Flexural Fatigue of Unbalanced Glass-Carbon Hybrid Composites

Unbalanced composite layups with bend-twist coupling show potential for aeroelastic tailoring in wind turbine blades. Before these materials can be implemented, their responses to long term cyclic loading must be considered. This paper studies the fatigue characteristics of an unbalanced glass-carbon hybrid laminate with a [45 glass /À45 glass / 24 carbon /24 carbon ] s layup. Flexural fatigue was performed at 7 different load magnitudes up to 1 Â 10 6 cycles to characterize the failure modes and fatigue life of the composite. Stiffness degradation occurred on the tension side due to matrix cracking and small regions of delamination on the glass plies, whereas the failure mechanism of the laminate was by delamination between the glass and carbon. S-N curves were generated from experimental results and static finite element analyses (FEA) based on interlaminar shear stresses and were compared with laminates from previous literature. It was determined that the interlaminar stresses were influenced more so by the lower stiffness of the unbalanced layup than by the induced torsional deflections: leading to the conclusion that bend-twist coupling had little influence on flexural fatigue of glass-carbon hybrid composites

A computational iterative design method for bend-twist deformation in composite ship propeller blades for thrusters

This study investigates the feasibility of utilising common composite material layup techniques in ship propeller blade design to achieve an automatic pitch adjustment through bending-induced twist deformation. A comprehensive design approach, including various reinforcement materials and arrangements, was employed to attain the desired foil pitching, while minimising other undesirable deformation modes. The design process involved iterative computational analysis using finite element analysis and a deformation mode analysis based on foil shape parameters. The research showed that the proposed design approach effectively found options to improve the desired foil parameter pitch, while minimising undesirable deformation modes such as blade deflection and foil shape change. Furthermore, the proposed blade design was tested in thruster steering operational conditions and was found to have a pitch change well matched, potentially countering some changes in fluid flow. When compared to Kumar and Wurm’s design, which only focused on the angular orientation of glass reinforcement, the proposed design was found to outperform the twisting by achieving the same twist for a blade half the length. This study provides valuable insights into the utilisation of composite materials in ship propeller design and highlights the potential for further improvement through a composite engineering design approach.publishedVersio

Buckling due to external pressure of a composite tube measured by Rayleigh optical backscatter reflectometry and analyzed by finite elements

There is a growing interest in replacing steel tubes that operate in high pressure and high temperature environments with composite tubes. Such applications can include drilling risers and drill strings for the offshore oil industry. Replacing steel with composites in such applications will greatly reduce the weight of the equipment and require less buoyancy elements built into the structures. This paper seeks to investigate how composite tubes behave when submerged and how optical fibers can be used as a health monitoring system for such applications utilizing Rayleigh optical backscatter reflectometry. A glass fiber filament wound tube of 100 mm inner diameter and 600 mm length with a layup of approximately [89°, ±12.7°, ±45°] was exposed to external hydrostatic pressure in an autoclave. Optical fibers glued to the outer surface of the tube were used to measure strain during testing. A strain field reading was carried out every 0.5 bar pressure increase and correlated well with strain fields from a finite element analysis of the tube. The finite element analysis predicted buckling at 4.33 bar, assuming no material failure; however, the tube buckled at 3.5 bar due to a sudden stiffness reduction from material failure. The optical fibers could detect the early failure and functioned well as a health monitoring system

Progressive fatigue failure analysis of a filament wound ring specimen with a hole

A progressive FEA mechanical fatigue degradation model for composites was developed and implemented using a UMAT user material subroutine in Abaqus. Numerical results were compared to experimental strain field data from high frequency digital image correlation (DIC) of split disk fatigue testing of pressure vessel cut outs with holes. The model correctly predicted the onset and evolution of damage in the matrix as well as the onset of fiber failure. The model uses progressive failure analysis based on the maximum strain failure criterion, the cycle jump method, and Miner’s sum damage accumulation rule. A parameter study on matrix properties was needed to capture the scatter in strain fields observed experimentally by DIC. S-N curve for the matrix material had to be lowered by 0% to 60% to capture the experimental scatter. The onset of local fiber failure had to be described by local S-N curves measured by DIC having 2.5 times greater strain than that of S-N curves found from standard coupon testin

Progressive Fatigue Failure Analysis of a Filament Wound Ring Specimen with a Hole

A progressive FEA mechanical fatigue degradation model for composites was developed and implemented using a UMAT user material subroutine in Abaqus. Numerical results were compared to experimental strain field data from high frequency digital image correlation (DIC) of split disk fatigue testing of pressure vessel cut outs with holes. The model correctly predicted the onset and evolution of damage in the matrix as well as the onset of fiber failure. The model uses progressive failure analysis based on the maximum strain failure criterion, the cycle jump method, and Miner’s sum damage accumulation rule. A parameter study on matrix properties was needed to capture the scatter in strain fields observed experimentally by DIC. S-N curve for the matrix material had to be lowered by 0% to 60% to capture the experimental scatter. The onset of local fiber failure had to be described by local S-N curves measured by DIC having 2.5 times greater strain than that of S-N curves found from standard coupon testing

A comprehensive numerical investigation of the impact behaviour of an offshore wind turbine blade due to impact loads during installation

For installing offshore wind turbines into deep waters, use of floating crane vessels is essential. One of the major challenges is their sensitivity to wave-induced vessel and crane tip motions, which can cause the impact of lifted components like blades and nacelle with nearby structures. The impact loads on fibre composite wind turbine blades are critical as several complex damage modes, capable of affecting the structural integrity, are developed. Planning of such installation tasks therefore requires response-based operational limits that consider impact loads on the blade along with their damage quantification. The research area considering the impact behaviour of the lifted blade is novel, and thus, the paper identifies vessel, blade and lifting parameters that determine impact/contact scenarios. Furthermore, for a case in which a lifted blade with its leading edge impacts the tower, a numerical modelling technique is presented in Abaqus/Explicit, and a comprehensive damage assessment of the blade and an investigation of the impact dynamics and energy evolution are performed. Sensitivity studies for two distinct blade designs and two different impact locations are considered. The results show that 7–20% of the impact energy is absorbed as damage in the blade, whereas the majority dissipates as rigid-body motions of the blade after the impact. The findings of the study highlight the requirement for advanced installation equipment, such as active tugger lines, to prevent successive impacts of wind turbine blades during installation.submittedVersionThis is a submitted manuscript of an article published by Elsevier Ltd in Ocean Engneering, 4 December 201

Designing Composite Adaptive Propeller Blades with Passive Bend–Twist Deformation for Periodic-Load Variations Using Multiple Design Concepts

Four plausible design concepts are applied together to investigate composite bend–twist propeller-blade designs that show high twisting per bending deflection. The design concepts are first explained on a simplified blade structure with limited unique geometric features to determine generalized principles for applying the considered design concepts. Then, the design concepts are applied to another propeller-blade geometry to obtain a bend–twist propeller-blade design that achieves a specific pitch change under an operational loading condition with a significant periodic-load variation. The final composite propeller design shows several times more bend–twist efficiency than other published bend–twist designs and shows a desirable pitch change during the periodic-load variation when loaded with a one-way fluid–structure-interaction-derived load case. The high pitch change suggests that the design would mitigate undesirable blade effects caused by load variations on the propeller during operation

A Global-local Damage Assessment Methodology for Impact Damage on Offshore Wind Turbine Blades during Lifting Operations

Lifting the latest generation offshore wind turbines using floating crane vessels is extremely challenging. This comes with an elevated risk of blades impacting the tower or surrounding structures due to excessive crane tip motions from wave induced vessel motions. The wind turbine blades are primarily made of composite materials and thus are extremely vulnerable to impact loads causing complex damages and failure modes. One of the most critical damage type for wind turbine blades is delamination because delaminations cannot always be visually detected but can cause significant strength and stiffness reductions. An explicit structural response based approach was proposed in the previous work which is used to derive response based operational limits for single blade lifting operation using floating vessels considering probability of contact/impact and damages in the blade. An assessment of such impact induced damages on the blade was mentioned which includes modelling and predicting damages in the blade for different contact scenarios representing lifting operations in different sea states along with post impact residual strength estimation. This would require an efficient damage assessment methodology which can be utilized in practice with acceptable accuracy along with a reasonable computational cost. In this work, a simplified global-local based damage assessment methodology is presented. The paper focusses on ’shell-to-solid submodelling’ based impact damage prediction along with a brief outline of ’shell-solid coupling’ based residual strength study. The paper further presents the submodelling technique for impact investigations on DTU 10 MW blade section for a case when a projectile impacts the leading edge. Intraply damage mode based on Hashin failure criteria and Puck’s action plane theory was utilized as VUMAT in Abaqus-Explicit along with surface based cohesive behavior to model the inter-laminar failure mode. Finally, the damages and failure modes in the blade including impact induced delaminations are reported

A Global-local Damage Assessment Methodology for Impact Damage on Offshore Wind Turbine Blades during Lifting Operations

Lifting the latest generation offshore wind turbines using floating crane vessels is extremely challenging. This comes with an elevated risk of blades impacting the tower or surrounding structures due to excessive crane tip motions from wave induced vessel motions. The wind turbine blades are primarily made of composite materials and thus are extremely vulnerable to impact loads causing complex damages and failure modes. One of the most critical damage type for wind turbine blades is delamination because delaminations cannot always be visually detected but can cause significant strength and stiffness reductions. An explicit structural response based approach was proposed in the previous work which is used to derive response based operational limits for single blade lifting operation using floating vessels considering probability of contact/impact and damages in the blade. An assessment of such impact induced damages on the blade was mentioned which includes modelling and predicting damages in the blade for different contact scenarios representing lifting operations in different sea states along with post impact residual strength estimation. This would require an efficient damage assessment methodology which can be utilized in practice with acceptable accuracy along with a reasonable computational cost. In this work, a simplified global-local based damage assessment methodology is presented. The paper focusses on ’shell-to-solid submodelling’ based impact damage prediction along with a brief outline of ’shell-solid coupling’ based residual strength study. The paper further presents the submodelling technique for impact investigations on DTU 10 MW blade section for a case when a projectile impacts the leading edge. Intraply damage mode based on Hashin failure criteria and Puck’s action plane theory was utilized as VUMAT in Abaqus-Explicit along with surface based cohesive behavior to model the inter-laminar failure mode. Finally, the damages and failure modes in the blade including impact induced delaminations are reported.publishedVersionCopyright © 2018 by ASM

A new method for assessing anisotropy in fused deposition modeled parts using computed tomography data

Voids in fused deposition modeled (FDM) parts are assumed to be a key driver for their anisotropic behavior. However, these assumptions are based on investigations of voids using only 2D data (microscopy images). This paper presents a new method to measure such voids by analyzing 3D-data of from X-ray computed tomography (CT), and application of this data for assessment of mechanical parameters. The article is divided into three parts, where the first part elaborates on a proposed method to assess and characterize the void geometry throughout uniaxial printed FDM parts using CT-data. The second part presents an investigation of the void configurations in samples manufactured using different process parameters, aiming to understand how variation in extrusion rate and compensation for non-linear dynamic extrusion behavior affects the void sizes. The third part displays how the information regarding void sizes could be further related to global mechanical properties, using a multiscale finite element approach. The present method of CT-data analysis gives a clear overview of the spatial variation of the void geometry, and findings from the investigated samples suggest that the size of voids have a large non-random spatial variation, highly dependent on the turning points of the toolpaths, and also significantly affected by accumulation of excess material. Printing at a low extrusion rate increases the void sizes considerably, while implementation of an extrusion dynamics compensation algorithm was found to have low impact on the void sizes. The multiscale finite element approach predicts anisotropic elastic behavior, significantly more compliant in the vertical and transversal direction, relative to the printing direction of the infill. It also predicts a non-isotropic strain energy density throughout the specimen, where the location and magnitude of the most energy dense locations vary significantly for different directions of loading, which implicates an anisotropic behavior in terms of failure, in accordance with literature