A model for the axisymmetric growth and coalescence of small internal voids in elastoplastic solids is proposed and assessed using void cell computations. Two contributions existing in the literature have been integrated into the enhanced model. The first is the model of Gologanu-Leblond-Devaux, extending the Gurson model to void shape effects. The second is the approach of Thomason for the onset of void coalescence. Each of these has been extended heuristically to account for strain hardening. In addition, a micromechanically-based simple constitutive model for the void coalescence stage is proposed to supplement the criterion for the onset of coalescence. The fully enhanced Gurson model depends on the flow properties of the material and the dimensional ratios of the void-cell representative volume element. Phenomenological parameters such as critical porosities are not employed in the enhanced model. It incorporates the effect of void shape, relative void spacing, strain hardening, and porosity. The effect of the relative void spacing on void coalescence, which has not yet been carefully addressed in the literature. has received special attention. Using cell model computations, accurate predictions through final fracture have been obtained for a wide range of porosity, void spacing, initial void shape, strain hardening, and stress triaxiality. These predictions have been used to assess the enhanced model. (C) 2000 Elsevier Science Ltd. All rights reserved.

An extended model for void growth and coalescence - application to anisotropic ductile fracture

Graded microstructure and mechanical properties of additive manufactured Ti–6Al–4V via electron beam melting

Hot stamping of boron steel sheets with tailored properties: A review

Engineering ceramics such as alumina, zirconia, silicon nitride and silicon carbide can now be manufactured reliably with reproducible properties As such, they are of increasing interest to industry, particularly for use in demanding environments, where their thermomechanical performance is of critical importance, with applications ranging from fuel cells to cutting tools One aspect common to virtually all applications of engineering ceramics is that eventually they must be joined with another material, most usually a metal The joining of engineering ceramics to metals is not always easy There are two main considerations The first consideration is the basic difference in atomic bonding: the ionic or covalent bonding of the ceramic, compared to the metallic bond The second consideration is the mismatch in the coefficient of thermal expansion In general, ceramics have a lower coefficient of thermal expansion than metals and, if high tensile forces are produced in the ceramic, either a

Joining of engineering ceramics

https://www.tpbin.com/Uploads/Subjects/0611b255-45d7-457a-8988-9c77b24b09c0.pdf

Complex unloading behavior: Nature of the deformation and its consistent constitutive representation

Hardness values as well as yield and tensile strength values were compiled for over 150 nonaustenitic, hypoeutectoid steels having a wide range of compositions and a variety of microstructures. The microstructures include ferrite, pearlite, martensite, bainite, and complex multiphase structures. The yield strength of the steels ranged from approximately 300 MPa to over 1700 MPa. Tensile strength varied over the range of 450-2350 MPa. Regression analysis was used to determine the correlation of the yield strength and the tensile strength to the diamond pyramid hardness values for these steels. Both the yield strength and tensile strength of the steels exhibited a linear correlation with the hardness over the entire range of strength values. Empirical relationships are provided that enable the estimation of strength from a bulk hardness measurement. A weak effect of strain-hardening potential on the hardness-yield strength relationship was also observed.

Correlation of Yield Strength and Tensile Strength with Hardness for Steels

The elastic moduli of four sheet steels were measured in continuous loading–unloading–loading (LUL) tests after different amounts of plastic pre-strain. The four materials were a low-strength steel (Mild270), a bake-hardenable steel (BH340) and two advanced high-strength steels (AHSS), DP490 and DP590. Hysteresis loops were observed due to a non-linearity of the elastic modulus during the unloading and reloading cycles. The total strain recovery during unloading could be separated into a linear part and a non-linear part. The latter was found to be proportional to the unloading stress for all materials. The unloading and reloading elastic moduli decreased as the plastic pre-strain increased and reached saturation towards specific constant values. They could well be approximated as a function of the plastic strain with an empirical exponential-type model, although there were some deviations for BH340. The baking heat treatment and different strain rate had little influence on the unloading and reloading elastic moduli. The increase of the non-linear elastic strain component as a function of the unloading stress could be explained by the Kocks–Mecking (KM) model in which the micro-plastic strain is related to the mobile dislocation density.

Nonlinear elastic behaviors of low and high strength steels in unloading and reloading

Comparative study of the prediction of microstructure and mechanical properties for a hot-stamped B-pillar reinforcing part

Equilibrium solubility products of molybdenum carbide and tungsten carbide in iron

Finite element simulations that predict the microstructure and properties of heat-treated steels can be significantly improved by incorporating appropriate models for the kinetics of various austenite transformations. In the present study the austenite decomposition kinetics for a 1045 steel was modeled using a modification of the transformation equation proposed by Li et al. [1]. The kinetics of the continuous cooling transformation were determined directly from an isothermal transformation diagram. To verify the predictions of the model, an end-quench test was used because it produces a wide range of microstructures. The microstructures predicted by the kinetics model for the end-quenched sample were confirmed by quantification of the microstructures observed in the end-quench experiments. Furthermore, the predicted hardness profile was in good agreement with the experimentally measured hardness profile. The kinetics model developed in the present study was compared to the models proposed by Kirkaldy and Venugopalan [2] and the unmodified model by Li. The present model provides a more accurate prediction. A microstructural-based hardness equation from the literature was also evaluated and it predicted hardness values that were above the experimentally measured values. The model we propose predicts the experimental hardness profile more accurately, since it is based on the calculated microstructure and experimental hardness values of martensite, bainite, and ferrite/pearlite.

Erik J. Pavlina

Papers

Correlation of Yield Strength and Tensile Strength with Hardness for Steels

Nonlinear elastic behaviors of low and high strength steels in unloading and reloading

Comparative study of the prediction of microstructure and mechanical properties for a hot-stamped B-pillar reinforcing part

Equilibrium solubility products of molybdenum carbide and tungsten carbide in iron

Kinetics modeling of austenite decomposition for an end-quenched 1045 steel