•SBS modifiers enhanced low-temperature crack resistance of asphalt binder.•High strain fatigue life of the SBS modified mastic asphalt mixtures was improved.•The SBS modified mixtures had greater ...flexural toughness than control mixtures.•The SBS modifiers was more substantial in retarding fatigue crack growth.
This study evaluated the fatigue performance of Styrene–Butadiene–Styrene (SBS) modified mastic asphalt mixtures used for bridge deck pavements. The effect of the type and content of newly developed SBS modifiers was investigated using typical binder tests. Four-point bending beam fatigue and indirect strength tests were conducted to examine fatigue and fracture behaviors of the SBS modified mastic asphalt mixtures. The SBS modifiers without CC double bonds enhanced the mechanical properties of the mastic asphalt binder and mixtures: lower stiffness after short- and long-term oxidation, significantly greater fatigue resistance at a higher strain level, and higher crack development resistance.
•The TiN coating increased the fatigue strength of TC4 substrate by 35%.•In high-cycle loading, fatigue cracks initiation dominates in coating/metal substrate system.•Enhancing coating plasticity ...boosts fatigue resistance in coating/metal substrate system.
This paper investigates the enhancement mechanism of mono- and multilayer coatings on the high-cycle fatigue behavior of TC4 under tension–tension. The morphology, phase composition, mechanical properties were measured by scanning electron microscope, X-ray diffractometer and nanoindentation. Electron back scatter diffraction was employed to investigate the fatigue failure mechanism. Median fatigue limits obtained by stair case method of TC4 with TiN coating, TiN/Ti (7:1), TiN/Ti (3:1), and uncoated TC4 after 1 × 107 cycles are 553 MPa, 422 MPa, 480 MPa, and 411 MPa, respectively. Under high-cycle loading, the hard-coating/TC4 substrate experiences fatigue failure through two mechanisms: coating cracking hastens the substrate's fatigue failure, or the fatigue source within the substrate creates sliding steps, ultimately resulting in failure. After 1 × 107 cycles under fatigue strength, the average dislocation density on TC4 as well as coated TC4 is similar. The plastic deformation resistant of TC4 under cyclic load was enhanced with nanoscale hard TiN coatings. This finding underscored that the hard coating significantly improves fatigue resistance by inhibiting crack initiation and accommodating substantial cyclic plastic strain. Furthermore, our research provides strong support for the application of hard ceramic coating on the surface strengthening of titanium alloy.
•Interlayer splitting failure can be avoided by using round tendons.•Cable fatigue life was found to be determined by tendon surface shape.•Variable-stiffness load transfer component can alleviate ...cable stress concentration.
The fatigue performance of fourteen basalt fiber reinforced polymer (BFRP) cables, each containing 37 tendons with a diameter of 4 mm, was investigated. Four testing schemes were employed to examine the failure mechanism and factors affecting fatigue behavior, including manufacturing technology, tendon surface shape, and anchoring method. The findings suggested that the fatigue life of the cable was controlled by the tendon surface shape, and subsequently affected by both anchoring method and manufacturing technology. The pretension method can eliminate the wedge action of the load transfer component (LTC). The splitting failure of ribbed tendons usually initiated from transverse cracking of resin matrix and eventually leaded to continuous interface debonding. Interlayer splitting in tendons can be avoided by adjusting the outer fiber from bending to flattening, which improves the tensile stiffness of the cable with round tendons under cycle load. The cable can achieve 2 million cycles while maintaining a stable deformation state, which is achieved by using round tendons in combination with a variable-stiffness LTC composed of epoxy resin and glass microfibers. The variable-stiffness LTC effectively alleviated stress concentration at the loading-end cable. The static anchoring efficiency of the cable with round tendons reached 110% after undergoing 2 million cycles.
•Fatigue behavior and failure modes of the friction connections were analyzed based on the specimens with four corrosion levels.•Contact analysis was performed based on the finite element model of ...the friction connections.•Fatigue life prediction method of the uncorroded friction connections were proposed and verified.•Corrosion effects on the fatigue life of the friction connections were investigated based on the prediction method.
In this paper, the corrosion effects on the fatigue performance of the friction connections are experimentally and numerically investigated. Fatigue test was conducted on the connections with four corrosion levels, and the failure mode and fracture surfaces were analyzed. Based on the finite element modeling of the connection, the crack initiation life caused by the fretting fatigue was calculated based on several multiaxial fatigue criteria, and the crack propagation life in the complex stress field was predicted using the AFGROW software. The results show that the fatigue life of the friction connections could be significantly reduced by corrosion, and the fatigue failure occurred near the minimum cross-section plane of the inner plates. It was also observed that the fatigue cracks initiated at the fretting wear scar and the corrosion pits at the hole edge for the uncorroded and corroded connections, respectively. The predictions show that the fatigue life prediction method in which the crack initiation and propagation lives are both considered can accurately predict the fatigue behavior of the uncorroded connections under different stress ranges. The fatigue life of the corroded friction connections with a mass loss ratio>7.8% can be estimated by assuming an initial crack at the hole edge in the minimum cross-section plane and ignoring the crack initiation life induced by fretting damage.
•A numerical method is proposed for the fatigue analysis of steel-UHPC composite decks.•Fatigue degradation of stud connectors is considered in the numerical method.•Effects of stud degradation and ...stud arrangement on the fatigue performance of steel-UHPC composite decks are evaluated.
The fatigue degradation of stud connectors is generally neglected in the fatigue analysis of steel-UHPC composite decks, which may lead to inaccurate results. This paper studies the effects of stud degradation and stud arrangement on the fatigue behavior of steel-UHPC composite decks via finite element analysis. A numerical method for the fatigue analysis of composite decks is proposed considering the fatigue degradation of studs. The numerical method is experimentally validated and applied to evaluate the fatigue performance of composite decks. The effect of stud arrangement on the fatigue response of composite decks is studied by parametric analysis. The results indicated the fatigue degradation of studs and the decrease in stud spacing caused more uniform distribution of shear forces at steel-UHPC interfaces. The fatigue degradation of stud connectors reduced the structural stiffness, while reducing the stud spacing enhanced the local stiffness but increased the stress ranges of some fatigue-critical details. Neglecting the stud degradation could lead to an underestimation of the fatigue life of stud connectors. This study advances the understanding of the fatigue behavior and the ability to analyze the fatigue behavior of steel-UHPC composite decks.
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•Commercially supplied Ti6Al4V powders show good consistency in terms of elemental composition and form.•Mechanical property characterisation of bulk material achieved all performance ...requirements within the ASTM standards and MMPDS/ESDU databases.•Parts produced from recycled Ti6Al4V powders had tensile mechanical properties within the tolerance bounds of those produced from virgin material.•Mixing virgin powders has limited impact on overall part performance despite minor differences in composition and form.•An effective powder certification programme is presented, which has substantial for use by industrial partners.
Metallic powder for Additive Manufacturing (AM) typically varies between different batches, while being supplied to achieve the same customer specification. In order to reduce this variation and minimise waste, batches are often mixed together in both their virgin and used form. However, the properties of bulk components must have limited variance in order to be reliably used in an industrial setting. This manuscript is focused on the analysis of Grade 5 Ti6Al4V powders (3 virgin, plus 2 blends) and the associated mechanical properties of Electron Beam Melted (EBM) AM specimens. Measurements were performed in accordance with the principles defined in the MMPDS Handbook, ESDU database, and ASTM F2924. The tensile, and fatigue properties of the EBM specimens were found to be superior when compared with Ti6Al4V properties within these standards. This demonstrated that these powders are suitable for a wide range of commercial applications, and that these blended powders (including used powders) are able to achieve these requirements. Additionally, the results provide a systematic route for powder verification and highlight the importance of adhering to standardised principles and specifications to ensure quality and reliability in metallic AM materials.
U-rib butt-welded connections in steel bridge decks are known to be highly susceptible to fatigue cracking, which can pose a direct threat to the safety and durability of bridge structures. Carbon ...fiber-reinforced polymer (CFRP) materials have shown promising potential for fatigue strengthening. This study investigated the effectiveness of CFRP application on the fatigue performance of U-rib butt-welded connections by employing full-scale fatigue tests and finite element analysis. Two single U-rib specimens with welded splice joints were initially tested to initiate real fatigue cracks under cyclic loading. Different techniques of CFRP installation were then proposed to promote the fatigue performance of cracked butt-welded connections. The failure modes and fatigue strength of the tested specimens were evaluated before and after strengthening. Research results showed that fatigue cracks were observed at the arc transition of butt welds, where remarkable incomplete penetration was also discovered. The fatigue strength grade of the tested U-rib butt-welded details was less than 71 MPa stipulated by Eurocode 3. However, after being repaired by CFRP sheet bonding, the equivalent fatigue life of U-rib butt welds with different damage degrees can be extended by 0.5–16.6 times that of the original ones. These findings suggest that CFRP strengthening should be applied instantly on U-rib butt-welded connections once fatigue cracks are found.
•An efficient of CFRP installation technique was proposed to repair U-rib butt-welded connections in OSD.•Full-scale fatigue tests of U-rib butt-welded connections before and after CFRP strengthening were conducted.•Wrapping CFRP strips adhesively can effectively prolong the remaining life of different cracked butt welds.
•1. Numerical analyses are performed on three types of bolted connections.•2. The effectiveness of the conventional segment approach is investigated.•3. Sufficient pretension force is beneficial for ...all three types of connections.•4. The C1 wedge connection is rather insensitive to the variation of pretension force.
The overall competitiveness of offshore wind turbine towers is significantly influenced by the selection of the connection. The following three types of connections: a conventional bolted ring flange (RF) connection, ring flange connection with defined contact surfaces (RFD), and C1 wedge connection (C1-WC) are considered. A quantitative comparison is made to enhance performance in a specific condition and enable further optimization of these connections in engineering practices. The study compares the tensile behaviour and fatigue performance of these connections by validated finite element (FE) simulation and analysis. The proposed FE modelling is based on a realistic geometry including all contacts present in the connections, steel full-range stress–strain relationship and ductile damage model. The efficiency and accuracy of the FE models are validated through the comparison with the performed tests. Then, a series of parametric FE analyses are carried out to examine the impact of the applied boundary conditions, bolt pretension level, and steel grade on the behaviour of connections. Load-displacement curves, bolt evolution curves, and stress responses are analysed to compare their tensile behaviour. The effectiveness of conventional segment specimen testing is evaluated thoroughly. For the fatigue performance of connections, the results indicate that the segment specimen testing substantially underestimates the fatigue performance of C1-WCs. This discrepancy is essential to be considered in the tower design. It is also noted that C1-WCs are rather insensitive to the variation of pretension force level, which show superiority to avoiding the difficulties associated with typically bolted joints. This research provides in-depth knowledge for the practical application of such connections and further optimization.
Additive manufacturing (AM) has attracted much attention due to its capability in building parts with complex geometries. Unfortunately, AM metals suffer from three major drawbacks, including high ...porosity, poor surface finish, and tensile residual stresses, all of which will significantly compromise the fatigue performance. These drawbacks present a major obstacle to the application of AM metals in industries that produce fatigue-sensitive components. Many post-processing methods, including heat treatment, hot isotropic pressing, laser shock peening, ultrasonic nanocrystal surface modification, advanced finishing and machining, and laser polishing, have been used to treat AM metals to decrease their porosity, improve the surface finish, and eliminate tensile residual stresses. As a result, significant improvement in fatigue performance has been observed. In this paper, the state of the art in utilizing post-processing techniques to treat AM metals and the effects of these treatments on the porosity, surface finish, and residual stresses of metal components and their resultant fatigue performance are reviewed.
•The mechanical behavior of a high-damping viscoelastic damper was investigated under various loading conditions.•The cyclic stability behavior of a viscoelastic damper was experimentally revealed ...for the first time.•Preloading is particularly beneficial to improve the cyclic stability of the viscoelastic damper during subsequent loading cycles.•High-cycle fatigue performance is sensitive to both loading strain amplitude and loading frequency.
This study explores the mechanical behavior of a viscoelastic damper (VED) under monotonic and cyclic loading, focusing on the cyclic stability of VEDs’ mechanical properties. The studied VED consists of 2 layers of elastomer compound sandwiched between 3 steel plates. The elastomer compound used in this study is designed to provide high damping capacity with relatively low stiffness. Nine damper specimens are manufactured, and each specimen is subjected to monotonic or cyclic loading to investigate the effects of strain amplitude, loading frequency, strain history, and high-cycle fatigue loading on the mechanical properties of VED. Hysteretic responses for each loading condition are obtained, and the variations of maximum force, storage shear modulus, loss shear modulus, dissipated energy, loss factor, and equivalent viscous damping ratio with different test parameters are examined. The experimental results show that VED can achieve a maximum shear strain amplitude of 543% under monotonic loading, and has low frequency dependency under cyclic dynamic loading. The VED has superior energy dissipation capacity with a maximum viscous damping ratio of up to 30%. The preloading strain history has a significant effect on the cyclic stability behavior of the VED. Furthermore, the high-cycle fatigue performance is sensitive to both loading strain amplitude and loading frequency.
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