Experimental investigation of steel 45 along some smooth curvilinear strain trajectory

В работе представлены экспериментальные результаты деформирования тонкостенного трубчатого образца по гладкой криволинейной траектории деформирования постоянной кривизны, в которой на каждом участке изменяется знак кривизны и смещается ее центр. Экспериментальное исследование выполнено на автоматизированном расчетноэкспериментальном комплексе СН-ЭВМ в девиаторном пространстве деформаций А.А. Ильюшина (жесткое нагружение) при одновременном комбинированном действии на тонкостенный трубчатый образец растяжения-сжатия и кручения. Исследованы скалярные и векторные свойства материала стать 45. Показано, что экспериментальные диаграммы, характеризующие скалярные и векторные свойства материала носят колебательный характер. The paper presents experimental results of deformation of a thin-walled tubular specimen along a smooth curvilinear strain trajectory of constant curvature, in which the sign of curvature changes at each section and its center shifts. Experimental data were obtained on the automated calculation-experimental complex SN-Computer in the deviator space of deformations A.A. Ilyushin (rigid loading) with a simultaneous combined action on the specimen of tensioncompression and torsion. Scalar and vector material properties of steel 45 are investigated. It is shown that experimental diagrams characterizing scalar and vector properties of the material have oscillatory character.

The effect of replacing non-analytic trajectories with break points on smooth paths to the complexity of deformation and loading processes of materials

This article is devoted to an experimental study of the effect of rounding off corner points of two-link strain trajectories on complex loading processes during elastoplastic deformation of materials. Replacing corner points in their vicinity with local sections of circles allows a nonanalytic trajectory to be replaced with a smooth trajectory. Experimental studies were performed on thin-walled tubular specimens of the low-carbon steel St3 on an SN-EVM automated testing system. The loading programs for tubular specimens were set in the Ilyushin's deviatoric strain space. The rounding of the corner point of a two-link strain trajectory with an angle of 90° between the branches by arcs of circles with curvatures of 200, 400, as well as the rounding of the corner point of a two-link strain trajectory with an angle of 135° between the branches by arcs with curvatures of 400, 800 are considered. The experimental data characterizing the vector and scalar properties of the material are presented. The experimental data show that the effect of complex loading on the relationship between stresses and strains in a curved section is not immediately apparent. In the curved section, the magnitude of the stress vector modulus first increases, and then decreases with the formation of stress dives. The minimum point of the stress dive is located on the next straight branch of the strain trajectory. In the curvilinear section, the angle of delay increases, and in the next straight branch it decreases, and with the increase of the strain it tends to be zero. The rate of decrease of the angle of delay depends little on the differences in the geometry of the previous history of strain trajectory. In the second straight branch, the experimental results for a smooth and original two-link strain trajectories become little distinguishable from each other. Thus, replacing the original non-analytical strain trajectory to a smooth trajectory affects the complexity of the process of deformation and loading of the materials only in the vicinity of the corner point. This circumstance can be taken into account when numerically modeling the processes of elastoplastic deformation of materials and integrating the defining relations, replacing nonanalytic trajectories with smooth ones. This can be taken into account in the numerical calculation of elastic-plastic deformation and integration of constitutive relations, replacing non-analytical strain trajectories by smooth ones.

Semi-Forward Adaptive Simulation Approach for Tube Hydroforming Loading Path Determination Using a Strain Trajectory Based Fuzzy Logic Control

Tube hydroforming process is a well-established manufacturing process widely employed to form tubular parts that are lighter and stronger compared to those from stampings. Nevertheless, determination of process loading paths, i.e. axial feed distance versus hydraulic pressure, still typically relies on trial-and-error FEM approach. In this paper, a semi-forward adaptive simulation concept is proposed as an effective FEM approach, able to select a feasible THF loading path within a single FEM simulation run. The semi-forward adaptive simulation technique is based on the ability to “adapt” or adjust the loading path as to keep the forming strains within a preferred stain trajectory over the course of a simulation run. Forming strains at the current simulation time step are used as inputs to the fuzzy logic control; the output sets are then used to readjust the loading path for the current and next time steps. This semi-forward adaptive simulation scheme allows one to “correct” the loading path at the current time step as well as to better predict the forming strains in the next time step. It was found that the corrective and predictive nature of this semi-forward simulation approach coupled with the strain trajectory based fuzzy logic control scheme could handle a highly non-linear forming behavior of tube hydroforming processes effectively. In this work, a feasible loading path was determined thru only one simulation run for successful hydroforming of an eccentric bulged tubular part.

The Effect of Material Models on Elastic Follow-Up

The phenomenon of elastic follow-up in high temperature piping has a long history and rules to limit its significance in design are well established. However, most design rules, and numerous associated supporting studies, have been limited to a simple power-law of creep, with variations to account for time- or strain-hardening in primary creep. A common feature of the most studies of elastic follow-up in structures subject to power-law creep is that a plot of (maximum) stress against strain—a so-called isochronous stress– strain trajectory—is almost insensitive to the creep law (in particular, the stress exponent in the power-law) and is almost linear (until perhaps the later stages of stress relaxation). A limitation of the power-law is that it assumes to be valid across all stress ranges, from low through moderate to high, yet it is well known that this is not generally the case. This paper aims to investigate the effect of stress-range dependent material models on the nature of elastic follow-up: both a simple two-bar structure (common in studies of elastic follow-up) and a detailed finite element analysis of a piping elbow are examined. It is found that stress-range dependent material models can have a significant effect on the accepted characteristics of elastic follow-up.

Stress relaxation and elastic follow-up using a stress range-dependent constitutive model

Despite the availability of detailed non-linear finite element analysis (FEA), some aspects of high-temperature design can still be best addressed through more simplified methods. One such simplified method relates to the problem of elastic follow-up where, typically in strain-controlled situations, elastic behaviour in one part of a structure can lead to large strain accumulation in another. Over the past 30 years, it has been shown that in regions with significant elastic follow-up, a plot of maximum stress against strain (a ‘stress-strain trajectory’) is virtually independent of the constitutive relation – a characteristic which can be used to estimate elastic follow-up for design purposes without detailed non-linear FEA. The majority of studies which have reported this independence on material behaviour have used simple constitutive models for creep strain, primarily based on power-law creep or variations. Recently, studies of the behaviour of high-temperature structures with a stress range-dependent constitutive law have begun to emerge. This article examines the problem of elastic follow-up using such a constitutive law for a classic two-bar structure and for a more complex structure using FEA. It is found that the independence of the stress–strain trajectory on constitutive equation is lost with a stress range-dependent relation.

Prediction of Mechanical Behavior of Equivalent Adhesive-Layer Using Theory of Duality of Famage

Concepts of equivalent adhesive-layer and Theory of Duality of Damage (TDD) are presented. Basic idea of the TDD is to assume that material damaged consists of two parts, i.e., Relative Non-Damaged Part (RNDP) and Complete Damaged Part (CDP). The mechanical behaviors of the material damaged can be simulated simultaneously by both mechanical behaviors of the RNDP and the CDP. The RNDP can be simulated by linear-elasticity and non-linear elasticity, respectively. The CDP can be approximately determined in engineering significant. Observed stress-strain relation of the equivalent adhesive layer of a steel/steel butt joint is measured. Evolution equation of damage of the equivalent adhesive-layer is established, and increment equation of stress-strain including effect of damage is given. The observed stress-strain relation is predicted through four damage parameters, i.e., plastic strain trajectory, plastic strain energy density, total strain trajectory, and total strain energy density. As a result, it is shown that the stress-strain curves predicted are of consistence with the observed stress-strain curve. The result predicted using total strain trajectory is better than others. It should be pointed out that the method presented in this paper could be applied to a variety of damaged structures not only to the equivalent adhesive-layer.

The mechanical power output of the pectoralis muscle of blue-breasted quail (Coturnix chinensis): thein vivolength cycle and its implications for muscle performance

SUMMARYSonomicrometry and electromyographic (EMG) recordings were made for the pectoralis muscle of blue-breasted quail (Coturnix chinensis) during take-off and horizontal flight. In both modes of flight, the pectoralis strain trajectory was asymmetrical, with 70 % of the total cycle time spent shortening. EMG activity was found to start just before mid-upstroke and continued into the downstroke. The wingbeat frequency was 23 Hz, and the total strain was 23 % of the mean resting length.Bundles of fibres were dissected from the pectoralis and subjected in vitro to the in vivo length and activity patterns, whilst measuring force. The net power output was only 80 W kg–1 because of a large artefact in the force record during lengthening. For more realistic estimates of the pectoralis power output, we ignored the power absorbed by the muscle bundles during lengthening. The net power output during shortening averaged over the entire cycle was approximately 350 W kg–1, and in several preparations over 400 W kg–1. Sawtooth cycles were also examined for comparison with the simulation cycles, which were identical in all respects apart from the velocity profile. The power output during these cycles was found to be 14 % lower than during the in vivo strain trajectory. This difference was due to a higher velocity of stretch, which resulted in greater activation and higher power output throughout the later part of shortening, and the increase in shortening velocity towards the end of shortening, which facilitated deactivation.The muscle was found to operate at a mean length shorter than the plateau of the length/force relationship, which resulted in the isometric stress measured at the mean resting length being lower than is typically reported for striated muscle.