Yield Stress Σ0 Research Articles

Effect of Tempering on Phase Transformations in Low-Alloy Steel with 1.6%Si

Low temperature tempering of a 0.53%C–1.6%Si–0.9%Mn–0.76%Cr–0.14%V–0.05%Nb steel provides combination of high yield stress σ0.2=1890 MPa with elongation-to-failure δ=6% and Charpy V-notch (CVN) impact energy of 11 J/cm2 due to precipitation of non-stoichiometric η-carbide Fe2C. Silicon suppresses precipitation of para-equilibrium cementite both from martensite and retained austenite. Orthoequilibrium cementite precipitate upon tempering at 500°С providing combination of σ0.2=1360 MPa with δ=9% and CVN impact energy of 18 J/cm2.

Effect of combined thermomechanical treatment on structure, mechanical properties, electrochemical behavior and functional corrosion fatigue of biodegradable Fe-30Mn-5Si alloy

In present study, the combined thermomechanical treatment (TMT), including the radial-shear rolling (RSR) at 900 °C followed by longitudinal rolling (RSR+LR) at 700 °C, was applied to biodegradable Fe-30Mn-5Si (wt%) alloy. The effect of these TMTs on the microstructure, phase composition, mechanical properties (ultimate tensile strength UTS, apparent yield stress σ0.2, relative elongation to failure δ, Young's modulus E), electrochemical behavior and functional corrosion-fatigue behavior in Hanks’ solution were studied. It was found that RSR leads to the formation of a statically recrystallized γ-austenite structure with an average grain size of 10±3 and 20±3 µm in the peripheral and central zones, respectively. The RSR+LR results in a mixture of dynamically recrystallized and dynamically polygonized structures with the average grain size of 5±1 µm. Moreover, RSR and RSR+LR lead to the formation of a single-phase FCC γ-austenite state compared to reference heat treatment (RHT), where microstructure is characterized by a two-phase state of FCC γ-austenite and HCP ε-martensite with an average grain size of 200–300 µm. Based on static mechanical tensile tests to failure, it was established that RSR and RSR+LR lead to a significant increase of UTS up to 770±21 and 935±55 MPa, σ0.2 up to 300±38 and 490±43 MPa, and δ up to 28±2 and 19±10 %, while maintaining acceptable of E value about 165±29 and 150±8 GPa, respectively as compared to 460±41 MPa, 210±91 MPa, 11±3 %, and 140±14 GPa after RHT. The electrochemical studies showed that single-phase structure (FCC γ-austenite) formed after RSR and RSR+LR leads to the non-critical biodegradation rate lowering as compared to the two-phase state (γ-austenite and ε-martensite) after RHT. Besides RSR and RSR+LR lead to significant improvement of functional corrosion-fatigue life in Hanks’ solution.

Synthetic oil gels with organoclays in the formulation of magnetorheological fluids

Magnetorheological fluids (MRF) are smart composite materials that, under an external magnetic field, show a reversible solid-liquid transition in less than 10 ms. This study aimed to evaluate which organoclays would jellify a synthetic oil for the formulation of MRF. Three dispersant additives for carbonyl iron powder were evaluated. Fifteen different gelling additives from four clay families, bentonites, hectorites, montmorillonites, and mixed mineral thixotropes (MMT), were dispersed in oil only, keeping the same concentration, without iron particles. The gels were then tested through amplitude and frequency sweeps in oscillatory rheometry to evaluate their viscoelastic behavior. The thixotropy of the gels was measured through the “three-interval” test in a rheometer. After selecting the best gelling additive to prepare the MRF, three dispersing additives had their rheology evaluated to determine the best magnetorheological effect and redispersibility after 1 year of sample preparation. In the linear viscoelastic region, all MMT clays resulted in a weak viscoelastic gel (G′∼100 to 300 Pa and G″∼30 to 50 Pa). Some of the bentonite clays jellified, and others did not. The best organoclays were montmorillonites and hectorites, which formed consistent viscoelastic gels (G′∼1 to 5 kPa and G″∼70 to 250 Pa). The best organoclay presented a yield stress σ0 = (42 ± 3) Pa, a storage modulus G′ = (2690 ± 201) Pa, and a cohesive energy density (CED) = 98 mJ/m3, and it was selected to explore the rheology of MRF with three dispersant additives: octan-1-ol, octan-1-amine, and L-α-Phosphatidylcholine. All the MRFs were prepared using carbonyl iron powder HS (BASF SE) in oil gels and with the same organoclay. All three dispersant additives showed a thixotropic recovery above 100% in the three-interval test. Regarding the redispersibility after 1 year, the MRF formulations with octan-1-amine and lecithin were reproved, as they reached normal force peaks of 19 and 24 N, while the work was 28 and 415 mJ, respectively. The best MRF was formulated with octan-1-ol, and resulted in a normal force of 0.33 N and 3.4 mJ at 35 mm of vane penetration. Therefore, we conclude that the MRF with octan-1-ol and montmorillonite #6 showed a better balance between thixotropy, MR effect, and, above all, good redispersibility.

Influence of Current Density upon Hydrogenation on the Shape Memory Effect of Binary TiNi Alloy Single Crystals

Some results concerning the hydrogen effect at electrolytic saturation at a current density of j = 1500 and 3500 A/m2 for 3 h at room temperature on the temperature dependence of the yield stress σ0.1(T) and the shape memory effect (SME) under tension of the [011]-oriented Ti-50.55%Ni (at.%) alloy single crystals are presented. It was shown that hydrogen is in a solid solution and forms particles of titanium hydride TiH2 after hydrogenation at j = 1500 and 3500 A/m2, respectively. Both hydrogen in the solid solution and TiH2 particles led to a decrease in the Ms temperature of the onset of the forward martensitic transformation (MT) upon cooling and the Md temperature (Md is the temperature at which the stresses for the onset of the stress-induced MT are equal to the stresses for the onset of plastic flow of the high-temperature B2 phase), and increased the yield stress σ0.1 of the B2 phase at the Md temperature compared to hydrogen-free crystals. It was found that the SME under stress depends on the tensile stress level and current density. The maximum SME εSME = 10 ± 0.2% at σex = 200 MPa and εSME = 10.5 ± 0.2% at σex = 300 MPa was observed in the hydrogen-free crystals and after hydrogenation at j = 1500 A/m2, respectively, which exceeded the theoretical value of lattice deformation ε0 = 8.95% for the B2-B19′ MT in [011] orientation under tension. At j = 1500 A/m2, the physical reason for the excess of the SME of the theoretical ε0 value was due to the increase in the plasticity of B19′ martensite upon hydrogenation. At j = 3500 A/m2, εSME = 8.0 ± 0.2%, and it was less than ε0 = 8.95% for B2-B19′ MT in [011] orientation under tension. The decrease in SME after hydrogenation at j = 3500 A/m2 was associated with the interaction of two types of B19′-martensite: oriented under stress and non-oriented, formed near TiH2 particles. It was shown that the redistribution of hydrogen in the bulk of the crystals during long-term holding for 168 h at 263 K after hydrogenation at j = 1500 A/m2 increases the SME relative to crystals without long-term holding: 3.5 times at 50 MPa and 1.8 times at 100–150 MPa. After long-term holding, εSME = 9.5 ± 0.2% at 150 MPa, which exceeds the theoretical value ε0 = 8.95% for B2-B19′ MT in [011] orientation under tension.

Comparative Study of the Relationship between Microstructure and Mechanical Properties of Aluminum Alloy 5056 Fabricated by Additive Manufacturing and Rolling Techniques.

In recent years, additive manufacturing of products made from 5000 series alloys has grown in popularity for marine and automotive applications. At the same time, little research has been aimed at determining the permissible load ranges and areas of application, especially in comparison with materials obtained by traditional methods. In this work, we compared the mechanical properties of aluminum alloy 5056 produced by wire-arc additive technology and rolling. Structural analysis of the material was carried out using EBSD and EDX. Tensile tests under quasi-static loading and impact toughness tests under impact loading were also carried out. SEM was used to examine the fracture surface of the materials during these tests. The mechanical properties of the materials under quasi-static loading conditions exhibit a striking similarity. Specifically, the yield stress σ0.2 was measured at 128 MPa for the industrially manufactured AA5056_IM and 111 MPa for the AA5056_AM. In contrast, impact toughness tests showed that AA5056_AM KCVfull was 190 kJ/m2, half that of AA5056_IM KCVfull, which was 395 kJ/m2.

The Temperature Dependences of Mechanical Properties, Deformation Hardening, and Fracture of FeMnNiCoCr Heterophase Alloy

It is established that the temperature dependence of the mechanical properties and deformation behavior of a heterophase multicomponent Cantor alloy (FeMnNiCoCr) and the mechanisms of its fracture under uniaxial static tension in the temperature range 77–300 K are determined by the mechanism of formation and distribution of dispersed phases in it. The heterogeneous formation of chromium-enriched σ‑phases and phases with an fcc crystal lattice,mainly at grain boundaries in the course of annealing of homogenized samples (when particles are inhomogeneously distributed over the structure) and at deformation defects in the course of annealing of preliminarily strained samples (when particles are distributed uniformly over the structure), takes place in the Cantor alloy as a result of annealing. It is found that the grain-boundary phases slightly affect the temperature dependence of yield stress σ0.2, the deformation behavior of the heterophase alloy and its mechanism, but contribute to a decrease in the plasticity and to the formation of brittle secondary cracks on fracture surfaces under low-temperature deformation. The complex effect of the dispersion and the grain boundary hardenings in samples with a uniform distribution of particles that are formed in the course of aging of pre-strained samples leads to a substantial increase in the strength properties of the Cantor alloy in the entire temperature range while maintaining high plasticity and a strong temperature dependence of σ0.2.

DSM with different strain hardening exponent for stainless steel lipped channel columns

This paper reports a comprehensive numerical investigation into the cross-section behavior and resistances of stainless steel lipped channel columns under axis compression. To obtain the influence of strain hardening index n and nominal yield stress σ0.2 on the design DSM compression resistance for a stainless steel lipped channel cross section, numerical parametric study has been firstly performed. It indicates that the strain hardening exponent n has a strong effect on the DSM strength prediction of stainless steel lipped channel columns, but nominal yield stress σ0.2 has a limited effect on the DSM curve due to it already included in the DSM. A DSM model was proposed that could take into account the strain hardening exponent n and different buckling modes, and a range of numerical parametric study was conducted. Based on the proposed DSM model, a set of DSM equations was proposed for stainless steel lipped channel column. The strength predictions formula is suitable for different types of stainless steel materials, and only the corresponding strain hardening coefficient n needs to be selected according to the stainless steel material. The comparison between the test results and design predictions indicates that the proposed equations are able to capture the nominal axial strength of the stainless steel lipped channel column

Effect of Cold Deformation and Annealing on the Microstructure and Tensile Properties of a HfNbTaTiZr Refractory High Entropy Alloy

The microstructure and tensile properties of HfNbTaTiZr after cold working and annealing were investigated. Cold work was introduced by axial compression followed by rolling resulting in a total thickness reduction of 89 pct without any evidence of cracking. The cold-worked material retained a single-phase microstructure and had a room temperature tensile yield stress σ0.2 = 1438 MPa, peak true stress σp = 1495 MPa, and true fracture strain ef = 5 pct. Annealing at 800 °C for up to 256 hours resulted in the precipitation of Nb and Ta rich particles with a BCC crystal structure inside a Hf-and-Zr-enriched BCC matrix. The second phase particles nucleated heterogeneously inside deformation bands and slip lines and coarsened during annealing. Analysis of the coarsening behavior suggested that kinetics were controlled by the diffusion of Nb and Ta. In the two-phase material, σ0.2 and σp decreased from 1159 to 1071 MPa and from 1174 to 1074 MPa, respectively, with an increase in particle diameter from 0.18 to 0.72 μm, while ef remained between 5 and 8 pct. Full recrystallization and normal grain growth, with the activation energy of 238 kJ/mol and activation volume of 5.3 to 9.6 m3/mol, occurred during annealing above 1000 °C. After heat treatment at this temperature, the alloy was characterized by a single-phase BCC structure with σ0.2 = 1110 to 1115 MPa, σp = 1160 to 1195 MPa, and ef = 12 to 19 pct with the maximum values attained after annealing for 1 hour.

Evolution of the structure and mechanical properties of sheets of the Al–4.7Mg–0.32Mn–0.21Sc–0.09Zr alloy due to deformation accumulated upon rolling

The mechanical properties and microstructure of sheets of an Al–4.7Mg–0.32Mn–0.21Sc–0.09Zr alloy deformed and annealed after rolling have been investigated. The total accumulated true strain was ef = 3.33–5.63, and the true strain at room temperature and at 200 °C was eс = 0.25–2.3. The strength properties of the sheets (yield stress σ0.2 = 495 MPa and ultimate tensile strength σu = 525 MPa) in the deformed state were greater than those after equal-channel angular pressing (ECAP) deformation. The mechanical properties of the deformed sheets after annealing depended on the size of subgrains inside the deformed grains bands with high-angle grain boundaries (HABs). With the increase in the annealing temperature from 150 to 300°С, the subgrain size increased from 80 to 300 nm. The relative elongation δ in the as-cast state and after annealing at 200–250°C (δ = 40–50%) was higher than that after annealing at 300–370°C (δ = 24–29%).

The Effect of Laves Phase (Fe,Al)2Zr on the High-Temperature Strength of Carbon-Alloyed Fe3Al Aluminide

The effects of carbon on the phase structure and on the yield stress σ 0.2 in the temperature range from 873 K to 1073 K (600 °C to 800 °C) of the Fe3Al type aluminides alloyed by Zr are analyzed. Four alloys with Zr and C in ranging from 1.0 to 5.0 at. pct of additives were used. The appearing of either Laves phase (Fe,Al)2Zr and/or carbides depend on the difference in concentrations, c Zr − c C. This parameter (c Zr − c C) has been selected instead of the concentration ratio c Zr/c C used in previous works since it exhibits a significantly better correlation with the Laves phase concentration which influences the high-temperature yield stress, σ 0.2, of the tested alloys. The presence of Laves phase or eutectic (matrix—Laves phase), respectively, enhances the value of the yield stress σ 0.2. The amount of Laves phase is decreased by the presence of C due to the affinity of carbon to Zr.

Preparation and mechanical properties of in situ TiCx–Ni (Si, Ti) alloy composites

Abstract Novel in situ TiCx reinforced Ni (Si, Ti) alloy composites with superior mechanical properties were prepared at 1250 °C for 30 min by pressureless sintering Ti3SiC2 (10 and 20 vol%) and Ni as precursors. The Ti3SiC2 particles decomposed into substoichiometric TiCx phase, while the additional Si and partial Ti atoms derived from Ti3SiC2 diffused into Ni matrix to form Ni (Si, Ti) alloy. The in situ formed TiCx phases are mainly dispersed on the grain boundaries of the Ni (Si, Ti) alloying, forming a strong skeleton and refining the microstructures of the metal matrix. The hardness, the yield stress σ0.2% and ultimate compressive strength of 20.6 vol%TiCx–Ni(Si, Ti) composite can reach 2.15±0.04 GPa, 466.8±55.8 MPa and 733.3±78.4 MPa, respectively. The enhanced mechanical properties of TiCx–Ni(Si, Ti) composites are due to the in situ formation of TiCx skeleton, the refined microstructures of Ni (Si, Ti) alloys and solid solution effects as well as good wettability between TiCx and Ni (Si, Ti) matrix.

Effects of Si addition on mechanical properties of copper severely deformed by accumulative roll-bonding

Effects of Si addition on mechanical properties of severely deformed copper by accumulative roll-bonding (ARB) have been investigated. Tensile tests and strain-rate jump tests have been carried out at room temperature. For annealed coarse-grained polycrystals, the difference in yield stress σ0.2 between pure copper and a Cu–1.64at.%Si alloy was only about 15 MPa while the difference became 170 MPa after the ARB process by six cycles. The strain-rate sensitivity m of pure copper increased with increasing the number N of the ARB cycles for N ≥ 5. However, the increase in m becomes less significant for Cu–Si alloys. These findings have been discussed in terms of thermally activated dislocation processes.

Ultrafine high-cobalt VK40 hard alloy. I. Structure and properties

Ultrafine WC-41 wt.% Co powders (VK40) are densified under 1000–1200 MPa at 950–1250 °C and in 0.13 Pa vacuum. It is examined how the pressing temperature and annealing at 1190 °C influence the density, structure, physical and mechanical properties of VK40 alloy. It is shown that high-pressure sintering produces dense samples with ultrafine structure (LWC = 0.35–0.45 µm) and low degree of contact for carbide particles (contiguity CWC = 0.08–0.1) in solid phase. The highest mechanical properties are exhibited by samples densified at 1150–1250 °C or by samples annealed after preliminary pressing at 1050–1150 °C. The alloy has the following properties: transverse rupture strength (TRS) of 3200–3400 MPa, fracture toughness of 25–33 MPa · m1/2, Vickers hardness of 7.5–7.7 GPa under 300 N, compressive strength of 2600–2800 MPa, compressive offset yield stress σ0.2 = 2200–2400 MPa, compressive plastic strain of 6.5–7.0%, and fracture energy of 180–200 MJ/m3. These mechanical properties of ultrafine VK40 alloy differ from those of standard impact-resistant coarse-grained hard metals in higher TRS, fracture toughness, and yield stress.

Analytical correlation of indentation experiments

We improve the analysis of indentation by employing a model of the expansion of a spherical cavity in which a generalization of the velocity field proposed by Avitzur for metal extrusion is considered; its components vary with the distance to the indenter apex r as 1/rs , with s a free parameter. By neglecting the material displacement we apply this model to conical indentation (apical angle 2θ) of an elastic solid (Young's modulus E), a rigid–perfectly plastic (RPP) solid (yield stress σ0) and elastic–perfectly plastic (EPP) solids with indentation index X = (E*/σ0) cot θ and estimate the hardness H and the shape ratio cp = h c/h, where h and h c are the penetration depth and the contact depth respectively. s is determined by minimizing the total work (elastic case) and the plastic power (RPP and EPP cases). The results of the model are in agreement with the available exact results (elastic case) and numerical results (RPP and EPP cases).

Structure and mechanical properties of the nitrogen-containing austenitic plate steel 04Kh20N6G11AM2BF

Structure and mechanical properties of the nitrogen-containing austenitic plate steel 04Kh20N6G11AM2BF with a thickness of 20 and 40 mm after hot rolling, quenching from different temperatures, and final strengthening by cold or warm deformation have been studied. For these large-section plates, sufficiently high mechanical properties were obtained, namely, the yield stress σ0.2 ≥ 690 MPa, the relative elongation δ ≥ 20%, the relative reduction ϕ ≥ 50%, and the impact toughness KCV +20 ≥ 100 J/cm2. This complex of strength and plastic properties of hot-rolled steel was produced after the quenching of the plates from 1150°C and subsequent strengthening warm (600°C) or cold (20°C) rolling with a reduction of up to 15%. These properties of steel were due to several causes, namely, the presence of nitrogen in the fcc solid solution, an increased density of dislocations (≈ 1010 cm−2), the precipitation of nanocrystalline vanadium nitrides with sizes of 2–4 nm, and the absence of large amounts of coarse near-boundary particles.

SEM online investigation of fatigue crack initiation and propagation in cast magnesium alloy

Magnesium (Mg) alloys have a unique combination of properties including low density and easy formability that are attractive for numerous technological applications. The requirement to reduce the weight of engineering components has recently triggered substantial research effort on the structural properties of this kind of alloy [1–3]. Compared to other lightweight wrought and cast materials such as aluminum and titanium, little work has been performed on the fatigue behavior of cast magnesium. Initial studies examined the low and high cycle fatigue of cast Mg [4, 5] but they concluded that traditional fatigue life prediction tools are often inaccurate for the cast Mg. Therefore, it is of great interest to search for a relationship between the fatigue failure mechanisms and microstructure in the cast Mg [6–9]. To gain a better understanding on the fatigue behaviors of this alloy, we carried out the fatigue crack initiation and propagation tests and investigated the fatigue crack growth path with notched specimens of the cast AM50 alloy with online SEM observation. The nominal composition of AM50 alloy contain about 5 wt% aluminum. The testing specimens with a 14 mm gage length and a 2.5 mm by 2.3 mm gage cross section were machined from plates supplied by Hydro’s Inc. The testing specimen had a notch radius of about ρ = 80 μm to elevate the local stress state in controlling the site of fatigue crack initiation. The surfaces of the samples were carefully polished prior to fatigue tests. All fatigue tests were performed in the chamber of the SEM. Fatigue tests were carried out at a stress ratio R = 0.1 under a sinusoidal variation. The maximum stress of 120 MPa was chosen as it is below the yield stress σ0.2 = 140 MPa. The whole process of fatigue crack initiation and propagation was monitored and recorded in situ at a frequency of 0.01 Hz at room temperature in order to clearly observe the open and closed crack status. The microstructure of cast AM50 alloy is present in the brittle eutectic phase Mg17Al12 (Its micro-hardness is about 88.34 MPa) with the α-Mg grains (Its micro-hardness is about 66.86 MPa). The microstructure has a significant influence on the me-

Finite-element analysis of deformation during indentation and scratch tests on elastic-perfectly plastic materials

Abstract We have studied the distribution of plastic strain around normal indentation and scratches in elastic-perfectly plastic materials. A three-dimensional finite-element analysis of a cone scratching and indenting elastic-perfectly plastic materials is presented. The indenter is the axisymmetric equivalent cone of the Berkovich indenter, with semiapical angle θ = 70.3°. The plastic behaviour of the material is modelled with the yield stress σ0. No strain hardening and no sensitivity to the strain rate occur. The elasticity of the material is modelled with Young's modulus E, which varies from 2.79 to 2793 GPa. In fact, the behaviour of the scratched or indented material depends on the parameter X = (E/σ0) cotθ, called the rheological factor (X = 1, …, 1000). For small rheological factors, the deformation is mainly elastic; for high rheological factors, the deformation is essentially plastic, and in this case the behaviour of the material is close to the behaviour of a metal. The contact between the indenter and the mesh is frictionless. We have defined a mean representative strain in indentation and scratch tests. This value is independent of the scratch length and the penetration depth. It has been shown that the mean representative strain increases with X, and that it is larger in scratch tests than in indentation tests.

Finite-element analysis of deformation during indentation and scratch tests on elastic-perfectly plastic materials

Abstract We have studied the distribution of plastic strain around normal indentation and scratches in elastic-perfectly plastic materials. A three-dimensional finite-element analysis of a cone scratching and indenting elastic-perfectly plastic materials is presented. The indenter is the axisymmetric equivalent cone of the Berkovich indenter, with semiapical angle θ = 70.3°. The plastic behaviour of the material is modelled with the yield stress σ0. No strain hardening and no sensitivity to the strain rate occur. The elasticity of the material is modelled with Young's modulus E, which varies from 2.79 to 2793 GPa. In fact, the behaviour of the scratched or indented material depends on the parameter X = (E/σ0) cotθ, called the rheological factor (X = 1, …, 1000). For small rheological factors, the deformation is mainly elastic; for high rheological factors, the deformation is essentially plastic, and in this case the behaviour of the material is close to the behaviour of a metal. The contact between the indenter and the mesh is frictionless. We have defined a mean representative strain in indentation and scratch tests. This value is independent of the scratch length and the penetration depth. It has been shown that the mean representative strain increases with X, and that it is larger in scratch tests than in indentation tests.

Elastic plastic mode III crack under internal shear

A complete solution is presented for the problem of a mode III crack in an infinite elastic perfectly-plastic solid under internal shear stress. This problem is the anti-plane strain equivalent of a mode I crack with internal pressure. The problem is transformed into a boundary value problem for a potential function. The particular case when the applied stress σA is equal to the yield stress σ0 is solved analytically, and the distance to the elastic-plastic boundary is obtained in closed form. The general case when σA σ0 is solved numerically by using the Boundary Element Method for potential problems. Numerical results are given for the distance to the elastic-plastic boundary and the crack tip opening displacement. The extent of the plastic zone ahead of the crack tip is shown to vary linearly with the ratio σA/σ0) when 0.5 ≤ (σA/σ0) ≤ 1.

A new method for evaluating stress-strain properties of metals using ultra-microhardness technique

Abstract A new method for evaluating the yield stress σ0.2 and the strain-hardening exponent n of metals is proposed through ultra-microhardness (UMH) technique with an application to fcc metals. UMH measurements with a triangular-base pyramidal indenter have been conducted on copper and copper-aluminum alloys under cold-rolled and annealed conditions at loads ranging from 0.05 g (4.9 × 10−2mN) to 50 g (49 mN), and their results are compared with those of the Vickers hardness (Hv) at 200 g (1.96 N) and of tensile tests. The method is based on Cahoon et al.'s relation that σ0.2(MPa) = 3.27Hv (0.1)n and is composed of (i) the determination of the relationship between Hv and ultra-microhardness (Hum), (ii) the evaluation of n through analyzing the load dependence of Hum and (iii) the evaluation of σ0.2 from Cahoon et al.'s relation together with the results on (i) and (ii). The value of n can be extracted through the UMH test, and the value of σ0.2 evaluated from the present method, shows good coincidence with that obtained by tensile tests.