We present a computational framework to explore the effect of microstructure and constituent properties upon the fracture toughness of fibre-reinforced polymer composites. To capture microscopic matrix cracking and fibre-matrix debonding, the framework couples the phase field fracture method and a cohesive zone model in the context of the finite element method. Virtual single-notched three point bending tests are conducted. The actual microstructure of the composite is simulated by an embedded cell in the fracture process zone, while the remaining area is homogenised to be an anisotropic elastic solid. A detailed comparison of the predicted results with experimental observations reveals that it is possible to accurately capture the crack path, interface debonding and load versus displacement response. The sensitivity of the crack growth resistance curve (R-curve) to the matrix fracture toughness and the fibre-matrix interface properties is determined. The influence of porosity upon the R-curve of fibre-reinforced composites is also explored, revealing a stabler response with increasing void volume fraction. These results shed light into microscopic fracture mechanisms and set the basis for efficient design of high fracture toughness composites.
This paper presents a new concept to place continuous curved fibres for CFRP composites, which can be fulfilled by potential additive or hybrid manufacturing technology. Based on the loading condition, principal stress trajectories are generated through finite element analysis (FEA) and used as the guidance of the placement paths for carbon fibres. Three numerical cases, an open-hole single ply lamina under uniaxial tension and an open-hole cross-ply laminate under biaxial tension and normal pressure, are studied and compared with traditional reinforced composites with unidirectional fibres. T…
We investigate the role of microstructural bridging on the fracture toughness of composite materials. To achieve this, a new computational framework is presented that integrates phase field fracture and cohesive zone models to simulate fibre breakage, matrix cracking and fibre-matrix debonding. The composite microstructure is represented by an embedded cell at the vicinity of the crack tip, whilst the rest of the sample is modelled as an anisotropic elastic solid. The model is first validated against experimental data of transverse matrix cracking from single-notched three-point bending tests.…
As far as the tensile properties of natural fibres as reinforcements for composites are concerned, flax fibres will stay at the top-end. However, an efficient conversion of fibre properties into their corresponding composite properties has been a challenge, due to the fibre damages done through the conventional textile methods utilised to process flax. These techniques impart disadvantageous features onto fibres at both micro, and mesolevel, which degrade the mechanical performances of flax fibre reinforced composites, FFRC. Undulation of fibre is one of those detrimental features that occur d…
In this contribution a method is introduced that allows for a linkage between the process-induced structural damage and the fracture behaviour. Based on an anisotropic elastic material model, different modelling approaches for initial damage effects are introduced and compared. The approaches are applied to remote laser cut carbon fibre reinforced polymers in order to model various thermally induced damage effects like chemical decomposition, micro-cracks and delamination. The dimensions of this heat affected zone are calculated with 1D-heat conduction. In experiment and simulation milled and …
Twill-weave carbon fibre reinforced polymer is measured as reflector material for electromagnetic waves at 60 GHz. The reflectivity at millimetre wavelength shows a predominant direction, which coincides with the diagonal pattern of the twill's top layer. In the remaining directions the investigated 2/2 twill-weave composite's reflectivity is almost isotropic.
Short-fiber-reinforced polymer composites are increasingly used in engineering applications and industrial products owing to their unique combination of superior mechanical properties, and relatively easy and low cost manufacturing process. The mechanical behavior of short carbon nanotube (CNT) polymer composites, however, remains poorly understood due to size and time limitations of experiments and atomistic simulations. To address this issue, the tensile fracture behavior of short CNT reinforced poly (methyl methacrylate) (PMMA) matrix composites is investigated using a coarse-grained (CG) m…
This study was aimed at investigating the influence of initial notch orientation on the translaminar fracture of woven-ply hybrid fibers reinforced thermoplastic polyether ether ketone (PEEK) laminates. This work is based on the experimental characterization of translaminar fracture of Single-edge-notch bending (SENB) specimens with two initial notches (0{\textdegree} and 45{\textdegree}). Such geometry results in a complex stress state within the laminates plies as well as simultaneous tension/compression failures. A digital image analysis technique has been implemented to monitor the crack i…
This paper addresses the numerical simulation of self-piercing rivetting processes to join fibre reinforced polymers and sheet metals. Special emphasis is placed on the modelling of the deformation and failure behaviour of the composite material. Different from the simulation of rivetting processes in metals, which requires the modelling of large plastic deformations, the mechanical response of composites is typically governed by intra- and interlaminar damage phenomena. Depending on the polymeric matrix, viscoelastic effects can interfere particularly with the long-term behaviour of the joint…
We derive a model for the finite motion of a magneto-elastic rod reinforced with isotropic (spherical) or anisotropic (ellipsoidal) inclusions. The particles are assumed weakly and uniformly magnetised, rigid and firmly embedded into the elastomeric matrix. We deduce closed form expressions of the quasi-static motion of the rod in terms of the external magnetic field and of the body forces. The dependences of the motion on the shape of the inclusions, their orientation, their anisotropic magnetic properties and the Young modulus of the matrix are analysed and discussed. Two case studies are pr…
The damage mechanisms and load redistribution of high strength TC17 titanium alloy/unidirectional SiC fibre composite (fibre diameter = 100 $μ$m) under high temperature (350 °C) fatigue cycling have been investigated in situ using synchrotron X-ray computed tomography (CT) and X-ray diffraction (XRD) for high cycle fatigue (HCF) under different stress amplitudes. The three-dimensional morphology of the crack and fibre fractures has been mapped by CT. During stable growth, matrix cracking dominates with the crack deflecting (by 50-100 $μ$m in height) when bypassing bridging fibres. A small numb…
Maintaining the correct fibre orientations and stacking sequence in carbon-fibre reinforced polymers (CFRP) during manufacture is essential for achieving the required mechanical properties of a component. This paper presents and evaluates a method for the rapid characterisation of the fibre orientations present in CFRP structures, and the differentiation of different stacking sequences, through the Radon-transform analysis of complex-valued eddy-current testing (ECT) inspection data. A high-frequency (20 MHz) eddy-current inspection system was used to obtain 2D scans of a range of CFRP samples…
This review summarizes progress on structural composites with carbon nanotube fibres. It starts by analyzing their development towards a macroscopic ensemble of elongated and aligned crystalline domains, alongside the evolution of the structure of traditional high-performance fibres. Literature on tensile properties suggests that there are two emerging grades: highly aligned fibres spun from liquid crystalline solutions, with high modulus and strength, and spun from aerogels of ultra long-nanotubes, combining high strength and fracture energy. The fabrication of large unidirectional fabrics wi…
The creep behaviour of a creep-resistant AE42 magnesium alloy reinforced with Saffil short fibres and SiC particulates in various combinations has been examined in the longitudinal direction, i.e., the plane containing random fibre orientation was parallel to the loading direction, in the temperature range of 175-300 C at the stress levels ranging from 60 to 140 MPa using impression creep test technique. At 175 C, normal creep behaviour, i.e., strain rate decreasing with strain and then reaching a steady state, is observed at all the stresses employed. At 240 C, normal creep behaviour is obser…
Accumulative Roll Bonding(ARB) process was used to develop few-layer graphene nano platelets reinforced aluminum matrix (GNPs/Al) composite in the form of sheets. Annealed Al sheets were ARB processed up to 6 pass along with coating of graphene between stacked sheets in first and second pass. Another set was prepared with same process parameter in the absence of graphene coating. Properties of these two set of samples were analyzed on the basis of film theory of ARB process which enables micro-level mixing of material on stacked layer interface. Hence the problem of graphene agglomeration was …
In this work, the mode I fracture toughness of dissimilar metal-composite adhesive joints is experimentally investigated using the double cantilever beam (DCB) test. The particular joint under study is resulted by the adhesive joining of a thin titanium sheet with a thin carbon fiber reinforced plastic (CFRP) laminate and is envisioned to be implemented in the hybrid laminar flow control system of future aircraft. Four different industrial technologies for the joining of the titanium and CFRP adherents are evaluated/compared; co-bonding with and without adhesive and secondary bonding using eit…
The susceptibility to delamination is one of the main concerns in fiber reinforced polymer composites (FRPs). This work demonstrates improvements of 60% in Mode-I fracture toughness after integration of thin (~30 micron), continuous veils of carbon nanotubes (CNTs) directly deposited onto carbon fiber fabric as the CNT are drawn from the gas-phase using a semi-industrial process. A combination of optical imaging, scanning electron microscopy and a Raman spectroscopy provide a new rapid tool to unambiguously determine the crack propagation path by simple visual inspection of fracture surface. T…
Flax fibre reinforced composites are becoming popular in the automotive and civil industries due to their environmentally friendly nature in terms of production and recycling and for their good specific strength. Textile structures undergo transverse compaction during composite manufacturing which changes the fabric thickness and ultimately fibre volume fraction of composites. Here, different flax fibre structures were investigated for compaction behaviour during composite forming to study the thickness changes of these fabrics under pressures between 1 and 10 bars. A range of composite manufa…
In this paper, the impact behaviour of composite laminates is investigated, and their potential for ballistic protection assessed, as a function of the reinforcing materials and structures for three representative fibre-reinforced epoxy systems involving carbon, glass, or para-aramid fibre reinforcements, respectively. A multiscale coupled experimental/numerical study on the composite material properties is performed, starting from single fibre, to fibre bundles (yarns), to single composite ply, and finally at laminate level. Uniaxial tensile tests on single fibres and fibre bundles are perfor…
The use of composite materials for structures subjected to impacts requires a deep understanding about the dynamic behaviour of the material. To this end, a physically-based computational micromechanics simulation tool has been developed to predict failure initiation in a composite ply over a wide range of strain rates. The computational micromechanics framework incorporates constitutive models for the fibre, matrix and fibre-matrix interface, which are partly calibrated with novel micromechanical testing techniques. The simulation tool was applied to two matrix-dominated deformation modes of …
The mechanical performance of reinforced composites is strongly influenced at different scales by the stress transferred at the matrix-fibre interfaces and at any surface where material discontinuity occurs. In particular, the mechanical response of elastomeric composites where the reinforcement is composed by cords with helically wound fibres is heavily compromised by fatigue and delamination phenomena occurring at cord-rubber as well as at the ply interfaces, since rubber and polymeric matrices are mainly vulnerable to the accumulation of deviatoric energy due to the shear stresses transferr…
This paper developed a fatigue-driven residual strength model considering the effects of low-velocity impact (LVI) damage and stress ratio. New fatigue failure criteria based on fatigue-driven residual strength concept and fatigue progressive damage model were developed to simulate fatigue damage growth and predict fatigue life for plain-weave composite laminates with LVI damage. To validate the proposed model, LVI tests of plain-weave glass fibre reinforced polymer 3238A/EW250F laminates were conducted, followed by post-impact constant amplitude tension-tension, compression-compression fatigu…
Trapped fields of over 20 T are, in principle, achievable in bulk, single-grain high temperature cuprate superconductors. The principle barriers to realizing such performance are, firstly, the large tensile stresses that develop during the magnetization of such trapped-field magnets as a result of the Lorentz force, which lead to brittle fracture of these ceramic-like materials at high fields and, secondly, catastrophic thermal instabilities as a result of flux movement during magnetization. Moreover, for a batch of samples nominally fabricated identically, the statistical nature of the failur…
