Constitutive Equation for Flow Stress in Superalloy 718 by Inverse Analysis under Hot Forming in a Region of Precipitation

The purpose of this study is to obtain a constitutive equation of high-accuracy flow stress in superalloy 718, which allows fabrication of highly reliable disks for gas turbine engines. Hot compression tests using superalloy 718 at deformation temperatures from 850 to 1100 °C, a 67% height reduction, and strain rates of 1, 10, and 25 s−1 were performed to investigate the flow stress behavior, which excludes environmental effects during hot working by inverse analysis. The effects of dynamic recrystallization and strain-induced dynamic precipitation on the flow stress were also investigated. The dynamically precipitated δ phases deformed at 1050 °C and γ″ phases deformed at 950 °C might affect the increase in the plastic modulus F1 and the decrease in the critical strain εc, deteriorating the accuracy of regression in terms of, for example, the strain rate sensitivity m and the temperature sensitivity A. A constitutive equation for a generalized flow curve for superalloy 718 is proposed by considering these effects.

Analytical and numerical study of influence of the shape of the section on lateral buckling of doubly symmetrical sections

This paper presents an analytical and numerical study of the lateral buckling of beams with double symmetrical I and H cross sections having substantially the same plastic modulus of resistance around the strong axis subjected by a uniformly distributed load in order to understand the influence of the one of the forms during lateral buckling. For this, a critical elastic moment analysis is carried out using ANSYS software using the element SHELL181 and analytical formulas from Eurocode3. Finally, there is a presentation of the non-linear behavior of these two cross sections.

Studi Analitik Karakteristik Penampang Baja Profil-I

Paper ini menyajikan hasil studi analitik tentang besaran karakteristik penampang baja profil-I berupa modulus elastis (Sx) dan modulus plastis penampang (Zx). Faktor bentuk penampang, yang merupakan perbandingan nilai Zx terhadap Sx, merupakan besaran utama yang digunakan untuk menghitung kapasitas momen plastis penampang baja. Khusus untuk baja profil-I yang dibuat dengan metoda canai panas, pada bidang pertemuan antara bagian sayap dan bagian badan terdapat bagian penampang seperempat lingkaran cekung yang memberikan kontribusi untuk nilai total besaran karakteristik penampang. Dalam penelitian ini, besaran karakteristik penampang dihitung dan dianalisis dengan menggunakan besaran karakteristik penampang dasar persegi panjang dan lingkaran. Analisa hasil perhitungan menunjukkan bahwa bagian penampang seperempat lingkaran cekung tersebut memberikan kontribusi yang konsisten terhadap nilai luas, modulus elastis dan plastis penampang, yakni dalam rentang sebesar 1.0 – 4,7%. Dari hasil penelitian ini juga diperoleh bahwa faktor bentuk penampang untuk profil-I yang umum digunakan berada dalam rentang nilai 1,102 – 1,147. Perhitungan nilai faktor bentuk penampang dengan dan tanpa mengikutsertakan bagian penampang seperempat lingkaran cekung memberikan hasil yang hampir sama dengan selisih rata-rata sebesar 0,001. Modulus plastis penampang dapat dihitung dengan menggunakan formula sederhana yang diusulkan pada artikel ini dengan tingkat akurasi yang sangat baik dengan deviasi sebesar 1.2 %. Untuk semua jenis ukuran penampang profil-I, formula ini bisa digunakan untuk menghitung modulus plastis penampang secara lebih sederhana. This paper presents the results of an analytical study of the characteristics of the I-profile steel cross-section in the form of elastic modulus (Sx) and plastic section modulus (Zx). The shape factor of the section, which is defined as the ratio of the value of Zx to Sx, is the principal quantity used to calculate the plastic cross-section moment capacity. Specifically for I-profile steels made by the hot-rolled process, in the area of ​​the junction between the flange and the web, there is a concave cross-section that contributes to the total value of the section characteristic. In this study, the magnitude of the cross-sectional characteristics is calculated and analyzed using the magnitude of the basic cross-section characteristics of rectangles and circles. Analysis of the calculation results shows that the cross-section of the concave quarter circle provides a consistent contribution to the area, elastic and plastic section modulus, which is in the range of 1.0 - 4.7%. From the results of this study, it was also found that the shape factor for the I-profile commonly used is in the range of values ​​1.102 - 1.147. Calculation of the cross-section form factor values ​​with and without including the concave quarter circle gives results that are almost the same as the average difference of 0.001. The plastic modulus of the cross-section can be calculated using the simple formula proposed in this article with a very good degree of accuracy with a deviation of 1.2%. For all types of I-profile cross-section sizes, this formula can be used to calculate the plastic section modulus easily.

Modeling Static Behavior of Rockfill Materials Based on Generalized Plasticity Model

Rockfill materials are commonly used for dam construction. Establishing an effective model that can reasonably describe the mechanical properties of rockfill material is very important for the calculation of earth-rock dam engineering. Based on the generalized plasticity model of sand, a modified generalized plasticity model suitable for rockfill material is established by modifying the plastic modulus. Focusing on three types of stress paths (e.g., CT test, CP test, and CR test), the stress path adaptability of the modified generalized plasticity is studied. Simulation results show that the proposed model can well predict the strength characteristics while it underestimates the shrinkage characteristics of rockfill materials for constant P test. It is difficult for the generalized plasticity model to predict larger radial shrinkage strain for constant stress ratio tests. This shortcoming can be improved by employing a modified dilatancy equation. Finally, by introducing critical state theory and considering the effect of initial void ratio on plastic modulus, a state-dependent generalized plasticity model is proposed and verified by experiment of granite rockfill materials and TRM with different void ratios. These works covers the most common stress paths related to the construction of earth-rock dams and can capture static behavior of rockfill materials.

Fully Atomistic Molecular Dynamics Computation of Physico-Mechanical Properties of PB, PS, and SBS

The physical properties—including density, glass transition temperature (Tg), and tensile properties—of polybutadiene (PB), polystyrene (PS) and poly (styrene-butadiene-styrene: SBS) block copolymer were predicted by using atomistic molecular dynamics (MD) simulation. At 100 K, for PB and SBS under uniaxial tension with strain rate ε ˙ = 1010 s−1 and 109 s−1, their stress–strain curves had four features, i.e., elastic, yield, softening, and strain hardening. At 300 K, the tensile curves of the three polymers with strain rates between 108 s−1 and 1010 s−1 exhibited strain hardening following elastic regime. The values of Young’s moduli of the copolymers were independent of strain rate. The plastic modulus of PS was independent of strain rate, but the Young’s moduli of PB and SBS depended on strain rate under the same conditions. After extrapolating the Young’s moduli of PB and SBS at strain rates of 0.01–1 s−1 by the linearized Eyring-like model, the predicted results by MD simulations were in accordance well with experimental results, which demonstrate that MD results are feasible for design of new materials.

The New Method in Calculating Columns and Beams Dimensions That Meets Requirements of The Strong Column-Weak Beam and Non-Soft Story

Situated at an earthquake prone area, buildings planning in Indonesia must implement earthquake resistant building principles. One of these principles is determining dimensions of columns and beams in the process of architectural designing.This act eventually affects the behaviour of the strong column-weak beam and the probability of bending failure due to soft story. At present time, there are no simple rules architects can use in calculating the dimensions of beams and columns that meet the criteria for strong column-weak beam and non-soft story. This paper is an effort to provide an input to the architects in designing the dimensions of the columns and beams. This research is a review result of three theories namely: 1). The theory of columns and beams preliminary design, 2). The theory of the strong column-weak beam concept, and 3). The theory of soft story and column slenderness. Those theories were then synthesized into a spreadsheet. To meet the criteria for strong column-weak beam and non-soft story, the following procedures must be done : 1). Determine the columns’ dimensions according to 0.15% of the columns’ cumulative tributary area, 2). Determine the beams’ dimensions according to 1/12 of the beams’ span and the beams’ plastic modulus, 3). Determine the columns’ dimensions and the columns’plastic modulus, 4). Determine the columns’ height based on the column slenderness criteria, and 5). Compare the columns plastic modulus and the beams plastic modulus and check whether they meet the criteria “the columns’plastic modulus ≥ 1.2 * the beams’ plastic modulus”.

Identification strategy influence of elastoplastic behavior law parameters on Gurson–Tvergaard–Needleman damage parameters: Application to DP980 steel

This work adopts elastic–plastic/damage coupling in order to describe tensile behavior with validation on the deep-drawing test of a DP980 Dual Phase steel sheet. The damage model used is the Gurson–Tvergaard–Needleman (GTN model). The hardening laws used are those of Swift (non-saturating law), Voce (saturating law), Hockett-Sherby (saturating law) and the two combined laws Swift/Hockett-Sherby and Swift/Voce. An identifying method for elastic–plastic parameters and GTN damage model parameters is presented using the software modeFRONTIER. This method based on the inverse analysis is also proposed for the identification of weighting coefficient α of the Swift/Hockett-Sherby combined hardening law. Finally, a parametric study was carried out to show that the plastic modulus can be considered as another criterion for the choice of a hardening law. Dependence of the damage model parameters to the hardening law is clearly established. The different behavior laws are introduced via a VUHARD type subroutine in the calculation code Abaqus.

Numerical Simulation of Spherical Indentation Method to Identify Metal Material Properties

The main objective of this paper is to study the indentation process of the spherical indenter by finite element method (FEM). Elastic-plastic model is established and the effect of metal material properties (plastic modulus, yield strength) on response of load-displacement curve during the loading-unloading process is discussed in detail. FEM results indicate that the maximum indentation depths are smaller with larger plastic modulus. For elastic–perfectly plastic materials, the equivalent plastic strain (EPS) grows with the increase of pressed depth and the plastic impact area is constantly changing. In addition, the generated Max depth decreases with the increase of yield strength under the same load. Besides, friction coefficients have little effect on the indentation process. This research provides a theoretical basis for experiment and engineering.