Ultimate Tensile Strength Σu Research Articles

Application of the Hydraulic Diameter of Interdendritic Space for Calculating the Ultimate Tensile Strength of Gray Cast Iron

A comparative analysis of methods for estimating the gray cast iron ultimate tensile strength σu by the hydraulic diameter of interdendritic space DHydIP and the volume fraction of primary austenite dendrites fdc is performed. Almost the same accuracy of cast iron castings σu estimation according to both these parameters DHydIP and fdc of the primary microstructure is shown.

The Study of the Copper Alloy Structure and Properties

This paper is devoted to the possibility of using tin as an alloying element in a copper alloy for the contact wire manufacture for high-speed electrified railways. To this end, laboratory experiments were carried out to determine the effect of tin on the structure, mechanical and electrical properties of samples, made of low-alloy system Cu-Sn alloys, under the cold deformation. Cast rods and rolled billets of CuSn0,2, CuSn0,4 and CuSn0,6 alloys are made. The cast rods macrostructure is studied. The analysis showed that with the introduction of tin into copper, there is no zone of columnar crystals in the macrostructure. Moreover, it was found that grains of α-solid solution of tin in copper have a shape close to equiaxial. A structure analysis of rolled billets showed that an increase in the deformation degree leads to grinding of crystalline grains. The mechanical properties of rolled billets were determined: ultimate tensile strength σU, offset yield strength σ0.2 and elongation δ50. The dependence of the electrical resistivity of rolled billets on the deformation degree and the tin content in the alloy is determined. Еhe higher the tin content in the alloy and the deformation degree is, the higher is the electrical resistivity. The electrical resistivity of samples, made of CuSn0.2 and CuSn0.4 alloys, coincides with the GOST R 55647-2018 requirements. The laboratory studies have shown that tin-containing copper alloys (Sn is up to 0.4 wt. %) can be recommended as a material for the manufacture of contact wire.

Failure Prediction of AISI 420 Martensitic Stainless Steel Using the Theory of Critical Distances

This work aims to evaluate the capability of the theory of critical distances (TCD) to predict the static failure of U-notched AISI 420 martensitic stainless steel specimens with different geometric features under pure bending loading. Theoretical estimates of the stress intensity factor during fracture onset were calculated according to the line (LM) and point methods (PM), which consider the characteristic length L, inherent strength σ0, and notch tip radius ρ. Initially, L and σ0 were determined on the basis of the material’s properties (i.e., fracture toughness KIc and ultimate tensile strength σu,t), resulting in imprecise estimates. Conversely, L and σ0 determined using the appropriate analysis of linear–elastic stress fields ahead of notches with different sharpness provided highly accurate predictions. The microscopic study of fractured specimens ensured better comprehension of the results. Moreover, the accurate values of L and σ0 were used to predict the failure of V-notched specimens.

Relation between the Hardness and the Strength of Gray Cast Iron with Allowance for the Structural Parameters

The factors that affect the relation between ultimate tensile strength σu and hardness HB of gray cast iron with flaked graphite are studied. The scatter of the ultimate tensile strengths at a given hardness is shown to be caused by one of the primary structure parameters, namely, the volume fraction of primary austenite dendritic crystals. The dependences derived in this work can be used to increase the accuracy of a rapid estimation of the quality of cast iron ingots.

Estimation of the Ultimate Tensile Strength of Steel from Its HB and HV Hardness Numbers and Coercive Force

A formula is derived to accurately describe the tabulated relation between the Brinell (HB) and Vickers (HV) hardnesses of steel over the entire range of their possible variation. This formula and the formulas describing the relation between the HB hardness of chromium–molybdenum and chromium–nickel steels and their ultimate tensile strength σu are used to analyze the change in σu of 38KhNM steel upon quenching and tempering. The data that reveal a relation between σu of 38KhNM steel and its coercive force are obtained.

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%).

On the relation between the strength and the plasticity of polymers

It is shown that the elongation to failure δ and ultimate tensile strength σu in polymers are related as σu(1 + δ) = su = const at the temperatures of non-Hookean entropy viscoelasticity. Different drawing from different initial states brings the structure of polymer to the limiting uniaxial structure with the same true stress of breaking carbon chains su.

Local strain energy to assess the static failure of U-notches in plates under mixed mode loading

The averaged value of the strain energy density over a well-defined volume is used to predict the static strength of U-notched specimens under mixed-mode conditions due to combined bending and shear loads. The volume is centered in relation to the maximum principal stress present on the notch edge, by rigidly rotating the crescent-shaped volume already used in the literature to analyse U- and V-shaped notches subject to mode I loading. The volume size depends on the ultimate tensile strength σu and the fracture toughness KIC of the material. In parallel, an experimental programme was performed. All specimens are made of polymethyl-metacrylate (PMMA), a material which exhibits quasi-brittle behaviour at -60°C. Good agreement is found between experimental data for the critical loads to failure and theoretical predictions based on the constancy of the mean strain energy density over the control volume.

Structure and properties of titanium-free maraging alloys

The changes in the structure, phase composition, and physicomechanical properties of titanium-free maraging alloys based on the Fe-15–23% Ni-(Co, Mo, V) system after heating to the single-phase α field and two-phase α + γ field have been studied. It has been established that the strengthening of N15K10M5F5-type maraging alloys is caused by the precipitation of fine particles (20–50 nm) of intermetallic phases such as the fcc Ni3(Mo, V) phase and the Fe2(Mo, V) Laves phase (in the N23K9M6 alloys, with the formation of the Ni3Mo and Fe2Mo phases). It has been shown that the two-step aging of the N15K10M5F5 alloy leads to an additional strengthening by 200–250 MPa and provides the achievement of the ultimate tensile strength σu=2400−2500 MPa. The high-strength N15K10M5F5 maraging alloys are obtained with two levels of the coercive force Hc: (a) semihard maraging alloys with Hc=20−50 Oe and σu=2100−2400 MPa; and (b) hard magnetic maraging alloys with Hc=180−230 Oe and σu=1500−1800 MPa. The high-strength titanium-free N15K10M5F5 and N23K9M6 maraging alloys possess many properties characteristic of structural, elastic, and magnetic alloys and are thus multifunctional materials. These alloys can be used for advanced high-tech articles and as high-strength magnetic materials.

Lifetime of concrete dam models under constant loads

This paper presents the results of crack creep tests on three dam models (240 cm high) made with three types of concrete, with maximum aggregate size Φ equal to 3.15, 12 and 25 mm. In order to characterize the material a series of tensile tests was performed for each kind of concrete. In this way the static parameters (Young’s modulusE, ultimate tensile strength σu, compressive strength σc, fracture energyGF) and creep laws were obtained.

Effect of prior austenite grain size and pearlite interlamellar spacing on strength and fracture toughness of a eutectoid rail steel

The influence of prior austenite grain size dγ, and true interlamellar spacing of pearlite St on the strength and fracture toughness of a eutectoid rail steel has been investigated. Specimens were machined from rail sections and heat treated to produce a wide variation in dγ and st. Mechanical properties studied included 0·2% proof stress σ0·2, ultimate tensile strength σu, tensile ductility δ, cleavage fracture stress σf, and plane strain fracture toughness K1c. All tests were performed at a temperature of −80°C. The values of σ0·2 and σu increase as st decreases. The proof stress is related to the mean free distance λin the pearlitic ferrite by a Hall–Petch equation. A microstructural dependence similar to that of σ0·2 is shown by σf and for all but the finest pearlites σf is interpreted as a shear stress controlled cleavage nucleation stress. The value of K1c first decreases with decreasing st and then increases for the finest spacings. This behaviour is attributed to a change in the micromechanism of cleavage nucleation as the pearlite spacing changes from coarse to fine. The value of dy has very little effect on K1c, but δ decreases progressively as dγ increases. The effect of dγ on K1c is negligible because the fracture process zone is much smaller than the grain size and therefore the grain boundaries cannot influence the fracture processes occurring at the crack tip. The tensile ductility is interpreted as the strain necessary to develop an internal microcrack which then propagates as a quasibrittle fracture. The size of the microcrack is shown to be related to the pearlite nodule size which in turn is related to dγ.MST/396

Effect of prior austenite grain size and pearlite interlamellar spacing on strength and fracture toughness of a eutectoid rail steel

The influence of prior austenite grain size dγ, and true interlamellar spacing of pearlite St on the strength and fracture toughness of a eutectoid rail steel has been investigated. Specimens were machined from rail sections and heat treated to produce a wide variation in dγ and st. Mechanical properties studied included 0·2% proof stress σ0·2, ultimate tensile strength σu, tensile ductility δ, cleavage fracture stress σf, and plane strain fracture toughness K1c. All tests were performed at a temperature of −80°C. The values of σ0·2 and σu increase as st decreases. The proof stress is related to the mean free distance λin the pearlitic ferrite by a Hall–Petch equation. A microstructural dependence similar to that of σ0·2 is shown by σf and for all but the finest pearlites σf is interpreted as a shear stress controlled cleavage nucleation stress. The value of K1c first decreases with decreasing st and then increases for the finest spacings. This behaviour is attributed to a change in the micromechanism of cleavage nucleation as the pearlite spacing changes from coarse to fine. The value of dy has very little effect on K1c, but δ decreases progressively as dγ increases. The effect of dγ on K1c is negligible because the fracture process zone is much smaller than the grain size and therefore the grain boundaries cannot influence the fracture processes occurring at the crack tip. The tensile ductility is interpreted as the strain necessary to develop an internal microcrack which then propagates as a quasibrittle fracture. The size of the microcrack is shown to be related to the pearlite nodule size which in turn is related to dγ.MST/396

A Study of Hysteresis Loops in Strain Cycling Fatigue and Life Estimation

Hysteresis loops were recorded intermittently but periodically during completely reversed, strain-controlled low cycle fatigue tests of four kinds of steel : a mild steel and three high strength steels. The longitudinal strain amplitude e±a was controlled over the gauge length of 12.5 mm on 8 mm diameter test section of the smooth, solid cylinder type specimen. After the conversion of the loops to true stress versus natural strain hysteresis loops, cyclic characteristics were studied on true stress amplitude, hysteresis energy and hysteresis loop shape.Main conclusions obtained are as follows : (1) The transition strain amplitude e*ta, on which neither cyclic hardening nor cyclicsoftening is occurred, is expressed as a function of ultimate tensile strength σu (kgf/mm2).log e*ta =0.0478 σu -4.544(2) Although plastic strain hysteresis energy per cycle ΔW behaves irregular and remarkable change in the beginning stage of cycling, that is approximately less than 2 percent of the crack initiation life, the change of ΔW is neglegible order after the beginning stage.The fatigue toughness Wf (kgf/mm2) is expressed as a function of ultimate tensile strength σu and visible crack initiation life Nc.Wf= (94.93-0.347σu) Nc0.335 (3) The ratio of ΔW to the product of true stress range and plastic strain range is not constant during the fatigue cycling, and the mean value of the ratio over the total cycling for a specimen is expressed as a function of the total strain amplitude.(4) The constants a and n in the n-th power strain hardening formula are expressed as a function of N and eta for the nearly total range of cycling excluding the beginning stage.An empirical formula was found between a and 1/n.1/n= (log a+1.623+0.376log σu)/(0.1539-1.169 logσu)(5) An estimation procedure for crack initiation life was proposed on the basis of the fatigue toughness, showing an estimation error less than 28 percent.