Number Of Loading Cycles Research Articles

Metallographic and ultrasonic studies of fatigue failure of ASTM 1020 steel in the base metal and heat affected zone

This paper deals with optical and ultrasonic investigations in the base metal and heat affected zone of welded specimens of ASTM 1020 steel under low-cycle fatigue. Development of persistent slip bands on the surface was observed using optical microscope. Differences in development of slip bands in the base metal and heat affected zone were analyzed. Acoustic birefringence of shear waves was measured by the ultrasonic pulse echo method. For the base metal, acoustic birefringence was found to decrease monotonously. For heat affected zone, acoustic birefringence was found to change non-monotonously up to cycle ratio of 0.3 and decrease monotonously after cycle ratio of 0.3. Based on the linear dependence of acoustic birefringence on the relative number of loading cycles, an ultrasonic technique is proposed for assessing fatigue damage.

Ways to determine reliability in the operation of ship parts made by banding method

In the development of modern shipbuilding conditions and the repair of ship units, a special role is given to the use of basic structural elements consisting of technological parts. When performing these steps, it is important to analyze the properties of the materials from which the technological components of ship equipment are made. Testing should be close to the operating conditions of ship axles and shafts, namely cyclic loading, aggressive and adhesive environment.
 Therefore, a special factor is the technological control over the sequence of manufacture, selection of materials, surfacing technology. All these requirements can be analyzed and predicted using computer modulation. Investigations of the properties of the transition layers of the weld and the base metal and their effect on the number of load cycles in the tests are also key. All conditions will be met with the optimal selection of the chemical component Ni - Cr, which provide the required level of doping. The hardness of the materials is ensured by the presence of Mg in the metal. Also important are the heat treatment modes that provide the desired final structure of the material for machining and surfacing. For this part and its elements, the best properties in terms of operation in fine austenitic and pearlitic structures.
 During the operation of ship shafts and axles, the propagation of puncture loads is performed due to the occurrence of final stresses at low-cycle and multi-cycle loads and subsequent fatigue of the structural lattice.
 When considering the range of materials used in combined structures is very large and includes most welded steels. According to the combination of materials in one unit, it is advisable to distinguish two main groups of structures: with welded joints of steels of the same structural class, but different alloying, and with welded joints of steels of different structural classes. In this regard, the decision to obtain a balanced bandage connection lies in obtaining a fine-grained structure of the weld metal and the seam area.

Assessment of the Technical Condition of the Emergency Heat Exchanger for the Reactor Plant of the B-320 Type in Order to Extend Its Service Life

Extending the life of nuclear power plants in Ukraine during in the super-project period, as in most countries operating nuclear power units, is an accepted strategy and is being implemented practically. In this regard, there is a need for verification calculation of the main elements The calculated analysis of the stress-strain state of the heat exchanger is carried out using the finite element method of power equipment that determine the resource characteristics. The technical condition of the emergency cooling heat exchanger for the power unit no. 3 of the SUNPP has been evaluated. The analysis of design, technical and operational documentation in the amount of preliminary evaluation of technical condition was performed. Potential mechanisms of wear of heat exchanger elements were determined. The technique of carrying out verification calculations for static, cyclic and seismic stability was described. The emergency cooling heat exchanger calculation model is made in the APM Structure 3D calculation code. The tense-deformed state of the heat exchanger is calculated using the finite-element method of resampling the design region. The results of the verification calculation of the emergency cooling heat exchanger in the calculated states corresponding to normal operating conditions, hydrotests and under seismic impacts in conditions of the maximum design earthquake were presented. The correspondence of the actual stresses in the calculation zones of the heat exchanger to the permissible values, specified in the current regulatory documentation was established. The amount of damageability to the heat exchanger elements was determined for the permissible number of load cycles. The cyclical strength of the elements of the emergency cooling heat exchanger, taking into account the period of application equal to 60 years inclusive, is ensured in accordance with the requirements.

Analysis of crack initiation location and its influencing factors of fretting fatigue in aluminum alloy components

To promote the development of fretting fatigue assessment and control technology for aircraft components, this paper uses the Crystal Plasticity Finite Element (CPFE) method and sub-modeling technology to study the Crack Initiation Location (CIL) of fretting fatigue in Aluminum Alloy (AA) specimens. The effects of external excitations such as normal load, tangential load, and axial stress on the CIL are investigated. It is found that the Most Likely Cracked (MLC) site revealed in a specimen and the CIL may always be consistent after a limited number of cyclic loadings, and they are both located at the hotspot on the contact surface or in the subsurface. The MLC site may also migrate from the hotspot on the contact surface to the hotspot in the subsurface with an increase of the cyclic number, and finally transform into a CIL. The relationship between the MLC site and the CIL of fretting fatigue and its influencing factors have also been described, as well as the identification method of the CIL of fretting fatigue, which provide theoretical and technical supports for anti-fretting fatigue design of AA components in service.

Stress–dilatancy behavior of dense marine calcareous sand under high-cycle loading: An experimental investigation

Calcareous sand is an important filling material in marine engineering. The accurate interpretation of the calcareous sand's stress–dilatancy behavior under high-cycle loading can help improve the long-term stability of marine reclamation infrastructures. In this study, drained monotonic and high-cycle triaxial tests were conducted on calcareous sand and siliceous sand. Results show that the stress–dilatancy behavior of calcareous sand under high-cycle loading differed significantly from that under monotonic loading. Due to the continuous adjustment of the internal structure and state parameter (ψ) during cyclic loading, the number of loading cycles (N) has a considerable effect on the stress–dilatancy behavior of calcareous sands. As N increases, the stress–dilatancy of dense calcareous sand gradually transforms from loading-induced contraction and unloading-induced dilation to loading-induced dilation and unloading-induced contraction. A phase transition state line of calcareous sand under long-term cyclic loading is found in the e-(p/pa)0.7 plane, where its gradient is insignificantly influenced by the initial state, whereas its intercept depends on the initial pressure. Furthermore, a correlation between the number of loading cycles and the flow rule considering the state parameter (ψ) was proposed to describe the direction of strain accumulation for calcareous sand.

The effect of overconsolidation on monotonic and cyclic behaviours of frozen subgrade soil

This paper presents an experimental investigation on the monotonic and cyclic behaviours of the overconsolidated subgrade soil used in the Lanzhou-Urumchi high-speed railway at the temperature of -3°C. The important mechanical parameters of the overconsolidated soil, i.e., failure strength, initial elastic modulus, accumulative permanent strain and resilientmodulus were experimentally studied by using triaxial tests. Testing results indicate that the failure strength, initial elastic modulus, dilatancy and stress–strain relationship of frozen sample are all dependent to the overconsolidation ratio (OCR). The failure strength is slightly more susceptible to the overconsolidation ratio than the initial elastic modulus. The anisotropically consolidated path (k0=0.5-1) has a negligibleimpact on the stress–strain-strength behaviors. The development characteristics of accumulative permanent strain and resilient modulus are collectively dominated by the overconsolidation ratio and shear stress amplitude. Axial permanent strain acceleratedly accumulates with the decrease of the overconsolidation ratio at the same shear stress amplitude. According to the shakedown theory, allowable cyclic stress ratio was introduced to analyze accumulative deformation characteristics of frozen sample. The overconsolidation ratio and loading cycle number have negligible influences on the allowable cyclic stress ratio of frozen subgrade soil. Four cyclic stress-paths with the same shear stress amplitude were adopted in triaxial cyclic tests with aim to investigate the path-dependent deformation behaviors of frozen subgrade soil. The relationships of axial permanent strain under different cyclic stress-paths are roughly proportional, regardless of the cyclic stress ratio (CRS) and loading cycle number. Those quantitativerelationships can be completely determined by the overconsolidation ratio and cyclic stress-path parameter. The effect of cyclic stress-path on resilient modulus is more than the effect of overconsolidation ratio and less than the effect of shear stress amplitude. Several empiricalmodelswere proposed for the overconsolidated subgrade soil at the negative temperature to characterize the evolution laws of the above-mentioned engineering properties. Those empiricalmodels are capable of giving well descriptions of the development of those engineering parameters for frozen subgrade soil over a wide range of the oveconsolidation ratio.

Experimental Investigation on the Behavior of Gravelly Sand Reinforced with Geogrid under Cyclic Loading

In view of the dynamic response of geogrid-reinforced gravel under high-speed train load, this paper explores the dynamic characteristics of geogrid-reinforced gravel under semi-sine wave cyclic loading. A number of large scale cyclic triaxial tests were performed on saturated gravelly soil reinforced with geogrid to study the influence of the number of reinforcement layers and loading frequencies on the dynamic responses of reinforced gravelly sand subgrade for high speed rail track. The variation of cumulative axial and volumetric strains, excess pore pressure and resilient modulus with number of loading cycles, loading frequency, and reinforcement arrangement are analyzed. The test results reveal that the cumulative axial strain decreases as the number of reinforcement layers increases, but increases with loading frequency. The resilience modulus increases with the number of reinforcement layers, but decreases as the loading frequency increases. The addition of geogrid can reduce the excess pore water pressure of the sample, but it can slightly enhance the rubber mold embedding effect of the sand sample. As the loading frequency increases, the rubber mold embedding effect gradually weakens.

Fatigue effects of embedding electric vehicles Charging Units into electrified road

A charging infrastructure network for Battery Electric Vehicles (BEV) is more than an option for the transportation scenarios of the next years. From a pavement engineering point of view, this network consists in prefabricated Charging Units (CU) embedded into the road pavement, generating additional questions related to the structural life of the pavements in which the CU are located. Moreover, even if in the available literature few studies describe the structural response of e-road, the long-term performances of pavements are not fully investigated. This is the reason why this research analyzes fatigue behavior of electrified road (e-road) in comparison with traditional road (t-road). In particular, the study is devoted to identifying the number of critical load cycles leading to failure an e-road pavement. As a second stage, the theoretical and numerical results are verified applying the findings obtained during the first stage of the research to a real case study: Viale Forlanini in Milan (Italy), which is an important two carriageway road connecting the city center to the Linate airport. As a result of these analyzes, interesting outcomes were obtained regarding the fatigue effects of embedding CU into road pavement, estimating the service life and demonstrating that CU seems to be compatible with the structural effectiveness of the pavement, as also confirmed by the case study results.

Effects of Temperature on the Evolution of Yield Surface and Stress Asymmetry in A356-T7 Cast Aluminium Alloy.

As the electrification of vehicle powertrains takes prominence to meet stringent emission norms, parts of internal combustion engines like cylinder heads are subjected to an increased number of thermal load cycles. The cost-effective design of such structures subjected to cyclic thermo-mechanical loads relies on the development of accurate material models capable of describing the continuum deformation behaviour of the material. This study investigates the effect of temperature on the evolution of flow stress under cyclic loading in A356-T7 + 0.5% Cu cast aluminium alloy commonly used in modern internal combustion engine cylinder heads. The material exhibits peak stress and flow stress asymmetry with the stress response and flow stress of the material under compressive loading higher than under tension. This peak and flow stress asymmetry decrease with an increase in temperature. To compare this stress asymmetry against conventional steel, cyclic strain-controlled fatigue tests are run on fully pearlitic R260 railway steel material. To study the effect of mean strain on the cyclic mean stress evolution and fatigue behaviour of the alloy, tests with tensile and compressive mean strains of +0.2% and −0.2% are compared against fully reversed (Rε = −1) strain-controlled tests. The material exhibits greater stress asymmetry between the peak tensile and peak compressive stresses for the strain-controlled tests with a compressive mean strain than the tests with an identical magnitude tensile mean strain. The material exhibits mean stress relaxation at all temperatures. Reduced durability of the material is observed for the tests with tensile mean strains at lower test temperatures of up to 150 °C. The tensile mean strains at elevated temperatures do not exhibit such a detrimental effect on the endurance limit of the material.

Critical shear strain and sliding potential of rock joint under cyclic loading

A new concept of critical shear strain ετcritical of rock joint under cyclic loading is presented, and the role of ετcritical in evaluating the sliding potential of rock joint is highlighted. A series of cyclic triaxial tests was conducted on a cylindrical rock joint specimen with a replicated rough surface representing a joint roughness coefficient JRC value of 12.6 oriented at 60° with respect to the horizontal plane. The experimental results indicate that the onset of instability of rock joint is suppressed with increase in confining pressure and number of loading cycles N until the normalized shear deformation increases beyond a threshold value of ετcritical. Generally, the critical strain of most rock types is considered in the proximity of 1% under small strain conditions [36–37], however, in this study, the critical strain concept is extended to the domain of rock joints, and a semi-empirical model to more rigorously quantify the critical shear strain (ετcritical) of rock joint is suggested considering the effect of joint roughness coefficient JRC, cyclic loading amplitude, and the number of loading cycles N. Also, a rational classification of Joint Sliding Potential (JSP) based on the ετcritical and normalized total shear strain εθN of rock joint is proposed to characterize the cyclic loading induced sliding instability of a rock discontinuity.

Investigation of fatigue crack propagation behavior in steel fiber-reinforced ultra-high-performance concrete (UHPC) under cyclic flexural loading

Fatigue crack propagation behavior in ultra-high-performance concrete (UHPC) containing different volume fractions of steel fibers is investigated under cyclic flexural loading at various stress levels. Evolutions of the crack mouth opening displacement, crack tip strain, and crack propagation length are characterized during continuous loading cycles via digital image correlation. Test data are fit to smooth, continuous logarithmic functions to discern relationships between evolving crack length and the number of loading cycles. The crack propagation rates of different UHPC specimens are then determined from the first derivative of these logarithmic functions. A critical crack length of approximately 20 mm is found in UHPC containing a fiber volume fraction (Vf) of 0.5%, while that of other specimens (Vf = 1.0%, 1.5%, and 2.0%) is found to approach 60 mm under the stress levels of 0.80, 0.75, 0.70 and 0.65. Strain diagrams obtained via DIC reveal no obvious changes for the crack growth along the y-direction in UHPC specimens containing fiber volume fractions of 0.5% and 1.0%, while a tendency for strain concentrations oriented at 45° characterizes crack development in specimens containing 1.5% and 2.0% volume fractions of fiber. Crack propagation rates during the stable stage of crack propagation decrease upon reducing applied stress level and with increased content of steel fiber reinforcement, providing predominant means to enhance fatigue life.

The probability of the existence of defects that lead to the destruction of the pressure vessel without leak

Relevance. To ensure the safety of a nuclear power plant on the basis of the requirements of norms and rules in the field of the use of atomic energy for pipelines of the primary circuit of a nuclear reactor, the design should apply the leak before break concept. The main idea of the concept is to prevent a sudden rupture of the pipelines of the reactor coolant loop, and consists in substantiating the fact that the rupture is preceded by the formation of a stable through crack, which is detected by the provided leak control means. When substantiating the concept, it is assumed that break without leak is an impossible event. This article provides a method for determining the probability of a failure event without a leak. Purpose - estimate the probability of the existence of a defect that can lead to the destruction of the vessel or pressure pipeline without leakage, as well as the probability of failure without leakage for a known number of loading cycles. Methods. To systematize the data obtained by different methods of non-destructive testing, conservative assumptions were used to determine the area of detected defects. On the basis of the obtained defect sizes, the defect size regions were determined, which can determine the scenarios of crack growth. Using the methods of mathematical statistics, the probability of the existence of a defect, which can lead to failure without leakage, was determined. Based on the methods of the theory of reliability, a comparison of the obtained probability of destruction with the admissible value is carried out. Results. A method for processing non-destructive testing data based on an assessment of the area of detected defects has been developed to systematize the data obtained by different non-destructive testing methods. The criterion for the development of cracks according to the scheme leak before destruction is determined. A method has been developed for determining the probability of a defect that can lead to failure without leakage. An example of calculation based on feed water pipelines is considered.

Experimental Study on the Evolution Trend of the Pore Structure and the Permeability of Coal under Cyclic Loading and Unloading.

In the deep mining process of coal seams, the mechanical environment of the coal body is complex and in the state of cyclic loading and unloading. The change in the stress state leads to the change in the pore characteristics and the permeability. To investigate the effects of cyclic loading and unloading on the pore characteristics and the permeability of coal, the seepage experiment was carried out for the coal samples using the self-developed triaxial permeation instrument. By pressure confining and continuous cyclic loading and unloading, the evolution of the porosity and the permeability of the coal samples was investigated. Under the condition of the experiment, the influences of the initial value of the confining pressure and the cyclic load amplitude on the evolution of the permeability and the pore structure characteristics of the coal samples were clarified. The experimental results showed that the porosity and the permeability decreased exponentially with an increase in the number of loading and unloading cycles, and this decreasing trend gradually weakened until the porosity and the permeability became relatively stable. When the cyclic load amplitude was the same and the confining pressure increased, the effective porosity of the coal body and the bound porosity decreased. When the confining pressure was the same and the cyclic load amplitude increased, the effective porosity of the coal body decreased and the bound porosity increased. The loss rate of the permeability of the coal samples increased gradually with an increase in the cyclic load amplitude. The same tendency was observed when the cyclic load amplitude was the same, and the confining pressure was different, while the increasing trend was not so obvious. By analyzing the relationship between the porosity and the permeability of the coal samples under different cyclic loading and unloading paths, it was found that the effective porosity and the permeability of the coal samples conformed to the power–law relationship in the process of cyclic loading and unloading, and the change in the cyclic load amplitude had a significant effect on this relationship. The influences of the cyclic load amplitude and the confining pressure on the stress sensitivity of the coal samples were considered, and the change factor of the stress sensitivity was introduced into the relationship between the porosity and the permeability. This relationship was established considering cyclic loading and unloading.

Cyclic settlement of ballast layer due to train passages at high speed and its reduction by asphalt trackbed

Ballasted track has been widely adopted in railway lines, even in high-speed railways. As the train speed increases, ballast layer has to undertake excessive settlement or severe degradation. To preserve rail network safety and ride quality more optimally, it is vital to get further insight into the cyclic accumulative deformation of ballast layer. This study concentrates on investigating cyclic settlement of railway ballast with an emphasis on the inside particle-scale interactions in conventional ballasted trackbed, and further in asphalt trackbed, a promising structural form of the granular track. The entire transversal cross-section of granular trackbed is modeled based on discrete element method with realistic polygon elements. The numerical model is validated with the measurements from full-scale model tests and then used to study the deformation behavior of railway ballast. Subsequently, the trackbed model with insertion of asphalt layer is established to investigate the reduction of permanent deformation in asphalt trackbed. The granular trackbeds under different train loading are analyzed in the end. Results indicate that the inter-particle structure in the ballast is stabilizing with an increasing number of loading cycles, contributing to less particle migration, so the growth rate of permanent deformation appears a slowing trend. Besides, the asphalt layer optimizes the distribution of contact chains in the ballast and reduces the intensities of contact forces, leading to a remarkable decrease in permanent deformation. Moreover, the higher train speed results in more active ballast particles so that the trackbed becomes hard to stabilize especially when the shakedown threshold is reached. The adverse impact derived from the train speed can be weakened effectively by the asphalt layer. This paper discusses the cyclic settlement of railway ballast and its reduction induced by the asphalt layer. These conclusions will guide the potential methods to alleviate the permanent deformation in high-speed railways, such as employing the asphalt trackbed or controlling the train speed.

Fatigue integrity assessment for tractor-mounted garlic-onion harvester

Tractor-mounted harvesters are operated under harsh conditions to dig deep-rooted crops on irregular soil conditions. Therefore, it is important to evaluate their fatigue strength by measuring random load characteristics that occur during operation. Based on this, highly reliable fatigue design that can be used safely without damage during the service life is required. In this study, the traction force of a tractor-mounted garlic-onion harvester was measured through a field test, and its fatigue damage was calculated based on the Rain-flow counting method and Goodman’s equation. In addition, a method of verifying the fatigue safety of the harvester by calculating the equivalent load and required test cycle for the accelerated life test in the laboratory was presented. The average traction force calculated from the torque history measured in field tests by attaching a torque meter to four tractor wheels at the actual harvesting site was found to be 8.51 kN. When the accelerated life test condition corresponding to the target life of 800 h was calculated using the presented method, the number of load cycles required under a maximum load of 12.37 kN and a minimum load of 7.56 kN was found to be 2.67 × 106 cycles.

Research on Hovercraft – Fatigue Cracks in the Engine Frame

Abstract Rescue patrol hovercrafts must meet the basic condition – high reliability of use in extreme conditions. The introduction to the work shows damage to the propulsion system and the fan tunnel structure resulting from a fatigue fracture of the attachment wound to the propulsion unit hull. In this paper, the author describes some ways of improving the engine frame structure. In the first phase of the exploitation crack testing of the hovercraft frame, the probable causes of damage were determined. The necessary output data for analysis of the load course were obtained from the operating documentation. The approximate number of variable load cycles acting on the frame truss rod was determined. Using the comparative testing methods, the service life of the frame was estimated. Probable resonance frequencies of the vibrating bars in the truss were determined. Vibration tests of the power transmission assemblies were carried out, which allowed to determine the amplitudes and frequencies of free vibrations. Finally, a modification of the frame shifting the resonant frequency range was proposed. In conclusions, changes to the design and a schedule of inspections were proposed. The newly designed engine frame should have an extended service life.

Investigations on Interface Shear Fatigue of Semi-Precast Slabs with Lattice Girders

Due to their high cost efficiency and flexibility, semi-precast concrete slabs with lattice girders are widely used in constructions all over the world. Prefabricated concrete slabs, combined with in situ concrete topping, exhibit a quasi-monolithic structural behavior in which lattice girders serve as vertical shear reinforcement and ensure the transfer of longitudinal shear within the interface, acting in combination with concrete-to-concrete bonding mechanisms. To be applicable in industrial and bridge construction, semi-precast slabs need to have sufficient resistance against fatigue failure. To improve and expand the limits of application, theoretical and experimental investigations are conducted at the Institute of Structural Concrete (IMB), RWTH Aachen University. To investigate the fatigue behavior of lattice girders, small size tests with lattice girder diagonals were carried out. These test results have been used to derive an S–N curve (S: stress, N: number of load cycles) for lattice girders for a more refined fatigue design. Subsequently, the fatigue behavior of semi-precast slabs with lattice girders was investigated by fatigue tests on single-span slab segments. The fatigue design regulations of lattice girders according to technical approvals can generally be confirmed by this test program; however, they tend to be conservative. The use of the derived S–N curve leads to significantly improved agreement of fatigue behavior observed in tests and design expressions.

Damage indicators for early fatigue damage assessment in WC-Co hardmetals under uniaxial cyclic loads at a stress ratio of R = −1 at elevated temperatures

WC-Co hardmetals are utilized as tool materials in metal cutting applications in which they are exposed to high mechanical cyclic loads and elevated temperatures. A better understanding of the failure mechanisms of WC-Co hardmetals under these application conditions and the ability to diagnose the damage evolution state are key factors to understand the limits of endurable cyclic load at a certain temperature. The aim of the current work was the experimental determination of stress-strain-hysteresis loops for the investigation of damage indicators in uniaxial cyclic tests at a stress ratio of R = σmin/σmax = −1 for two WC-10 wt% Co hardmetals at 700 °C and 800 °C in vacuum. An increase in the stress-strain-hysteresis loop area and tension-compression-strain asymmetry was recorded with increasing number of load cycles at 800 °C, with earlier failure than at 700 °C. The relationship between the stress-strain-hysteresis loop parameters and the damage evolution state at the microstructure level, as well as the deformation behavior of WC- and Co-phases with increasing number of load cycles, were analyzed. To this end, the microstructure for one WC-Co hardmetal grade was analyzed by scanning electron microscopy and electron backscatter diffraction after cyclic testing up to defined numbers of load cycles at 800 °C. It was observed that the hysteresis loop area and strain asymmetry coincide with the formation of nanopores at WC/WC interfaces and WC/Co phase boundaries, which enlarge to form larger cavities with increasing number of load cycles. Additionally, electron backscatter diffraction data showed that the fcc Co-phase partially transformed into hcp Co under cyclic loading. All specimens, in which an increase in the stress-strain hysteresis loop area or strain asymmetry was observed, ultimately failed when a sufficiently high number of load cycles was applied. Thus, these results indicate that the investigated parameters are reliable indicators for bulk material damage.

Comparative Test on the Bond Damage of Steel and GFRP Bars Reinforcing Soft Rock Slopes

Soft rock slopes were anchored with traditional steel bars and new Glass Fibre Reinforced Polymer (GFRP) bars. The difference in the anchorage performance of the two kinds of anchorage elements in soft rock and expansive soil was studied by an in-situ test. The results show that cyclic load can aggravate the bond damage of the interface between grouting body and both kinds of bars used in soft rock. Compared with the number of cyclic loads applied, the previous maximum load is the main factor that influences the bond damage of the anchorage bar. Under constant loading, the interface bond behaviour of GFRP bar is better than the steel bar. Because of the small difference in elastic modulus between the GFRP bar and the grouting body, the interface bond around the GFRP bar can invoke more resistance of the grouting body efficiently which demonstrates its more effective anchorage performance than the steel bar under the same conditions. The anchorage structure of steel bar in soft rock can generate larger interfacial relative displacement with increasing load than the GFRP bar in the anchorage section, even though the elastic modulus of steel is much larger than GFRP. In the expansive soil, the anchorage structure deformations of steel and GFRP bars are almost the same because of the weaker bond at the interface of the grouting body and the surrounding soil than that of the bar interface. Under the ultimate loading of the anchorage structure in soft rock, the steel bar with 450 MPa which is less than its ultimate strength shows the failure of the bar body pulling-out, and the GFRP bar with 508 MPa which is larger than its ultimate strength shows the failure of the bar body by fracture. The steel bar anchorage structure in soft rock is destroyed at the interface around the grouting body. The results show that the GFRP bar performs more efficiently than the steel bar.

Characteristics of cyclic undrained model SANISAND-MSu and their effects on response of monopiles for offshore wind structures

Optimised design is essential to reduce the cost of monopiles for offshore wind turbines. For this purpose, an in-depth understanding of the behaviour of monopile–soil interaction is required. As more wind farms are planned in seismically active areas, the undrained behaviour of sandy soils (and the possibility of soil liquefaction) and these soils’ effects on monopile cyclic response need critical evaluation. Considering the lack of well-established test programs, implicit three-dimensional (3D) finite-element (FE) methods stand out as a robust tool to identify and highlight the governing geo-mechanisms in monopile design. In this work, an implicit 3D FE implementation of SANISAND-MS for undrained soil behaviour, termed SANISAND-MSu, is deployed in OpenSees to serve these objectives. The role of pore-water pressure on monopile performance is comprehensively investigated by comparisons between drained and undrained soil behaviour. Local soil responses are studied in detail in relation to parameters in laboratory soil testing and application to monopile geotechnical design. The results of simulations are also used to evaluate numerical p–y curves as a function of the number of load cycles on the pile. The conclusions in this work contribute to ongoing research on monopile–soil interaction and support the development of lifetime analysis for monopile–soil systems.