Experimental and numerical modelling of the residual stresses induced in orthogonal cutting of AISI 316L steel

Residual stresses in the machined surface layers are affected by the cutting tool, work material, cutting regime parameters (cutting speed, feed and depth of cut) and contact conditions at the tool/chip and tool/workpiece interfaces. In this paper, the effects of tool geometry, tool coating and cutting regime parameters on residual stress distribution in the machined surface and subsurface of AISI 316L steel are experimentally and numerically investigated. In the former case, the X-ray diffraction technique is applied, while in the latter an elastic–viscoplastic FEM formulation is implemented. The results show that residual stresses increase with most of the cutting parameters, including cutting speed, uncut chip thickness and tool cutting edge radius. However, from the range of cutting parameters investigated, uncut chip thickness seems to be the parameter that has the strongest influence on residual stresses. The results also show that sequential cuts tend to increase superficial residual stresses.     

An analysis of through-thickness residual stresses in aluminium FSW butt joints

In the paper, the results of a wide experimental campaign on friction stir welding (FSW) of aluminum alloys are reported. The attention was focused on the through-thickness residual stresses that occur on aluminum joints, after the welding process. In detail, using the hole-drilling method the residual stresses distribution in the zone close to the tool shoulder border of the joint advancing side, has been investigated; four different aluminum alloys and three different process conditions have been considered. The experimental analysis has shown that unlike traditional welding processes, the residual stresses are negative in the surface of the examined zone, and increase with depth until values of about 100–150 MPa that occur at a depth of about 0.5–1.0 mm. As expected, the maximum value of the residual stresses induced by the FSW process influences the mechanical behavior of the joint significantly, as it has been observed for the AA6082-T6 aluminum alloy by considering its static and fatigue resistance.Such results corroborate that the hole-drilling method, widely employed in the industrial field due to its simplicity and low cost, can be used for an accurate estimation of the maximum residual stresses that occur in an aluminum butt joint obtained by friction stir welding.     

A new two-dimensional ultrasonic assisted grinding (2D-UAG) method and its fundamental performance in monocrystal silicon machining

A new two-dimensional (i.e., elliptical) ultrasonic assisted grinding (UAG) technique is proposed to achieve high material removal rate and high surface quality in the machining of hard and brittle materials such as monocrystal silicon. In this method, the workpiece attached on an elliptical ultrasonic vibrator is ground with a resin bond diamond grinding wheel under the presence of elliptical ultrasonic vibration. The elliptical ultrasonic vibrator is produced by bonding a piezoelectric ceramic device (PZT) on a metal elastic body (stainless steel, SUS304) and its detailed structure/dimensions are determined by FEM (finite element method) analysis. When two alternating current voltages with a phase difference are applied to the PZT at the same frequency that is close to the resonant frequency of the longitudinal mode and bending mode of vibrator, two ultrasonic vibrations are generated simultaneously, and the synthesis of the vibrations results in an elliptical motion on the end face of the vibrator. If the phase difference is set at 0° or 180°, two kinds of one-dimensional ultrasonic vibrations, i.e., axial or vertical vibrations, can be obtained. Grinding experiments are carried out involving monocrystal silicon to confirm the performance of the proposed elliptical UAG. In addition, grinding experiments under the presence of the axial and vertical ultrasonic vibrations and the absence of ultrasonic vibrations, i.e., conventional grinding, are also carried out for comparison. The obtained results show that: (1) compared with conventional grinding, the axial ultrasonic vibration results in greatest improvement in the work surface quality and a slight reduction in the grinding forces; (2) under the vertical ultrasonic vibration, the grinding forces are decreased significantly but the surface roughness is increased slightly; (3) elliptical ultrasonic vibration leads to the significant reduction of both the surface roughness and grinding forces. These indicate that the high efficiency and high-quality grinding of monocrystal silicon can be performed with the proposed two-dimensional ultrasonic assisted grinding technique.     

Measurement of residual stresses in austenitic stainless steel weld joints using ultrasonic technique

Abstract

A methodology has been developed using a non-destructive ultrasonic technique for measuring surface/subsurface residual stresses in 7 mm thick AISI type 316LN stainless steel weld joints made by activated tungsten inert gas and multipass tungsten inert gas welding processes. Measurement of residual stresses using an ultrasonic technique is based on the effect of stresses on the propagation velocity of elastic waves. Critically refracted longitudinal L _CR wave mode was employed and accurate transit time measurements were made across the weld joints. Quantitative values of the longitudinal residual stresses across the weld joints were estimated from the measured transit times and predetermined value of acoustoelastic constant for AISI type 316LN stainless steel. The nature of the residual stress profiles and their variations across the two types of weld joints were compared and interpreted.     

Generalized modeling of drilling vibrations. Part I: Time domain model of drilling kinematics, dynamics and hole formation

This two part paper presents a comprehensive exercise in modeling dynamics, kinematics and stability in drilling operations. While Part II focuses on the chatter stability of drilling in frequency domain, Part I presents a three-dimensional (3D) dynamic model of drilling which considers rigid body motion, and torsional–axial and lateral vibrations in drilling, and resulting hole formation. The model is used to investigate: (a) the mechanism of whirling vibrations, which occur due to lateral drill deflections; (b) lateral chatter vibrations; and (c) combined lateral and torsional–axial vibrations. Mechanistic cutting force models are used to accurately predict lateral forces, torque and thrust as functions of feedrate, radial depth of cut, drill geometry and vibrations. Grinding errors reflected on the drill geometry are considered in the model. A 3D workpiece, consisting of a cylindrical hole wall and a hole bottom surface, is fed to the rotating drill while the structural vibrations are excited by the cutting forces. The mechanism of whirling vibrations is explained, and the hole wall formation during whirling vibrations is investigated by imposing commonly observed whirling motion on the drill. The time domain model is used to predict the cutting forces and frequency content as well as the shape of the hole wall, and how it depends on the amplitude and frequency of the whirling vibration. The model is also used to predict regenerative, lateral chatter vibrations. The influence of pilot hole size, spindle speed and torsional–axial chatter on lateral vibrations is observed from experimental cutting forces, frequency spectra and shows good similarity with simulation results. The effect of the drill–hole surface contact during drilling is discussed by observing the discrepancies between the numerical model of the drilling process and experimental measurements.     

The surface layer of surface-hardened parts of heat-resisting alloys

Conclusions The effect of surface hardening by cold working depends mainly on the stability of residual compressive stresses. The residual stresses decrease greatly in the first hours at elevated temperature and then change slowly. The time that the effect of surface hardening is retained in heat-resisting alloys can be determined approximately — from the decoration of the structure with dislocations — by metallographic examination.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 56–58, February, 1971.     

Change of residual stresses in rolls during operation

Conclusions The redistribution of residual stresses in surface layers of rolls during operation in cold rolling mills is due to the manufacturing technique and operating conditions.The principal means of improving the durability of rolls are the use of new steels with structural stability and rehardening of rolls after a given operating period to reestablish the original stresses.Elektrostal' Factory of Heavy Machine Construction. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 72–75, January, 1975.     

Non-destructive measurement of residual stresses in carbon steel weld joints

Abstract

Residual stress measurements have been carried out on 8 and 12 mm thickness carbon steel single V weld joints by X -ray diffraction and ultrasonic techniques. The maximum tensile and maximum compressive stresses on the surface of the 12 mm carbon steel weld joint are higher than those on the surface of the 8 mm carbon steel weld joint. The results also indicate that the variation in the surface residual stress across the weld is different from that for the through thickness residual stresses. The effect of constraint, which depends on the thickness of the weld joint, is found to influence the surface and through thickness residual stresses. The effect of stress relief annealing heat treatment on residual stresses was also studied.     

Modelling of multiple impacts for the prediction of distortions and residual stresses induced by ultrasonic shot peening (USP)

During a manufacturing process, the ultrasonic shot peening (USP) technique can be used as the final surface treatment. The aim of this operation is to introduce surface compressive residual stresses in order to prevent crack propagation advancement. Although the numerical simulation method is able to predict the level of residual stresses in a peened part, the 3D modelling of the real USP process, in which many successive and shifted impacts take place, is very delicate to perform and costly in terms of computing time and memory space required. In this paper, a two step method based at first on the calculation of the averaged plastic strain tensor in a half-space by using a semi-analytical method and in a second time on the transfer of this plastic strain field to a finite element model is proposed in order to simulate the effects of the USP process in thin structures. The accuracy and advantages of the semi-analytical method are validated by a benchmark with several finite element codes. Experiments, similar to the Almen test, are performed on thin plates of Inconel 600. Numerical results in terms of distortions and residual stresses are compared with the experimental data.     

Application of the LCR ultrasonic technique for evaluation of post-weld heat treatment in steel plates

Ultrasonic travel times obtained with the LcR wave are able to distinguish between stress relieved and non-stress relieved 13 mm (1/2 in) thick, steel plates. Two 1.22 m (48 in) square plates were patch welded in the centre to create a residual stress field, and one of the plates was stress relieved. The LcR ultrasonic technique sends a critically refracted longitudinal wave travelling beneath the plate surface, and the stresses in the plate affect the travel times through the acoustoelastic relationship. The L_CR travel-time measurements not only distinguished between residual stress states in the plate, but also gave some information on their distribution and magnitude. Neither texture nor localized residual stresses affect the results. These findings demonstrate the potential usefulness of the technique for evaluating the state of post-weld heat treatment in structural steels.     

Change in residual stress with low-temperature tempering of rolls

Conclusion With low-temperature tempering (120–225°) the changes in residual stresses in rolls are due mainly to structural transformations in the surface layer. With decomposition of martensite the compressive stresses in the surface layer decrease, but at the boundary between the hardened and transition layer a substantial inflection of the stress curve appears. With decomposition of retained austenite the compressive stresses in the surface layer increase due to which the inflection of the stress curve is suppressed and the distribution of tangential stresses becomes more favorable.Elektrostal' Factory of Heavy Machine Construction. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 75–77, January, 1976.     

The use of ultrasonics in the optimisation of welding processes

Summary

A non‐destructive method for measurement of residual welding stress is described. The results are in good agreement with another proven semi‐destructive method. Excellent practical perspectives for a vast range of parameters, important to welders, with a direct influence on length of service life are given.

The welding process creates complex residual stress fields which may now be evaluated experimentally by various semi‐destructive or destructive methods.

In the case of welded compounds, these stresses are often high and may reach the elastic limit of the base metal, thus influencing the mechanical properties of welded assemblies.

A new non‐destructive, ultrasonic technique of evaluating stresses is presented here. The potential uses of this technique are to measure near surface stress and apply it to the optimisation of welding processes.     

The effects of machined workpiece surface integrity on the fatigue life of γ-titanium aluminide

Tension–tension tests on turned, electro-chemical machined (ECM) and electro-discharge textured (EDT) specimens made from Ti–45Al–2Nb–2Mn+0.8 vol% TiB₂ alloy, showed the turned specimens to have a higher fatigue strength 475 MPa. It is likely that this was due to the presence of highly compressive surface residual stresses caused by the turning operation.     

Structural and phase transformations in plasma planing of rail steel

Conclusions As a result of plasma heating of railroad rails in the process of their plasma-planing, structural and phase transformation occur in the surface of the heated layer to be machined, residual stresses and a multilayered structure forming. However, these layers are removed by the cutting tool, and as a result the machined surface is free of defects.Leningrad Polytechnic Institute. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 52–54, April, 1983.     

Characterization of ultrasonic Rayleigh surface waves in asphaltic concrete

This research examines the application of ultrasonic Rayleigh surface waves to the non-destructive evaluation (NDE) of asphaltic concrete in the frequency range 40–100 kHz. Two ultrasonic parameters, the phase velocity and amplitude attenuation, are considered to be sensitive to local compositional and structural variations and are measured. A wedge technique is used to generate Rayleigh surface waves in an asphaltic concrete beam with uniformly distributed aggregate, and this technique is shown to be effective in launching Rayleigh waves in this highly viscoelastic (absorptive) and heterogeneous medium. Three different ultrasonic detection setups using contact and non-contact transducers as receivers are examined and their results are compared. The experimental results show that the wedge generation technique along with an air-coupled receiving transducer with a finite-size aperture is the most reliable for characterizing Rayleigh waves in asphaltic concrete. It is also experimentally demonstrated that the proposed setup may be used to detect aggregate segregation in asphaltic concrete.     

Variation in the surface properties of high chromium iron components due to laser irradiation and shot blasting

Conclusion Mainly tensile residual stresses are generated at the surface of cast and heat-treated high chromium iron due to laser action. Here, maximum residual stresses were noted at the edge of the melt zone, whereas they occurred in the central portion in the hardened (without fusion) zone. The highest residual stresses are generated in the hardened zone, such that _x = 2140 and 450 N/mm² in the cast and heat-treated irons respectively. Laser hardening of heat-treated iron produces a large number of cracks, these being accompanied by a reduced residual stresses level. Preheating to 400°C with an optimum hardened zone structure enables cracking to be avoided. The subsequent effect from a shot stream forms cold work hardened layers in which the tensile stresses are altered to compressive stresses. The hardened layers depth and residual stresses distribution type along the surface of blades used in shot blasters is determined by the shot attack angle.Physical Institute, Samara. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 10–13, July 1992.     

High-Temperature Stress Measurements During the Oxidation of NiAl

The growth stresses in -alumina scales growing on stoichiometric NiAlduring oxidation in air at 1100°C have been measured by two X-raydiffraction techniques: the classic rocking technique and a newly developedfixed-incidence multiplane (FIM) technique. The growth stresses were foundto be within the experimental uncertainty of the measurements, i.e., nearzero. Measurement of the residual stresses using an optical-fluorescencespectroscopy (OFS) technique in adherent regions of the scale, after coolingto room temperature, were consistent with the growth stresses having beennegligibly small. These measurements contrast with previous measurements ofgrowth stresses in -alumina growing on Fe–Cr–Al alloys,using the FIM technique, which indicated compressive growth stresses on theorder of 1 GPa. Possible reasons for these differences are discussed.     

Thermo-optical modulation for improved ultrasonic fatigue crack detection in Ti–6Al–4V

Pulsed infrared laser irradiation was used to positively identify small fatigue cracks on the surface of fatigue damaged Ti–6Al–4V specimens. The resulting transient thermoelastic deformation perceptibly changes the opening of partially closed surface cracks without affecting other scatterers, such as surface grooves, corrosion pits, coarse grains, etc. that might hide the fatigue crack from ultrasonic detection. We found that this method, which was previously shown to be very effective in 2024 aluminum alloy, must be modified in order to successfully adapt it to Ti–6Al–4V titanium alloy, where significant thermo-optical modulation was found even from straight corners or open notches. This spurious modulation is caused by direct thermal modulation of the sound velocity in the intact material rather than thermal stresses via crack closure. Different methods have been developed to distinguish direct thermal modulation from crack-closure modulation due to thermoelastic stresses. It was found that the modified thermo-optical modulation method can increase the detectability of hidden fatigue cracks in Ti–6Al–4V specimens by approximately one order of magnitude.     

Grinding-hardening with liquid nitrogen: Mechanisms and technology

This paper studies an innovative development of a steel grinding–hardening technology using an inert cryogen—liquid nitrogen. It was found that phase transformations took place during grinding with the application of liquid nitrogen and resulted in hardened surface layer in a ground component. The layer had a fine laths martensite structure which gave rise to a remarkably high hardness. It was also shown that the treatment can produce superior surface integrity, with compressive surface residual stresses and without surface oxidation. Due to the inert nature of the liquid nitrogen, the grinding process becomes environmentally conscious.     

Experimental study of nonlinear Rayleigh wave propagation in shot-peened aluminum plates—Feasibility of measuring residual stress

Shot-peening is widely used in the aerospace industry to enhance the resistance of structural components to fatigue damage and stress corrosion by putting the outside layer of a component under an initial, residual compressive stress. The ability to measure these near-surface residual stresses is useful from a quality control and certification perspective, and can help predict the fatigue life of shot-peened components. This paper presents experimental results to examine the feasibility of measuring near-surface residual stresses using nonlinear Rayleigh surface waves. Experiments are conducted on aluminum alloy (AA 7075) samples shot-peened at different peening intensities and thus with different levels of residual stresses. The surface roughness of these samples is also measured. The nonlinear ultrasonic results show a large increase in the acoustic nonlinearity parameter, indicating the potential of nonlinear ultrasonics for the in situ measurement of near-surface residual stresses. The effects of surface roughness and the driving frequency on the measured acoustic nonlinearity parameter are briefly discussed. Finally, a preliminary model is used to interpret some experimental results. Future work to evaluate the separate contributions of cold work, residual stress and surface roughness to the total measured nonlinearity is also discussed.