Specimen Temperature Research Articles

Experimental study on flexural capacity and fire resistance of high strength Q690 steel flush end-plate connections

High-strength steel is widely used in building structures, but fire-induced damage and collapse of high-strength steel structures cause huge economic losses. As a primary part of the structure, the reliability of beam–column joints is essential for the structure’s fire safety. This paper presents an experimental study on high-strength Q690 steel flush end-plate connections (Q690-FEC) at ambient and elevated temperatures. Ultimate bending capacity tests were conducted at ambient temperature to investigate its structural performance, where initial rotational stiffness, bending capacity, and ultimate rotation were obtained. Numerical models were developed to reproduce the tests, and parametric analyses were performed to investigate the influence of load ratio, end-plate thickness, and bolt diameter. Transient fire-resistance tests were performed on specimens with different end-plate thicknesses, where specimen temperature, furnace temperature, and joint rotation were measured. The test results indicate that increasing end-plate thickness has little influence on the critical temperature and fire resistance. Finally, a rotation-temperature relationship model was proposed to predict the fire behavior of Q690-FEC and validated against the experimental data.

Preparation of metakaolin-fly ash cenosphere based geopolymer matrices for passive fire protection

In this paper, fly ash cenosphere (FAC) with spherical and hollow structure has been adopted as a pore-forming agent to prepare low density and high strength geopolymer foams. Serial analyses of physical properties, mineral characterization, and thermostability have been employed to investigate the feasibility of metakaolin (MK)-FAC based geopolymer for passive fire protection. FAC addition not only significantly decreases the dry bulk density and thermal conductivity of geopolymer blocks, but also helps to achieve acceptable compressive strength. Meanwhile, FAC addition into geopolymer matrices has brought obviously negative effects on heat transfer and led to the reaction enthalpy rise under high temperature. Owing to the conversion of the amorphous geopolymer gel at the surface to ceramics and excellent thermal insulation performance, the reverse-side temperatures of the geopolymer specimens with FAC addition from 30 to 90 wt% always maintain at about 260 °C until the end of the fire resistance tests. Although weak reactions between alkali activator and FAC have happened and enhanced the bonding between FAC and geopolymer gels, the improvement in physical properties of the MK-FAC based geopolymers would mainly be attributed to the physical characteristics of the FAC. This study could open opportunities to employ MK-FAC geopolymers as alternatives in the application of thermal insulation and fire protection.

A concise study on essential parameters for the sustainability of Lagoon waters in terms of scientific literature

Agriculture encompasses both plant growing (agronomy, horticulture, and forestry) and animal husbandry. Aquaculture is the aquatic embodiment of agriculture. Lagoons are the main sources of aquaculture in various countries around the world which especially yield shrimp, finfish, macrophytes, and mollusk. Agricultural effluents are highly affecting the lagoon water quality parameters in Sri Lanka since most of the agricultural farmlands in the country are on coastal landmasses. It leads to the increased risks of lagoon water contamination. Therefore, it is essential to identify the water quality parameters affected by anthropogenic agricultural activities and establish their threshold limits for ensuring the sustainability of lagoons. This study has identified the influential lagoon water quality parameters associated with agricultural effluents using bibliographic references, tested the existing values of the most influential parameters in five Sri Lankan lagoons, and briefly discussed their fate and transport. The lagoon water quality was classified into biological, physical, and chemical parameters and studied for their importance in enhancing the water quality. The overall experimental findings on temperature, turbidity, pH, salinity, DO, BOD, COD, phosphates, nitrates, ammonia content, and faecal coliforms in water specimens suggest that the selected Sri Lankan lagoons are heavily polluted because of the accumulation over the decades from the agricultural lands which worsens even more with this salinity from the seawater when the tide comes in. This paper concludes that there is a growing need for mechanisms that can be used to monitor and apply control measures to effectively manage lagoon water quality not only for the integrity of the lagoon itself but also for the dependent ecosystems both in and out of the lagoon.

Utilization of Ag ions to improve room-temperature TCR of La0.85-Sr0.15Ag MnO3 polycrystalline ceramics

In this work, silver-doped La0.85-xSr0.15AgxMnO3 (LSAMO, 0.05 ≤ x ≤ 0.20) polycrystalline ceramics were prepared by the sol-gel method. The experimental characterization of ceramics revealed that Ag ions were bounded with the lattice matrix. The resistivity and the corresponding peak temperature coefficient (TCR) of LSAMO ceramics were systematically tuned by changing the Ag dopant content. Adjusting the proportion of Ag enabled one to vary the metal-insulator transition temperature (TMI) for LSAMO specimens in a wide range, and their peak resistivity temperature (Tp) was increased from 299.6 to 335.7 K. At the same time, the peak TCR value achieved its maximum of 15.2% K−1 at the doping molar ratio x of 0.15 and the peak resistivity temperature (Tk) of 294.1 K. In addition, the electrical transport was described in the context of the small polaron hopping (SPH) model and the phenomenological percolation model (PP) over the metal-insulator transition region. Under the combined action of the Jahn-Teller (JT) effect, the double exchange (DE) mechanism and the PP model, LSAMO ceramics possessing high TCR at room temperature were obtained by varying the amount of Ag doping. The observed properties suggest LSAMO material can be used in advanced uncooled infrared bolometers.

Maternal spawning experience and thermal effects on offspring viability of chub mackerel and their influence on reproductive success

Maternal effects on offspring viability significantly contribute to the productivity and resilience of exploited marine fish populations. The temporal trend of biomass of chub mackerel (Scomber japonicus) in the western North Pacific showed cyclic fluctuation patterns, but it has been rapidly increasing since 2011. Although there are several assumptions regarding the mechanisms of the population dynamics of this species in these waters, there is a contradiction in the effects of thermal environmental conditions on recruitment success. We explored the effects of maternal age and/or previous spawning experience on egg and offspring traits of captive chub mackerel in response to thermal conditions. Moreover, from the relationship between the growth rate and temperature experienced by captive fish, the experienced temperatures of wild specimens were assessed. The sizes of eggs spawned from females aged 1–3 years were negatively correlated with temperature, but the effects of maternal age on egg size and nutrition were significant with larger and nutrient-rich eggs spawned from 2- or 3-year-old females (repeat spawners) than those from 1-year-old females (first-time spawners) at a given temperature. Such temperature- and maternal-age-dependent egg traits reflected the standard length of first-feeding larvae. The effects of maternal age on the starvation tolerance of larvae after hatching and body sizes of first-feeding larvae were also evident in larvae derived from 3-year-old females showing longer starvation tolerance and larger body heights than those from 1-year-old females. Further, larvae derived from 3-year-old females grew significantly faster than those from 1-year-old females at the tested temperatures. The process of ontogenetic development and growth rate of captive specimens until age 25 days were positively correlated with temperature. Meanwhile, the estimated temperatures experienced by wild specimens until age 25 days ranged from 18.0 to 20.3°C. These findings suggested that there were opposing thermal responses between maternal and offspring traits of chub mackerel, but the temperatures experienced by the main recruit fish may be restricted within the range of temperatures available for spawning. We discuss the mechanisms of reproductive success of this species in accordance with the maternal spawning experience and thermal effects on life history traits.

The curious case of the second/end peak in the heat release rate of wood: A cone calorimeter investigation

AbstractThe reasons behind the occurrence of a second/end peak heat release rate (PHRR) during wood combustion under radiative heating were determined. Effects of the type of rear material, wood thickness, char progression, and its microstructure, as well as moisture content/transport in spruce wood, were studied. Rear materials used were insulating Kaowool, conducting steel, and the same wood but physically separated from test specimen by aluminium foil. The intensity of the second/end PHRR with Kaowool was almost 50% more than that of the sample with steel. Thus, the second/end peak is governed by the boundary condition defined by the rear material, which determines the heat losses at the rear side of the specimen and consequently the temperature of the specimen. Higher specimen temperature enhances the pyrolysis rate, thereby causing the second/end PHRR. The appearance times and values of the second/end PHRR for 30, 20, and 10 mm wood were 1740 s/78 kWm−2, 685 s/134 kWm−2, and 450 s/160 kWm−2, respectively. Char progressed to the rear of the samples even with a thin (8 mm) conductive steel substrate. Cracks in char grew almost three times wider during the second/end PHRR compared to the sample with no second/end peak. Char cracking had no significance on the time of occurrence of the second/end PHRR but affected the overall heat release. High moisture content reduced the charring rate and delayed the time of occurrence of the second/end PHRR as more water was needed to undergo a phase change, requiring a higher amount of energy.

Role of microstructure reactivity and surface diffusion in explaining flash (ultra-rapid) sintering kinetics

The competition between sintering and coarsening is cited by numerous authors as one of the potential factors for explaining the ultra-rapid sintering kinetics of flash sintering. In particular, surface diffusion is a mechanism decreasing the driving force of sintering by changing the initial highly reactive microstructures (particle contact) into poorly reactive porous skeleton structures (spherical porosity). We show by finite element simulations that flash SPS experiments high specimen temperatures close to 2000 °C. These high temperatures are not sufficient to explain the ultra-rapid sintering kinetics if typical spherical pore theoretical moduli are employed. On the contrary, reactive experimentally determined moduli succeed in explaining the ultra-rapid sintering kinetics. Mesoscale simulations evidenced that the origin of such reactive experimental moduli is a porous skeleton geometry with a significant delay in surface diffusion and particle rearrangement. This highlights the important role of the surface diffusion negation (favoring higher stress intensification factor) in flash sintering.

The Estimation of Taylor-Quinney Coefficients Using Small Ring Specimens

BackgroundThe use of the Taylor-Quinney coefficient for introducing a thermal dissipation term into material models relies on understanding its dependencies. These are usually determined through extensive experimentation, wherein temperature variations are monitored in a test piece during mechanical loading.ObjectiveThis study aims to reduce the cost and time necessary to determining the dependencies of the Taylor-Quinney coefficient by proposing a novel small specimen inverse testing method and demonstrating its use on aluminium alloy 7175.MethodsThe method proposed is based on mechanical testing of a novel small ring specimen in parallel with FEA simulations. In the experiments, small rings of 7175-T7351 aluminium alloy, 20 mm in outer diameter, were loaded between two pins for different pin displacement rates (namely 1, 1.5 and 2 mm/s) at room temperature and the local specimen temperature field was monitored using an infra-red thermal camera. Fully coupled thermal-mechanical simulations of the tests were performed using a range of Taylor-Quinney coefficients, and the resulting temperature evolutions compared to the experimental results in order to determine appropriate coefficient values for the material.ResultsThe method presented shows good repeatability and allows for clear observation of thermal dissipation. Taylor-Quinney values ranging 0.51-0.59 are reported for the 7175 alloy, in line with values reported in the literature for similar alloys. Density, specific heat capacity and thermal conductivity, fundamental thermal material properties necessary for the simulations, are also reported for the alloy.ConclusionsThe method detailed shows promise for determining Taylor-Quinney coefficients in a wide range of experimental conditions and is proposed as a cheap and fast alternative to full-scale specimen testing of Taylor-Quinney coefficients. Taylor-Quinney values obtained for 7175 aluminium are shown to be much lower than the value of 0.9 often proposed for materials.

Influence of single-pulse and high-amplitude current on springback and mechanical properties of AA5052 aluminum alloy sheets

Springback is a key challenge in quasi-static (QS) stamping, which seriously affects the forming accuracy of aluminum alloy. A multi-pulse and low-amplitude current is widely used to reduce the springback of aluminum alloys. However, the increase in workpiece of current severely affects the material performance. Herein, a single-pulse and high-amplitude current is employed to eliminate springback of V-shaped parts in a short time (<500 μs). With an increase in discharge voltage, the springback of V-shaped parts decreases. Compared with QS stamping, the average values of yield strength and tensile strength decrease by 9.2% and 1.2%, while the average values of elongation increases by 18.9% after discharge under 10 kV. The increase in temperature of tensile specimen is found to be 5.6 °C at 10 kV. Thus, the thermal effect caused by a pulse current renders a small influence on the properties of V-shaped components. Moreover, the texture and microstructure before and after discharge are studied using electron backscattered diffraction electron backscattered diffraction and transmission electron microscopy measurements. Briefly, the grain size increases and texture strength decreases under the influence of pulse current. Also, dislocation entanglement at grain boundaries is reduced, compromising the strength and springback effect. This study provides experimental and theoretical bases for eliminating springback of Al alloys with a large pulse current. • The springback of the V-shaped parts is completely eliminated in the presence of pulse current, corresponding to a discharge voltage of 10 kV. • The influence of single-pulse and high-amplitude current on the material mechanical properties and microstructure is analyzed. • The yield strength and tensile strength decrease after discharge treatment, whereas the elongation increases. • After pulse current treatment, the proportion of low-angle grain boundaries (LAGBs) decreased, as well as the dislocation density at grain boundaries and intercrystalline regions was reduced.

Sliding contact performance of injection moulded and selective laser sintered polyamide under dry and lubricated conditions

PurposeThis paper aims to understand the effect of the manufacturing process on the frictional and wear performance of polyamide.Design/methodology/approachPin specimens were manufactured through injection moulding (IM) and selective laser sintering (SLS) manufacturing processes. The friction and wear performance was evaluated using a pin-on-disc configuration under dry and oil-lubricated conditions. The friction coefficient, wear resistance and surface temperature of specimens were measured, and failure morphology analysis was carried out to understand the mechanism.FindingsSLS material exhibited significantly less friction, wear and surface temperature than IM material under dry conditions. Reduced ductility due to the sintering contributes to reduced friction, wear and heat generation. Under the dry condition, IM material exhibited plastic flow and roll-shaped deformation, whereas SLS material exhibited only local degradation due to its lesser ductility. Lubrication reduced friction and temperature for both SLS and IM materials. The porous nature of the sintered surface absorbed the lubricant and released it while sliding, which is confirmed by the brown-coloured wear track.Originality/valueThe study provides valuable input to the designers on the sliding contact performance of commonly adopted two different manufacturing processes of polymers; IM and SLS manufacturing.

Development of Fixtures and Methods to Assess the Durability of Balance of Systems Components

The degradation of photovoltaic (PV) balance of systems (BoS) components is not well studied, but the consequences include offline modules, strings, and inverters; system shutdown; arc faults; and fires. A utility provider experienced a ∼30% failure rate in their power transfer chain, originally attributed to branch connectors. Field-failed specimen assemblies were, therefore, examined, consisting of cable connector, branch connector, and discrete fuse components. In this study, unused field-vintage specimens are examined using a benchtop prototype fixture to identify the most influential environmental stressors on BoS components as well as the effect of external mechanical perturbation. The prototype fixture was used to develop a perturbation capability for future use in the combined-accelerated stress testing chamber. The benchtop experiments were also used to develop the in-situ data acquisition of specimen current, voltage, and temperature. A significant increase in operating temperature (∼100 °C from ∼40 °C) and a different failure mode (arcing at the metal pins rather than overheating of the fuse filament) were observed promptly once periodic mechanical perturbation was applied. The current at failure was decreased from 35 A (measured for static specimens, with failure occurring in the fuses) to 15 A (for tests with mechanical perturbation, with failure at the male/female metal pin connection). After initial examination using X-ray computed tomography, the external plastic was machined away from failed specimens to allow for failure analysis, including the extraction of the internal convolute springs for morphological examination (optical and electron microscopy). Chemical composition analysis included energy-dispersive X-ray spectroscopy, differential scanning calorimetry, and Fourier transform infrared spectroscopy.

Characterization of Thermal Barrier Coatings Using an Active Thermography Approach

The aim of this paper is to define and set up an experimental procedure, based on active thermography, for the characterization of coatings for industrial applications. This procedure is intended to be a fast and reliable method, alternative to the consolidated one described in International Standards. In more detail, a classical active thermographic set up, and not a dedicated apparatus, was used for that aim, and data processing techniques referred to the analytical approach described in Standards. The active thermography procedure provided the measurement of the surface temperature of specimens undergoing a thermal excitation, applied by means of a laser pulse (Pulsed Technique). Temperature data processing, according to and adapting the Standard procedures, allowed to obtain thermal conductivity and diffusivity information. In particular, two coating processes (Atmospheric and Suspension Plasma Spray) applied to the same base material, Inconel 601, and the same coating material were investigated. These results were compared in terms of thermal properties variation with respect to base and coated materials, and in terms of different coating processes (APS and SPS). Obtained results were also compared to those available in literature.

Experimental investigation of heat treated alloy for hardness using multiple linear regression model

Quenching media, temperature and time plays vital role to improve the mechanical properties of metal and alloys. Tap water blend with cow urine different compositions hot metal at different temperature interval and quenched the blend and find the hardness values Al 2585 alloy. Cow urine contains different ingredients to enhance the mechanical properties of the meal and alloy. Ingredients like sodium and silicon some other elements present homogeneously improve properties like tensile strength, yield strength and hardness. Sodium refine the micro structure and silicon interlocking the grain boundaries of the metal. The model defined the relationship existing between the two variables of % of blend and temperature of specimen and hardness value, the dependent variables. This was correlated with existing theories are the relationship between Hardness and two variables. A analytical model was developed for the fore casting of hardness, it was proved and certified to be a positive valuation tool for estimating the hardness on the heat treatment process.

Optimal design and experimental study of horn antenna in pavement microwave deicing technology

To effectively improve the efficiency of microwave deicing on pavement and guide the engineering application of microwave deicing technology, the optimization design of horn antenna was investigated. In this study, based on the experimental method of control variables, the influence of horn antenna on microwave deicing efficiency was explored, and the relatively optimal shape and size of horn antenna were obtained through comparative analysis. The results demonstrate that the width of the horn antenna has the greatest impact on the microwave deicing range, followed by the overall height of the horn antenna. The wider the horn antenna width, the larger the deicing range. The lower the overall height of the horn antenna, the larger the deicing range. The temperature rise rate is mainly affected by the overall height of the horn antenna, followed by the width of the horn antenna. The higher the overall height of the horn antenna, the faster the temperature rise rate, and the narrower the width of the horn antenna, the faster the temperature rise rate. When the overall height of the horn antenna is high, the vertical wall can improve the deicing efficiency. When the overall height of the horn antenna is low, the vertical wall will reduce the deicing efficiency. The deicing effect of the horn antenna numbered #1 is the best among the ten groups of horn antennas. It can raise the temperature of the concrete specimen with an ice layer by 55.4 °C in 1 min, and the deicing area is up to 158.59cm2.

Microstructure and mechanical behaviour of 3D printed ultra-high performance concrete after elevated temperatures

This study investigated the characteristics of 3D printed ultra-high performance concrete (3DP-UHPC) after elevated temperatures. The effects of the bonding strip, steel fibre, specimen preparation method, loading direction and temperature on the fire resistance of 3DP-UHPC were analysed. The variations in microstructure and mineral composition of 3DP-UHPC after different temperatures were examined using scanning electron microscopy (SEM) and energy spectrum analyser (EDS). The strength degradation mechanism of 3DP-UHPC after the elevated temperatures was revealed in terms of the macro and micro levels. Meanwhile, the compressive strength of 3DP-UHPC after the elevated temperatures was measured, and its corresponding compressive constitutive model was proposed. The experimental results indicated that 3DP-UHPC had certain fire resistance, and the addition of steel fibre and the preparation method improved its fire resistance. The expansion of the crack at the junction of the steel fibre and matrix, as well as the oxidation and decarburization of steel fibre, affected the compressive strength of 3DP-UHPC after 400 ℃. During heating, water vapour escaped from the weak interface of the bonding strip endowed 3DP-UHPC with slightly better elevated-temperature burst resistance as compared to mould-casting ultra-high performance concrete (MC-UHPC). The compressive strength of 3DP-UHPC was the highest after 300 ℃ for the target temperatures set in this study, but the temperature had little effect on the strength difference between each direction of 3DP-UHPC. The compressive constitutive model of 3DP-UHPC after the elevated temperatures was developed, facilitating its engineering application in the field of fire safety.

Effect of the environment on home-based self-sampling kits for anal cancer screening

BackgroundAnal cancer incidence has increased in Western countries in recent decades and currently there are no consensus screening guidelines. Home-based self-sampling kits might facilitate screening for anal precancer/cancer but could require travel through postal mail where they may experience extreme temperatures or long transport times. ObjectiveTo determine the effect of the environment on specimen adequacy for HPV genotyping of a mailed home-based self-sampling anal cancer screening kit. Study designThe Prevent Anal Cancer (PAC) Study in Milwaukee, Wisconsin recruited men who have sex with men (MSM) and transgender persons 25 years of age and older. Participants were randomized to receive a mailed self-sampling kit or attend a clinic for screening. Kits were insulated with foam and included a device to record temperature every twenty minutes. Samples were returned via mail and underwent HPV genotyping using the SPF10-LiPA25 assay which also detected human RNase P to determine specimen adequacy by qPCR. For the first 93 kits, logistic regression assessed associations between specimen inadequacy and temperature, freeze-thaw cycle, presence of fecal matter, and number of days in an uncontrolled environment. ResultsMost specimens (92.5%) were adequate for HPV genotyping. Specimen inadequacy was not associated with temperature, freeze-thaw cycle, or transit time. Fecal matter was present more often in inadequate (71.4%) compared to adequate specimens (16.3%) (p = .004). ConclusionsThese real-world data from mailed home-based anal self-sampling kits found that environmental conditions did not affect specimen adequacy. While over 90% of specimens were adequate, presence of fecal matter predicted specimen inadequacy.

Eucalyptus Bark Residue Application for Poly(Vinyl Chloride) Composite Production: Influence of Fiber Size and Content

Background: Brazil is the world’s largest producer of short fiber cellulose, generating large amounts of eucalyptus bark residue (EBR). Aiming to obtain composites known as wood plastic composites (WPC), the effect of ground EBR addition to a poly(vinyl chloride) (PVC) matrix was studied, considering different granulometries and matrix/load proportions. The influence of fiber content addition and particle size range was analyzed in terms of mechanical and thermal properties of the PVC-EBR fiber composites obtained. Finally, by comparing these properties with those reported in the literature, the viability of EBR application as filler/reinforcement in a WPC with PVC matrix was verified. Objective: The main objective of the present study was to evaluated the influence of EBR fiber size and content in the WPC with PVC matrix, aiming to reduce the costs and improve its mechanical and physical properties. Materials and Methods: The processing method for prepared the composites were two-roll milling and subsequent hot pressing. The residue was characterized via chemical and thermogravimetric analyses, scanning electron microscopy (SEM), and aspect ratio determination. Composite evaluation involved density, tensile and flexural tests, impact resistance, heat deflection temperature (HDT), moisture absorption, and SEM of tensile fractured specimens. Results: Tensile and flexural moduli were improved with fiber addition attaining 46% and 58% increases, respectively, with better results for smaller particle size fibers; impact resistance and elongation at break, however, were reduced, attaining 48% and 5% of the control sample’s properties. SEM images reveal fiber detachment and pull-out due to their low matrix adhesion. EBR fibers cause more void formation due to low interface adhesion, which results in poor stress transference from the matrix to the fiber, in addition to EBR acting as stress concentrators in the PVC matrix; therefore, impact fracture occurs with lower energy levels. Discussion: Regions with fiber detachment and pullout from the matrix are visible, clearly demonstrating the low adhesion properties of the phases and also in accordance with the observed decrease in mechanical properties for both fibers. SEM images indicate that fibers can be considered foreign particles inside the PVC matrix, acting as stress concentrators. Also, since fibers have diameters larger than the voids caused by crazing, planar density is reduced in the direction perpendicular to chain stretching leading to low strain at break values. Composites of fiber with finer particle showed fewer voids, possibly indicating a more efficient adhesion for fibers. This could be due to a higher penetration of polymeric chains in the rugosity of finer fibers, leading to higher values of tensile strength. Conclusion: The addition of EBR content increased especially flexural and tensile moduli whilst elongation at break and impact resistance are reduced. The reduction in tensile strength due to poor fiber-matrix interfacial adhesion, though significant, allowed the use of composites with higher fiber additions. The use of EBR is coherent with the concept of circular economy. Thus, higher fiber additions relate directly to money savings since this residue costs less than PVC, and also this is an environmentally correct destination for this residue since WPC is long-term usable allowing for recycling.

Electron-beam-induced charging of an Al[formula omitted]O3 nanotip studied using off-axis electron holography

Electrostatic charging of specimens during electron, photon or ion irradiation is a complicated and poorly understood phenomenon, which can affect the acquisition and interpretation of experimental data and alter the functional properties of the constituent materials. It is usually linked to secondary electron emission, but also depends on the geometry and electrical properties of the specimen. Here, we use off-axis electron holography in the transmission electron microscope to study electron-beam-induced charging of an insulating Al2O3 nanotip on a conducting support. The measurements are performed under parallel electron illumination conditions as a function of specimen temperature, electron dose, primary electron energy and surface cleanliness. We observe a lack of reproducibility of charge density measurements after cycling the specimen temperature. Surprisingly, we find both positively and negatively charged regions in closely adjacent parts of the specimen.

Exploration of atom probe tomography at sub-10K

The operating temperature is a critical parameter in atom probe tomography experiments. It affects the spatial precision, mass resolving power and other key aspects of the field-evaporation process. Current commercially available atom probes operate at a minimum temperature of ∼25 K when measured at the specimen. In this paper, we explore and implement changes to the mechanical design of both the LEAPⓇ and EIKOS™ atom probe microscope systems manufactured by CAMECAⓇ to enable a specimen temperature in the sub-10 K regime. We use these modified instruments to analyze four materials systems: pure Al (in both pulsed-voltage and pulsed-laser mode), pure W (pulsed-voltage mode only), doped Si, and GaN (pulsed-laser mode only). The effects of conducting atom probe experiments in the sub-10 K regime were assessed with reference to a range of quantitative analysis metrics related to spatial precision, mass resolving power, stoichiometry and charge-state ratio. We demonstrate that the spatial precision is significantly improved with decreasing temperature, whilst the effect on mass resolving power is relatively minor. The enhanced spatial precision is significant insofar as it enables lattice planes from the doped Si samples to be resolved. Furthermore, mass spectral analysis, lower noise floors and changes in the field evaporation process enabled more accurate GaN compositional measurements. We discuss the significance of these findings for the semiconductor and metallurgical industries and the potential opportunities for further investigations of this parameter space.

Experimental Investigation of Factors Influencing the Determination of the Onset of Yielding by Temperature Measurement

The cooling of the material during elastic tensile loading is well known as the thermoelastic effect. It is already known that the temperature minimum at the elastic-plastic transition can be used for the determination of the onset of yielding. Conceivable parameters for this have already been presented and investigated. Within this study factors influencing the specimen temperature during tensile loading and unloading are experimentally analyzed to improve the determination approach and the understanding of it. Furthermore, the robustness and repeatability of the measurement and evaluation procedures are analyzed. Therefore, cyclic tensile tests with the mild steel DC06 and the high strength steel CR590Y980T (DP1000) are performed with four PT1000 sensors applied on the specimen. The temperature behavior during elastic loading, elastic-plastic elongation and elastic unloading is separately evaluated. Different strain rates are investigated to better understand the strain-dependent heat development and its influence on the temperature-dependent evaluation. In this way, correlations between strain rate and thermal conduction due to prevailing temperature differences are found and their influence on the temperature-based determination of the onset of yielding is analyzed. Therefore, the yield stress at temperature minimum YSTmin as well as an additional yield stress at zero plastic strain YS0 are evaluated for all experiment settings. In a comprehensive experimental study, the standard deviations are compared and thus conclusions can be drawn about the robustness of the determination methods.