Elevated Temperature Tests Research Articles

Performance evaluation of lightweight insulating plaster for enhancing the fire endurance of high strength structural concrete

Structural concrete is a widely used building material due to its versatile characteristics including higher compressive strength and longevity. However, when exposed to fire, concrete experiences faster degradation in its mechanical properties and is also susceptible to spalling. To overcome this problem, the possibility of lightweight plaster application on High Strength Concrete (HSC) is explored in the presented investigation. Insulation plasters, namely Sand Plaster (SP), Gypsum Perlite Plaster (GPP), and Gypsum Mineral Wool Plaster (GMP) were developed. This investigation evaluates the compressive strength, bond strength, and shear strength of concrete which is exposed to the standard fire temperature. Varying cooling conditions which involved air and water were adopted to cool the concrete specimens after the elevated temperature test. Further, the damaged concrete and the plaster were examined to analyse the physical changes. Analysis of the study reveals that more number of denser surface cracks and higher mass loss was observed for reference and SP specimens. Temperature penetration at the core of cube, bond, and shear specimens is less for the GPP and GMP specimens when compared with the SP specimens. At higher temperatures (986 °C), the reference and SP specimens show a lower bond and shear strength with higher slip values. Specimens insulated with GPP and GMP exhibited a low-temperature penetration at the core portion. Also, the results of the study reported the higher residual compressive, bond, and shear strength compared to other specimens. • Insulation plasters were developed to protect the concrete from fire exposure. • Effect of heating and cooling on mechanical properties of concrete were reported. • Residual bond and shear strength of plastered and unplastered concrete were analysed. • Specimens with Gypsum Mineral wool plaster offered excellent protection.

The influence of cement kiln dust on strength and durability properties of cement-based systems

There are very few studies in the literature on the usage of CKD in cementitious systems. This article presents the laboratory study results on the influence of cement kiln dust (CKD) on the properties of mortar made with cement kiln dust and Portland cement. The article aims to prevent CKD's (known as a hazardous waste product) damage to nature by utilizing CKD in cementitious systems and contributing to sustainability by reducing cement amount in the cementitious system. For this purpose, 5%, 10%, 15%, and 20% of CKD were replaced with cement and binary cementitious systems were formed. For all mortar mixes, the water/binder ratio was kept constant at 0.5, and the sand/binder ratio was 3. Workability, dry unit weight, water absorption ratio and porosity, flexural strength, compressive strength, abrasion, carbonation, and high-temperature resistance tests were performed on the mortar specimens. Based on the results of laboratory work, it was observed that the replacement of CKD with cement reduces the workability of fresh mortar. Compressive and flexural strengths of CKD-added mixtures were found to be equivalent or insignificantly lower than that of the control sample. The addition of CKD had a negligible effect on water absorption and porosity of samples. Besides, the residual compressive strength determined after the elevated temperature test for the sample made with CKD were found to be equivalent or higher compared to the control sample. Present laboratory studies showed that utilization of CKD in cementitious mortar system is feasible in terms of testing conducted.

High temperature nanoindentation of iron: Experimental and computational study

• Nanoindentation is simulated based on the tensile deformation data. • Dislocation density pattern under the indent analyzed by TEM. • CPFEM simulations agree well with nanoindentation. Application of reduced activation ferritic/martensitic (RAFM) steels as the structural material in future fusion reactors requires the knowledge of their mechanical properties under relevant operational conditions i.e. temperatures and irradiation by fast neutrons. Execution of the neutron irradiation and post irradiation examination is expensive and lengthy, therefore experimental and computational solutions to ease the characterization of as-irradiated materials are in the scope of interests of nuclear materials scientific community. Moreover, ion irradiation is considered as one possible way to surrogate high flux neutron irradiation damage. The extraction of the mechanical properties after ion irradiation primarily relies on the nanoindentation techniques and its subsequent post-processing to extract engineering relevant information, although some innovative techniques such as compression micropillars and micro-tensile testing also exist. In this work, we have performed nanoindentation on BCC iron, as the basis material for ferritic steels, by using a new Bruker stage developed for high temperature operation. The obtained results were analyzed by means of crystal plasticity finite element method (CPFEM), whereas the constitutive laws of the material were derived and established by using tensile deformation data, thus providing an interconnection of material's behavior under compressive and tensile deformations. The microstructural features such as indentation pile-up formation or dislocation density evolution were obtained by using transmission and scanning electron microscopy, and were compared with the predictions derived by the developed CPFEM model. It is demonstrated that a good agreement between the CPFEM and experimental data set, including tensile and compressive loads as well as associated microstructural changes, is obtained at room temperature and elevated temperature tests.

High Temperature Testing of NMC/Graphite Cells for Rapid Cell Performance Screening and Studies of Electrolyte Degradation

LiNi0.5Mn0.3Co0.2O2/graphite cells with two different electrolytes underwent charge-discharge cycling at 70 °C. The 70 °C condition reduced the time it took for cells to lose significant capacity. Studies of the changes to the electrolyte after cycling by gas chromatography/mass spectrometry (GC/MS) and by Nuclear Magnetic Resonance spectroscopy (NMR) suggest that the same processes which cause cell failure and electrolyte degradation at 40 °C and 55 °C occur at 70 °C, only at an accelerated rate. Transition metal dissolution from the positive electrode was tracked using X-ray fluorescence studies of the negative electrode after testing. Based on the confidence obtained that the same degradation processes were occurring; advanced graphites were screened in NMC811/graphite cells at 70 °C. Differences in cell lifetime were apparent in weeks at 70 °C while the same differences took much longer to observe at 40 °C. It is our opinion that elevated temperature testing of Li-ion cells at 70 °C is a viable rapid screening technique for advanced electrolytes and advanced electrode materials.

Nanoindentation testing of high burn-up fast reactor mixed oxide fuel

Continued research into the mechanical properties of nuclear fuel is necessary to improve modeling of the pellet-cladding mechanical interactions that occur in nuclear reactors during operation. Small scale mechanical testing with focused ion beam equipment can provide a means to study the mechanical properties of irradiated nuclear fuels by measuring their mechanical properties on minute volumes of material. In this work, room temperature nanoindentation measured the hardness and Young's modulus of fast reactor mixed oxide (MOX) fuel irradiated to 183 GWd/tHM. The hardness of the MOX fuel had a measured value of 11.2 ± 0.4 GPa. The Young's modulus of the MOX fuel had a value of 158 ± 6 GPa. The measured hardness and Young's modulus are discussed in the context of the available literature data. In addition, pathways toward elevated temperature testing and other mechanical properties are proposed.

Masking Effect of LPSO Structure Phase on Wear Transition in Mg97Zn1Y2 Alloy

Room- and elevated-temperature wear tests were conducted using a pin-on-disk testing machine to study wear behavior of Mg97Zn1Y2 alloy and role of long-period-stacking-ordered (LPSO) structure phase in mild–severe wear transition (SWT). Variation of wear rate exhibited a three-stage characteristic with load at various test temperatures, i.e., a gradual increasing stage, a slightly higher plateau stage, and a rapid rising stage. The wear mechanisms in the three stages were identified using scanning electron microscope (SEM), from which the first stage was confirmed as mild wear, and the other two stages were verified as severe wear. The interdendritic LPSO structure phase was elongated into strips along the sliding direction with Mg matrix deformation in the subsurface, plate-like LPSO structure phase precipitated at elevated temperatures of 150 and 200 °C. The fiber enhancement effect and precipitation effect of LPSO structure phase resulted in a little difference in wear rate between the first and second stages, i.e., a masking effect on SWT. Microstructure and microhardness were examined in the subsurfaces, from which the mechanism for SWT was confirmed to be dynamic recrystallization (DRX) softening. There is an apparently linear correlation between the critical load for SWT and test temperature, indicating that SWT is governed by a common critical DRX temperature.

Plastic deformation of AA6061-T6 at elevated temperatures: Experiments and modeling

• The work-hardening of AA6061-T6 between room temperature to 500 °C is investigated. • Diffuse necking is observed early on in the elevated temperature tests. • The work-hardening curves are identified using a finite element model of necking. • Rate-dependence is necessary for the work-hardening curves at elevated temperatures. • Swift/Voce with Johnson-Cook strain-rate dependence is sufficient and very accurate. The temperature-dependent work-hardening of AA6061-T6 aluminum alloy is investigated using a combined experimental-numerical approach. Uniaxial tension experiments are performed from room temperature to 500 °C, and the force-displacement curves up to fracture are established. Both the yield strength and the work-hardening rate of the material decrease with increasing temperature. Despite the marked increase in the elongation-to-fracture, the uniform elongation remains limited, indicating the early appearance of diffuse necking in the elevated temperature tests. A simplified technique for identifying the work-hardening curves at elevated temperatures and beyond the limit of uniform deformation in uniaxial tension is proposed. The technique uses an isothermal , rate-dependent, finite element (FE) model of the experiments. The post-necking hardening curve is represented by a hybrid Swift/Voce hardening law combined with a form of Johnson-Cook strain-rate dependence. To identify the material model parameters at each temperature, an objective function that correlates the experimental and FE-predicted force-displacement curves is constructed and minimized. These model parameters are then fit with Fourier series across the temperature range considered here, providing smooth functions suitable for subsequent implementation in FE analyses of forming and structural problems. As an illustration, it is shown that a FE model utilizing these material parameters reproduces the full-field features of the elevated temperature experiments very well.

Dynamic mechanical response and damage mechanisms of nacre-inspired 2024Al/B4C composite at elevated temperature

In this study, the nacre-like 2024Al/B 4 C composites with a lamellar-interpenetrated architecture, virtually free of pores and cracks, were fabricated through combining freeze casting with pressure infiltration, and their quasi-static and dynamic compressive properties were investigated over the temperature ranged from 25 to 500 °C. The dynamic compressive strength and strain were greater than quasi-static ones due to strain-rate hardening and adiabatic heating softening mechanisms. Regardless of strain rates, the compressive strength decreased with temperature, while the failure strain increased. This could be explained by four main fracture phenomena including cracking of B 4 C and intermetallic compounds (IMCs), matrix deformation and interfacial debonding. The matrix deformation prevailed actively at high temperatures, with a reduced overall trend towards cracking and interfacial debonding. The interfacial debonding and particle cracking acted as the dominant factors that deteriorated the compressive behavior, whereas the soften matrix induced by elevated test temperatures effectively blocked the crack propagation that favorably worked for the strain. As the temperature was raised, the softened matrix destabilized particle skeleton with the deformation behavior of the composites determined by the alloy matrix. However, recrystallization occurred within the alloy matrix, accompanied by a reduction in dislocation density, which degraded the strength of the composites. The elevated temperatures significantly enhanced the strain rate sensitivity of the composites because of the matrix softening yielding a greater proportionate enhancement of particle stress at high temperature than at low temperature.

Laboratory Evaluation of the Thermal Breakout Method for Maximum Horizontal Stress Measurement

Measuring in situ stress is essential for many problems in geomechanics, and the maximum horizontal stress is the most difficult to constrain. We are developing an extension of the breakout method to measure maximum horizontal stress in regions where natural breakouts do not occur. In the novel thermal breakout method, additional compression which leads to breakout development is induced by heating the borehole wall. In the present study, we validated the method experimentally in a true-triaxial apparatus on samples with predrilled boreholes. Two rocks were selected for laboratory testing: high-porosity Berea sandstone and low-porosity Niagaran dolomite. Prior to main true-triaxial tests, we carried out standard testing to characterize the strength, elasticity and thermal properties. The true-triaxial experiments consisted of: (1) room-temperature tests where samples were first loaded mechanically until the breakout formed, and (2) elevated-temperature tests where samples were loaded mechanically within the elastic range with additional compression induced thermally. Breakout initiation was monitored by acoustic emission sensors mounted on the pistons that applied horizontal stresses. The magnitude of induced thermal stress was calculated from temperature measurements around the borehole wall. In both rock types, we created thermally induced breakouts and examined analytical expressions to constrain maximum horizontal stress based on strength, elastic and thermal properties of the rocks.

Microstructure and mechanical properties of difficult to weld Rene 77 superalloy produced by laser powder bed fusion

Fabrication of γ′ precipitation strengthened nickel-based superalloys via laser powder bed fusion still remains a challenge. In this study, Rene 77, a high γ′ containing superalloy that is considered as difficult to weld, was processed by laser powder bed fusion. Crack-free parts with high density were fabricated without any compositional modifications or preheating of the built plate. This defect-free structure was maintained upon solutionizing and aging heat treatment. The microstructure of the samples has been characterized in detail following the fabrication and after the heat treatment. Scanning electron microscopy analysis revealed that the as-built microstructure consists of columnar grains mainly aligned in the <100> direction along with extremely fine γ′ precipitates and spherical cell boundary carbides. The grain structure and texture were unaffected by the applied heat treatment due to the pinning effect exerted by the carbide particles. Development of a bimodal γ′ distribution including cuboidal primary and spherical secondary precipitates was observed in the heat-treated sample. Additional carbide formation as a discontinuous grain boundary film was also seen. Tensile deformation behavior for both conditions was also tested at room temperature and 810 °C. Measured strength values for all test conditions were higher compared to a wrought and heat-treated alloy tested at room temperature. The as-built sample showed hardening and loss of ductility during elevated temperature testing due to γ’ precipitation at the test temperature. The microstructure of the heat-treated sample was not altered during testing at 810 °C. However, improved elongation behavior and transition in fracture mode from cleavage to ductile fracture were observed due to microtwin formation at elevated temperatures.

Experimental and numerical study of the behavior of HSLA and DP cold‐formed high‐strength steels at elevated temperature

AbstractDue to the rapid development in steel manufacture, a new generation of structural cold‐formed advanced high strength steels have been developed. However, due to the variations in chemical composition, their material properties have not been fully understood, which includes the mechanical performance when exposed to fire. Therefore, a series of steady‐state elevated temperature tests were conducted on dual phase (DP) and high‐strength low alloy (HSLA) steels with different thicknesses and nominal yield strengths up to 700 MPa to investigate their performance in the range of 20°C to 700 °C. This paper presents detailed results and discussion of the experimental study. A two‐stage plus linear model based on Ramberg‐Osgood equation is proposed to depict the stress‐strain relationship for the materials at elevated temperature. The prediction of the new material model and common existing material models to represent the material properties of steel at elevated temperatures are compared to the test data and current code predictions.

Investigating Degradation Modes in Zn‐AgO Aqueous Batteries with In Situ X‐Ray Micro Computed Tomography

AbstractTo meet growing energy demands, degradation mechanisms of energy storage devices must be better understood. As a non‐destructive tool, X‐ray Computed Tomography (CT) has been increasingly used by the battery community to perform in situ experiments that can investigate dynamic phenomena. However, few have used X‐ray CT to study representative battery systems over long cycle lifetimes (&gt;100 cycles). Here, the in situ CT study of Zn–Ag batteries is reported and the effects of current collector parasitic gassing over long‐term storage and cycling are demonstrated. Performance representative in situ CT cells are designed that can achieve &gt;250 cycles at a high areal capacity of 12.5 mAh cm−2. Combined with electrochemical experiments, the effects of current collector parasitic gassing are revealed with micro‐scale CT. The volume expansion and evolution of ZnO and Zn depletion are quantified with cycling and elevated temperature testing. The experimental insights are utilized to develop larger form‐factor (4 cm2) cells with electrochemically compatible current collectors. With this, over 500 cycles at a high capacity of 12.5 mAh cm−2 for a 4 cm2 form‐factor are demonstrated. This work demonstrates that in situ X‐ray CT used in long cycle‐lifetime studies can be applied to examine a multitude of battery chemistries to improve performances.

Closing repository void spaces using bentonite: does heat make a difference?

Bentonites are commonly proposed for use in the geological disposal of high heat generating radioactive wastes. Repository designs include bentonite as a buffer to occupy the void space around the waste canisters because of the favourable properties it can exhibit that enhance the isolation and containment functionality of the repository. Many repository concepts introduce small voids within the bentonite because the buffer is incorporated as individual bricks stacked around the waste canisters. These voids must be closed to prevent the persistence of high permeability pathways for fluids. As bentonite hydrates, it expands and can exert a considerable swelling pressure on the surrounding host rock. The bentonite also expands to fill the engineering cavities inherently present in the repository, but the non-uniform development of total stress and pore pressure could cause persistent material heterogeneities to occur. This is likely to be exacerbated by the thermal gradients existing between the hot waste and the temperature of the surrounding host rock in the early stages of repository post-closure. Whilst this is an area of ongoing research, the final extent of bentonite homogenisation within the repository and for how long property variations persist, is not well understood. In this study, four tests were conducted on pre-compacted, sodium-activated MX80 bentonite samples placed next to a water-filled engineering void, to examine the effect of elevated temperature on the development of swelling and swelling pressure as a function of sample size. The sample lengths were chosen to give small bentonite-to-void ratios, and to represent extremities of behaviour, such that an acceptable upper limit of void size might be established. The results demonstrated that even under extreme bentonite-to-void ratios, the bentonite was able to swell and completely fill the void space, exerting a small but measurable swelling pressure. Under the conditions of this study, the results have shown larger end-of-test swelling pressures and higher final dry densities along their entire length than shown in equivalent tests conducted at ambient temperature. In addition, the elevated temperature tests showed a rapid initial increase and then decrease in swelling pressure at the start of testing, approaching an asymptote in swelling pressure more quickly, whilst uptaking less water than in the ambient temperature case. This implied that heating the bentonite reduced the test duration by about 60%, which is most likely explained by a reduction in the viscosity of the test permeant at higher temperatures.

Crack growth threshold testing using flat-bottom hole specimens

This study benchmarks a relatively new axisymmetric specimen concept for use in threshold testing, where the crack initiates and grows from the corner of a flat-bottomed circular hole in a cylindrical specimen while the bottom of the hole is cyclically loaded with a flat-ended plunger. The Flat-Bottom Hole (FBH) specimen is configured so the stress intensity naturally decreases as the crack grows radially outward at constant cyclic load, favoring self-centering, highly circular crack growth, and thus enabling tightly repeatable results especially for threshold testing. Because the specimen achieves K-shedding without load shedding, the opening at every point along the crack is constantly increasing during constant load amplitude growth, minimizing the threat of remote closure. Contrary to most conventional specimens, the circular crack front makes no intersection with a free surface, resulting in a crack front of uniform constraint and, where applicable, a uniform crack closure state. In practice, the specimen can be made quite small in size compared to other specimens of similar function. Two configurations are described, one for ambient testing, and one for elevated temperature testing. The K-solution and displacement solution obtained using FRANC2D are presented. Test results include data for Ti 6A-4V forging and Inconel 718 forging.

Enhancing Lithium Manganese Oxide Electrochemical Behavior by Doping and Surface Modifications

Lithium manganese oxide is regarded as a capable cathode material for lithium-ion batteries, but it suffers from relative low conductivity, manganese dissolution in electrolyte and structural distortion from cubic to tetragonal during elevated temperature tests. This review covers a comprehensive study about the main directions taken into consideration to supress the drawbacks of lithium manganese oxide: structure doping and surface modification by coating. Regarding the doping of LiMn2O4, several perspectives are studied, which include doping with single or multiple cations, only anions and combined doping with cations and anions. Surface modification approach consists in coating with different materials like carbonaceous compounds, oxides, phosphates and solid electrolyte solutions. The modified lithium manganese oxide performs better than pristine samples, showing improved cyclability, better behaviour at high discharge c-rates and elevated temperate and improves lithium ions diffusion coefficient.

The Investigation of Microstructure and Mechanical Behavior and the Fractographic Analysis of the Ti49.1Ni50.9 Alloy in States with Different Activation Deformation Volumes

In this article, the microstructure and mechanical behavior of the Ti49.1Ni50.9 alloy with a high content of nickel in a coarse-grained state, obtained by quenching, ultrafine-grained (obtained through the equal-channel angular pressing (ECAP) method) and nanocrystalline (high pressure torsion (HPT) + annealing), were investigated using mechanical tensile tests at different temperatures. Mechanical tests at different strain rates for determining the parameter of strain rate sensitivity m were carried out. Analysis of m showed that with an increase in the test temperature, an increase in this parameter was observed for all studied states. In addition, this parameter was higher in the ultrafine-grained state than in the coarse-grained state. The activation deformation volume in the ultrafine-grained state was 2–3 times greater than in the coarse-grained state at similar tensile temperatures. Fractographic analysis of samples after mechanical tests was carried out. An increase in the test temperature led to a change in the nature of fracture from quasi-brittle–brittle (with small pits) at room temperature to ductile (with clear dimples) at elevated temperatures. Microstructural studies were carried out after the tensile tests at different temperatures, showing that at elevated test temperatures, the matrix was depleted in nickel with the formation of martensite twins.

Effect of mold temperature and additive migration on scratch behavior of TPOs at elevated temperatures

Abstract Scratch performance of thermoplastic olefins (TPOs) has been considered one of the required properties for automotive applications. The scratch resistance of TPOs can be enhanced by utilization of commonly used slip additives such as erucamide. When TPOs are injection molded, the mold temperature impacts the migration of the slip additive toward the surface and the surface crystallinity of the TPOs, which has been shown to influence scratch resistance. In order to evaluate the effect of the mold temperature and erucamide migration on scratch behavior at elevated temperatures, this research has adopted the ASTM D7027/ISO 19252 linearly increasing normal load scratch test methodology to investigate the scratch behavior of the model TPOs at 25 °C, 50 °C, and 75 °C. This study provides a comprehensive understanding on the effects of mold temperature, slip additive, elevated testing temperature, and thermal aging on scratch behavior of TPOs.

Evaluation of the brittleness and viscosity of metals upon tensile testing

The indicators of the brittleness and viscosity of metals calculated from their mechanical properties are considered with allowance for the stress state proceeding from the results of tensile testing of cylindrical smooth and notched samples of perlite 16KhSN, martensitic-aging (maraging) 03Kh11N10M2T, and austenitic 10Kh11N23T3MR steels. Tests were carried out on a UEM-10TM tensile strength testing machine, deformation diagrams developed on a scale of ~50:1 at a deformation rate of 5 mm/min. The sample size before and after testing were measured using a micrometer and an ISA-2 comparator with an accuracy of ±10–3 mm. Pendulum impact bending tests were carried out on a MK15 with the same cylindrical notched samples used to plot the plasticity and viscosity diagrams depending on the Bridgman stress state stiffness index. The new indicators of the brittleness λ = εk/η and viscosity η = (Sk/σb) – 1 (where εk = ln(1/(1 – ψk)) is the true limit plasticity) are proposed proceeding from the testing data. The special feature of the brittleness index λ is growth of the index with increase in the metal strength, e.g., due to pre-deformation or strengthening heat treatment procedures. However, a decrease in the groove radius on the samples, i.e., an increase in the Bridgman stress state stiffness, has almost no effect on the brittleness value λ, but is accompanied by a correlation decrease in the values of the viscosity indices η and the ultimate ductility εk of steels. The curves of the temperature dependences of the mechanical properties of steels 16KhSN and 03Kh11N10M2T show that anomalies in the brittleness indices λ observed at elevated test temperatures can be attributed to the structural transformations like increase in the grain size of 16KhSN steel or in the amount of the residual austenite in 03Kh11N10M2T steel due to reverse martensitic transformation. In this case, the temperature dependences of the viscosity η and brittleness λindicators change in the opposite way.

Monitoring Damage in Nonoxide Composites at High Temperatures Using Carbon-Containing CVD SiC Monofilament Fibers as Embedded Electrical Resistance Sensors

Abstract Electrical resistance (ER) has become a technique of interest for monitoring SiC-based ceramic composites. The typical constituents of SiC fiber-reinforced SiC matrix composites, SiC, Si, and/or C, are semiconducive to some degree resulting in the fact that when damage occurs in the form of matrix cracking or fiber breakage, the resistance increases. For aero engine applications, SiC fiber reinforced SiC, sometimes Si-containing, matrix with a boron nitride (BN) interphase are often the main constituents. The resistivity of Si and SiC is highly temperature dependent. For high temperature tests, electrical lead attachment must be in a cold region which results in strong temperature effects on baseline measurements of resistance. This can be instructive as to test conditions; however, there is interest in focusing the resistance measurement in the hot section where damage monitoring is desired. The resistivity of C has a milder temperature dependence than that of Si or SiC. In addition, if the C is penetrated by damage, it would result in rapid oxidation of the C, presumably resulting in a change in resistance. One approach considered here is to insert carbon “rods” in the form of CVD SiC monofilaments with a C core to try and better sense change in resistance as it pertains to matrix crack growth in an elevated temperature test condition. The monofilaments were strategically placed in two nonoxide composite systems to understand the sensitivity of ER in damage detection at room temperature as well as elevated temperatures. Two material systems were considered for this study. The first composite system consisted of a Hi-Nicalon woven fibers, a BN interphase and a matrix processed via polymer infiltration and pyrolysis (PIP) which had SCS-6 monofilaments providing the C core. The second composite system was a melt-infiltrated (MI) prepreg laminate which contained Hi-Nicalon Type S fibers with BN interphases with SCS-ultramonofilaments providing the C core. The two composite matrix systems represent two extremes in resistance, the PIP matrix being orders of magnitude higher in resistance than the Si-containing prepreg MI matrix. Single notch tension–tension fatigue tests were performed at 815 °C to stimulate crack growth. Acoustic emission (AE) was used along with ER to monitor the damage initiation and progression during the test. Post-test microscopy was performed on the fracture specimen to understand the oxidation kinetics and carbon recession length in the monofilaments.

Thermal–mechanical deformation of Galfan-coated steel strands at elevated temperatures

Abstract The deformation of Galfan-coated steel strands at elevated temperatures causes prestress loss and structural stiffness reduction, which leads to a reduction in the overall bearing capacity and the collapse of the structure. Hence, it is necessary to investigate the deformation of Galfan-coated steel strands at elevated temperatures. In this study, elevated temperature tests were performed on 24 Galfan-coated steel strands, and the deformation behavior of Galfan-coated steel strands of different diameters under eight different stress–temperature conditions were analyzed. The temperature deformation curves of the strands were plotted for temperatures ranging from 30 to 500 °C. In addition, an equation that expresses the relationship between deformation, temperature, and initial stress in the thermal–mechanical coupling state in the heating stage was derived. The parameters in the equation were fitted, and a uniform expression of the parameters was derived. Furthermore, the equation showing the relationship between the parameters for the creep model and temperature T for the constant-temperature stage was established