Cr‐1Mo‐0.2V (P91‐type) Steel under Constant Load and Constant Stress

The creep behaviour of 9Cr‐1Mo‐0.2V (P91‐type) steel was studied at elevated temperatures of 625 to 675 °C. These temperatures considerably exceed the maximum service temperature of this steel, which is approximately 600 °C. Uniaxial creep tests were performed under constant load and constant stress at initial stresses of 120 to 240 MPa. These tests are considered as short‐term tests and they can even be applied for creep lifetime assessment, albeit with certain limitations. However, the main purpose of this work was to find a constitutive creep law that would satisfactorily describe the creep behaviour of P91‐type steel and enable a comparison of the results obtained with both kinds of creep tests, i.e., under constant load and constant stress.It is well known that the minimum creep strain rate of P91‐type steel cannot be satisfactorily described by the simple Arrhenius‐type power‐law constitutive model. Therefore, an improved stress‐dependent energy‐barrier model for the description of the creep behaviour of P91 steel was used. The model showed that there is a small difference in the apparent activation energy between constant‐load and constant‐stress creep tests. The obtained values of the stress‐dependent activation energies are, in both types of test, considerably higher than the activation energy for lattice diffusion. This is in good agreement with the literature data, although the obtained activation energies are not so strongly stress dependent. The Monkman‐Grant relation showed that the minimum creep strain rate is not quite inversely proportional to the time‐to‐rupture for both constant‐load and constant‐stress creep tests.

T/P23, 24, 911 and 92: New grades for advanced coal-fired power plants—Properties and experience

After the development of the well-known T/P91 grade in the early 1980s and the long industrial experiences since the early 1990s, it has been necessary to develop new steels to answer the demand of the powergen industry. New (ultra) super critical boilers require materials with advanced creep properties to reach severe steam parameters. For the 2.25% Cr family, grades 23 and 24 are now available to be used instead of the previous grade 22 with many technical and economical advantages. For the 9% Cr steels, new grades such as T/P911 and T/P92 have been developed with higher creep properties than T/P91. Thanks to its large industrial experience in these new grades, Vallourec & Mannesmann Tubes and Boehler Thyssen Schweisstechnik have now worldwide references of use with these new steel grades. In this paper, information on properties, behaviour and workability will be presented with a focus on • elevated temperature properties and allowable stresses, • oxidation and maximum service temperature and • weldability procedures and recommendations.

Enhanced voided piezoelectric polymer for underwater acoustic sensors

A charged voided polymer has been shown to exhibit large piezoelectricity. This material consists of injected air bubbles into polypropylene. This sheet of voided material is then biaxially stretched to elongate the voids. After stretching this material, a strong electric field is applied to cause dielectric breakdown of the gas in the voids, creating electric charges that are trapped in the polymer frame. Since the sides of the voids have opposite charges, they form macroscopic dipoles. When an external force is applied to this material, the voids become narrower, causing stronger dipole strength. A simple model of this voided material was implemented to derive formulas to estimate its piezoelectric constant, electromechanical coupling factor, resonance frequency, and sensor sensitivity based on electrical and mechanical properties of the polymer and gas in the voids. These formulas and a survey of available polymers and gases yielded promising combinations that result in more sensitive voided materials that satisfy selected criteria. These criteria include high sensitivity and maximum service temperature, low dissipation factor, and high dynamic compressibility, but low hydrostatic compressibility. This talk will describe the model, derive the formulas, uncover measured properties of candidate polymers and gases, and show calculated sensitivity of selected polymer/gas combinations.

Effect of hot water immersion on the performance of carbon reinforced unidirectional poly(ether ether ketone) (PEEK) composites: Stress rupture under end-loaded bending

This paper describes the behaviour of AS4 and T700SC reinforced PEEK composites (SUPreM™ and ACP-2) under applied compressive bending strain. The effect of an increased molecular weight of the polymer matrix on the residual time under endloaded compression bending conditions is studied. Generally for a given composite material, the higher the testing temperature and the applied strain the faster the failure occurs. At test temperatures exceeding the glass transition temperature or at high strain ratios the time-to-failure for CF/PEEK composites follows a master curve. The residual times under endloaded compression bending conditions increase with increasing toughness of the PEEK matrix but decrease with increasing tensile strength of the reinforcing fibres. It seems that the better the fibre/matrix adhesion the lower is the time to failure of an endloaded composite, because more load is transferred from the matrix into the fibres. In order to simulate composite applications under ‘harsh’ conditions the CF/PEEK composites have been exposed to boiling water. PEEK is known to be highly resistant to environmental effects, but water uptake significantly influences the overall performance of CF/PEEK composites under endloaded compression bending conditions. The tensile properties of the composites have been measured as function of exposure time in boiling water. The fibre dominated uniaxial tensile strength is not/or only slightly affected by the boiling water conditioning even after extended exposure times but the transverse tensile strength decreases significantly after exposure to boiling water. The performance of SUPreM™ CF/PEEK-150 and 450 composites under endloaded compression bending conditions are positively affected by water conditioning whereas APC-2 fails at shorter residual times. The fracture behaviour under endloaded conditions is also affected by the ingress of water into the composite. The obtained results show clearly that applications of thermoplastic composites leading to large out of plane deformations can only be ‘safe’ if the maximum service temperatures of the finished part will be well below the glass transition temperature of the polymer matrix otherwise even at low bending radii a dramatic failure of the material cannot be excluded.

Performance of thermal barrier coatings on γ-TiAl

The current development of new generation gamma titanium aluminides is expected to result in alloy chemistries and microstructures capable of operating at temperatures in excess of 850 °C. Under these conditions, environmental and thermal protection becomes a concern since oxidation might eventually limit the maximum service temperatures achievable. Therefore protective coatings are necessary to exploit the full potential of gamma titanium aluminides at moderately elevated temperatures; however, as yet no coating system tested has proven sufficient performance for long-term use in automotive and aerospace applications. Thermal barrier coatings (TBCs), typically applied to nickel-based alloys, offer the potential to increase the service temperature of components by lowering the metal surface temperature in combination with cooling systems. The paper is focussed on development of thermal barrier coatings for gamma titanium aluminides. Different coatings were used for oxidation protection and bond coat application. Substrate specimens were either pre-oxidized or coated with PVD-Al 2 O 3 , TiAl-CrYN, or diffusion aluminides. Yttria-stabilized zirconia TBCs were deposited applying electron-beam physical vapour deposition. Cyclic and quasi-isothermal oxidation tests were carried out at 900 °C in air. Post-oxidation analysis of the coating systems was performed using scanning electron microscopy with energy-dispersive X-ray spectroscopy. Zirconia top coats offer a promising thermal protection concept to be applied on γ-TiAl components. However, high oxidation resistance has to be supplied by protective coatings. Diffusion layers of the TiAl 3 aluminide provided excellent environmental protection because of the formation of a continuous alumina scale. No spallation of the thermal barrier coatings was observed on aluminized specimens during 1000 1-h cycles and 3000 h of cyclic and isothermal oxidation testing, respectively.

Failure of pultruded GRP single-bolt tension joints under hot–wet conditions

An experimental study of the effects of hot–wet conditions on the load carrying capacity of pultruded GRP (glass reinforced plastic) single-bolt tension joints has been carried out. The bolted joints were failed in tension after being immersed in water at three temperatures for two periods of time. Two joint geometries, defined in terms of end distance and width to bolt diameter, were tested with the pultrusion and tension axes coincident. The reductions in the load capacities of the joints due to the hot–wet conditions were quantified and shown to be very large. For example, it was found that more than 60% of the load carrying capacity of a single-bolt tension joint was lost after being immersed in water for 6.5 weeks at 60 °C. This temperature is lower than the manufacturer’s recommended maximum service temperature for this type of pultruded GRP material.

Bonding of silicon nitride using preceramic polymer and germanium powders for potential fuel cell applications

A new method for bonding blocks of Si3N4 has been developed that produces bonds whose maximum service temperature is equal to the temperature used during the bonding process. In the present paper a system consisting of blocks of Si3N4 coated with a preceramic film containing a fine dispersion of silicon and a thin layer of germanium powder has been investigated to determine the effect of the thickness of the germanium film. The maximum service temperature is not determined by the melting point of the germanium since the germanium forms a higher melting point solid solution with the silicon in the film. Control of the thickness of the germanium film is found to be critical as a thicker layers results in lower strength bonds owing to differences in thermal expansion, and the maximum service temperature is lower owing to the lower liquidus temperature of the leaner Ge–Si solid solution. This technique has potential applications in fuel cells as a result of the small differences in thermal expansion coefficients and firing shrinkage in fuel cell materials, thus allowing successful fabrication and joining of monolithic solid oxide fuel cells (MSOFCs) with few defects.