Josip Brnić

Large rotation analysis of elastic thin-walled beam-type structures using ESA approach

In this work a non-linear analysis of beam-type structures with a thin-walled cross-section is presented. Using updated Lagrangian formulation and the non-linear displacement field of asymmetric cross-section accounting for large rotation effects, the incremental equilibrium equations of a beam element are obtained. Material is assumed to be isotropic and linear elastic. Obtained geometric potential of internal moments corresponds to semitangential behaviour providing the joint equilibrium of non-collinear elements. External stiffness approach is applied in the force recovery phase by introducing the external stiffness matrix. The accuracy of presented finite element algorithm is validated through the test problems.

Tool Material Behavior at Elevated Temperatures

In this article experimentally obtained data related to material mechanical properties, material behavior at elevated temperatures and numerical modeling of material creep responses are presented. Tensile tests at different elevated temperatures are carried out, and for some of these temperatures one-dimensional short time creep tests for different constant stresses are made. Before presented experimental investigations the used materials were not treated. The curves representing specimen strain elongation are also presented. The materials under consideration are 56NiCrMoV7 (1.2714) and X153CrMoV12 (1.2379).

NONLINEAR STABILITY ANALYSIS OF THIN-WALLED FRAMES USING UL{ESA FORMULATION

This work presents a one-dimensional finite element formulation for nonlinear analysis of spaced framed structures with thin-walled cross-sections. Within the framework of updated Lagrangian formulation, the nonlinear displacement field of thin-walled cross-sections, which accounts for restrained warping as well as the second-order displacement terms due to large rotations, the equations of equilibrium are firstly derived for a straight beam element. Due to the nonlinear displacement field, the geometric potential of semitangential moment is obtained for both the torsion and bending moments. In such a way, the joint moment equilibrium conditions of adjacent non-collinear elements are ensured. Force recovering is performed according to the external stiffness approach. Material nonlinearity is introduced for an elastic-perfectly plastic material through the plastic hinge formation at finite element ends and for this a corresponding plastic reduction matrix is determined. The interaction of element forces at the hinge and the possibility of elastic unloading are taken into account. The effectiveness of the numerical algorithm discussed is validated through the test problem.

50CrMo4 Steel-Determination of Mechanical Properties at Lowered and Elevated Temperatures, Creep Behavior and Fracture Toughness Calculation

In this paper some interesting experimentally determined actualities referring to the 50CrMo4 steel are presented. In that way, the material mechanical properties are derived from uniaxial tensile tests at lowered and elevated temperatures. Engineering stress versus strain diagrams for both of mentioned temperatures, curves representing the effect of temperature on specimen elongation and short-time creep curves are given. Notch impact energy test was also carried out. Taking into consideration service life of final product of the mentioned steel widely used in engine and machine technology, all of the mentioned data may be relevant during design and manufacturing procedure.

Structural Steel ASTM A709-Behavior at Uniaxial Tests Conducted at Lowered and Elevated Temperatures, Short-Time Creep Response, and Fracture Toughness Calculation

This paper presents the temperature dependence of the mechanical properties of structural high-strength low-alloy (HSLA) ASTM A709 Gr50 steel (En10025: S355 JO; DIN: ST 52-3U). Engineering stress-strain diagrams at lowered and elevated temperatures are presented. Creep responses for selected constant stresses at selected temperatures are also presented and are fit with a rheological model. Additionally, a relation between impact toughness and fracture toughness is proposed and is validated using results from notch impact tests on a Charpy pendulum impact machine.

Responses of Austenitic Stainless Steel American Iron and Steel Institute (AISI) 303 (1.4305) Subjected to Different Environmental Conditions

In this paper some experimentally obtained results regarding mechanical properties at both low and elevated temperatures as well as short-time creep behavior of American Iron and Steel Institute (AISI) 303 (1.4305) austenitic stainless steel are presented. These results can be of importance in the design procedure for engineering components made of the considered material. The mentioned properties/strengths and short-time creep behavior were determined by uniaxial tests at different temperatures using materials testing machine. Impact energy was determined using the Charpy impact machine, while material hardness was determined using a universal hardness testing machine. For appropriate stress levels at selected temperatures, creep behavior modeling is displayed. Engineering fracture toughness assessment is based on experimentally obtained Charpy V-notch impact energy.

LARGE DISPLACEMENT BEAM MODEL FOR CREEP BUCKLING ANALYSIS OF FRAMED STRUCTURES

In this work, a one-dimensional beam model for buckling analysis of framed structures under large displacement creep regimes is presented. The equilibrium equations of a prismatic and straight spatial beam element are formulated in the framework of corotational description, using the virtual work principle. Although the translations and rotations of the element are allowed to be large, the strains are assumed to be small. The material of a framed structure is assumed to be homogenous and isotropic. The bilinear elastic–plastic model with isotropic hardening and the power creep law are adopted for describing the inelastic behavior of the material. The numerical algorithm is implemented in a computer program called BMCA and its reliability is validated through test examples.

Updated Lagrangian formulation for nonlinear stability analysis of thin-walled frames with semi-rigid connections

This paper presents a one-dimensional (1D) finite element formulation for the nonlinear stability analysis of framed structures with semi-rigid (SR) connections. By applying the updated Lagrangian incremental formulation and the nonlinear displacement field of thin-walled cross sections, the equilibrium equations of a straight beam element are first developed. Force recovering is performed according to the external stiffness approach. Material nonlinearity is introduced for an elastic-perfectly plastic material through the plastic hinge formation at finite element ends. To account for the SR connection behavior, a special transformation procedure is developed. The effectiveness of the numerical algorithm discussed is validated through the test problems.

Analysis of the Mechanical Behavior, Creep Resistance and Uniaxial Fatigue Strength of Martensitic Steel X46Cr13

The article deals with the analysis of the mechanical behavior at different temperatures, uniaxial creep and uniaxial fatigue of martensitic steel X46Cr13 (1.4034, AISI 420). For the purpose of considering the aforementioned mechanical behavior, as well as determining the appropriate resistance to creep and fatigue strength levels, numerous uniaxial tests were carried out. Tests related to mechanical properties performed at different temperatures are presented in the form of engineering stress-strain diagrams. Short-time creep tests performed at different temperatures and different stress levels are presented in the form of creep curves. Fatigue tests carried out at stress ratios R=0.25 and R=−1 are shown in the form of S–N (fatigue) diagrams. The finite fatigue regime for each of the mentioned stress ratios is modeled by an inclined log line, while the infinite fatigue regime is modeled by a horizontal line, which represents the fatigue limit of the material and previously was calculated by the modified staircase method. Finally, the fracture toughness has been calculated based on the Charpy V-notch impact energy.

Mechanical Properties, Short Time Creep, and Fatigue of an Austenitic Steel

The correct choice of a material in the process of structural design is the most important task. This study deals with determining and analyzing the mechanical properties of the material, and the material resistance to short-time creep and fatigue. The material under consideration in this investigation is austenitic stainless steel X6CrNiTi18-10. The results presenting ultimate tensile strength and 0.2 offset yield strength at room and elevated temperatures are displayed in the form of engineering stress-strain diagrams. Besides, the creep behavior of the steel is presented in the form of creep curves. The material is consequently considered to be creep resistant at temperatures of 400 °C and 500 °C when subjected to a stress which is less than 0.9 of the yield strength at the mentioned temperatures. Even when the applied stress at a temperature of 600 °C is less than 0.5 of the yield strength, the steel may be considered as resistant to creep. Cyclic tensile fatigue tests were carried out at stress ratio R = 0.25 using a servo-pulser machine and the results were recorded. The analysis shows that the stress level of 434.33 MPa can be adopted as a fatigue limit. The impact energy was also determined and the fracture toughness assessed.