Leaf springs are critical components for the railway vehicle safety in which they are installed. Although these components are produced in high-strength alloyed steel and designed to operate under ...cyclic loading conditions in the high-cyclic fatigue region, their failure is still possible, which can lead to economic and human catastrophes. The aim of this document was to precisely characterise the mechanical crack growth behaviour of the chromium-vanadium alloyed steel representative of leaf springs under cyclic conditions, that is, the crack propagation in mode I. The common fatigue crack growth prediction models (Paris and Walker) considering the effect of stress ratio and parameters such as propagation threshold, critical stress intensity factor and crack closure ratio were also determined using statistical methods, which resulted in good approximations with respect to the experimental results. Lastly, the fracture surfaces under the different test conditions were analysed using SEM, with no significant differences to declare. As a result of this research work, it is expected that the developed properties and fatigue crack growth prediction models can assist design and maintenance engineers in understanding fatigue behaviour in the initiation and propagation phase of cracks in leaf springs for railway freight wagons.
Fatigue damage modelling and life prediction of engineering components under variable amplitude loadings are critical for ensuring their operational reliability and structural integrity. In this ...paper, five typical nonlinear fatigue damage accumulation models are evaluated and compared by considering the influence of load sequence and interaction on fatigue life of P355NL1 steels. Moreover, a new nonlinear fatigue damage accumulation model is proposed to account for these two effects. Experimental datasets of pressure vessel steel P355NL1 and four other materials under two‐block loadings are used for model comparative study. Results indicate that the proposed model yields more accurate fatigue life predictions for the five materials than the other models.
•Fretting-fatigue failure initiates micro cracks at the trailing edges induced by mixed slip regime.•Larger fretting amplitude induces larger tangential force and friction, but smaller fatigue ...life.•Fretting scar depth increases as fretting-fatigue proceeds while its growth rate reduces greatly.•Larger fretting amplitude (normal force) makes mixed slip regime great (materials brittler).•Relative sliding and contact stresses can lead to fretting-fatigue failure of bridge cables.
Bridge cables are subjected to small relative sliding and high contact stresses among wires under fluctuating loads and repeated bending, eventually leading to fretting-fatigue failure. This paper presents a series of fretting fatigue tests with different fretting and fatigue parameters to investigate the tribological properties, fretting fatigue characteristics and fracture failure mechanism. Results show that the fretting-fatigue failure evolved from surface micro cracks at the trailing edges generated from a mixed slip regime. Larger fretting amplitude induced larger tangential force and coefficient of friction, and decreased life. Fretting scar depth increased as fretting-fatigue proceeded while the growth rate was declining.
•Highly stressed volume (HSV)-based method for modeling both notch fatigue and size effects.•Proposed relation of equivalent highly stressed region based on the maximum local stress.•A dynamic model ...coefficient to characterize different HSVs with similar stress state on fatigue life.•Proposed model predictions agree well with the probabilistic scatter bands of experiments.
Modeling of the notch and size effects on fatigue behavior of materials is vital for ensuring structural integrity and reliability of engineering components. This study presents a methodology considering both effects of notch and size to analyze the fatigue life distribution of specimens with different geometries using the highly stressed volume approach. Specifically, a dynamic model coefficient considering the influence of different maximum local stresses is developed by modeling the size effect of highly stressed volumes with Weibull distribution. Experimental data of three aluminum and titanium alloys are utilized for model validation and comparison. Fatigue lives of three materials with different geometries are evaluated respectively, and predicted P-S-N curves indicate that proposed model predictions agree well with the probabilistic scatter band of experimental results.
Fatigue life prediction of materials can be modeled by deterministic relations, via mean or median S-N curve approximation. However, in engineering design, it is essential to consider the influence ...of fatigue life scatter using deterministic-stochastic methods to construct reliable S-N curves and determine safe operation regions. However, there are differences between metals and composites that must be considered when proposing reliable S-N curves, such as distinct fracture mechanisms, distinct ultimate strengths under tension and compression loading, and different cumulative fatigue damage mechanisms including low-cycle fatigue. This study aims at conducting a review of the models used to construct probabilistic S-N fields (P-S-N fields) and demonstrate the methodologies applied to fit the P-S-N fields that are best suited to estimate fatigue life of the selected materials. Results indicate that the probabilistic Stüssi and Sendeckyj models were the most suitable for composite materials, while, for metals, only the probabilistic Stüssi model presented a good fitting of the experimental data, for all fatigue regimes.7
•A stress gradient-based factor for notch effect correction under multiaxial stress states.•A critical plane damage parameter considering stress gradient correction.•A computational framework for ...multiaxial fatigue life prediction considering notch effects.•Proposed solution yields accurate correlations of both smooth/notched specimens fatigue data.
Aero engine components like compressor discs normally operate under harsh conditions like complex multiaxial stress states. Notch effect is often critical for structural integrity assessment in virtue of complex structure and discontinuities. According to the notch effect under cyclic loadings, a computational framework for multiaxial fatigue analysis of compressor discs is established by coupling finite element (FE) simulation of stress gradient with Fatemi-Socie (FS) criterion. Specifically, a notch support extension method accounting for stress gradient effect is elaborated through elasto-plastic FE analysis, which can be determined for fatigue life prediction of arbitrary shaped components. Experimental fatigue data for smooth and notched specimens of TC4 and GH4169 alloys demonstrated the appropriateness of the proposed computational approach. The applicability and performance of the prediction model to a compressor blade-disc attachment subjected to field spectra is presented. Results show that testing effect can be significantly reduced by using this framework with acceptable prediction accuracy.
Micro-milling of cemented carbides is a challenging task due to their high hardness, low toughness and high wear resistance. Ensuring good surface quality and dimensional accuracy is crucial for ...extending parts service life, which in turn enhances economical and environmental sustainability. This paper is mainly focused on evaluating surface formation mechanisms, scale effects, fracture behaviour and chip formation using distinct cemented carbide micro-milling tools with multi-layer diamond HF-CVD. In order to achieve higher precision and more efficient micro-milling operations on WC-15Co and WC-10Co, a systematic experimental approach has been carried out. The influence of cutting parameters, achievable surface quality and defects occurrence were thoroughly examined. Experimental results evidence the influence of operational conditions on the chip formation of cemented carbides as well as an important impact of the utilized cutting tool. Micro-pits, cracks, thin ploughing layer and fractured workpiece edges are amongst the observed surface damage mechanisms. A ductile cutting regime of the high-hardness composite material is confirmed, exhibited by the plastic deformation even when small depths of cut are considered.
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•A modified generalized strain energy (MGSE) criterion for multiaxial fatigue analysis.•Comparative study on critical plane criteria for ductile/brittle materials.•Proposed MGSE ...criterion yields better predictions for ductile/brittle materials.•Modified SWT criterion provides accurate predictions only for brittle materials.
This paper conducts a comparative evaluation on typical critical plane criteria, including Fatemi-Socie, Wang-Brown, modified Smith-Watson-Topper (MSWT) and proposed modified generalized strain energy (MGSE) criteria for multiaxial fatigue analysis of ductile/brittle materials. Experimental datasets of four materials under uniaxial tension, torsion and proportional/non-proportional multiaxial loadings are introduced for model comparison. This study results indicate that criteria with additional material constants yield robust life predictions for different materials. Moreover, the criteria with shear and uniaxial fatigue properties are respectively suitable for ductile and brittle materials, particularly the MGSE superior to others for ductile/brittle materials while MSWT only for brittle materials.
Fused filament fabrication (FFF) is an extrusion-based process that allows quick and inexpensive part production, practically without any geometric limitations, offering flexibility, promoting ...reduction in costs and lead-time in an industrial scenario. Being one of the most widespread additive manufacturing techniques, the process has evolved introducing new and advanced materials (e.g. high-performance polymers and composites). Despite its advantages, the process is vastly overlooked due to its high level of anisotropy, poor surface roughness and lack of geometric accuracy caused by the layer thickness. To reduce this effect, a sequence of laborious manual operations can be performed, which may result in time-consuming and inaccurate results. Therefore, efforts have been made towards the development of hybrid manufacturing technologies by combining FFF process and subtractive equipment, aiming to solve these limitations. In this work, two complementary methodologies analysing the behaviour of FFF PA12 and short fibre–reinforced PA12 printed parts when subjected to a subtractive approach are presented. The first experimental plan took into account the final surface roughness (
R
a
and
R
z
) via full factorial design of experiments (DOE) and analysis of variance (ANOVA) considering the influence of distinct printing orientations, two types of cutting tools and machining parameters such as, cutting speed, feed and cutting depth. An analysis on tool wear and SEM microscopy to the machined surface was also performed. The second approach was carried out via Taguchi and ANOVA, considering the first experimental approach results. Thus, milling parameters were the focus, evaluating the final material surface roughness, being now monitored the cutting forces and tool wear analysis in order to understand their influence on the final results. It is shown that it is possible to machine PA12-based FFF printed parts without any major problems such as layer delamination. A decrease in
R
a
,
t
of 1931% to 0.99
μ
m for PA12CF and 2255% for PA12 to 0.96
μ
m was achieved, proving the overall machinability of the materials. It was found that PA12 creates higher levels of cutting loads and increased tool wear, thus indicating that short fibre presence improves the material machinability, while parameters such as building orientation do not possess any influence on the final surface roughness.
Steel railway bridges of all types comprise a large portion of the infrastructure inventory of several countries. Due to the ageing of these structures and increasing traffic loadings, structural ...fatigue increasingly became an important concern, leading to bridges deterioration. In this context, it is well-known that welded connections are among the weakest locations in steel bridges since they are prone to stress concentrations leading to the initiation of fatigue cracks. Although its importance, the study of the development history of welding technology applied to steel bridges is often overlooked in introductory texts about fatigue of metallic bridges. However, to understand the historical development of welding in steel bridges construction and its impact on fatigue design is fundamental, mainly because fatigue evaluation depends on the age of structures. The goal of this paper is to review the history of fatigue cracking of welded railway bridges, discussing the structural behaviour of welded bridges under dynamic traffic loads and the different causes of fatigue damage of welded connections. The presented case studies cover a period from the beginning of application of welding to steel bridges in the 1930s, revisiting well-known cases of cracks documented in the literature due to their historic relevance and presenting also recent cases of the last decades due to new traffic conditions related to Heavy Traffic Loads (HAL) and High-Speed Trains. For this purpose, an in-depth literature review covering more than one-century history was carried out, providing a multidisciplinary analysis with insights into the welding history and practice and fatigue of welded joints, especially applied to steel railway bridges.
•An in-depth literature review comprehending welding applied to steel railway bridges.•Presentation of the historical development of welded railway bridges construction.•Classic and recent examples of fatigue cracking of welded connections separated by type of cause.•Illustration of the causes of fatigue with bridge case studies of different ages and countries.
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