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Item type:Publication, Access status: without files , Capabilities of robot-based double-sided incremental hot-forming of fiber-reinforced thermoplastics(Soc. for the Advancement of Material and Process Engineering, 2026-04); ; ; ; Thermoplastic composites are gaining interest for their good recyclability, in addition to their mechanical performance and light weight potential. However, conventional molding processes for thermoplastic composites, such as hot pressing, require full-surface, geometry-specific molding tools and are therefore associated with high investment costs and long lead times until production can start. This is a strong drawback for manufacturing of small series, prototypes or in case of geometry changes. A promising flexible alternative is incremental forming, where geometry-agnostic tool tips exert local force to successively form the part. This allows for the economical and quick production of small part quantities. This work investigates the capabilities of a novel double sided incremental hot-forming process that employs two cooperating robots to drape a heated organosheet into the targeted shape. The process is assessed regarding mechanical performance, geometric accuracy and economic efficiency. The analysis shows that the presented process is capable of producing a wide variety of geometries with viable accuracy and good mechanical performance. The economic assessment reveals a clear advantage in both lead time as well as per part cost for small lot sizes.Publicationtype: Conference Paper40 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Numerical investigation of the bearing performance of Thin- and Thick-Ply hybrid laminates(Elsevier, 2024-07-09); ; ; ; This publication presents a numerical investigation of Thin-Ply Hybrid CFRP bolted joints. In addition to Thin- and Thick-Ply specimens, hybrid specimens are investigated by substituting a part of the 90° CFRP layers with stainless steel foils. The numerical investigations are based on preliminary experimental work, which showed that fibre kinking led to final failure. A modelling strategy that includes 3D stress states and fibre kinking is chosen. The influence of micro-damages such as matrix cracks decreases with decreasing layer thickness. Therefore, and to avoid high computational power, primarily micro-damages such as matrix cracks are not included. The results of the simulations of the Thin-Ply and the hybrid samples show a good agreement with the experimental results. By hybridisation, the bearing performance can be significantly increased. It is shown that the modelling approach of not including micro-damage is well applicable for thinner plies but reaches its limits for thicker plies.Publicationtype: Journal Article31 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Bearing strength high performance fibre metal thin-ply laminates(Queen's University Belfast, 2023); ; ; ; Publicationtype: Conference Paper50 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Numerical simulation of the bearing failure mechanism of thin-ply metal laminates(International Committee on Composite Materials, 2023); ; ; ; Within this study, the influence of a local hybridisation of Thin- and Thick-Ply laminates under bearing conditions was investigated by numerical simulations. The hybridisation was carried out by substituting 90° layers with stainless steel patches locally in the area of the load introduction. The stainless steel patches or foils had the same thickness as the prepreg layers. This prevents any unintentional change or disturbance of the laminate geometries. The CompDam - Deformation Gradient Decomposition (DGD) damage model was chosen for the numerical investigations. The study results showed that a reduction in layer thickness is associated with increased bearing strength. The bearing strength improvement of hybrid specimens is significantly higher for Thin- and Thick-Ply specimens. An improvement of almost 50 % could be achieved. Fibre kinking led to final failure for all configurations. The initiation of fibre kinking occurred in the 0° layers, which has the highest compressive stress. However, it could be observed that using stainless steel patches reduces the maximum compressive stress in the middle 0° layer. Thus, the initiation of fibre kinking shifted to higher strains or stresses, resulting in a higher bearing strength.Publicationtype: Conference Paper32 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Bearing strength high performance fibre metal thin-ply laminates(Composite Construction Laboratory, 2022-06); ; ; ; Publicationtype: Conference Paper85 246 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Damage tolerance and notch sensitivity of bio-inspired thin-ply Bouligand structures(Elsevier, 2021-07); ; ; ; Different bio-inspired Bouligand thin-ply Carbon-Fibre-Reinforced Plastic (CFRP) laminates with a pitch angle as low as 2.07∘ are realised, which is the smallest pitch angle realised in literature. The angle is therefore close angles found in biological microstructures. Low-Velocity Impact (LVI) and residual compressive strength tests determined the damage tolerance of the structures. Investigated were two different interlaminar fracture toughnesses and two different metal-Bouligand-CFRP-layups. The low pitch angle results in significantly higher residual strengths than 45∘ quasi-isotropic (QI) layups, despite the significantly lower proportion of 0∘ fibres. Higher fracture toughness and hybridisation with steel layers lead to reduced matrix damage without increasing residual compressive strength. In-plane plane tension properties are determined with a pitch angle of 2.59∘. The results reveal, that the unnotched tensile strength is significantly lower. However, only helicoidal, sub-critical matrix cracking and no delaminations occur before final failure. The sub-critical matrix cracking leads to almost no notch sensitivity and a similar open-hole-tensile strength to 45∘-QI layups despite the low number of 0∘-fibres.Publicationtype: Journal ArticleScopus© Citations 14 92 425 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Fatigue and fatigue after impact behaviour of Thin- and Thick-Ply composites observed by computed tomography(Elsevier, 2021-07); ; ; ; This study investigates the influence of load ratio and impact damage on the fatigue behaviour of high-performance carbon fibre reinforced polymers (CFRP) with areal fibre weights between 30 gsm and 360 gsm. For undamaged samples, the ultimate tensile and compressive strength, as well as the fatigue properties, are evaluated with regard to their layer thicknesses. The fatigue tests were performed under tension-tension (R=0.1), tension-compression (R=-0.5) and compression-compression (R=10) regime. The results are illustrated as a constant-life diagram, and a piecewise linear interpolation examines a first prediction. The results show that static and fatigue performance improves with decreasing layer thickness. Particularly under tension-compression loading, significant improvements are observed, due to the suppression of matrix cracks and delaminations with thinner layers. In addition, the effect of low-energy impact on the fatigue behaviour of Thin- and Thick-Ply laminates is investigated. The tests demonstrate that although the delamination area is larger, Thin-Ply laminates can sustain higher stresses and still reach the same number of load cycles in contrast to Thick-Ply laminates. Computed tomography measurements visualize 3-dimensional the damage progression after various cycles and prove that the Thin-Ply composites show no increase in the damaged area during fatigue. The interlaminar stress at the delamination is not sufficient for expansion. In contrast, in the case of thicker layers, the damage growths progressively throughout the whole sample with increasing number of cycles.Publicationtype: Journal ArticleScopus© Citations 19 182 305 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Damage tolerance of few-layer graphene modified CFRP: From thin-to thick-ply laminates(2021-06-16); ; ; ; Low impact resistance and high notch sensitivity are significant drawbacks of carbon-fibre-reinforced plastics (CFRP). The addition of carbon nanoparticles (CNP), a third phase, reduces this deficit through additional energy-consuming mechanisms. The influence of CNP modification on strength and damage behaviour cannot be separated from the effect of layer thickness because it controls the stress state in the entire laminate. This study investigates the influence of few-layer graphene (FLG) modification on CFRP with layer thicknesses varying from ultra-thin-ply (28μm, 30g/m ) to thick-ply (220μm, 240g/m ). The mode I and mode II inter-laminar energy release rates increased significantly with the FLG modification. It also increased the damage initiation stress for notched laminates of all layer thicknesses, thereby increasing the useable design space. The FLG modification also increased the ultimate notched strength for the ultra-thin ply laminates, thereby reducing the high notch sensitivity which is the limiting factor for their application. In the case of low-velocity impact damage, the modification of thick-layer laminates improves the residual compressive strength. FLG modification leads to a considerable improvement in the compressive strength. The selection of CNP was based on a comprehensive investigation of the fracture toughness of the prepreg resin/CNP nanocomposites. The particle loading and type was selected for FLG with a 25μm sheet size and 0.05 wt %.Publicationtype: Journal Article76 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Mechanical properties and failure mode of thin-ply fiber metal laminates under out-of-plane loadingIn this study, fiber metal laminates (FMLs), which consisted of thin-ply prepreg and stainless steel layers with a ply thickness of 0.04 mm, were fabricated with the aim of suppressing the fiber breakage that decreases the compression-after-impact (CAI) strength. Then, static flexural tests of FMLs were conducted to investigate the effects of the number of metal layers on the failure mode and mechanical properties during static out-of-plane loading, and the results were compared with those of our previous impact and CAI tests. The results confirmed that the plastic deformation of metal layers improved the energy dissipation and thus failure occurred in a limited range of locations. Furthermore, the investigation of the in situ stress during flexural tests by finite element method (FEM) analysis revealed that a hybrid material that both suppresses ply failure and has a high modulus of the metal can be realized owing to the constraining effect of thin-ply laminates.Publicationtype: Journal Article34 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Steel foil reinforcement for high performance bearing strength in Thin‐Ply composites(Elsevier, 2021-03); ; ; ; This study investigates the influence of local hybridization of Thin and Thick-Ply CFRP laminates on the open-hole and bearing properties. The area weight of the CFRP unidirectional prepregs used is 40 gsm in the case of Thin-Ply layers and 160 gsm in the case of Thick-Ply layers. The steel used is a 1.4310 stainless-steel foil with the same layer thickness as the prepregs. In the hybrid area, 90 layers were locally replaced by stainless steel patches. The local metal foil content varies from 6.25%, 12.5% to 25.0%. For notched laminates, the open hole tensile strength is significantly decreased with thinner layer thicknesses. The failure behavior changes from complex delamination dominated failure to brittle failure. By using stainless steel foils in the regions of stress concentrations, energy can be dissipated by plastic deformation of the steel foil and stresses can be deflected to neighbouring areas. For Thin-Ply samples with a local steel content of 25% the open hole tensile strength increases by 64% in comparison to the reference Thin-Ply specimens and the sensitivity towards stress concentrations decreases. The bearing strength of the hybrid CFRP laminates is increased by up to 54.6% in comparison to the reference material, due to the confinement of the steel foil and the resulting higher compressive strength and the plastic deformation at high stresses. The stress–strain diagrams and micrographs of the fibre metal samples reveal that damage is initiated before the maximum bearing strength. However, the damage offset bearing strength increase concerning the specific density of the material significantly.Publicationtype: Journal ArticleScopus© Citations 13 158 423