Elevated Temperature Tests Research Articles

Superplastic Behavior of Copper-Modified 5083 Aluminum Alloy

An AA5083 aluminum alloy was modified with two different levels of Cu additions, cast by direct-chill method, and thermo-mechanically processed to sheet gauge. Copper additions reduced sheet grain size, decreased tensile flow stress and significantly increased tensile elongation under most elevated temperature test conditions. The high-Cu (0.8 wt.%) alloy had the finest grain size 5.3 μm, a peak strain-rate sensitivity of 0.6 at a strain-rate of 1 × 10−2 s−1, and tensile elongation values between 259 and 584% over the temperature range, 400-525 °C, and the strain rate range, 5 × 10−4 to 1 × 10−2 s−1, investigated. In biaxial pan forming tests, only the Cu-containing alloys successfully formed pans at the higher strain rate 10−2 s−1. The high-Cu alloy showed the least die-entry thinning. Comparison of ambient temperature mechanical properties in O-temper state showed the high-Cu alloy to have significantly higher yield strength, ultimate strength, and ductility compared to the base 5083 alloy.

Structural response of restrained steel columns at elevated temperatures. Part 2: FE simulation with focus on experimental secondary effects

This paper presents finite element simulations of a series of elevated temperature tests on axially-restrained steel columns conducted at Nanyang Technological University. The test results have been presented in the companion paper (Part 1), which also includes analytical predictions of failure times based on the Rankine formula extended to the elevated temperature case. The columns with different axial restraint ratios were subjected to a constant axial load ratio. This paper focuses on accurate simulation of secondary effects arising from the experiments, namely, initial crookedness and boundary friction. An approach to correctly ascertain the axial restraint stiffness and rotational restraint stiffness due to inevitable friction effects is discussed in detail. Good agreement between FE predictions and experimental results on column internal force and lateral displacement validates the proposed numerical approach. In addition, the effects of load eccentricity, boundary friction and steel material models on column failure time are also examined. These effects are shown to have significantly influenced the structural response of heated columns.

A Statistical Study of Sn Whisker Population and Growth During Elevated Temperature and Humidity Tests

Storage tests at elevated temperature and humidity conditions have been widely adopted as one of the major acceleration tests for Sn whisker growth. However, the driving force associated and the nucleation and growth process of whiskers are yet to be fully understood. In this paper, Sn whisker growth on Cu leadframe material at two different test conditions is compared. Both loose and board-mounted components were used. At each read point, the length and location of every whisker observed was recorded. Statistical characteristics and growth rate of the whisker population will be presented for each of the tests conditions. On loose components, corrosion of the Sn finish was observed near the tip and the dam bar cut area of the leads with backscatter scanning electron microscopy (SEM) and optical microscopy. The entire population of whiskers was located in these corroded areas, and there were zero whiskers located in the noncorroded areas on the same leads. On board-mounted components, the corrosion level of the Sn finish, as well as the whisker population and length was greatly reduced compared to those on the loose components. These results suggest that the corrosion of Sn finish in high-temperature and high-humidity conditions is the major driving force for whisker growth. The cause for the difference between the loose and board-mounted components is also analyzed

A Practical Viscoplastic Damage Model for Lead-Free Solder

This paper summarizes the results of a program to construct an internal variable viscoplastic damage model to characterize 95.5Sn–3.9Ag–0.6Cu (wt.%) lead-free solder under cyclic thermomechanical loading conditions. A unified model is enhanced to account for a deteriorating microstructure through the use of an isotropic damage evolution equation. Model predictions versus experimental data are given for constant strain-rate tests that were conducted at strain rates of 4.2×10−5s−1 and 8.3×10−4s−1 over a temperature range from −25°Cto160°C; cyclic shear tests; and elevated-temperature creep tests. A description is given of how this work supports larger ongoing efforts to develop a predictive capability in materials aging and reliability, and solder interconnect reliability.

Experimental determination of friction coefficients between thermoplastics and rapid tooled injection mold materials

PurposeTo determine static friction coefficients between rapid tooled materials and thermoplastic materials to better understand ejection force requirements for the injection molding process using rapid‐tooled mold inserts.Design/methodology/approachStatic coefficients of friction were determined for semi‐crystalline high‐density polyethylene (HDPE) and amorphous high‐impact polystyrene (HIPS) against two rapid tooling materials, sintered steel with bronze (LaserForm ST‐100) and stereolithography resin (SL5170), and against P‐20 mold steel. Friction tests, using the ASTM D 1894 standard, were run for all material pairs at room temperature, at typical part ejection temperatures, and at ejection temperatures preceded by processing temperatures. The tests at high temperature were designed to simulate injection molding process conditions.FindingsThe friction coefficients for HDPE were similar on P‐20 Steel, LaserForm ST‐100, and SL5170 Resin at all temperature conditions. The HIPS coefficients, however, varied significantly among tooling materials in heated tests. Both polymers showed highest coefficients on SL5170 Resin at all temperature conditions. Friction coefficients were especially high for HIPS on the SL5170 Resin tooling material.Research limitations/implicationsApplications of these findings must consider that elevated temperature tests more closely simulated the injection‐molding environment, but did not exactly duplicate it.Practical implicationsThe data obtained from these tests allow for more accurate determination of friction conditions and ejection forces, which can improve future design of injection molds using rapid tooling technologies.Originality/valueThis work provides previously unavailable friction data for two common thermoplastics against two rapid tooling materials and one steel tooling material, and under conditions that more closely simulate the injection‐molding environment.

Assessment of Bismaleimide-modified Cyanate Ester as Matrix Resin for Elevated Service Temperature Carbon Composite Applications

Bisphenol A-based cyanate ester resin (BADCy) was modified with different amounts of bismaleimide (BMI) to improve the thermomechanical properties of the parent resin. The DSC investigation of the curing of mixtures of BADCy and BMI suggested that they cured in one single step and addition of BMI shifted the cure initiation and peak curing temperatures of BADCy to higher temperatures. The addition of BMI delayed the gelation times of BADCy. The BMI modification of BADCy did not seem to affect the high Tg of BADCy but a marginal increase in water absorption was seen. Flexural strength of carbon composites with BADCy increased considerably upon modification with BMI. The elevated temperature testing of carbon composites made with BMI-modified BADCy suggest that they retain their advantageous mechanical properties quite well even at 120 C.

Fracture Mechanism in Fatigue of Ni-Base Superalloy Inconel 718 at Elevated Temperatures

In order to investigate the fracture mechanism in fatigue of Ni-base superalloy at elevated temperatures, rotating bending fatigue tests were carried out for Inconel 718 at 500°C and 600°C up to 108 cycles. At both temperatures, fracture occurred from a subsurface of the specimen in long life region, though the origin of fracture was the specimen surface in short life region. Consequently, S-N curves showed a two-step shape in elevated temperature tests. Although a surface crack was observed similar to the result at room temperature even in long life region at elevated temperatures, the surface crack stopped propagating. In this case, interganular cracks were observed at an origin of subsurface fracture. The subsurface damage was initiated at the early stage of fatigue life.

Mechanical Behavior of a Tri-modal Al Matrix Composite

AbstractMechanical milling at cryogenic temperatures (cryomilling) was applied to fabricate a composite powder with 20 wt. % B4C (submicron-to-several microns in size) in a nanocrystalline (NC) 5083 Al matrix. A uniformly blended powder with 50 wt. % cryomilled composite powder and 50 wt. % coarse-grained (CG) 5083 Al powder was degassed, cold isostatic pressed (CIPped) and extruded to form a composite with 10 wt. % B4C, 50 wt. % CG 5083 Al and balance NC 5083 Al. This tri-modal material was then tested for mechanical behavior under compressive and tensile load conditions at various temperatures. The composite exhibited an extremely high yield stress at room temperature, but limited ductility. Although the composite lost its strength at elevated testing temperatures rapidly, the retained strength was still much higher than that of the conventional 5083 Al. The composite exhibits its highest ductility of 26% at 200°C under tensile load. In compression, it plastically deformed uniformly at all the elevated temperatures (≥373 K) and did not fracture even when the deformation exceeded 30%. The microstructure of this composite, including the distribution of each phase, the grain sizes of the Al matrix, the interfaces between these three phases, and the fracture surfaces were characterized using transmission electron microscopy (TEM) and optical microscopy (OM) techniques. The relationship between the microstructures and mechanical properties was discussed.

Part 7: Culverts and Hydraulic Structures: Stress Crack Resistance of Corrugated High-Density Polyethylene Pipes in Different Test Environments and Temperatures

Corrugated high-density polyethylene (HDPE) pipe 36 in. (900 mm) in diameter was evaluated for its stress crack resistance with the notched constant ligament stress test (ASTM F 2136). Test specimens were taken directly from the pipe liner to include the processing effects. In addition to the standard test condition of 10% Igepal solution at 50°C, tests were performed in water and air at temperatures of 60°, 70°, and 80°C. The test data were analyzed with the ISO 9080 method to define the transition point and ductile-to-brittle curve. The results indicate that the 10% Igepal solution greatly accelerates the stress cracking process, whereas the stress cracking behavior in water and in air is aggressive and practically the same. Activation energies in both ductile and brittle portions of the curve are in general agreement with the literature for HDPE resins. The results indicate that the rate processing method is an accurate model with which to extrapolate data from elevated test temperatures to lower service temperatures. However, Popelar's shift method tends to overestimate the failure times.

Stress Crack Resistance of Corrugated High-Density Polyethylene Pipes in Different Test Environments and Temperatures

Corrugated high-density polyethylene (HDPE) pipe 36 in. (900 mm) in diameter was evaluated for its stress crack resistance with the notched constant ligament stress test (ASTM F 2136). Test specimens were taken directly from the pipe liner to include the processing effects. In addition to the standard test condition of 10% Igepal solution at 50°C, tests were performed in water and air at temperatures of 60°, 70°, and 80°C. The test data were analyzed with the ISO 9080 method to define the transition point and ductile-to-brittle curve. The results indicate that the 10% Igepal solution greatly accelerates the stress cracking process, whereas the stress cracking behavior in water and in air is aggressive and practically the same. Activation energies in both ductile and brittle portions of the curve are in general agreement with the literature for HDPE resins. The results indicate that the rate processing method is an accurate model with which to extrapolate data from elevated test temperatures to lower service temperatures. However, Popelar's shift method tends to overestimate the failure times.

Moment–rotation–temperature curves for semi-rigid joints

Although connections are known to have a very significant effect on the behaviour of steel and composite framed buildings in the event of fire, the cost of high temperature tests on the broad range of connections used in practice means that their influence is not well detailed in current design codes. The paucity of data also limits the effective use of numerical models developed to simulate the behaviour of complete structures at elevated temperature. This research describes a series of elevated temperature tests conducted on beam-to-column connections. This paper presents moment–rotation–temperature curves for a variety of connections.

A Comparative Investigation of the Li Insertion Properties of the Novel Fluorophosphate Phases, NaVPO4 F and LiVPO4 F

The electroactive vanadium fluorophosphate compounds, and have been successfully synthesized using a range of preparative strategies, including solid state (ceramic), hydrothermal, and ion exchange methods. In all preparative approaches a carbothermally synthesized vanadium(III) phosphate, was used as a suitable intermediate phase. The is found to crystallize with a tetragonal symmetry (space group and is structurally related to the previously reported sodium aluminum fluorophosphate phase, Low rate testing of the solid state and hydrothermally prepared samples reveals a reversible specific capacity in the range 97-110 mAh/g, and this performance is coupled to exceptional insertion stability at both 23 and 60°C. The voltage profile response during extraction/insertion for the system is consistent with the alkali ions occupying two energetically nonequivalent crystallographic sites within the fluorophosphate framework. The phase crystallizes with a triclinic structure (space group and is found to be isostructural with the known mineral, Tavorite, High-resolution electrochemical measurements reveal a structured voltage response for the lithium extraction process consistent with the lithium ions occupying two crystallographic positions. For the solid-state synthesized sample, the discharge process suggests a two-phase insertion mechanism coupled to phase nucleation behavior. Elevated temperature testing indicates that the lithium extraction process may yield the novel delithiated phase, The reversible specific capacities for the solid-state and ion-exchanged materials are found to approach 120 mAh/g and when coupled to an average discharge voltage in the range 4.10-4.20 V vs. Li, we believe this insertion system may offer some favorable characteristics for commercial application. © 2004 The Electrochemical Society. All rights reserved.

High Strain Rate Response of Cross-Linked and Linear PVC Cores

The compressive response of cross-linked and linear PVC foam core materials, namely, H130 and HD130 having identical densities were evaluated. Both cores were subjected to compressive loading at various strain rates ranging from quasi-static to 1560 s1. At quasi-static loading, the compressive strength of the H grade was approximately 30% higher than the HD grade. On the other hand, at HSR loading the HD grade was 20% higher. HSR tests were also conducted at various temperatures ranging from 25 to 12°C. It was observed that degradation of strength was more severe for the HD grade as temperatures increased. A recovery of the cores original volume was also noticed during high strain rate and elevated temperature tests. Accordingly, residual properties were determined. Results show that only the residual properties of the HD grade were affected by temperature.

8.5Nb–TiAl alloy with fine grains

One 8.5Nb–TiAl-based alloy, whose nominal chemical composition is Ti–45Al–8.5Nb–0.3W–0.3B–0.05Y at% (TAWBY) was presented, including various annealing treatments after cladding insulting forged with homogeneous microstructures. This alloy was developed as cast grains with the size of 25 μm whereas the β (B 2) phase exists in TAWBY alloy. The mechanical properties were conducted in the field of tensile tests at ambient and elevated temperature, fracture toughness, and plasticity behavior tests. Finally, the microstructures and phase analysis were also observed by OM, TEM and SEM methods. The mechanical properties for TAWBY alloy were compared with Ti–46Al–5Nb–1W, Ti–48Al–8Nb–1B, Ti–44Al–4Nb–4Zr–1B, Ti–47Al–2Nb–2Cr–4Ta and K5 alloys. TAWBY alloy was shown to have the best properties. Under the same conditions, TAWBY alloy exhibits the same perfect properties as the K5 alloy and so on.

Electrochemical Insertion Properties of the Novel Lithium Vanadium Fluorophosphate, LiVPO4 F

The novel fluorophosphate compound, Å, Å, Å, has been synthesized by a novel two-step reaction method based on a carbothermal reduction (CTR) process. In the initial CTR step, vanadium pentoxide, ammonium dihydrogen phosphate, and a high surface area carbon are reacted under an inert atmosphere to yield the trivalent vanadium phosphate, The transition-metal reduction is facilitated by the high temperature carbothermal reaction based on the transition. These CTR conditions favor stabilization of the vanadium as as well as leaving residual carbon, which is useful in the subsequent electrode processing. In the second incorporation step, the CTR is reacted with LiF in an argon atmosphere to yield the single phase product. Preliminary electrochemical evaluation of the carried out at 23°C indicates a reversible specific capacity of around 115 mAh/g, a performance roughly equivalent to cycling of in Elevated temperature testing suggests that the extraction process may yield the novel delithiated phase, High resolution measurements reveal a structured voltage response for the lithium extraction process characterized by two well-defined peaks in the differential capacity data. The corresponding discharge process, centered at around 4.19 V vs. Li, indicates a two-phase reaction mechanism coupled to phase nucleation behavior. The insertion properties of the are compared with the other vanadium-based polyanion materials, namely and The demonstrated performance suggests that the insertion system may offer some properties favorable for commercial application. © 2003 The Electrochemical Society. All rights reserved.

The effect of metal fibers on the friction performance of automotive brake friction materials

This study investigates the effect of different metallic fibers upon friction and wear performance of various brake friction couples. Based on a simple experimental formulation, friction materials with different metal fibers (Cu, steel, or Al) were fabricated and then evaluated using a small-scale friction tester. Two different counter disks (gray cast iron and aluminum metal matrix composite (Al-MMC)) were employed for friction tests. The friction tests were carried out at two different temperature ranges: ambient and elevated temperatures. Results from ambient temperature tests revealed that the friction materials with Cu fibers showed a pronounced negative μ– ν (friction coefficient versus sliding velocity) relation when the friction material was rubbed against gray cast iron disks, implying that stick–slip may occur at low speeds. The negative μ– ν relation was not observed when the friction material with Cu fibers was rubbed against the Al-MMC counter surface. On the other hand, elevated temperature tests showed that the friction material with Cu fibers exhibited better fade resistance than the others. The test results also showed that the friction material with steel fibers was not compatible with Al-MMC disks due to severe material transfer and erratic friction behavior during sliding at elevated temperatures.

Enbedding optical fibers in metal alloys

This article presents a new method for embedding optical fibers into a nickel alloy and gives the results for a long-term test with thermal cycling of two fiber-optic Bragg gratings embedded in nickel alloy. We embedded these Bragg gratings in a piece of Inconel 600 (a nickel alloy) using vacuum brazing. We then thermally cycled this piece between 500, 525, and 550/spl deg/C for about six months while monitoring the reflected wavelengths of the gratings. We tested two other embedded gratings for 68 hours at 600/spl deg/C. Some microscopic cross sections of the embedded fibers are presented. The results show that fiber sensors embedded in metal can operate reliably at very high temperature and in harsh environments. We hope that the results from the long-term, elevated temperature test will make it possible to apply the technology of fiber-optic sensing in new and demanding monitoring applications, especially at high temperatures in energy production.

Structural behaviour of cold-formed thin-walled short steel channel columns at elevated temperatures. Part 2: Design calculations and numerical analysis

The companion paper has presented results of elevated temperature tests on 52 cold-formed thin-walled channels under compressive load. This paper presents the results of theoretical studies using a number of different calculation tools, these including simple design calculations based on modifying a few current design methods and a commercial finite element package ABAQUS. The design methods considered in this paper include the British standard BS5950 Part 5, Eurocode 3 Part 1.3 and the American Specification AISI. Modifications of the current design equations are made to enable them to include distortional buckling, the effects of service holes and elevated temperatures. To enable BS5950 Part 5 and Eurocode 3 Part 1.3 to predict the ultimate strength of thin-walled columns with a service hole, the AISI (1996) design method is introduced. To extend the capacity of these design methods to deal with distortional buckling failure mode, the method of Young, Kwon and Hancock for calculating distortional buckling capacity is introduced in these codes. Finally, the ambient temperature design methods are modified to take into account changes in the strength and stiffness of steel at elevated temperatures. From extensive comparisons between the results of tests, code predictions and numerical analyses, it may be concluded that by adopting the aforementioned modifications, the current code design methods can be easily modified to consider these advanced modes of behaviour. For finite element analyses, both geometrical and material non-linearities are taken into account. The high temperature stress–strain relationships of steel are determined according to Eurocode 3, Part 1.2 or Outinen et al.

Microstructural Changes in Liquid‐Phase‐Sintered Silicon Carbide during Creep in an Oxidizing Environment

The knowledge of the microstructural evolution during exposure to high temperatures is important to understanding the mechanisms responsible for the creep resistance of silicon carbide (SiC) ceramics. This includes not only the phase transformation of the SiC grains, but also the phase transformations of the oxynitride grain‐boundary phases. For this study, a series of SiC specimens were prepared with varying molar ratios of AlN‐Y2O3 additives. Increased creep resistance was observed in specimens with an additive system containing a 2:3 molar ratio or 60 mol% Y2O3. A continuous oxide layer of Y2Si2O7 formed at the surface during elevated temperature testing in air. No blistering or cracking was observed in this oxide coating. Further increase of the creep resistance was achieved by a post‐sintering nitrogen anneal.

Evaluation of creep behavior of near-eutectic Sn–Ag solders containing small amount of alloy additions

Understanding and quantification of creep behavior of lead-free solder joints are essential for lifetime prediction of electronic systems. This is especially true for circuits with surface mount and chip components that are subjected to severe environments and higher temperatures. Creep deformation behavior of Sn–4Ag–0.5Cu, Sn–3.5Ag–0.5Ni and Sn–2Ag–1Cu–1Ni solder alloys was determined at room temperature (25 °C) and at elevated temperature (85 °C) using miniature single shear lap joint specimens that are comparable in size to actual solder joints used in electronic packaging. Various creep parameters such as global creep strain, secondary creep rates as well as the strain for the onset of tertiary creep in the solder joint were determined. The effects of Cu and Ni alloy additions on the creep properties of eutectic Sn–3.5Ag solder joints were studied by comparing with the creep deformation behavior of eutectic Sn–3.5Ag solder joints that were used as the baseline. General findings in this study revealed that the creep resistance of Sn–4Ag–0.5Cu solder joints is comparable to but slightly higher than that of eutectic Sn–3.5Ag solder joints at both room and elevated testing temperatures, particularly at lower stresses. The Sn–3.5Ag–0.5Ni solder joints have comparable creep resistance to Sn–4Ag–0.5Cu and eutectic Sn–3.5Ag solder joints at 85 °C, but much better creep resistance at room temperature. The Sn–2Ag–1Cu–1Ni solder joints were two orders of magnitude less creep resistant than solder joints made with other solder materials at 85 °C. However, the shear strains for the onset of tertiary creep in Sn–2Ag–1Cu–1Ni solder joints were found to be the highest at 85 °C. Microstructural analysis showed significant creep deformation along Sn grain boundaries.