Fatigue Strength Research Articles

Experimental study on the compressive fatigue performance of nano-silica modified recycled aggregate concrete

This study focused on the compressive fatigue performance of nano-silica (NS) modified recycled aggregate concrete (RAC). 108 prism specimens with varying replacement ratios (i.e., 0 %, 50 %, and 100 %), NS soaking concentrations (i.e., 0 %, 1 %, 2 %, and 3 %), and stress levels Smax (i.e., 0.75, 0.8, 0.85, and 0.90) were designed for compressive fatigue test. The failure process and failure modes for the specimens were observed, the fatigue life curves of NS modified RAC under different design parameters were measured. Moreover, the relationships between different design parameters and fatigue life, fatigue strength were analyzed. The results revealed that the failure modes for specimens with different design parameters were mainly shear failure, conical failure and mixed failure. Fatigue life exhibited significant changes under different stress levels, decreasing notably with increasing stress levels. As the recycled coarse aggregate (RCA) replacement ratio increased, fatigue life demonstrated a decreasing trend. Based on the two-parameter Weibull distribution function, the fatigue life equation considering the influence of variable parameters under different failure probabilities was proposed. When the failure probability was 0.5, the specimen with a NS soaking concentration of 2 % exhibited the highest fatigue strength at the same replacement ratio.

Consequence of coherent Cu5Zr precipitates and Cu2O passive layer formation on the corrosive behaviour of additively processed Cu-Cr-Zr alloy in simulated seawater

Abstract The Cu-Cr-Zr copper alloy is known for its outstanding electrical conductivity and fatigue strength. However, the corrosion behaviour of the copper alloy should also be taken into account when adopting it in industrial applications, especially in the marine environments. This research aims to fabricate Cu alloy coupons using the Laser Powder Bed Fusion (LPBF) technique and subsequently test their corrosive performance in simulated seawater. This research confirms that the Cu5Zr precipitate formation during the LPBF process and the Cu2O passive layer formation were the main reason for the enhanced corrosive behavior of the LPBFed copper alloy. The OM (Optical Microscope), FESEM (Field Emission Scanning Electron Microscope) images supported in evaluating melt pool formations and irregularities, and also confirmed the polycrystalline structure. The diffraction pattern from the TEM (Transmission Electron Microscope) analysis confirmed the formation of Cu5Zr precipitate and grain size distribution, while their orientations were obtained from the EBSD (Electron Based Scattered Diffraction) EBSD analysis. Micro hardness was executed on the scanning and building directions, and it was found that the building direction possessed higher hardness of 54 HV0.3 which was 5% higher than in the scanning direction. This significant fluctuation in the hardness value is due to the closely packed equiaxed and columnar grains along the outer and inner regions of the melt pools. Potentio-dynamic polarization (PD) and electrochemical impedance spectroscopy (EIS) tests were performed on the printed copper alloy parts for various immersion periods of 0, 9, 18 and 38 h. Further, the XRD (x-ray Diffraction) analysis was performed on the corroded surface and it confirmed the Cu2O passive layer and the occurrence of Cu5Zr precipitate. The occurrence of Cu5Zr precipitates and Cu2O passive layer formation helped attain the maximum polarization resistance of 2033.8 ohm and minimum current density of 5.928 × 10−6 A cm−2 with minimum surface roughness of 3.447 μm.

Psychological needs, self-efficacy, motivation, and resistance training outcomes in a 16-week barbell training program for adults.

Despite extensive research on the relationship between psychological factors and aerobic training, there remains a gap in understanding these relationships within resistance training (RT), particularly barbell-based RT. This study aimed to examine the associations between basic psychological needs, behavioral regulation, self-efficacy, and a longitudinal barbell-based RT program for adults. Forty-three adults (M age = 45.09 ± 10.72) were recruited from the Competitive Edge resistance training program at a medical fitness center in Northwest Montana. The study followed an 18-week schedule: 8 weeks of training, 1 week of active recovery, and 8 additional weeks of training. The results reveal several significant findings. First, the basic psychological need for competence significantly increased from baseline (M = 5.06) to post-program (M = 5.30), (p = 0.017). Second, the composite score of the BREQ-3 significantly predicting muscular strength improvements in the deadlift (β = 3.64, p = 0.039). Third, both mastery (p = 0.021) and resilience (p = 0.007) self-efficacy subscales increased from baseline to post-program. Fourth, exploratory analyses indicated that the reasons to exercise scale predicted increases in muscular endurance with the weight management (β = 10.016, p = 0.046) and solitude (β = 6.792, p = 0.037) subscales. These findings highlight the importance of psychological factors in predicting strength outcomes and muscular endurance, suggesting that psychological interventions may complement physical training to maximize benefits. This research contributes valuable insights into how psychological factors influence training outcomes, potentially guiding future interventions and program designs to better support strength development and endurance in resistance training contexts.

Comparative Impact of Core Stabilization vs Proprioceptive Neuromuscular Facilitation Exercises on Muscle Activation, Endurance, and Balance in Obese Children: A Randomized Controlled Trial.

BACKGROUND The purpose of the study was to compare the effects of core stabilization exercise (CSE) and proprioceptive neuromuscular facilitation (PNF) exercise on core muscle activation, core muscle endurance, proprioception, and balance in 80 obese children. MATERIAL AND METHODS In this single-blind, randomized controlled study, 80 obese children aged 10-13 years were randomly divided into 3 groups. The first group received CSE (n=27) and the second group received PNF exercises (n=27) 3 days a week for 8 weeks. The third group, which was the control group (n=26), received no treatment. Participants were evaluated before treatment (BT) and after treatment (AT) and at follow-up (3 months after treatment). Core muscle activation level was evaluated by Sahrmann Core Stability test (SCST), lumbar core muscle endurance was evaluated by McGill core endurance tests, and lumbar joint position sense (JPS) was evaluated by laser cursor. The single-leg standing balance test (SLSBT) and Y balance test (YBT) were used for static and dynamic balance, respectively. RESULTS AT and at follow-up, core activation, core endurance, JPS, and static balance were significantly different between the groups (P<0.05). There was no significant difference between the groups in YBT dominant and non-dominant side mixed reach distances (P>0.05). Clinical effect sizes were higher in the CSE group for all outcome measures. CONCLUSIONS CSE and PNF exercises improve the level of core muscle activation, lumbar core muscle endurance, lumbar JPS, and balance in obese children. However, the results of this study show that CSE are more clinically effective in obese children. The effects decline in the medium term.

Multi Autonomous Underwater Vehicle (AUV) Distributed Collaborative Search Method Based on a Fuzzy Clustering Map and Policy Iteration

Collaborative search with multiple Autonomous Underwater Vehicles (AUVs) significantly enhances search efficiency compared to the use of a single AUV, facilitating the rapid completion of extensive search tasks. However, challenges arise in underwater environments characterized by weak communication and dynamic complexities. In large marine areas, the limited endurance of a single AUV makes it impossible to cover the entire area, necessitating a collaborative approach using multiple AUVs. Addressing the limited prior information available in uncertain marine environments, this paper proposes a map-construction method using fuzzy clustering based on regional importance. Furthermore, a collaborative search method for large marine areas has been designed using a policy-iteration-based reinforcement learning algorithm. Through continuous sensing and interaction during the marine search process, multiple AUVs constantly update the map of regional importance and iteratively optimize the collaborative search strategy to achieve higher search gains. Simulation results confirm the effective utilization of limited information in uncertain environments and demonstrate enhanced search gains in collaborative scenarios.

Muscle strength in sport climbing: a systematic review and meta-analysis.

This study aimed to synthesize the literature comparing muscle strength and endurance characteristics between 1) sport climbers and non-climbing controls; 2) sport climbers at different performance levels; and 3) boulderers and lead climbers. A systematic literature search (PubMed, Embase and SportDiscus) was performed. Inclusion criteria involved participants aged ≥18, muscular performance measurements and comparisons of either: climbers and non-climbers, boulder climbers and lead-climbers, or climbers of different levels. Meta-analyses comparing grip strength and muscle endurance of the forearm between sport climbers and non-climbers, and finger strength between boulders and lead climbers were conducted providing the standardized mean difference (SMD). A total of 960 climbers and 301 non-climbers were included in the study. The data showed: 1) Compared to non-climbers, climbers showed significantly higher grip strength: SMD 1.82 (95% CI 1.23; 2.41, P<0.001) and underarm endurance: SMD 0.70 (95% CI 0.17; 1.24, P=0.01); 2) compared to lead-climbers, boulder climbers showed significantly higher finger strength: SMD 1.08 (95% CI 0.54; 1.62, P<0.001); 3) higher-level climbers showed better finger strength, grip strength, forearm endurance and powerslap when compared to lower-level climbers. Climbers had superior grip strength and forearm endurance compared to non-climbers. High-level climbers exhibited better finger strength, grip strength, forearm endurance and powerslap, when compared to lower-level climbers. Finally, boulder climbers exhibited greater finger strength than lead-climbers. These findings expand our understandings of climbers' physical attributes across disciplines and levels.

Assessment of hybrid machine learning models for non-linear system identification of fatigue test rigs

The prediction of system responses for a given fatigue test bench drive signal is a challenging problem, since highly dynamic loads from measurement campaigns must be reproduced accurately. Linear frequency response function models are commonly used for this system identification task, but energy intensive experimental iterations are required to account for system non-linearities. Two novel hybrid modeling strategies are suggested, which augment existing approaches using non-linear Long Short-Term Memory networks. These are trained and deployed on short subsequences of measurement data and recombined using a windowing technique, which enables their application to measurement data with high sampling rates. In addition to fatigue test bench commissioning, these hybrid models can also be employed in the field of virtual sensing. The approach is tested using non-linear experimental data from a servo-hydraulic test rig and this dataset is made publicly available. A variety of metrics in time and frequency domains, as well as fatigue strength under variable amplitudes, are employed in the evaluation. It is shown, that hybrid models can successfully use frequency response function models as a linear baseline estimate, which is further improved by Long Short-Term Memory networks to enable non-linear predictions.

Research on the effect of manufacturing processes on the fatigue life of TC4 fasteners

Abstract TC4 fasteners have the characteristics of high specific strength and yield ratio, excellent high and low temperature performance, corrosion resistance, etc., and are widely used in many fastener fields, including aerospace. In long-term use, fatigue fracture has become the main failure mode of TC4 bolt fasteners. The common manufacturing processes of TC4 fasteners include shot peening, bottom corner rolling pressure, anodizing and molybdenum disulphide coating, etc. At present, few researchers have studied the effect of the stress level of the manufacturing process on the fatigue life of TC4 fasteners. Therefore, this paper designs the process and parameter influence test from the perspective of different manufacturing processes, and analyses the fatigue test results to reveal the influence mechanism of different processes on the fatigue life of TC4 fasteners. The research results show that the increase of residual compressive stress greatly improves the fatigue strength of fasteners, the shot peening process improves the fatigue life of TC4 fasteners by increasing the residual stress of fasteners, and rolling pressure also increases the surface residual compressive stress. However, it is necessary to find suitable rolling parameter values, and anodizing reduces the residual compressive stress of fasteners. The coating of molybdenum disulfide also reduces the residual stress value of the fastener surface and leads to a decrease in fatigue life. Therefore, in order to control the fatigue life of TC4 fasteners, it is necessary to carry out the shot peening process, and control the rolling pressure, anodizing time and the coating thickness of molybdenum disulfide. The research in this paper provides a reference for the subsequent research on fastener fatigue strength control.

Fatigue strength of repair‐welded headed studs

AbstractWelded connections of headed studs are highly stressed details in bridge structures in steel‐concrete composite construction and are largely responsible for the functionality of the supporting structures. At the same time, this detail requires a lot of resources due to the high welding effort and therefore has a major influence on the economic success. An important criterion for the economic and ecological balance of the structure is the durability of the welded joint, which is quantified by the fatigue strength. The welding of headed studs for composite bridges is usually carried out using fully mechanised drawn arc stud welding in accordance with EN ISO 14555. Due to the process, stud welds that do not fulfil the standard requirements for flawless condition may occur in individual cases. The design rules for stud load‐bearing capacity in accordance with EN 1994‐2 are based on tests and only apply to connections produced using drawn arc stud welding. In the past, there were practicable and tacitly accepted solutions for repairing such sporadically occurring faulty welds, but these were never systematically investigated. Particularly against the background of fatigue loading, repair‐welded stud connections are now to be systematically investigated in a project funded by the AIF. The article provides an overview of the execution of stud welded joints and presents the tests planned in the project in order to achieve a practicable recommendation for the repair welding of headed studs.

Comparison of trunk muscle endurance between women with and without chronic neck pain

PurposeTo compare trunk flexor, extensor, and lateral flexor muscle endurance between women with moderate to severe disability due to chronic neck pain (CNP) and asymptomatic women. DesignObservational case-control study. MethodsThirty women with CNP and Neck Disability Index scores ranging from 30% to 70% and 28 asymptomatic women were included. The visual analog scale was used to assess neck pain intensity at rest and during activity. To assess trunk muscles endurance, trunk flexor endurance test, Sorensen test, and side bridge endurance test were performed. ResultsAnalysis of covariance indicated that neck pain group had lower body mass index-adjusted endurance times of trunk flexor, extensor, and lateral flexor muscles with large effect sizes (p < .001, η2 = 0.378-0.696). Trunk flexor endurance time showed a moderately negative correlation with neck pain intensity at rest and a weakly negative correlation with neck disability score (r = –460 and –365, p < .05). ConclusionsWomen with moderate to severe disability due to CNP exhibited decreased trunk muscle endurance, which may be a predisposing factor for low back pain. Also, trunk flexor endurance was related to neck pain complaints. A holistic approach, addressing the entire spine rather than focusing solely on the cervical region, might be useful for managing CNP. Clinical ImplicationsThe findings of reduced endurance in trunk muscles should be considered when incorporating interventions in the management of CNP to effectively address pain and disability.

Elucidating the effect of cyclic plasticity on strengthening mechanisms and fatigue property of 5xxx Al alloys

The strength of non-heat-treatable 5xxx Al alloys is derived from solid solution strengthening and strain hardening, the absence of a precipitation strengthening response results in their lower strength. In this study, significant improvements in strength can be achieved by subjecting three different Mg concentrations 5xxx Al alloys to cyclic plasticity. A quantitative analysis of the respective contributions to the yield strength has been conducted by combining transmission electron microscopy and atom probe tomography. Additionally, the fatigue performance and fatigue mechanism of the cyclic strengthened 5xxx Al alloys have been thoroughly studied due to its transformation from non-heat-treatable to precipitation strengthening. We demonstrate that the high-cycle fatigue (HCF) strength of the cyclically strengthened state only experiences a minor improvement compared to the as-received state, which is significantly disproportionate to the enhancement in tensile strength. This disparity is primarily attributed to the changes in microstructure and fatigue mechanisms, resulting in a reduction in fatigue ratio. This study provides important insights for expanding research on cyclic plasticity methods in fatigue performance, and can aid in the development of improved processes for optimal fatigue resistance.

Effects of Supplementation with Omega-3 and Omega-6 Polyunsaturated Fatty Acids and Antioxidant Vitamins, Combined with High-Intensity Functional Training, on Exercise Performance and Body Composition: A Randomized, Double-Blind, Placebo-Controlled Trial.

The aim of this study was to investigate the effects of a supplement rich in ω-3 and ω-6 polyunsaturated fatty acids (PUFAs) and antioxidant vitamins on physical performance and body composition following a period of high-intensity functional training (HIFT). Nineteen healthy young adults (nine males, ten females) underwent an 8-week HIFT program (3 days·week-1) where they were randomized 1:1 into either the supplement group (SG)-n = 10, receiving a 20 mL daily dose of a dietary cocktail formula (Neuroaspis™ PLP10) containing a mixture of ω-3 and ω-6 PUFAs (12,150 mg), vitamin A (0.6 mg), vitamin E (22 mg), and γ-tocopherol (760 mg)-or the placebo group (PG)-n = 9, receiving a 20 mL daily dose of virgin olive oil. Body composition, cardiorespiratory fitness, muscle strength, and muscle endurance were assessed before and after the training period. Body mass did not change, but muscle mass increased by 1.7 ± 1.9% or 0.40 ± 0.53 kg in the SG (p = 0.021) and decreased by 1.2 ± 1.6% or 0.28 ± 0.43 kg (p = 0.097) in the PG, compared with baseline. VO2max, vertical jump, squat 1RM, bench press 1RM, and muscle endurance increased similarly in both groups. The effects of HIFT on physical performance parameters, muscle damage, and inflammation indices were not affected by the supplementation. In conclusion, HIFT combined with high doses of ω-3 and ω-6 PUFAs and antioxidant vitamins resulted in a small but significant increase in muscle mass and fat reduction compared with HIFT alone.

Construction of Wushu Routine Training Program for Wellness Promotion in Secondary School Students

Background and Aim: As an important way of small and medium-sized sports communication, the current schools propose to stimulate the physical quality of middle school students in Wushu training. Wushu training is also to train primary and middle school students to enhance their physical fitness, enhance their self-confidence, and improve their emotional conditions. Therefore, the research goal of this paper is to promote the construction of healthy Wushu sports training programs for middle school students. The main research objects of this paper are middle school students. Research method: this study adopts the literature method, questionnaire method, and experimental comparison method of the exercise intervention of middle school students’ physique and mental health, in this paper, a total number of 50 students in Xianyang City, 50 were tested, and 30 could not be tested due to some reasons, such as lower limb injury, cardiopulmonary disease, and other symptoms. Result: After the eight-week Wushu routine exercise training intervention, the lung capacity increased (endurance quality), sitting forward flexion (flexibility quality), high leg lift (coordination ability), and 50 m short distance running (speed strength quality) were all improved and enhanced. the improvement of emotional state, self-confidence, and the improvement of anti-frustration ability to establish a sense of achievement reduce anxiety, and resist depression was significantly reduced. the subjects of lung capacity increase, flexibility, coordination, speed strength and aerobic endurance, anxiety, and depression mood significantly decreased. The results: the main ways to stimulate the physical quality of middle school students through Wushu routine training. It shows that wushu routine training can not only improve the physique of middle school students, but also promote mental health, and provides a certain basis for exercise training practice through exercise intervention experiments. Conclusion: After the eight-week Wushu routine training intervention, the lung capacity increased (endurance quality), sitting forward flexion (flexibility quality), high leg lift (coordination ability), and 50 m short distance running (speed strength quality) were all improved and enhanced. the improvement of emotional state, and self-confidence, and the improvement of anti-frustration ability to establish a sense of achievement reduces anxiety and resist depression was significantly reduced.

The Combined Effects of Endurance and Strength Training on Exercise Tolerance and Quality of Life in Patients with COPD

Chronic Obstructive Pulmonary Disease (COPD) significantly impairs exercise tolerance and quality of life due to respiratory and systemic effects. Exercise training, including endurance and strength modalities, is a cornerstone of pulmonary rehabilitation, yet the combined effects of these training methods remain underexplored. This study aimed to evaluate the combined effects of endurance and strength training on exercise tolerance and quality of life in COPD patients. A randomized controlled trial was conducted involving 100 COPD patients assigned to four groups: Endurance Training, Strength Training, Combined Training, and Control. The interventions were implemented over 12 weeks, with outcomes assessed pre- and post-intervention, including the six-minute walk test (6MWT) for exercise tolerance and the St. George’s Respiratory Questionnaire (SGRQ) for quality of life. Statistical analyses included ANOVA and post-hoc comparisons to determine group differences. The Combined Training group demonstrated the most significant improvement in exercise tolerance, with a mean increase of 72.4 meters in 6MWT distance, compared to 48.7 meters in the Endurance group and 34.2 meters in the Strength group. Quality of life, measured by SGRQ, improved significantly across all intervention groups, with the greatest reduction in total SGRQ scores observed in the Combined Training group (12.6 points), indicating enhanced physical and psychological well-being. Additional improvements in muscle strength and endurance capacity were also most pronounced in the Combined Training group. Combined endurance and strength training provide superior benefits in enhancing exercise tolerance, muscle strength, and quality of life in COPD patients compared to either modality alone. These findings support the integration of multimodal exercise regimens in pulmonary rehabilitation programs to optimize outcomes for COPD patients.

High predicted durability for the novel small-diameter OmniaSecure defibrillation lead

BackgroundDefibrillation leads remain the Achilles heel of implantable cardioverter-defibrillators. As patients with implantable cardioverter-defibrillators are living longer and battery longevity increases, more durable leads are needed. The LEADR trial evaluated the novel, lumenless, small-diameter, OmniaSecure defibrillation lead and demonstrated favorable safety and efficacy profile as well as zero fractures through 12.7 ± 4.8 months and remains in clinical follow-up. To augment the clinical trial, advanced cardiac lead reliability modeling was used to project long-term lead durability. ObjectiveWe aimed to project the 10-year fracture-free survival of the OmniaSecure defibrillation lead using reliability modeling. MethodsThe validated reliability model, which incorporates patient and bench test data, was used to project the 10-year fracture-free survival of the OmniaSecure lead. A subset of LEADR trial patients underwent biplane fluoroscopy imaging during cardiac and patient motion to evaluate the lead’s bending curvature in vivo. Bench tests then reproduced these use conditions with greater bending curvatures than observed in patients to exaggerate stress on the lead and to evaluate the lead fatigue strength. ResultsThe reliability modeling projects a 98.2% fracture-free survival rate of the OmniaSecure lead at 10 years, including a 10-year fracture-free survival rate of 97.9% in adolescents, exceeding both the modeled and clinical 10-year performance of the highly reliable, larger diameter Sprint Quattro lead. ConclusionConsistent with early clinical trial experience, modeling projects highly durable 10-year performance of the OmniaSecure lead, including within the active adolescent pediatric population, which may uniquely benefit from a novel 4.7F defibrillation lead designed for reliability. ClinicalTrials.gov identifierNCT04863664

Study of the fatigue fractography of dual phase low carbon steel used in automotive industry

Fatigue properties play a crucial role as they are vital to ensuring the durability and integrity of components subjected to repeated loading conditions over long periods. The main objective of this work is to investigate the fatigue behavior of dual-phase low-carbon steels used in automotive applications using a rotating bending fatigue machine. Heat treatments were carried out to analyze the microstructure's effect on the fatigue properties, including quenching low-carbon steel samples at 800 °C and 900 °C. Hardness and tensile tests were performed, and the microstructure was inspected to examine the constitute phases. With the assistance of a scanning electron microscope, fractographic analyses were carried out to reveal the fracture features of the samples at different lifetime ranges. The results show that various failure mechanisms occur depending on the stress levels. Additionally, the specimens quenched at 900 °C exhibited higher fatigue strength.

Remaining Fatigue Strength of an Orthotropic Steel Deck with Respect to a Repair Method by Cold Joining Techniques

AbstractThe increased traffic loads of the last decades led to an overload of the existing infrastructure. Especially for orthotropic steel decks of bridges, which are prone to fatigue fractures, this have led to structural damages of different categories. With respect to category 2 damages and their retrofit, this paper presents results of fatigue tests on the nonwelded constructional details of an old, demolished orthotropic steel deck. The samples were extracted from a highway bridge with an orthotropic steel deck built in Germany in the 1970s. In comparative fatigue tests on identical constructional details made of new material with the same steel grade, the remaining fatigue strength was determined. Based on the problem of manganese sulfides in old steels the potential of the repair method by cold joining techniques was emphasized. Characteristic load‐bearing capacities for a Eurocode 3‐compliant design of a structural blind fastener were determined and their use in a pilot project was reported.

Experimental and CFD investigation of fatigue damage of welded cantilever under high-speed train

This paper deals with the fatigue damage of the welded cantilever under a high-speed train subjected to wind-induced loading using a field test campaign and a CFD (Computational Fluid Dynamic) simulation. The results show that significant airflow pressure on the cantilever frames and the structural resonance are the main cause of the fatigue damage of welded joints. During long-term operation, the free end of the cantilever tends to vibrate undesirably, which affects the service life of the structure. Firstly, a finite element model with constant amplitude of wind pressure is created based on the current design specifications to assess the static and fatigue strength of the cantilever. The simulation results show that the structural strength meets the standard design requirements. However, the results of the field test show that the acceleration at the free end of the cantilever is 32.0 m/s2, which far exceeds the relevant requirements. Meanwhile, there is a significant difference in aerodynamic pressure on the frame surfaces between the leading and trailing cars. An aerodynamic model is created for two full-size cars with the CFD method. The results show that FIV (flow-induced vibration) is the main cause of the continuous vibration of the elastic cantilever frame as long as the wake shedding occurs at a frequency close to the natural frequency of the frame. This study provides a reference for the aerodynamic fatigue design of the equipment mounted high-speed trains, especially for structures with low stiffness affected by open airflow.

Post-Processing of Inconel 718 Alloy Fabricated by Additive Manufacturing: Selective Laser Melting

The review analyses Inconel 718 (IN718) alloy, which is the nickel-based superalloy and has great application in industries due to its superior mechanical properties even at elevated temperatures by means of the solid-solution strengthening and precipitation strengthening. However, because of the tool over-wear, poor part surface integrity, high hardness and low thermal-conductivity properties, it is difficult to manufacture finished products with using conventional machining methods. It is especially urgent for the products of complex designs. In this regard, justification is given for the widespread use of modern additive manufacturing (AM) for the fabrication of the products from IN718. The most popular is AM based on the selective laser melting (SLM) technique, which can fabricate complex geometries with superior material properties. At the same time, the metal parts fabricated by SLM suffer from excessive residual porosity, residual tensile stress in the near-surface layer, and the formation of a relatively rough surface. In addition, the SLM-inherited surface defects can cause stress concentration to initiate cracks, reducing the fatigue strength of the printed parts. The review focuses on identifying potential solutions to the surface-finish complex additive manufactured to improve the surface properties to meet the industry requirements. Therefore, the improvement of the IN718-alloy-parts’ surface properties printed by the SLM becomes especially relevant. Currently, different surface post-processing technologies are being developed to obtain the expected surface quality of the SLM-components. As demonstrated, the finish surface enhancement treatments led to significant improvement in the wear resistance, corrosion resistance, increase in fatigue life, and tensile strength of the metallic materials. Therefore, adapting surface post-processing technologies has become a growing area of interest as an effective tool for improving the functionality and service lifetime of SLM IN718-alloy components. The review aims to analyse the main results of the most systematic studies of the currently developed surface post-treatments aimed to improving the surface-structure quality and properties of the IN718 parts fabricated by SLM. These results contribute to a better understanding of the role of the various-parameters’ effects on the surface improvements during the surface post-processing and changes in the structure–phase state, and physical, chemical and mechanical properties. Examples of the effects of a series of surface post-processing methods are presented: laser polishing, mechanical magnetic polishing, cutting finish-machining operations, shot peening, sandblasting technique, ultrasonic-impact treatment, and electrochemical polishing.

Surface integrity and high-cycle fatigue life of direct laser metal deposited AISI 431 alloys modified by plasticity ball burnishing

Laser metal deposition (LMD) as an additive manufacturing (AM) is widely used to repair and extend wear and fatigue life of the critical components. This paper has investigated the application of ball burnishing (BB) to improve surface integrity and high-cycle fatigue resistance of LMDed AISI 431 alloys. Results showed that the BB treated samples exhibited significant surface finish improvement by lowering roughness by 91 %. Microhardness increased from 490 to 530 HV0.1, an increase by 10 % with a modified depth of 400 µm from the top surface. XRD results showed a peak shift and increase in FWHM by up to 17 %. This had been corroborated by EBSD exhibiting a 20 % increase in dislocation density and 24 % increase in localised misorientation within microstructure. As a result, the overall high cycle fatigue strength of the burnished sample increased by 50 %, and the cracks initiated from sub-surface level defects at a depth of 350 μm below the top surface, delaying the crack propagation and fracture failure. The findings clearly highlight that the burnishing treatment can be a plausible approach in improving the dynamic fatigue resistance and the overall service life of LMDed AISI 431 steel alloys components in engineering applications.