Stress Of AISI Research Articles

Minimization of Milling-Induced Residual Stresses in AISI 1045 Steel: Process Optimization using Design of Experiments Taguchi Method

Minimization of Milling-Induced Residual Stresses in AISI 1045 Steel: Process Optimization using Design of Experiments Taguchi Method

Investigation of the effect of residual stresses in the subsurface on process forces for consecutive orthogonal cuts

The quality and surface integrity of machined parts is influenced by residual stresses in the subsurface resulting from cutting operations. These stress characteristics can not only affect functional properties such as fatigue life, but also the process forces during machining. Especially for orthogonal cutting as an appropriate experimental analogy setup for machining operations like milling, different undeformed chip thicknesses cause specific residual stress formations in the subsurface area. In this work, the process-related depth profile of the residual stress in AISI 4140 was investigated and correlated to the resulting cutting forces. Furthermore, an analysis of the microstructure of the cut material was performed, using additional characterization techniques such as electron backscatter diffraction and nanoindentation to account for subsurface alterations. On this basis, the influence of process-related stress profiles on the process forces for consecutive orthogonal cutting strategies is evaluated and compared to the results of a numerical model. The insights obtained provide a basis for future investigations on, e. g., empirical modeling of process forces including the influence of process-specific characteristics such as residual stress.

Turning parameters effects in residual stresses of AISI 1045 steel

The main objective of this work was to evaluate the influence of turning parameters on the generation of residual stresses in AISI 1045 steel bars. Therefore, effects of four main parameters as feed rate, cutting velocity, tool nose radius, and rake angle were analyzed. Residual stresses investigation through X-ray diffraction (XRD) was carried out at different depths (surface, 5, 10, 20, 50, and 75 μm). As the samples showed distinct roughness patterns with variable amplitude and shape, and based in a previous work, samples were classified in two main groups accordingly with surface finishing (regular and irregular). The current results showed that feed rate and cutting speed played the major influence on residual stress distributions. Moreover, the tool nose radius affected surface residual stresses, whereas the rake angle did not significantly change it. Finally, samples could be divided in two residual stress groups, showing a direct relation of surface finishing quality and residual stresses.

Effect of Speed, Feed and Depth of Cut on Machining Induced Residual Stresses in Aisi 1045 Steel

Residual stress that are induced during machining of components plays a significant part in the endurance and life of the component. The magnitude and nature of the residual stresses have been of interest to many researchers across the globe. The present work involves methodology to find out the influence of factors on the residual stresses. The machining parameters were varied and the residual stresses were determined using non-destructive method, namely X-ray diffraction. Using statistical methods, the influence of the machining parameters was ascertained. This paper aims at investigating the residual stresses in AISI 1045 steel, induced due to milling. AISI 1045 steel was considered as it is a widely used material and its applications are innumerable. It was observed that speed and feed have significant influence on stresses left behind after the machining is completed. Using statistical techniques a mathematical model was developed which is further used to predict the residual stresses. The error percentage of the predicted values was less than 5%. The results obtained were promising and future work involves the optimization of the machining parameters.

Effect of multi-dimensional ultrasonic-assisted pulsed-laser surface irradiation on residual stress in AISI 1045 steel

The multi-dimensional ultrasonic-assisted pulsed-laser surface irradiation method was introduced to relieve the residual stress in the AISI 1045 steel specimen based on the Nd:YAG pulsed-laser machine. In this stress relief process, the acoustic energy was imposed into the AISI 1045 steel specimen accompanied by the pulsed-laser surface irradiation, which could be called as the multi-dimensional ultrasonic-assisted stress relief (MDUASR). The mechanism of the MDUASR was discussed based on the thermal activation theory. In addition, the experiments for the MDUASR and the multi-dimensional ultrasonic stress relief (MDUSR) were carried out to validate the residual stress relieving effect and the energy-saving effect of the MDUASR. The results show that the MDUASR has good effect on relieving residual stress and the MDUASR can reduce the energy consumption compared with the MDUSR. Furthermore, the mechanism of the MDUASR can be attributed to the metal softening effect and the dynamic stress effect. The findings confirm that the thermal energy induced by pulsed-laser surface irradiation can be adequately utilized to enhance the metal plasticity, which results in that the residual stress relieving effect of the MDUASR can be improved compared with the MDUSR. It can be concluded that the MDUASR belongs to an energy-saving and green environmental protection technology during the manufacturing process.

Application of high-energy oscillating electric current pulse to relieve pulsed-laser surface irradiation induced residual stress in AISI 1045 steel

Abstract

Laser peening without coating induced phase transformation and thermal relaxation of residual stresses in AISI 321 steel

Abstract Laser peening without coating (LPwC) was performed on austenitic stainless steel AISI 321 with a power density of 5.97 GW cm − 2 and pulse densities of 1600, 2500 and 3900 pulses cm − 2 . A large compressive residual stress resulted for 1600 pulses cm − 2 . Surface roughness was found to have increased to a relatively smaller extent with lesser number of valleys or peaks. Micro-hardness increased after the process with the depth of hardened layer extending up to 900 μm. LPwC induced martensitic phase transformation (about 18% in volume fraction) was observed near treated surface. Microstructures confirmed the phase transformation effect. The grains were not refined as a result of single LPwC scan. Thermal relaxation of residual stresses at 700 °C for 2 h were 41% in longitudinal and 140% in transverse (relative to LPwC scanning) directions. The influential factors on stress relaxation were discussed. No significant reduction in hardness was seen after thermal treatment. Followed by the thermal treatment, fully austenitic phase was recovered.

Application of Computational Intelligence and Knowledge-Based System in Predicting Flow Stress of AISI 4340

Prediction of flow stress of any engineering material is vital for modeling its plastic deformation process and for having estimate of force and power requirements in various manufacturing processes. The paper focuses on the application of two most important tools of artificial intelligence: computational intelligence and knowledge-based system, in predicting flow stress of a common high-strength low-alloy steel type, AISI 4340. The estimation process is based on different settings of material’s microstructure (quantified by hardness), applied temperature, strain, and strain rate. The simulation results of both tools show a great deal of agreement with the experimental data. The prediction results are also compared with the estimations made by a commonly used empirical model.

Flow Stress Optimization for Machining Simulations

Flow stress is a vital input data for machining simulations, which is experimentally measured from Split Hopkinson pressure bar (SHPB) tests. However such flow stress does not fit machining conditions of strain, strain rate and temperatures and lead to serious simulation errors. In this research work an integrated Taguchi – Finite element (FE) methodology is adopted to optimize the flow stress of AISI 1045 steel material for orthogonal machining. The flow stress computed from the optimization approach along with thermo physical material properties are input into the FE code. The FE cutting forces and chip thickness ratio (CTR) showed an improvement of 6-8% and 2-4% over conventional Johnson – Cook (JC) models. An optimum set of JC model parameters were found from the study. The JC parametric analysis indicated high cutting force sensitivity to yield strength and CTR sensitivity to yield strength, strain hardening and thermal softening.

Changes in the axial residual stresses in AISI 1045 steel bars resulting from a combined drawing process chain

The present paper investigates the redistribution of residual stresses resulting from manufacturing steps in the production of cold-drawn AISI 1045 steel bars. The main steps in this process chain are the pre-straightening of coiled material, shot-blasting, cold-drawing, cutting, and final straightening with crossed rolls. Drawing and final straightening parameters were changed to evaluate their influence on the residual stress distributions as measured by X-ray diffraction and hole-drilling techniques after the different manufacturing steps. It was found that, depending on the manufacturing parameters, the pre-straightened material generates non-homogeneity of residual stresses which can remain even after the last manufacturing steps. The angle between the crossed rolls in the final straightening has a high influence on the homogeneity of the surface residual stresses. Both the drawing angle and the angle between the crossed rolls significantly affect the residual stress depth distribution.

Numerical analysis of the tool wear effect in the machining induced residual stresses

Machining is a dynamic process involving coupled phenomena: high strain and strain rate and high temperature. Prediction of machining induced residual stresses is an interesting objective at the manufacturing processes modelling field. Tool wear results in a change of tool geometry affecting thermo-mechanical phenomena and thus has a significant effect on residual stresses. The experimental study of the tool wear influence in residual stresses is difficult due to the need of controlling wear evolution during cutting. Also the involved phenomena make the analysis extremely difficult. On the other hand, Finite Element Analysis (FEA) is a powerful tool used to simulate cutting processes, allowing the analysis of different parameters influent on machining induced residual stresses. The aim of this work is to develop and to validate a numerical model to analyse the tool wear effect in machining induced residual stresses. Main advantages of the model presented in this work are, reduced mesh distortion, the possibility to simulate long length machined surface and time-efficiency. The model was validated with experimental tests carried out with controlled worn geometry generated by electro-discharge machining (EDM). The model was applied to predict machining induced residual stresses in AISI 316 L and reasonable agreement with experimental results were found.

Investigation on the Residual Stress of AISI 4047 Low Alloy Steel Laser Welded

The residual stress in steel welding can highly influences the performance of the joint during its working life. Both boundary conditions and metal phase transformations have influence on the levels of the residual stress in the weld. In this paper the residual stress for AISI 4047 bead-on-plate samples were measured by strain gage method after laser welding with different values for the laser speed and power, and focus height. The laser used for this project was the ROFIN DC 015 Industrial CO2 Slab Laser. This laser, registered as class 4 laser product in accordance with the European Norm EN 60825 is an high frequency excited, diffusion cooled C02 gas laser, designed to be used for processing materials in a industrial environment. The measurement procedure was performed on all the welded specimens taking notes of 3 strains (ε1 ε2 ε3) relative to as many gages at different depths, following the American Society for Testing Materials (ASTM) standard. Thereafter the residual stresses were calculated by means of a non-linear finite element analysis. The analysis took in account the thermo-mechanical phenomena with temperature dependent steel properties. The other considered also the phase transformation and phase-dependent thermal and mechanical properties.

Relaxation of Residual Stress in AISI 347 Welded Pipe: A Time-of-Flight Neutron Diffraction Study

Abstract The residual stress state in an AISI 347 welded pipe for nuclear applications has been investigated by means of neutron time-of-flight diffraction. Two kinds of welds were compared: a ‘bare’ manual and a dressed tungsten inert gas (m-TIG with and without last pass heat sink, respectively). Thorough investigations along a line transverse to the weld seam and through-thickness have been carried out with very fine-step scans. Complementary microstructural investigations have been carried out by means of optical microscopy. Results show that the grain size varies from the parent material to the heat affected zone and weld pool. Some martensite is present in the parent material because of the cold working following each welding pass. In the weld pool, the heat flow seems to be redistributed effectively by the cap pass of the LPHSW. Although the microstructural heat affected zone is rather small, the effect of the weld on the stress state seems to extend further (the so-called strain affected zone). In...

Effects of warm peening on fatigue life and relaxation behaviour of residual stresses in AISI 4140 steel

A new device has been built which allows shot peening in an air blast machine at elevated temperatures. The effects of conventional shot peening and peening at elevated temperatures on the characteristics of regions close to the surface, on the stability of residual stresses and half widths of X-ray interference lines and on the fatigue strength are presented for a quenched and tempered AISI 4140 steel (German grade 42CrMo4). The alternating bending strength is increased by warm peening compared with conventional shot peening. Additional investigations of samples conventionally peened and then annealed confirm that these effects are due to the stability of the dislocation structure, which is highly affected by strain ageing effects. This causes an additional benefit owing to higher stability of the residual stresses induced.

Influence of ultrasonic cavitation on surface residual stresses in AISI 304 stainless steel

The effect of ultrasonic cavitation in water on residual stress changes in AlSl 304 stainless steel has been investigated. Studies indicate that high-intensity ultrasonic cavitation introduces a very high compressive residual stress at the surface (due to work-hardening) even for short durations of exposure at ambient temperatures. With increased exposure, the stresses become more compressive; however, they tend to reach a saturation value. Different combinations of temperature, time and cavitation intensity were tried out and the best effects were noticed for a treatment temperature of 5 °C. 304 stainless steel was chosen for the present study on account of its amenability to strong work-hardening. The test specimen was attached to the tip of an ultrasonic vibrator and immersed in the cavitating liquid, i.e. water. However, even in situations where the specimen was kept in a stand-off position close to the vibrator tip (with water in between) similar effects were noticed. The maximum depth of hardening was found to be about 70 μm. During this process, there was also a mild roughening of the surface. An incidental observation pertains to the formation of both “α” and “∈” martensites at the surface detectable by X-ray diffractometer recordings for specific conditions of cavitation treatment. The required high intensities of vibration in this study were obtained through an in-house built highpower ultrasonic generator working at a frequency around 20 kHz.