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A plastic constitutive equation incorporating strain, strain-rate, and temperature

The strain, strain rate and temperature dependency of a boron steel, which was isothermally deformed under uniaxial compression tests, has been investigated at temperatures between 600 and 900°C, and at strain rates of 0.1, 1.0 and 10.0 s −1 . Two constitutive models were used to correlate the plastic behavior: the Voce constitutive relation in combination with the kinetic model proposed by Kocks and the phenomenological model proposed by Molinari–Ravichandran. The Kocks model has been introduced in the Voce formulation to describe the temperature and the strain rate dependency of the saturation stress and of the yield stress. The Molinari–Ravichandran model is based on a single internal variable that can be viewed as being related to a characteristic length scale of the microstructure that develops during deformation. It has been shown that the plastic behavior of the boron steel can be well described using these two models.

Constitutive relationships for 22MnB5 boron steel deformed isothermally at high temperatures

Forming limit diagram (FLD) is an important performance index to describe the maximum limit of principal strains that can be sustained by sheet metals till to the onset of localized necking. It is useful tool to access the forming severity of a drawing or stamping processes. In the present work, FLD has been determined experimentally for Ti-6Al-4 V alloy at 400 °C by conducting a hemispherical dome test with specimens of different widths. Additionally, theoretical FLDs have been determined using Marciniak Kuczynski (M-K) model. Various yield criteria namely: Von Mises, Hill 1948, Hill 1993 and Cazacu Barlat in combination with different hardening models viz., Hollomon power law (HPL), Johnson-Cook (JC), modified Johnson-Cook (m-JC), modified Arrhenius (m-Arr.), modified Zerilli–Armstrong (m-ZA) have been used in M-K analysis for theoretical FLD prediction. The material properties required for determination of yield criteria and hardening models constants have been calculated using uniaxial tensile tests. The predicted theoretical FLDs results are compared with experimental FLD. It can be observed that influence of yield criterion in M-K analysis for theoretical FLD prediction is predominant than the hardening model. Based on the results; it is observed that the theoretical FLD using Cazacu Barlat and Hill 1993 yield criteria with m-Arr. hardening model has a very good agreement with experimental FLD.

Experimental and theoretical investigation of forming limit diagram for Ti-6Al-4 V alloy at warm condition

Influence of temperature and strain rate on tensile work hardening behaviour of type 316 LN austenitic stainless steel

The effect of tensile prestraining on the ductile fracture behaviour of two varieties of Cu-strengthened HSLA steels has been studied. It was observed that for both the HSLA steels the fracture toughness, JC, remained invarient up to 2% prestrain, beyond which it decreased deleteriously. The nature of variation of fracture toughness with prestrain has been explained in terms of variation of the tensile flow properties of the steels with prestrain. A model correlating fracture toughness and the tensile flow properties has been proposed and it is demonstrated that the predictions of the model matched closely with the experimental observations.

Effect of prestrain on fracture toughness of HSLA steels

The stress-strain data of a high-strength low-alloy (HSLA) steel were measured at different temperatures and analyzed in terms of strain-hardening laws proposed by Hollomon,[1] Ludwik,[2] Swift,[3] and Voce.[4] Four methods of analysis, as suggested by Kleemola and Nieminen (K-N),[7] Crussard and Jaoul (C-J),[16] Ramani and Rodriguez (R-R),[11] and Guimaraes (G),[15] have been employed. The C-J analysis has been extended to the Voce equation for the first time. The results have been discussed in terms of the linear correlation coefficient and error in the estimation of uniform strain. The Voce equation has been found to describe the flow be-havior most accurately. The observed increase in flow stress in the dynamic strain aging (DSA) range has been explained in terms of temperature-dependent strain-hardening parameters. It has been established that with increase in the value of the Voce strain component, nv, the magnitude of the saturation stress approaches that of the ultimate tensile stress. A linear relationship has been established between ultimate tensile stress and saturation stress.

Analysis of the temperature dependence of strain-hardening behavior in high- strength steel

The performance of rails in service is greatly influenced by the presence of metallurgical defects. Hydrogen-induced shatter crack is the most prominent among these and has been discussed in detail. Principal causes of rail failure have been outlined and different types of defects leading to failure of rails during service have been documented. Wear of rails which accounts for reduced life has been considered. Influence of microstructure on wear rate has been described.

N. S. Mishra

Papers

Analysis of the temperature dependence of strain-hardening behavior in high- strength steel

Defects in rails