Wide Range Of Test Temperatures Research Articles

Superior performance of a trailing edge low-latitude population of an intertidal marine invertebrate

The objective of this study is to compare ecologically relevant measures of performance over a broad range of latitude of a species subjected to climate change. Do populations change in relative function over a wide range of latitude? Are populations at the low latitude trailing edge in danger of extinction in the onset of thermal stress? Coastal marine species with planktonic larvae can range over an enormous span of latitude and thermal environments. The fiddler crab Leptuca pugilator extends from high-latitude (41.75°N) winter-frozen Massachusetts tidal flats in the north to subtropical low latitude flats in Florida (24.55°N), where they may be active at the surface over most of the year. We characterized the air environment for males at three sites (New York – latitude 40.0°N, Beaufort, North Carolina – latitude 34.7°N, Panacea Florida, latitude 30.0°N) over the geographic-thermal range, and found major differences in temperature, wind speed, humidity, and vapor pressure deficit. Florida L. pugilator males preferred warmer sand than North Carolina and New York crabs. Local adaptation to latitude-dependent thermal conditions might suggest tradeoffs in performance as a function of temperature. We examined measures of predator escape performance (running speed and righting speed) and overall condition reflecting endurance rivalry success (endurance on a treadmill and major claw closing force) over a wide range of test temperatures. Predator escape rates increase steadily with increasing temperature, but endurance rivalry measures show an intermediate temperature peak of performance. We tested the hypothesis of tradeoffs, with expected local superiority of performance according to regional thermal differences. But instead, the trailing edge Florida males were superior to the higher latitude populations, over a broad range of temperature, but especially at higher temperatures, for all four types of performance measures. The trailing edge population of L. pugilator, in thermal terms, is therefore likely not vulnerable to near future further effects of warming in terms of performance measures related to male reproductive and feeding activities and escape from predators. Fiddler crabs appear to display niche conservatism for stronger performance at tropical temperatures. Such a natural tropical superiority in performance might have to be accommodated in future conceptions of response of marine species to climate change with broad latitudinal distributions in the tropics.

Computation and experimental analysis of the resistance of superalloys to low cycle deformations

Diagrams of cyclic elastoplastic deformation in a general case characterize the resistance of a material to a low cycle loading and display a relation between current values of stresses and strains during deformation process. Those diagrams in the mechanics of deformation and fracture are described by rather complicated state equations with a nonlinear dependence on conditions and modes of loading including temperature, deformation rate, cycle form, type of the stress state, absolute size of sections, working medium, type of constructional material, etc. The entity of aforementioned factors affects a shape of the deformation curve (diagram) of the material and key parameters of the corresponding state equations, including basic characteristics of the mechanical properties, i.e., the elasticity module, yield point and ultimate stress, indicators of static and cyclic hardening. Experimental data on the kinetics of cyclic and one-way accumulated plastic strains in each loading half-cycle (cycle) obtained in static and low cycle tests of nickel superalloy specimens revealed that change in deformation characteristics exhibit a drastically nonlinear character in conditions of cyclic elastoplastic strain which is described on the basis of power equations and corresponding parameters of cyclic deformation diagrams. The parameters of those equations depend on the type of cyclically hardening/softening or stable material under deformation of the material in elastoplastic region. It is noted that resistance of materials to cyclic elastic-plastic strain can be described by a set of analytical expressions containing a kinetic function (which changes with number of loading half-cycles) in the form of power or exponential expressions depending on the cyclic properties and characteristics of the mechanical properties of the specific structural material. The obtained calculated and experimental data on the kinetics of strain of the alloy under study in conditions of cyclic elastoplastic loading, as well as on the parameters of the strain diagram (which are basic characteristics for the corresponding state equations) provide the possibility to take full advantage of using the deformation-kinetic criteria of damage accumulation under considered loading conditions to calculate the fatigue life of the structural elements manufactured from the alloy and operated, as a rule, under severe temperature and heavy-loaded conditions. The results of the experiments and calculations are given in the form of diagrams of cycle-by-cycle kinetics of the cyclic and accumulated plastic strains of the material for the soft and hard modes of loading in a wide range of test temperatures.

Evaluation of Age-Hardening on Long-Term Aged Asphalt Binders

Oxygen reacts with asphalt binders over time. This time-dependent reaction generates aged asphalt binder that is vulnerable to diseases (i.e., fatigue cracking) in the service stage. Investigation into oxidative aging and its impact on asphalt binder property improve the evaluation of asphalt concrete performance. This paper studied the long-term oxidative aging of unmodified, styrene–butadienestyrene (SBS)- modified and rubber-modified binders. Chemical changes in the binder were tracked by carbonyl area index measured with Fourier-transform infrared reflection spectrometer. The SBS- and rubber-modified binders showed a fewer increase of carbonyl area index than unmodified binders from the same refinery after pressure aging vessel (PAV) protocol. This study also evaluated the change in the binder viscosity that was calculated from dynamic moduli and phase angles. One previous study has proposed a generic hardening susceptibility (GHS) model to describe the linear correlation between the change of logarithmic viscosity and the change of carbonyl area index. This study modified the preliminary GHS model to improve the prediction accuracy of the long-term aged binder viscosity based on the linearity principle between total logarithmic viscosity and carbonyl area index in a wide range of testing temperatures and loading frequencies (between 20 °C and 85 °C and frequencies between 0.0159 Hz and 3.99 Hz). This linearity defines a GHS parameter that can indicate the age-hardening of the binder viscosity. Comparison between model predicted viscosities and measured viscosities shows that the GHS model can predict the viscosity of PAV-aged binder at the investigated temperature and frequency using carbonyl area index and GHS parameter.

Structure and Properties of TiAl-Based Alloys Doped with 2 at.% Mo

Arc-melted Ti100–xMo2Alx alloys (where x is 44, 46, 48, and 50 at.% Al) that were produced from pure components were examined by X-ray diffraction and scanning electron microscopy with electron microprobe analysis (SEM/EDX). The melting points and solid-phase transformations were studied by differential thermal analysis (DTA) and the mechanical properties by fracture toughness, bending, and compression tests. The CALPHAD approach was used for thermodynamic calculation of phase equilibria in the composition region under study. The cast alloys mainly consist of a lamellar structure formed by lamellas of γ-TiAl and α2-Ti3Al phases with submicron thickness and a cubic Ti55Mo4–6Al39–40 phase of A2 type (β) or B2 type (β0). In the γ-TiAl-based alloys, molybdenum behaves as a low-melting dopant, enriching the grain periphery. The standard mechanical characteristics of the alloys were determined and their structural sensitivity was analyzed. All studied alloys demonstrate excellent high-temperature strength. The yield stress is 400–600 MPa in the temperature range 20–750°C. The strength slightly increases at 300 and 600°C under dynamic strain ageing. The strain hardening parameters were established over a wide range of test temperatures. The temperature dependence of the strain hardening coefficient and strain hardening index was analyzed for alloys in different phase and structural states. In the temperature range from 20 to 600°C, the strain hardening index and coefficient were found to vary slightly. The strain hardening index increased from n = 0.6 to n = 0.95 with aluminum content changing from 44 to 50 at.%, which indicates that the strain hardening mechanism changes with variation in the alloy phase constituents.

Low temperature mechanical behaviour of PVDF: cryogenic pre-treatment, quasi-static, cyclic and dynamic experimental testing and modelling

PVDF has historically drawn the interest of the scientific community because of its mechanical response to external stimuli. Recently, novel 3D printing techniques have been proposed to manufacture responsive PVDF components, leading to the reconsideration of this polymer in many applications (i.e., sensor-actuator or energy harvesting systems). During manufacturing and/or service conditions, PVDF structures can be subjected to large deformations that, eventually, can involve low temperature loading (e.g., piezoelectric sensors for aircrafts). In this work, a deep mechanical characterisation of PVDF specimens is carried out under low temperature conditions. To this end, we first evaluate potential effects of cryogenic pre-treatment going beyond the glass transition temperature of the polymer. Then, mechanical tests are conducted at different loading conditions and a wide range of testing temperatures from room to temperatures below glass transition: quasi-static compression tests, cyclic loading tests, and high strain rate tests. The complete set of experiments is analysed together to identify slow and fast relaxation mechanisms within the polymeric structure and motivate a new constitutive model. Finally, taking the experimental observations as formulation's basis, a thermodynamically consistent constitutive model is developed for finite deformations. This model describes the mechanical behaviour of PVDF as the combination of slow and fast response and accounts for strain rate dependency, temperature sensitivity, hysteresis and thermal evolution during the deformation process. The results from this work provide a full study of the mechanical behaviour of PVDF at low temperature, considering effects of both pre-treatment and testing temperature, and a new modelling tool to predict its response under a wide range of room-to-low temperature loading conditions.

Material and structural behaviour of PMMA from low temperatures to over the glass transition: Quasi-static and dynamic loading

This work aims at characterizing the mechanical behaviour of polymethyl-methacrylate (PMMA) under high velocity impact conditions over a wide range of testing temperatures. To this end, the mechanical response at uniaxial compression is studied for both quasi-static and dynamic conditions covering testing temperatures below, at and above glass transition. A pseudo-brittle to ductile transition in the failure of PMMA is observed at a threshold that depends on testing temperature and strain rate. This analysis allows for the interpretation of the perforation impact tests and to explain the principal deformation and failure mechanisms. To complete the study, the Richeton model to predict yielding is revisited. Finally, we provide a new constitutive model for finite deformations to further identify the deformation mechanisms governing the mechanical behaviour of PMMA and the influence of temperature and strain rate on them.

Individual temperature based models for nondestructive evaluation of complex moduli in asphalt concrete

The rheological properties of bituminous materials play important roles in the selection of paving materials, and analysis and design of asphalt pavements. The series of models developed in this study are composed of five formulations for the creation of the dynamic modulus mastercurve at a wide range of testing temperatures. The predictability of these models is assessed by comparing the predicted dynamic modulus mastercurves of different mixtures with measured ones from a nondestructive impact resonance (IR) test. This assessment shows that the predictions match the dynamic modulus values measured from different techniques with a good level of accuracy.

Anisotropy influence on flow behaviour and plastic instability of Ti6Al4V sheets deformed in a wide range of temperatures and strain rates

Abstract Ti6Al4V sheets are usually difficult to form at room temperature as a consequence of their reduced number of slip systems. The heating of the alloy below the β-transus temperature is recognized to enhance its formability, reducing the flow stress and increasing the ductility. However, the effect of the sheet anisotropy on the material flow behaviour and plastic instability at varying temperature and strain rate has not been studied systematically, yet. To this aim, uniaxial tensile tests were carried out in a wide range of testing temperatures (from room temperature to 800°C) and strain rates (0.01, 0.1, 1 s-1) to assess the anisotropy effects. Strain hardening, strain rate sensitivity, and Lankford coefficients were evaluated as a function of the testing parameters and sample orientation. Furthermore, a numerical model of the uniaxial tensile tests was developed and calibrated making use of the Barlat-Lian-1989 yield criterion and a hardening rule, which was adapted to take into account the anisotropic behaviour at different temperatures. It was proved that the developed model was capable of predicting the strain localization in the sample gauge length due to plastic instability as well as its thickness distribution at varying temperature and strain rate.

Leakage behaviour of elastomer seals under dynamic unloading conditions at low temperatures

In technical applications, static seals are sometimes also subjected to dynamic loadings. Therefore, the leakage behaviour under dynamic conditions has to be evaluated as well. For this purpose, FKM elastomer seals have been tested by using newly designed equipment that allows for rapid partial release of the seal and simultaneous leakage rate measurement at a wide range of test temperatures. Furthermore, material characterisation was done by using Dynamic Mechanical Analysis, Differential Scanning Calorimetry and Compression Set. It was shown that, under static conditions, the leakage rate increased significantly during cooling at temperatures around 18 K lower than the glass transition range. On reheating, the seal's functionality was restored in the high temperature region of the glass rubber transition. In the subsequent dynamic release tests, that comprised a reduction of the seal compression within 1 s from 25% to 23%, increased leakage rates were observed in the high temperature region of the glass transition range. It was shown that the temperature that is critical for increased leakage is significantly lower under static conditions compared to dynamic conditions. The obtained leakage rates for static tests and dynamic release tests at different temperatures were analysed with reference to results of the material characterisation.

Application of Small Punch Tests for Screening of Mechanical Properties for T91 Steel

The T91 steel is considered a perspective structural material for Generation IV (GEN IV) nuclear reactors components. The operating conditions of GEN IV nuclear reactor, which include higher operating temperatures, higher neutron fluencies and using liquid metals as coolants, constitute new challenges for structural materials validation. To properly assess the impact of radiation, thermal, load and environmental damage the screening test procedures for initial overview of the induced changes of mechanical properties need to be developed and validated. One of the test procedures with potential to be used for the mechanical properties screening is Small Punch test. Small Punch test receive considerable attention since their development in the 1980's. The use of miniaturized test specimen constitutes minimal requirements for the test material and the option of obtaining the test material directly from the component. They have been successfully used on industrial scale for design life extension of components for energy industry in the past. In this paper we address the issue of the Fracture Appearance Transition Temperature (FATT) determination by the means of Small Punch test for the T91 steel, manufactured according to ASTM standard A387-Ed99. The test specimen were manufactured and used for the experiments in a wide range of test temperatures. Multiple levels of deformation energy were used to provide more representative interpretation of the test data. A data fit is applied on the deformation energy – test temperature dependence to obtain the value of FATT from Small Punch test, which is subsequently correlated to the values obtained from testing sub-size Charpy specimens.

Characterization of stress–strain relationships in Al over a wide range of testing temperatures

The stress–strain relationships characterizing plastic deformation of aluminum are described over a wide range of testing temperatures by applying both a widely used phenomenological relationship and a well-known dislocation-based model. It is shown that over the whole range of testing temperatures the trapping of mobile dislocations and the annihilation of forest dislocations are controlled by the same thermally-activated dislocation motion, thereby leading to a simplified model which uses only two parameters to describe the multiplication and the annihilation rates of dislocations. The temperature dependence of these two microscopic quantities is explained. Furthermore, correlations between the characteristics of macroscopic and microscopic descriptions were established over a wide range of testing temperatures for pure Al.

Temperature Effects on the Deformation Behavior of High‐Density TRIP Steel and Particle‐Reinforced TRIP Steel/Zirconia Honeycombs Under Quasi‐Static Compressive Loading

The interactions between microstructure evolution and mechanical properties of square‐celled TRIP steel and particle‐reinforced TRIP steel/zirconia honeycombs are investigated over a wide range of test temperatures. Based on a powder metallurgical route of a ceramic extrusion technology, two‐dimensional channeled structures are made of an austenitic AISI 304 CrNi‐steel or a TRIP steel matrix composite with up to 10 vol.% of a MgO partially stabilized zirconia (Mg‐PSZ) ceramic. Honeycomb specimens with a cell frame of 196 cpsi and a relative density of 0.37 (viz. 2.9 g cm−3) are tested under quasi‐static compression in out‐of‐plane loading direction at temperatures between ‐196 °C and 150 °C. During compression, the cellular materials deform in a strain‐dominated buckling mode initiating a plastic hinge formation in the cell walls at higher strain levels. Their crush resistance is intensively controlled by the material design including the plastic yield and strengthening mechanisms of the TRIP steel matrix and the constraint or particle reinforcement effects of the embedded zirconia ceramic. Since the thermodynamic driving force for the α′‐martensite nucleation and the intrinsic stacking fault energy are strongly influenced by temperature, different material strengthening and softening processes and a varied microstructure evolution are detected. A sigmoidal initial stress‐strain response as well as the highest compression stress are measured at test temperatures below room temperature due to a pronounced α′‐martensite volume fraction. However, at higher test temperatures, mechanical twinning and dislocation glide are the dominant deformation mechanisms. In summary, strength, ductility and energy absorption which identify the crashworthiness of the honeycombs, are significantly affected by the temperature‐sensitive macro‐ and microstructure phenomena.

A microscopic stored energy approach to generalize fatigue life stress ratios

The uniaxial, isothermal fatigue behavior of the fcc, γ′ strengthened nickel-based superalloy, Waspaloy, 1 Waspaloy is a registered trademark of United Technologies Corporation. 1 measured over a wide range of test temperatures and fatigue stress ratios, is analyzed and modeled. The modeling approach attempts to reconcile the experimentally observed fatigue lives to the effects of temperature and stress ratio using functions that consider simultaneously active mechanisms in competition; mechanical damage and thermally activated, stress relaxation. A semi-empirical relationship for the Basquin fatigue equation, generalized for temperature and stress ratio, is developed and correlated to the experimental results. The correlated model predicts fatigue life is determined by a damage parameter depicted by a molar elastic strain energy density per cycle; a consequence of dislocation enabled, strain accommodation mechanisms operative at local stress concentrations within the fatigue tested substructure.

The effect of scale levels of rotational plastic deformation modes on the strain resistance of polycrystals

Experiments on polycrystalline lead alloys with different states of grain volumes and boundaries under tension in a wide range of test temperatures have been performed. The qualitative and quantitative characteristics of the grain size dependence of the strain resistance of the examined materials are shown to be substantially affected by the development of rotational plastic deformation modes at different scale levels. This effect must be accounted for in the interpretation of the parameters of the Hall-Petch equation in the framework of the multiscale approach employed in physical mesomechanics.

Effect of crumb rubber modifiers on high temperature susceptibility of wearing course mixtures

This paper investigates the effects of different sizes of crumb rubber modifier (CRM) on the high temperature susceptibility of three gradations (AC-10, AC-20 and PA) of wearing course mixtures. A wet process and 10% CRM by total weight of binders were used in these studies and the control variables for these studies included three CRMs of sizes 0.15 mm, 0.30 mm and 0.60 mm. The evaluations were twofold. Firstly, a comparison of the properties of those modified and unmodified binders at a wide range of testing temperatures and ageing conditions was conducted. Secondary, a comparison of the rutting resistance of the CRM and conventional mixtures was made. The results show that all the CRMs have overall contributed to better performance of both binders and mixtures at high temperatures. In addition, among these three CRM sizes, mixtures modified with 0.15 mm CRM exhibited the best effect on the dense-graded mixture (AC-10 and AC-20) whereas mixtures modified with 0.60 mm CRM exhibited the best effect on the open-graded mixture of porous asphalt (PA).

Rational Modeling of Tertiary Flow for Asphalt Mixtures

The objective of this research study was to evaluate several mathematical models to be used in calculating the onset of tertiary flow [referred to as the flow number (FN) parameter] for asphalt mixtures. The FN indicates the onset of shear deformation in asphalt mixtures, which is a significant parameter in evaluating rutting in the field. The FN is obtained from the repeated load permanent deformation (RLPD) laboratory test. Current modeling techniques in determining the FN use a polynomial model fitting approach, which works well for most conventional asphalt mixtures. However, analysis and observations on the use of this polynomial model for rubber-modified asphalt mixtures showed problems in identifying the true FN values. The scope of the work included the collection and analysis of more than 300 RLPD test data files, which comprised more than 40 mixtures, a wide range of test temperatures, and several stress levels. A new comprehensive mathematical model was recommended to accurately determine the FN. The results and analysis were evaluated through manual calculations and found to be accurate, rational, and applicable to all mixture types, whether a tertiary stage was reached or not.

Microstructure, mechanical property and oxidation property in Ni 3Si–Ni 3Ti–Ni 3Nb multi-phase intermetallic alloys

Microstructure, high-temperature compressive and tensile deformation, and oxidation property of multi-phase intermetallic alloys, which were based on the Ni 3Si–Ni 3Ti–Ni 3Nb pseudo-ternary alloy system and composed of L1 2, D0 24 and D0 a phases, were investigated. The microstructures of these multi-phase intermetallic alloys were largely dependent on alloy composition. The Widmansttaten-like Ni 3Ti(D0 24) phase was precipitated from L1 2 matrix by a solid-state reaction, accompanied with a certain orientation relationship and habit plane. The tensile stress as well as the tensile elongation of these multi-phase alloys increased with increasing Si content, i.e. the volume fraction of L1 2 phase in the wide range of test temperatures. Fifty parts per million boron addition to these multi-phase intermetallic alloys resulted in increased tensile stress and tensile elongation. It was found that the multi-phase intermetallic alloy with a high Si content had good oxidation resistance, accompanied with a continuous silicate layer. From an overall evaluation of the properties examined, it was shown that the multi-phase intermetallic alloy that had a high Si content and was composed of L1 2 matrix dispersed by D0 24 and D0 a phases had the most favorable properties as high-temperature mechanical and chemical materials.

Microstructures and Mechanical Properties in Ni3Si-Ni3Ti-Ni3Nb-Based Multi-Intermetallic Alloys

ABSTRACTMicrostructure, high-temperature tensile deformation and oxidation property of Ni3Si-Ni3Ti-Ni3Nb multi-phase intermetallic alloys with a microstructure consisting of L12, D024 and D0a phases were investigated. The tensile stress as well as the tensile elongation of these multi-phase alloys increased with increasing Si content, i.e. the volume fraction of L12 phase in the wide range of test temperatures. 50-ppm boron addition to these multi-phase intermetallic alloys resulted in increased tensile stress and tensile elongation. The multi-phase intermetallic alloy with a high Si content had good oxidation resistance, and also the boron addition to this alloy resulted in enhanced oxidation resistance. From an overall evaluation of the properties examined, it was shown that the multi-phase intermetallic alloy, which has a high Si content and is composed of L12 matrix dispersed by D024 and D0a phases, had the most favorable properties as high-temperature mechanical and chemical materials.

Thermomechanical behavior of virgin and highly crosslinked ultra-high molecular weight polyethylene used in total joint replacements

Three series of uniaxial tension and compression tests were conducted on two conventional and two highly crosslinked ultra-high molecular weight polyethylenes (UHMWPEs) all prepared from the same lot of medical grade GUR 1050. The conventional materials were unirradiated (control) and gamma irradiated in nitrogen with a dose of 30 kGy. The highly crosslinked UHMWPEs were gamma irradiated at room temperature with 100 kGy and then thermally processed by either annealing below the melt transition at 110°C or by remelting above the melt transition at 150°C. The true stress–strain behavior of the four UHMWPE materials was characterized as a function of strain rate (between 0.02 and 0.10 s −1) and test temperature (20–60°C). Although annealing and remelting of UHMWPE are primarily considered as methods of improving oxidation resistance, thermal processing was found to significantly impact the crystallinity, and hence the mechanical behavior, of the highly crosslinked UHMWPE. The crystallinity and radiation dose were key predictors of the uniaxial yielding, plastic flow, and failure properties of conventional and highly crosslinked UHMWPEs. The thermomechanical behavior of UHMWPE was accurately predicted using an Arrhenius model, and the associated activation energies for thermal softening were related to the crystallinity of the polymers. The conventional and highly crosslinked UHMWPEs exhibited low strain rate dependence in power law relationships, comparable to metals. In light of the unifying trends observed in the true stress–strain curves of the four materials investigated in this study, both crosslinking (governed by the gamma radiation dose) and crystallinity (governed by the thermal processing) were found to be useful predictors of the mechanical behavior of UHMWPE for a wide range of test temperatures and rates. The data collected in this study will be used to develop constitutive models based on the physics of polymer systems for predicting the thermomechanical behavior of conventional and crosslinked UHMWPE used in total joint replacements.

Measurement of thermal conductivity of polymers using an improved Lee's Disc apparatus

An improved Lee's Disc apparatus was designed and utilised to measure the thermal conductivity of various commercial polymers such as low-density polyethylene, polystyrene, polypropylene and poly(ether ether ketone) over a wide range of test temperatures from 40 to 400 °C. The measurements were carried out under vacuum such that convective heat losses were minimised. It was found that the thermal conductivity of semi-crystalline polymers, below melting temperature ( T m ), was dependent on their density and degree of crystallinity and, above T m , on the chain mobility and degradation effects. The thermal conductivity of the amorphous polymer was dependent on mobility of polymer chains below the glass transition temperature ( T g ) and on the density above T g The effect of density, degree of crystallinity and heating/cooling were also separately investigated and found to influence the thermal conductivity of the polymers used.