Intermediate Strain Levels Research Articles

Selective electron beam additive manufacturing of a nanoparticle-strengthened medium-entropy alloy for cryogenic applications

A strong, ductile medium-entropy alloy, MEA, (CoCrNi)94Al3Ti3 with few defects was fabricated using the selective electron beam additive manufacturing technique. Due to preheating the substrate at 1173 K, the as-printed MEA showed coherent L12 nanoparticles (dia.∼112 nm, volume fractioñ8.9 %) in 68 μm grains with a dual {100}<011> + {100}<001> texture. The as-built alloy exhibited a yield strength (YS) of 612 MPa, an ultimate tensile strength (UTS) of 1020 MPa, and an elongation to failure (ε) of 37 % at 298K. These values increased when testing was at 77 K, i.e. YS of 811 MPa, UTS of 1339 MPa, and an ε of 39 %. After tensile failure, the LAGBs and GND densities sharply increased at both temperatures to accommodate strain gradient along with <111> fiber texture. The lack of annealing twin boundaries led to a relatively low strain hardening rate (SHR) of 2500 MPa at 298 K and 3890 MPa at 77 K (at 5 % strain) as compared to values of thermo-mechanically processed (CoCrNi)94Al3Ti3. The SHR curves exhibited three distinct stages, where an abrupt upturn at an intermediate strain level can be attributed to the occurrence of DTs and SFs at 77 K, and the appearance of SFs at 298 K.

Deformation twinning and the role of stacking fault energy during cryogenic testing of Ni-based superalloy 625

Ni-based superalloys play a crucial role in various high-temperature applications, where their exceptional mechanical properties and resistance to corrosion are highly desirable. However, their response to low temperatures, especially concerning strain hardening, microstructural evolution, and deformation mechanisms, requires further scrutiny. In this study, we investigate the influence of temperature on the stacking fault energy (SFE) and its implications on deformation twinning in Alloy 625. Uniaxial tensile tests are performed at 298 K, 173 K and 77 K. The study reveals a notable increase in strain hardening at intermediate strain levels, suggesting the activation of a secondary deformation mechanism. To gain deeper insights, crystal plasticity-based simulations using the DAMASK framework are employed, complementing the experimental outcomes. Deformation twins are consistently observed at all temperatures, albeit with a small volume fraction and thickness. The critical strain for twinning decreased with decreasing temperature. Based on the numerous literature studies, experimental and computational observations, the SFE of the material is estimated to be constant over the studied temperature range.

Inference of grain boundary sliding and co-rotation of α/β phases during superplastic deformation of Zr-2.5%Nb at 700 °C through EBSD measurements

Present study explains the micromechanics of superplastic deformation of Zr-2.5 wt.%Nb alloy using EBSD analysis. The alloy when deformed in tension at 700 °C and 10−3 s−1 exhibited superplastic flow with total elongation of 650%. Different samples were deformed to intermediate strain levels for characterizing microstructure evolution and subsequently, establishing the underlying micro-mechanisms. EBSD measurements showed that local misorientations within grains did not develop during the superplastic flow. Texture weakening in α and β-Zr phases was observed and it has been shown that the resultant texture is not due to slip-based deformation. Misorientation angle distribution plots revealed a peak at 45° that corresponded to the interface angle between the Burgers OR related α and β phases. The fraction of these interfaces remained unaffected during the superplastic flow. It is concluded that the superplastic flow in Zr-2.5Nb at 700 °C is accommodated by Rachinger grain boundary sliding and co-rotation of α/β grains.

Interpretation of small and intermediate strain characteristics of Hostun sand for various stress states

Small and intermediate strain properties of soils are key parameters to assess ground motion characteristics during an earthquake and other dynamic events. These properties are affected by various parameters. Among them, the effect of anisotropic stress state on the soil specimen is interest of investigation in this paper. Experiments were carried out using the modified resonant column device at Ruhr Universität Bochum on dry Hostun sand with relative density of 35%-95%. The results show the significant effect of density and anisotropic stress states on the small strain properties, Gmax, of Hostun sand. At intermediate strain level, the results show the significant effect of anisotropic stress state on the shear stiffness and damping ratio. In addition, it is concluded that the effect of compression stress component on the small and intermediate strain properties is more significant than the effect of the deviatoric stress component. At the end, the paper shows the successful application of stress-based approach to describe G(γ) and η(γ) in Hostun sand subjected to the isotropic and anisotropic stress states.

A Practical Approach for the Estimation of Strength and Resilient Properties of Cementitious Materials

Cementitious stabilization of granular soils has been proven to be a cost-saving option for the use of materials with marginal quality in the construction and rehabilitation of pavement structures. The orthogonal load distribution capacity of the Cement-Stabilized Materials (CSM) is typically characterized by Unconfined Compressive Strength (UCS), Indirect Tensile Strength (IDT), and Resilient Modulus (Mr) tests in the laboratory. The aforementioned parameters and properties are integral components of the analysis and design of pavements with stabilized layers. Time and budget constraints make it impractical for many state agencies to complete the full laboratory characterization protocols to determine all the design input parameters. Therefore, in many cases, the design engineers opt out of laboratory testing and primarily rely on past experience and engineering judgments to assign design input parameters. Such an approach compromises the reliability of the pavement life predictions, and can potentially incur unforeseen costs to the traveling public. This study was designed to bridge this gap by developing a series of statistically robust relationships between the laboratory achived data to provide an estimate of the design input parameters. To accomplish this objective, 570 stabilized cylindrical specimens were prepared and subjected to UCS, IDT, and submaximal modulus tests at three strength ratio levels. Subsequently, the relationships between the IDT, UCS, and resilient modulus at small-strain and intermediate strain levels were developed in this study. Such relationships can serve as a valuable means for the estimation of the tensile and compressive strength of the CSM for pavement design.

Mechanical behavior of airbag fabrics under quasi-static loading: an experimental evaluation of macro- and meso-scopic properties

In this paper the current generation of 350 dtex airbag coated and uncoated fabrics are examined experimentally under a multitude of simple and complex deformations. The geometric dimensions of the fabric architecture and the load–elongation behavior of the yarn constituents are studied. Furthermore, deformational shear behavior of airbag fabrics, which have not previously been investigated, are examined here. The stress–strain behavior of the yarn as well as the fabrics with and without coating are found to be highly nonlinear. Under uniaxial loading, nonlinearities of the fabric occur at lower strains due to crimp of the fabric, whereas under biaxial loading, the nonlinearity occurs at low and intermediate strain levels resulting from a combination of the inherent nonlinear material response of the yarn and geometric changes in the fabric structure. The data generated not only provide the basis for structural analysis of the airbag, but can also be used to develop more sophisticated definitions of the constitutive behavior of the fabric.

Study of Dislocation Substructures in High-Mn Steels by Electron Channeling Contrast Imaging

We have investigated the formation of dislocation substructures in high-Mn steels by electron channeling contrast imaging in the SEM. The coupling of electron channeling contrast imaging (ECCI) with electron backscatter diffraction (EBSD) provides an efficient and fast approach to characterize dislocation substructures under controlled diffraction conditions with enhanced contrast. The dislocation substructure of high-Mn steels at intermediate strain levels is characterized by cells and cell blocks with strong crystallographic orientation dependence. We observe a significant effect of strain path on dislocation patterning. Microband formation is enabled under shearing conditions. We explain this effect on terms of Schmid’s law.

Constrained and free uniaxial stretching induced crystallization of polyethylene film: A comparative study

Constrained and free uniaxial stretching induced crystallization of high density polyethylene (HDPE) film were studied with in situ synchrotron radiation small and wide-angle X-ray scattering (SR-SAXS, SR-WAXS). According to the initial structure after stretching, as well as the structural evolution, three characteristic regions can be defined in strain space for both stretching modes, while the strain boundaries between different regions are different for the two stretching modes. Region I is located at low strain levels where completely twisted lamellae are induced. Region II is in an intermediate strain level, which induces the formation of partially twisted lamellae with relatively large lateral size (defined as quasi-micro-fibrils). Region III with large strain produces flat lamellae with small lateral dimensions (micro-fibrils). During the crystallization process, a new type of lamellar stack with smaller long period forms in regions II and III while no new types of lamellae appear in region I for both stretching modes. Along the strain space, the scenario of constrained stretching delays the transition from region I to region II, as well from region II to region III. Also, the draw ratio windows of region I and region II are enlarged by constrained stretching, which is more favorable for film processing.

비틂전단시험에 의한 서해안 새만금 모래의 동적특성 연구

The dynamic characteristics of west coast sand were investigated in order to evaluate the design properties of the offshore wind turbine foundations to be constructed in the West Sea. Torsional shear tests were performed at different confining pressures and densities on specimens constituted by the dry fluviation method. The strain-dependent shear modulus and damping curves were obtained, together with modulus degradation curves. The results show that the confining pressure is more influential on the dynamic characteristics of the sand than the density. It was also found that the dynamic curves from this study were similar to those proposed by others. The modulus degradation ratio G/G 1st varies slightly at a small strain level, but increases significantly once beyond the intermediate strain level.

Compression and Deformation of Cylindrical Rubber Blocks

In the present study, compression and deformation behavior of vulcanized cylindrical rubber blocks has been examined using imaging techniques. Quantitative measurements of bulge radius and the associated lateral profile of the uniaxially loaded rubber blocks have been carried out experimentally using a newly developed imaging tool. The maximum bulge radius obtained using this method has shown good agreement with the established models. A significant increase in contact area has been observed in the images under large compressive strains. Also, at an intermediate strain level, a unique low intensity band occurred in the image between the outer ring and the center of compressed blocks. The nonlinear characteristics are obvious from the experiments conducted on the bonded cylinders using the developed imaging tool. It is evident from images that the deformed lateral profiles at larger compressive strain does not have parabolic shape and appeared to be more flat. Moreover the reliability of the testing tool has been evaluated and a data measurement technique has been proposed to characterize the behavior of rubber blocks under large compressive strains.

입도조정된 조립재료의 탄성계수에 대한 연구

In the element test for coarse granular materials, the grain size distributions of the materials are often adjusted, in case the grain size of coarse material in the field is larger than the available maximum grain size of the laboratory test equipment. In this study, we carried out the large cyclic triaxial test to evaluate the effect of the grain size distribution adjustment on Young`s modulus in small to intermediate strain level. The test results showed that the coarse granular materials with the adjusted grain size distribution underestimated Young`s modulus of the original materials. The difference of Young`s modulus was larger in small strain level than in intermediate strain level.

Deformation mechanisms in high-manganese steels showing twinning-induced plasticity: Fine-grained material and single crystals at ambient and cryogenic temperatures

By conducting monotonic tension tests in different temperature regimes, including temperature changes at intermediate strain levels, the hardening behavior of commercial steel showing twinning-induced plasticity was investigated. To study the effect of grain size, both single crystals and fine-grained material were employed. Unexpectedly, the microstructural evolution at liquid nitrogen temperature and at 163 K was very similar to that observed at room temperature despite the differences in the stacking fault energies at these temperatures.

Experimental Evidences of the Effect of Fibres in Reinforcing a Sandy Gravel

Studies regarding fibre-reinforcement are restricted to clays, silty and sandy soils. No information is available on gravels. It is worth checking the effect of randomly oriented discrete fibres also on such soils to see if they can be beneficial and to get a better insight into the grain to soil interaction mechanism. In this paper, the effect of a small amount of fibres having high aspect ratio on a sandy gravel was analysed by means of tests carried out in a large triaxial apparatus. Specimens of both natural and fibre-reinforced sandy gravel were prepared by wet tamping at different relative densities, and were tested along monotonic and cyclic stress paths. The results show that the addition of a small amount of fibres causes a slight increase in peak strength and a larger increase in ultimate strength at small confining stress, with an overall more ductile behaviour. The cyclic tests at small confining stress and intermediate strain levels show that, for the lowest applied strain (of the order of 10−2%), the stiffness was larger for the reinforced specimens, with a much sharper decrease at larger strains and final values similar for the reinforced and non-reinforced materials.

Use of calibration chamber as a large triaxial apparatus

A segment of a gravel column, 1 m high and 0.53 m in diameter, was modelled in a calibration chamber. The reconstituted sample was consolidated at a given confining pressure and then subjected to axial load exerted by the upper and lower membranes. Volumetric changes in both membranes and in internal chamber were measured. Up to 2% vertical strain was reached and internal friction angle was evaluated. Secant modulus of deformation was determined at considerable strains and at intermediate strain level in the unloading–reloading cycle. For the latter several times higher modulus was found.

Application of Nonlinear Superposition to Creep and Relaxation of Commercial Die-Casting Aluminum Alloys

Die-cast aluminum alloys are heavily used in small engines, where they are subjected to long-term stresses at elevated temperatures. The resulting time-dependent material responses can result in inefficient engine operation and failure. A method to analytically determine the stress relaxation response directly from creep tests and to accurately interpolate between experimental time-history curves would be of great value. Constant strain, stress relaxation tests and constant load, creep tests were conducted on aluminum die-casting alloys: B-390, eutectic Al–Si and a 17% Si–Al alloy. A nonlinear superposition integral was used to (i) interpolate between empirical primary inelastic creep-strain and stress-relaxation time histories and (ii) to determine the stress relaxation response from corresponding creep data. Using isochronal stress-strain curves, prediction of the creep response at an intermediate stress level from empirical creep curves at higher and lower stresses resulted in a correlation (R) of 0.98. Similarly for relaxation, correlations of 0.98 were obtained for the prediction of an intermediate strain level curve from higher and lower empirical relaxation curves. The theoretical prediction of stress relaxation from empirical creep curves fell within 10% of experimental data.

Model for nonlinear wave propagation derived from rock hysteresis measurements

We develop a method for modeling nonlinear wave propagation in rock at intermediate strain levels, that is, strain levels great enough that nonlinearity cannot be neglected but low enough that the rock does not incur macroscopic damage. The constitutive model is formulated using a singular‐kernel endochronic formalism which satisfies a number of observational constraints, including producing a power law dependence of attenuation (Q−1) on strain amplitude. One free parameter represents cubic anharmonicity, and we set it to agree with laboratory observations of harmonic distortion. Another free parameter controls the amount of hysteresis; it is set to approximate laboratory stress‐strain curves. The resulting phenomenological model provides a convenient means to parameterize laboratory observations in a form suitable for efficient wave propagation calculations. We solve one‐dimensional wave propagation problems for this constitutive model using both finite difference and pseudospectral methods. Quasi‐harmonic wave propagation in the Berea sandstone model shows several departures from results obtained with nonlinear elasticity: (1) more rapid decay with distance of the fundamental frequency component due to nonlinear, amplitude‐dependent attenuation; (2) enhanced excitation of the third‐order harmonic, in agreement with laboratory observations, and saturation, with propagation distance, of the harmonics. This behavior reflects competing effects of harmonic amplitude growth via nonlinear energy transfer from the source frequency and amplitude‐dependent energy dissipation due to hysteresis. We also find that a two‐frequency source function generates harmonics with frequencies which can be expressed as linear combinations of integer multiples of the source frequencies, in agreement with published laboratory results.

Similitude for Shaking Table Tests on Soil-Structure-Fluid Model in 1g Gravitational Field

A similitude is derived for the shaking table tests on saturated soil-structure-fluid model in 1 g gravitational field. The main tool used for deriving the similitude is the basic equations which govern the equilibrium and the mass balance of soil skeleton, pore water, pile and sheet pile structures, and external waters such as sea. In addition to the basic equations, an assumption is made upon the constitutive law of soil; i. e. the stress-strain relation is determined irrespective of the confining pressures if appropriate scaling factors are introduced for the stress and the strain for taking the effect of the confining pressures into account. Applicability of this assumption is examined by using the presently available data under the confining pressures ranging from 0.05 to 1 kgf/cm2 (from 5 to 98 kN/m2) and 0.05 to 4 kgf/cm2 (from 5 to 392 kN/m2). The results indicate that the assumption is applicable within the intermediate strain levels; i. e. the strain levels which are lower than the strains at failure. In consequence, the similitude derived in the present study is applicable to the model tests in which the major concern is directed toward the deformation, rather than the ultimate state of stability, of the soil-structure-fluid system.

Large wire drawing plastic deformation in aluminum and its dilute alloys

The microstructures and hardening characteristics of Al and Al with dilute additions of soluble and insoluble impurities were compared during wire drawing at room temperature to true strains (e w ) of 4.95. Three stages of microstructure change are observed: formation of a dislocation cell structure; cell boundary sharpening and cell size refinement; dynamic recrystallization. A minimum effective cell size is reached at an intermediate strain level corresponding approximately to the onset of dynamic recrystallization. The amounts and types of impurities at levels less than 1 pct have a great effect on the details of the microstructural changes as well as the hardening characteristics. 99.98 pct pure Al alternately saturates and hardens frome w = 0 to 4.95. Al-0.6 Fe (insoluble) work softens neare w = 3.5. Al-0.2 Mg (soluble) and EC Al (with 0.15 pct soluble and insoluble impurities) both work harden at a diminishing rate toe w ≃1.25 then enter a linear hardening stage which persists toe w ≃5. A linear relation between yield strength and inverse cell size is established for EC Al and Al-0.2 Mg in the cell refinement strain range; however, the Petch slope is much less than that of similar Al alloys subjected to elevated temperature dynamic or static recovery. Al-0.6 Fe does not exhibit a consistent linear relation between yield strength and inverse cell size. These differences can be attributed to the degree of recovery and the interrelation between cell size, cell boundary character and total dislocation density.