Laws of Influence of Structural Characteristics on the Strength and Crack Resistance of Aging Metallic Materials

Nizhnik, S. B.; Usikova, G. I.

doi:10.1007/s10778-005-0060-1

Cited by 6 publications

(12 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…1a [10,15]), the following notation is used: the first subscript on ( ) ( , , ) K M C MN 1 1 2 3 = stands for longitudinal, transverse, and normal directions of the applied force (these directions coincide with the rolling, transverse, and normal (to the rolling plane) directions, respectively); the second subscript (N = m) stands for the direction in which a mode I crack propagates in the corresponding plane (mn) = (23), (13) Formulas (1.2) and (1.3) are based on the experimentally justified proportional relationship between the dimensional parameters of the plastic zone at the crack tip x mn 0( ) and the average distances between particles of the hardening phases on the associated planes (mn) of the object l 0( ) mn as well as on the functional relationship between the parameter l 0( ) mn and the density of hardening-phase particles f c mn ( ) [19]. Because these particles appear under final heat treatment of ageing alloys (hardening ageing) mainly on the grain boundaries in the matrix phase, we may assume that their relative density on the grain boundaries parallel to the planes (mn) is proportional to the area of these boundaries on the corresponding planes (mn), this area being dependent on e and referred to the total area A mn ( ) of the grain boundaries in unit volume:…”

Section: Basic Relationsmentioning

confidence: 99%

“…We will develop and experimentally validate a structural mechanical approach to evaluating and predicting the anisotropy of the fracture toughness K 1C of FCC-metals (aluminum alloys) loaded in the rolling direction, in the transverse direction, and normally to the rolling plane. The approach is based on the modification of the Hahn-Rosenfield model proposed in [3,4,19] to estimate the fracture toughness …”

mentioning

confidence: 99%

See 1 more Smart Citation

Anisotropy of the fracture toughness of structurally inhomogeneous ageing alloys

Kaminsky

Nizhnik

2009

Int Appl Mech

Self Cite

View full text Add to dashboard Cite

The dependence of the fracture toughness K 1C of rolled ageing alloys with structural and crystallographic textures on the loading direction is established. A formula describing the anisotropy of the K 1C and including structural parameters of structurally textured alloys on planes of growth of mode I cracks is derived and validated for aluminum alloys. The influence of crystallographic planes and crack growth direction on K 1C is analyzed for titanium alloy as a rolled material with crystallographic texture Introduction. The anisotropy of strength, plasticity, and crack resistance of structural materials caused by deformation (rolling, forging, forming, etc.) and hardening heat-treatment is studied in [1,2,[5][6][7][8]. Such thermomechanical actions are widely used in forming structural elements for modern engineering. Of importance is to optimize the thermomechanical conditions that would provide the necessary anisotropy of the crack resistance of the material, which would enhance the operational reliability of structures.The research in the field may be developed by establishing the dependence of the anisotropy of the crack resistance of structural alloys on their structural inhomogeneity at the meso-, micro-, and nano-levels, including structural and crystallographic texture [1,5,15]. These types of structural inhomogeneity often appear simultaneously but have different effects on the anisotropy of crack resistance under thermomechanical loads. The structural texture of ageing alloys represents directional changes in the shape, dimensions, and orientation of grains and subgrains of the matrix phases and in the distribution density of disperse particles of the hardening phases on the crack growth planes. This determines the direction of structural embrittlement. The crystallographic texture represents the preferential orientation of crystallites, restricting the number of active slip planes in certain crack growth directions and, therefore, the capability of the material to form plastic zones at the crack tip in these directions, which reduces crack resistance [3,4]. The effect of the crystallographic texture on the anisotropy of crack resistance is much stronger in metals with a hexagonal close-packed (HCP) lattice. Such a lattice has much less active slip systems compared with the face-centered (FCC) and body-centered (BCC) cubic lattices [13].The influence of these types of structural inhomogeneity on the anisotropy of crack resistance is poorly understood. This is why it is impossible to establish the general pattern of its manifestation considering that structural alloys have many phases and their matrix phases have lattices of different types.The present paper examines the individual effects of the structural and crystallographic textures (caused by rolling and heat treatment) of ageing alloys on the anisotropy of crack resistance.1. Influence of Structural Texture on the Anisotropy of Fracture Toughness. We will develop and experimentally validate a structural mechanical approach to evaluating and predi...

show abstract

Section: Basic Relationsmentioning

confidence: 99%

mentioning

confidence: 99%

Anisotropy of the fracture toughness of structurally inhomogeneous ageing alloys

Kaminsky

Nizhnik

2009

Int Appl Mech

Self Cite

View full text Add to dashboard Cite

show abstract

“…We study, on the example of aging N18K8M5T steel, the yield surface for biaxial tension, for different offset-strain values δ (from 0 to 0.2%) and consider physical processes in the material in the range of small elastoplastic strains. The steel contains, in wt.%, 0.02C, 18.2Ni, 0.68Ti, 5.03Mo, 8.6Co, 0.11Al, 0.02Si, 0.005P, 0.005S) (Nizhnik and Usikova, 2005). The study was carried out using tubular specimens (the gauge length, outer diameter, and wall thickness are 100, 30, and 0.8 mm, respectively) fabricated from a cold-drawn rod.…”

mentioning

confidence: 99%

“…The steel contains, in wt.%, 0.02C, 18.2Ni, 0.68Ti, 5.03Mo, 8.6Co, 0.11Al, 0.02Si, 0.005P, 0.005S) (Nizhnik and Usikova, 2005). The study was carried out using tubular specimens (the gauge length, outer diameter, and wall thickness are 100, 30, and 0.8 mm, respectively) fabricated from a cold-drawn rod.…”

mentioning

confidence: 99%

On the Choice of an Offset-strain Value in Determining Yield Surfaces

Bastun

Nizhnik

2007

Int J Fract

View full text Add to dashboard Cite

The choice of an offset-strain value in experimental determination of the yield surfaces, that controls the plasticity condition, the size and shape of the crack-tip plastic zone and the value of the correction factor for plasticity, is discussed. The results are illustrated by yield curves for aging steel in the metastable state under biaxial tension.1.Introduction. The shape and the size of the plastic zone near the crack tip affect fracture behavior of metallic materials, and the length of the plastic zone in the direction of crack propagation affects the correction factor in the expression for the effective crack length. The shape and size of the plastic zone are defined by the plasticity condition represented by the yield surface in the stress space. The yield surface depends on the yield strength, degree of anisotropy, character of strain hardening (in the case of subsequent yield surfaces), material structure and the offsetstrain value.Correlation of the plastic zone size with the strain hardening parameters and the plasticity condition were considered earlier on the example of mode I crack (Bastun, 1999). The influence of the material structure in the plastic zone on the fracture toughness characteristics was addressed in the work of Kaminsky and Nizhnik (1995). The problem of choice of the offset-strain value has been discussed from 1970's (Zyczkowski, 1981;Michno and Findley, 1976;Kachanov, 1971;Phillips, 1974), but it has not been fully clarified (Lebedev et al, 2000;Miastkowski and Szczebiot, 2001).2. Experimental procedure. We study, on the example of aging N18K8M5T steel, the yield surface for biaxial tension, for different offset-strain values δ (from 0 to 0.2%) and consider physical processes in the material in the range of small elastoplastic strains. The steel contains, in wt.%, 0.02C, 18.2Ni, 0.68Ti, 5.03Mo, 8.6Co, 0.11Al, 0.02Si, 0.005P, 0.005S) (Nizhnik and Usikova, 2005). The study was carried out using tubular specimens (the gauge length, outer diameter, and wall thickness are 100, 30, and 0.8 mm, respectively) fabricated from a cold-drawn rod. Blanks for specimens were subjected to austenization at temperature 860ºC (maintained for 25 min) with subsequent cooling to room temperature in the atmosphere of argon. As a result, the material has acquired the metastable structure of martensite, which represents a solid solution oversaturated with alloying elements. Biaxial tension was performed in accordance with the technique described in the works (Bastun, 1994; Bastun and Kaminskii, 2005), which involves loading specimens with an axial force and internal pressure along different rectilinear paths using a force type testing machine. 3. Results and discussion. As the preliminary tests showed, in the range of small elastoplastic strains the material exhibits substantial difference in the tensile and compressive strengths, with the tensile strength being higher. This fact is attributed to LETTERS IN FRACTURE AND MICROMECHANICS

show abstract

“…This is manifested by an increased scatter in hardness (as a strength parameter) throughout the service life [7]. Because of the high reliability demands for such structures, it appears important to enhance the stability of fracture resistance by optimizing the structure of high-strength materials during manufacture to make them more ductile.The structural characteristics of high-strength materials responsible for fracture can be specified by means of structural mechanics [17] using the basic relations of physics of strength and fracture [10,13,21]. Among such characteristics are experimentally justified structural dependences of strength, ductility, and ductile-brittle transition temperature and dislocation failure criteria, which generally indicate how the structural parameters of a material should be changed to enhance its fracture resistance [9,18].…”

mentioning

confidence: 99%

Structural approach to enhance the fracture resistance of high-strength metallic materials

2006

Self Cite

View full text Add to dashboard Cite

The paper proposes an approach to form (by special heat treatment) a structure and phase composition of martensitic steel that would enhance its ductility in the high-strength state. A correlation is experimentally established between the stability of fracture resistance and ductility in linear and plane stress states. The behavior of the scatterband of the ultimate strength with increase in the degree of ductility is analyzed. The possibility of predicting the ultimate strength from the lower edge of its scatterband is demonstrated with an example of a circular cylindrical shell Keywords: structural approach, martensitic steel, ductility, scatterband of ultimate strength, linear and plane stress statesIntroduction. Design of low-weight structures used in aircraft and space-and-rocket technologies permit high stresses. Such structures are made of high-strength materials. Because of their low ductility, such materials are highly sensitive to the presence of defects, which results in a significant scatter in strength. The allowable stress might appear to fall within the scatterband of the ultimate strength.The ductility of a material can also be substantially reduced by accumulated microdamage caused by radiation [1, 15], compound stress [4,6,16], and low temperatures [6]. This is manifested by an increased scatter in hardness (as a strength parameter) throughout the service life [7]. Because of the high reliability demands for such structures, it appears important to enhance the stability of fracture resistance by optimizing the structure of high-strength materials during manufacture to make them more ductile.The structural characteristics of high-strength materials responsible for fracture can be specified by means of structural mechanics [17] using the basic relations of physics of strength and fracture [10,13,21]. Among such characteristics are experimentally justified structural dependences of strength, ductility, and ductile-brittle transition temperature and dislocation failure criteria, which generally indicate how the structural parameters of a material should be changed to enhance its fracture resistance [9,18].For example, the Cottrell-Petch criterion defines conditions to optimize the structure of multiphase systems at the meso-, micro-, and nanolevels with regard to the size of matrix grains and subgrains and the volume fraction and morphology of strengthening precipitates, which determine the ability to relax stress concentrators by local yielding rather than by cracking. For some classes and states of structural metals, we experimentally established, using structural approaches [5,18], a correlation between a tensile ductility index (maximum percent elongation as a measure of stress relaxation, the opposite of cracking) and the size of the crack-tip fracture process zone.The approaches of thermal and thermomechanical structural optimization were tested against maraging steels. This had the effect of enhancing stability and fracture resistance with a simultaneous reduction in the weight of welded shel...

show abstract

Laws of Influence of Structural Characteristics on the Strength and Crack Resistance of Aging Metallic Materials

Cited by 6 publications

References 9 publications

Anisotropy of the fracture toughness of structurally inhomogeneous ageing alloys

Anisotropy of the fracture toughness of structurally inhomogeneous ageing alloys

On the Choice of an Offset-strain Value in Determining Yield Surfaces

Structural approach to enhance the fracture resistance of high-strength metallic materials

Contact Info

Product

Resources

About