Simulating Large-Scale Fatigue Test Specimens for Offshore Wind Monopiles

2017 ◽  
Author(s):  
Feargal Brennan ◽  
Athanasios Kolios ◽  
Isaac Tavares
Keyword(s):  
Fatigue Test ◽  
Size Effects ◽  
Large Scale ◽  
Fatigue Testing ◽  
Fatigue Tests ◽  
Offshore Wind ◽  
Structural Details ◽  
Local Detail ◽  
Future Test

Size effects are extremely important to understand and accounting for their inclusion in fatigue tests is imperative in order to produce meaningful results. This can however be problematic as in dealing with very large offshore structural details and sections, testing to destruction can involve extremely large loads and gripping arrangements that can be cost prohibitive. It is therefore important to be able to simplify test specimens so that the local detail is retained without losing important size influences. This paper describes an investigation into whether or not extracted specimens from actual Offshore Wind Monopile Sections are in fact the best choice for fatigue testing. The results are analysed and a recommendation is made for future test programmes involving offshore wind monopile and tower applications.

Large-Scale Resonant Fatigue Testing of Welded Tubular X-Joints for Offshore Jacket Foundations

2019 ◽  
Author(s):  
Jeroen Van Wittenberghe ◽  
Philippe Thibaux ◽  
Maarten Van Poucke
Keyword(s):  
Large Scale ◽  
Fatigue Testing ◽  
Water Pressure ◽  
Limit State ◽  
Fatigue Tests ◽  
Offshore Wind ◽  
Design Standards ◽  
Initiation Phase ◽  
Out Of Plane ◽  
Jacket Structures

Abstract Offshore wind turbines are being installed in deeper water and with more powerful generators resulting in more severe loading conditions on its foundations such as jacket structures. Because the main loading is due to wind and currents, the dominant design limit state is fatigue. The fatigue performance of the tubular joints used in jacket structures has been assessed several decades ago based on test results with limited component dimensions (diameter and wall thickness). In addition, improvements of welding methods and evolution of steel grades are not considered in the current design standards. To provide experimental fatigue-life data on large-scale structures a test program has been carried out on 4 welded tubular X-joints. Each X-joint consists of two horizontal braces with a diameter of 711 mm welded to a central vertical tubular member with 806 mm diameter. The X-joint has a total length of 7.5 m and has two identical welds that are fatigue tested. The fatigue tests are carried out on an innovative resonant bending fatigue test rig that allows to load the specimen in in- and out-of-plane direction at a different amplitude to obtain an even stress distribution over the circumference of the welds. The tests are carried out at a speed close to the resonance frequency of the X-joint. During the test, hotspot strains are measured using strain gauges and a limited amount of water pressure is used to detect through-thickness cracks. The tests are carried out in two phases. During the crack initiation phase, the sample is loaded in both the in- and out-of-plane mode. Once cracks are detected, the test is continued in the crack propagation phase with loading in the plane where cracks had been initiated until through-thickness cracking appeared. During this phase the beach marking technique has been used to mark the shape of the fracture surface at different moments during the fatigue tests. The testing program is part of the RFCS project JABACO that aims to reduce offshore wind cost by incrementing prefabrication of the jacket substructure.

Fatigue Capacity of Stiffener to Web Frame Connections

2009 ◽  
Author(s):  
Torbjo̸rn Lindemark ◽  
Inge Lotsberg ◽  
Joong-Kyoo Kang ◽  
Kwang-Seok Kim ◽  
Narve Oma
Keyword(s):  
Fatigue Test ◽  
Test Data ◽  
Large Scale ◽  
Fatigue Tests ◽  
Life Assessment ◽  
Shear Stresses ◽  
Test Model ◽  
The Difference ◽  
Marine Engineering ◽  
Plate Connections

Daewoo Shipbuilding & Marine Engineering Co., Ltd. (DSME), StatoilHydro and DNV established a common project to investigate the reason for the difference between calculated fatigue lives and the in-service experience and to assess the fatigue capacity of stiffener web connections subjected mainly to web frame shear stresses. The main objective of the work was to establish fatigue test data and perform numerical analysis of collar plate connections in order to provide improved confidence in analysis methodology for fatigue life assessment. Large scale fatigue tests of different types of connections were carried out to obtain fatigue test data of collar plate connections. Finite element analyses were carried out for comparison with fatigue test data and with measured stresses on the test model. Based on this work recommendations on fatigue design analysis of connections between stiffeners and web frames have been derived. The background for this is presented in this paper.

Fatigue Testing of Large-Scale Models of Submarine Structural Details

1965 ◽  
Vol 2 (03) ◽  
pp. 299-307
Author(s):  
Frank W. Dunham
Keyword(s):  
Cyclic Loading ◽  
Large Scale ◽  
Fatigue Testing ◽  
Fatigue Cracks ◽  
Pressure Variation ◽  
Test Tank ◽  
Initiation And Propagation ◽  
Scale Models ◽  
Structural Details

The conversion of a 30-ft-dia test tank to a facility for subjecting large-scale models of submarine structural details to cyclic loading is described. By means of automatically controlled valves, models were subjected to a pressure variation simulating a submarine diving to its test depth and returning to the surface. The cyclic rate was slightly less than one per minute. The system was so designed that the test tank itself was not subjected to the pressure variations. Details of a series of models designed to simulate particular structural details of interest in recent submarine construction are described. Results of the tests to date are summarized, and several observations relative to the initiation and propagation of fatigue cracks in submarine structural details are presented.

Dynamic Behavior and Design of Fatigue Test Specimens

1971 ◽  
Vol 93 (1) ◽  
pp. 340-342
Author(s):  
Barry Wolf
Keyword(s):  
Dynamic Behavior ◽  
Fatigue Test ◽  
Fatigue Testing ◽  
Fatigue Tests ◽  
Regions Of Interest ◽  
Simple Criterion ◽  
The Stability

In tension-tension, as well as in compression-tension, fatigue testing it has been observed that there exist combinations of loading and specimen characteristics for which the specimen becomes unstable. The theory explaining this behavior is well known and stability curves which predict the stability or instability of the specimen have been tabulated. Unfortunately these tabulations do not extend into the regions of interest for actual fatigue tests. The present work outlines the theory and offers a simple criterion for the design of stable fatigue tests which results from the extension of these stability curves.

scholarly journals Fatigue Behavior of Smart Composites with Distributed Fiber Optic Sensors for Offshore Applications

2021 ◽  
Vol 6 (1) ◽  
pp. 2
Author(s):  
Monssef Drissi-Habti ◽  
Venkadesh Raman
Keyword(s):  
Composite Structures ◽  
Large Scale ◽  
Fiber Optic ◽  
Fatigue Behavior ◽  
Turbine Blades ◽  
Mechanical Tests ◽  
Fiber Optic Sensors ◽  
Fatigue Tests ◽  
Offshore Wind ◽  
Smart Composites

Continuous inspection of critical zones is essential to monitor the state of strain within offshore wind blades, thus, enabling appropriate actions to be taken when needed to avoid heavy maintenance. Wind-turbine blades contain various substructures made of composites, sandwich panel, and bond-joined parts that need reliable Structural Health Monitoring (SHM) techniques. Embedded, distributed Fiber-Optic Sensors (FOS) are one of the most promising techniques that are commonly used for large-scale smart composite structures. They are chosen as monitoring systems for their small size, being noise-free, and low electrical risk characteristics. In recent works, we have shown that embedded FOSs can be positioned linearly and/or in whatever position with the scope of providing pieces of information about actual strain in specific locations. However, linear positioning of distributed FOS fails to provide all strain parameters, whereas sinusoidal sensor positioning has been shown to overcome this issue. This method can provide multiparameter strains over the whole area when the sensor is embedded. Nevertheless, and beyond what a sensor can offer as valuable information, the fact remains that it is a “flaw” from the perspective of mechanics and materials. In this article and through some mechanical tests on smart composites, evidence was given that the presence of embedded FOS influences the mechanical behavior of smart composites, whether for quasi-static or fatigue tests, under 3-point bending. Some issues directly related to the fiber-architecture have to be solved.

Pseudo Fatigue Testing for Rapid Certification to Service

2014 ◽  
Vol 891-892 ◽  
pp. 1059-1064 ◽  
Author(s):  
Lorrie Molent ◽  
Simon A. Barter ◽  
Matthew Gordon ◽  
Liam Weibler
Keyword(s):  
Fatigue Test ◽  
Fatigue Testing ◽  
Critical Item ◽  
Aircraft Design ◽  
Fatigue Tests ◽  
Full Scale ◽  
Damage State ◽  
Proof Testing ◽  
The Cost ◽  
Size Estimates

Aircraft full-scale fatigue tests are expensive to conduct and they are a critical item on the certification path of any aircraft design or modification. Two aspects that contribute to the cost of a test are its duration and the loads spectrum development process. This paper provides a summary of a proposed supplemental pseudo full-scale fatigue test (FSFT) aimed at rapid certification. In this instance the method was developed with the aid of extant FSFTs that were found to be deficient. The proposed process involves the development of proof loads, damage size estimates, a loads application rig, insertion of the target damage or modifications and conducting proof testing. As all locations with a propensity to crack are known, the process is considered to be the equivalent of having conducted a representative fatigue test for the required service life target and then demonstrating adequate residual strength (i.e. proof testing the damage state at the end of a FSFT).

Design Analysis and Fatigue Testing of the Typical Structural Details of Aluminium Ships

2018 ◽  
Author(s):  
Huilong Ren ◽  
Kaikai Ma ◽  
Chenfeng Li ◽  
Zhichao Zhang ◽  
Weijun Xu ◽  
...  
Keyword(s):  
Fatigue Strength ◽  
Aluminium Alloy ◽  
Fatigue Testing ◽  
Hot Spot ◽  
Fatigue Tests ◽  
Material Strength ◽  
Original Design ◽  
Hot Spot Stress ◽  
Strength Assessment ◽  
Structural Details

Aluminium alloy is widely used structural design in light-weighting design. Due to the material strength loss in welding, fatigue strength of typical joints fabricated by aluminium alloy is more sensitive than steel joints. The aim of this study is to investigate one aluminium detail of the longitudinal through the transverse, with high-performance of fatigue strength compared to the original design. The alloy of longitudinal is AA6082-T6 and the other components (including plate and transverse) is AA5083-H2. Firstly, eight schemes of structural details with various configurations of bracket and / or stiffener are designed. Based on the finite element analyses, the stress distribution of panels with eight designed details is obtained under typical loading condition respectively. According to the principle of hot spot stress being minimum, the optimal detail is determined, which using stiffener reinforced on both sides of transverse. Secondly, the fatigue tests of the optimal detail were designed and carried out. The testing panels consist of 2-span and 3 longitudinal stiffeners, and the frame with optimal joints is located in the middle of the panels. The test panels were simply supported at two ends with applied cyclic loading in the middle panel. According to the designed loading scheme (loading level, frequency, etc.), the fatigue tests of the panels with typical detail were carried out. The hot stress and the cycle times of the typical detail under different load levels were obtained. Based on the test data, the S-N curve of the typical detail in aluminium alloy is established. Finally, the fatigue strength assessment of the typical detail in target ship is performed based on the Miner’s linear cumulative damage theory and established S-N curve. The results show that the fatigue life of proposed optimal detail meets the design requirements of the target ship. The S-N curve of the typical detail made of AA6082-T6 obtained in this study can be also used for other aluminium ships with similar structural details.

scholarly journals A novel rotor blade fatigue test setup with elliptical biaxial resonant excitation

2019 ◽  
Author(s):  
David Melcher ◽  
Moritz Bätge ◽  
Sebastian Neßlinger
Keyword(s):  
Fatigue Test ◽  
Rotor Blade ◽  
Natural Frequencies ◽  
Fatigue Testing ◽  
Fatigue Tests ◽  
Test Method ◽  
Test Time ◽  
Biaxial Test ◽  
Test Setup ◽  
Biaxial Tests

Abstract. The full-scale fatigue test of rotor blades is an important and complex part of the development of new wind turbines. It is often done for certification according to the current IEC (2014) and DNV GL AS (2015) standards. Typically, a new blade design is tested by separate uniaxial fatigue tests in both main directions of the blade, i.e. flapwise and lead-lag. These tests are time consuming and rather expensive due to a high number of required load cycles, up to 5 million. Therefore, it is important to run the test as efficiently as possible. During fatigue testing, the rotor blade is excited at or near its resonant frequency. The trend for new rotor blade designs is toward longer blades, leading to a significant drop in their natural frequencies, and a corresponding increase in test time. In order to reduce the total test time, a novel test method aims to combine the two consecutive uniaxial fatigue tests into one biaxial test. The biaxial test excites the blade in both directions at the same time and at the same frequency, resulting in an elliptical deflection path of the blade axis. Using elliptical loading, counting of damage equivalent load cycles is simplified in comparison to biaxial tests with multiple frequencies. In addition, the maximum loads in both main directions remain separated, while off axis loading is introduced. To achieve such a test, specific load elements need to be arranged to equalize the natural frequencies of the test setup for both test directions. This is accomplished by adding stiffness or inertial effects in a specific direction.

scholarly journals Innovative Adaptive Control of Material Fatigue Test Machines Using an MCS Controller

2018 ◽  
Vol 1 (1) ◽  
pp. 287-294
Author(s):  
Adam Heyduk ◽  
Krystian Kalinowski ◽  
Roman Kaula ◽  
Joachim Pielot
Keyword(s):  
Fatigue Test ◽  
Feedback Loop ◽  
Fatigue Testing ◽  
Reference Signal ◽  
Nonlinear Behavior ◽  
Fatigue Tests ◽  
Significant Deterioration ◽  
New Approach ◽  
Control Quality ◽  
Material Fatigue

Abstract The paper presents some issues related to the control of fatigue test machines based on W(t) parameter taking into account the simultaneous interaction of stress and strain. This parameter is defined as a product of these values. Such a research method represents a new approach in fatigue testing with an innovative control system. Because of the W(t) function characteristics, the system presents nonlinear behavior and there is a significant deterioration of the control quality and the controlled signal significantly differs from the reference signal waveform. This problem can be solved by introducing a nonlinear block into the feedback loop. Fatigue tests have been carried out for sinusoidal and randomized reference signal waveforms. These tests have proved that the controlled signal follows reference values with an appropriate control quality.

Fatigue Assessment of “Corroded” Mooring Chain

2019 ◽  
Author(s):  
David A. Baker ◽  
Zhen Li ◽  
Sue Wang ◽  
Xiying Zhang ◽  
Yunliang Shao ◽  
...  
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Fatigue Test ◽  
Best Practice ◽  
Fatigue Testing ◽  
Fatigue Tests ◽  
Element Analysis ◽  
Cycle Count ◽  
Remaining Fatigue Life ◽  
Mooring Chain

Abstract Assessment of corroded mooring chain for continued service is a challenging task faced by industry. Current best practice relies heavily on qualitative inspection information collected during inspection campaign. There has been little investigation into this practice and whether it is an appropriate technique or can be improved. To address this issue, the Fatigue of Corroded Mooring Chains (FoCCs) Joint Industry Project (JIP), initiated in 2016 with fifteen (15) participating organizations, including oil majors, chain manufactures, consulting firms, and classification societies, to examine assessment methods for evaluating remaining fatigue life. JIP teams were formed to progress fatigue testing and finite element objectives. One such team, comprised of ExxonMobil, ABS and Asian Star Anchor Chain, has performed an additional series of fatigue tests beyond the core JIP work effort. A fatigue test was conducted to 1) demonstrate the utility of finite element analysis in the assessment of fatigue life and 2) demonstrate performance of simulated damage. This unique fatigue test program was conducted on mooring chain with manufactured “corrosion pits” of different dimensions. All chain surface features were digitally recorded and converted into finite element models. These models were subsequently analyzed to compare with test results — both cycle count and failure location. This paper presents the findings from these fatigue tests and finite element analyses and how they can be utilized for assessment of remaining fatigue life.

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