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Although additive manufacturing is fast gaining traction in the industrial world as a reputable manufacturing technique to complement traditional mechanical machining, it still has problems such as porosity and residual stresses in components that give rise to cracking, distortion, and delamination, which are important issues to resolve in structural load-bearing applications. This research project focused on the characterization of the evolution of residual stresses in Ti-6Al-4V extra-low interstitial (ELI) additive-manufactured test samples. Four square thin-walled tubular samples were deposited on the same baseplate, using the direct energy deposition laser printing process, to different build heights. The residual stresses were analysed in the as-printed condition by the neutron diffraction technique and correlated to qualitative predictions obtained using the ANSYS software suite. Good qualitative agreement between the stress measurements and predictions were observed. Both approaches revealed the existence of large tensile stresses along the laser track direction at the sections that were built last, i.e., centre of the top layers of the samples. This in addition leads to large tensile stresses at the outer edges (corners) which would have the effect of separating the samples from the baseplate should the stresses exceed the yield strength of the material. Such extreme conditions did not occur in this study, but the stresses did lead to significant distortion of the baseplate. In general, the microstructures and spatial elemental mapping revealed a strong correlation between the macro-segregation of elemental V and the distribution of the β-phase in the printed parts.

Prediction of residual stresses in adhesively bonded joints is a major topic among practitioners, as they significantly contribute to failure. The experimental determination of relevant material properties, like shrinkage, modulus development, and relaxation behavior, is considered highly complex. Viscoelastic and numerical models are often simplified to suit specific applications. However, most of them do not consider all relevant parameters or limited portions of the curing process. This publication addresses the lack of experimental methods to determine cure-dependent properties of reactive adhesives to use them as input for FE modelling to predict cure-induced stresses. The authors focus on extended rotational rheometry (ExRheo), to determine shrinkage, shear modulus, and relaxation in dependency of curing time for three adhesives. The relationship between change of viscoelastic properties, shrinkage, and curing degree is determined through DSC and kinetic modelling. The experimental results are modelled to be implemented in a numerical analysis in order to predict cure-induced stresses in constrained rheological experiment in ExRheo. Numerical results show very good agreement with the experiments, which validate the methodology. For the first time, shrinkage induced residual stresses are modelled ab initio over the curing process, without any assumptions, solely based upon direct experimental data using a single device.

This paper investigated the effect of shot peening on the strength and corrosion properties of 6082-T651 aluminium alloy. The microstructure, surface roughness, microhardness, residual stresses, and corrosion behaviour were investigated and compared with those of untreated aluminium alloy. Cracks and delaminations in the surface layer could only be seen on the treated specimens at a working pressure of 4 bar and 8 bar, while no such effect was observed at a working pressure of 1.6 bar. The surface roughness was increased more than 15 times after shot peening at a working pressure of 8 bar. Shot peening resulted in an increase in microhardness of 27% and a deeper layer with higher compressive residual stresses compared to the untreated specimens. All treated specimens exhibited improved corrosion resistance with a lower degree of anodic dissolution. The current density of the treated specimen with the lowest surface roughness was more than two-fold lower than that of the untreated specimen.

In this study, a novel approach for residual stress (RS) distribution on forged AA7175 is considered to replace and simplify the manufacturing process, based on the lean manufacturing concept. AA7175 alloy is a quench-sensitive material applied in the aeronautics industry, which is subjected to vibration and cyclic loads leading to fatigue failure. Generally, costly postprocessing operations, such as shot peening, are used to modify RS on the surfaces of parts. Considering the fact that this operation is usually performed manually and is costly, the industrial sectors have been searching for an alternative to simplify the process. Here, quenching and T74 aging are found to advantageously modify RS distribution by forming compressive RS on parts’ surface layers. The proposed heat treatment allows for the removal of the shot-peening process, helping to reduce the costs associated with the manufacturing process and to increase production quality.

The powder metallurgical manufacturing of gears offers a promising opportunity in terms of reducing the noise emission and increasing the power density. Sintered gears weigh less than conventional gears and potentially have a better noise-vibration-harshness behaviour, due to the remaining porosity. However, the potential of sintered gears for highly loaded applications is not fully utilised yet. Six variants of surface densified and case-hardened sintered gears from Astaloy Mo85 are tested to analyse the impact of the densification and case hardening depths on both the tooth root and flank load bearing capacities. Experimental investigations including metallography and computer tomography are carried out to characterise the microstructure. Furthermore, a simulation model is developed to quantitatively describe the residual stress and hardness profiles after the heat treatment. The load bearing capacity was improved by increasing the densification and case hardening depths, where the effect of the case hardening was identified to be predominant.

As basements of offshore wind turbines (OWTs) in deep water (>50 m), jacket structures are an economic alternative to monopiles. For this reason, the structural durability of jackets has become more important. In such structures, welded tubular joints are weak points for fatigue design. The harmful effect of tensile residual stresses in welding joints is well known. For these reasons, the residual stresses and the loading stresses of offshore jacket structures were determined by X-ray diffraction (XRD) using a mobile diffractometer. This allows us to directly determine the load stress at the fatigue-critical locations, namely at the weld toe at the testing rig. High tensile residual stresses up to 250 MPa were determined in a welded (and unloaded) condition. At a loaded structure (10,000 load cycles), a lower residual stress level was determined. During loading, a local increase in the stress at the welded joint that is between 1.4 and 4 times higher than the applied nominal stress was determined. Furthermore, it is shown that additional treatment (grinding and clean blasting) influences the local stress state significantly.

Fatigue properties of parts are of particular concern for safety-critical structures. It is well-known that discontinuities in shape or non-uniformities in materials are frequently a potential nucleus of fatigue failure. This is especially crucial for the Ti6Al4V alloy, which presents high susceptibility to the notch effect. This study investigates how post-processing treatments affect the mechanical performance of Ti6Al4V samples manufactured by laser powder bed fusion technology. All the fatigue samples were subjected to a HIP cycle and post-processed by machining and using combinations of alternative mechanical and electrochemical surface treatments. The relationship between surface properties such as roughness, topography and residual stresses with fatigue performance was assessed. Compressive residual stresses were introduced in all surface-treated samples, and after tribofinishing, roughness was reduced to 0.31 ± 0.10 µm, which was found to be the most critical factor. Fractures occurred on the surface as HIP removed critical internal defects. The irregularities found in the form of cavities or pits were stress concentrators that initiated cracks. It was concluded that machined surfaces presented a fatigue behavior comparable to wrought material, offering a fatigue limit superior to 450 MPa. Additionally, alternative surface treatments showed a fatigue behavior equivalent to the casting material.

On principle of equivalent tensions of adhesive connection, the estimation of remaining tensions is conducted in coverage. For this purpose, graphic differentiation of experimental dependence of adhesive durability is utilized from the thickness of coverage. Functional connection is set between adhesive durability, thickness of coverage, critical deformation of basis and remaining tensions. It allows choosing the parameter When using electrical contact treatment after gas-thermal spraying of coatings, positive results were obtained: the value of residual stresses does not exceed 200 MPa; parts with gas-thermal coatings that have undergone electrocontact treatment are characterized by a smooth change in hardness from the coating to the surface of the part and an increased diffusion zones of the system «basis-coverage» at finish treatment and exploitation. the amount of pressure and the technological scheme of the electrical contact treatment process significantly affect the level of residual stresses and the adhesion strength of the coatings. From this point of view, preference should be given to the application of coatings by gas-thermal spraying with subsequent electrical contact treatment with a gradual increase in temperature and pressure of the process. The method of graphic differentiation of the experimental dependence of the adhesive strength on the thickness of the coating was used to determine the residual stresses in the coatings obtained by gas-thermal spraying with subsequent electrical contact treatment. According to the principle of equivalence of residual stresses and critical deformation of the part during peeling of the coating, a functional relationship of adhesive strength, thickness of the coating, critical deformation of the part and residual stresses was established. This dependence allows you to determine the characteristics of coated parts for their operating conditions. У статті, виходячи з принципу еквівалентних напружень адгезійного зв`язку, проведена оцінка залишкових напружень в газотермічному покритті. Для цього використано графічне диференціювання експериментальної залежності адгезійної міцності від товщини покриття. Встановлено функціональний зв'язок між адгезійною міцністю, товщиною покриття, критичною деформацією основи та залишковими напруженнями. Це дозволяє обирати параметри поверхонь деталей із газотермічними покриттями при їх проектуванні, створенні та експлуатації.

During production, operation, transportation, and aging of finished products, stresses occur in the pipe metal. As a rule, these residual stresses affect the quality of pipes. The presence of residual stresses in products can cause brittle fracture, cracking due to corrosion, reduced elasticity, warping, etc. The development of methods for managing residual stresses in metals and products is the realization of a powerful reserve for improving the quality of metal products, which means increasing the reliability of machinery. The question arises as to which method, convenient in production conditions, should be used to assess residual stresses. A simple and affordable method for estimating residual stresses is needed in production conditions. This paper presents a simplified method for estimating residual stresses in pipes. The purpose of the work is to improve and present a methodology for estimating tangential and axial residual stresses in cold-formed pipes and tubes after heat treatment according to the method of M.M. Davydenko. Research methods: M.M. Davydenko's method for cutting rings and cutting strips from pipes. Calculation of residual stresses. Results. The method for estimation of tangential and axial residual stresses in pipes after cold deformation and after heat treatment is improved and presented. The formulas for calculating residual stresses are given. Practical value. Pipe plants need to estimate residual stresses to develop technological processes for the manufacture of new types of pipes and to meet pipe standards. The improved and presented methodology will help manufacturers in assessing residual stresses. Conclusions. Modern methods for assessing residual stresses have been considered. A methodology for calculating tangential and axial residual stresses according to M.M. Davydenko by cutting rings and cutting strips from the metal of the studied pipes is presented. The methodology is officially registered, which allows it to be used for official assessment of pipe quality., Мета роботи: удосконалення та виклад методики оцінювання тангенціальних та осьових залишкових напружень у холоднодеформованих трубах та трубах після термічної обробки методом М. М. Давиденка. Методи досліджень: метод М. М. Давиденка розрізання кілець та вирізання смуг із труб. Розрахунки залишкових напружень. Результати. Удосконалено та наведено методику оцінювання тангенціальних та осьових залишкових напружень у трубах після холодної деформації та після термічної обробки. Наведено формули розрахунку залишкових напружень. Практичне значення. Трубним заводам для розроблення технологічних процесів виготовлення нових видів труб та для виконання стандартів на труби потрібна оцінка залишкових напружень. Удосконалена та викладена методика допоможе виробникам в оцінюванні залишкових напружень. Висновки. Розглянуто сучасні методи оцінювання залишкових напружень. Наведено методику розрахунку тангенціальних та осьових залишкових напружень за М. М. Давиденком розрізанням кілець та вирізанням смуг із металу досліджуваних труб. Методика офіційно зареєстрована, що дозволяє застосовувати її для офіційного оцінювання якості труб.

This study investigates the stress corrosion cracking (SCC) behavior of type 316L stainless steel (SS316L) produced with sinter-based material extrusion additive manufacturing (AM). This technology has been shown to produce SS316L with microstructures and mechanical properties comparable to its wrought counterpart in the annealed condition. However, despite plenty of research on SCC of SS316L, little is known about SCC in sinter-based AM SS316L. This study focuses on the influence of sintered microstructures on susceptibility to SCC initiation and crack-branching. Custom-made C-rings were exposed to different stress levels in acidic chloride solutions at various temperatures. To better understand the SCC behavior of SS316L, solution-annealed (SA) and cold-drawn (CD) wrought SS316L were tested for comparison. Results showed that sinter-based AM SS316L was more susceptible to SCC initiation than SA wrought SS316L but more resistant than CD wrought SS316L. Moreover, sinter-based AM SS316L showed noticeably better resistance to crack-branching than both wrought SS316L counterparts. The investigation was supported by comprehensive pre- and post-test microanalysis using light optical microscopy (LOM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and micro-computed tomography (micro-CT)

Laser surface treatment conducted at different power levels is an option to modify titanium bone implants to produce nano- and microtopography. However, such processing can lead to excess mechanical stress within the surface layer. This research aims to calculate the level of such residual stresses after the surface processing of Ti grade IV, Ti15Mo, and Ti6Al7Nb alloys with an Nd:YAG laser. Light and scanning electron microscopies (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffractometry (XRD), optical profilography, and nano-indentation tests were applied to characterize the surface zone. The laser processing resulted in a distinct surface pattern and the formation of remelted zones 66–126 µm thick, with roughness values ranging between 0.22 and 1.68 µm. The mechanical properties were weakly dependent on the material composition. The residual stresses caused by the laser treatment were moderate, always tensile, increasing with loading, and was the highest for the Ti15Mo alloy.

The residual stress state of the machined sub-surface influences the service quality indicators of a component, such as fatigue life, tribological properties, and distortion. During machining, the radius of the cutting edge changes due to tool wear. The cutting-edge rounding significantly affects the residual stress state in the part and the occurring process forces. This paper presents a tool wear prediction model based on in-process measured cutting forces. The effects of the cutting-edge geometry on the force behavior and the machining-induced residual stresses were examined experimentally. The resulting database was used to realize a Machine Learning algorithm to calculate the hidden value of tool wear. The predictions were validated by milling experiments using rounded cutting edges for different process parameters. The microgeometry of the cutting edge could be determined with a Root Mean Square Error of 8.94 μm.

The built-in heterogeneity of the composite laminates has been exploited to tailor the stiffness and strength requirements of modern structures to meet the specific functional demands. However, the non-homogeneity in these composites is the root cause for most of their failures. One of the undesirable consequences of the inherited heterogeneity is the development of cure-induced stresses during composite manufacturing. This work aims to investigate the influence of process-induced stresses on interlaminar radial strength in curved composite laminates. Glass-Epoxy (GE) laminates of two different thicknesses were prepared by hand lamination technique using V-shaped tooling and cured under room temperature. The state of residual stresses in GE laminates is varied by post-curing these laminates at different temperatures. Curved bending strength (CBS) and corresponding interlaminar radial stress for delamination of L-bend laminates were evaluated experimentally using four points bending test. The residual stress profile in each GE laminate is experimentally characterized by employing the Slitting method. The results indicate that the residual stresses have a negligible effect on the critical stress for initial delamination in GE laminates. But, the critical stress for delamination was found to be independent of the laminate thickness and increased with higher curing temperatures. The delaminated surfaces of L-bend laminates were studied using a scanning electronic microscope (SEM). The enhancement in the critical stress due to post-curing can be attributed to the improved fiber-matrix interfacial bonding with higher curing temperature.

The existence of residual stresses in unloaded arteries has long been known. However, their effect is often neglected in experimental studies. Using a recently developed modelling framework, we aimed to investigate the role of residual stresses in the mechanical behaviour of the tri-layered wall of the pig thoracic aorta. The mechanical behaviour of the intact wall and isolated layers of n = 3 pig thoracic aortas was investigated via uniaxial tensile testing. After modelling the layer-specific mechanical data using a hyperelastic strain energy function, the layer-specific deformations in the unloaded vessel were estimated so that the mechanical response of the computationally assembled tri-layered flat wall would match that measured experimentally. Physiological tension–inflation of the cylindrical tri-layered vessel was then simulated, analysing changes in the distribution of stresses in the three layers when neglecting residual stresses. In the tri-layered model with residual stresses, layers exhibited comparable stresses throughout the physiological range of pressure. At 100 mmHg, intimal, medial, and adventitial circumferential load bearings were 16 $$\pm$$ ± 3%, 59 $$\pm$$ ± 4%, and 25 $$\pm$$ ± 2%, respectively. Adventitial stiffening at high pressures produced a shift in load bearing from the media to the adventitia. When neglecting residual stresses, in vivo stresses were highest at the intima and lowest at the adventitia. Consequently, the intimal and adventitial load bearings, 23 $$\pm$$ ± 2% and 18 $$\pm$$ ± 3% at 100 mmHg, were comparable at all pressures. Residual stresses play a crucial role in arterial mechanics guaranteeing a uniform distribution of stresses through the wall thickness. Neglecting these leads to incorrect interpretation of the layers’ role in arterial mechanics.

The residual stresses state that a mechanical part obtained after machining is a crucial factor that impacts its in-service performance. This stress state is influenced by the thermomechanical loads exerted on the parts during the machining process, which are, in turn, determined by the tool parameters, process, and machining conditions. The aim of the present research was to anticipate how the cutting tool’s edge radius, rake angle, and clearance angle would affect the forces, temperature, and residual stresses induced while orthogonally cutting aluminum AA6061-T6. To achieve this, two-dimensional DEFORM™ software was utilized to develop a finite element model. The residual stresses trend results obtained demonstrated that rake angles of 0° and 17.5–20° values with a small edge radius (5 to 10 µm) and clearance angles of 7 and 17.5° values gave higher compressive stresses. The obtained simulated results were in good agreement with the experiments. The cutting forces, the temperature, and the maximum and minimum machining-induced residual stresses were found to be influenced more by the tool edge radius and the tool rake angle. The influence of the clearance angles on the above-mentioned machining responses was the least. Residual stresses can have a significant impact on the in-service performance of machined parts. The obtained results will help engineers select or design tools that promote a desired surface integrity during machining. This task is not obvious in practice because of difficulties in measuring residual stresses and also because the machining parameters and the tool geometry parameters have different and opposite impacts on thermo-mechanical loads, productivity, and on machining induced residual stresses.

Quantitative and qualitative residual stress evolution in low-alloyed steel during heat treatment is investigated on three different length scales for sourgas resistant seamless steel tubes: on the component level, on the level of interdendritic segregation and on precipitate scale. The macroscopic temperature, phase and stress evolution on the component scale result from a continuum model of the heat treatment process. The strain and temperature evolution is transferred to a mesoscopic submodel, which resolves the locally varying chemistry being a result of interdendritic segregation. Within the segregation area and the surrounding matrix precipitates form. They are categorized with respect to their tendency for formation of microscopic residual stresses. After rapid cooling macroscopic stresses up to 700 MPa may form dependent on the cooling procedure. Mesoscopic stresses up to Δ50 MPa form depending on the extent of segregation. Carbides and inclusions occuring in low-alloyed steel are ranked by their tendency for residual stress formation in the iron matrix. This scale bridging study gives an overview of residual stresses, their magnitude and evolution on three different length scales in low-alloyed steels and the results presented can serve as a input for steel design.

U radu su ispitana zaostala naprezanja koja se javljaju u TiN prevlaci na čeliku EN DIN 100Cr6. Rad se sastoji od teorijskog i eksperimentalnog dijela. U teorijskom dijelu detaljno je obrađena toplinska obrada čelika EN DIN 100Cr6, te njegova mikrostruktura. Obzirom da su uzorci prevlačeni TiN prevlakom opisana su svojstva i primjena prevlake, postupci prevlačenja iz parne faze PVD i PACVD i ispitivanje zaostalih naprezanja na površini prevlaka metodom rendgenske difrakcije. Na kaljenim i popuštenim uzorcima s prevlakom TiN izmjerena je debljina prevlake kalotestom i prionjivost prevlake prema normi VDI 3198. Rendgenskom difrakcijom izmjerena su zaostala naprezanja na površini diska od kaljenog i popuštenog čelika EN DIN 100Cr6 te diskovima s prevlakom PVD TiN i PACVD TiN u tri smjera pod međusobnim kutom od 45°. U svim ispitanim slučajevima nastala su vlačna zaostala naprezanja.. Na površini kaljenog i popuštenog čelika zasotala naprezanja iznose od 150 MPa do 190 MPa, na površini PVD TiN prevlake zaostala naprezanja iznose od 40 MPa do 60 MPa i na površini PACVD TiN prevlake zaostala naprezanja iznose od 115 MPa do 155 MPa. In this thesis, residual stresses that occur in TiN coatings on DIN 100Cr6 steel were examined. The final thesis consists of a theoretical and experimental part. In the theoretical part, the heat treatment of EN DIN 100Cr6 steel and its microstructure are discussed in detail. Since the samples were coated with TiN, the properties and application of the coating, as well as the PVD and PACVD coating processes and residual stress testing on the surface of the coatings using X-ray diffraction, were described. The thickness of the TiN coating and its adhesion according to the VDI 3198 standard were measured on hardened and tempered samples with TiN coating. Using X-ray diffraction residual stresses on the surface of the disk made of hardened and tempered EN DIN 100Cr6 steel, as well as disks with PVD TiN and PACVD TiN coatings were measured in three directions at an angle of 45° to each other. In all cases, tensile residual stresses were observed. Residual stresses on the surface of hardened and tempered steel ranged from 150 MPa to 190 MPa, while residual stresses on the surface of PVD TiN coatings ranged from 40 MPa to 60 MPa, and residual stresses on the surface of PACVD TiN coatings ranged from 115 MPa to 155 MPa

The process of cold expansion creates compressive stresses around the mounting hole, which can help to reduce stress concentrations during the loading of a structure. A numerical simulation using the finite element method was conducted to analyse the effect of cold expansion on perforated plates of different thicknesses. The simulation considered the thickness of the plate and the tapered mandrel and examined the induced residual stresses. The results showed that the magnitude of the circumferential residual stresses varied depending on the thickness of the plate and that the extent of the zone of compressive stresses was strongly affected by the plate thickness. These findings are particularly relevant to the optimisation of the cold expansion process, as the optimal parameters for a particular plate thickness may not be optimal for some other thickness. Therefore, the results of this study can guide the optimisation of the cold expansion process for different plate thicknesses.

This study aims to demonstrate the capability of the digital image correlation (DIC) technique for evaluating full-field residual stresses in wire and arc additive manufactured (WAAM) components. Investigations were carried out on WAAM steel parts (wall deposited on a substrate) with two different wall heights: 24 mm and 48 mm. Mild steel solid wire AWS ER70S-6 was used to print WAAM walls on substrates that were rigidly clamped to H-profiles. DIC was used to monitor the bending deformation of WAAM parts during unclamping from the H-profiles, and residual stresses were calculated from the strain field captured during unclamping. Residual stresses determined from the proposed DIC-based method were verified with an analytical model and validated by the results from established residual stress measurement techniques, i.e., the contour method and X-ray diffraction.

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2023; Aachen 1 Online-Ressource (2023). = Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2023, In the industrial applications, thermally-driven manufacturing approaches such as welding and additive manufacturing are widely used to assemble and create metallic parts. The Gas tungsten arc welding (GTAW) is fusion welding process used to join two or more metallic components together. On the other hand, additive manufacturing (AM) is a revolutionary manufacturing technique used to construct objects of sophisticated geometries by successively melting layers of metallic powder. In both GTAW and AM, the material being treated undergoes complex multiphysical phenomena driven by the rapid heating-cooling cycles. Therefore, understanding and investigating these fusion processes are essential to gain insight into the coupled multiphysical phenomena occurring during melting, remelting, and solidification processes. One of the main aims in the underlying work is to establish an approach to understanding the distribution mechanism of stresses and deformations. It has been reported that modeling the thermomechanical responses in welding and AM is very time consuming and computationally demanding. Therefore, simplifications are required to improve the performance and allow the modeling of larger domains with a sufficient accuracy. In this thesis, a thermomechanical modeling approach is developed to understand the fundamental physics of thermally-driven processes with the aim of predicting the temperature field and the final state of residual stresses in GTAW and AM. To this end, a macroscopic material modeling approach is developed based on a continuum mechanical framework in which the welded or AM part is represented as a homogenized continuous medium. Following the thermodynamically consistent formulation, the approach leads to volume-coupled nonlinear partial differential equations (PDEs). The formulations employ the phase-field method (PFM) in a novel way to describe the state of the material and to track its phase change from solid (hard) and unconsolidated powder to liquid (soft) and finally to a solidified state. Furthermore, PFM enables the definition of the material properties as functions of the material state, i.e., hard, soft, or powder state. The material states (phases) are separated by a diffuse interface that allows smooth transition of these states across the interface. In particular, the phase-field and phase-field history variables are utilized to propose expressions for phasefield-dependent material properties. In this treatment, a realistic description of the material parameters is achieved based on the material state, which leads to a reduction in the modeling complexity. The formulation of the phase-field thermo-elastoplastic model leads to the coupled governing PDEs, which are complemented by constitutive relations and evolution equations. Regarding the elastoplastic response in metals, two different plasticity models are described and implemented, i.e., the return mapping method and the incremental method, following the J2 theory with the isotropic strain hardening law. Furthermore, numerical investigations are performed to compare the performance of the implemented models using the open-access finite element package FEniCS Project. To validate our modeling approaches, representative examples of two and three-dimensional GTAW and selective laser melting are implemented and solved using the finite element method. In these initial-boundary-value problems, the temperature fields and residual stresses are compared with reference solutions from the literature., Published by Aachen

This paper presents a novel method for the design of purely elastic interference fits by exploiting the plastic properties of a material. In this process, the elastic potential of the material is expanded by the targeted application of residual stresses and material strengthening, in such a way that additional operational loads due to rotating bending moments, torsion, temperature changes, and centrifugal forces are absorbed by the hub in a purely elastic manner, and plastic deformations are avoided. In the ideal case, the performance shown by the connection can be almost doubled compared to conventional elastically joined interference fits. Compared with conventional elastically–plastically joined interference fits, a specifically defined additional safety against plastic deformation can be guaranteed. In addition to the prerequisites of plasticity theory, the fundamental aspects of the process are presented and investigated on the basis of two-dimensional numerical calculation models. Both ideal plastic and hardening material models were used. The results of this work showed that previous stress limits can be significantly increased up to full plastic loading and that the utilization of plastic material properties is also made possible by plastic conditioning for applications that were previously designed to be purely elastic.

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This study aims to quantify the influence of laser peening on the structural integrity of a FSWelded aluminium fuselage joint. Fatigue tests with different stress amplitudes were performed for samples in as-machined and friction stir welded conditions to characterise the loss of fatigue strength and the effect of stress amplitude on the degradation of fatigue life. Optimisation of laser parameters was carried out to achieve an appropriate through-thickness stress profile. The optimised parameters were used to peen tensile coupon specimens and analyse the fatigue life recovery. The residual stress fields were quantified using the central incremental hole drilling method on peened and unpeened samples. It was found that both the microstructure and superposition of residual stresses from the welding process and peening treatment play a crucial role in the fatigue behaviour of the FSWelded joint. Using the parameters and layout described in this article, laser peening was able to increase the fatigue life of as-welded samples by a factor of 2.4 for the lower end of the load spectrum tested. This represents a recovery of 65% when compared to the pristine aluminium reference samples.

Carburizing heat treatment is widely used in the fabrication of gears to improve their fatigue performance. The effects of carburizing process on the material properties surface hardness, residual stresses, retained austenite of case-hardened 18CrNiMo7-6 and the consequential fatigue strength have not been studied in detail. In this research, the high-cycle fatigue performance of uncarburized and carburized 18CrNiMo7-6 gear steel were studied. In addition, the evolution processes of hardness, microstructure and residual stress of carburized specimens during the fatigue test were observed quasi-in situ. The initiation of fatigue cracks was also analyzed by SEM and the transformation of retained austenite during the fatigue test was observed by TEM. The results showed that the fatigue strength of carburized specimens has an increase-decrease trend with the increase of effective case depth. Besides, the fatigue failure mode of steel changes from surface failure to internal failure after being carburized, during which retained austenite plays an important part. In addition, if a large amount of retained austenite exists in the specimen with internal failure, the high-density twin martensite region formed by the retained austenite transformation can act as the crack initiation site, which is harmful to fatigue performance.

As a new surface treatment technology, laser shock peening (LSP) is a multi-point overlay process of single-point laser shock. In this study, the finite element method (FEM) was used to build a model of single-point laser shock, and the model was verified by experiments. The difference in residual stresses between the experimental and simulated results was less than 20%. Then, the effects of the stress field and deformation of 20CrMnTi with different laser shock parameters were simulated and analyzed. According to the mechanical response of 20CrMnTi to different laser shock parameters, the optimal shocking process parameters for single-point shocking via LSP were determined to be a shock energy of 5 J, a laser pulse width of 20 ns, and an impact number of 5. Lastly, a simulation of multi-point laser shock was performed with the optimal parameters, and the residual compressive stress values of multi-point impacts are close to those of single-point impacts under the same process conditions.

U diplomskom radu obrađena je tema analize zaostalih naprezanja pri MIG i TIG zavarivanju visokolegiranih Cr-Ni čelika. Rad se sastoji od teorijskog i eksperimentalnog dijela. U teorijskom dijelu rada detaljno su opisani pojmovi vezani uz nastanak zaostalih naprezanja u zavarenim konstrukcijama te je dan pregled metoda mjerenja zaostalih naprezanja s posebnim naglaskom na mjerenje rendgenskom difrakcijom. Nadalje, proučena je problematika zavarljivosti visokolegiranih Cr-Ni čelika te su za TIG i MIG postupke zavarivanja definirani načini odabira dodatnih materijala i zaštitnih plinova. U eksperimentalnom dijelu rada provedeno je zavarivanje sučeljenog spoja od austenitnog nehrđajućeg čelika TIG i MIG postupkom zavarivanja te je za svaki postupak provedeno mjerenje zaostalih naprezanja rendgenskom difrakcijom. Provedena je analiza rezultata zaostalih naprezanja. Također, na uzorcima je provedeno mjerenje deformacija kao i makro analiza. The topic of residual stress analysis during MIG and TIG welding of high-alloyed Cr-Ni steel was dealt within the thesis. The thesis consists of a theoritical and an experimental part. In the theoretical part of the paper, concepts related to the occurrence of residual stress in welded structures are described in detail, and there is an overview of residual stress measurement methods with special emphasis on X-ray diffraction measurement. Furthermore, the issue of weldability of high-allyoed Cr-Ni steels was studied, and methods of selecting filler materials and shielding gases were defined for TIG and MIG welding processes. In the experimental part of the thesis, the butt joint was welded from austenitic stainless steel using the TIG and MIG welding process, and the residual stresses were measured by X-ray diffraction for each process. An anaysis of the residual stress results was carried out. Also, the deformation measurements and macro analysis were performed on the samples.

Метою дипломної роботи є дослідження впливу послідовності встановлення елементів кріплення у орбітальному напрямку секцій фюзеляжу на величини залишкових напружень та деформацій, а також знаходження такого варіанту послідовності встановлення елементів кріплення для мінімізації їх впливу. В даній роботі розглядаємо типову секцію літака Boeing 787 та варіанти встановлення елементів кріплення, що можуть зустрічатися у авіації. Для вирішення завдання використовувалися аналітичні методи, оскільки моделювання за допомогою чисельних методів конфігурації з’єднання двох секцій фюзеляжу для 460 кріпильних елементів не уявлялося можливим. The aim of the thesis is to study the influence of the sequence of installation of fasteners in the orbital direction of the fuselage sections on residual stresses and deformations, as well as to find such a variant of the sequence of installation of fasteners to minimize their impact. In this work, we consider a typical section of the Boeing 787 aircraft and options for installing fasteners that can be found in aviation. Analytical methods were used to solve the problem, since numerical modeling of the configuration of the connection of two sections of the fuselage for 460 fasteners was not considered possible.

The new alloying concept of multi-element systems with defined entropy (HEA—high-entropy alloy; MEA—medium-entropy alloy) is gaining increasing importance in materials research. Significantly improved properties or combinations of properties are shown by some HEA/MEA systems. Thus, primarily the production and resulting microstructures of HEA, as well as its properties, have been investigated so far. Furthermore, processing is a main issue in transferring HEA systems from the laboratory to real components. Since welding is the most important joining process for metals, it is crucial to investigate the influence of welding to guarantee component integrity. Welding leads to residual stresses, which significantly affect the component integrity. Hence, the focus of this study is the residual stress formation and distribution in a CoCrFeMnNi HEA and ternary CoCrNi MEA using two different welding processes: tungsten inert gas (TIG) welding and solid-state friction stir welding (FSW). As a pathway for the application of HEA in this investigation, for the first time, residual stress analyses in realistic near-component specimens were performed. The residual stresses were determined by X-ray diffraction (XRD) on the surfaces of top and root weld side. The results were correlated with the local welding microstructures. The results show that both FSW and TIG generate significant tensile residual stresses on the weld surfaces in, and transverse to, the welding direction. In the case of FSW of the CoCrFeMnNi HEA, the longitudinal residual stresses are in the range of the yield strength of approx. 260 MPa in the weld zone.

Namen diplomskega dela je bila raziskava vpliva nitridiranja na spremembo dimenzij elementov iz 42CrMo4 jekla oblike polnih obročev in C-obročev. Nitridiranje temelji na obogatenju površinskega sloja z dušikom, ki sam ali pa v spojini povzroča površinsko utrditev. Obogatitev površinskega sloja povzroči povečanje volumna in posledično spremembo dimenzij elementa in nastanek notranje napetosti. Na spremembo geometrije elementa lahko vplivajo tudi v materialu prisotne notranje napetosti. Eksperimentalno delo je obsegalo merjenje zaostalih notranjih napetosti v jeklu v dobavnem stanju, po žarjenju za odpravo zaostalih napetosti in nitridiranju. Merjenje oblik in dimenzij smo izvedli s 3D koordinatnim merilnikom. Za karakterizacijo mikrostrukture smo uporabili svetlobno in vrstično elektronsko mikroskopijo. Rezultati preiskave kažejo, da je na spremembo dimenzij preizkušancev najbolj vplival dušik, ki privede pod vplivom difuzije do nastanka površinskega sloja nitridov. Po nitridiranju na površini ostanejo tlačne napetosti, ki povečajo obrabno obstojnost in dinamično trdnost površine. Pri toplotnih obdelavah nastale termične napetosti zaradi neenakomernega ohlajanja po globini nimajo opaznega vpliva na spremembo dimenzij elementov. The objective of this study was to investigate the effect of nitriding on the change in element dimensions of full circles and C-circles of 42CrMo4 steel. Nitriding is based on the enrichment of the surface layer with nitrogen, which alone or in compounds causes surface hardening. The enrichment of the surface layer leads to an increase in volume and thus to a change in element dimensions and the development of residual stresses. The change in element geometry can also be affected by the presence of residual stresses in the material. Experimental work includes measurement of residual stresses in the initial state of the steel, after annealing to relieve residual stresses, and after nitriding. A 3D coordinate measuring machine was used to measure shapes and dimensions, and an optical microscope and a scanning electron microscope were used to characterize the microstructure. The results of the study show that the change in the dimensions of the subjects was most affected by nitrogen, which leads to the formation of a surface layer of nitrides through diffusion effects. After nitriding, only compressive stresses remain on the surface, which increases the durability and dynamic hardness of the surface. During heat treatment, the new thermal stresses have no noticeable effect on the change of element dimensions due to the non-uniform cooling in depth.

This paper presents the results of research dealing with assessing the welding effect (temperature–stress cycles) on the residual stresses in these steels. Residual stresses, remaining in the material after technological processing, pose a risk, especially at the areas of local stress peaks. During the real welding, residual stresses achieve their highest values in the heat-affected zone (HAZ), which is very narrow and therefore quite problematic to be studied in detail. Therefore, a methodology of temperature–stress physical simulations has been developed to study residual stresses in the HAZ over a 6.5 times larger section of the test sample. Thus, temperature cycles corresponding to the real welding were applied to the samples in the thermo-mechanical simulator, Gleeble 3500. Subsequently, the residual stresses were determined by the X-ray diffraction method. At the same time, the influence of annealing temperature on the residual stress reduction and redistribution was also investigated. Obtained results were compared and discussed with the similar studies about HSLA and duplex steels.

Fine-grained steels, which belong to the HSLA (High-Strength Low-Alloy) group of steels, are increasingly used for parts of statically and dynamically loaded constructions. Due to the thermal effect of welding, combined with the inherent stiffness and clamping stiffness of the part, residual stresses are generated in the HAZ (heat-affected zone) which affect the fatigue life of the sub-weld and the entire construction. In this article, a specific temperature cycle measured during welding is used, which, together with a defined clamping stiffness, produces residual stresses of a defined shape and value in the sample. Subsequently, the effect of these stresses on the fatigue life on the change of the S–N curve compared to the annealed material, is assessed. Temperature cycles were applied using a Gleeble 3500 and the residual stresses were analyzed by X-ray diffraction (XRD). It was found that the effect of residual stresses decreased the fatigue strength by 33% compared to the annealed material. It was further found that by using annealing to reduce the residual stresses, it is possible to restore the fatigue life of S700MC steel to the original value of the base material.

Low weight and high strength are significant factors in the current decade’s spread of composite sandwich materials. Previous studies have proven that forming stiffening ribs in these materials through the Single Point Incremental Forming (SPIF) process is possible and gives encouraging results. On the other hand, knowledge of residual stress (RS) values that form during the manufacturing process is essential, as they may affect the structural integrity of manufactured elements, whether in compression or tension. The investigation of the RS in the composite materials formed by the SPIF process using the XRD method was very limited in the previous studies, so this research aims to apply the X-ray diffraction (XRD) method to determine RS on the part of the LITECOR® sandwich material formed using SPIF. LITECOR® consists of a plastic core between two layers of steel. In this study, three types of LITECOR® were used with differing plastic core thicknesses of 0.8, 1.25, and 1.6 mm, while the steel layers’ thickness remained the same at 0.3 mm. The axial and traverse RSs were measured in five positions on both sides of the formed part. It was found that the achieved RSs varied from tensile to compressive along the formed regions. It was found that the residual stress values in both directions were inversely proportional to the thickness of the plastic core. It was noted that the highest RS values were in the unformed base metal, after which the RS was reduced on both sides of the SPIF-formed region, followed by a rise in the RS at the concave of the SPIF-formed region. The maximum measured RS for X-axes was 1041 MPa, whereas, for Y-axes, it was 1260 MPa, both of which were recorded on the back side at a thickness of t = 0.8 mm.

This study focuses on the role of the damage evolution when estimating the failure behavior of AISI 1045 steel for sensing and measuring metal cutting parameters. A total of five Lagrangian explicit models are established to investigate the effect of applying damage evolution techniques. The Johnson–Cook failure model is introduced once to fully represent damage behavior, i.e., no damage evolution is considered, and as a damage initiation criterion in the remaining approaches. A fracture energy-based model is included to model damage propagation with different evolution rates. Temperature-dependent and temperature-independent fracture energy models are also investigated. Dry orthogonal cutting and residual stresses measurements of AISI 1045 are conducted for validation. The significance of the damage evolution is investigated using honed-tool and sharp-tool models. Including the damage evolution led to a prediction of higher workpiece temperatures, plastic strains, cutting forces, and residual stresses, with no clear differences between linear and exponential evolution rates. The role of damage evolution is more evident when temperature-dependent evolution models are used.

Additive manufacturing (AM) has seen remarkable development in recent years due to relatively high efficiency of the process. Cold spraying (CS) is a particular method of AM, in which titanium and titanium alloy powders are used. CS is a very competitive technology enabling the deposition of coatings, repairing machine parts, and manufacturing new components. For specific applications, the surface of cold-sprayed materials may require further processing. This paper reports an attempt to employ laser surface treatment (LST) of cold-sprayed coatings on an aluminium alloy substrate. The influence of laser beam interaction time on the coatings’ properties was analysed. The microstructure was investigated and observed employing scanning electron microscopy (SEM). To evaluate residual stress after CS and LST, the sin2ψ technique was used. Investigations were also performed on Vickers hardness, contact angle, and surface roughness. Significant changes in the surface morphology of the coatings and elevated residual stress levels dependent on the laser beam interaction time were observed. Increased Vickers hardness was recorded for titanium alloy Ti6Al4V. LST also led to increased surface hydrophilicity of the modified materials Ti and Ti6Al4V.

Conventional thermal spraying processes are almost exclusively carried out in an air atmosphere, resulting in the oxidation of the particle surfaces and interfaces within the coating and between the substrate and coating. Furthermore, the initial process of surface activation conventionally takes place in an air atmosphere, preventing an oxide-free interfacial transition. Consequently, the application of spraying materials with high oxygen affinity represents a major challenge. To overcome these issues, the present study utilized silane-doped inert gases to create an environment in which the oxygen concentration was equivalent to the residual oxygen content in an extreme high vacuum. By transferring the corundum blasting and coating process (wire arc spraying) to this environment, materials with a high oxygen affinity can be applied without oxidation occurring. For industrial use, this is an interesting prospect, e.g., for repair coatings, as the homogeneity of the composite is improved by a non-oxidized coating. Using the example of arc-sprayed copper coatings, the microstructure and mechanical properties of the coatings were analysed. The results showed that the oxide-free, wire arc sprayed copper coatings exhibited an improved wetting behaviour resulting in a significant reduction of the coating porosity. Moreover, the improved wetting behaviour and led to an increase in the bonding rate and apparent Young’s modulus. Contrary to expectations, the residual stresses decrease although relaxation mechanisms should be inhibited, and possible reasons for this are discussed in the paper.

Residual stress measurement is of utmost importance for the safety and reliability of engineering components and has been an active area of scientific research. Relaxation techniques such as hole drilling, slitting and ring core method are widely applied semi destructive techniques for residual stress measurements in polymer composites. This article reviews the recent literature on the measurement of residual stress in polymer composite by employing the above-mentioned relaxation techniques. This article summarizes the categories of residual stresses, causes of formation, techniques of measurements and also briefly outlines the chronological developments of the Hole drilling and slitting method. The article also provides a comparative summary of these relaxation methods.

Recent strides in wire + arc additive manufacturing (WAAM) of aluminum components present unique chances for more enhancements in their properties. More studies were done by controlling manufacturing parameters, the wire properties, arc mode, and applying post-process treatment to regulate the microstructure and mechanical characteristics of the fabricated aluminum parts. In this paper, a wide range of previous late studies has been chosen to research the different attempts leading to an enhancement in the mechanical properties of aluminum components fabricated with WAAM. A discussion of the challenges of applying WAAM for aluminum alloys is also reviewed. The main purpose of this paper is to evolve a detailed understanding of the mechanical characteristics of the deposited aluminum components at various conditions.

Dissertação de Mestrado Integrado em Engenharia Mecânica apresentada à Faculdade de Ciências e Tecnologia O trabalho realizado aborda a implementação do método do furo incremental em laminados híbridos fibra-metal CFRP-aço como ferramenta experimental para a determinação das tensões residuais através das camadas do laminado, a partir das deformações causadas pela relaxação das tensões residuais devido à presença do furo. Neste trabalho foram utilizados provetes semelhantes com a configuração CFRP-aço [02/aço]s. Visto tratar-se de um material laminado, em que as camadas do polímero reforçado com fibras têm características ortotrópicas, houve necessidade de se proceder a uma simulação numérica através do método dos elementos finitos para determinar os coeficientes de calibração necessários para o cálculo das tensões residuais. O cálculo das tensões baseou-se no chamado método integral iterativo não regularizado. Foi objetivo principal do trabalho implementar o método integral com regularização de Tikhonov para a determinação das tensões residuais não uniformes libertadas, visto ser uma ferramenta essencial para suavização e eliminação de dispersão nos resultados de problemas numéricos inversos, comparando os resultados obtidos com os dois métodos: método integral regularizado e não regularizado.A implementação dos métodos foi realizada utilizando a linguagem de programação Python, por forma a obter-se computacionalmente a distribuição das tensões residuais através das camadas do laminado fibra-metal.Os resultados obtidos permitiram validar a utilização do método do furo incremental, aliado ao método integral com regularização de Tikhonov para o cálculo de tensões residuais não uniformes em laminados fibra-metal. Apesar de alguma dispersão observada nas tensões residuais determinadas em profundidades mais elevadas, os métodos utilizados permitiram determinar o perfil de tensões residuais ao longo da espessura de vários furos em provetes de CFRP-Aço. Houve uma concordância entre os resultados obtidos pelos métodos utilizados, identificando claramente as singularidades nas interfaces entre as camadas de fibras orientadas e na interface fibra-metal. The work conducted addresses the implementation of the incremental hole drilling method in CFRP-steel laminates as an experimental tool for the determination of residual stresses through the laminated layers, from the deformations caused by the relaxation of residual stresses due to the presence of the hole. Since it is a laminate material, in which the fibre-reinforced polymer layers have orthotropic characteristics, it was necessary to carry out a numerical simulation using the finite element method to determine the necessary calibration coefficients for the calculation of the residual stresses. The stress calculation was based on the so-called iterative integral method. In this work, the integral method with Tikhonov regularization was used to determine the non-uniform residual stresses released, as it is an essential tool for smoothing and elimination of scattering in the results of inverse numerical problems.The implementation of the methods was carried out using Python programming language, to computationally obtain the distribution of residual stresses through the layers of the fibre-metal laminate.The obtained results contribute towards validating the use of the incremental hole drilling method, combined with the integral method with Tikhonov regularization, for the calculation of non-uniform residual stresses in fibre-metal laminates. Despite some observed scattering in the residual stresses determined at deeper depths, the methods used allowed the determination of profiles of residual stresses along the thickness of several holes in CFRP-Steel specimens. There was an agreement between the results obtained by the methods used, clearly identifying the singularities at the interfaces between the layers of oriented fibres and in the fibre-metal interface.

Wire arc additive manufacturing (WAAM) is an additive manufacturing process based on the arc welding process in which wire is melted by an electric arc and deposited layer by layer. Due to the cost and rate benefits over powder-based additive manufacturing technologies and other alternative heat sources such as laser and electron beams, the process is currently receiving much attention in the industrial production sector. The gas metal arc welded (GMAW) based WAAM process provides a higher deposition rate than other methods, making it suitable for additive manufacturing. The fabrication of mild steel (G3Si1), austenitic stainless steel (SS304), and a bimetallic sample of both materials were completed successfully using the GMAW based WAAM process. The microstructure characterization of the developed sample was conducted using optical and scanning electron microscopes. The interface reveals two discrete zones of mild steel and SS304 deposits without any weld defects. The hardness profile indicates a drastic increase in hardness near the interface, which is attributed to chromium migration from the SS304. The toughness of the sample was tested based on the Charpy Impact (ASTM D6110) test. The test reveals isotropy in both directions. The tensile strength of samples deposited by the WAAM technique measured slightly higher than the standard values of weld filament. The deep hole drilling (DHD) method was used to measure the residual stresses, and it was determined that the stresses are compressive in the mild steel portion and tensile in austenitic stainless steel portion, and that they vary throughout the thickness due to variation in the cooling rate at the inner and outer surfaces.

The resistance to delamination in polymer composite depends on their constituents, manufacturing process, environmental factors, specimen geometry, and loading conditions. The manufacturing of laminated composites is usually carried out at an elevated temperature, which induces thermal stresses in composites mainly due to a mismatch in the coefficient of thermal expansion (CTE) of fiber and matrix. This work aims to investigate the effect of these process-induced stresses on mode-I interlaminar fracture toughness (GI) of Glass-Carbon-Epoxy (GCE) and Glass-Epoxy (GE) composites. These composites are prepared using a manual layup technique and cured under room temperature, followed by post-curing using different curing conditions. Double cantilever beam (DCB) specimens were used to determine GI experimentally. The slitting technique was used to estimate residual stresses (longitudinal and transverse direction of crack growth) inherited in cured composites and the impact of these stresses on GI was investigated. Delaminated surfaces of composites were examined using a scanning electron microscopy (SEM) to investigate the effect of post-curing on the mode-I failure mechanism. It was found that GI of both GE and GEC composites are sensitive to the state of residual stress in the laminas. The increase in the GI of laminates can also be attributed to an increase in matrix deformation and fiber–matrix interfacial bond with the increase in post-curing temperature.

V zaključni nalogi obravnavamo primer, ko so deformacijska stanja troslojnega kompozitnega nosilca odvisna od snovnih in geometrijskih lastnosti ter od zaostalih napetosti v posameznih plasteh nosilca. Izpeljali smo enačbe za izračun lege nevtralne osi in velikosti radija ukrivljenosti vzdolž celotnega nosilca. Na podlagi dobljenih enačb smo zapisali programsko kodo, ki nam poda deformacijsko obliko nosilca glede na izbrane lastnosti in predpisane zaostale napetosti. V posebnem primeru, ko imamo po vsem nosilcu konstantne snovne, geometrijske in zaostale napetosti, dobimo na tem odseku upogibnico, ki ustreza krožnemu loku. Numerično dobljene oblike smo primerjali z eksperimentalno dobljenimi. Rešili smo tudi inverzni primer, pri katerem smo s pomočjo analize slike deformiranega nosilca, ob znanih materialnih in geometrijskih lastnostih, določili potek zaostalih napetosti v posameznih plasteh. Pokazali smo, da izpeljane enačbe ustrezno opišejo dejansko deformacijo nosilca. In the final thesis, we consider the case where the deformation states of a three-layer composite beam depend on the material and geometrical properties and on the residual stresses in the individual layers of the beam. We have derived equations that govern the position of the neutral axis and the magnitude of the radius of curvature along the entire beam. Based on the equations obtained, we wrote a computer code that gives the shape of the deformed beam according to the selected properties and the prescribed residual stresses. In a special case, when the material, geometric and residual stresses are constant throughout the beam, a shape corresponding to a circular arc is obtained. The numerically obtained shapes were compared with those obtained experimentally. We have also solved the inverse problem using image analysis of the deformed beam with known material and geometric properties and determined the residual stresses in the individual layers. We have shown that the derived equations adequately describe the actual deformation of the beam.

One of the major challenges in high-deposition rate Directed Energy Deposition processes is the resultant residual stresses generated during material deposition, often leading to distortion and poor material characteristics. Important part families suitable for DED process in aerospace sector are thin-wall components, characterized by a large base surface area with rib-like strengthening structures. Here, the substrate plate can be designed to be a part of the final component. The integration of substrate plate into final component results in possible deformation due to residual stress release during machining. This paper therefore investigates the effect of various powder-based Laser Metal Deposition process parameters and strategies on the residual stress state of the additively manufactured Ti-6Al-4V components and the resulting stress release during machining process. The analysis has been carried out during the machining process by including in-process strain measurements of the substrate. The embraced layer removal method allows the determination of machining zone specific stress release mapping, based on an analytical and FEM-model. Hence, the initial residual stress state of the builds was calculated, which revealed that although the heat treatment resolved most of the residual stresses, also in heat treated parts residues were identified depending on the part clamping during the treatment. Furthermore, the study revealed that the significant residual stresses are present in the layers close to the substrate.

Shot-peening treatment was applied to a quenched and tempered DIN 34CrNiMo6 steel to improve its high-cycle R: -1 axial fatigue strength. Compared with the machined condition, the increase in the fatigue limit was 21.8%. S-N curves for shot-peened and the as machined condition were presented and compared with those obtained in previous research for rotating bending fatigue, including curves for mirror-polished specimens. The applied shot-peening treatment in this work (I-sp: 8A and 200% coverage) for quenched and tempered (Q + T) DIN 34CrNiMo6 steel introduced a compressive residual stress field and an increase in surface roughness, as well as minor variations in microstructure, hardness and the FWHM (full width of the diffraction peak at half maximum intensity) parameter. The introduced compressive residual stress field tended to reduce when an external stress is applied. This was due to the onset of plastic strain. In this paper, two types of quasi-static tests were conducted by applying an axial stress with six different magnitudes and in the two directions (compressive or tensile). This was in order to assess their influence on the relaxation of surface residual stresses. Due to the introduced compressive residual stresses, if the applied stress was compressive, the onset of plastic deformations was achieved with a lower stress magnitude. In addition, surface residual stress relaxation under cyclic applied stress was evaluated at four different stress magnitudes. Due to the cyclic-softening behaviour of this Q + T steel, its cyclic mechanical properties must be considered to assess the onset of plastic strains. With the experimental data, a logarithmic model to predict the evolution of surface residual stresses with the number of cycles for different applied stress magnitudes was presented. The authors wish to acknowledge the financial support received from the Department of Research and Development of the Basque Government, the UPV/EHU University, through the Research Project Reference: Grupos GV IT947-16.

This study presents the formulation for the propagation of ultrasonic waves in a unidirectional composite material made of carbon fiber (HexTow® AS4/HexPly® 8552), widely used in the aeronautical industry. Understanding the mechanisms governing propagation is fundamental for employing ultrasonic technique to measure mechanical stresses in aeronautical components made of composites, using acoustoelasticity. The approach adopted consists of estimating velocity for different fiber angles and, with these estimates, validating the theoretical model to be proposed. Thus, the study is subdivided into two parts, the objective of part A is to propose an ultrasonic wave propagation equation that considers the longitudinal and transverse acoustoelastic constants instead of the third-order elastic constants individually, the deformations and hygrothermal mechanical stresses based on the classical theory of laminates, considering the orientation of the fiber of the composite material. Part B compares the analytical model and the experimental results. Reasonable alternatives were proposed as methods of adjustment, and the correction that considers the cross sectional thermal stresses was found to be the best one. The possible sources of variation found include the residual stress generated during the curing process. The results indicate that the model is able to describe the phenomenon and that this thermal component of deformation generates stresses that considerably affect the wave velocity.

This study aims to formulate an ultrasonic longitudinal wave propagation in a unidirectional composite HexTow® AS4/HexPly® 8552, considering the classical laminated theory, residual stresses, mechanical hygrothermal effect, and acoustoelasticity. The approach estimates the velocity for various fiber orientation angles and validates it experimentally. To achieve the proposal, the work was divided into two parts. The theoretical background and the proposed model were the objectives of part A. Part B is dedicated to validating the previously proposed model and proposing adjustment methods. The residual stress generated by the curing process is a possible source of the variation found. The study showed that the and the thermal component during the manufacturing process considerably affects the velocity of the longitudinal wave., OLIVEIRA, D. M. G.; GONCALVES, V. V. ; SANTOS, A. A. "Modelling the effect microscale residual stress on acoustoelasticity in carbon fiber composities – Part A: Theoretical background.". In Proceeding of the 6th Brazilian Conference on Composite Materials. (Part of ISSN 2316-1337), Organised and Edited By R.J. da Silva & T.H. Panzera, 2022, pp. 473 - 478. DOI: https://doi.org/10.29327/566492

This study aims to formulate an ultrasonic longitudinal wave propagation in a unidirectional composite HexTow® AS4/HexPly® 8552, considering the classical laminated theory, residual stresses, mechanical hygrothermal effect, and acoustoelasticity. The approach estimates the velocity for various fiber orientation angles and validates it experimentally. To achieve the proposal, the work was divided into two parts. The theoretical background and the proposed model were the objectives of part A. Part B is dedicated to validating the previously proposed model and proposing adjustment methods. The residual stress generated by the curing process is a possible source of the variation found. The study showed that the and the thermal component during the manufacturing process considerably affects the velocity of the longitudinal wave.

This study presents the formulation for the propagation of ultrasonic waves in a unidirectional composite material made of carbon fiber (HexTow® AS4/HexPly® 8552), widely used in the aeronautical industry. Understanding the mechanisms governing propagation is fundamental for employing ultrasonic technique to measure mechanical stresses in aeronautical components made of composites, using acoustoelasticity. The approach adopted consists of estimating velocity for different fiber angles and, with these estimates, validating the theoretical model to be proposed. Thus, the study is subdivided into two parts, the objective of part A is to propose an ultrasonic wave propagation equation that considers the longitudinal and transverse acoustoelastic constants instead of the third-order elastic constants individually, the deformations and hygrothermal mechanical stresses based on the classical theory of laminates, considering the orientation of the fiber of the composite material. Part B compares the analytical model and the experimental results. Reasonable alternatives were proposed as methods of adjustment, and the correction that considers the cross sectional thermal stresses was found to be the best one. The possible sources of variation found include the residual stress generated during the curing process. The results indicate that the model is able to describe the phenomenon and that this thermal component of deformation generates stresses that considerably affect the wave velocity., OLIVEIRA, D. M. G.; GONCALVES, V. V. ; SANTOS, A. A. "Modelling the effect microscale residual stress on acoustoelasticity in carbon fiber composities – Part B: Validation and adjustment.". In Proceeding of the 6th Brazilian Conference on Composite Materials. (Part of ISSN 2316-1337), Organised and Edited By R.J. da Silva & T.H. Panzera, 2022, pp. 467- 472. DOI: https://doi.org/10.29327/566492

Liquid-assisted laser ablation (LALA) has gained substantial attention as a method that can achieve desired chemical and physical properties. The fabrication of carbides (CdCO3), oxides (CdO), and hydro-oxides (Cd(OH)2) on Cd surfaces make them more useful in industrial and biomedical applications due to the enhancement of their physical properties. For this purpose, LALA of Cadmium (Cd) is performed using a KrF Excimer laser (248 nm, 20 ns) at varying numbers of pulses from 500 to 2000 at constant fluence (3.6 Jcm−2) in deionized water (DI) and ethanol. A comparison of the ablation behavior of Cd in DI water and alcohol (ethanol) environments is discussed in the present work. The surface structuring and enhancement of mechanical properties are also discussed in correlation with the changes produced in its crystallinity due to the increase in the chemical reactivity of Cd in both ambient environments. The surface features, chemical composition, structural and compositional analysis, and mechanical properties of irradiated targets are evaluated using a Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), Fast Fourier Transform Infrared spectroscopic (FTIR), Energy Dispersive X-ray Spectroscopy (EDS), and a Nano-hardness tester. Pores, cavities, hillocks, wave-like ridges, nanoparticles, flake-like structures, and periodic surface structures are distinguished features on the Cd surface after irradiation. However, the density and size of pores and cavities are higher in water, whereas ethanol is favorable for the growth of craters and ripples. These features are attributable to various thermal and chemical phenomena induced by laser heating at the solid–liquid interface. Ethanol-assisted ablation is more favorable for enhancing the hardness of Cd as compared to DI water-assisted ablation due to the presence of maximum compressive stresses and minimum crystallite size (C.S.) caused by the diffusion of carbon into the target surface.

Resumo Materiais, quando sob carregamento em ambientes agressivos, como é o caso dos aços de tubulações no setor de petróleo e gás, estão sujeitos à fragilização por hidrogênio devido às condições ambientais. A susceptibilidade do tubo a tal fragilização está diretamente relacionada, entre outros fatores, ao nível de tensões residuais presentes; e impõe ao material severas e danosas reduções de propriedades mecânicas. Nesse contexto, devido à necessidade cada vez mais frequente de evitar falhas catastróficas que conduzem a perdas irreparáveis para os seres humanos e o ambiente, são destinados maciços investimentos para o aprimoramento das propriedades mecânicas e grandes esforços para compreender os mecanismos que levam aos danos causados pelo hidrogênio. A compreensão do efeito das tensões residuais originadas pelos diferentes processos ao qual o aço é submetido ainda é bastante escassa e nem sempre há uma unanimidade entre pesquisadores. Diante desta problemática, o presente trabalho, através de uma revisão bibliográfica, objetiva oferecer uma abordagem de como as tensões residuais podem afetar o nível de fragilização nos aços API 5L, bem como uma melhor compreensão dos mecanismos e dos fatores que facilitam a dissolução do hidrogênio na rede cristalina destes materiais. Abstract Materials, when loaded in aggressive environments, as high strength low alloy pipeline steels used in Oil and Gas industry, are subjected to hydrogen embrittlement due to the environment conditions. The pipeline susceptibility is related to, among others factors, residual stresses; and causes several losses of mechanical properties. In this context, due to the increasingly frequent need to avoid catastrophic failures leading to irreparable losses to humans and the surrounding environment, massive investments are made to improve mechanical properties and to understand the mechanisms that lead to damages caused by hydrogen. The actual bibliography about the residual stresses influence is very scarce and there is not always an unanimity between researchers. This study, aims to offer an approach about how the residual stress can affect the embrittlement level, as well as better understanding about the mechanism and factors that facilitate the dissolution of hydrogen on crystalline lattice.