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Reaction injection pultrusion (RIP) combines the injection pultrusion process with reaction injection molding (RIM) techniques to yield one of the more novel methods of thermoplastic matrix pultrusion. An experimental set‐up was designed and built to pultrude nylon‐6 RIM material and continuous E‐glassfiber. Well‐impregnated nylon‐6 composites with 66.5, 68.8, 71.1, and 73.3 vol% fiber were produced. Internal temperature profile within the die was recorded during the process, and physical properties of resulting composites were measured. This paper presents results of the effect of fiber content, die temperature profile and pulling speed variations on internal temperature profile, monomer conversion, and physical properties. The study showed that increasing pulling speed lowered both peak temperature and monomer conversion. Higher die temperatures accelerated the reaction, resulting in a higher exotherm, a higher peak temperature, and a higher monomer conversion within the range investigated. Shear strength, flexual strength, flexual modulus, and transverse tensile strength were proportional to monomer conversion. Flexual modulus increased with higher fiber content within the range observed. Data allow the proper combination of die temperature profile and pulling speed to be selected to achieve a desired level of monomer conversion and physical properties. Results of this study provide basic information required for product design with nylon‐6 composites as well as tool design, selection of processing conditions, and quality control for the process.

Abstract. Wind energy is foundational for achieving 100 % renewable electricity production and significant innovation is required as the grid expands and accommodates hybrid plant systems, energy-intensive products such as fuels, and a transitioning transportation sector. The sizable investments required for wind power plant development and integration make the financial and operational risks of change very high in all applications, but especially offshore. Dependence on a high level of modeling and simulation accuracy to mitigate risk and ensure operational performance is essential. Therefore, the modeling chain from the large-scale inflow down to the material microstructure, and all the steps in between, needs to predict how the wind turbine system will respond and perform to allow innovative solutions to enter commercial application. Critical unknowns in the design, manufacturing, and operability of future turbine and plant systems are articulated and recommendations for research action are laid out. This article focuses on the many unknowns that affect the ability to push the frontiers in the design of turbine and plant systems. Modern turbine rotors operate through the entire atmospheric boundary layer, outside the bounds of historic design assumptions, which requires reassessing design processes and approaches. Traditional aerodynamics and aeroelastic modeling approaches are pressing against the boundaries of applicability for the size and flexibility of future architectures and flow physics fundamentals. Offshore turbines have additional motion and hydrodynamic load drivers that are formidable modeling challenges requiring innovation. Uncertainty in turbine wakes complicates both structural loading and energy production estimates and requires advances in plant operations and flow control to achieve full energy capture and load alleviation potential. Opportunities in co-design can bring controls upstream into design optimization if captured in design-level models of the physical phenomena. It is a research challenge to integrate improved materials into the manufacture of ever-larger components while maintaining quality and reducing cost. High-performance computing used in high-fidelity, physics-resolving simulations offer opportunities to improve design tools through artificial intelligence and machine learning. Finally, key recommended actions needed to continue the progress of wind energy technology toward even lower cost and greater functionality are summarized.

Abstract. Wind energy is foundational for achieving 100 % renewable electricity production, and significant innovation is required as the grid expands and accommodates hybrid plant systems, energy-intensive products such as fuels, and a transitioning transportation sector. The sizable investments required for wind power plant development and integration make the financial and operational risks of change very high in all applications but especially offshore. Dependence on a high level of modeling and simulation accuracy to mitigate risk and ensure operational performance is essential. Therefore, the modeling chain from the large-scale inflow down to the material microstructure, and all the steps in between, needs to predict how the wind turbine system will respond and perform to allow innovative solutions to enter commercial application. Critical unknowns in the design, manufacturing, and operability of future turbine and plant systems are articulated, and recommendations for research action are laid out. This article focuses on the many unknowns that affect the ability to push the frontiers in the design of turbine and plant systems. Modern turbine rotors operate through the entire atmospheric boundary layer, outside the bounds of historic design assumptions, which requires reassessing design processes and approaches. Traditional aerodynamics and aeroelastic modeling approaches are pressing against the limits of applicability for the size and flexibility of future architectures and flow physics fundamentals. Offshore wind turbines have additional motion and hydrodynamic load drivers that are formidable modeling challenges. Uncertainty in turbine wakes complicates structural loading and energy production estimates, both around a single plant and for downstream plants, which requires innovation in plant operations and flow control to achieve full energy capture and load alleviation potential. Opportunities in co-design can bring controls upstream into design optimization if captured in design-level models of the physical phenomena. It is a research challenge to integrate improved materials into the manufacture of ever-larger components while maintaining quality and reducing cost. High-performance computing used in high-fidelity, physics-resolving simulations offer opportunities to improve design tools through artificial intelligence and machine learning, but even the high-fidelity tools are yet to be fully validated. Finally, key actions needed to continue the progress of wind energy technology toward even lower cost and greater functionality are recommended.

The initiation and growth of damage due to compressive cyclic loading was investigated in [±45n/0n]s graphite/epoxy laminates where the “effective ply thickness” was varied by allowing n to take on the values 1, 2, and 3. A total of 35 axially loaded sandwich specimens with 6.35-mm-diameter holes were cycled at 7 Hz at peak stress levels of 52% to 72% of the static ultimate compressive stress of 425 MPa (which was experimentally determined to be independent of the value of n). Out-of-plane moiré interferometry and pulse-echo ultrasound techniques were used to nondestructively inspect the specimens and showed that three distinct modes of damage growth occur in these laminates. Delamination which initiates at the hole and grows in a radial or transverse fashion occurred only in 60% of the [±45/0]s specimens. For these two types of damage, the growth was rapid and led to catastrophic failure of the specimen. The remainder of the [±45/0]s specimens and all the laminates where the effective ply thickness was doubled and tripled, [±452/02]s and [±453/03]s, exhibited delaminations which initiated at the hole edges and grew parallel to the load direction with the width of the delamination equal to the width of the hole. Catastrophic failure did not occur in these cases. There is a linear relationship between the delamination length and the logarithm of the number of applied load cycles in all these cases. However, the delamination initiated earlier and at lower stress levels for laminates with larger effective ply thicknesses. Specimen sectioning and microscopic examination show that this damage depends on the development of splitting in the 0-deg plies and subsequent delamination as a result of shear failure at the −45°/0° ply interface in the region between the splits. Several [0/±45]s and [02/±452]s coupon specimens were cycled in tension and this splitting and subsequent delamination also developed. Residual tensile strength tests conducted on graphite/epoxy coupons debonded from the honeycomb after cycling showed a 50% increase in tensile strength over undamaged specimens with 6.35-mm-diameter holes. This is attributed to the redistribution of stress around the hole due to the relieving of stress concentration in the 0-deg plies by the splitting and delamination.