Modeling ductile to brittle transition temperature of functionally graded steels by artificial neural networks

In the present paper, shear buckling analysis of the orthotropic heterogeneous FGM plates is investigated for the first time. Moreover, influence of the Winkler-type elastic foundation is considered. The material properties are assumed to have in-plane orthotropy and transverse heterogeneity. The most accurate approach, i.e., the three-dimensional elasticity is employed instead of using the approximate plate theories. In contrast to all of the available displacement-based buckling analyses that have employed C0-continuous commercial finite element codes or semi-analytical methods, present formulations are C2-continuous due to using the proposed 3D cubic B-spline element. Results are derived based on principle of minimum potential energy and a non-linear finite element procedure utilizing a Galerkin-type 3D cubic B-spline solution algorithm. Buckling loads are detected based on a generalized geometric stiffness concept. In this regard, effects of both the prebuckling and buckling states are considered. To present a better imagination and more detailed discussions, details of the buckling mode shapes and the foundation interaction are discussed for plates with simply-supported edges. In addition, the more practical free and clamped edge conditions are also considered.

Three-dimensional non-linear elasticity-based 3D cubic B-spline finite element shear buckling analysis of rectangular orthotropic FGM plates surrounded by elastic foundations

Microhardness profile prediction of a graded steel by strain gradient plasticity theory

Charpy impact energy of functionally graded steels produced by electroslag remelting composed of graded ferrite and austenite layers together with bainite or martensite intermediate layer in the form of crack arrester configuration has been investigated. The results obtained in the present study indicate that the notch tip position with respect to bainite or martensite layer significantly affects the impact energy. The closer the notch tip to the tougher layer, the higher the impact energy of the composite due to increment of energy absorbed by plastic deformation zone ahead of the notch and vice versa. Empirical relationships have been determined to correlate the impact energy of functionally graded steels to the morphology of layers.

Impact Energy of Functionally Graded Steels in Crack Arrester Configuration

In this article, a model based on gene expression programming for pre- dicting ductile-to-brittle transition temperature of functionally graded steels in both crack divider and crack arrester configurations has been presented. Functionally, graded steels containing graded ferritic and austenitic regions together with bainite and martensite intermediate layers were produced by electroslag remelting. For the purpose of building the model, training and testing using experimental results from 140 specimens produced from two basic composites were conducted. The data used as input in gene expression programming models are arranged in a format of six parameters that cover the FGS type, the crack tip configuration, the thickness of graded ferritic region, the thickness of graded austenitic region, the distance of the notch from bainite or martensite intermediate layer, and temperature. According to these input parameters, in the gene expression programming, the ductile-to-brittle transition temperature of each FGS specimen was predicted. The training and testing results in the gene expression programming model have shown strong potential for predicting the ductile-to-brittle transition temperature of each FGS specimens.

Modeling Ductile-to-Brittle Transition Temperature of Functionally Graded Steels by Gene Expression Programming

Tensile behavior of functionally graded steels produced by electroslag refining has been studied. Functionally graded steels containing layers of ferrite, austenite, bainite, and martensite may be fabricatedvia diffusion of alloying elements during electroslag remelting. Tensile strength of the composites depends on the composition and number of layers and those have been modeled based on the tensile behavior of individual phases. The yield stress of each element in the composites is related to the microhardness value of that element. Considering the Holloman relation for the true stress-strain behavior of each element, the tensile strength of an individual element is also related to the microhardness value of that element. By applying the rule of mixtures, the tensile strengths of the composites were determinedvia the numerical method. The obtained results are in good agreement with the experimental results.

R. Parastar Namin

Papers

Tensile behavior of functionally graded steels produced by electroslag remelting