Showing papers in "Applied Composite Materials in 2022"

Aachen Technology Overview of 3D Textile Materials and Recent Innovation and Applications

Abstract: Abstract This paper provides an overview of the recent definition, technologies and current trends regarding 3D fabrics. In this paper a definition of 3D fabrics, including spacer fabrics, is given and the recent technologies regarding weaving, braiding, weft and warp knitting and tailored fiber placement are presented. Furthermore, an overview of the latest developments in 3D fabrics at the Institut für Textiltechnik of RWTH Aachen University is presented including: large circular 3D knitting, braided and woven structures for medical purposes, newest testing methods and equipment for spacer fabrics, multiaxial fabrics for composites, warp knitted spacer fabrics for space and construction applications, ceramic matrix composite 3D braiding and 4D textiles.

Evaluating the Lightning Strike Damage Tolerance for CFRP Composite Laminates Containing Conductive Nanofillers

Abstract: Conductive nanofillers, such as carbon nanotube, graphene nanoplatelets, and carbon black particles (with diameters in nanometers) have been shown to enhance the electrical conductivity of fiber reinforced polymer matrix composites in many existing studies. The motivation is primarily for lightning strike protection, electromagnetic interference shielding, de-icing, and the manufacturing of lightweight electronic components. In this paper, we evaluate the lightning strike damage tolerance of carbon fiber reinforced polymer (CFRP) matrix composite laminates containing conductive nanofillers with varying weight fractions, including carbon black (CB), carbon nanotubes (CNT), and a mix of CB and CNT, through simulated lightning strike tests, followed by both non-destructive ultrasonic inspection and destructive sectioning to characterize the damage inflicted by the simulated lightning strike. Three-point flexural tests are performed to evaluate the residual strength retained by all CFRP specimens. Results show that lightning strike damage experienced varying levels of reduction for CFRP composite specimens containing conductive fillers in comparison to the baseline specimen without fillers. Notably, the delamination only penetrated to the interface between the 1st and 2nd layer for the specimen with 0.25 wt.% CNT in comparison to the baseline CFRP specimen for which the delamination penetrated to the interface between the 5th and 6th layer. Moreover, the retention of the flexural modulus increased from 26.5% to a maximum of 95.0% for the specimen with 0.25 wt.% hybrid CB and CNT. Yet, we show that using our chosen conductive fillers cannot fully eliminate lightning strike damage. Additionally, adding conductive fillers could compromise the flexural properties. We provide discussions on future recommendations on using conductive fillers for the lightning strike protection of CFRP composites.

Numerical Investigation of Multi-scale Characteristics of Single and Multi-layered Woven Structures

Abstract: Abstract Resin flow through multi-ply woven fabrics is affected by the fibre orientation and laminate stacking sequence during the impregnation process. This is characterised by permeability, which measures the ability of transferring fluids within a 2D or 3D layered woven fibre architecture (i.e., through a porous medium). The work aims to investigate the feasibility of characterising macro-scale flow permeability via the micro-meso-scale (dual-scale) permeability across and along woven yarns, with different structures of yarn nesting, non-shifting, and ply orientation. The permeability characterisation is performed using Ansys-Fluent software package where textile architectures and resin flow in porous media are simulated. The results show that in- and out-plane permeability of the nested, non-shifted and oriented single-ply woven preforms are different than that corresponding to multi-layered plates, making them only applicable for dual-scale permeabilities. However, with a number of plies in the multi-ply woven fabrics — e.g., 9-ply and 5-ply, for in- and out-of-plane flows, respectively — the dual-scale permeabilities can be extended to macro-flow making them applicable at all scales (multi-scale flow). The calculated in-plane multi-scale permeabilities are then used in the 2D simulations and compared with the analytical solution of the Darcy’s equation, which resulted in a very good agreement.

On the Effect of Dielectric Breakdown in UD CFRPs Subjected to Lightning Strike Using an Experimentally Validated Model

Abstract: To meet worldwide increases in energy demands Wind Turbine (WT) manufacturers are producing turbines with longer blades to generate more electrical energy. To lightweight these blades, Carbon Fibre Reinforced Polymers (CFRP) have been introduced in load carrying structures such as the WT blade sparcaps. The introduction of CFRPs presents new challenges in integrating protection from lightning strikes. The semi-conductive nature of CFRPs adds an additional electrical path to ground, and the anisotropic nature of the material properties, in particular the thermal and electrical conductivities, creates large amounts of resistive heating. The aim of this paper is to develop and validate a modelling approach to predict lightning damage in unidirectional (UD) CFRP materials. The proposed model uses an approximate approach that includes the electric field dependency to simulate dielectric breakdown. The model predictions are validated against experimental data and observations obtained from simulated direct lightning strike tests conducted on UD CFRP laminates. A comparison between the experimental results and the proposed model shows good ability to accurately predict the shape, volume, and depth of the inflicted damage. Furthermore, the proposed model is benchmarked against conventional damage models reported in literature, and a clear improvement of the predictive capability is demonstrated, especially with respect to the predicted depth of damage.

Numerical Investigation of the Effect of Open Holes on the Impact Response of CFRP Laminates

Abstract: Abstract The presence of open holes changes the behaviour of composite laminates when subjected to mechanical loads creating critical zones with a high probability of interlaminar and intralaminar damage initiation. While open holes in composite laminates are a requirement in many situations such as assembly needs, wiring, and maintenance access, their influence on the impact response of composite laminates is still poorly understood. In this paper, a numerical study was performed on Carbon Fibre Reinforced Polymer (CFRP) composite laminates with open holes subjected to low velocity impacts. The influence of the distance between open holes to impact origin, hole diameter, and the number of open holes on mechanical response and failure was studied using a FE model based on the inter-fibre failure criterion of Cuntze to account for the progressive intralaminar failure. The interlaminar failure was considered by using zero thickness cohesive elements based on the cohesive zone model. The results showed that i) open holes change the shape and size of the damage caused by low velocity impact and ii) that the presence of an open hole close to the impact origin in-plane spread of damage is stopped resulting in more severe damage and a smaller projected damage area compared to the control specimen. In addition, the presence of open holes in most cases did not change the locality of the low velocity impact but rather changed the severity of the damage in the local impact zone.

Infrared Image Processing to Guide the Identification of Damage and Dissipative Mechanisms in 3D Layer-to-Layer Woven Composites

Abstract: This article discusses techniques that aim at facilitating the identification of dissipative mechanisms activated in woven composites under cyclic loadings. The focus is put on the post-processing of thermal measurements acquired during heat build-up experiments, as these are usually used to identify the dissipation sources. The importance of motion compensation pre-processing is demonstrated as it is shown that the latter enhances the quality of the evaluated thermoelastic and dissipation fields. Two specific post-processing techniques are presented in this article. The first one analyzes temperature or thermoelastic fields and searches to detect thermal events associated with the creation of cracks. The second one is based on a Fourier decomposition of thermal fields and aims at highlighting an increased contribution of friction as a dissipation source.

Joining High Thickness Materials by Sewing – first Modelling Steps of the Stitched Place

Abstract: Abstract Many textile products are using materials with higher thickness like foams, spacer fabrics and nonwoven materials in order to provide comfortable softness of the contact surface to the body. Such materials are often joint to another external layer who have to provide optical and mechanical stability of the system, and are joined together into a 3-dimensional geometry. This paper analyses some steps of joining such materials by sewing. The forces in the sewing threads are analyzed analytically. A numerical model based on finite element method (FEM) is implemented in LS-Dyna and the process of compaction of the sewing line, based on the thread force is simulated. The thread force propagation is numerically analyzed in the time, at different friction coefficients and for different foam stiffness. All simulations demonstrate logical results and can be used as a fundament for more complex investigations and optimizations of such products.

Editorial

Abstract: Editorial

Manufacturing Defects in Thermoplastic Composite Pipes and Their Effect on the in-situ Performance of Thermoplastic Composite Pipes in Oil and Gas Applications

Abstract: Abstract Thermoplastic composite pipes (TCP) are a form of fibre reinforced thermoplastic pipes that have proven benefits such as being lightweight and non-corrosive. However, during manufacturing, certain defects are induced because of certain parameters which eventually affect TCP performance in-service. Current manufacturing techniques are challenged with on-the-spot detection as the pipe is regularly monitored. When a defect is noticed, the process stops, and action is taken. However, stopping the process is costly; hence it is vital to decrease downtime during manufacturing. Potential solutions are through process optimisation for defect reduction and an in-depth understanding of the effect of parameters that cause defect formation in the pipe. This article provides an overview of manufacturing influence on the end performance. This is intimately linked to the material features, properties, and performance in-service. The material features are the determinants for the manufacturing technique to be used. For TCP, it is a melt fusion bonding process involving heating and consolidation among other factors such as the consolidation speed and pull force. Thermal behaviour is essential at this phase as it determines the curing rate and this study indicates that laser heating is the better heat source in efficiency terms. Defects such as fibre misalignments, voids, and delamination are induced during manufactuirng are explored. The sources of these defects have been discussed herein as well as the secondary defects caused by them with the consideration of residual stress impact. The presence of manufacturing defects has been identified to influence the strength and stiffness, interlaminar shear strength, toughness, and creep performance. In addition the study shows there is a need to explore the state of the art in defect characterization during manufacturing for TCP. The in-situ characterization aims to derive high-quality TCP with reduced defects and need for repairs, and increased production rate in safe and eco-friendly conditions while maintaining the current manufacturing process. Graphical abstract

Experimental Investigation of the Interlaminar Failure of Glass/Elium® Thermoplastic Composites Manufactured With Different Processing Temperatures

Abstract: The aim of this study is to evaluate the effect of the processing temperature on the interfacial failure of glass/Elium® 150 composites. The vacuum assisted resin transfer molding technique (VARTM) was used to manufacture glass/Elium® 150 composites at three different process temperatures: room temperature (24℃), 50℃ and 80℃. The interlaminar shear strength, mode I and mode II interlaminar fracture toughness of the laminates were determined by performing the short beam shear (SBS), double cantilever beam (DCB) and end notched flexure (ENF) tests, respectively. It was found that the increase in processing temperature improved the interlaminar shear strength, mode I and mode II interlaminar fracture toughness by approximately 41%, 66% and 227%, respectively. A combined compressive and shear failure mode was found in SBS tests. Fiber bridging was present for all the composite specimens in DCB tests according to the travelling recording camera images. Fracture surface images obtained by scanning electron microscopy (SEM) after the ENF tests revealed that a better fiber-matrix bonding and a ductile matrix failure were obtained for higher processing temperatures.