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Item type:Publication, Access status: with files , Interphase-engineering by atomic layer deposition of nacre-inspired alumina composites(Elsevier, 2026-01-03); ; ; ; Nacre, also known as mother of pearl, is a layered brick-and-mortar structure composed of hard mineral platelets and soft organic protein. Found in the inner shells of certain mollusks, this natural architecture has evolved to optimize mechanical properties for the protection of the organism. The unique structured design of nacre and its exceptional mechanical performance have inspired the development of synthetic nacre-like materials. In this work, we introduce a novel approach for fabricating nacre-inspired ceramic composites using atomic layer deposition (ALD) to engineer the interphase, or “mortar”, between aligned alumina platelets. ALD, known for its sub-nanometer thickness control and conformal coating capabilities, enables uniform tuning of the interphase thickness from 30 nm up to 120 nm, offering a significant advantage in tailoring the mechanical properties of ceramic-ceramic composites. Our results reveal a direct correlation between ALD-deposited aluminum oxide thickness and enhanced mechanical performance, with increased modulus and hardness observed as the mortar thickens. Three-point bending tests further show that flexural strength is maximized with thicker ALD coatings . In situ micromechanical testing reveals crack initiation at surface defects in micro-cantilevers, with cracks effectively deflected by the nacre-inspired architecture. This resultsin an average flexural strength of approximately 400 MPa, achieved without additional heat treatment or sintering. The precision of ALD in creating conformal interphases is critical to the improved structural integrity and performance of the composite, demonstrating its potential asa powerful technique for fabricating high-performance, bio-inspired ceramic composites.Publicationtype: Journal Article40 18 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Vibro-acoustic modulation based measurements in CFRP laminates for damage detection in Open-Hole structures(2023-10-01); ; ; The occurrence of matrix cracks, fibre failures and delaminations results in a critical degradation of the structural integrity of composites. A reliable early detection of these damages is mandatory for a safe operation. In this paper, the application of Vibro-Acoustic Modulation measurement in notched carbon fibre reinforced polymers (CFRP) for damage detection is demonstrated. A piezoceramic actuator introduces an ultrasonic signal into the specimen, which is modulated by a low-frequency vibration excited by a servo-hydraulic testing system. The specimens tested are open hole tensile specimens according to ASTM D5766, made from a quasi-isotropic CFRP layup. Degradation in the form of matrix cracks or delaminations localised along the drill hole significantly reduces the stiffness and can be detected as a modulation increase. Taking into account the extent of the crack size and the acoustic emission (AE), a magnitude estimate of the modulation increase is possible. In consequence, the presented method can be used for damage monitoring in CFRP.Publicationtype: Journal Article25 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Impact damage detection in glass fibre reinforced polymers via electrical capacitance measurements on integrated carbon fibre bundles(2022-02); ; ; Impact damages are critical for fibre reinforced polymers, as they can lead to large delaminations that strongly influence the structural integrity of the components. Therefore, reliable detection of impact damages through structural health monitoring is desired. This paper demonstrates a method for the detection and size estimation of impact damages in glass fibre reinforced polymers using capacitance measurements on integrated carbon fibre bundles. Therefore, individual rovings of glass fibre fabrics are replaced by carbon fibre rovings. After infusion of the laminate, the electrical capacitance is measured between the carbon fibre bundles. Damage in the form of matrix cracks or delaminations results in incorporated air that changes the permittivity of the material and, therefore, can be detected as a capacitance decrease. Considering the magnitude of capacitance decrease, a size estimation of the impacts is possible. Consequently, the presented method can be used for in-situ monitoring of damages in glass fibre reinforced polymers.Publicationtype: Journal Article79 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Tensile creep behaviour of unidirectional flax fibre reinforced bio-based epoxy composites(2020-04); Composites made of natural fibres are promising in applications of structural components. Their creep resistance is a very important characteristic to be evaluated but is not well understood. This work investigates creep response of a unidirectional flax fibre reinforced bio-based epoxy under various tensile stress levels. Acoustic emission detection and fracture surface morphology analysis were utilized to analyse the creep mechanisms. In addition, a flax fibre pre-treatment using a green chemical (furfuryl alcohol) was applied in order to reduce to creep deformation. The results show that unidirectional flax fibre composites exhibit perceivable creep at low stress levels and have a relatively short creep rupture life at high stress levels. The creep deformation at low stress can be ascribed to the time-dependent shear deformation of matrices at interface area (hemicellulose/pectin matrix at fibrils interface and the epoxy at fibres interface). Creep at high stress are characterized with a development of extensive damage events and doesn't show typical three-stage creep deformation behaviour over creep life. Composites with furfuryl alcohol treated flax fibres displayed a reduced creep deformation of about 30% than their untreated counterparts at the same creep stress, proving that treating flax fibres with furfuryl alcohol is efficient to improve the creep resistance of flax fibre composites.Publicationtype: Journal Article95 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , New test approach to determine the transverse tensile strength of CFRP with regard to the size effectThe subject of this work is the investigation of the size effect on transverse strength of CFRP. A new test approach uses the remaining parts of already tested specimens for a second transverse tensile test. With this method it is analysed, whether first failure is dominated by the most critical flaw inside the material or at a load that is equivalent to the maximum tensile strength of the matrix. Thickness of the specimens is varied to study the influence of specimen volume on transverse tensile strength. Test results show that strength follows the trend of defect distribution with increasing strength for decreasing volume. Second failure strength is higher than first failure strength, showing that first failure occurs at the most critical defect and gives no evidence of the maximum transverse tensile strength of the material. Stress at second failure showed less scatter, proving good applicability of the proposed test method.Publicationtype: Journal Article66