Consideration Of Residual Stresses Research Articles

Fatigue Strength Assessment of Friction Welds under Consideration of Residual Stress.

A reliable local-fatigue assessment approach for rotary friction-welded components does not yet exist. The scope of this paper is to present test results for the fatigue behaviour of rotary friction-welded solid shafts made of structural steel S355J2G3 (1.0570) and an approach to fatigue assessment considering residual stress. In contrast to fusion-welded joints, components made by rotary friction welding usually contain compressive residual stress near the weld, which can significantly affect the fatigue strength. For this purpose, specimens were welded and characterised, including metallographic micrographs, hardness measurements, and residual stress measurements. The fatigue tests were performed with a constant amplitude loading in tension/compression or torsion with R = -1. All specimens were investigated without machining of the weld flash, either in the as-welded state or after a post-weld stress-relief heat treatment. In addition, the friction welding process and the residual stress formation were analysed using numerical simulation. The characterisation results are integrated into a fatigue assessment approach. Overall, the specimens perform comparatively well in the fatigue tests and the experimentally observed fatigue behaviour is well described using the proposed local approaches.

A two-point fatigue strength assessment for surface-hardened notched components under consideration of residual stresses based on the local strain approach

The “Guideline non-linear” of the German Research Association for Mechanical Engineering provides a fatigue strength assessment for machine components based on the local strain approach. Currently, this assessment is limited to homogeneous components and without the possibility to consider residual stresses. The methods are thus inadequate for surface-hardened components, where the presence of material inhomogeneity and the introduced residual stresses significantly impacts fatigue life and the potential failure origin. In the following paper, an adaptation of the proof of structural durability of the guideline is shown, that firstly includes a two-point assessment and the estimation of load cycles to crack initiation at two failure-relevant points simultaneously. This enables the consideration of inhomogeneous material states, since the failure of surface-hardened components may initiate from the notch root as well as from the transition area between the low-strength core material and the high-strength surface layer. Secondly, the consideration of the residual stress state for both failure-relevant points is also introduced as part of the adapted fatigue strength assessment.

Effect of stacking sequence and interlayer toughening in ＋/−45 laminates

This paper investigates the combined effects of stacking sequence and interlayer toughening on the mechanical response and failure modes of ±45° carbon fiber reinforced laminates, comprising experimental and numerical studies. Two material systems (T800H/3631, T800S/3900) and three stacking sequences (4 double plies, 4 plies, 8 plies) have been analyzed. Digital Image Correlation (DIC) and a high resolution edge camera were utilized to capture the intricate crack patterns in each ply. This paper also addresses the challenge of the nonlinear in-plane shear characterization of the lamina, and proposes an amendment to the existing ASTM standard to obtain the in-situ non-linear response and the lamina shear strength with the consideration of residual stresses. The complex progression of micro-damage, matrix cracks and delamination as well as the final two-piece failure were captured by the enhanced semi-discrete damage modeling (eSD2M) framework. A parametric study was performed to reverse-engineer the most critical parameters such as interlayer strengths and toughnesses. The obtained values reflect the difference in the interlayer composition between the two material systems.

Effects of state‐of‐the‐art residual stress models on the member and local stability behaviour

AbstractResidual stresses have considerable effect on both the local and the member stability behaviour of steel structures. Previous studies have shown that the structural stability behaviour depends on both the distribution and the amplitude of the residual stresses. The residual stress distribution is affected by the cross‐section geometry, the steel grade and the manufacturing process, e.g. flame cutting and the welding procedure. A realistic consideration of residual stresses is necessary for an efficient and safe design of steel structures.This article presents an experimental and numerical study on the influence of residual stresses on the stability behaviour of structural members, i.e. steel columns and beams considering a variety of cross‐sectional slenderness, i.e. plastic, compact and slender cross‐sections are taken into account. A novel residual stress model for welded I‐shaped sections was developed and evaluated using test data. This model takes into account the main influencing parameters, i.e. the cross‐sections geometry, the steel grade as well as manufacturing process with thermal cuts or non‐thermal cuts of the steel plates. The novel residual stress model is then used to investigate the stability behaviour in terms of a numerical simulation study. The result of the study allows to propose an improvement of the buckling curve selection for welded high strength steel columns and beams.

Numerical Study of Non‐linear Buckling Analysis for Steel and Partial Concrete Encased Composite Columns

AbstractBuckling is a complex phenomenon, influenced by the non‐linear material properties, as yielding of steel, cracking of concrete as well as, slenderness, geometrical imperfection and residual stresses. The design codes provide essential rules for mechanical resistance, stability and safety aspects. However, the current Eurocodes essentially stipulates engineering models that can easily be transferred to classical structural analysis, but often do not guide sufficiently the application and evaluation of advanced numerical analysis.The present study investigates the buckling analysis of steel and partial encased composite columns. Different definitions for geometrical imperfections and residual stresses are considered. The geometrical imperfections are taken into account in accordance with prEN1993‐1‐14 [2]and EN1090‐2 alternatively. The residual stresses are based on prEN1993‐1‐14 [2] and ECCS – Pub. No.33. In addition, analysis without the consideration of residual stresses are investigated. The scope is to assess the non‐linear finite element analysis (GMNIA), comparing the behavior of hot‐rolled and welded steel cross‐section as well as the impact of additional reinforced concrete encasement. Guidance for the numerical analysis for steel and composite columns is developed.

A Novel Residual Stress Model for Welded I‐sections and the Influence on the Stability Behaviour

AbstractResidual stresses have a marked influence on the stability behavior of steel members. Previous studies have shown that the structural behavior depends on both the distribution and the size of residual stresses. The residual stress distribution is affected by the cross‐section geometry, the steel grade and the manufacturing process, e.g. flame cutting and the welding procedure. A realistic consideration of residual stresses is necessary for economic models for design purposes and a safe design of steel structures.This paper presents an experimental and numerical study on the influence of residual stresses on the stability behavior of structural members, i.e. steel columns and beams. A novel residual stress model for welded I‐shaped sections was developed and evaluated using test data. This model takes into account the main influencing parameters, i.e. the cross‐sections geometry, the steel grade as well as manufacturing process with thermal cuts or non‐thermal cuts of the steel plates. The novel residual stress model is then used to investigate the structural stability behavior in terms of a numerical simulation study. The result of the study allows to propose an improvement of the buckling curve selection for welded high strength steel columns and beams.

Young’s modulus and ferroelectric property of BaTiO3 films formed by aerosol deposition in consideration of residual stress and film thickness

Film thickening by aerosol deposition (AD) is effective for the fabrication of self-sustained piezoelectric energy harvesting devices. Here we investigated the properties, microstructure, and residual stresses of BaTiO3 films deposited by AD at different film thicknesses. The Young’s modulus measured by the nanoindentation test showed no thickness dependence; however, it increased from approximately 130– 160 GPa with annealing. Ferroelectric hysteresis curves showed that the increase in film thickness facilitated polarization switching. The microstructure of the films showed no significant changes with the film thickness, while the results of X-ray diffraction and finite element analysis of thermal stress showed that the residual stress after annealing depended on the film thickness. The energy harvesting performance of the BaTiO3 films deposited by AD may increase owing to the residual stress, rather than the increase in the film thickness.

On the evolution of residual stresses due to cooling considering martensitic phase transformation

AbstractThe direct consideration of residual stresses can positively influence the properties of a component and offers a new perspective compared to the typical strategy of avoiding residual stresses. Instead of minimizing residual stresses in forming processes, their consideration can positively influence the properties of the final component. For instance, the targeted adjustment of residual stresses can extend the service life or durability and improve the manufacturability of metal components. This is investigated in current research using experimental and numerical analyses on a cylindrical component with eccentric hole made of steel 100Cr6. Here, the cooling process after hot bulk forming is simulated to analyze the influence of microscopic phase evolution on the macroscopic stress distribution. For this purpose, different variants of the microstructural evolution described by a random process are compared.

Correction to: Engineering model for the quantitative consideration of residual stresses in fatigue design of welded components

Correction to: Engineering model for the quantitative consideration of residual stresses in fatigue design of welded components

Method for Calculating Plastic Deformation of High Resolution and Large Contact Area

AbstractIn a rolling contact, the tribological properties in terms of friction, wear, and fatigue are significantly influenced by the surface roughness. Due to solid contact of the surfaces in the contact area, the roughness and thus also the tribological properties change during the service life of the contact. The initial load leads to major changes of the tribological properties figured out by Brecher et al. (2019, “Influence of the Metalworking Fluid on the Micropitting Wear of Gears,” Wear, 61(434–435), p. 202996). Prediction of the initial changes in topography in the contact area is necessary for specific optimization of rolling contacts. Especially for dry rolling–sliding contact, the roughness of the surfaces is crucial for the lifetime, which is part of the investigations within the DFG priority program 2074 (357505886). In this work, an elastic-plastic contact algorithm for calculating plastic deformation for dry contact of rough surfaces with large contact area and high resolution is presented. Due to the nonlinearity behavior associated with plastic deformation, the plastic contact algorithm is based on an iterative approach. An optimized meshing strategy is implemented to calculate the elastic pressure distribution on the surface. Corresponding to the two-dimensional pressure distribution, the three-dimensional stress distribution allows the consideration of residual stresses and interactions of the microscopic peaks of the rough surface. Furthermore, the three-dimensional plastic strain distribution allows the application of an analytical approach to represent the plastic deformation of the surface. Finally, the solution of a plastic contact calculation with an exemplary topography measured on a real rough surface is presented.

Probabilistic Risk of Titanium Disks Considering Residual Stresses of Hard Alpha Inclusions

In aeroengine titanium alloy components, hard alpha (HA) inclusions strongly affect material performance, especially in terms of fatigue properties. Residual stresses caused by thermal expansion mismatch during the cooling process affect the fatigue life of metal components. This study proposes a method of probabilistic risk assessment for aeroengine disks considering the residual stresses of HA inclusions. Specifically, numerical procedures are adopted to investigate the residual stresses of an inclusion under surface effects, and a functional relationship model of residual stresses under surface effects is proposed. To deal with the randomness of inclusion size and position, a calculation criterion for the residual stresses of an inclusion is established. Analysis of an aeroengine compressor disk shows that the expected decline in the failure risk of the disk is approximately 27% under the consideration of residual stresses. The proposed method predicts the failure risk more accurately, and is thus valuable for the safety assessment of an aeroengine titanium disk.

An enhancement of the current design concepts for the improved consideration of residual stresses in fatigue-loaded welds

The consideration of residual stresses in fatigue-loaded welds is currently done only qualitatively without reliable knowledge about their real distribution, amount and prefix. Therefore, the tools which enable a more or less unsafe consideration in design concepts are mainly based on unsafe experiences and doubtful assumptions. Since the use of explicitly determined residual stresses outside the welding community is state of the art, the target of the presented paper is to show a practicable way for an enhanced consideration of residual stresses in the current design tools. This is not only limited on residual stresses induced by welding, but also on post-weld treatment processes like HFMI or shot peening. Results of extended experiments with longitudinal fillet welds and butt welds of low and high strength steels evidently show that an improved use of residual stresses in fatigue strength approximation enables a better evaluation of peening processes as well as of material adjusted welding procedures or post-weld stress relief treatments. The concept shows that it is generally possible to overcome the existing extremely conservative but although unsafe rules and regulations and may also enable the improved use of high strength steels.

Advanced calculation of the stress distribution in milling tools during cutting under consideration of residual stresses and tool wear

Milling is an irreplaceable technology for finishing turbomachinery components made of nickel-based alloys. Cutting tools in milling are exposed to high thermomechanical loads causing tool wear or ultimately tool failure. The initial condition of the tool’s surface layer determines the propagation of tool wear. “Surface layer” denotes the zone near the tool surface, which is affected mechanically, thermally, and chemically during the manufacturing process of the tool (e.g. due to grinding, polishing). So far, only limited knowledge is available on the specific effects of wear-induced changes in tool geometry as well as of residual stresses on the distribution of stresses in the cutting wedge of milling tools. This publication presents a method to consider residual stresses of cutting tools and tool wear in a 2D FEM chip formation model for detailed analysis of certain tool failure phenomena in the milling process. In order to represent a depth distribution of residual stresses in the surface layer of the uncoated tool in the simulation, residual stress measurements at grinded milling tools were performed. Tool wear was taken into account by adapting the geometry of the cutting tool. The geometry changes were based on measurements of the width of the flank wear land and of the cutting edge radius. Principal stresses and von Mises equivalent stress distribution were analyzed. The described method may improve the understanding of surface layer effects on tool life of milling tools. With decreasing chip thickness, a second, more localized zone of tensile stresses was formed at the rake face subsurface, which can be critical in terms of fracture. With compressive residual stresses and with increased flank wear, these critical tensile stresses were reduced or even eliminated.

A numerical study of the effect of phase evolution on residual stresses during cooling

AbstractThe consideration of residual stresses in forming processes is a promising opportunity to influence the final component's properties in a positive manner. Instead of their minimization, a targeted application of residual stresses can extend life time or durability and enhance manufacturability of metallic components. For this reason, detailed experimental and numerical analyses are an object of current research. Here, the cooling process is simulated in order to analyze the influence of the microscopic phase evolution on the macroscopic stress distribution in a cylinder with eccentric hole made of steel 100Cr6.

Editorial on Special Issue “Fatigue and Fracture Behaviour of Additive Manufacturing Mechanical Components”

This Special Issue presents the latest advances in the field of fatigue and fracture performances of additively manufactured mechanical components, including components made of traditional materials (metals, sintered steels, etc.) but undergoing complex loading conditions (multiaxial fatigue and mixed mode fracture). This Special Issue is composed of seven papers covering new insights in structural and material engineering. The advent of additive manufacturing (AM) processes applied to the fabrication of structural components creates the need for design methodologies and structural optimization approaches that take into account the specific characteristics of the process. While AM processes give unprecedented geometrical design freedom, which can result in significant reductions of component weight (e.g., through part count reduction), they have implications in the fatigue and fracture strength due to residual stresses and microstructural features. This is due to stress concentration effects and anisotropy that still need research. The papers of this Special Issue report on numerical simulation and experimental work, or a combination of both. The application of damage and fracture mechanics concepts, the appraisal of stress concentration effects, and the consideration of residual stresses and anisotropic behaviour are tackled for a range of structural applications from biomedical engineering to aerospace components.

Multi-Scale Modeling of Curing Residual Stresses in Composite with Random Fiber Distribution into Consideration

During curing process of composites, residual stresses inevitably develop and play an important role in the final mechanical properties of composites. Therefore, the consideration of residual stresses when designing composite structure is necessary. The causes of residual stresses are well known on the part and fiber-matrix level. However, the influence of the part level factors on micro residual stresses is less known and rarely investigated. This work aims at a better understanding of the effects of macro-level factors, including temperature variation and mechanical strains on micro-scale stresses. To this end, a multi-scale method is developed, which consists of a macro-scale model to capture temperature variation and mechanical strains field under a given cycle condition, and a RVE (Representative Volume Element) to predict residual stresses in matrix. The results demonstrate that the maximum micro residual stress in matrix presents about almost 52% reduction in the model with part-level information into consideration as compared with the results without considering the multi-scale effect. It can be also seen that with multi-scale effect into account, the matrix in the RVE experienced tensile residual stresses in the matrix-poor locations and compressive residual stresses in the matrix-poor locations.

Residual Stress–Based Fatigue Design of Welded Structures

Abstract Fatigue design concepts for welded structures generally consider residual stresses as a factor affecting the mean stress influence. Residual stresses are mostly interpreted as mean stresses. In addition, high tensile residual stresses are conservatively assumed, resulting in maximum effective load stresses from fatigue loading in the order of the yield strength. The consequence of this is that additional static load stresses may have no influence on the resulting fatigue strength because the local effective mean stress (residual stresses and load mean stresses) is always high. The related evaluation concepts neither distinguish between different steel grades nor between different origins and amounts of possible residual stresses in welded joints. The real magnitude of existing residual stresses is also usually not considered, because in practice, usually no explicit knowledge of the residual stresses at critical sites of a construction is available because residual stress measurements are not state of the art in welding practice. For an explicit consideration of residual stresses in design concepts, the sign, the initial amount, and especially the amount of the residual stresses after a load induced relaxation must be considered. Therefore, the steel grade and the condition of the material are of great importance, as well as the local stress condition influenced by welding-induced notch geometry. The article shall give an overview about the state of the art of consideration of residual stresses in fatigue design concepts for welded structures and the background of their development. Finally, a new approach shall offer a possibility for an enhanced consideration of residual stresses in design concepts based on the explicit knowledge about the effective residual stresses that can actually be observed with different measurement concepts.

High temperature fracture toughness and residual stress in thermal barrier coatings evaluated by an in-situ indentation method

High temperature fracture toughness and residual stress are important for the evaluation of TBCs. In this paper, an in-situ high temperature indentation method was originally developed to investigate the high temperature fracture toughness and residual stress in a typical TBC, nanostructured 8 wt% yttria partially stabilized zirconia (YSZ) coating. The cracks caused by in-situ high temperature indentation tests were observed, and high temperature fracture toughness and residual stress were experimentally measured. The fracture toughness was measured to be 1.25, 0.91 and 0.75 MPa*m1/2 at 25, 800 and 1000 °C, respectively. The residual stress was measured to be − 131.3, − 55.5 and − 45.5 MPa, correspondingly. Moreover, the residual stress and fracture toughness both decrease with increasing environmental temperature. It is also found that the fracture toughness without consideration of residual stress is significantly larger than the intrinsic fracture toughness, which may result from the compressive stress state.

Fatigue damage evolution and lifetime prediction of welded joints with the consideration of residual stresses and porosity

This work investigates the fatigue damage evolution of butt welded joints under cyclic loading through a continuum damage mechanics approach. A coupled thermal-mechanical analysis is conducted to evaluate the residual stresses induced by welding processes, which are used as the initial state in the fatigue damage analysis. An elasto-plastic fatigue damage model that takes into account the porosity-induced stress concentration in the weld zones of joints is developed to study their damage evolution. The fatigue lifetimes of these joints with different pore conditions are predicted and show consistency with the experimental results. The residual stress level is found to decrease due to the combined effects of the plastic deformation and fatigue damage.

Engineering model for the quantitative consideration of residual stresses in fatigue design of welded components

Residual stresses are one of the major factors influencing the fatigue strength of welded components. However, the current IIW bonus factor concept for the mean stress correction is limited to a qualitative evaluation of residual stress effects. By combining residual stress measurements and fatigue testing, the authors derive an improved bonus factor concept that considers residual stresses quantitatively. The proposed concept considers the combined effect of load mean stresses and cyclically stabilized residual stresses. It is pointed out that the yield strength is not a capable measure to determine whether residual stresses have “low” or “extreme” impact on the fatigue strength of welded steels. It is rather recommended to evaluate residual stress effects based on the effective stress ratio reflecting local loading conditions.