Applied Loading Conditions Research Articles

Finite Element Modeling of Beam-to-Column Steel Timber Composite Joints with Different Parameters

This study presents a comprehensive three-dimensional finite element modeling and parametric analysis of composite beam-to-column joints in steel–timber composite structures. The investigation encompassed a variety of shear connector configurations, end plate designs, and bolt dimensions, aiming to elucidate their respective influences on the structural performance and behavior of these joints. Through meticulous numerical simulation, this research sought to enhance the understanding of the interactions and load transfer mechanisms within composite connections, thereby contributing to the optimization of design practices in the field of structural engineering. The load–displacement relationship for timber–steel composite joints subjected to monotonic loading was investigated using ABAQUS 6.14 software. This study systematically analyzed the effects of various parameters, including different configurations of shear connectors, end plate thicknesses, and bolt dimensions, on the overall performance of the joints. Through this comprehensive numerical analysis, the research aimed to provide deeper insights into the mechanical behavior and structural integrity of these composite connections under the applied loading conditions. A non-linear finite element model of timber was developed and verified with the results of the experiment in this study. The findings are discussed in detail, highlighting the intricate relationships between the selected parameters and their respective effects on the performance and overall stability of the composite connections. This thorough evaluation aimed to enhance the understanding of how these variables interact within the context of composite joint design and behavior. Finally, design recommendations for composite structures, such as the dimensions of the bolt, end plate thickness, and different sizes of shear connectors are provided.

The length of fracture process zone deciphers variations of rock tensile strength

Tensile strength is one of the most critical design factors in many rock engineering projects. However, despite many available testing techniques, an accurate estimation of the true tensile strength of quasi-brittle rock-like materials is yet a controversial problem since it can vary by the shape and size of a test specimen, the adopted test method, and applied loading conditions. Different studies have tried to address this issue by providing (mainly empirical) laws for determining variations of rock tensile strength as a function of a particular test parameter such as specimen size. In this study, however, a new general approach is presented that can decipher the tensile strength variations of rock under various testing conditions. Using coupled Finite Fracture Mechanics (FFM), it is first proved that the length of the Fracture Process Zone (FPZ) can be determined with accuracy and ease using the energy criterion of coupled FFM. Then, the length of FPZ is used in the stress criterion of coupled FFM to determine rock tensile strength. The failure stress of a material is then proved to be mainly a function of the FPZ length following a power law originated from the Linear Elastic Fracture Mechanics (LEFM). The results assist in deciphering variations of rock tensile strength related to the sample size and test method.

Crack propagation effects on the critical temperature degradation of superconducting Nb3Sn single crystal

The irreversible degradation of Nb3Sn critical performance caused by the crack propagation brings challenges to the reliability of Nb3Sn service equipment. In this paper, the crack propagation behavior of Nb3Sn single crystal was studied by molecular dynamics method. The results show that amorphous transformation occur in Nb3Sn samples with cracks under the applied loading conditions. On the basis of these results, the electronic structures of different regions in the cracked sample are studied by first principles method. The critical temperature response in this process is analyzed in combination with our proposed trans-scale electromechanical coupling model. The physical mechanism behind the critical temperature degradation caused by the transition between the cracked surface and the amorphous zone at the crack tip is discussed. Amorphous states and the crack surface destroy the special kind of bonding in the atom chain direction, inducing the electronic band structure distortions. The density of states curve of Nb3Sn no longer exhibits the characteristic peaks near the Fermi surface observed in cubic crystalline Nb3Sn. The intrinsic relationship between the crack propagation, the electronic structure evolution driven by the local atomic rearrangements, and the irreversible critical temperature degradation of cracked Nb3Sn is revealed by the given model. The results deepen the understanding of the electromechanical coupling behavior of Nb3Sn under complex deformation.

The ANALYSIS of the MECHANICAL PROPERTIES of REGIONAL PIPELINES

Piston pumps and compressors are widely used for exploration and transportation of oil and gas. Piston machines are heavy-duty systems that are still failure prone due to high stresses and wear proses. Increasing the efficiency and durability of the piston compressors, pumps, internal combustion engines, etc. directly depends on the correct calculations and designing of these elements. Using ANSYS software, simulation and stress analysis are performed on the basis of the 405GP15/70 and ARIEL heavy-duty balanced opposed piston compressors used in the Caspian Sea-Black Sea Region. During working of the machines and equipment a number of the processes interconnected and causing each other are proceeds (dynamic processes, wear of the interfaced details, change of mechanical properties of materials, etc.). Improvement of modelling of technical condition of cars and mechanisms on a multicriteria basis is one of the actual directions of modern engineering science. The improvement of methods of modelling of change of technical conditions of the piston mechanisms taking into account interrelation of dynamic characteristics, the wear interfaced details and the diagnosed mechanical parameters considered in this article. By observing the analysis results, we can decide whether our designed pipelines are safe or not under applied load conditions. The durable and reliable work of compressor-pump stations used in the oil and gas industry has great importance for practice. Investigation of complex problems with respect to friction and wear (clearances), stresses, and thermodynamics phenomena in the piston machines, and oil and gas pipelines gives the opportunity to solve the problems of increasing the durability of these machines and pipelines. Confirmation that the new methodologies can be produced by the current supply chain improving manufacturing efficiency and reducing the environmental and social impact of the supply chain.

Comparison of Tribological Characteristics of LM13/B4C and LM13/Ilmenite Composites at High-Temperature Conditions

Abstract In this work, high-temperature tribological characteristics of ilmenite-reinforced LM13 aluminum alloy–based matrix composites (AMCs) and boron carbide–reinforced AMCs are compared. Stir-cast composites were processed using boron carbide (covalently bonded discontinuous particles (CDP)) and ilmenite (natural discontinuous particles (NDP)) particles separately as reinforcements. The particle size range was 106–125 µm, and reinforcement levels were 5, 10, and 15 wt% for both types of composites. Both composites exhibited a uniform distribution of reinforced particles and grain refinement. Compared to the LM13 base alloy, NDP composite containing 15 wt% reinforcement showed significant improvement in hardness (57%), coefficient of friction (57%), mild-to-severe wear transition temperature, average steady-state wear-rate (49%), and coefficient of thermal expansion (55%). CDP-15 composite showed slightly better properties than NDP-15 composite. Microstructure refinement, increased dimensional stability, formation of the oxide layer, and formation of tribolayer due to reinforcement of the ceramic fillers were the main reasons for the improvement in properties of processed AMCs. Scanning electron microscope (SEM)-energy dispersive spectroscopy (EDS) of wear tracks-debris showed abrasive/delamination wear as the main mechanism for materials loss. The research showed that the low-cost ilmenite particles can substitute for the very costly boron carbide particles as reinforcements in AMCs used for dry sliding wear applications under high operating temperatures–applied load conditions of the order of 300 °C–49 N.

Thermal Analysis of Different Piston Head Profiles by using FEM

The objective of this research work is to optimize the stress variations at the top of the piston in real engine conditions. During this pressure analysis on the examined surface of the piston, the thermal behavior is examined. The operating gas pressure, temperature and piston material functions are used as investigation functions. The analyzes carried out showed that the upper part of the piston could be damaged or broken due to the temperature caused by the working conditions, as the replacement of damaged or non-functioning parts is very expensive and usually difficult to obtain. Concave and convex piston profile designed in Solid Work 2023, used to design the piston geometry and for FEM analysis to optimize the thermal behavior of the used ANSYS R23.0 piston. Aluminum alloy and gray cast iron material for piston construction. Stress and displacement are analyzed for the piston by applying pressure to it in the structural analysis. By observing the results of the analysis, we can decide whether the piston we are designing is safe or not under the applied load conditions. Heat flow and thermal temperature distribution are analyzed using piston surface temperatures in thermal analysis.

Effect of Stress Ratio, Constraint, and Load History on the Intrinsic and Extrinsic Components of Threshold Stress Intensity

Abstract Threshold intensity range, ΔKth, was experimentally investigated as the sum of two components, both of which are sensitive to applied loading conditions. The intrinsic component, ΔKth,i, is characterized as a sole function of a near-tip stress parameter, σ*, in much the same way as fatigue limit depends on mean stress or stress ratio. The extrinsic component, ΔKcl, is the attenuated fraction of crack tip response because of crack wake contact, whose exact value is not readily measured at threshold. The ΔKth,i versus σ* relationship is established using a specially designed load shedding process under constant baseline maximum load, with σ* modulated through periodic overload-underload combinations whose periodicity is regulated to avoid undue crack extension at threshold. This relationship is then used to extract the ΔKcl component from ΔKth readouts obtained on the same batch of material using conventional load shedding procedure. The effect of constraint on ΔKth and its two components was studied using specimens with sharp side grooves to maximize constraint across the crack front. The study was performed on a medium strength low-alloy steel.

Investigation of Microstructure and Wear Behaviors of AZ91 Alloy Under Different Heat Treatments

This article aims to experimentally investigate the effect of heat treatment applied to AZ91 magnesium alloys on wear behavior under different applied load conditions. Apart from as-cast AZ91 alloy, AZ91 alloy samples were subjected to both solid-solution treatment (400°C for 16 hours) and three different aging processes (216°C for 4, 8 and, 12 hours) under three different applied loads (10 N, 25 N and, 50 N). Microstructural, characteristic, hardness, friction coefficient, and wear rate behavior under various applied loads were investigated against each other.
 
 The results showed that the wear rate increased in all samples with the applied load, while the friction coefficient decreased. While the highest wear rate was observed only in the solid-solution treated sample, it was observed that the wear rate changed inversely with the aging time. Furthermore, the micro-hardness increased in direct proportion with the aging time. While it was observed that the sample, which was aged for 12 hours, wore 13.6% less under 10 N load than the sample that was only treated with solid-solution, the results showed that the same sample wore about 25% less under 50 N load. The increase in β-precipitates in the structure with the aging period increased the micro-hardness, while the increase in hardness decreased the wear.

Single and Multiple Gate Design Optimization Algorithm for Improving the Effectiveness of Fiber Reinforcement in the Thermoplastic Injection Molding Process.

Fiber reinforcement orientation in thermoplastic injection-molded components is both a strength as well as a weak point of this largely employed manufacturing process. Optimizing the fiber orientation distribution (FOD) considering the shape of the part and the applied loading conditions allows for enhancing the mechanical performances of the produced parts. Henceforth, this research proposes an algorithm to identify the best injection gate (IG) location/s starting from a 3D model and a user-defined load case. The procedure is composed of a first Visual Basic Architecture (VBA) code that automatically sets and runs Finite Volume Method (FVM) simulations to find the correlation between the fiber orientation tensor (FOT) and the IG locations considering single and multiple gates combinations up to three points. A second VBA code elaborates the results and builds a dataset considering the user-defined loading and constraint conditions, allowing the assignment of a score to each IG solution. Three geometrical components of increasing complexity were considered for a total of 1080 FVM simulations and a total computational time of ~390 h. The search for the best IG location has been further expanded by training a Machine Learning (ML) model based on the Gradient Boosting (GB) algorithm. The training database (DB) is based on FVM simulations and was expanded until a satisfactory prediction accuracy higher than 90% was achieved. The enhancement of the local FOD on the critical regions of three components was verified and showed an average improvement of 26.9% in the stiffness granted by a high directionality of the fibers along the load path. Finite element method (FEM) simulations and laboratory experiments on an industrial pump housing, injection-molded with a polyamide-66 reinforced with 30% of short glass fibers (PA66-30GF) material were also carried out to validate the FVM-FEM simulation frame and showed a 16.4% local stiffness improvement in comparison to the currently employed IG solution.

Study of the Friction Behavior of Embedded Fibers in YG8 Surface Grooves.

YG8 is a common cemented carbide material with excellent mechanical properties and mechanical properties, so it is widely used in the actual industry. However, due to the active chemical properties and strong affinity of tungsten alloy steel, it is easy to produce bonding and peeling in application, resulting in an unstable process and short service life. In order to control and reduce the surface wear of YG8 cemented carbide, groove-textured surface (GS) and flocking surface (FS) were prepared on smooth surface (SS). The friction characteristics of the samples were studied under different applied load conditions. The results show that the average friction coefficient of SS, GS and FS is inversely proportional to the load in dry/oil environment. Compared with SS, FS exhibits the lowest friction coefficient, which is reduced by 30.78% (dry friction) and 13.13% (oil lubrication). FS effectively improves the tooth jump phenomenon of the sample and the amplitude of the friction coefficient, friction force and load, and has the best anti-friction characteristics. At the same time, the FS with the fastest contact angle drop at any time also showed excellent wetting ability, and the wear rate decreased by an order of magnitude. The implantation of fibers in the groove inhibits the spalling and furrow of wear track, which is attributed to the effect of fibers on damage repair. In the friction process, FS increases the content of the O element and induces the formation of oxides. The friction mechanism is mainly chemical wear. The excellent tribological properties of FS have a good guiding significance and theoretical support for improving the tribological properties of high hardness material surfaces.

Explorations of knitted shape memory alloy actuation behavior under high loads via finite element analyses and experimental studies

The properties of shape memory alloy (SMA) wires have long been leveraged across a variety of industries. While the response of such SMA forms implemented as straight axial actuators is well understood, curved and complex configurations such as knits have received far less attention. Considering 2D configurations, it is well known that knits exhibit more in-plane compliance than weaves and meshes, the curved wires comprising the former being much more flexible than the straight wire segments in the latter. In addition, knitted structures are uniquely highly tailorable. Knitting techniques and patterns developed in the textile industry allow for variable materials and geometries in the same structure, allowing for a large range of tailored macro-structure responses. Existing efforts to model the behavior of knitted SMA structures are lacking; though finite element analysis (FEA) models have been presented for knit SMAs, these models either only consider superelastic SMA behavior, or, in those that account for actuation behavior, the applied load conditions studied are insufficient to fully leverage the thermally induced strain recoverability of SMAs. This work seeks to develop and validate a finite element model for the actuation of SMA knitted structures where individual SMA wire components are axially stressed to more than 100 MPa. A representative volume element is developed for a common knit pattern, and macro-structure responses are explored and compared with experiments. This research provides a foundation for better understanding fundamental capabilities and responses of knitted SMA structures, allowing for better design, functionality, and customizability of the applications into which they are incorporated, enabling development of unique soft actuators. A shape-set sample examined herein generated 13% extension (analogous to strain) and recovered more that 6% under a load associated with 100 MPa stress in a straight wire, and a sample knit off-the-spool generated over 20% extension and recovered 9% for the same load.

Effects of Predefined Thermomechanical Procedure on the Microstructure and Mechanical Properties of the Two-Way Shape Memory Effect in the NiTi Alloy

In the current paper, a predefined thermomechanical procedure has been applied to the two-way shape memory effect (TWSME) in a NiTi alloy to study the effect of two different applied load conditions on the induced martensitic state. The microstructure of the strips was studied using optical microscopy (OM), scanning electron microscopy (SEM) fitted with an EDS microprobe, and microhardness tests at the end of both the training and thermal cycles. Inducing internal stresses along specified directions during training cycles results in the formation of oriented martensitic variants rather than expected twinned martensitic variants upon cooling. It was found that the microstructure is made up of interlocking martensitic lathes, including the fine martensite colony next to the coarse martensite lathes. Furthermore, the results of the average hardness tests for bending at one point and three points were 241 and 247 HV0.2, respectively. It was shown that only the cubic austenitic phase (B2) and the martensitic monoclinic phase (B19′) experience transformation. The results reveal that homogeneous bending in three locations leads to achieving the best difference between high- and low-temperature curvatures after training.

Effect of Uniaxial Compression Frequency on Osteogenic Cell Responses in Dynamic 3D Cultures.

The application of mechanical stimulation on bone tissue engineering constructs aims to mimic the native dynamic nature of bone. Although many attempts have been made to evaluate the effect of applied mechanical stimuli on osteogenic differentiation, the conditions that govern this process have not yet been fully explored. In this study, pre-osteoblastic cells were seeded on PLLA/PCL/PHBV (90/5/5 wt.%) polymeric blend scaffolds. The constructs were subjected every day to cyclic uniaxial compression for 40 min at a displacement of 400 μm, using three frequency values, 0.5, 1, and 1.5 Hz, for up to 21 days, and their osteogenic response was compared to that of static cultures. Finite element simulation was performed to validate the scaffold design and the loading direction, and to assure that cells inside the scaffolds would be subjected to significant levels of strain during stimulation. None of the applied loading conditions negatively affected the cell viability. The alkaline phosphatase activity data indicated significantly higher values at all dynamic conditions compared to the static ones at day 7, with the highest response being observed at 0.5 Hz. Collagen and calcium production were significantly increased compared to static controls. These results indicate that all of the examined frequencies substantially promoted the osteogenic capacity.

Simultaneous enhancement of strength-ductility via multiple precipitates and austenite in a novel precipitation-hardened martensitic stainless steel

In this study, the advantages of the novel precipitation-hardened martensitic stainless steel (abbreviated as novel steel) in terms of an excellent strength–ductility balance are fully elucidated utilizing various methods and tests. The novel steel increases the yield and ultimate tensile strength from 1480 ± 20 MPa and 1500 ± 18 MPa to 1530 ± 15 MPa and 1650 ± 20 MPa, respectively, and simultaneously improves the elongation from 9.7 ± 0.5% to 17.8 ± 1.1% over that of conventional PH13–8Mo steel. Specifically, the novel steel is mainly strengthened and toughened by three factors, including fine grain strengthening, precipitation strengthening of multiple precipitates (Cu, NiAl) and the TRIP effect. The contribution of fine grain strengthening is quantitatively evaluated through the Hall–Petch relationship. Meanwhile, the value of strengthening contributions by multiple precipitates are quantitatively evaluated through the shearing or Orowan mechanism. Significantly, compared with conventional PH13–8Mo steel, the addition of Cu leads to the formation of multitudinous metastable austenite in the novel steel. The TRIP effect can be generated by metastable austenite upon applied loading conditions. An accessible pathway is found to exploit high-performance stainless steel.

Static structural and aerodynamics analysis of 3D printed flapping wing mechanism of butterfly inspired ornithopter

The wing flapping motion of butterfly is more straight forward, and its wing morphology is simple. The wingspan is also large enough to make it as a mid-size ornithopter. Based on these reasons, the ornithopter based upon the morphology of butterfly is studied. The objective of this three-dimensional numerical study is to investigate the butterfly ornithopter for its aerodynamic parameters for varied angle of attacks (-6° to 6°) and perform static structural analysis on the 3D printed flapping wing mechanism. The materials chosen for the wing is polypropylene fumarate, carbon fibre rods and Mylar films. The investigations are carried out using ANSYS Mechanical Workbench and ANSYS Fluent. The shear stress is evenly distributed throughout the wing structure for both the applied load conditions. Moreover, the maximum values of equivalent stress and equivalent elastic strain is observed in local concentrations at the position where the Mylar film material wing membrane is connected to the carbon fibre rod. The deformation pattern is maximum at the wingtips (0.08569 for pressure 4.8 Pa; 0.067697 for pressure 3.8 Pa) and minimal near the support sections. The maximum lift with minimum drag is observed at angle of attack + 2°.

Study on microstructure, mechanical and wear behavior of AA7075/hBN composites fabricated via liquid metallurgy

These research works investigate microstructure, mechanical strength and wear characteristics of AA7075/ hBN composites. AA7075/hBN composites are manufactured through two- step stir casting techniques with varying (0–7.5 wt%) hBN particles and subjected to T6 heat treatment. The optical microscopy of the composites shows that the reinforcement particles were distributed finely and with few cluster formations. The results stated that improved hardness on AA7075/5.0 wt% hBN composite as compared to as-cast alloy. The wear behaviour of alloy and composites are analysed on a pin-on-disc tribometer with varying applied loads of (20–60 N), a sliding velocity of 2.0 m/s, and a sliding distance of 3000 m, with EN31 steel as a counterpart. The wear rate and coefficient of friction of the composite reduced as the hBN particle concentration increased. A scanning electron microscope (SEM) is used to analyses the wear process on the worn surface, its reveals abrasion, oxide layer, and delamination as wear mechanisms under varying applied load conditions.

Influence of tungsten carbide raw materials to microstructure and wear performance on PTA hard-facing materials with its micro-mechanism analysis

The wear performance of the plasma transferred arc (PTA) welding hard-facing materials manufactured reinforced by cast WC/W2C and coarse grain WC with different shapes are investigated. Coarse grain WC-Ni coating shows the best wear resistance in a high applied load condition, with spherical reinforced particles give higher wear performance than angular shape. WC, W2C, γ-Ni, M23C6, and M7C3 (M = Cr, Fe, W, and Ni) are detected in PTA coatings. The spherical cast and angular cast WC/W2C particles contain a higher volume of W2C, which is easier to be dissolved during the PTA welding process, resulting in lower retained reinforced particle volume and more precipitates concentration. In the PTA coating, the cast WC/W2C particles have a higher hardness, whereas the matrix has a relatively low hardness. The wear performance of PTA coating is more affected by the hardness rather than the coefficient of friction (COF). At a load of 5 N applied on the Si3N4 ball, the contact area between reinforced particles and counterparts, resulting in wear resistance is controlled by the hardness of the reinforced particles. When the load increases to 10 N, the hardness of the matrix controls wear performance. The precipitates formed between the carbides and matrix smooth the interface and strengthen the bonding, which prevents the cast WC/W2C from being pulled out from the matrix during the wear test.

Diffusion and redistribution of hydrogen atoms in the vicinity of localized deformation zones

The presence of hydrogen atoms in the lattice of polycrystalline metals can lead to hydrogen embrittlement. The diffusion of hydrogen atoms and formation of hydrides depend on several parameters such as the microstructure of the metal alloy, the presence of stress risers, and the applied loading condition. In this study, a non-local crystal plasticity finite element model is coupled with hydrogen diffusion equations to study the effects of such parameters on the stress-assisted diffusion of hydrogen atoms in zirconium polycrystals. The concentrations of hydrogen atoms in the lattice and dislocation trap sites under different scenarios are studied to deconvolute the effects of texture, microstructure, and applied strain on hydrogen diffusion. It is shown that the concentration of hydrogen in the lattice peaks in the vicinity of grain boundaries and most importantly, at the triple-junction points. It is further shown that in localized deformation zones, such as twin or notch tips where dislocations concentrate, the effects of trapped hydrogen content can be significant.

Viscous Behavior and Constitutive Modeling of Peaty Soil in Kunming, China

The Kunming peaty soil exhibits distinct physical and mechanical properties from the inorganic clay due to the special soil-forming process and material composition. To better understand the viscous behavior of peaty soil, a series of laboratory tests, including four types of oedometer tests (one- and multistage loading creep tests, constant rate of strain tests, and constant rate of stress) and constant rate of strain undrained triaxial compression tests, are conducted on the Kunming peaty soil. The experimental results demonstrate that the Kunming peaty soil shows significant secondary compression during oedometer creep tests. Meanwhile, the variations of the measured preconsolidation pressure and undrained shear strength with the strain rate are essentially linear in log-log plot for the examined range of strain rate. Based on the generalized power law overstress viscoplastic theory, it is confirmed that the rate-sensitivity and time-dependency of the Kunming peaty soil can be uniformly described using the sensitivity parameter involved in the theory, regardless of the applied loading conditions. The average value of 0.06 for the sensitivity parameter is generally greater than those for inorganic clay, indicating that the Kunming peaty soil exhibits more significant viscous behavior. Finally, by using the yield surface of the modified Cam–clay model, an overstress elastic-viscoplastic model is established and numerically implemented. The numerical model with a unique sensitivity parameter can well predict the rate-sensitive and time-dependent response of Kunming peaty soil under different loading conditions.

Crack initiation mechanisms in Ti-6Al-4V subjected to cold dwell-fatigue, low-cycle fatigue and high-cycle fatigue loadings

Although Ti-6Al-4V is the most commonly used titanium alloy in the aerospace industry, the mechanisms governing crack initiation in the different fatigue regimes are not well understood yet. This situation partly pertains to a competition between multiple crack initiation mechanisms. In particular, applied loading conditions were identified as a key parameter governing the transition between mechanisms. The fatigue behavior of Ti-6Al-4V with a bi-modal microstructure was investigated in the present study using different waveforms, load ratios and frequencies to clarify this feature. A detailed characterization of the main crack initiation sites was carried out to identify microstructural configurations governing crack nucleation in low-cycle dwell-fatigue, low-cycle fatigue and high-cycle fatigue regimes. While lifetimes and fracture surfaces showed a good consistency with data from prior studies, a single microstructural configuration was found involved with the formation of crack initiation facets. All investigated cracks leading to specimen failure were nucleated along (0001) twist grain boundaries exhibiting similar features. Based on this finding, a criterion is proposed to identify candidates for crack initiation. This also demonstrates no major sensitivity of the critical microstructural configurations to environment, free surface, loading conditions and, as shown in previous studies, microstructure and composition. However, conventional fatigue failure results from one, or a few, surface or subsurface crack initiation sites while dwell-fatigue failure involves the formation of multiple internal cracks. This is accompanied by a significant dwell-fatigue life debit at peak stress magnitudes close to the yield strength. Features of microstructural configurations prone to crack nucleation are finally compared with data reported in existing literature to propose a mechanism of crack formation in Ti alloys.