The effect of the roller profile oncave-in defect in reshaping processby considering nonlinear combine strain hardening

The reshaping process of pipes is an important method in producing non-circular pipes. Desired profile products are produced by passing round pipe through the rotating rollers. Cave-in defect is one of the common defects in the reshaping process. Roller design issues can decrease this kind of defect. In this paper, a method based on the slab method and the incremental plasticity has been presented to the numerical study of a 2D reshaping process. For investigating the Cave-in defect, the contact model has been developed. The concept of element elongation has been introduced to increase the accuracy of the contact model. Based on the presented method, numerical software has been developed to simulate the 2D reshaping process. Elastic-plastic equations for this subject have been driven based on the incremental method, J yielding criterion, and non-linear combined hardening. The effects of the radius of the roller profile on cave-in defects have been investigated by using the presented software (DARF). A set of experiments has been conducted in a forming station to verify the results. Results show that the presented model has higher accuracy than the Abaqus commercial software in predicting the cave-in defect. Based on the results of the model, the local increase of yielding stress directly affects the cave-in defect. Also, a meaningful relationship between the radius of the roller and the amount of the cave-in has been observed.

Investigating the Effect of Internal Pressure and Thickness of Thick-Walled Cylindrical Vessels on the Ratcheting Strains under Compressive Cycling Loading Using the Quasi-Creep Method

Thick-walled vessels have many applications in military, chemical, and aerospace industries and also in nuclear facilities. Increasing the internal pressure inside these vessels can take some of the layers of the vessel into the plastic zone. If this happens several times, we will see the accumulation of plastic strains called ratcheting. This paper assumes that the thick-walled vessel is subjected to a cyclic internal pressure between zero and a maximum value. In order to analyze this phenomenon, first, we present the quasi-creep method, and then we validate this method using the finite element Abaqus Software based on the combined hardening model. Then we employ this method to evaluate the effect of internal pressure and thickness of the vessel on the amount of ratcheting strains in different cycles. In the end, the results of this research and the accuracy and speed of the quasi-creep method are stated.

Technological features of anode dissolution in a combined hardening treatment when developing high-speed rotors

Is studied of the features of anodic dissolution in the process of local combined processing of metal removal points with surface defects arising during balancing of high-speed rotors in connection with the softening of working surfaces from unwanted technological heredity. The ways of improving the processes of their technological refinement using local hardening methods are shown, calculation formulas are given technological parameters of the anode process.

Material Flow in Infeed Rotary Swaging of Tubes

Rotary swaging is an incremental metal forming process widely used to reduce the cross–section of parts. For tubular parts, the final wall thickness also changes during the process. The lubricant condition is a factor, which affects these geometry changes. Beneath the change of the geometry, the complex material flow during the process determines the final geometry and the mechanical properties. Therefore, with a thorough insight into the material flow, it could be understood how to control it in order to achieve desired properties. Producing tubes with uniform outer diameter and changing inner profiles is an application of this method. Furthermore, applying this method, different local cold hardening could be achieved by different total strain. In this study, the dependency of the material flow on the lubrication conditions was investigated. Simulations with combined hardening material models were verified by the change of the wall thickness of tubes. It was found that friction condition significantly influences the back shifting of the workpiece and the elongation caused by each stroke. Results from simulations and experiments showed that a certain lubricant condition leads to the highest axial elongation of the workpiece.

Investigation of Hardening Law on Welding Residual Stress Analysis for Nickel Based Alloy 82 Weld Metal

There are three types of hardening laws for evaluating welding residual stress with the finite element method (FEM): kinematic hardening law, isotropic hardening law, and combined hardening law that combine these. The purpose of this paper is to investigate which hardening law is more appropriate for the evaluation of welding residual stress of alloy 82. We first performed two types of welding tests: welding both ends of a plate, and welding the periphery of a disc. We then compared the results of mock-up welding tests with the analysis results of welding residual stress with the kinematic hardening law and combined hardening law. Both the kinematic hardening law and the combined hardening law showed a welding residual stress distribution close to the results of the mock-up welding tests, but the combined hardening law tended to be closer to the mock-up results. Therefore when it is necessary to confirm the welding residual stress of alloy 82, it is considered appropriate to apply the combined hardening law.

Mode I Ductile Crack Growth of 1TC(T) Specimen Under Large Cyclic Loading: Part IV

Ductile crack growth calculation method under excessive cyclic loading in a fitness for service rule has not been established even in Mode I. Since 2017 to 2019 the author had tried to establish how to determine the parameters of the combined hardening rule and applied it to simulate the ductile crack growth behavior of the 1TC(T) specimens of the different loading levels for ferritic steel. Also ΔJ calculation using the reference stress method, and the transferred crack growth rate from a code were applied to estimate the ductile crack growth. Several equations of the reference stress method were tried to apply in the previous paper. Further the prediction procedure using the ΔJ, the reference stress method and da/dN-ΔJ curve based on the JSME rules on fitness for service (FFS) was applied to the pipe fracture tests under cyclic loading and its applicability was discussed for the case of a pipe structure in the previous paper. In this paper similar procedures were applied to 1TC(T) specimens of stainless steel. The combined hardening rule was applied for the constitution law of stress-strain curve. The numerical simulation with the combined rule traced the load-load line displacement curve under the cyclic loading experiments of 1TC(T). Also austenitic stainless fatigue crack growth rate (FCGR) in air condition from the JSME rules on FFS bounded the experimental crack growth rate, which means the FCGR of the JSME rules is applicable to fatigue crack growth calculation.

Surface Hardening of Machine Parts Using Nitriding and TiN Coating Deposition in Glow Discharge

Surface hardening of machine parts substantially improves their performance. The best results are obtained when combined hardening consists of surface nitriding and subsequent deposition of hard coatings. The nitriding of machine parts immersed in the plasma of glow coatings have been studied, and the study results are presented. Titanium atoms for coating synthesis are obtained via titanium evaporation in a hollow molybdenum anode of the discharge. Stable evaporation of titanium occurs only when the power density of electrons heating the liquid titanium does not exceed ~500 W/cm2. To start evaporation, it is only necessary to reduce the gas pressure to 0.02 Pa. To stop evaporation, it is enough to increase the gas pressure to 0.1 Pa. Fast argon and nitrogen atoms used for cleaning the machine parts, heating them, and bombarding the growing coating are obtained using a grid composed of plane-parallel plates under high negative voltage and immersed in plasma.