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Item type:Publication, Access status: with files , Round-robin programme for longitudinal tensile testing of unidirectional composites: results, conclusions, and recommendations(Elsevier, 2025-11-01); ; ; The longitudinal tensile behaviour is one of the most important and basic characteristics of a unidirectional composite, yet its experimental characterisation is not straightforward. Therefore, we conducted a round-robin programme with seven test labs and six coupon designs where the panels were manufactured and cut by the same lab. Our results indicate that careful manufacturing and cutting enable consistent and reliable results for the different labs and coupon designs. High-speed videos confirmed that many coupons failed away from the grips, which is the targeted failure location. In addition to the modulus, failure strain and strength results, we present results and novel recommendations related to the coupon preparation and testing methodology. We recommend using a non-contact strain measurement method and discarding tests with significant stress drops before final failure.Publicationtype: Journal Article113 26 - 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 Paper52 - 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 Paper34 - 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 253 - 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 13 162 425 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influence of delamination characteristics in carbon fibre/epoxy laminates on signal features of pulse thermography(Springer, 2014-12-10); ; ; ; Carbon fibre reinforced polymer specimens were used in double cantilever beam tests in order to investigate the influence of delamination characteristics on multiple signal features extracted from active thermography data. During mechanical loading, delamination opening and growth were induced, allowing controlled setting of different configurations. In addition to the standardised specimens, specimen geometries were altered to investigate delamination depth and influences from two overlapping delaminations in different depths. The thermography data was obtained from a measurement where the specimens were subjected to a rectangular long pulse emitted from a halogen light. From the data various signal features were extracted. Correlations between signal features such as phase angle difference and delamination opening were investigated. Furthermore, a comparison of the relation between extracted features allowed identifying different sections of the delamination, proving the methods applicability as a detailed classification tool. Due to the high number of features extracted robustness is increased.Publicationtype: Journal Article61 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , 36 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Experimental determination of the true epoxy resin strength using micro-scaled specimensIn fibre reinforced composite materials, the matrix is the continuous phase, but the inter-fibre distance is rather small. The strength and the capability of plastic deformation is controlled by the matrix physics properties as well as by the acting stress state and the stressed volume. A new method is explained to produce fibres from epoxy resin. The single fibre strength was measured according to the standard test method for single fibre tests. The measured strength data of these thin epoxy resin fibres is close (60%) to the theoretical strength. The mechanism of fracture was identified by fractographic studies as cohesive failure initiated at pre-existing voids or void nucleation and growth. Before final rupture, the fibres showed necking and plastic deformation, which is a surprising behaviour for a brittle epoxy resin.Publicationtype: Journal Article17 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Micro/macro-mechanical approach of first ply failure in CFRPA combined experimental and numerical study has been carried out in order to predict initial failure in transversely loaded carbon fibre/epoxy composites. Three-point bending experiments on macroscopic composite specimens with special laminate lay-ups were carried out in a scanning electron microscope (SEM). The in-situ experiments allow observing the onset of microscopic composite failure under transverse loading and measurement of the global applied load at onset of failure. The experimental results show that interfacial failure was the dominating failure mechanism. The interfacial stresses at initiation of failure were determined successfully by a non-linear micro/macro FE-Analysis and compared with experimental results obtained from 3-point bending tests of standard composite specimens. The results show that the interfacial normal strength (INS) governs the failure process.Publicationtype: Journal Article29