An experimental investigation into damage modes and scale effects in CFRP open hole tension coupons

An experimental investigation was conducted to study the effect of notch size and length scale on the damage of carbon fibre-reinforced composite specimens. Open hole tension specimens in a range of configurations were tested quasi-statically to ultimate failure. The load response, damage modes and strain field development were experimentally recorded. The results demonstrated that changing the ply thickness and specimen dimensions markedly affected the damage modes and specimen behaviour. This output provides key insights into the nature of composite behaviour, and is also critical for the development and validation of analysis methodologies capturing damage initiation and progression

Intelligence in structural health monitoring of composite structures using a robust signal processing protocol

This paper reports the development of a Structural Health Monitoring (SHM) system for a 2-D polymeric composite T-joint, used in maritime structures. The system developed relies on the examination of the strain distribution of the structure under operational loading and passing this data through a series of in-house developed pre-processing algorithms and eventually onto an Artificial Neural Network (ANN)-based inference engine. This system prompted the development of sophisticated pre-processing algorithms for the strain data. Improvements of 82% or more in detection accuracy were observed when these algorithms were invoked. Finite Element Analysis (FEA) was also conducted with delaminations of variable sizes at various locations in two structures, a composite beam and a T-joint. This paper focuses on a few normalization procedures that were developed to reduce the dependency of the algorithm on variables such as loading vectors. The work here also demonstrates the capability of the algorithm to detect and quantify instances when multiple damage zones are present

Review of methodologies for composite material modelling incorporating failure

Advanced composite materials are finding increasing application in aerospace, marine and many other industries due to the advantages in performance, structural efficiency and cost they provide. However, despite years of extensive research around the world, a complete and validated methodology for predicting the behaviour of composite structures including the effects of damage has not yet been fully achieved. The Cooperative Research Centre for Advanced Composite Structures (CRC-ACS) is leading a currently running collaborative project to develop a methodology for determining mechanical behaviour and failure in composite structures. Key drivers of the project are the use of multi-axial testing machines for material characterisation and an appreciation of the issues involved due to the different length scales of any analysis. As part of the project, a critical review was performed to assess the state of the art in material constitutive modelling and composite failure theories. This paper summarises the results of the review, which includes a discussion of the various theories and approaches within the context of the dissipated energy density framework. The results of the review will be applied within the project to select appropriate constitutive modelling and failure approaches for implementation within a data-driven material characterisation methodology

Damage prediction models for composite T-Joints in marine applications

For a monocoque hull structure, the bulkhead is used to separate the hull into many compartments. A typical joint between the hull and bulkhead used in such structure is known as a T-joint. It consists of composite overlaminates over a shaped fillet to allow the transmission of direct and membrane shear stresses. This paper describes the numerical solutions of the analytical approach in studying of the effect of disbond for a composite ship T-Joint using two methods, the VCCT (Virtual Crack Closure Technique) and CTE (Crack Tip Element) method. The analysis was conducted for T-Joints with various disbond sizes. It was subjected to a straight pull-off load to simulate normal operational conditions. An experimental investigation was conducted to validate the FE (Finite Element) models. The results of the numerical and experimental studies are discussed to corroborate the effectiveness of using fracture mechanics for this analysing this structure. A modified CTE model for the T-joint is proposed to enable a like-for-like comparison to that evaluated by the VCCT method

Loaded carbon composite scarf joints subject to impact

Bonded composite scarf repairs are often used when a flush surface is required for aerodynamic or stealth reasons. Such repairs on the external surface of an aircraft are subject to the same impact risk as that of the parent structure. Consequently, it is essential to assess their durability in the case of impact. A previous preliminary experimental study found an instance of catastrophic failure of a composite scarf joint subject to impact whilst prestrained to 3000 μ. It was postulated that this phenomenon is a result of failure in the joint due to the combination of the prestrain and global structural oscillations resulting from the impact event. In this investigation, a previously applied finite element model is extended to more accurately replicate such catastrophic failure. The effect of lay-up sequence on adhesive failure is studied

An analysis methodology for failure in postbuckling skin-stiffener interfaces

Blade-stiffened structures have the potential to produce highly efficient structures, particularly when the large strength reserves available after structural buckling, in the postbuckling range, are exploited. In experimental tests of postbuckling stiffened structures made from fibre-reinforced composites, failure typically initiates at the interface of the skin and stiffener and leads to rapid and even explosive failure. A methodology has been developed for analysing collapse in postbuckling composite structures that involves predicting the initiation of interlaminar damage in the skin-stiffener interface. A strength-based criterion is monitored in each ply using a local model of the skin-stiffener interface cross-section. For the analysis of large structures, a global analysis is first run to obtain the complete postbuckling deformation field, which is then input onto a local model using a global-local analysis technique. The coordinates of the local model can easily be moved to rapidly assess failure initiation at numerous skin-stiffener interface locations throughout the global structure. The analysis methodology is compared to experimental results for two-dimensional T-section specimens and large, fuselage-representative stiffened panels and is shown to give accurate predictions of the failure load and failure mechanisms. The use of the approach for the analysis of postbuckling composite structures has application for the design and certification of the next generation of aircraft

Gene expression profiling in equine polysaccharide storage myopathy revealed inflammation, glycogenesis inhibition, hypoxia and mitochondrial dysfunctions

<p>Abstract</p> <p>Background</p> <p>Several cases of myopathies have been observed in the horse Norman Cob breed. Muscle histology examinations revealed that some families suffer from a polysaccharide storage myopathy (PSSM). It is assumed that a gene expression signature related to PSSM should be observed at the transcriptional level because the glycogen storage disease could also be linked to other dysfunctions in gene regulation. Thus, the functional genomic approach could be conducted in order to provide new knowledge about the metabolic disorders related to PSSM. We propose exploring the PSSM muscle fiber metabolic disorders by measuring gene expression in relationship with the histological phenotype.</p> <p>Results</p> <p>Genotypying analysis of GYS1 mutation revealed 2 homozygous (AA) and 5 heterozygous (GA) PSSM horses. In the PSSM muscles, histological data revealed PAS positive amylase resistant abnormal polysaccharides, inflammation, necrosis, and lipomatosis and active regeneration of fibers. Ultrastructural evaluation revealed a decrease of mitochondrial number and structural disorders. Extensive accumulation of an abnormal polysaccharide displaced and partially replaced mitochondria and myofibrils. The severity of the disease was higher in the two homozygous PSSM horses.</p> <p>Gene expression analysis revealed 129 genes significantly modulated (p < 0.05). The following genes were up-regulated over 2 fold: IL18, CTSS, LUM, CD44, FN1, GST01. The most down-regulated genes were the following: mitochondrial tRNA, SLC2A2, PRKCα, VEGFα. Data mining analysis showed that protein synthesis, apoptosis, cellular movement, growth and proliferation were the main cellular functions significantly associated with the modulated genes (p < 0.05). Several up-regulated genes, especially IL18, revealed a severe muscular inflammation in PSSM muscles. The up-regulation of glycogen synthase kinase-3 (GSK3β) under its active form could be responsible for glycogen synthase (GYS1) inhibition and hypoxia-inducible factor (HIF1α) destabilization.</p> <p>Conclusion</p> <p>The main disorders observed in PSSM muscles could be related to mitochondrial dysfunctions, glycogenesis inhibition and the chronic hypoxia of the PSSM muscles.</p

Damage in single lap joints of woven fabric reinforced polymeric composites subjected to transverse impact loading

Single lap joints of woven glass fabric reinforced phenolic composites, having four different overlap widths, were impacted transversely using a hemispherical impactor with different velocities in the low velocity impact range. The resulting damage was observed at various length scales (from micro to macro) using transmission photography, ultrasonic c-scan and x-ray micro tomography (XMT), in support of each other. These experimental observations were used for classification of damage in terms of damage scale, location (i.e. ply, interfaces between plies or bond failure between the two adherends) and mechanisms, with changing overlap width and impact velocity. In addition, finite element analysis was used to simulate delamination and disbond failure. These simulations were used to further explain the observed dependence of damage on overlap width and impact velocity. The results from these experiments and simulations lead to the proposal of a concept of lower and upper characteristic overlap width. These bounds relate the dominant damage pattern (i.e. scale, location and mechanism) with overlap width of the joint for a given impact velocity range.National University of Sciences and Technology, NUST, Pakistan: The University of Manchester, EPS fellowshi