Residual Stress Profiles Research Articles

Piezospectroscopic analysis of mechanical stresses in Si3N4 and AlN irradiated with high-energy bismuth ions

Depth-resolved Raman piezospectroscopy was used to study residual mechanical stress profiles in polycrystalline silicon and aluminum nitrides irradiated with 710 MeV bismuth ions to fluences of 1×1012, 2×1012, and 1×1013 cm-2. It was found that stress fields of opposite signs are formed in the irradiated Si3N4 layer, separated by a buffer zone located at a depth coinciding with the thickness of the sample layer, amorphized at high ion fluences due to multiple overlapping of track regions. At great depths, tensile stresses witch magnitude reaches their maximum value in the region of the end of the ion range are detected. In contrast to Si3N4, radiation-stimulated changes in mechanical stresses in AlN were within the measurement error throughout the entire thickness of the irradiated layer, except of the near-surface region. The observed effect is associated with the different structural sensitivity of silicon and aluminum nitrides to high-density ionization - the formation of amorphous latent tracks in Si3N4 and their absence in AlN.

Analysis of shot peening residual stress distribution based on dislocation configuration

The distribution profile of residual stress on the surface layer of shot-peened materials is often in a hook shape. We analysed the distribution characteristics of residual stress by detecting dislocation configurations. The position of maximum compressive residual stress (MCRS) shifts inward with an increase in shot peening strength. It was found that long-term orderly dislocation pile-up groups frequently appeared in the MCRS region. The location of MCRS is not necessarily related to maximum dislocation density. At low strength, both the maximum dislocation density and the MCRS are on the surface region. At high strength, the surface region structures are composed of sub-grains and dislocation cells. The position of maximum dislocation density is between the surface region and the MCRS.

Analysis of Fatigue Strength of L-PBF AlSi10Mg with Different Surface Post-Processes: Effect of Residual Stresses

Space and aerospace industries has been starting in the recent years the replacement process of parts and components obtained by traditional manufacturing processes with those produced by Additive Manufacturing (AM). The complexity of the obtainable parts makes, in general, challenging the superficial post processing of some zones, making a stringent requirement the investigation of the fatigue performances of components with rough superficial state or machined. The aim of this work is then to analyse and compare the fatigue performances of an additively manufactured (AMed) AlSi10Mg material considering both the effects of the manufacturing defects and residual stresses related to three different superficial states, namely machined, net-shape and sandblasted. The residual stress profiles of the three superficial states were found to play a key role in determining the fatigue properties of the analysed material, while the manufacturing defects at the failure origin were found to be comparable among the three series. To take into account the combined effect of residual stresses and manufacturing defects a fracture mechanics approach was considered for the estimation of the fatigue performances in both infinite and finite life regimes. It was found that by considering the nominal measured residual stress profiles in the fracture mechanics model the estimations were satisfactory compared to the experimental data-point. To increase the accuracy of the fatigue life estimations a series of numerical analyses were performed aimed to investigate the residual stresses relaxation during the cyclic loading. The adoption of the relaxed residual stress profiles in the fracture mechanics model resulted in good estimations respect to the experimental data-points, highlighting the necessity in adopting such developed approaches during the design phase of AM parts and components.

Investigation of Surface Integrity Induced by Various Finishing Processes of AISI 52100 Bearing Rings.

Surface integrity induced by finishing processes significantly affects the functional performance of machined components. In this work, three kinds of finishing processes, i.e., precision hard turning, conventional grinding, and sequential grinding and honing, were used for the finish machining of AISI 52100 bearing steel rings. The surface integrity induced by these finishing processes was studied via SEM investigations and residual stress measurements. To investigate rolling contact fatigue performance, contact fatigue tests were performed on a twin-disc testing machine. As the main results, the SEM observations show that precision hard turning and grinding introduce microstructural alterations. Indeed, in precision hard turning, a fine white layer (<1 μm) is observed on the top surface, followed by a thermally affected zone in the subsurface, and in grinding only, a white layer with 5 μm thickness is observed. However, no microstructural changes are found after sequential grinding and honing processes. White layers induced by precision hard turning and grinding possess compressive residual stresses. Grinding and sequential grinding and honing processes generate similar residual stress distributions, which are maximum and compressive at the machined surface and tensile at the subsurface depth of 15 μm. Precision hard turning generates a “hook”-shaped residual stress profile with maximum compressive value at the subsurface depth and thus contributes as a prenominal factor to the obtainment of the longest fatigue life with respect to other finishing processes. Due to the high quality of surface roughness (Ra = 0.05 μm), honing post grinding improves the fatigue life of bearing rings by 2.6 times in comparison with grinding. Subsurface compressive residual stresses, as well as low surface roughness, are key parameters for extending bearing fatigue life.

Residual Stresses in Ultrafine‐Grained Laminated Metal Composites Analyzed by X‐ray Diffraction and the Hole‐Drilling Method

Accumulative roll bonding is an advanced manufacturing process, which is capable of simultaneously refining the grain size into the nanometer regime and bonding different metallic sheet materials. Herein, homogenous aluminum/aluminum as well as heterogeneous aluminum/steel laminated metal composite (LMCs) are fabricated. The residual stresses are experimentally determined by X‐ray diffraction and the hole‐drilling method. Generally, a complex residual stress profile is found in all LMCs. The level of residual stress strongly depends on the bonded materials. Compressive residual stresses are induced in all sheets in the near surface area. These stresses range from −5 MPa in aluminum to −240 MPa in steel. In the homogenous aluminum/aluminum LMCs, compressive stresses up to −26 MPa in the softer layers and tensile stresses up to 30 MPa in the stronger layers are built up. This is different to heterogeneous aluminum/steel LMCs, where tensile stresses up to 40 MPa in the softer aluminum layers and compressive stresses up to −72 MPa in the inner harder steel layers are present. Based on the results obtained it is possible to directly design the material combination or stacking architecture of ultrafine‐grained LMCs to tailor the residual stress profile.

Fatigue Bending of V-Notched Cold-Sprayed FeCoCrNiMn Coatings

Cold-spray coatings were produced by FeCoCrNiMn high-entropy alloy powders deposited on carbon steel substrate. The coatings were realized at intermediate temperature and high pressure (at 1100 °C and 7 MPa). The coating microstructure was characterized by scanning electron microscopy and X-ray diffraction, revealing a very dense deposition and high flattening ratio of the splatted particles. This had a large influence on the strong adhesion of the coating to the substrate. The hardness and residual stress profiles were measured through nanoindentation and X-ray diffraction from the peak broadening measured layer by layer. The cyclic behavior of the coatings was evaluated through three-point bending tests performed on V-notched samples coated via cold spray. Cyclic tests were performed at different maximum strokes from 0.3 to 3.6 mm in order to monitor the crack initiation and propagation during bending tests. The fracture surface aspect was analyzed by scanning electron microscopy in order to reveal the fracture mechanisms in different deformation conditions.

Interlaboratory Reproducibility of Contour Method Data in a High Strength Aluminum Alloy

BackgroundThe contour method for residual stress measurement has seen significant development, but an experimental reproducibility study utilizing physical samples has not been published.ObjectiveA double-blind reproducibly study is reported, having scope beginning with EDM cutting and ending with residual stress calculation.MethodsA reinforced I-beam sample geometry is identified for its unique residual stress profile when extracted from residual stress bearing quenched aluminum bar (7050-T74). Contour measurements are prescribed on a midplane of symmetry with dimensions 24.0 mm by 50.0 mm. Fourteen identically prepared samples are fabricated from a single long bar with well characterized and uniform residual stress. Five samples throughout the bar are identified for planning measurements to validate sample uniformity and overall suitability of the residual stress field. The planning measurements employ a range of techniques: contour method, neutron diffraction, and hole-drilling. Eight samples are distributed to an international group of participants to execute their standard measurement practice. A double-blind process is followed to provide anonymity.ResultsResults are provided by eight participants: six being self-similar and two being quite different, the latter set aside as outliers. An average residual stress field is established from non-outlying results and the spatial distribution of reproducibility standard deviation is determined. The average stress field ranges from -60 to 70 MPa and the reproducibility standard deviation averages 8.1 MPa on the measurement plane. The average reproducibility standard deviation is about 3 × larger for points within 1.0 mm of plane boundaries (17.6 MPa) than for the remaining points (6.1 MPa).ConclusionsReproducibility standard deviation (among different labs) for contour method residual stress measurement is found to be very similar to repeatability standard deviation (in a single lab) reported in prior work. The reproducibility observed here, for the entire measurement process, is also similar to that found in a prior reproducibility study limited to contour method data analysis.

Effect of thermo-mechanical loading on machining induced residual stresses in ultrasonic vibration assisted turning of Ti6Al4V alloy

The study of residual stresses induced during machining is of considerable importance due to their effect on fatigue life of machined components. The metallurgical changes occurred due to thermo-mechanical phenomenon in cutting process affects the distribution of residual stress in machined components. Ultrasonic vibration assisted turning (UVAT) is effective machining process for low thermal conductivity materials like Ti6Al4V alloy and improves the surface characteristics by reducing cutting force and cutting temperature. In this paper, experimental and finite element (FE) studies are conducted to study the circumferential and axial residual stress distribution in UVAT of Ti6Al4V alloy. FE model is developed to study the effect of vibrating parameter (ultrasonic power intensity) and cutting parameters (cutting speed, feed rate, and depth of cut) on the residual stress profiles of machined surface. The FE simulation results of cutting force and cutting temperature are validated with experimental results. The circumferential and axial surface residual stresses obtained from FE simulation are also compared with experimental results using X-ray diffraction method. The effect of thermo-mechanical loading on residual stress distribution is analyzed with respect to force components (cutting force and feed force) and cutting temperature. Finally, the effect of each cutting parameter on subsurface layer of machined component is analyzed.

Understanding the role of in-flight particle temperature and velocity on the residual stress depth profile and other mechanical properties of atmospheric plasma sprayed Al2O3 coating

This report deals with the influence of particle temperature and velocity on the microstructure, mechanical properties and residual stress depth profile of plasma sprayed alumina coating. The coatings were produced by varying the particle temperature while maintaining a relatively fixed particle velocity, and vice versa. Residual stress profiles were acquired by measuring the stress in successive layers using X-ray Sin2ψ technique. A substantial increase in hardness and indentation modulus by 76% and 64%, respectively were observed with an increase in particle temperature. With an increase in velocity, coating porosity was found to decrease initially. However, at a high velocity, porosity again increased to a limited extent. The mechanical properties were found to depend strongly on porosity. An increase in particle temperature resulted in an increase in the tensile residual stress in the coatings. Moreover, partial recovery of the grit blasted compressive substrate occurred during spraying owing to an annealing effect.

Effects of square spot size and beam quality on residual stress of 7050 aluminum alloy by laser shock peening

Laser shock peening is a promising surface modification technology to improve the properties of metal. In this work, the spatial distribution model of the shock wave pressure induced by laser shock peening was proposed by matching the pit profile. The relationship between laser beam quality and shock wave pressure distribution was analyzed. And the shock wave pressure profile changes caused by the lateral expansion of plasma were quantitatively calculated. Results showed that the proportions of the flat-topped part and the edge gradient part of the pits formed by different spot sizes are basically the same. As the spot size increases, the range of residual stress increases. Compared with the flat-topped part length of the beam quality profile, the flat-topped part length of the shock wave pressure profile is reduced by about 14% due to lateral expansion of the plasma. Simulated residual stress and deformation profiles are in an agreement with the measured data in all cases.

Evolution of residual stress through the processing stages in manufacturing of bore-chilled sand-cast aluminum engine blocks with pressed-in iron liners

To minimize the carbon footprint of the transportation industry, manufacturers and engineers are continuously trying to improve the efficiency of the combustion engine. However, due to the presence of iron cylinder liners in the engine block, high tensile residual stresses are generated during the manufacturing process which leads to a large reduction of the alloy’s useable strength. Thus, the present study utilized neutron diffraction to study, for the first time, the evolution of residual stress of sand-cast aluminum engine blocks that have eliminated the iron cylinder liners from the casting process and mechanically inserted them after heat treatment and machining operations. Moreover, this study also examined the effects that cylinder bore chills have on the resulting residual stress profiles. The replacement of the iron liners shifted the stress mode from purely tension to purely compression until the bore chills were removed. Following the removal of the bore chills, the maximum tensile stress at the top of the cylinder bridge was ~ 70% lower than the engine’s predecessor which was produced with iron liners. Moreover, in the production-ready state (i.e., T7 heat treated and press-fit liners inserted), the stress mode maintains the partially compressive nature, thereby lowering the material’s susceptibility to crack growth and propagation.Graphical Abstract

Numerical investigation of sequential cuts residual stress considering tool edge radius in machining of AISI 304 stainless steel

Residual stress affects component performance, and the existence of pre-stress changes the residual stress of machined surfaces as well, emphasizing the importance of studying the evolution of residual stress in sequential cutting. This paper reports a numerical investigation of the machining-induced residual stress profile of sequential cuts for orthogonal cutting of AISI 304, considering the effects of edge radius and cutting depth. A Coupled Eulerian-Lagrangian (CEL) model is employed for the first time to stably simulate the evolution of residual stress of multiple sequential cuts. The effectiveness of the proposed method is verified by comparing the chip formation and surface residual stress between simulated and experimental results. The cutting force and cutting temperature, as well as mechanical and thermal loads, are extracted to explain the generation and evolution of residual stress in sequential cutting. It is found that the residual stress on the machined surfaces will decrease during sequential cutting, and a stable value can be reached after approximately six sequential cuts. With the progress of sequential cutting, a larger honed tool edge radius and cutting depth will lead to a slower reduction of residual stress.

Predicting the flexural strength of chemically strengthened aluminosilicate glass plates with fractography

This work introduces a novel, fractographic method to extend the current, state-of-the-art, fractographic techniques to chemically strengthened (CS) glasses with large, surface flaws. The proposed method uses proven relationships based on dimensional analysis to correlate the flexural fracture strength to newly-introduced, fractographic length-scales. The technique requires knowledge of the residual stress profile and access to standard visualization tools such as optical microscopes. The proposed methodology was validated on three sets of aluminosilicate CS glass plates with depth of the compressive layer (DOL)ranging between 28~54μm and surface stress 980–1140 MPa, and one set of untreated plates. For the CS and untreated glass plates considered, the proposed fractographic technique estimated the fracture strength within (2 ± 11)% of experimental values, which is comparable to the accuracy of fractographic techniques currently used for annealed, brittle specimens.

Influence of induction hardening residual stresses on rolling contact fatigue lifetime

Rolling contact fatigue is a unique mode of fatigue that components under cyclic contact loading experience. In this work, the impact of induction hardening residual stresses in rolling contact fatigue lifetime is investigated experimentally and numerically using the Dang Van multiaxial criterion. Various residual stress fields from induction hardening are simulated using the finite element method and are mapped into a classical mono-contact finite element model. The impact of induction hardened residual stresses on the lifetime of a component has been investigated, and the importance of incorporating the residual stress profile into fatigue life assessments is affirmed.

Evolution of temperature and residual stress behavior in selective laser melting of 316L stainless steel across a cooling channel

PurposeThe current investigation aims at observing the influence of the cooling channel on the thermal and residual stress behavior of the selective laser melting (SLM)316L uni-layer thermo-mechanical model.Design/methodology/approachOn a thermo-mechanical model with a cooling channel, the effect of scanning direction, parallel and perpendicular and scan spacing was simulated. The effect of underlying solid and powder bases was evaluated on residual stress profile and thermal variables at various locations.FindingsThe high heat dissipation of solid base due to high cooling rates and steep thermal gradients can reciprocate with smaller melt pool temperature and melt pool size. Given the same scan spacing, residual stresses were found lower when laser scanning was perpendicular to the cooling channel. Moreover, large scan spacing was found to increase residual stresses.Originality/valueCooling channels are increasingly being used in additive manufacturing; however, their effect on the residual stress behavior of the SLM component is not extensively studied. This research can serve as a foundation for further inquiries into the impact of base material design such as cooling channels on manufactured components using SLM.

Depth-resolved residual stress evaluation from X-ray diffraction measurement data using the approximate inverse method

Abstract The paper deals with the depth determination of residual stress states from diffraction data. First an historical overview of the known approaches is given. Then we apply the approximate inverse method to this problem. This method is known to be very efficient and stable with respect to noise-contaminated data. It is even possible to prove convergence and it allows an error estimate of the calculated depth resolved residual stress profile.

Coupled Modeling Approach for Laser Shock Peening of AA2198-T3: From Plasma and Shock Wave Simulation to Residual Stress Prediction

Laser shock peening (LSP) is a surface modification technique to improve the mechanical properties of metals and alloys, where physical phenomena are difficult to investigate, due to short time scales and extreme physical values. In this regard, simulations can significantly contribute to understand the underlying physics. In this paper, a coupled simulation approach for LSP is presented. A global model of laser–matter–plasma interaction is applied to determine the plasma pressure, which is used as surface loading in finite element (FE) simulations in order to predict residual stress (RS) profiles in the target material. The coupled model is applied to the LSP of AA2198-T3 with water confinement, 3×3mm2 square focus and 20 ns laser pulse duration. This investigation considers the variation in laser pulse energy (3 J and 5 J) and different protective coatings (none, aluminum and steel foil). A sensitivity analysis is conducted to evaluate the impact of parameter inaccuracies of the global model on the resulting RS. Adjustment of the global model to different laser pulse energies and coating materials allows us to compute the temporal pressure distributions to predict RS with FE simulations, which are in good agreement with the measurements.

Residual stress profiles induced by machining of two types of 27MnCr5 hardened steels

This paper investigates the influence of heat treatment on the surface integrity induced by a hard turning operation on a 27MnCr5 carburized steel. Two heat treatments have been investigated, leading to two residual stress profiles. After that, the steels with the two different case hardened conditions have been hard turned. Residual stress profiles induced by hard turning are analyzed for various cutting speeds and tool flank wear. As a result, it is shown that the final residual stress profiles generated after hard turning depends strongly on the original residual stress profiles.

A Multiscale Study on Machining Induced Surface Integrity in Ti-6Al-4V Alloy

This study adopted a multiscale surface integrity approach (macro, micro, and sub-micro scale) to study the effects of cutting conditions and varying cutting fluid applications on the final surface state in Ti-6Al-4V alloy. Surface integrity parameters that were studied in this work are surface roughness, subsurface microhardness, residual stresses, and microstructural alterations. The results show that there is some correlation between microstructural and mechanical characteristics of machining-induced surface integrity. Also, different residual stress profiles were obtained for TMQF (Targeted Minimum Quantity Fluid) machining (compressive residual stress profile) and flood machining (tensile residual stress profile), which underlines the importance of selecting the right cutting fluid application. This work could aid in choosing the right cutting fluid application for the finish machining operation of Ti-6Al-4V alloy to obtain a desired final superior surface integrity. TMQF application conditions produced better surface integrity metrics (lower surface roughness, compressive surface residual stresses, and no undesirable microstructural damage) compared to flood fluid application while finish machining of Ti-6Al-4V titanium alloy.

Experimental investigation on surface integrity in a face milling operation

This paper discusses the influence of surface milling on the surface integrity of a 15-5PH martensitic stainless steel. Among the surface integrity features, surface roughness and residual stress profiles are particularly studied. This experimental work aims at characterizing the sensitivity of three technological parameters, namely the number of teeth, the axial runout of the milling cutters and the tilt angle. On these features, it is shown that the surface roughness is determined by the axial runout of the milling cutter when milling with multiple cutters without tilt angle. In contrast, the residual stress state is not significantly affected by any of these parameters.