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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.

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.

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.

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.

International audience

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.

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.

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.

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.

Thin-walled milled monolithic aluminum workpieces are common in the aerospace industry, because of their advantages such as favorable material properties, established design methods, good machinability, known performance and reliable inspection techniques. Machining-induced residual stresses (MIRS) and initial bulk residual stresses (IBRS) are known to be the key factor for causing distortion of those workpieces. In this study the effect of both types, the milling path strategy and the wall thickness on the distortion is analyzed. A developed 3D linear elastic finite element (FEM) model, considering both types of RS as input, and predicting the resulting part distortion, is extended by using the true milling path as well as all RS contained in the entire workpiece. The simulation outcome is validated by experiments and distortion minimization techniques are derived. The results show that the model predicts the distortion shape and level for different wall thicknesses and milling strategies with a high accuracy. The experiments indicated that the distortion of low IBRS parts with 3 mm wall-thickness could be minimized by 42% by only changing the milling path. The simulation highlighted, that for smaller wall thicknesses, the distortion minimization potential is even higher (e.g. 2 mm wall thickness: up to 69% distortion minimization). For high IBRS parts, milling the inverse form of the predicted shape on the backside of the workpiece represents an alternative, which led up to a reduction of the distortion by 77%. In general, three main categories for precontrol distortion techniques can be identified as the process parameters, the part topology and the process strategy.

The material extrusion additive manufacturing (MEAM) process for polymers seems straightforward. However, several controlled and uncontrolled factors affect the 3D printed product quality, e.g., MEAM process parameters, thermomechanical properties of the material, and part design. Therefore, it is crucial to understand these interlinked factors of part geometry, material properties, and 3D printing (3DP) process parameters to optimize 3D printed product quality. The numerical models and simulation tools can predict the thermomechanical performance of the MEAM process under given input parameters (material, design, and process variables) and reduce the research and development costs significantly. However, the numerical models and tools need further exploration and validation of simulation predictions for their adaptability and reliability. Therefore, in this study, numerical simulations were performed to observe the impact of process parameters on the part quality of MEAM 3D printed components. The two crucial process parameters (i.e., extrusion temperature and layer resolution) were varied while keeping the other process parameters, part geometry (tensile testing coupon), and material properties (acrylonitrile butadiene styrene (ABS)) constant. These two process parameters were sequentially optimized for optimum part quality, first by varying the extrusion temperature and secondly by changing the printing resolution using the optimum printing temperature. The 3DP process quality was evaluated in terms of dimensional accuracy, distortions, and residual stresses. Finally, the specimens were 3D printed under similar process conditions to validate the numerical model predictions.

The disadvantages of widely used austenitic stainless steels are their low hardness and relatively low fatigue strength. Conventional chemical-thermal surface treatments are unsuitable for these steels since they create conditions for inter-granular corrosion. An effective alternative is a low-temperature surface treatment, creating an S-phase within the surface layer, but it has a high cost/quality ratio. Austenitic steels can increase their surface micro-hardness and fatigue strength via surface cold working. When the goal is to increase the rotating bending fatigue strength of austenitic chromium-nickel steels, and the requirements for significant wear resistance are not paramount, diamond burnishing (DB) has significant potential to increase the fatigue strength and, based on the cost/quality ratio, can successfully compete with low-temperature chemical-thermal treatments. The main objective of this study is to establish the effect of DB on the rotating fatigue strength of AISI 304 L chromium-nickel austenitic steel. The influence of DB parameters on the surface integrity (SI) characteristics was studied. Optimal DB parameters under minimum roughness and maximum micro-hardness criteria were obtained. Rotating bending fatigue tests of the diamond burnished (in a different manner) and untreated specimens were performed. DB implemented via parameters providing maximum micro-hardness increased fatigue limit by 38% compared to untreated specimens.

Die Prozessführung der inkrementellen Blechumformung beeinflusst maßgeblich den Eigenspannungszustand einer gefertigten Komponente und damit die Produkteigenschaften. Eine kontinuierliche Variation des Zustellinkrements im Umformprozess ermöglicht die lokale Ausbildung vordefinierter Eigenspannungen im Bauteil. Um die lokale Beeinflussung von Eigenspannungen zu analysieren, werden vier Prozessrouten mit unterschiedlichen Zustellinkrement-Kombinationen zur Herstellung einer Kegelstumpfgeometrie experimentell verglichen. Eine Änderung der Zustellinkremente im Prozess verursacht eine Erhöhung des Eigenspannungsniveaus bei sonst gleichbleibenden Produkteigenschaften., The process parameters of the incremental sheet metal forming have a significant influence on the residual stress state of a manufactured component and its product properties. A continuous variation of the tool step-down during the forming process allows a local induction of predefined residual stresses in the component. To analyze the local influence of residual stresses, four process routes with different step-down increment combinations are compared experimentally to manufacture a truncated cone geometry. A change of the step-down increment during the forming process causes components with higher residual stress level with otherwise identical product properties.

For the fatigue life of thin-walled components, not only fatigue crack initiation, but also crack growth is decisive. The phase-field method for fracture is a powerful tool to simulate arbitrary crack phenomena. Recently, it has been applied to fatigue fracture. Those models pose an alternative to classical fracture-mechanical approaches for fatigue life estimation. In the first part of this paper, the parameters of a phase-field fatigue model are calibrated and its predictions are compared to results of fatigue crack growth experiments of aluminium sheet material. In the second part, compressive residual stresses are introduced into the components with the help of laser shock peening. It is shown that those residual stresses influence the crack growth rate by retarding and accelerating the crack. In order to study these fatigue mechanisms numerically, a simple strategy to incorporate residual stresses in the phase-field fatigue model is presented and tested with experiments. The study shows that the approach can reproduce the effects of the residual stresses on the crack growth rate.

The aim of this work is to generate an advantageous compressive residual stress distribution in the surface area of hot-formed components by intelligent process control with tailored cooling. Adapted cooling is achieved by partial or temporal instationary exposure of the specimens to a water–air spray. In this way, macroscopic effects such as local plastification caused by inhomogeneous strains due to thermal and transformation-induced loads can be controlled in order to finally customise the surface-near residual stress distribution. Applications for hot-formed components often require special microstructural properties, which guarantee a certain hardness or ductility. For this reason, the scientific challenge of this work is to generate different residual stress distributions on components surfaces, while the geometric as well as microstructural properties of AISI 52100 alloy stay the same. The changes in the residual stresses should therefore not result from the mentioned changed component properties, but solely from the targeted process control. Within the scope of preliminary experimental studies, tensile residual stresses in a martensitic microstructure were determined on reference components, which had undergone a simple cooling in water (from the forming heat), or low compressive stresses in pearlitic microstructures were determined after simple cooling in atmospheric air. Numerical studies are used to design two tailored cooling strategies capable of generating compressive stresses in the same components. The developed processes with tailored cooling are experimentally realised, and their properties are compared to those of components manufactured involving simple cooling. Based on the numerical and experimental analyses, this work demonstrates that it is possible to influence and even invert the sign of the residual stresses within a component by controlling the macroscopic effects mentioned above.

Additive manufacturing (AM) is a unique manufacturing process that disrupted completely the way which components are made, since this process is capable of producing complex parts layer after layer. As a matter of fact, one of its distinct technologies is metal laser beam powder bed fusion (mLB-PBF), also known as selective laser melting (SLM) or direct metal laser sintering (DMLS), which creates metallic parts with the aid of a high-energy laser beam. One of the most employed superalloys in this technology is the Inconel 718 (IN718), a precipitation-hardened alloy that is used in the marine, nuclear power plants, gas turbines, and aerospace field due to its capacity of retaining good mechanical properties at high temperatures. The research novelty of this review manuscript is the compilation of all kinds of information from the last 15 years of investigation about IN718 parts produced via mLB-PBF, namely, information related to distinct heat treatments and the influence they have in increasing mechanical properties of the manufactured components, as well as reducing residual stresses (RS) and part porosity. Throughout the review, it can be seen that the expected microstructure in the as-built state is characterized by fine columnar grains and a saturated γ matrix with the presence of the Laves phase and carbides. However, distinct heat treatments can be employed which lead to the dissolution of the undesired phases (Laves and carbides), the precipitation of the strengthening phases (γ’ and γ”), and the porosity decrease. Furthermore, it was also shown that heat treatments as well as optimized process parameters can be held accountable for lowering the RS of the IN718 manufactured parts. Nevertheless, there are still some problems to overcome, namely, the mechanical properties variability when subjecting IN718 powder to different process parameters. Moreover, the RS evolution under different heat treatments needs to be further investigated.

Residual stresses are usually associated with stresses induced by heterogeneous deformations as a cause of phase transition and thermal stress. The residual stresses can appear during the manufacturing process, repair process, or in some cases due to operational loads. These stresses should be taken into account in the structural integrity evaluation of low-toughness materials or in the case of fatigue and/or stress corrosion cracking (SCC) situations. Indeed, it is known that residual stresses affect crack growth rates. For a better understanding of how these stresses can interact with crack propagation in pre-strained stainless-steel specimens, numerical modeling has been performed. The tension of the compact tension (CT) specimen was simulated and as a result, the stress intensity factor (SIF) was calculated. The main goal of this paper is to numerically calculate the stress intensity factors along the crack front of the CT specimen with residual stresses and compare them with the results of tension of the same specimen just without residual stresses. For this task finite element analysis (FEA), code CAST3M was used. Simulation results showed that the higher SIF values were calculated at the sides and the lower in the middle part of the CT specimen machined from a highly pre-strained plate which is opposite to what could be expected in a specimen without residual stresses.

A numerical study of the mechanical behavior of aluminum matrix–carbide particle composites subjected to combined thermomechanical loading is carried out. The composite structure, corresponding to that observed experimentally, is explicitly taken into account in the calculations. The mechanical response of the aluminum matrix and carbide particles is described using the isotropic elastic–plastic and elastic–brittle models. A fracture criterion of the maximum equivalent stress acting in the local regions of volumetric tension is used to study the crack initiation and propagation in the particles. The dynamic plane stress boundary value problems of cooling and tension of the composites are solved by the finite element method ABAQUS/Explicit. The influence of the cooling-induced residual stress and thermomechanical properties of the matrix and particle materials on the strength of the composites is investigated. A positive or negative effect of the residual stress is found to depend on the ratio between the particle strength and the matrix yield stress. Compressive residual stress formed in the particle after the cooling increases the strength of composites with hard matrices and low-strength particles. A decrease in the matrix–particle interfacial curvature results in a change in the fracture mechanism from in-particle cracking to debonding, which increases the composite strength. Composite elongation upon the fracture onset decreases with the volume fraction of the particles.

Concerning the increasingly widespread utilization of the finite element method (FEM), the concept of the so-called virtual factory is also gaining ground, and not only in the engineering industry. This approach does not use numerical simulations of individual production technologies separately but treats the entire production process as a chain of interrelated technologies. Thus, the output data from one technology is taken as input data for the following technology. The resulting thermal and mechanical effects are then not only dealt with within one technology but always comprehensively within the production process. In the consideration of the loading and subsequent service lives of manufactured components, values of residual stresses are one of the very important characteristics. For these reasons, this paper deals with the effect of residual stresses’ magnitude and distribution during the formation and the final springback of the seamed pipe end section with and without respect to the influence of the preceding welding. The resulting residual stress values from numerical simulations are subsequently compared with the actual values of residual stresses experimentally measured using X-ray diffraction.

International audience; Shot peening of turbine disk engines is performed in the aerospace industry in order to enhance fatigue life. This surface enhancement method generates beneficial modifications like superficial compressive residual stresses that are known to delay crack initiation and propagation. In the same way, work hardening is also introduced at the surface of the part during shot peening and can have a significant influence on fatigue crack initiation. Taking this parameter into account in the fatigue design of parts, in addition to the residual stresses, is a real challenge to be the most predictive. One possibility for this is to be able to predict it during the modeling of the shot peening process. In the present work, various peening conditions are considered in order to be able to propose a model able to account for the influence of coverage and Almen intensity on residual stresses and work hardening. The studied material is Inconel 718, commonly used for aeronautical parts. The X-ray diffraction method is used to obtain the in-depth residual stress and work-hardening profiles. A three-dimensional numerical model is proposed to predict these quantities. Efforts are made to consider all recent advances in three-dimensional simulation of the process, in terms of coverage assessment, shot and treated part modeling. The numerical results are compared to the experimentally measured residual stresses and work hardening.

One of the frequent causes of aviation incidents and accidents is the failure of technical equipment and the destruction of aircraft (AC) constructions resulting from unacceptable deformations and structural destruction of the parts operating under high mechanical loads. Operation of parts, assemblies and units of aeronautical equipment in the most typical cases does not allow their plastic strain. Thus, in accordance with the airworthiness standards, aeronautical equipment should not be used under the conditions leading to the occurrence of dangerous permanent yielding and fatigue damage to the material in its structures. The probability of these negative factors is determined by the stress condition of the aircraft structural component material during operation. An important factor that determines the stress condition as well as the technical condition of an object of technology is residual stresses, most often available in the material of the part. In particular, the summation of the residual stresses with the stresses of the operating load can lead to the exceedance of the critical values stress condition indicators, for example, the fatigue margin or the yield point of the material. In view of this, the development of new technologies that will provide information on the actual technical condition of the structure of each aircraft during its operation considering residual stresses is a critical task. The article describes a possible approach to evaluating and predicting the technical condition of the structural materials of assemblies and units operating under cyclic loading based on determining the change of residual stresses level on the surface of the parts during their operation. As a method for determining residual stresses, the X-ray diffractometric method was chosen, as it is characterized by high accuracy and reliability of the results obtained. The developed approach was tested on the components of the aircraft air conditioning system (turbo-refrigeration unit). The results of evaluating the technical condition of the parts conform to the facts of their operational damage. In these circumstances, although the proposed approach cannot currently be used directly on board an aircraft for continuous monitoring of the technical condition of aircraft structural materials, however, its development seems to the authors to be promising for these purposes.

Hybrid Metal Extrusion & Bonding (HYB) is a new solid-state joining method for metals and alloys that utilizes continuous extrusion as a technique to enable aluminum filler metal additions. Previous works showed that this method is well suitable for joining dissimilar metals such as steel and aluminum. In the present paper a Finite Element model for the thermal residual stresses were implemented employing the FE code WELDSIM. As a starting point, the results of a semi-analytical heat generation model previously implemented for HYB process of aluminum butt welds were used to estimate the net power input as a sum of contributions that are dependent on the welding parameters i.e. the welding speed, the rotational speed and the material properties. Subsequently, the thermal stresses occurring in the material and finally the residual stresses were determined. In the present work, predictions of the FE model for different sets of welding parameters are presented and discussed.

In this work, Design of Experiments is applied to identify which factors mostly influence the residual stress distribution in an hourglass specimen subject to the impact of a foreign object. The specimen is made of 7075-T6, that is one of the most popular alloys in the aeronautical sector. After the impact, the specimen is assumed to be tested with an axial or bending fatigue load. For this reason, the study is conducted on the axial stresses induced by the impact of the object on the specimen, assessed by means of finite element analysis. Only the stresses in the region x=[-2 mm; 2 mm], with x=0 corresponding to the position of the minimum cross section of the specimen before the impact, were considered. In this region, stress concentrations are probable during the fatigue test. The results showed that high impact forces induce high tensile stresses, unfavorable from a fatigue point of view. Therefore, it is preferable that the impacting object has a low weight and reduced speed.

In this article, a three-dimensional finite element model is used to predict the growth of cracks at the weld toe of a T-joint. The model is developed using the MSC Marc software. Fatigue life is estimated by integrating the Paris-Erdogan law and the stress intensity factors are obtained by the virtual crack closure technique. The influence of residual stresses generated by plastic deformation at the weld toe on the crack propagation speed is analyzed. The existence of residual compression stress fields causes a delay in crack growth. The obtained results are compared with the integration solutions of the Paris-Erdogan law using the stress intensity factor computed through the Mk factor proposed by Bowness and Lee, included in BS 7910 standard.

International audience; Machining thin workpieces is a challenging task as geometrical errors may result from the combination of several phenomena. Among these, elastic workpiece deformation and machining induced residual stresses may be predominant sources due to low part stiffness. There is a lack of studies trying to quantify the influence of machining induced residual stresses on the total geometrical errors. A thorough experimental methodology isdeveloped to quantify the influence of both phenomena separately by comparing the workpiece shape and dimensions, in-situ, before and after machining, using laser sensors. The proposed methodology can also be used to quantify the geometrical errors linked to clamping or stress rebalancing following material removal. The case study is the finish turning of thin Inconel 718 workpieces using carbide tools. In the studied case, machininginduced residual stresses are responsible for 3–32 % of the total geometrical errors depending on tool wear and cutting parameters.

Relevance. The paper considers shot blasting, which is a widely used method for improving the surface properties of parts (such as fatigue strength, hardness, and elongation) due to cold plastic deformation, which results in nanostructuring of the surface of the processed material, accompanied by a reduction in the grain size of its crystal structure. The conditions for the formation of a nanostructured surface layer when processing parts with a shot stream are studied. The aim of the work is to determine the conditions of nanostructuring during shot blasting due to plastic deformation, determined by the impact of the shot, which collides with the treated surface at high speed. Methods. To solve the stated problems, we used the solution of the contact problem of the theory of elasticity on the action of a concentrated force on the elastic half-space, the role of which is played by the workpiece. The conditions of the onset of plastic deformation in the surface layers of the workpiece are determined. Cold plastic deformation provides nanostructuring of the surface layer of the workpiece, increasing strength, fatigue life, atomic diffusion and improving tribotechnical characteristics. Results. Based on the contact problem of the theory of elasticity, the problem of the formation of a nanostructured layer on the surface of the workpiece during shot blasting has been solved. An analytical dependence has been obtained, which allows predicting the transition of the material to a plastic state and nanostructuring the surface of the workpiece during shot blasting.

A methodology for measuring residual stresses based on drilling small diameter holes with subsequent fixation of deformation using a strain gauge as applied to thin-walled complex parts of gas turbine engines has been presented. It is known that the bulk of the details of small-sized short-life aircraft engines are thin-walled and have a complex profile and a variable cross-section in the direction of the main axes of symmetry. At the same time, the geometrical features of the parts and the specifics of the technology of their manufacture can lead to the formation of uneven high residual stresses on the surface and depth. Stresses with technological and structural stress concentrators can lead to premature occurrence and propagation of fatigue cracks at relatively low cyclic voltages. The measurement of residual stresses by hole drilling has great potential for modern aircraft mechanical engineering of gas turbine engines. Measurement of residual stresses and their depth distribution on thin-walled folding-profile surfaces of titanium alloy parts hardened by steel balls in an ultrasonic field was performed. It was used tensometric method of measuring deformation after drilling holes. The method of measuring residual stresses is based on measuring strain by a strain gauge outlet during step-by-step drilling of a hole. It was shown that the method of drilling small holes has several advantages over the method of layer-by-layer removal of thin layers of metal, which is widely used in the aviation industry. It was also established that the accuracy of determining the magnitude of stresses is significantly affected by the following factors: the accuracy of the positioning of the drill relative to the plane of the part being studied, its temperature, the actual drilling depth at each step, the dwell time at each depth, the frequency and time of interrogation of the sensors, calibration of the tensor sockets and strain gauge, etc. The proposed method for measuring residual stresses makes it possible to take into account their nature and shape of distribution, as well as to evaluate their value on folding thin-walled aerodynamic surfaces of parts made of titanium alloy after ultrasonic hardening or diamond smoothing.

The physics fundamentals and advantages of ring-rolling the products are described. The analysis of production volumes of the products by ring-rolling in Europe is carried out. The definition of rings of low rigidity is given. The problems of using of the ring-rolling for their production, the main errors and deformations arising in the process of manufacturing of rings of low rigidity are considered. The ways of increasing the geometric accuracy of the rings and relieving residual stresses are analyzed. The fundamental advantage of the method of dynamic stabilization of rings of low rigidity to other types of correction is explained. A brief description of the device expanders for dressing rings of low rigidity with a wedge mechanism is presented. The problems of correction with their use are characterized. As a fundamentally new technological operation that increases the accuracy of manufacturing of rings of low rigidity and reduces residual stresses in them, an effective technology of dynamic stabilization, cyclic loading, is proposed. The prospects of using the cyclic loading method to increase geometric accuracy and reduce residual stresses in rings of low rigidity are substantiated. Recommendations are given on the creation of universal installations for the dynamic stabilization of rings of low rigidity in order to eliminate the deformations that have arisen during the production process and relieve residual stresses after the rings are manufactured on ring-rolling complexes. The calculated dependences for the design of installations for the dynamic stabilization of rings with outer diameters up to 3,000 mm and weight up to 1,000 kg are given. The results can be used to increase the accuracy of manufacturing of rings billets of low rigidity during their planned production at the Belarusian Automobile Plant BelAZ and other enterprises.

Introduction . The study results on the multicontact shock-vibrating machining using a ball-rod hardener are presented. Methods of surface plastic deformation processing, their advantages are described. The tool circuit diagram is given. Features, technological advantages, and the application area of the ball-rod hardening are specified. Materials and Methods . When conducting theoretical studies on the processing, factors, which affect the quality of the surface layer of the machined parts, were established. Dependences are given for calculating the surface roughness, the hardened layer depth, and the deformation ratio under ball-rod hardening. While studying the generation of residual stresses, the dependence for calculating the residual stresses generated in the surface layer of the machined part was specified. Results . The experimental findings of the processing requisite for verification of the adequacy of the theoretical models, as well as the routine of the experiments, are presented. A table and graphs clearly confirming good convergence of the theoretical and experimental data are given (the difference does not exceed 20%). Residual stresses in the surface layer are compressive which enables to predict high performance properties of the machined parts. The value of residual stresses on the workpiece surface is in the range of 130÷200 MPa. The depth of compressive residual stresses is in the range of 0.9-1 mm. The fatigue characteristic variation, the ultimate stresses of the cycle in depth, which affects the endurance limit, is calculated. It has been established that the processing of workpieces by a ball-rod hardener provides increasing the ultimate cycle stress under repeated loading by 27-35%. Discussions and Conclusions . The design methodology of technological process of ball-rod hardening can be used under the development of production at the machine-building enterprises. In accordance with the recommendations, the limits of the required quality parameters of the workpiece surface layer are set; the parameters of the ball-rod hardener, the interference fit and the radius of rod sharpening are selected. Quality parameters of the surface layer are calculated. Correction of the selected modes and re-calculation of the parameters of the machined surface are carried out until all the specified characteristics are located within the required limits.

This paper presents results obtained via experimental measurements of residual stresses in the cross sections of longitudinal welded pipes. The experiment was carried out in different dimensions and thickness of the pipes where it is noticed that the smaller the diameter of the pipe, the greater the residual stresses because the degree of deformation during the production of pipes with smaller diameter is greater. Residual stresses are measured with strain gages set upon the outside wall of the pipes. The results received from the gages show considering amount of stress captured in the pipe wall because of cold plastic formation process [1]. After cutting the rings, their opening is recorded, which is variable and depends on several parameters such as: ring diameter, thickness, type of material and its reinforcement as well as the degree of plastic deformation when forming the pipe sheath [2]. The difference in the display of the measuring tape when the ring is in the open and closed position is the residual deformation that corresponds to the residual stresses that occurs in the ring.

In this study, the fatigue strength of 316 L stainless steel manufactured by selective laser melting (SLM) is evaluated. The effect of powder layer thickness and postmachining is investigated. Specimens were produced with 30 and 50 µm layer thickness and tested under high cycle fatigue in as-printed and postmachined conditions. Examination of the specimens reveals that in the as-printed condition, fatigue strength suffers from high roughness and surface tensile residual stresses as well as defects such as pores and lack of fusion voids. After machining, the fatigue strength was improved due to lower surface roughness, presence of compressive residual stresses, and removal of surface porosity. The results show that increasing the layer thickness (within the range tested) has a minor negative impact on fatigue strength; however, it has a major positive impact on the productivity of the SLM process. In addition, it is clear that the impact of postmachining on fatigue is far greater than that of the layer thickness. © 2020, The Author(s). Funding details: 2015-03457; Funding text 1: Open access funding provided by RISE Research Institutes of Sweden. This work was supported by Sweden’s Innovation Agency [Grant Number: 2015-03457]. Ms. Anna Larsson and Mr. Heike Henrich from Höganäs AB are acknowledged for performing porosity and metallography analyses.

The present work aims at investigating the effect, in terms of residual stress prediction, determined by the adoption of different material constitutive models in the Finite Element simulation of the casting process of a superduplex stainless steel benchmark, from the cooling after the pouring phase to the subsequent heat treatment (heating and water quenching). A 3D thermo-mechanical Finite Element (FE) model was created with the commercial code Abaqus: the preliminary thermal problem, i.e. the determination of the heat transfer coefficients during both the mould cooling and the quenching, was solved by means of an inverse analysis approach by minimizing the difference between the numerical evolution of temperature and the experimental acquisition coming from real casting test. Two separate routes were followed according to the adopted constitutive equations: modelling the material as (i) elasto-plastic or (ii) elasto-viscoplastic. The numerical prediction of the residual state of stress in terms of casting relaxation was compared with the experimental data after the cut of the casting using an electro-discharge machine. The analysis revealed that when the elasto-viscoplastic modelling was adopted, the simulations underestimated the relaxation with an error larger than 50%; on the other hand, the elasto-plastic model leads to an overestimation with an error of about 30%.

International audience; Zirconia based bio-ceramics such as ZTA (Zirconia-toughened alumina) composite are often used in orthopaedic and dental implants. The hydrothermal ageing behaviour of zirconia in humid environments is an important factor affecting the lifetime of these biomaterials. It is a tetragonal-to-monoclinic phase transformation that has been shown to be both temperature-and stress-dependant. Here, ZTA composites with zirconia inclusion particles of different sizes were prepared. The influence of zirconia inclusions on internal stresses and thus on ageing behaviour was studied by Raman micro-spectroscopy and X-ray diffraction. The results show that the ageing kinetics result from a balance between stiffer matrix and increased tensile stress in the zirconia inclusion as the local alumina fraction increase. As a result, the maximum monoclinic fraction formed after1200 h ageing at 134°C decreases with increasing alumina content, showing the predominance of the stabilization of tetragonal particles by a stiff matrix over their destabilization by tensile stress. Wei et al. Internal stresses and matrix stiffness influences ageing of ZTA, Acta Mater. 2020 2

In this investigation, a T-joint numerical welding simulation of thick steel plates is performed to estimate transient temperature distributions, residual stress field and model deflections. A sequential simulation method is applied in the numerical simulation, where the thermal analysis is done by using the EBD technique to simulate the weld wire melting and metal filler addition while the mechanical analysis is performed in one step without EBD to shorten the calculation time. Thermocouples, non-destructive X-ray diffraction and semi-destructive hole-drilling methods are used to measure the temperature and residual stress distributions. In the thermal analysis, a simplified heat flux is used which causes a relatively large temperature discrepancy in the weld pool area between the numerical and experimental results. The calculated temperature histories outside the weld pool and its vicinity correlate very well with the experimental measurements with an acceptable discrepancy of approximately 4%. The residual stresses are firstly measured on the model surface without electropolishing and then two times after that, at depths of 0.005 and 0.015 mm. The results of residual stress obtained by numerical modelling and measurement with X-ray agree better when the electropolishing removing layer is set to 0.015 mm, due to a significantly smaller effect of surface conditions that originate from steel plate production.

Ion implantation has been shown to improve adhesion strength of AlCrSiN coatings due to a synergic enhancement on fracture toughness and load bearing capability of the substrate that can potentially increase the in-service efficiency of coated cutting tools. In this work, AlCrSiN coatings deposited by PVD on WC-Co substrates implanted with Ti, Cr and N ion species have been processed. The mechanical properties and adhesion have been characterized by contact techniques and the residual stress of the coatings and substrates have been evaluated using FIB-DIC technique and Vickers indentation tests, respectively. An improvement of adhesion strength is obtained for treated substrates, especially for those implanted with titanium and chromium ions. This improvement is attributed to the introduction of residual stresses in the substrate, which increases its fracture toughness and enhances its load bearing capability. Work funded through The Spanish Ministry of Science, Innovation and Universities through grants PGC-2018-096855-B-C41, PGC-2018-096855-B-C42 and PGC-2018-096855-A-C44

Введение. В статье представлены результаты исследований остаточных напряжений в покрытиях, нанесенных плазменным напылением с оплавлением. Материалы и методы. Получены аналитические зависимости, показывающие влияние остаточных напряжений в покрытиях на прочность их сцепления с основой, и на их базе предложена уточненная математическая модель, устанавливающая закономерности влияния температурно-временных параметров плазменного оплавления на уровень остаточных напряжений. Результаты и обсуждение. Приведены результаты математического моделирования формирования остаточных напряжений в плазменных покрытиях с учетом времени и температуры их оплавления. Получены уравнения, позволяющие оценить динамику изменения температур покрытия и восстанавливаемой детали, с помощью которых можно оценить зависимости касательных напряжений от толщины наносимых покрытий. При этом погрешность расчетов варьируется в диапазоне 7–10 %. На основе выявленных закономерностей физико-механических и эксплуатационных свойств плазменных покрытий разработана математическая модель распределения остаточных напряжений в зоне контакта системы «деталь-покрытие». Численное исследование остаточных напряжений в плазменных покрытиях проводили на основе разработанных программных комплексов «Plasma Expert» и «Protection», открывающих широкие возможности для конечно-элементного описания исследуемой системы «деталь-покрытие». Заключение. Теоретически и экспериментально доказано, что при оптимальных значениях основных технологических параметров и режимов плазменного напыления процесс оплавления позволяет значительно снизить внутренние остаточные напряжения в покрытиях и повысить их износостойкость., Introduction. The article presents the results of studies of residual stresses in coatings applied by plasma sputtering with reflow. Materials and methods. Analytical dependences have been obtained showing the effect of residual stresses in coatings on the strength of their adhesion to the substrate and on their basis a refined mathematical model has been proposed that establishes the regularities of the influence of temperature-time parameters of plasma reflow on the level of residual stresses. Results and discussion. The results of mathematical modeling of the formation of residual stresses in plasma coatings, taking into account the time and temperature of their melting are presented. The equations allowing to estimate dynamics of change of temperatures of a covering and the restored detail by means of which it is possible to estimate dependences of tangential stresses on thickness of the applied coverings are received. At the same time, the calculation error varies in the range of 7–10 %. Based on the revealed regularities of the physical, mechanical and operational properties of plasma coatings, a mathematical model of the distribution of residual stresses in the contact zone of the part-coating system has been developed. It is worth noting that mathematical modeling was carried out taking into account the Poisson's ratio and Hooke's law. The numerical study of residual stresses in plasma coatings was carried out on the basis of the developed software complexes «Plasma Expert» and «Protection», which open up wide possibilities for a finite element description of the investigated system «detail-coating». Conclusion. It is theoretically and experimentally proved that at optimal values of the main technological parameters and modes of plasma spraying, the reflow process can significantly reduce the internal residual stresses in coatings and increase their wear resistance.

A Finite Element Model is developed to represent the mechanical behavior of WC-10 wt.% Co in compression tests. In this research, realistic three-dimensional model is obtained by slicing a sample by Focused Ion Beam and reconstituting it, resulting in two interpenetrated phases. The brittle WC phase is defined as elastic. The Co phase includes plasticity. The post sintering cooling is simulated, followed by a loading-unloading compression cycle. The results are then compared with experimental data obtained by neutron diffraction. The residual thermal stresses in both phases are in good agreement with the data obtained by neutron diffraction, featuring high tensile stress in the Co phase and moderate compressive stress in the WC phase. The elastic strain in the Co phase shows a good agreement in the loading cycle, but presents some differences in the unloading cycle. The plastic model applied to the Co phase is then modified to improve the accuracy of the simulation, showing a final good agreement with the experiment.

[EN] 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 monocontact 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. Acknowledgments This project has received funding from the European Union's Hori-zon 2020 research and innovation program under grant agreement No 851245. The authors would also like to acknowledge the collaboration with TTT Goiko on the preparation of test specimens and post-mortem analyses.

In the recent years, laser powder bed fusion of aluminum alloys has attracted extensive attention due to their capacious application in the biomedical, aerospace, and other industrial sectors. This is due to the combined capabilities of the laser powder bed fusion process and aluminum alloys bringing about complex shapes with high performance associated with light-weight design. Despite their high potential, parts produced by laser powder bed fusion suffer from residual stresses, surface irregularities and sub-surface defects limiting their full exploitation in fatigue sensitive applications. Consequently, post-processing methods such as laser shock peening can be employed to countermeasure these short-comings. This article reports on the effect of laser shock peening on the fatigue life of AlSi7Mg alloy fabricated via laser powder bed fusion. Laser shock peening induced a substantial improvement (around 50%) in the fatigue life when compared to the as-built parts. The improve-ments were attributed to the closure of surface and sub-surface pores, re-entrant surface features and in particular, induced compressive residual stress profile. The effects of laser shock peening were investigated through systematic multi-scale analysis through destructive and non-destructive methods. Furthermore, a simple fracture mechanics model was utilized to elucidate the effect of induced compressive residual stresses as the principal actor in the corresponding fatigue life improvement.

The procedure generally used to remove bacterial biofilm adhering to the surface of titanium on dental implants is implantoplasty. This treatment is based on the machining of the titanium surface to remove bacterial plaque. In this study, we used 60 grade 4 titanium implants and performed the implantoplasty protocol. Using X-ray diffraction, we determined the stresses accumulated in each of the as-received, machined and debris implants. The resistance to corrosion in open circuit and potentiodynamically in physiological medium has been determined, and the corrosion potentials and intensities have been determined. Tests have been carried out to determine ion release by ICP-MS at different immersion times. The results show that the corrosion resistance and the release of titanium ions into the medium are related to the accumulated energy or the degree of deformation. The titanium debris exhibit compressive residual stresses of −202 MPa, the implant treated with implantoplasty −120 MPa, and as-received −77 MPa, with their corrosion behavior resulting in corrosion rates of 0.501, 0.77, and 0.444 mm/year, respectively. Debris is the material with the worst corrosion resistance and the one that releases the most titanium ions to the physiological medium (15.3 ppb after 21 days vs. 7 ppb for as-received samples). Pitting has been observed on the surface of the debris released into the physiological environment. This behavior should be taken into account by clinicians for the good long-term behavior of implants with implantoplasty.

In the current practice of applying carbide-based coatings by thermal spraying, the starting material usually contains a metal binder. However, it is important to study the possibility of spraying binder-free carbides, since the metal components usually reduce the operating temperature and corrosion resistance of cermet coatings. In this work, a powder of chromium carbide, Cr3C2, was sprayed using a CCDS2000 detonation gun. Acetylene–oxygen mixtures C2H2 + kO2 with k varying from 0.8 to 3.0 were used as an energetic material. Due to chemical reactions between Cr3C2 and the detonation products, the coatings were of composite nature (multi-phase materials) with a composition depending on k. At k values in the range from 0.8 to 1.1, along with Cr3C2, the coatings contained chromium carbonitride Cr3N0.4C1.6. In the k range from 1.3 to 2.0, Cr7C3 and Cr were the main components of the coatings. As k was increased to 3.0, along with Cr7C3 and Cr, the CrO and Cr2O3 oxides formed in the coatings. The mechanical properties and wear resistance of the coatings were found to depend on their phase compositions. Coatings produced by detonation spraying of Cr3C2 powder may be useful for increasing the corrosion resistance of machine parts to mineral acids and high-temperature oxidation resistance.

A thermo-mechanical wafer-to-wafer bonding process is studied through experiments on the glass frit material and thermo-mechanical numerical simulations to evaluate the effect of the residual stresses on the wafer warpage. To experimentally characterize the material, confocal laser profilometry and scanning electron microscopy for surface observation, energy dispersive X-ray spectroscopy for microstructural investigation, and nanoindentation and die shear tests for the evaluation of mechanical properties are used. An average effective Young’s modulus of 86.5 ± 9.5 GPa, a Poisson’s ratio of 0.19 ± 0.02, and a hardness of 5.26 ± 0.8 GPa were measured through nanoindentation for the glass frit material. The lowest nominal shear strength ranged 1.13 ÷ 1.58 MPa in the strain rate interval to 0.33 ÷ 4.99 × 10−3 s−1. To validate the thermo-mechanical model, numerical results are compared with experimental measurements of the out-of-plane displacements at the wafer surface (i.e., warpage), showing acceptable agreement.

This study examined the effect of an imposed equibiaxial pre-stress (EBPS) on the evaluation of mechanical properties, using the depth-sensing indentation method with a point-sharp indenter, through a numerical analysis of indentations simulated with the 3D finite element method. The predicted elastic modulus, E*, and yield stress, Y*, were used as elastic and plastic deformation resistances under the indentation, respectively. It was found that both increased nominally with the increase in compressive EBPS and decreased with the increase in tensile EBPS, even though the induced change in the piling-up or sinking-in around the indentations was not significant. The effect of EBPS on E* was described by the Hooke’s law for an isotropic elastoplastic material, whereas that on Y* was accounted for by the change in the von Mises stress due to EBPS.