Hardening effects on formability limit prediction based on gurson-type damage models and bifurcation analysis

In this work, ductility limits of metallic materials, associated with the occurrence of strain localization, are predicted using the GTN damage model coupled with bifurcation theory. The resulting approach is implemented into the finite element code ABAQUS within the framework of large plastic strains and a fully three-dimensional formulation. A parametric study with respect to damage and hardening parameters is conducted in order to identify the most influential material parameters on strain localization. The analysis shows that the damage parameters have a significant impact on the predicted ductility limits, while the effect of hardening parameters on strain localization depends on the choice of void nucleation mechanism

Impact of microstructural mechanisms on ductility limits

In order to investigate the effects of microstructure and deformation mechanisms on the ductility of multiphase steels, a formability criterion based on loss of ellipticity of the boundary value problem is coupled with an advanced multiscale model accounting for intragranular microstructure development and evolution. The resulting large strain elastic–plastic single crystal constitutive law (based on crystal plasticity) is incorporated into a self-consistent scale-transition scheme. The present contribution focuses on the relationship between the intragranular microstructure of B.C.C. steels and their ductility. The model allows interesting comparisons in terms of formability limits for different dislocation networks, during monotonic loading tests applied to polycrystalline aggregates.ArcelorMittal & CNR

From Brittle to Ductile Fracture in Disordered Materials

We introduce a lattice model able to describe damage and yielding in heterogeneous materials ranging from brittle to ductile ones. Ductile fracture surfaces, obtained when the system breaks once the strain is completely localized, are shown to correspond to minimum energy surfaces. The similarity of the resulting fracture paths to the limits of brittle fracture or minimum energy surfaces is quantified. The model exhibits a smooth transition from brittleness to ductility. The dynamics of yielding exhibits avalanches with a power-law distribution

Strain Limits for Concrete Filled Steel Tubes in AASHTO Seismic Provisions

INE/AUTC 13.1

The ideal of the certainty in law: the skin and the heart of law

The doubt about certainty like an absolute value in law and as an ideal full in legal system (argument about impossibility) is a controversial fact in contemporary legal theory. In this text I examine some contemporary doctrines about the classic understanding (in critical sense) of this ideal. I have selected the most representative doctrines: doctrine about "open texture of Law" (H.L.A. Hart), starting point in this discussion; doctrine about "Il Diritto mite" (G. Zagrebelsky), from the continental European legal tradition at present; and doctrine about "vagueness in Law" (T.A.O. Endicott), this doctrine is the most recent, from the Anglo-Saxon legal tradition. Finally, in Conclusions, I analyze if this doubt (argument about impossibility) contaminates (in some sense) to the concept of law or to the characteristics that describe law in the contemporary Constitutional State

Low temperature tensile properties of line pipe steels

Given the expected increase in Arctic oil and gas exploitation, there is a demand for high-strength line pipe steels able to cope with the Arctic climate. The state-of-the-art of the tensile properties of API 5L steels at low temperatures is reviewed and discussed. Well-known characteristics such as an increase in strength and Young’s modulus with decreasing temperatures are confirmed. The Y/T ratio is fairly unaffected by changes in temperature. Lüders elongation manifests itself at low temperatures where the Lüders plateau tends to increase. Conflicting statements about the relation between ductility and temperature were found. Altogether, quantifiable test results are scarce, especially for the high strength grades from API 5L X90 grade onwards. The urgent need for more tensile strength and ductility data of these steels at low temperatures is stated and defended

The impact of hydrogen on the ductility loss of bainitic Fe–C alloys

The influence of hydrogen on the mechanical properties of generic lab-cast Fe-C bainitic alloys is studied by tensile tests on notched samples. The bainitic microstructure is induced in a 0.2% C and 0.4% C Fe-C alloy by an appropriate heat treatment. The hydrogen embrittlement susceptibility is evaluated by mechanical tests on both in situ hydrogen pre-charged and uncharged specimens. The observed ductility loss of the materials is correlated with the present amount of hydrogen and the hydrogen diffusion coefficient. In addition to the correlation between the amount of hydrogen and the hydrogen-induced ductility loss, the hydrogen diffusion during the tensile test, quantified by the hydrogen diffusion distance during the test, appears to be of major importance as well

High temperature compositions Patent

Method for producing refractory molybdenum disilicide

Temperature effects on material characteristics

Some of the physical properties of the main elements of interest in high temperature technology are reviewed. Some general trends emerge when these properties are viewed as a function of melting point, but there are a few notable exceptions. Titanium, zirconium, niobium and tantalum all have disappointingly low moduli; chromium is excellent in many ways, but has a limited ductility at lower temperatures; molybdenum oxidises catastrophically above about 700° C, and niobium suffers from severe oxygen embrittlement. Beryllium and carbon (in the graphitic form) both stand out as exceptional materials, both have very low densities, beryllium a very high modulus but an unfortunately low ductility, while graphite has a relatively low strength at the lower temperatures, although at temperatures of 2000° C and above it emerges as a quite exceptional (and probably as the ultimate) high temperature material. Some of the fundamental factors involved in high temperature material development are examined, in the light, particularly, of past progress with the nickel alloys. If a similar progress can be achieved with other base elements then a considerable margin still remains to be exploited. Protection from oxidation at high temperatures is evidently a factor of major concern, not only with metals, but with graphite also. Successful coatings are therefore of high importance and the questions they raise, such as bonding, differential thermal expansion, and so on, represent aspects of an even wider class covered by the term “composite structures". Such structures appear to offer the only serious solution to many high temperature requirements, and their design, construction and utilization has created a whole series of new exercises in materials assessment. Matters have become so complex, that a very radical and fundamental reassessment is required if we are to change, in any very significant way, the wasteful and ad hoc methods which characterise so much of present-day materials engineering

Fundamental aspects of and failure modes in high-temperature composites

Fundamental aspects of and attendant failure mechanisms for high temperature composites are summarized. These include: (1) in-situ matrix behavior; (2) load transfer; (3) limits on matrix ductility to survive a given number of cyclic loadings; (4) fundamental parameters which govern thermal stresses; (5) vibration stresses; and (6) impact resistance. The resulting guidelines are presented in terms of simple equations which are suitable for the preliminary assessment of the merits of a particular high temperature composite in a specific application