1,721,037 research outputs found
Creating more gradual failure in high performance composites via hybridisation: 28th Annual Technical Conference of the American Society for Composites 2013, ASC 2013
No full textHybrid glass laminates with thin carbon plies were tested in tension. Results are presented showing the effects of the proportion and absolute thickness of the carbon on the response and failure mechanisms. It is demonstrated that with the right choice of parameters catastrophic failure can be avoided, and a more gradual, pseudo-ductile failure achieved
Extracting interlaminar cohesive laws from displacement field measurements: 29th Annual Technical Conference of the American Society for Composites, ASC 2014; 16th US-Japan Conference on Composite Materials; ASTM-D30 Meeting
No full textCohesive/interface elements are one of the successful numerical tools that have been recently applied to many different problems and shown good results in modelling crack development. However, most applied cohesive laws are hypothetical and are not based on experimental measurements. The aim of this study is to investigate the damage development at a delaminating interface and to propose a method by which the mode-II traction-separation law can be extracted experimentally. To find the traction-separation law, both variables (traction and separation) need to be evaluated separately at the interface. Mode-II separation can be found by subtracting the displacements on each side of the interface, however finding the value of traction (shear stress) at the interface is more difficult. As a first step, the shear strain field is found from the available displacement field measurements and then, the shear stress is worked out using the shear constitutive law. After validating the proposed method against FE simulations, the experimental displacement field is used to find the traction-separation law. The overall form of the traction-separation law can be approximated by a trapezoidal shape
Post-impact behaviour of pseudo-ductile thin-ply angle-ply hybrid composites
No full textThis work experimentally explores the post-impact behaviour of thin-ply angle-ply pseudo-ductile carbon fibre laminates subjected to tensile load. Indentation and low-speed impact tests were performed on standard tensile test specimens. Non-destructive tests were used to investigate the damage propagation. Digital Image Correlation (DIC) was adopted to detect the strain distribution during tensile tests. Post-damage pseudo-ductile behaviour was retained in angle-ply hybrid composites subjected to tensile loading conditions
Unidirectional hybrid composite overload sensors: 21st International Conference on Composite Materials, ICCM 2017
No full textA purpose-designed, thin-ply interlayer glass/carbon hybrid composite overload sensor concept is presented, which can be used for structural health monitoring (SHM) of composite structures, with potential for safer operation in service. It has been demonstrated that the sensors work satisfactorily and the striped pattern in the composite structure gives a visual indication of overload of the substrate. An analytical model developed here allows for these sensors to be tailored to suit different substrate materials and design strains. The sensors - comprising a single layer of Ultra-High Modulus (UHM) carbon/epoxy and S-glass/epoxy material - were characterised by experimental strain measurements, and finite element analysis (FEA) regarding their accuracy and the effect of their stiffness on the utilized substrate
Pseudo-ductility by fragmentation of central unidirectional plies in thin CFRP angle-ply laminates: 16th European Conference on Composite Materials, ECCM 2014
No full textPseudo-ductile metal-like tensile stress-strain responses with 700 MPa "yield stress" plateau and 4.0% failure strain have been achieved experimentally using thin-ply carbon epoxy prepreg and [+26n/0]S (n = 8 and 10) layups. Analysis of tested specimens has been conducted using microscopy and ultrasonic C-scan. These show that periodic fibre breakages in the 0° plies lead to local delaminations that propagate along the 0°/ - 26° interfaces. This gradual failure process of fragmentation and dispersed local delamination allows the demonstrated pseudo-ductile strains
Thin ply carbon/glass hybrid laminates to activate new damage mechanisms under indentation
Get PDFLow velocity impacts on composite laminates can cause a significant amount of delamination that is often referred to as barely visible impact damage (BVID). This damage can cause significant degradation of structural properties, especially the compressive strength after impact. The aim of this work was to utilise thin ply carbon/glass hybrid laminates to activate new types of damage mechanisms under indentation (quasi-static impact) that are more gradual and easier to detect. Therefore, 3 different types of hybrid composite plates fabricated from novel hybrid architectures of thin ply high modulus carbon (HS40) and standard thickness S-glass laminates were investigated. For comparison, a laminate containing only S-glass plies was investigated as well. The investigated specimens were interrupted at different load-levels and a detailed assessment of the damage evolution was carried out using X-ray Computed Tomography (CT). For all the hybrid configurations, a larger damage area was observed mostly under the indenter and the delaminations were smaller in the middle plies compared to the upper plies. In contrast, for the Glass laminates the delaminations were larger in the middle plies compared to the upper plies. For the hybrid laminates, the percentage of the first load drop in the global load-displacement curves was lower whereas the percentage of the stiffness reduction after the first load drop was higher, compared to the Glass laminate. Overall the hybrid results showed some different damage mechanisms, i.e. carbon ply fibre fracture and delamination under the indenter, with a gradual failure behaviour and less damage to the inner layers. The degradation mechanisms were visually detectable from the indented face from the early stage of the loading for some of the hybrid configurations, which can act as impact damage indicator.</p
Hybrid composites with aligned discontinuous fibres: 16th European Conference on Composite Materials, ECCM 2014
No full textHigh performance composites can replace metals in many applications because of their exceptional strength and light weight, but brittle failure is an undesirable characteristic. Hybridisation is one of the approaches to overcome this limitation of composites because hybrid composites provide the potential for tailoring a response with desired stiffness, strength and ductility. In this paper, hybrid composites consisting of unidirectional continuous glass laminates and aligned discontinuous carbon preforms developed by the HiPerDiF (High Performance Discontinuous Fibre) method were tested in tension. The hybrid composite is designed as a layer-by-layer system to achieve pseudo-ductile response. Results are presented showing the effects of the proportion and absolute thickness of the aligned carbon preform on the failure modes. This paper also introduces the advantages of the aligned discontinuous carbon preforms produced by the HiPerDiF method in layer-by-layer hybrid composites
The effect of the Weibull modulus on the shape of the stress-strain curves of thin-ply pseudo-ductile hybrid composites
No full textThis paper presents a numerical approach using ABAQUS CAE scripting to simulate the mechanical response of thin-ply pseudo-ductile hybrid composites. A parametric study demonstrates that interface critical fracture energy is essential for accurately modeling damage mechanisms and mechanical behavior. Correct shear strength identification enables the model to capture experimental observations, including fragmentation and the plateau region in the stress–strain curve. The analysis shows that the mechanical behavior of these composites is largely independent of fragmentation location patterns in the low-strain layer. Results emphasize the significant impact of the Weibull modulus on the stress–strain response, with careful selection leading to strong correlation with experimental data. Notable differences in best-fit Weibull moduli were observed for different materials, with higher values for high modulus carbon fibers
Reducing the notch sensitivity of quasi-isotropic layups using thin-ply hybrid laminates: 30th Annual Technical Conference of the American Society for Composites, ASC 2015
No full textThe concept of stress concentration suppression using thin-ply pseudo-ductile hybrid composites is presented in this paper. In previous works, it has been shown that it is possible to achieve high amounts of pseudo-ductility in Uni-Directional (UD) and multi-directional laminates. In this work, the requirements for thin-ply hybrid sublaminates to suppress/reduce notch sensitivity in quasi-isotropic laminates with an open hole is studied. A User Material subroutine (UMAT) has been developed in ABAQUS which can replicate the typical response of pseudo-ductile thin-ply hybrids. This UMAT was then used to study several idealised responses and find the important parameters controlling the fibre failure in notched specimens. The stress concentration factor in the 0° layer has been selected as a measure of notch sensitivity. The ratio of pseudo-ductile strain to initiation strain has also been found to be a useful parameter in comparing different fibre direction tensile responses. The stress concentration factors of the 0° layer found from two different tensile response shapes of UD sub-laminates were found to be very similar when they were plotted versus the ratio of pseudo-ductile strain over initiation strain. These results show that the stress concentration factor varies between 3 for linear elastic material response to 1 for sub-laminates with pseudo-ductile strain to initiation strain ratio of 3. This suggests that optimal structural response can be achieved with thin ply hybrids if the failure strain of the low strain material to high strain material is about 25%
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