Room Temperature Elastic Modulus Research Articles

The Thermo-Elastic Properties and Damping of U-6wt%Nb

While thermal expansion data exists for quenched (as well as aged) U-6wt%Nb, there is wide variation in the reported room temperature elastic moduli. To better understand the room temperature elastic behavior and to address the complete absence of data on the temperature dependence of the elastic moduli, room temperature and in-situ elevated temperature resonant ultrasonic spectroscopy (RUS) was performed along with x-ray diffraction (XRD) and dilatometry using a thermomechanical analyzer (TMA). An in-situ small- and wide-angle x-ray scattering (SAXS/WAXS) experiment was performed on a companion sample to help interpret the results. The room temperature polycrystalline dynamic moduli were measured to be E = 95.4 ± 4.5 GPa and G = 35.2 ± 0.2 GPa, respectively. As the temperature is raised, the stiffness slowly decreases, consistent with the empirical rule proposed by Varshni, up to the point of precipitation of the equilibrium α-U phase, which is stiffer than the martensitic phases. Homogenization theory of composites can be used to rationalize the observed response at high temperatures and after high-temperature exposures. Aging of the material at low temperatures (≤200°C) does not affect the linear elastic stiffness, but does impact the damping behavior which can be measured through RUS. This change in damping provides another perspective on the microstructure changes induced by low-temperature aging which also result in significant strengthening.

Long-term service induced mechanical properties change of hot-end welding metals in a retired CrMoV bainitic gas turbine rotor

This research focused on evaluating the mechanical properties change of Welding Metals (WMs) at the turbine-end (hot-end, working beyond 500 °C) of a retired CrMoV bainitic gas turbine rotor serving over 14 years, by comparison to those WMs at the compressor-end (cold-end, working below 300 °C). After long-term service, the room-temperature elastic modulus and the bainitic microstructure of hot-end WMs stayed almost the same as those of cold-end WMs, but the high-temperature elastic modulus and the dislocations density of the former became higher than those of the latter. The above change, especially the change of high-temperature elastic modulus produced significant influences on the tensile, fatigue and creep behaviors of hot-end WMs, which further led to a higher tensile and creep strength but a lower ductility, as well as a better fatigue crack propagation resistance under high-temperature condition. A correlation between the high-temperature elastic modulus change and the tensile/fatigue/creep behaviors change was established for hot-end WMs based on mechanics modelling, which provided a feasible way to monitor the rotor properties change.

Research on suitable strength, elastic modulus and abrasion resistance of Ti–Zr–Nb medium entropy alloys (MEAs) for implant adaptation

Attributed to their excellent strength, toughness, hardness, wear resistance and corrosion resistance, some Ti-rich high entropy alloys (HEAs) and medium entropy alloys (MEAs) are develop as one of potential implant materials, however poor ductility at room temperature and high elastic modulus limit their application. To obtain implant materials more suitable for human bone, five Ti–Zr–Nb MEAs (TiZrNb, Ti40Zr40Nb20, Ti45Zr35Nb20, Ti45Zr45Nb10, and Ti50Zr40Nb10) were designed and fabricated. All alloys possessed BCC structure, low elastic modulus (52 ± 2–73 ± 3 GPa), and high yield strength (675 ± 18–830 ± 21 MPa) with elongation over 11%. The solid solution strengthening model and transition metal bond energy model were used to analyze their yield strength and elastic modulus, and the latter can make up for the limitations of concentration (VEC) in predicting elastic modulus. The abrasion test shows that their corrosion resistance is equivalent to that of Ti6Al4V and wear loss of MEAs ranges from 0.02054 mm3 to 0.1164 mm3.

Mechanical properties of graphene, defective graphene, multilayer graphene and SiC-graphene composites: A molecular dynamics study

In this article, using molecular dynamics (MD) simulation, several mechanical properties of graphene were calculated for pristine single layer graphene sheet (SLGS), defective SLGS, multilayer graphene sheets (MLGS) without defects and for composites of SiC and graphene. Firstly, the room temperature elastic moduli (Young's, shear and bulk), constants and Poison's ratios were simulated for the above structures and then their properties such as stress vs strain under tensile and compressive loading were simulated within the temperature range of 300K–2000K. The simulations were performed in both zigzag and armchair directions of graphene surface and differences were observed in the mechanical properties. Simulations revealed that the location of defects as well as their type influence the elastic moduli and constants at room temperature and that their tensile and compressive properties vary with temperature. For both MLGS, and SiC-graphene composites, the properties improved with increase in number of continuous graphene layers.

Depth-Sensing Hardness Measurements to Probe Hardening Behaviour and Dynamic Strain Ageing Effects of Iron during Tensile Pre-Deformation.

This work reports results from quasi-static nanoindentation measurements of iron, in the un-strained state and subjected to 15% tensile pre-straining at room temperature, 125 °C and 300 °C, in order to extract room temperature hardness and elastic modulus as a function of indentation depth. The material is found to exhibit increased disposition for pile-up formation due to the pre-straining, affecting the evaluation of the mechanical properties of the material. Nanoindentation data obtained with and without pre-straining are compared with bulk tensile properties derived from the tensile pre-straining tests at various temperatures. A significant mismatch between the hardness of the material and the tensile test results is observed and attributed to increased pile-up behaviour of the material after pre-straining, as evidenced by atomic force microscopy. The observations can be quantitatively reconciled by an elastic modulus correction applied to the nanoindentation data, and the remaining discrepancies explained by taking into account that strain hardening behaviour and nano-hardness results are closely affected by dynamic strain ageing caused by carbon interstitial impurities, which is clearly manifested at the intermediate temperature of 125 °C.

Microscale fracture of chromia scales

Native protective oxide scales offer resistance against corrosion for high temperature materials, which often work in extreme conditions of varying mechanical and thermal loads. The integrity of such layers is of critical importance, since their damage can lead to significant reduction in material life. Mechanical data such as fracture strain and elastic modulus are required to include oxides in material life estimation models for high temperature materials, but there is lack of such data. Their thickness is in the μm range, which makes mechanical testing for property determination difficult. Here we present a micro-mechanical testing method, based on bending of micro-cantilevers produced by focused ion beam milling, capable of circumventing the limitations of conventional approaches. We apply this method to chromia thermally grown on pure chromium, and measure fracture strains at room and high temperatures (600 °C). The measured fracture strains were found to be higher at room temperature, due to a larger fraction of transgranular fracture. Surprisingly, a large fraction of transgranular fracture was seen even in the presence of stress concentrations at grain boundaries. Removal of the stress concentrations accentuated the propensity for transgranular cracking at room temperature. Realistic values of room temperature elastic modulus were obtained as well. The observed mixed trans- and intergranular cracking points towards the need for dedicated investigations of both oxide grain boundary strength and cleavage resistance of single crystals in order to fully understand the failure mechanisms in thermally grown oxide scales.

Mechanical properties of amorphous silicon carbonitride thin films at elevated temperatures

The mechanical properties of amorphous silicon carbonitride (a-SiC x N y ) films with various nitrogen content (y = 0–40 at.%) were investigated in situ at elevated temperatures up to 650 °C in inert atmosphere. A SiC film was measured also at 700 °C in air. The hardness and elastic modulus were evaluated using instrumented nanoindentation with thermally stable cubic boron nitride Berkovich indenter. Both the sample and the indenter were separately heated during the experiments to temperatures of 300, 500, and 650 °C. Short duration high temperature creep tests (1200 s) of the films were also carried out. The results revealed that the room temperature hardness and elastic modulus deteriorate with the increase of the nitrogen content. Furthermore, the hardness of both the a-SiC and the a-SiCN films with lower nitrogen content at 300 °C drops to approx. 77 % of the corresponding room temperature values, while it reduces to 69 % for the a-SiCN film with 40 at.% of nitrogen. Further increase of temperature is accompanied with minor reduction in hardness except for the a-SiCN film with highest nitrogen content, where the hardness decreases at a much faster rate. Upon heating up to 500 °C, the elastic modulus of the a-SiCN film decreases, while it increases at 650 °C due to the pronounced effect of short-range ordering. The steady-state creep rate increases at elevated temperatures and the a-SiC exhibits slower creep rates compared to the a-SiCN films. The value of the universal constant x = 7 relating the W p/W t and H/E * was established and its applicability was demonstrated. Analysis of the experimental indentation data suggests a theoretical limit of hardness to elastic modulus ratio of 0.143.

Elastic strain energy induced by epsilon martensitic transformation and its contribution to the stacking-fault energy of austenite in Fe–15Mn–xC alloys

The elastic strain energy and its contribution to the stacking-fault energy (SFE) of γ austenite were quantitatively investigated as a function of the C concentration in Fe–15Mn–(zero to 0.37)C (wt.%) alloys. The elastic strain energy was evaluated in both the homogeneous and inhomogeneous states using measured values for molar volume change, strain, and the elastic properties, which are affected by the γ to ε martensitic transformation. Both the molar volume change and the strain decreased with increasing C concentration, primarily due to the reduction in lattice contraction along the c-axis of the ε phase. The addition of C decreased the room-temperature elastic moduli of the alloys with a dual-phase microstructure of γ and ε. The elastic moduli of the ε phase decreased more rapidly with increasing C concentration than did the elastic moduli of the γ phase. Both the homogeneous and inhomogeneous strain energy values exponentially decreased with increasing C concentration. These values were similar because of the insignificant difference in the shear modulus between the γ and ε phases. The contribution of each energy term to the SFE decreased in the following order: chemical, interfacial, elastic strain, and magnetic energies. Whereas the magnetic energy has been considered for calculating the SFE, the elastic strain energy has been neglected until now. Accordingly, we realized that the elastic strain energy should be considered for more accurate SFE calculation, particularly for Fe-high Mn alloys with C concentrations less than 0.4wt.%.

Thermal Variation of Elastic Modulus on Nanocrystalline NiCuZn Ferrites

The nanopowders of Ni0.38Cu0.12Zn0.5Fe2O4 with particle size, 20 nm have been synthesised using Microwave-Hydrothermal method and characterized. Then the ferrite samples were microwave sintered at different temperatures in an air atmosphere and characterized. The magnetic properties were measured at room temperature. The dielectric constant (ɛ), initial permeability (μi) and quality factor (Q) has been measured on sintered samples at 1 MHz. Thermal variation of initial permeability has been measured over temperature range of 300 K–600 K. A detailed study of elastic behaviour of NiCuZn ferrites has been under taken using a composite piezoelectric oscillator method over a temperature of 300 K–600 K. The room temperature elastic moduli is found to be slightly sample dependent and decreases with increasing the temperature, except near the Curie temperature, TC, where a small anomaly is observed. The internal friction at room temperature is also found to be more particle size dependent. The temperature variation of internal friction exhibits a broad maximum around 500 K, just below Curie temperature TC 530 K. The above observations were carried on in the demagnetized state; on the application of a 400 mT magnetic field allowed us to reach the saturated state of the sample at any of the measuring temperature. The anomaly observed in the thermal variation of elastic moduli and internal friction is explained with the help of temperature variation of magneto-crystalline anisotropy constant.

The Role of Point Defects in the Mechanical Behavior of Doped Ceria Probed by Nanoindentation

AbstractThe influence of dopant size and oxygen vacancy concentration on the room temperature elastic modulus and creep rate of ceria doped with Pr4+, Pr3+, Lu3+, and Gd3+, is investigated using a nanoindentation technique. Measurements are conducted with both fast (15 mN s−1) and slow (0.15 mN s−1) loading modes, including a load‐hold stage at 150 mN of 8 s and 30 s, respectively. Based on the data obtained using the fast loading mode, it is found that: 1) the dopant size is a primary determinant of the elastic modulus—the larger dopants (Pr3+ and Gd3+) produce lower unrelaxed moduli which are independent of the oxygen vacancy concentration. 2) The rearrangement of point defects is the major source of room temperature creep observed during load‐hold. Pr3+‐ and Gd3+‐doped ceria display the higher creep rates: due to their large size, they repel oxygen vacancies (VO), thereby promoting the formation of O7–CeCe–VO complexes that are capable of low temperature rearrangement. Lower creep rates are observed for Pr4+‐ and Lu3+‐doped ceria: the former has no vacancies and the latter, immobile vacancies. 3) Nanoindentation is a practical technique for identifying materials with labile point defects, which may indicate useful functionality such as high ionic conductivity, large electrostriction, and inelasticity.

Processing and characterization of porous Ti2AlC with controlled porosity and pore size

In this work, we demonstrate a simple and inexpensive way to fabricate porous Ti2AlC, one of the best studied materials from the MAX phase family, with controlled porosity and pore size. This was achieved by using NaCl as the pore former, which was dissolved after cold pressing but before pressureless sintering at 1400°C. Porous Ti2AlC with samples a volume fraction of porosity ranging from ∼10 to ∼71vol.% and different pore size ranges, i.e. 42–83, 77–276 and 167–545μm, were successfully fabricated. Fabricated samples were systematically characterized to determine their phase composition, morphology and porosity. Room temperature elastic moduli, compressive strength and thermal conductivity were determined as a function of porosity and/or pore size. For comparison, several samples pressureless-sintered without NaCl pore former, or fabricated by spark plasma sintering, were also characterized. The effects of porosity and/or pore size on the room temperature elastic moduli, compressive strength and thermal conductivity of porous Ti2AlC are reported and discussed in this work. It follows that porosity can be a useful microstructural parameter to tune mechanical and thermal properties of Ti2AlC.

Room temperature elastic moduli and Vickers hardness of hot-pressed LLZO cubic garnet

Cubic garnet Li6.24La3Zr2Al0.24O11.98 (LLZO) is a candidate material for use as an electrolyte in Li–Air and Li–S batteries. The use of LLZO in practical devices will require LLZO to have good mechanical integrity in terms of scratch resistance (hardness) and an adequate stiffness (elastic modulus). In this paper, the powders were fabricated by powder processing of cast ingots. All specimens were then densified via hot pressing. The room temperature elastic moduli (Young’s modulus, shear modulus, bulk modulus, and Poisson’s ratio) and hardness were measured by resonant ultrasound spectroscopy, and Vickers indentation, respectively. For volume fraction porosity, P, the Young’s modulus was 149.8 ± 0.4 GPa (P = 0.03) and 132.6 ± 0.2 GPa (P = 0.06). The mean Vickers hardness was 6.3 ± 0.3 GPa for P = 0.03 and 5.2 ± 0.4 for P = 0.06.

Mechanical properties of polycrystalline RuSr 2GdCu 2O 8 superconductor

The main objective of this paper is to report the room temperature hardness and elastic modulus of the RuSr 2GdCu 2O 8 superconductor phase by instrumented indentation. Polycrystalline samples were produced by a solid state reaction technique. The samples were also characterized by scanning electron microscopy, X-ray diffraction and electrical resistivity measurements. The influence of porosity on the mechanical properties was avoided by considering only those indentations inside the grains. The hardness and elastic modulus were 8.6 GPa and 145 GPa, respectively. These values are comparable with those of Y-123. The indentation fracture toughness evaluated after conventional Vickers indentation was 1.9 MPa m 1/2.

Relaxation phenomena in tellurite glasses

The new semiconducting noncrystalline solid “tellurite glasses” of the form 0.7 TeO2–(0.3−x)V2O5–xAnOm have been prepared in bulk form with different compositions where AnOm is CeO2 or ZnO and x=0.03,0.05,0.07,0.10 mol %. Longitudinal ultrasonic attenuation in these glasses has been measured at frequencies of 2, 4, 6, and 8 MHz and in the temperature range of 100–300 K. The results showed the presence of a very well defined peak which shifts to higher temperature with increasing frequency, suggesting a kind of relaxation process. The acoustic activation energy, as well as the relaxation frequency, has been calculated and correlated with the relaxation strength for each composition. Correlations between the present low temperature of ultrasonic attenuation and the previous room temperature elastic moduli have been achieved for both glass series.

A comparison of results obtained using different methods to assess the elastic properties of ceramic materials exemplified for Ba0.5Sr0.5Co0.8Fe0.2O3−δ

Different mechanical testing methods have been used to assess the elastic behavior of the mixed ion electron conducting perovskite Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF). Although the main aim is the comparison of the testing techniques for ceramic material in general, experiments have been performed at RT and up to 900 °C to illustrate the capabilities of the utilized methods for a perovskite with a stiffness anomaly. BSCF specimens in disc shape and tubular geometry provided by different suppliers were tested in biaxial bending by ring-on-ring testing and under uniaxial stress in O-ring and under compression loading. The elastic modulus was determined as a function of temperature up to 900 °C. In addition, the room temperature elastic modulus was measured using depth-sensitive indentation.

Evaluation of elastic properties of reduced NiO-8YSZ anode-supported bi-layer SOFC structures at elevated temperatures in ambient air and reducing environments

Elastic properties of Ni-8YSZ anode-supported bi-layer SOFC structures were studied at elevated temperatures up to 1,000 °C in both ambient air and H2 environments. The anode samples with desired porosity and microstructure were fabricated by reducing a NiO-8YSZ anode precursor structure in a gas mixture of 5% H2–95% Ar at 800 °C for selected time periods up to 8 h. The development of the essential porous microstructure in forming the Ni-8YSZ cermet phase was analyzed with SEM. It was observed that the room temperature elastic moduli and hardness of the anode samples decrease significantly with increasing fraction of reduced NiO. Since the elastic properties of fully dense Ni, NiO, and 8YSZ are comparable to each other, the decrease in the magnitude in elastic moduli and hardness is evidently due to the colossal increase in porosity in the reduced Ni-8YSZ cermet anodes because of the reduction of NiO to Ni. At elevated temperatures, the Ni-8YSZ anodes show a complex profile of Young’s modulus as a function of temperature, which is significantly different from the unreduced NiO-8YSZ samples. When studied in ambient air, the Young’s modulus of the Ni-8YSZ samples decrease slowly up to ~250 °C, then more rapidly from 250 to 550 °C, and finally it increases monotonically with the increase in temperature. However, in reducing environment, the Young’s moduli values decrease continuously throughout the temperature range. Two sets of samples of different thicknesses were studied simultaneously to highlight the effects of the sample thickness on the elastic properties of the anodes.

Mechanical Characterization of KMPR by Nano‐Indentation for MEMS Applications

Abstract: The elastic modulus and hardness of a novel negative photoresist, KMPR, under different heat treatment temperatures, have been characterized in this work using a combination of nanoindentation, uniaxial tension and vibration tests. There are two major conclusions. First, the material exhibits strong anisotropy. The apparent modulus obtained by the indentation method (6.5–7.5 GPa) is higher than that characterized by the uniaxial tensile test (1.07 GPa). The modulus issue is further validated by the subsequent vibration test data. Second, the apparent modulus and the apparent hardness vary with heat treatment temperatures. The room temperature elastic modulus decreased with an increase of the processing temperature but the apparent hardness essentially exhibited an opposite trend. It is suggested that this unusual result was caused by the pile‐up effect during the indentation process.

Mechanical and thermal behavior of clay/epoxy nanocomposites

Clay/epoxy nanocomposites with concentrations of 1–10 wt.% of clay particles were prepared by shear mixing. The mechanical and viscoelastic behavior of nanocomposites was investigated using a servohydraulic testing machine and a dynamic mechanical analyzer, respectively. It was found that the addition of clay particles improved both the elastic modulus and storage modulus of pure epoxy significantly and the higher the clay content, the higher the modulus of the nanocomposite. The elastic modulus of the nanocomposites was also measured at elevated temperatures and was found to decrease gradually with temperature followed by a sudden drop at T g, which showed a monotonic drop with increasing clay content. However, the effect of thermal exposure above T g was found not to affect their room temperature elastic modulus. The thermal expansion coefficient (CTE) of both pure epoxy and nanocomposites was measured using a thermomechanical analyzer and it was found that the incorporation of clay particles reduced the CTE of pure epoxy.

Experimental and numerical study of the room temperature elastic modulus of model materials with partly bonded matrix/particles interfaces

This work is devoted to the use of model materials with simplified microstructures in order to characterise the elastic behaviour of real refractory material. Two-phase model materials with vitreous matrix and spherical dense alumina inclusions were manufactured. The thermal expansion mismatch between the two selected constituent phases (Δ α ≠ 0) induces interfacial matrix/inclusions decohesions. Because analytical models are not suited to describe such materials we have develop a numerical approach of the problem using the finite element method (ABAQUS package). The location and orientation of the decohesive zone are studied to show the dependence of the room temperature Young’s modulus on the state of the matrix/inclusions interface. As a first approach, virtual models containing a single inclusion were studied by numerical simulation. Then, to be more close to the samples tested in experiments, virtual multi-inclusions models were considered. The geometric modelling of these models required the use of original software, developed in C++ language in the laboratory, which allows the automatic geometry generation.

Large amplitude light-induced motion in high elastic modulus polymer actuators

Well-defined gradients in molecular alignment have been used as tools to generate large amplitude, light-induced deformations in stiff polymer networks. These systems are reversible, monolithic and based on a simple one-step self-assembly process. To fabricate the actuators, diacrylate dopants containing azobenzene moieties were blended with liquid crystalline diacrylate hosts and photopolymerized in a twisted configuration. The resulting twisted networks were heavily crosslinked with room temperature elastic moduli on the order of 1 GPa. Regardless of the temperature with respect to the glass transitions, subsequent exposure to UV radiation induced anisotropic expansion/contraction, and simple variations in geometry were used to generate uniaxial bending or helical coiling deformation modes. Because mechanical energy is directly related to elastic modulus, these systems are expected to provide significantly greater work output than contemporary polymer actuator materials.