Subcomponent Testing Research Articles

Cohesive zone modelling to predict crack growth under fatigue loading

This manuscript presents the partial results in the development of numerical models based on Cohesive Zone Modelling to analyse quasi-static and fatigue crack propagation in adhesive interfaces. This work applied to adhesive interface between fibre laminates and structural epoxy adhesive of a wind turbine blade 3rd shear-web connection to the trailing edge panels. Fracture characterization experiments using the Double Cantilever Beam with Unequal Bending Moments (DCB-UBM) specimen are performed, and results are used to determine different modelling parameters, such as the mixed-mode cohesive laws and fatigue damage parameters for cohesive crack propagation. The developed numerical model is compared and validated against sub-component testing on two different scale levels, using a Modified Tear Test (MTT) specimen geometry with simplified geometry and loading, and a more complex geometry sub-component specimen with a simplified Shear Web Disbond Test (SBDT). The work is carried out as part of the CORTIR-II project, funded by the Danish Ministry of Energy.

Development of the test method for wind turbine blade subcomponent under combined bending and torsion loads

The conventional full-scale wind turbine blade testing method is unable to study the detailed structural response of blades' key subcomponents under complex loads. Therefore, developing an efficient and reliable blade subcomponent testing method is of great significance for investigating the structural characteristics of blades. This paper develops an innovative blade subcomponent test method framework, which is capable of studying the structural response under combined bending and torsion load conditions. A high-fidelity finite element model corresponding to the framework that considers nonlinear factors is established. This study further investigated the influence of boundary conditions on the results. The results showed that the test method proposed in this paper is reasonable, and the experiment based on this method is successfully conducted. The contact nonlinearity and size effects will affect the accuracy of the test results, which can be avoided by adjusting the size of the clamp.

Root Causes and Mechanisms of Failure of Wind Turbine Blades: Overview

A review of the root causes and mechanisms of damage and failure to wind turbine blades is presented in this paper. In particular, the mechanisms of leading edge erosion, adhesive joint degradation, trailing edge failure, buckling and blade collapse phenomena are considered. Methods of investigation of different damage mechanisms are reviewed, including full scale testing, post-mortem analysis, incident reports, computational simulations and sub-component testing. The most endangered regions of blades include the protruding parts (tip, leading edges), tapered and transitional areas and bond lines/adhesives. Computational models of different blade damage mechanisms are discussed. The role of manufacturing defects (voids, debonding, waviness, other deviations) for the failure mechanisms of wind turbine blades is highlighted. It is concluded that the strength and durability of wind turbine blades is controlled to a large degree by the strength of adhesive joints, interfaces and thin layers (interlaminar layers, adhesives) in the blade. Possible solutions to mitigate various blade damage mechanisms are discussed.

MicroPulse DIAL (MPD) – a diode-laser-based lidar architecture for quantitative atmospheric profiling

Abstract. Continuous water vapor and temperature profiles are critically needed for improved understanding of the lower atmosphere and potential advances in weather forecasting skill. Ground-based, national-scale profiling networks are part of a suite of instruments to provide such observations; however, the technological method must be cost-effective and quantitative. We have been developing an active remote sensing technology based on a diode-laser-based lidar technology to address this observational need. Narrowband, high-spectral-fidelity diode lasers enable accurate and calibration-free measurements requiring a minimal set of assumptions based on direct absorption (Beer–Lambert law) and a ratio of two signals. These well-proven quantitative methods are known as differential absorption lidar (DIAL) and high-spectral-resolution lidar (HSRL). This diode-laser-based architecture, characterized by less powerful laser transmitters than those historically used for atmospheric studies, can be made eye-safe and robust. Nevertheless, it also requires solar background suppression techniques such as narrow-field-of-view receivers with an ultra-narrow bandpass to observe individual photons backscattered from the atmosphere. We discuss this diode-laser-based lidar architecture's latest generation and analyze how it addresses a national-scale profiling network's need to provide continuous thermodynamic observations. The work presented focuses on general architecture changes that pertain to both the water vapor and the temperature profiling capabilities of the MicroPulse DIAL (MPD). However, the specific subcomponent testing and instrument validation presented are for the water vapor measurements only. A fiber-coupled seed laser transmitter optimization is performed and shown to meet all of the requirements for the DIAL technique. Further improvements – such as a fiber-coupled near-range receiver, the ability to perform quality control via automatic receiver scanning, advanced multi-channel scalar capabilities, and advanced processing techniques – are discussed. These new developments increase narrowband DIAL technology readiness and are shown to allow higher-quality water vapor measurements closer to the surface via preliminary intercomparisons within the MPD network itself and with radiosondes.

Understanding progressive failure mechanisms of a wind turbine blade trailing edge section through subcomponent tests and nonlinear FE analysis

This paper presents a comprehensive study on structural failure of a trailing edge section cut from a composite wind turbine blade. The focus is placed on understanding progressive failure behavior of the trailing edge section in subcomponent testing during its entire failure sequence. Digital Image Correlation (DIC) is used to capture buckling deformation and strain distributions of the specimen. Detailed post-test inspection is performed to identify failure modes and failure characteristics. A nonlinear Finite Element (FE) model that accounts for all observed failure modes is developed based on continuum damage mechanics and progressive failure analysis techniques. Multiple structural nonlinearities due to buckling, contact and material failures are included in the model to predict the failure process. The study shows that in addition to the buckling-driven failure phenomenon, the surface contact of sandwich panels contributes to the failure process of the trailing edge section. Foam materials start to fail before the ultimate load-carrying capacity of the specimen is reached, while both composite materials and adhesive materials fail in the post-peak regime. The matrix-dominant failure and delamination develop before the fiber-dominant failure in composite laminates. The proposed FE model captures the progressive failure process of the trailing edge section reasonably well.

Trailing edge subcomponent testing for wind turbine blades–Part A: Comparison of concepts

AbstractAs a complement to the mandatory structural full‐scale test for wind turbine blades, the method of subcomponent testing has recently been proposed by international standards and guidelines for the experimental investigation of design‐critical full‐scale parts. This work investigated different subcomponent test (SCT) concepts for a trailing edge of an outboard segment from a 34‐m blade. Detailed analytical models to design the SCT concepts with regard to the boundary conditions were derived. Finite element analyses of the SCT's linear response were benchmarked against each other and against the full blade model in terms of displacements, rotations, in‐plane strains, and energy consumption. All SCT concepts were in good agreement with the full‐scale test with respect to the longitudinal strain response but showed deviations in the transverse and shear strain, as well as in the rotational and displacement response.

Benefits of subcomponent over full-scale blade testing elaborated on a trailing-edge bond line design validation

Abstract. Wind turbine rotor blades are designed and certified according to the current IEC (2012) (International Electrotechnical Commission) and DNV GL AS (2015) (Det Norske Veritas Germanischer Lloyd Aksjeselskap) standards, which include the final full-scale experiment. The experiment is used to validate the assumptions made in the design models. In this work the drawbacks of traditional static and fatigue full-scale testing are elaborated, i.e., the replication of realistic loading and structural response. Subcomponent testing is proposed as a potential method to mitigate some of the drawbacks. Compared to the actual loading that a rotor blade is subjected to under field conditions, the full-scale test loading is subjected to the following simplifications and constraints: first, the full-scale fatigue test is conducted as a cyclic test, wherein the load time series obtained from aeroservoelastic simulations are simplified to a damage-equivalent load range. Second, the load directions are typically applied solely in two directions, often pure lead–lag and flapwise directions which are not necessarily the most critical load directions for a particular blade segment. Third, parts of the blade are overloaded by up to 20 % to achieve the target load along the whole span. Fourth, parts of the blade are not tested due to load introduction via load frames. Finally, another downside of a state-of-the-art, uni-axial, resonant, full-scale testing method is that dynamic testing at the eigenfrequencies of today's blades with respect to the first flapwise mode between 0.4 and 1.0 Hz results in long test times. Testing usually takes several months. In contrast, the subcomponent fatigue testing time can be substantially shorter than the full-scale blade test since (a) the load can be introduced with higher frequencies which are not constrained by the blade's eigenfrequency, and (b) the stress ratio between the minimum and the maximum stress exposure to which the structure is subjected can be increased to more realistic values. Furthermore, subcomponent testing could increase the structural reliability by focusing on the critical areas and replicating the design loads more accurately in the most critical directions. In this work, the comparison of the two testing methods is elaborated by way of example on a trailing-edge bond line design.

Similitude analysis of thin-walled composite I-beams for subcomponent testing of wind turbine blades

In this study, the I-beam structure of a utility-scale blade is used as the basis for the design of a small-scale subcomponent emulating the same type of structural element of a utility-scale wind turbine blade. Governing equations for the bending of a shear deformable thin-walled composite I-beam are considered. Similitude theory is applied to derive the corresponding scaling laws. Accuracy of the derived scaling laws in predicting the strain and displacement fields of the full-scale I-beam is considered as a design criterion for small-scale I-beams. Both complete and partial similarity cases are discussed. A novel approach is proposed to design partially similar scaled I-beams with totally different layups from those of the full-scale I-beam. Using the proposed technique, scaled-down composite I-beams are designed that predict the strain and displacement fields of their full-scale parent I-beam with very good accuracy.

Physics Analysis and Optimization Studies for a Fusion Neutron Source Based on a Gas Dynamic Trap

To further investigate the fusion neutron source based on a gas dynamic trap (GDT), characteristics of the GDT were analyzed and physics analyses were made for a fusion neutron source based on the GDT concept. The prior design of a GDT-based fusion neutron source was optimized based on a refreshed understanding of GDT operation. A two-step progressive development route of a GDT-based fusion neutron source was suggested. Potential applications of GDT are discussed. Preliminary analyses show that a fusion neutron source based on the GDT concept is suitable for plasma-material interaction research, fusion material and subcomponent testing, and capable of driving a proof-of-principle fusion fission hybrid experimental facility.

A Gas Dynamic Trap Neutron Source for Fusion Material and Subcomponent Testing

The successful operation (with β ≤ 60%, classical ions and electrons with Te = 250 eV) of the gas dynamic trap device at the Budker Institute of Nuclear Physics in Novosibirsk, Russia, extrapolates to a 2 MW/m2 dynamic trap neutron source (DTNS), which burns only ~100 g of tritium per full-power year. The DTNS has no physics, engineering, or technology showstoppers; the extension of neutral beam lines to steady state can use demonstrated engineering; and it supports near-term tokamaks and volume neutron sources. The DTNS provides a neutron spectrum similar to that of ITER and satisfies the missions specified by the materials community to test fusion materials (listed as one of the top grand challenges for engineering in the 21st century by the U.S. National Academy of Engineering) and subcomponents (including tritium-breeding blankets) needed to construct DEMO. The DTNS could serve as the first fusion nuclear science facility (FNSF), called for by ReNeW (the Research Needs Workshop), and could provide the data necessary for licensing subsequent FSNFs.

Driven dart impact response and simulation of a multi-layer HDPE

A finite element (FE) modelling method consists of FE representation of the structure and material model(s) with input parameters. To develop a suitable FE modelling method representing the deformation of multi-layer high-density polyethylene (HDPE) fuel tanks in crash events, a combined experimental and computational approach was proposed. It included material characterisation, material modelling, FE simulations and experimental validations at the levels of subcomponent and full-size structures. This paper focuses on the modelling of multi-layer HDPE under impact loading. Driven dart impact experiment was carried out at different rates at ambient temperature and −40°C. A plasticity material law with rate-dependent yield and failure was employed to simulate the large deformation and fracture behaviours of multi-layer HDPE under impact. The results showed that the impact responses of the multi-layer HDPE can be obtained by FE simulations using plasticity material models. However, some of the material parameters obtained from uniaxial tension experiments need to be adjusted to simulate the driven dart impact where biaxial tension presents, indicating that material models established solely with uniaxial test data may not be sufficient at structural levels. To validate material models, subcomponent testing and modelling is necessary.

The influence of flow-induced anisotropy on the impact behaviour of injection-moulded short-fibre composites

The objective of this paper was to develop further the concept of subcomponent testing, as suggested by Stephenson, Turner and Whale, to cover an assessment of the impact properties of polymer and composite components. To this end disks of polypropylene and glass-fibre-reinforced polypropylene were cut from plaques moulded with a range of gateing systems and subjected to mechanical testing at a range of speeds. Slow indentation testing could not distinguish between disks with or without a central weld-line, whereas instrumented falling-weight impact tests produced different failure modes and significant changes in the amount of energy absorbed between specimen subsets. The concept of sub-component testing is supported by these results while the need for the sub-components to be tested over a realistic range of conditions is highlighted.

Multidimensional gas turbine combustion modeling Applications and limitations

I. Introduction A TYPICAL empirical gas turbine cornbustor design and jTlLdevelopment approach is based on extensive use of an experience data base and empirical (semianalytical) correlations along with extensive component and subcomponent testing. Such an approach has historically been fairly successful in developing combustors based on proved design concepts. Empirical methods exhibit limitations in a number of critical areas, some of which are: 1) Empirically based design methods have shown severe limitations in scaling combustors. 2) If significantly big jumps are required in the technology levels (e.g., combustor temperature rise, cycle pressure ratio, cornbustor performance, and durability levels), combustion engineers are hesitant to use empirical correlations based on an available experimental data base. 3) The applicability of experience correlations (developed for a certain design concept) is quite limited for some other novel or revolutionary combustion concepts. 4) With ever exacting design requirements of advanced technology combustors (combustor operating conditions, wide operability, low smoke, and significantly improved durability characteristics), better tools are needed to achieve an optimum solution to satisfy conflicting combustor design requirements. The first extensive effort to develop and demonstrate an empirical/analytical combustor design methodology was initiated by the U.S. Army Research and Technology Laboratories in 1975. This technique was successfully applied in the design and development testing of two full-scale small reverse-flow annular combustors.1 Simultaneously, this new methodology was being used and refined under the NASA Pollution Reduction Technology Program. How this method was used for the design and development testing of a premix/prevaporized combustor is described in Ref. 2. In parallel with these two efforts, the empirical/analytical design procedure was being used for developing a ceramic combustor, which needed to have significantly lower wall temperature gradients for structural durability.3'4 Subsequent to successful applications of the empirical/analytical combustor design methodology, a number of advanced technology combustors have been developed with the aid of analytical models, as described in Sec. III. Section II describes the methodology. Although the method has been useful in providing design guidance, the model limitations are evident in regard to accuracy of the state-ofthe-art numerics and physical submodels of turbulence, turbulence/chemistry interaction, spray evaporation/mixing, soot formation/oxidation, and radiation. Some of these deficiencies are discussed in Sees. IV and V.

Materials and design aspects of the RIGGATRON TM tokamak

The successful development of the RIGGATRON TM tokamak depends on the close coupling of analysis, design, materials/fabrication development and testing. Operating conditions in these compact, high-field copper alloy machines are considerably more severe than in conventional superconducting tokamaks. The design needs of the critical components, including the toroidal field coil, the ohmic heating coil, and the first wall/vacuum vessel have resulted in the development, testing and qualification of high-strength, high-conductivity copper alloys, new dielectric concepts and advanced fabrication techniques. Intensive materials property testing on conductor alloys and dielectric materials has led to the definition of specific design criteria for the relatively short lifetime RIGGATRON devices. To date, the key design and materials issues related to the construction of the FDX experimental machines have been resolved, and the program is moving into the design verification, subcomponent testing and prototype manufacturing stage.