Clemens Dransfeld

• Professor
• Professor at Delft University of Technology

North Thin Ply Technology (NTPT) supplies a wide range of high performance thin ply prepreg materials. Thin plies are now used in a wide range of high-performance composite applications such as aerospace, motorsport, sporting equipment and many others. NTPT's thin ply technology is based on the concept of plotting 2-dimensional multilayered preform...

Fast-curing epoxy polymers allow thermoset parts to be manufactured in minutes, but the curing reaction is highly exothermic with heat flows up to 20 times higher than conventional epoxies. The low thermal conductivity of the polymer causes the mechanical and kinetic properties of parts to vary through their thickness. In the present work, silica n...

Thin-ply composites are rapidly gaining interest in the composite industry, not only because of the larger design possibilities that they offer, but also because of positive size effects that have been shown to improve performance in various loading conditions [1]. In this work, carbon fiber-epoxy composites of different ply thicknesses (30g/m2 to...

Understanding the microstructural variability in unidirectional composite prepreg tapes is relevant to investigating mechanisms of tape microstructure formation, their impact on its processability and the mechanical performance of the final composite part. It has been shown that three-dimensional microstructural variability at the single-fibre leve...

Ultrasonic welding of fibre-reinforced thermoplastics is a joining technology with high potential for short welding times and low energy consumption. While the majority of the current studies on continuous ultrasonic welding have so far focused on woven reinforcements, unidirectional materials are preferred for highly loaded aerospace components du...

This study focuses on the spring-back as a function of the degree of cure on single-curved metal-composite laminates. The manufacturing through a hot-pressing process involves different (curing) stages and can reduce the spring-back with the proper combination of forming and curing. The cure-dependent spring-back is measured and analysed as a funct...

The research focuses on the simultaneous deformation of uncured metal-composite laminates under the press forming process of a double-curved dome part. The study is designed to evaluate the influence of material type, inter-ply friction and clamping force by the use of a finite element modelling method. The result shows that the main failure mode f...

Modeling the consolidation of fiber‐reinforced thermoplastic composites at the part level presents a formidable computational challenge due to the multi‐scale nature of the process. In this article, a method to bypass the multi‐scale problem by homogenizing the micro scale and describing the medium with characteristic parameters is described. The m...

The aim of this study was to characterise the microstructural organisation of staple carbon fibre-reinforced polymer composites and to investigate their mechanical properties. Conventionally, fibre-reinforced materials are manufactured using continuous fibres. However, discontinuous fibres are crucial for developing sustainable structural second-li...

Toughness of epoxies is commonly improved by adding thermoplastic phases, which is achieved through dissolution and phase separation at the microscale. However, little is known about the synergistic effects of toughening phases on multiple scales. Therefore, here, we study the toughening of epoxies with layered poly(ether imide) (PEI) structures at...

Chopped Tape Thermoplastic Composites (CTTCs) offer high formability and performance for complex-shaped components in the aerospace and automotive industries. However, the mesoscopic discontinuity leads to spatial variabilities and correspondingly high scatter in the elastic properties of CTTCs due to the random orientations of chopped tapes and ch...

Autoclave curing is one of the most energy consuming processes in manufacturing carbon fibre reinforced polymers. In order to improve the energy efficiency, one needs to understand energy usage in an autoclave and factors that influence it. This work presents two thermodynamic based models for estimating energy consumption in an autoclave. The firs...

A new model is proposed for the consolidation of hybrid textiles, in which air entrapment and dissolution are considered. One of the key parameters is tow permeability, which is described by the analytical model of Gebart and validated at very high fibre volume fractions by direct tow permeability measurement. The model also takes into account the...

Thermoplastic compression resin transfer moulding coupled with injection moulding is an appealing process for the production of thermoplastic composites. However, its implementation at an industrial scale remains challenging as variotherm injection moulding could prevent solid skin formation in the parting line, making cavity sealing difficult. In...

Carbon fibre/epoxy composite joints were assembled with Poly-etherether-ketone (PEEK) and Poly-ethylenimine (PEI) films using a co-curing process to prepare single-lap joint specimens. The joints were tested under quasi-static loading conditions at 22 °C and 130 °C and a fatigue loading condition. The experimental results demonstrated better or com...

Discontinuous tape composites have considerable attention due to their high formability and tailorable structures. Despite their advantages, this discontinuity leads to complex structures and makes it difficult to predict their mechanical properties. On the other hand, they have high orientational and dimensional sensitivity, which causes spatial v...

Discontinuous tape composites (DTC) have properties such as notch insensitivity, short processing times, and large shaping freedom. However, the mechanical behaviour of randomly oriented tape (ROT) composites is less predictable compared to continuous fibre composites due to the mesoscopic heterogeneity of the material. Controlling the tape alignme...

Exploring routes for the effective use of recycled carbon fibres (rCFs) is critical to close the loop in the life cycle of carbon fibres. This work demonstrated a potential of using rCFs for interlayer toughening of carbon fibre/epoxy composites. Nonwoven mats based on rCFs and commingled rCFs/Polyphenylene-sulfid (PPS) fibres were used to interlay...

The unique sensing features of the tilted Fibre Bragg Grating (TFBG) as a single three-parameter optical sensor are demonstrated in this work, to monitor the manufacturing process of composite materials produced using Vacuum Assisted Resin Transfer Moulding (VARTM) process. Each TFBG sensor can measure simultaneously and separately strain, temperat...

This study presents two novel methods for in situ characterization of the reaction-diffusion process during the co-curing of a polyetherimide thermoplastic interlayer with an epoxy-amine thermoset. The first method was based on hot stage experiments using a computer vision point tracker algorithm to detect and trace diffusion fronts, and the second...

Epoxies are inherently brittle materials and to overcome this brittleness, a second microphase (i.e., thermoplastic) is typically added. This modification of epoxy resin using thermoplastics results in reaction-induced phase separating morphologies in the micrometer range. In this study, the influence of the curing history, beyond phase separation,...

The outstanding properties of carbon fibre-reinforced polymer composites are affected by the development of its microstructure during processing. This work presents a novel approach to identify microstructural features both along the tape thickness and through the thickness. Voronoi tessellation-based evaluation of the fibre volume content on cross...

The effects of laser-induced deconsolidation on the compaction process of CF/PEEK tapes were investigated. First, tapes with different degrees of deconsolidation were manufactured using a laser heater. This procedure re- sulted in samples with different waviness, thickness, void content and surface roughness values. Then, as-received and laser-deco...

Forming process with pre-stacked and uncured thermoset fibre metal laminate offers improved deformability compared to full-cured laminate especially for the production of complex structural components. This work investigated the friction behaviour at the metal-prepreg interface of glass fibre reinforced aluminium laminate through an inter-ply frict...

Understanding the three-dimensional variability of unidirectional composites is relevant to the material performance and the development of advanced material modelling strategies. This work proposes a new methodology for the characterisation of unidirectional composites, showcased on carbon fibre/poly(ether-ether-ketone) tapes. Three microstructura...

In this study, the effect of rapid laser heating, which is typical during laser-assisted fiber placement (LAFP), on the micro- and meso- structure of the thermoplastic tape was investigated. Thermoplastic tapes were heated above the melting temperature with different heated lengths (30 and 80 mm and heating times (0.2 and 0.8 s) in a dedicated expe...

The out-of-plane permeability of two glass fibre fabrics was measured by 26 institutions using silicone oil as a test fluid. Participants in this study were free to select the test procedure, specimen dimensions and data analysis method, provided that testing was carried out at three target fibre volume fractions, 46 %, 50 % and 54 %. While results...

The effect of thermal contact resistance (TCR) correlated to the degree of intimate contact (DIC) between the incoming tape and the substrate on the temperature history during laser-assisted fiber placement (LAFP) was investigated. A novel experimental methodology was designed to understand the effect with a non-contact method which did not influen...

Ultrasonic welding is a promising technology to join fibre-reinforced thermoplastic composites. While current studies are mostly limited to fabric materials the applicability to unidirectional materials, as found in aerospace structures, would offer opportunities for joining primary aircraft structures. However, due to the highly anisotropic flow o...

This paper reports the results of an international benchmark exercise on the measurement of fibre bed compaction behaviour. The aim was to identify aspects of the test method critical to obtain reliable results and to arrive at a recommended test procedure for fibre bed compaction measurements. A glass fibre 2/2 twill weave and a biaxial (±45°) gla...

The effect of ply thickness on the notch sensitivity and bearing properties on carbon fibre reinforced polymer composites and their hybrid laminates with steel foils were studied. Laminates with ply thicknesses of 0.3 mm and 0.03 mm comprising of CFRP and hybrid laminates were manufactured and characterized using tension, open hole tension and doub...

ConThP: Consolidation of thermoplastic hybrid yarn materials Hybrid yarn materials are rarely used since the simulation of complex shapes is not possible with state-of-the-art models. Therefore, a 3D consolidation approach is developed and implemented into finite element analysis. Impregnation is investigated based on a model textile topology consi...

About a century ago, Knudsen derived the groundbreaking theory of gas diffusion through straight pipes and holes, which since then found widespread application in innumerable fields of science and inspired the development of vacuum and related coating technologies, from academic research to numerous industrial sectors. Knudsen's theory can be strai...

Epoxy resins are widely used for different commercial applications, particularly in the aerospace industry as matrix carbon fibre reinforced polymers composite. This is due to their excellent properties, i.e., ease of processing, low cost, superior mechanical, thermal and electrical properties. However, a pure epoxy system possesses some inherent s...

Interlaying thermoplastic veils into carbon fibre/epoxy composites has proved to significantly increase the interlaminar fracture toughness. The main toughening mechanism is thermoplastic fibre bridging for the non-meltable veils and matrix toughening for the meltable veils. Herein, to take advantage of different toughening mechanisms, hybrid melta...

A high-power UV-irradiation technique was proposed for the surface treatment of PPS and PEEK composites, aiming to achieve good adhesion with epoxy adhesives. The composite substrates were rapidly UV-irradiated for a duration of between 2-30 s, and then bonded using an aerospace film adhesive to produce joints. Tensile lap-shear strength and mode-I...

About a century ago, Knudsen derived the groundbreaking theory of gas diffusion through straight pipes and holes, which since then found widespread application in innumerable fields of science and inspired the development of vacuum and related coating technologies, from academic research to numerous industrial sectors. Knudsen's theory can be strai...

Efficient joining of hybrid thermoset/thermoplastic composite joints is critical to produce high performance lightweight structures while keeping the cost low. Herein, a high-power UV-irradiation technique was proposed to rapidly active the surfaces of PEEK and PPS composites for the following co-cure joining with epoxy composites. A single lap-she...

The compatibility between the majority of thermoplastic veils (TPVs) and epoxies is typically poor, owing to the inherently low surface energies of thermoplastics. This tends to largely affect the toughening performance of TPVs as interlayer materials of carbon fibre/epoxy composites. The traditional methods for surface activation of thermoplastics...

In this work, we will demonstrate the abilities of tilted Fibre Bragg Grating (TFBG) as single three-parameter optical sensor, in monitoring the curing process and the internal state of thin and thick glass/epoxy composites manufactured using vacuum assisted resin infusion process. The TFBG sensors are embedded between the layers of the composite m...

Intimate contact development under LAFP-specific thermal and mechanical boundary conditions/interactions and the effect of process parameters are investigated. One-layer, unidirectional strips of CF/PEKK material were placed with different process parameters on a flat tool surface to create different intimate contact conditions. The concept of effe...

Passive spanwise bending shape-adaption has the potential to increase the efficiency and manoeuvrability of vehicles with wing-like structures. By utilisation of compression flange buckling, the in-plane stiffness can be tuned to design beams with contrasting pre-buckling and post-buckling bending stiffness. The investigated concept is experimental...

Passive spanwise bending shape-adaption has the potential to increase the efficiency and manoeuvrability of vehicles with wing-like structures. By utilisation of compression flange buckling, the in-plane stiffness can be tuned to design beams with contrasting pre-buckling and post-buckling bending stiffness. The investigated concept is experimental...

Delignified densified wood represents a new promising lightweight, high-performance and bio-based material with great potential to partially substitute natural fiber reinforced- or glass fiber reinforced composites in the future. We here present two versatile fabrication routes and demonstrate the possibility to create complex composite parts.

The development of sustainable materials from renewable resources is one of the key challenges in today's materials science. Wood has great potential to play an important role in future materials advancement due to its excellent mechanical properties and high abundance. In this regard, two novel concepts for the development of high-performance wood...

Natural materials such as wood exhibit high mechanical properties through cellulose structured at multiple length scales and embedded in a matrix of similar chemical structure. These hierarchical materials have inspired the design of lightweight composites composed of naturally occurring polymers. However, the close proximity of melt and decomposit...

To reduce the cycle time of structural, automotive thermoplastic composites, we investigated the potential of direct thermoplastic melt impregnation of glass fabrics using an injection moulding process. At the high pressures that occur during the process, the effect of the fabric architecture on the impregnation, compaction, volume fraction and per...

Natural fibre (NF) reinforced composites offer high specific mechanical properties and are an ecological alternative to synthetic fibre-reinforced composites. While having great potential, their use today is limited to non-structural applications, mostly with epoxy or polypropylene matrices. This work studies suitable high-performance thermoplastic...

Within this study, the resistance welding of thermoset composite with thermoplastic boundary layers was investigated. The specimens were prepared by co-curing a thermoplastic layer, which created an interphase with the epoxy matrix by reaction induced phase separation. The resistance welding of such specimens was investigated in a custom built weld...

Reinforced polymer‐based composites are attractive lightweight materials for aircrafts, automobiles, and turbine blades, but still show strength and fracture toughness lower than traditional metals. An interesting approach to address this issue is to fabricate composites with structural features that absorb part of the elastic energy stored in the...

Thin-ply composites represent a promising approach to further improve the performance of carbon fibre composite structures thanks to their ability to delay the onset of matrix cracking and delamination up to the point of fibre dominated failure. However, this increased strength comes with a more brittle failure response which raises concerns on dam...

To evaluate compatibility between a substrate and a thermoplastic polymer, the established methodology is to estimate their surface composition in terms of surface energy components, utilizing the results of contact angle measurements of probe liquids onto substrate and polymer surfaces at room temperature. Using this methodology, polymer surfaces...

Fast-cure epoxy systems are used for the mass production of composite parts with cycle times in the minute range. One of the major difficulties observed when processing fast-cure resins is their strong exothermic reaction during cure. This may result in a significant temperature overshoot and large temperature gradients over the thickness, and ther...

The direct growth of carbon nanotubes (CNTs) on carbon fibres (CF) is a novel approach for a secondary reinforcement and an increase of surface area of the CF-matrix interface in composite materials. We are coating the CF with an alumina film by means of atomic layer deposition (ALD) in order to protect them during the process. We propose a new str...

Carbon fibre reinforced polymer (CFRP) parts can be functionalized with thermoplastic surfaces in order to be assembled through welding as a cost-efficient alternative to traditional joining techniques such as mechanical fastening or adhesive bonding. In the process of functionalizing the CFRP, curing an epoxy resin in the presence of a thermoplast...

The core – sheath interfacial interactions in a bicomponent thermoplastic filament have been analyzed by means of an adapted micro-mechanical approach for interfacial pull-out. The method relies on a specimen preparation procedure that selectively removes a segment of the sheath component while leaving the core intact. This adaptation of the classi...

The increasing use of carbon fibre reinforced polymer (CFRP) composites in aviation and automotive industries has led to the adoption of automated production methods such as pultrusion or resin transfer moulding (RTM) for cost reduction in the production lightweight structures. These processes however, offer limited freedom to locally reinforce str...

Thermoplastic matrix materials have advantages of fast processing, recyclability, high fracture toughness and offer alternative joining processes like welding. However, thermoplastic matrix materials have a higher viscosity than thermoset resins, which makes the impregnation of fabrics more difficult, especially at the high fibre volume fractions n...

The importance of the interphase as the material part for transferring stress is widely recognized [1]; however, the wetting behaviour of molten polymers during composite manufacturing or how the interface is formed at high temperature between the molten thermoplastic and the hot fibre surface are yet to be studied in detail. The final mechanical p...

To simultaneously address the lower toughness and the build-up of internal heat for fast-curing epoxy matrices, the influence of nominal 100 nm and 300 nm core-shell rubber (CSR) particles on the properties and rheo-kinetics were studied. The fracture energy was enhanced by a factor of 14.5, up to 2572 ± 84 J m⁻² with 14.5 wt% of the nominal 300 nm...

The rheological properties of epoxy matrices and adhesives during cure are modelled in this work. Three epoxy-amine systems, designed for different applications with distinct curing behaviours, were investigated. Curing times ranged from a few seconds to upwards of 220 min depending on the cure temperature and formulation of the epoxy. The presente...

The damping behaviour of continuous carbon fibre and flax fibre reinforced polymer (CFRP and FFRP) composites was studied by comparing angle-ply laminates. Using logarithmic decrement measurements, dynamic mechanical analysis and vibration beam measurements, the damping was described as the specific damping capacity ψ in order to compare data using...

Composite materials based on carbon fiber (CF) are prone to failure at the fiber-matrix interface upon compression or stress transverse to the fiber axis. The direct growth of carbon nanotubes on CF constitutes a novel approach to enhance the mechanical properties of the interface. However, the challenge is that, during the growth, tensile properti...

Fast-curing epoxies allow parts to be manufactured in minutes, but the curing is highly exo-thermic and the low thermal conductivity causes the properties vary through the thickness. The addition of silica or core-shell rubber nanoparticles reduces the exotherm, and improves the mechanical properties. Little toughening was obtained with silica nano...

This article describes how the strong exothermic reaction of a fast-cure epoxy can be better controlled with the addition of non-reactive silica nanoparticles, further enhancing the benefits of a fast process, the toughness and the ability to understand the properties of thicker composite parts. F ast-cure epoxy systems are used for the mass produc...

The objective of this paper was to understand the damping of carbon-and flax-fibre reinforce polymers. We analysed carbon and flax symmetric angle ply laminates for a series of layup angles of 0 • , ±10 • , ±20 • , ±30 • , ±60 • , 90 •. We measured both series using dynamic mechanical analysis (DMA) and vibration beam measurements (VBM). Our result...

Natural fibres (NF) have shown to be a suitable alternative to glass fibres as reinforcing material in polymer composites since they offer similar specific strength and stiffness. Thus, those composites may be readily used in the automotive, sport and leisure. However, most of today's natural fibre applications are based on discontinuous fibre arch...

Thermoplastic carbon fibre reinforced polymers (CFRP) have a potential for recycling by re-melting the polymeric matrix. The authors choose a novel approach to separate thermoplastic CFRPs into fragments using high voltage pulses through a method known as electrodynamic fragmentation (EDF). The method was applied to a rotorcraft door hinge which wa...

Natural fibre thermoplastic composites may be manufactured using a film stacking process, where fibre-preforms and matrix films are stacked alternately. The process has shown great potential due to the high flexibility referring to the stacking sequence and the using of simple tooling concepts, which may easily be scaled for industrial applications...

In this paper the influence of the fabric architecture on the processing window for a pressure controlled through-thickness impregnation of dry fabrics with thermoplastic melt is discussed by measuring and implementing the compaction and permeability behaviour of two reference fabrics in a numerical analysis of the impregnation process. For the two...

The failure of carbon fibre reinforced polymers (CFRP) is typically governed by compressive failure in the fibre direction or insufficient transverse strength and occurs at a fibre-matrix interface. A novel approach of enhancement of the interface is the development of hierarchical composites based on growth of carbon nanotubes (CNT) on the carbon...

Fast-cure resins combined with high pressure liquid composite moulding processes (LCM) such as compression resin transfer moulding (CRTM) may be used to produce composite parts with cycle times of only a few minutes. Processing of such fast-cure resins adds difficulties to manufacturing due to the high exothermic reaction during cure, where gelatio...

The advantages of thin-ply composites such as increased onset of damage, much improved fatigue life and hot-wet resistance have been shown in several recent studies. The decreased inter- and translaminar toughness and the lack of a highly toughened thin-ply system constituted drawbacks limiting their potential application to damage-tolerance driven...

The objective of this paper was to develop cure kinetic models to describe the B-stage curing and co-curing assembly of carbon fibre reinforced thermosetting polymer (CFRP) composites. Starting from the analytical model, temperature cycles and experimental procedures are developed to join a B-stage CFRP part to a reinforcing B-stage CFRP patch for...

The end of life of carbon fibre-reinforced polymer (CFRP) structures represents a major challenge to the aerospace industry, as new European regulations are demanding recycling solutions that can be complicated and expensive to apply. This study aims to address new practical ways to recycle CFRP materials. CFRP materials with a polyether ether keto...

In this study, composites with discontinuous 'brick-and-mortar' architecture, consisting of conceptually stiff load-carrying bricks connected by a mortar material, were treated. The bricks were composed of unidirectional pre-impregnated tapes with a thermoplastic matrix, and a very thin interface of thermoplastic material represented the mortar. Th...

Fast-curing epoxy polymers allow composite parts to be manufactured in minutes, but the curing reaction is highly exothermic with heat flows up to 20 times higher than conventional epoxies. The low thermal conductivity of the polymer causes the mechanical and kinetic properties of parts to vary through their thickness. In the present work, silica n...

The objective was to study the bearing properties of steel foil and carbon fibre reinforced polymer composite (St-CFRP) laminates. Extremely thin carbon fibre plies offer an improved onset of damage and less accumulation of damage prior to ultimate failure; ply level hybridisation can enhance the bearing properties. Both effects were studied to bet...

Steel foil carbon fibre reinforced polymer composite (CFK) laminates, (St-CFK) were studied for improvement of the bearing properties. The bearing load was found to double with 25 % ply substitution in the St-CFK composite and optical analysis shows extensive plastic deformation in the joint, hence producing a structural joining method that may fai...

Current applications of composite materials have been focussing on the use in thin shells and continuous profiles, commonly being manufactured on the approach of a layered structure. The aim of this work was to evaluate the eligibility of a process based on compression moulded thermoplastic chopped tapes as a candidate to replace complex CNC machin...

This research presents analytical models to describe the cure kinetics of an epoxy resin, and then implements the models to create partially cured carbon fibre reinforced polymer structures that have been locally reinforced. A full process for co-curing B-staged composite parts was developed, including cure kinetic and glass transition modelling of...