Metallic Structural Components Research Articles

One-step fabrication of AlPO4 nanosheet reinforced ceramic coatings with improved fracture toughness and hydrogen resistance

Ceramic coatings have great potential in protecting vital metal structural components in hydrogen energy and nuclear fusion reactors. Fracture toughness and hydrogen permeation resistance are two key characteristics that determine life span and performance of these coatings. However, there is still no strategy to simultaneously enhance both of these two characteristics. Herein, we developed a one-step approach to fabricate AlPO4 nanosheet reinforced α-Al2O3 ceramic coating with simultaneously enhanced fracture toughness and hydrogen permeation resistance. Different from the external nanosheet addition method of the conventional techniques for fabricating nanosheet reinforced coatings, AlPO4 nanosheets were in-situ formed within α-Al2O3 ceramic coating though a one-step heat treatment process. Owing to the positive reinforcing effect of AlPO4 nanosheets, the fracture toughness of the coating increases by 3 times, achieving an ultrahigh KIC value of 7.1 MPa/m2. Meanwhile, the hydrogen permeation resistance of the coating increases by 78 %, reaching as high as 3440 times that of the steel substrate. Additionally, the Cr–P bonds formed between the coating and substrate ensure their good bonding, with their bonding strength increasing up to 36 MPa. The combination of high hydrogen permeation resistance, high fracture toughness, and high bonding strength makes the AlPO4 nanosheet reinforced ceramic coating a promising alternative for reducing hydrogen permeation in various hydrogen-related fields. This study also provides critical insights and practical guidelines for constructing high-performance functional coatings via nanosheet reinforcement.

Nacre-like surface nanolaminates enhance fatigue resistance of pure titanium

Fatigue failure is invariably the most crucial failure mode for metallic structural components. Most microstructural strategies for enhancing fatigue resistance are effective in suppressing either crack initiation or propagation, but often do not work for both synergistically. Here, we demonstrate that this challenge can be overcome by architecting a gradient structure featuring a surface layer of nacre-like nanolaminates followed by multi-variant twinned structure in pure titanium. The polarized accommodation of highly regulated grain boundaries in the nanolaminated layer to cyclic loading enhances the structural stability against lamellar thickening and microstructure softening, thereby delaying surface roughening and thus crack nucleation. The decohesion of the nanolaminated grains along horizonal high-angle grain boundaries gives rise to an extraordinarily high frequency (≈1.7 × 103 times per mm) of fatigue crack deflection, effectively reducing fatigue crack propagation rate (by 2 orders of magnitude lower than the homogeneous coarse-grained counterpart). These intriguing features of the surface nanolaminates, along with the various toughening mechanisms activated in the subsurface twinned structure, result in a fatigue resistance that significantly exceeds those of the homogeneous and gradient structures with equiaxed grains. Our work on architecting the surface nanolaminates in gradient structure provides a scalable and sustainable strategy for designing more fatigue-resistant alloys.

The Method and Experiment of Detecting the Strength of Structural Components Utilizing the Distributed Strain of Sensing Optical Fibers Demodulated by OFDR.

Defects occurring during the welding process of metal structural components directly affect their overall strength, which is crucial to the load-bearing capacity and durability of the components. This signifies the importance of accurate measurement and assessment of weld strength. However, traditional non-destructive testing methods such as ultrasonic and non-contact camera inspection have certain technical limitations. In response to these issues, this paper analyzes the detection principle of weld strength, revealing that weld defects reduce the effective area of the structural bearing section and cause stress concentration around them. Through repeated experimental data analysis of samples, strain distribution data along the one-dimensional direction caused by defects such as slag inclusion and porosity were obtained. Experimental results show that this method can identify defect types in welds, including slag inclusion, porosity, and unevenness, and accurately measure the location and size of defects with a precision of 0.64 mm, achieving qualitative analysis of weld defects. Additionally, by deploying distributed optical fiber sensors (DOFS) at different vertical distances along the weld direction, the propagation law of stress induced by different types of weld defects on samples was thoroughly analyzed. This further validates the advantages of this method in weld strength detection, including high spatial resolution, high sensitivity, and non-destructive measurement.

Bending behaviour of surface corroded and perforated corroded steel tubes repaired by laser cladding additive manufacturing

In recent years, laser cladding (LC) technology has been increasingly applied and investigated for repairing damaged surface on metal structural components. However, there are limited experimental studies on the bending behaviour of the LC repaired steel components. And an effective repair method for the perforated corroded steel components is still lacking, therefore, this paper introduces a novel LC repair method for such steel tube. Four-point bending tests were conducted on four specimens, including one intact steel tube (IT), one surface corroded steel tube (SCT), one surface corroded steel tube repaired by LC (SRT), and one perforated corroded steel tube repaired by LC (PRT) to verify the effectiveness of the LC repair methods by evaluating their structural performance in terms of bending capacity, rotational stiffness, and ductility. The experimental results showed that the bending strength and rotational stiffness of the SRT and PRT can be fully restored and even slightly higher than those of the IT. The strain analysis indicated that the LC repair method can significantly reduce stress/strain concentration caused by surface corrosion and perforation corrosion. The experiments were replicated numerically by means of finite element (FE) analysis and parametric studies were performed to investigate the effect of different factors on the bending behaviour of the PRT and SRT. Furthermore, design formula for predicting the elastic bending capacity of the LC repaired steel tube was developed.

Research Progress on Electrochemical Machining Technology

Electrochemical machining (ECM) is an excellent technique of processing for metallic materials, widely used in the shaping and preparation of metal structural components. According to the size requirements of the processed structures, in this paper, the current status of ECM development is introduced from the aspects of macro-electrochemical machining and micro-electrochemical machining; and its advantages and disadvantages are summarized, which provides significant reference for the further development of ECM.

Advances in Understanding the Evolution Mechanism of Micropore Defects in Metal Materials under External Loads

Micropores are one of the critical factors affecting materials’ performance and service life. As the need for a deeper understanding of micropore evolution and damage mechanisms grows, assessing the mechanical properties of materials containing micropores and predicting the lifespan of related metal structural components becomes increasingly complex. This paper focuses on the evolution process, regularities, and research methods of micropores in metal materials. Based on recent research and practical applications, the key stages of micropore evolution are discussed, encompassing nucleation, growth, coalescence, collapse, interaction, and the influence of other microstructures. Firstly, the advantages and limitations of commonly used characterization methods such as scanning electron microscopy, transmission electron microscopy, and X-ray computed tomography are introduced in the study of micropore evolution. Subsequently, critical theoretical models for micropore evolution, such as the Gurson model and its extensions, are summarized. By using a multiscale approach combining the crystal plasticity finite element method, dislocation dynamics, and molecular dynamics, the factors influencing the micropore evolution, such as external stress conditions, internal microstructures, and micropore characteristics, are specifically elaborated, and the basic physical mechanisms of micropore evolution are analyzed. Finally, a comprehensive review and summary of current research trends and key findings are provided, and a forward-looking perspective on future research directions is presented.

VBA fatigue analysis program for metallic structural components preliminary design

The main objective of this paper is to describe the creation and use of a fatigue analysis program written in VBA, designed for the preliminary sizing of metallic structural components used in aerospace applications, subjected to one or multiple fatigue loading cases. The VBA programing language was chosen because of its direct control over the most common spreadsheet computational program, Microsoft Excel. Metal fatigue analysis is an important type of analyses for modern structures. Fatigue failure accounts for around 80-90 percent of common structural failures, and therefore, a quick and reliable analysis is necessary so as to evaluate the structure’s bearing capacity to fatigue load. Due to the nature of the fatigue load and the importance of the structural component, such an analysis can be very time consuming, starting from the finite element model preparation and going through the actual analysis; thus, there is a need for a tool that can evaluate the stress data from the numerical simulation and give reliable information about the behavior of the structural component.

Accuracy of Variational Formulation to Model the Thermomechanical Problem and to Predict Failure in Metallic Materials

The main purpose of this study is to develop a variational formulation for predicting structure behavior and accounting for damage mechanics in metallic materials. Mechanical and coupled thermomechanical models are used to predict failure in manufacturing processes. Ductile failure is accompanied by a significant amount of plastic deformation in metallic structural components. Finite element simulation of damage evolution in ductile solids is presented in this paper. Uncoupled models are implemented in a finite element model simulating deep drawing as well as cutting processes. Based on the Johnson–Cook model, the effect of deformation on the evolution of flow stress is described. The combined effect of strain, strain rate, and temperature on plasticity and damage behavior in cutting processes is considered. The accuracy of these models is verified when predicting ductile damage in forming and cutting processes.

Formability of roll-formed carbon fibre reinforced metal hybrid components and its experimental validation

Carbon Fibre Reinforced Metal Hybrid (CFRMH) materials that combine a sheet metal substrate with a reinforcing carbon fibre patch represent a promising solution to reduce weight while increasing the structural and crash performance of future automotive vehicles. CFRMHs cannot be formed with conventional stamping processes and at high volumes. This currently reduces their widespread application. Roll forming is increasingly used in the automobile industry for the forming of lightweight and high-strength metal structural components. The major deformation mode in roll forming is simple bending and this reduces interlaminar shear and compressive stresses that lead to fibre failure and delamination issues when stamping CFRMH sheet materials. This work analyses the potential of applying the conventional roll forming process for the manufacture of a simple top hat section shape from CFRMH sheet. For this, first, the material is produced in a hot press and then formed to shape in a laboratory roll forming facility at room temperature. Different layup sequences are tested, and component quality is analysed after roll forming by visual inspection. The results suggest that roll forming presents a promising manufacturing method for the production of automotive components from CFRMH sheets. The roll formed open shells are joined to produce crash box structure and tested in 3-point bending. The results show that depending on the fibre orientation a significant increase in weight specific strength is achieved.

Fatigue Life Prediction of Structures With Interval Uncertainty

Abstract A new method for reliable fatigue life prediction in metal structural components is developed, which quantifies uncertainties using interval variables. Using this crack-initiation-based method, first, the uncertainties in laboratory test data for the fatigue failure of a structural detail are enumerated. This uncertainty quantification is performed through an interval-based enveloping procedure that relates the interval stress ranges to the number of cycles to failure. This will lead to the construction of an interval S–N relationship. Next, the uncertainties in field test data are enumerated in the extremum values of each stress range, as intervals, leading to the construction of interval stress ranges. For both the laboratory and field data uncertainty analyses, the mean stress effects are considered. Next, the interval damage accumulated over the duration of the field data is determined using the constructed interval S–N relationship and the obtained interval stress ranges. Then, the interval existing damage and interval remaining life are determined. Finally, as a conservative measure, the minimum remaining fatigue life is obtained in which all uncertainties are considered. A numerical example illustrating the developed method is presented, and the results are compared with results obtained by both Monte Carlo simulation and optimization. Using this method, for the numerical example considered, it is shown that the results for bounds on the existing damage and the remaining fatigue life are sharp. Moreover, due to its set-based approach, the method is significantly more computationally efficient when compared with iterative procedures.

Influence of crack nucleation location on fretting fatigue crack path

Fretting is a contact phenomenon affecting the behaviour of metallic structural components subjected to vibrations or small oscillatory movements, and it has been recognized as the primary failure mode in many engineering applications. In more detail, due to the high stress gradients in the vicinity of the surface between two components in contact, the nucleation of cracks appears, thus leading to the failure of the metallic structure. In such a condition, the main cracks are expected to nucleate in correspondence to the stress concentration region, that is, the edge of the contact. However, cracks starting within the contact zone close to the edge are often experimentally observed. In the present paper, an analytical methodology recently proposed for the fretting fatigue assessment of metallic structures is employed in order to simulate an experimental campaign available in the literature, carried out on a 7050-T7451 aluminium alloy. Such a methodology is based on the joint application of the multiaxial fatigue criterion by Carpinteri et al. and the critical direction method by Araújo et al. First, the crack path orientation is determined for each loading configuration tested in the above-mentioned experimental campaign, by assuming the crack nucleation location in correspondence to the contact trailing edge. Then, a crack nucleation location inside the contact surface is adopted, in order to evaluate the crack path orientation. Finally, the results obtained are compared to the experimental observations available in the literature.

An implicit numerical scheme for cyclic elastoplasticity and ratcheting under plane stress conditions

The paper reports the development of an implicit numerical scheme for plane stress cyclic elasto-plasticity, capable of integrating a wide range of hardening rules, and simulating multi-axial ratcheting in metal structural components. Constitutive relations account for von Mises yielding in combination with mixed hardening. Emphasis is given to the kinematic hardening part, which is described with an advanced multiple back-stress model suitable for multi-axial material ratcheting simulation. The constitutive equations are integrated implicitly, and the accuracy of the algorithm is assessed via iso-error maps. Two main novelties of the algorithm refer to the incremental update of the internal variables through the solution of a single scalar equation, and the explicit formulation of the consistent tangent moduli. The numerical scheme is implemented within the finite element environment as an external material subroutine, and its computational efficiency is demonstrated through the simulation of large-scale experiments on pipe elbows. Using the proposed computational framework, two kinematic hardening rules are employed to simulate the elbow response with emphasis on local strain amplitude and accumulation (“ratcheting”). The good comparison between numerical and experimental results demonstrates the computational efficiency of the numerical scheme and highlights some key issues concerning multi-axial ratcheting simulation.

Mechanical Deburring of Drilling-Induced Exit Burrs in Carbon Fibre Reinforced Polymer Composites

Carbon fibre reinforced polymer (CFRP) composites have excellent specific mechanical properties, which have contributed to the replacement of metallic structural components in high-tech sectors. However, the anisotropic and inhomogeneous properties of CFRPs render them difficult to cut. Burr is one of the main machining-induced macro-geometrical defects in CFRPs. Even though burr does not weaken the resultant strength of the composites (unlike delamination), its removal is time-consuming and costly. The main aim of the present paper is to investigate the efficiency of the mechanical deburring method. Deburring experiments were carried out on unidirectional CFRP, based on a full factorial experimental design using a special solid carbide cutting tool. The effects of feed and cutting speed were analysed using digital image processing and visual evaluation of high-resolution images. The experimental results show that the examined factors seem to have no significant effect on the results over the applied parameter range, because the exit burrs were successfully removed at each parameter setting. Furthermore, during the deburring process, the formation of a significant amount of chamfers was observed. Since the size of the chamfers depends on the size of delamination-induced material deformation and process control, it should be either compensated for or monitored in the future to develop a more reliable deburring process.

Coupled numerical simulation of low-cycle fatigue damage in metal components

A coupled cyclic plasticity-damage model is implemented for simulating low-cycle fatigue in metal components. Constitutive relations account for J2-flow theory with nonlinear kinematic/isotropic hardening, coupled with isotropic continuum damage mechanics. The damage potential is written in a general form, allowing for implementing different damage models. An implicit numerical integration scheme is developed and the incremental update of the internal variables is achieved through the solution of a single scalar equation. Consistent linearisation of the integration algorithm is provided explicitly to guarantee robustness of the proposed algorithm. The algorithm is implemented in a user subroutine and is inserted into a commercial finite element software. Its accuracy and computational efficiency are demonstrated through numerical simulation of large-scale experiments on metal piping components that failed under low-cycle fatigue loading. The numerical analyses are conducted using finite element models of different mesh density, implementing an appropriate simulation methodology. A simple and efficient damage evolution function is employed, regularised with respect to the element’s size, so that the numerical results present negligible mesh dependency. Excellent comparison is observed between experimental and numerical results in terms of global structural response, local strains and the number of cycles for developing through-thickness crack, indicating that the present formulation can be used as an efficient numerical tool for simulating inelastic damage and low-cycle fatigue in large-scale metal structural components.

The nature of nonmetallic inclusion distribution in the weld metal structural components at arc welding methods

The nature of nonmetallic inclusion distribution in the weld metal structural components at arc welding methods

Improvement in fatigue strength of 41Cr4 steel through slide diamond burnishing

Slide burnishing (SB) is a static mechanical surface treatment based on the severe plastic deformation of the surface for which the contact between the deforming element and the surface being treated is sliding friction. SB improves the surface integrity of metal structural and machine components dramatically. This paper is devoted to improving the fatigue strength of 41Cr4 steel hourglass-shaped specimens subjected to SB with a spherical-ended deforming diamond via different combinations of basic governing parameters. Since the residual compressive stresses introduced play a significant role for the fatigue behavior of the burnished components, a comprehensive parametric study of the SB process was conducted using fully coupled thermal-stress finite element (FE) simulations. The FE model’s adequacy was proven via comparison of the FE results for the residual stresses with X-ray diffraction measurements. The results obtained show that the diamond radius and the burnishing force have the strongest effects on the residual stresses, which, in turn, have a significant influence on the fatigue strength, respectively, fatigue life. An extensive experimental investigation of the effect of the selected SB basic parameters on the fatigue limit of the slide burnished specimens was carried out using Locatti’s method. The latter is based on the Palmgren–Miner linear damage hypothesis, which is a particular case of a general cumulative damage theory. A planned experiment was carried out, with the governing factors changed among four levels. Regression analysis of the experimental results was carried out, and a model for predicting the fatigue limit was obtained. Based on the model obtained, a one-purpose optimization was carried out using a genetic algorithm. By means of the optimal basic parameters, the fatigue limit of the processed specimens was increased by 22.7%—from 440 to 540 MPa. The fatigue life increased more than 100 times over after SB with the optimal basic parameters.

Microstructure and Mechanical Property of Ti-5Al-2.5Sn/Ti-6Al-4V Dissimilar Titanium Alloys Integrally Fabricated by Selective Laser Melting

Metallic structural components made from dissimilar titanium alloys are playing important roles in high-end industries such as aerospace and aviation. In this paper, a Ti-5Al-2.5Sn/Ti-6Al-4V dissimilar titanium alloy material was additively manufactured by the selective laser melting (SLM) process. Interface characteristics, microstructure, and mechanical properties of the SLM-deposited samples before and after complete annealing treatment were researched to provide some technical basics for the integral fabrication of dissimilar titanium alloy components. The results demonstrated that a defect-free metallurgical bonded interface with a ~ 70-μm-wide element inter-diffusion region could be obtained between the Ti-5Al-2.5Sn and Ti-6Al-4V layers under both the as-deposited and the complete annealing states. The interfacial bonding strength between the dissimilar titanium alloys was always higher than the strength of the Ti-5Al-2.5Sn layers. Microstructure evolution and element inter-diffusion mechanisms of the SLM-produced Ti-5Al-2.5Sn/Ti-6Al-4V samples were also revealed and related to the change in mechanical properties.

A new vibro-acoustic modulation technique for closed crack detection based on electromagnetic loading

The detection of closed cracks is crucial to the assessment of the integrity of metal structural components. In recent years, the ultrasonic nonlinear technology has been increasingly utilized in such detection. With this technology, the vibro-acoustic modulation (VAM) technique is found to be reliable and sensitive. In this study, the technique is implemented through electromagnetic loading to enhance the sensitivity of ultrasonic detection and evaluation of closed cracks. The proposed VAM technique based on electromagnetic loading involves opening and closing of the closed crack with Lorentz force emanating from the loading coil and magnet instead of mechanical equipment, which can concentrate the loading energy around the closed crack rather than on the whole specimen. The opening and closing of the closed crack can enhance the nonlinearity effect when ultrasonic signal propagates through it. The comparative experiments performed in this study demonstrate that the proposed VAM technique based on electromagnetic loading has a considerable potential in the ultrasonic evaluation of closed cracks. The influence of different electromagnetic loading parameters on the modulation effect are also investigated experimentally.

Linear and Non-Linear Stress Analysis for the Prediction of Fracture Toughness for Brittle and Ductile Material using ASTM E399 and ASTM E1290 By ANSYS Program package

Prediction of fracture toughness value of most the metallic materials is a very important issue to be consider in designing of engineering structural components like pipes, flow tanks and pressure vessel where it can be used in the evaluation of critical crack length that is consider very important factor in non-destructive testing because during inspections of these components, the critical crack length is being compared with the minimum allowable flow size. Fracture toughness value can be predicted by using two different types of experimental tests such as ASTM-E399 (which is used to predict fracture toughness under plane strain condition for brittle materials which undergo to small plastic deformation) and ASTM-E1290 (which is used to predict fracture toughness for ductile materials which undergo to large plastic deformation). These experimental tests utilize specimens such as compact tension specimen CT and three-point bend specimen SENB which must be pre-cracked. However, manufacturing of pre-cracked in metallic structural components before testing is expensive and time-consuming process, thus in the current study, fracture toughness will be predicted by using economized method in both time and cost that is the finite elements method by using ANSYS PROGRAM Where, a three-dimensional model has been designed by using two different types of elements (plane-82) and (solid-95).Firstly, two-dimensional model mesh will be idealized by using element type (plane-82) due to ANSYSY PROGRAM can pick–up singularity for two dimensional model only, but in order to obtain more accurate results, a three dimensional model will be designed by utilizing Sweep Model with restriction with ANSYSY abilities in the treatment of fracture mechanics problems for three dimensional model analysis where the element length must be ranging from 1to4 in all directions. In elastic region, the fracture toughness is been predicted directly from ANSAYS PROGRAM using the specification in ASTM-E-399 for compact tension specimen for practical design problems. But in elastic-plastic region, the fracture toughness is been predicted by using the crack tip opening displacement model (CTOD-Model) using the specification in ASTM-E-1290 for three-point bend specimen for practical design problem. The critical value for crack tip opening displacement will be calculated after extracting load-displacement data from ANSAYS PROGRAM then using these data in (CTOD-Model) which is separated into two components, elastic and plastic, the elastic component has been estimated using Dug Dual-Model, while the plastic component will be estimated using Plastic Hinge-Model. However, the fracture toughness value that has been predicted by finite element method from non –linear elastic analyses and from non –linear elastic-plastic analyses gives excellent results which are very close to the experimental results with error ratio ranging between (10% to 14%).

Detection of rational frequency of the sample incremental loading during its tests for endurance on the basis of a synergetically organized acoustic emission

The article considers results of the evaluation of rational frequency effecting the sample when implementing the method of determining the fatigue characteristics of materials based on synergistically organized emission of stress waves. The essence of this process lies in the fact that a flow of the emission signal is formed with a small-scale loading of the tested sample at each step of loading. At the same time, another series of dislocations is being generated, capable of reaching the crystal surface at the next moment of loading and emitting a stress wave. The magnitude of this signal characterizes the processes occurring in the material at a particular load, and allows the power parameters corresponding to such value as endurance limit to be recorded. The purpose of this work is to determine the frequency of small-scale loading, providing the maximum wave signal when implementing the method for determining the fatigue characteristics of materials based on synergistically organized emission of stress waves. The analysis of the movement of material elements was made. Based on previously published materials on the use of synergistically organized acoustic emission, the process of behavior of the metal structural components was analyzed; the process of the behavior of its grain under the influence of dislocation movements is identified and described. The strength of each such impact was represented by the delta function. The behavior of metal grains was described by the second order differential equation. The probability of a grain moving from impulse action from the side of lying crystals and from its own impulses is described by the density of movement probability of this grain. Considering jointly the dynamic and probabilistic description of the grain behavior, the Kolmogorov – Focker – Planck equation was obtained. Due to the fact that in the present work, the oscillatory nature of the metal grain movement was of interest, the above-mentioned equation was transformed into a wave-mechanical function of the process of grain behavior. The solution of wave-mechanical function is wave equation. As a result of consideration of the wave equation, natural frequency of material grain oscillations was revealed. This frequency falls in the range of frequencies that can be reproduced under stepwise loading of the test sample. This makes it possible to realize a resonance effect as applied to behavior of the metal crystal structure. Thus, frequency at which fluctuations in the material structure at the grain level will resonate with an external effect on the sample is determined. Resonant interaction of the material structure and external incremental loading of the sample will ensure a more powerful value of the emission signal at the same value of the steps under small-scale loading.