Fatigue Strength Research Articles

Fatigue characteristics of a newly developed laser powder bed fused scandium-free Al-Mg-Zr-Mn alloy

This study investigates the fully reversed force-controlled fatigue response of a newly developed laser powder bed fused (LPBF) Al-Mg-Zr-Mn alloy (EOS Al5X1) in the post-aged condition. The fatigue behavior revealed a defect-driven response with a fatigue strength of approximately 140 MPa at 5 million cycles. Comprehensive microstructural analyses, including grain size, texture, and precipitate characterization, were performed using advanced microscopy techniques. Additionally, X-ray computed micro-tomography (XCT) was employed to assess defect size and distribution, yielding a relative density of 99.93 %. Fracture surfaces of all fatigue-failed specimens were examined using optical and scanning electron microscopy to determine the primary failure mechanisms, with a focus on distinguishing between defect-driven and microstructural causes. The results indicated that nearly all specimens, tested across seven stress levels, exhibited crack initiation from process-induced volumetric defects, such as pores and lack of fusion. At lower stress levels (up to 195 MPa), single crack initiation sites driven by defects were identified at either surface or subsurface locations. In contrast, at higher stress levels (234 to 351 MPa), multiple crack initiation sites were observed, also at the surface or subsurface.

Anomaly detection by X-ray tomography and probabilistic fatigue assessment of aluminum brackets manufactured by PBF-LB

The assessment of safety-critical components for fatigue applications is a key requirement for metal additive manufacturing (AM) applications. Material anomalies play a relevant role in determining the fatigue resistance properties of a component. X-ray computed tomography (CT) helps collect important information on these flaws, such as their size and position within a part.In this study, we discuss how to employ anomaly data detected on an AlSi10Mg bracket manufactured by laser-powder bed fusion to describe the prospective allowable life of a component under a given operating condition.A statistical analysis was conducted on the specimens and component to derive the correlation between different resolution scans and analyze the uncertainties of the micro-CT measurements. The full-scale non-destructive evaluation (NDE) can be constrained to large voxel sizes. Eventually, the authors proposed a fully probabilistic route for assessment instead of a simple deterministic assessment based on safety factors. This assessment enables designers to consider the uncertainties of the assessment (uncertainties of micro-CT detection and the model for fatigue strength).

Research on the influence of out-of-plane loads on the fatigue life of metal structures

Abstract For civil aircraft structures, in-plane tensile, compressive, shear, and their combined forms of loads are the usual loads on plate and shell structures, while bending moments, torsion, and other forms of loads are mainly borne by assemblies consisting of multiple parts. However, some plate and shell structures are subjected to in-plane loads while also being affected by out-of-plane loads. In order to study the difference between the fatigue performance of plate and shell structures under the influence of out-of-plane load and the fatigue performance under the effect of pure in-plane load, the axial tensile fatigue test considering the out-of-plane load is carried out, which demonstrates the negative effect of the out-of-plane load on the axial tensile fatigue strength of the structure. At the same time, a new structural fatigue life prediction method considering out-of-plane loads is established by combining finite element analysis, which can more accurately predict the structural fatigue life under the influence of out-of-plane loads and provide support for metal structure fatigue analysis.

A finite fracture mechanics approach to estimate the fatigue strength of V-notched bars under multiaxial loading

The current study aims to assess the high cycle fatigue strength of sharply V-notched bars under mixed mode I/III loading by applying the coupled Finite Fracture Mechanics (FFM) approach. FFM provides strength predictions by simultaneously satisfying a stress condition and an energy balance. A novel semi-analytical implementation of the FFM criterion is presented for the first time to account for a multiaxial fatigue loading by assuming that fracture early propagates along the notch bisector plane through a circumferential-shaped crack. To validate the model, fatigue life predictions are then compared with a large variety of experimental data related to several metals, V-notch configurations and different multiaxial loading conditions. Although the adopted hypotheses are simplistic and do not fully encompass all the physical phenomena that occur in the multiaxial fatigue process, the approach reveals to be a reliable tool for obtaining semi-analytical fatigue limit predictions useful for engineering design practice.

Unnotched fatigue behavior of the laser powder bed fused and hot isostatic pressed Inconel 718 at 600 °C

The microstructure and mechanical properties of hot isostatically pressed (HIP) Inconel 718 additively manufactured using the laser beam powder bed fusion (LPBF) process were investigated at 600 °C, with emphasis on the high cycle fatigue behavior evaluated using the rotating bend fatigue tests, and elucidation of the role of γ” precipitate size on the fatigue resistance. Experimental results show that the unnotched fatigue strength (σf) of the peak aged alloy improves only by 7 % after HIP, as compared to that of the non-HIP peak aged alloy, despite a significant improvement in the ductility due to HIP. Over-aging the HIP alloy, however, led to a further enhancement (by ∼14 %) in σf. Fractographic analyses suggest that the fatigue crack initiation occurs from the intrusions and extrusions on the fracture surface of both versions of the aged alloy. Microstructural investigations reveal the presence of persistent slip bands (PSBs) with different morphologies in peak- and over-aged microstructures. A change in the deformation mechanism due to the size of precipitates was identified to be the reason for the formation of nano-grains (through dynamic recrystallization) within the PSBs of the alloy with a coarse γ” microstructure. In several {110} grains, ∼5 μm thick nanocrystalline grain zones formed on the specimen surface; they completely suppressed the formation of PSBs and enhanced the fatigue resistance of the HIP LPBF IN718 alloy in the over-aged condition.

Fatigue performance of repair-welded and HFMI-treated transverse stiffeners

AbstractLarge portions of infrastructure buildings, for example, highway and railway bridges, are steel constructions and reach the end of their service life due to an increase of traffic volume. Repair welding can restore the current welded constructional detail with a similar fatigue strength. However, due to the increase of fatigue loading (traffic), an increase of fatigue strength is needed in such bridge structures. For this reason, the combination of repair welding and high-frequency mechanical impact (HFMI) treatment was investigated in this study in order to quantify the increase of fatigue life by combining both methods. For this, transverse stiffeners made of steel grade S355J2 + N were subjected to fatigue loading until a pre-determined crack depth was reached. The cracks were detected by non-destructive testing methods. Weld repair was realized by removing the material containing the crack and re-welded by a gas metal arc welding (GMAW) process, following that post weld treated was applied by HFMI-treatment and the specimens were subjected to fatigue loading again. Hardness profiles, weld geometries, and residual stress states were investigated for both the original and the repaired condition. In the repaired condition without additional HFMI treatment, a similar fatigue life than in the original condition is observed for the specimens. The repair-welded and HFMI-treated specimens reach a significant higher fatigue life compared to the repaired ones in the as-welded condition.

Synchronized Multi-Laser Powder Bed Fusion (M-LPBF) Additive Manufacturing: A Technique for Controlling the Microstructure of Ti–6Al–4V

One of the technological hurdles in the widespread application of additive manufacturing is the formation of undesired microstructure and defects, e.g., the formation of columnar grains in Ti-6Al-4V—the columnar microstructure results in anisotropic mechanical properties, a reduction in ductility, and a decrease in the endurance limit. Here, we present the potential implementation of a hexagonal array of synchronized lasers to alter the microstructure of Ti–6Al–4V toward the formation of preferable equiaxed grains. An anisotropic heat transfer model is employed to obtain the temporal/spatial temperature distributions and construct the solidification map for various process parameters, i.e., laser power, scanning speed, and the internal distance among lasers in the array. Approximately 55% of the volume fraction of equiaxed grains is obtained using a laser power of P = 500 W and a scanning speed of v = 100 mm/s. The volume fraction of the equiaxed grains decreases with increasing scanning velocity; it drops to 38% for v = 1000 mm/s. This reduction is attributed to the decrease in absorbed heat and thermal crosstalk among lasers, i.e., the absorbed heat is higher at low scanning speeds, promoting thermal crosstalk between melt pools and subsequently forming a large volume fraction of equiaxed grains. Additionally, a degree of overlap between lasers in the array is required for high scanning speeds (v = 1000 mm/s) to form a coherent melt pool, although this is unnecessary for low scanning speeds (v = 100 mm/s).

Quantitative assessment of compression fatigue history effect on the subsequent tension fatigue limit of strain localized material

This study conducts compressive fatigue tests with an extended notch on a strain-localized material for quantitative evaluation of damage during compression fatigue and the corresponding effect of loading history on subsequent tensile fatigue limits. Hence, fatigue crack “growth” and “propagation” of two types are found in damage accumulation (DA) mode. The former features several simultaneous multi-crack initiations and independent extensions. Contrarily, the latter features coalescence between the main and secondary cracks. Moreover, the near-crack-tip mechanics causing crack extension and non-propagation in the respective fatigue crack extension types are discussed. Furthermore, a method for subsequent tensile fatigue limit prediction considering the compression fatigue effect is proposed by studying the non-propagating crack length, Vickers hardness, and residual stress in the DA mode during compression fatigue, corresponding to Murakami–Endo’s equation parameters for a mechanically small crack. Thus, this study is anticipated to hold great significance for understanding fatigue damage caused by different load blocks and improving Miner’s rule.

Evaluation of the Mechanical Properties and Fatigue Resistance of the ZrO2CeYAl2O3 Composite

This work aimed to evaluate the fatigue limit of the zirconia ceramic composite stabilized with yttria and ceria reinforced with alumina platelets (ZrO2CeYAl2O3) and characterize the mechanical properties of sintered specimens. Bar-shaped specimens were compacted by uniaxial pressing in a rigid die and sintered at 1500 °C-2 h. Subsequent characterizations included quantitative phase analysis by X-ray diffractometry, determination of density, modulus of elasticity, microhardness, fracture toughness, four-point flexural strength, and fatigue limit. Observations of fracture mechanisms were carried out using confocal and scanning electron microscopy (SEM). The sintered samples presented values above 98% of relative density. Complex microstructures with equiaxed, homogeneously distributed submicrometer grains and planar alumina platelets were observed by SEM. The composite samples showed high values of fracture toughness due to the transformation, during the test, from the tetragonal to monoclinic phase, causing an increase in volume and creating compression zones around the crack, making it difficult to propagate. The average flexural strength reached 445.55 MPa, with a Weibull modulus (m = 16.8), revealing low flexural rupture stress data dispersion. In the composite evaluated in this work, the occurrence of the tetragonal → monoclinic transformation that occurs in the Ce-TZP present at the triple points and grain boundaries during cyclic loading produces “crack tip shielding”, that is, a restricted elastic zone (zone shielding) that surrounds the crack tip. This phenomenon leads to a reduction in the stress intensity factor at the tip of the crack and slows down its growth, generating an increase in the fatigue resistance of the composite.

Improving the Fatigue Performance of Binder Jet Manufactured 316L by Severe Shot Peening Surface Modification

Binder jetting is a rapidly evolving additive manufacturing technique, challenging the dominance of laser powder bed fusion in metal fabrication. This study focuses on the material properties of austenitic stainless steel 316L produced via binder jet technology. Porosity remains a significant challenge across additive manufacturing methods, adversely affecting material properties and fatigue life. To address this issue, we propose a novel approach employing severe shot peening as a post-processing treatment to enhance the material's characteristics. Microstructural analysis, including electron backscatter diffraction (EBSD), coupled with tensile testing, was conducted to evaluate the mechanical properties. Additionally, fatigue behavior was investigated under both axial and flexural bending loading conditions. The results revealed a substantial increase in material strength achievable through the post-treatment. Notably, the fatigue limit of the material in bending fatigue was elevated from 120 MPa to 190 MPa, indicating a significant enhancement in fatigue performance. This study contributes new insights into the enhancement of fatigue resistance in binder jet-manufactured 316L stainless steel through surface modification techniques. The findings underscore the potential of severe shot peening as an effective strategy to improve material properties and expand the applicability of binder jet printing in demanding industrial applications.

Effects of Physical Activity Level and Sedentary Behavior on the Musculoskeletal System in Young Adults

Aim: The aim of this study is to investigate the relationship between the level of physical activity and sedentary behavior in young adults aged 18-35 and to evaluate the effects of this relationship on musculoskeletal pain, posture, muscle shortness, and trunk muscle endurance. Methods: In this cross-sectional descriptive study, conducted at the Faculty of Health Sciences of a university between March 2018 and August 2018, 219 students were included. Data were obtained by using the case report form which determines the demographic characteristics and sedentary behavior of the students, The International Physical Activity Index - short form, posture analysis form, muscle shortness evaluation form, and trunk muscle endurance evaluation form. Results: In the study, 66.2% of patients were female and 33.8% were male. In the evaluation of physical activity level, the ratio of highly active individuals in males, and inactive and insufficiently active individuals in females was significantly higher (p <0.05). Musculoskeletal pain was significantly higher in inactive and insufficiently active individuals (p<0.001). A negative correlation existed between physical activity level and pain frequency, duration, and scores (p<0.001). There was a positive correlation between trunk endurance tests and physical activity and exercise participation. Non-exercisers showed shortening of lumbar extensor muscles and gastrosoleus, with increased thoracic kyphosis (p<0.05). Daily sitting time correlated positively with elbow, wrist, and knee pain, and lumbar lordosis (p<0.05). Those spending more time at the computer experienced higher levels of head-neck and elbow pain, pain duration, muscle shortness, thoracic kyphosis, shoulder protraction, and anterior head tilt (p<0.05). Conclusion: In young adults, increasing physical activity and reducing daily sitting time are necessary to prevent musculoskeletal pain and reduce postural deformities. Keywords: Musculoskeletal diseases, musculoskeletal pain, physical exertion, posture, sedentary behavior, trunk muscular endurance, young adult.

Short-chain fatty acids enhance muscle mass and function through the activation of mTOR signalling pathways in sarcopenic mice.

Sarcopenia is a prevalent muscle disorder in old people leading to higher fracture rate, mortality, and other adverse clinical outcomes. Evidence indicates that short-chain fatty acids (SCFAs), which are beneficial gut microbial metabolites, were reduced in old people with sarcopenia. This study aimed to determine whether the use of SCFAs as a supplement can be a therapeutic strategy of sarcopenia in a pre-clinical model. Seven-month-old pre-sarcopenic senescent accelerated mouse prone 8 (SAMP8) mice received daily SCFAs cocktail (acetate, butyrate, and propionate) for 3months. Age-matched senescence accelerated mouse resistant 1 (SAMR1) and SAMP8 mice receiving sodium-matched drinking water were control groups. The gut microbiota composition analysis of aged mice with or without sarcopenia was conducted by 16S rDNA sequencing. Gut barrier-related proteins and lipopolysaccharide (LPS) concentration were biomarkers of gut permeability. Colon inflammation levels, circulatory SCFAs concentration, muscle quality, function, and underlying pathways were detected by cell number counting, RT-qPCR, gas chromatography-mass spectrometry, measurements of muscle wet weight and grip strength, ex vivo functional test, treadmill endurance test, transcriptomic sequencing, morphological and immunofluorescent staining, as well as western blot. To investigate the role of mTOR signalling pathways in SCFAs treatment, C2C12 myotubes were treated with rapamycin. Aged SAMP8 mice had different microbiota composition, and lower serum butyric acid compared with SAMR1 mice (P<0.05). SCFAs treatment reversed the increment of colon inflammation (2.8-fold lower of il-1β) and gut barrier permeability (1.7-fold lower of LPS) in SAMP8 mice. Increased muscle mass, myofibre cross-sectional area, grip strength, twitch and tetanic force were found in SCFAs-treated mice compared with control SAMP8 mice (P<0.05). Anti-fatigue capacity (1.6-fold) and muscle glycogen (2-fold) also improved after SCFAs treatment (P<0.05). Transcriptomic analysis showed that AMPK, insulin, and mTOR pathways were involved in SCFAs treatment (P<0.05). Regulation of AKT/mTOR/S6K1 and AMPK/PGC1α pathways were found. SCFAs attenuated fat infiltration and improved mitochondria biogenesis of atrophic muscle. In vitro studies indicated that SCFAs inhibited FoxO3a/Atrogin1 and activated mTOR pathways to improve myotube growth (P<0.05), and rapamycin attenuated the effect of SCFAs through the inhibition of mTOR pathways. This study demonstrated that bacterial metabolites SCFAs could attenuate age-related muscle loss and dysfunction, and protein synthesis-related mTOR signalling pathways were involved both in vivo and in vitro.

Physical Training Methods to Improve the Physical Condition Components of Elite Taekwondo Athletes in The Kyorugi Category: A Systematic Review

Objectives. The study aimed to provide a systematic review of physical training methods to improve the physical condition components of elite taekwondo athletes in the kyorugi category. Materials and methods. An extensive literature assessment of earlier research was carried out. The objective was to examine articles published between 2020 and 2024 that describe strategies for improving the physical condition component of taekwondo athletes. The electronic search was conducted using Google Scholar, PubMed, Web of Science, and Scopus. The articles that addressed methods for enhancing physical condition through exercise were compiled. Results. Sixty publications used training approaches to enhance the physical condition component of elite taekwondo athletes in the kyorugi category. Based on the physical state that is assessed and improved, items are categorized. Among the physical training methods that can be applied in the Taekwondo category of kyorugi are plyometric training, circuit training methods, speed, agility, and quickness (SAQ) training; strength training, endurance training, flexibility training, reaction training, power training, coordination training, balance training, resistance training, and functional training. Conclusions. After thorough analysis, several training techniques have been shown to be effective in enhancing the physical attributes of elite taekwondo athletes in the kyorugi category. These attributes include flexibility, response, strength, power, coordination, agility, speed, balance, and VO₂max.

Increase the speed of running 100 meters using the bench and skipping training methods

Background and Study Aim. Running 100 meters requires optimal speed, strength, and physical endurance. Running speed is often a key indicator of physical ability and athletic performance. However, not everyone achieves optimal speed and physical ability in running the 100 meters. Many factors influence a student's running performance, including the training methods used. The aim of the research is to determine the increase in speed for running 100 meters using bench and skipping training methods. Material and Methods. This research is an experimental study aiming to find cause and effect relationships in one or more experimental groups through different training treatments. The design used is a two-group pretest-posttest design. The participants were male students actively involved in sports activities, capable of performing running techniques well, and willing to participate in the training sessions. Initially, students underwent a pretest to determine their treatment group by ranking the pretest scores. This allowed the formation of two groups: one group of 15 students participating in bench climbing exercises, and another group of 15 students engaging in skipping exercises, using ordinal pairing. The instrument used for the 100-meter running test is the 100-meter running test. Results. Based on the results of hypothesis testing using pretest and posttest t-tests, the 100-meter running speed after bench up and down training was 4.621. The pretest and posttest data for 100-meter running speed with skipping training was 4.790. For the posttest, the running speed for 100 meters with bench up and down training and skipping training was 4.240. The two-way p-value was 0.000, which is less than 0.05, indicating a significant difference in the 100-meter running speed before and after the exercise. Conclusions. Bench climbing exercises can increase the strength of the primary leg muscles used in sprinting, such as the quadriceps, hamstrings, and calves. These exercises improve body balance and coordination, which are crucial for efficient running posture and technique. Meanwhile, skipping can enhance explosive power and the ability of leg muscles to generate power quickly and efficiently. Skipping also improves coordination between hands and feet, aiding in maintaining rhythm and efficiency in running movements. Overall, bench climbing exercises are more effective in improving 100-meter running performance compared to skipping exercises.

Validity and reliability of the physical fitness test instrument for retired martial art athletes

Background and Study Aim. Developing exercise programs to maintain the fitness and health of retired athletes is crucial as a preventive measure against common health problems in this population. Equally important is the creation of an exercise evaluation tool to assess the effectiveness of these programs. This study aims to test the validity and reliability of a physical fitness test instrument for retired martial arts athletes. Material and Methods. This study used an evaluation approach with data collected through tests and measurements. A total of 147 subjects participated. For validity testing, there were 35 retired male martial arts athletes and 37 retired female athletes. For reliability testing, there were 36 retired male and 39 retired female martial arts athletes. The instruments used included body mass index (BMI) measurements with digital scales, flexibility measurements with the sit-and-reach test, muscle strength measurements with a leg and back dynamometer, and cardiovascular endurance measurements with the Cooper test. Validity was assessed using a concurrent validity approach. Reliability was tested using the test-retest method. The Pearson product-moment correlation was used for validity analysis, while Cronbach's alpha was used to assess reliability. The JASP software was used for the analysis. Results. For male athletes, the r-values for each test item exceeded the r-table value of 0.275, confirming the validity of the body mass index (BMI), sit-and-reach test, leg and back dynamometers, and the Cooper test. Similarly, female athletes demonstrated r-values above the r-table value of 0.267, confirming the validity of all test items. The reliability of each item was confirmed by Cronbach’s alpha values, which were above the 0.7 threshold for both male and female athletes. The Cronbach's alpha value for BMI was 0.998 for both male and female athletes, indicating excellent reliability. Other test items, such as flexibility and muscle strength, also showed strong reliability, with Cronbach’s alpha values ranging from 0.742 to 0.985. Conclusions. The study highlights the importance of developing valid and reliable instruments to assess the physical fitness of retired martial arts athletes. Such instruments are essential for monitoring the effectiveness of training programs aimed at maintaining the health and fitness of retired athletes. The findings of this research confirm the value of structured fitness tests. These tests effectively evaluate key physical components such as body composition, flexibility, muscle strength, and cardiovascular endurance.

Analysis of the features of the operating conditions of modern gas turbine blades and review of methods for determining their high-temperature strength parameters

The subject of the study is modern methods and materials for the manufacture of gas turbine blades, as well as approaches and methods for assessing their dynamic and static strength under high-temperature loading. The first purpose of the article is to describe the main methods of manufacturing turbine blades, provide examples of the materials used and the features of their crystal structure. The second purpose of the article is to review approaches to ensuring the dynamic and static strength parameters of single-crystal turbine blades, in particular, to avoid dangerous resonance modes, to study the parameters of anisotropic creep, high-temperature fatigue life, and long-term strength. The goal of the article is to highlight the main advantages and disadvantages of existing methods, approaches and techniques for assessing and ensuring high-temperature strength parameters of turbine blades under static and dynamic loading, in order to select the objectives of further research. Methods used to create the publication: methods of analysis and comparison, which were used to search and compare open literature sources of information in accordance with the purpose of the article, as well as the method of deduction, which was used to identify the main shortcomings of existing methods for assessing the high-temperature strength of gas turbine blades under static and dynamic loading to outline the goals of further research. The following results have been obtained. Literature sources related to the methods of manufacturing turbine blades, namely, directional crystallization and single-crystal casting, were analyzed. The advantages of single-crystal alloys for the manufacture of turbine blades, namely increased heat strength, heat resistance, fatigue strength, durability and crack resistance, are emphasized. The main modern methods for assessing the high-temperature strength of gas turbine blades with regard to the anisotropic characteristics of single-crystal alloys are analyzed and described. Conclusions. This publication presents information about gas turbine blades, in particular, provides meaningful information about the methods of their manufacture, as well as the materials used to produce them. The study analyses and identifies the main damaging effects on gas turbine blades during their operation. The material describes the achievements of scientists who have developed numerical and experimental methods for assessing the impact of the anisotropic characteristics of single-crystal nickel heat-resistant alloys on the fatigue strength, durability and creep of turbine blades.

Comparative Study of High-Cycle Fatigue and Failure Mechanisms in Ultrahigh-Strength CrNiMoWMnV Low-Alloy Steels

This study provides a thorough analysis of the fatigue resistance of two low-alloy ultrahigh-strength steels (UHSSs): Steel A (fully martensitic) and Steel B (martensitic–bainitic). The investigation focused on the fatigue behaviour, damage mechanisms, and failure modes across different microstructures. Fatigue strength was determined through fully reversed tension–compression stress-controlled fatigue tests. Microstructural evolution, fracture surface characteristics, and crack-initiation mechanisms were investigated using laser scanning confocal microscopy and scanning electron microscopy. Microindentation hardness (HIT) tests were conducted to examine the cyclic hardening and softening of the steels. The experimental results revealed that Steel A exhibited superior fatigue resistance compared to Steel B, with fatigue limits of 550 and 500 MPa, respectively. Fracture surface analysis identified non-metallic inclusions (NMIs) comprising the complex MnO-SiO2 as critical sites for crack initiation during cyclic loading in both steels. The HIT results after fatigue indicated significant cyclic softening for Steel A, with HIT values decreasing from 7.7 ± 0.36 to 5.66 ± 0.26 GPa. In contrast, Steel B exhibited slight cyclic hardening, with HIT values increasing from 5.24 ± 0.23 to 5.41 ± 0.31 GPa. Furthermore, the martensitic steel demonstrated superior yield and tensile strengths of 1145 and 1870 MPa, respectively. Analysis of the fatigue behaviour revealed the superior fatigue resistance of martensitic steel. The complex morphology and shape of the NMIs, examined using the 3D microstructure characterisation technique, demonstrated their role as stress concentrators, leading to localised plastic deformation and crack initiation.

Rolling Contact Fatigue Behaviors of 20CrNi2Mo Steel by a New Carbon and Nitrogen Composite Infiltration Process

ABSTRACTIn this paper, a new type of composite infiltration process was adopted for 20CrNi2Mo steel. Rolling contact fatigue (RCF) tests were carried out on the specimens treated with carburizing (C) and composite infiltration with carburizing and nitriding (C‐N). The results showed that after C and C‐N treatments were performed, the surface microhardness was increased by 78% and 114%, respectively, and the maximum CRS were −220 and −530 MPa. Moreover, the residual austenite volume fraction was controlled to approximately 10% for each treated sample. The fatigue limit of the C‐N sample was 11.3% higher than that of the C sample. The fatigue failure mechanisms are caused by the maximum shear stress distribution and surface roughness. The surface layer of the C‐N sample with higher hardness and more compressive residual stress inhibited the initiation of fatigue cracks, and the appropriate residual austenite in the carbon‐nitrogen infiltrated layer inhibited the propagation of fatigue cracks.

Fatigue Strength Analysis of Rail Fastening Baseplate

Superstructural elements of a railway track experience dynamic loads varying over time. As a consequence, this is accompanied by the initiation and accumulation of fatigue damages. Defects in intermediate rail fastening are quite difficult to identify using flaw detection methods, and some can be destructed. In particular, rail fastening baseplates often fail due to insufficient fatigue strength.Purpose: To investigate the fatigue strength of rail fastening baseplate.Methodology: Development of the mathematical model of deformation based on the finite element method (FEM). Strength analysis of the baseplate using the model of a variable-thickness slab resting on a nonlinear elastic foundation. The latter is modeled by a set of rods with nonlinear deformation and parameters determined by compression tests of the baseplate. A mathematical model developed in COSMOS software for the FE analysis of the stress-strain state of the baseplate at a time-varying load from rolling equipment and assembly forces from attaching the baseplate to the sleeper and rail.Research findings: The cyclic loading parameters are obtained at dangerous points of the baseplate and its durability is analyzed at different loads with respect to unevenness of track settlement and failure of bolt connections of rail fasteners. The influence of these factors on actual loads on the rail fastener is determined. It is found that the service life of the baseplate mainly depends on the dynamic load.

Formulation and Characteristics of Hydrogel Patch Containing Pineapple Peel (Ananas comosus L.) Ethanol Extract

Abstract Pineapple peel (Ananas comosus L.) contains bioactive compounds such as flavonoids and the enzyme bromelain, which possess antioxidant, anti-inflammatory, antibacterial, and anticancer properties, and the ability to accelerate wound healing. Hydrogel patches, as a formulation for transdermal delivery, are effective in wound healing due to their hydrophilic properties that maintain moisture and prevent bacterial infection in open wounds. This study aims to develop and test the characteristics of hydrogel patch formulations containing ethanol extracts of pineapple peel with varying concentrations of 10%, 20%, and 30%, compared to a control (hydrogel patch without pineapple peel extract). A series of evaluation tests were conducted to assess the patch characteristics, including organoleptic tests, pH, absorbency, weight uniformity, swelling ratio, patch thickness, and folding endurance. The results showed that the concentration of pineapple peel extract affects the hydrogel patch characteristics. The higher the extract concentration, the darker the patch color, but the pH, absorbency, and swelling ratio decrease. Patches with higher extract concentrations also showed an increase in weight. Absorbency tests indicated that none of the formulas met the acceptance criteria (&lt;10%), with absorbency results of 22.97%, 11.60%, and 21.95% for 10%, 20%, and 30% extract concentrations, respectively, and 23.43% for the control. Swelling ratio and thickness tests showed the best results for the control, followed by the 10%, 20%, and 30% extract concentrations. The folding endurance test showed that the control and 10% extract formula had good results (&gt;300 folds), while higher extract concentrations reduced the folding endurance of the hydrogel patch .Keywords: extract, pineapple peel, hydrogel patch, formulation, patch characteristics