Delamination analysis of holed composite laminates using interface elements

In this paper interface element with de-cohesive constitutive law is used to predict the failure load of laminates containing a central hole in which delamination is the dominant failure mode of them. For this purpose, the initiation and propagation of inter- laminar crack are modeled using our in hose FEM code. It is shown that at a certain load step, the interface elements between the two layers of -45° and 0° fail abruptly. It is also shown that the predicted failure stresses of laminates with various thicknesses are in an acceptable agreement with the experimental results

Shear-Mode Viscoelastic Damage Formulation Interface Element

In this paper, a viscoelastic-damage cohesive zone model is formulated and discussed. The interface element constitutive law has two elastic and damage regimes. Viscoelastic behaviour has been assumed for the shear stress in the elastic regime. Three element Voigt model has been used for the formulation of relaxation modulus of the material. Shear Stress has been evaluated in the elastic regime of the interface with integration over the history of the applied strain at the interface. Damage evolution proceeds according to the bilinear cohesive constitutive law up to the complete decohesion. Numerical examples for one element model has been presented to see the effect of parameters on cohesive constitutive law

The High Strain Rate Tension Behaviour of Pseudo-ductile High Performance Thin Ply Carbon/Glass Hybrid Composites

No abstract available

A Comparison of Damage Mechanisms in Scaled Static Indentation Tests on Glass and Carbon Fibre Laminates

No abstract available

Benzothiazole Thioflavin T improves obesity-related symptoms in mice

Background and Purposes: In order to counteract the obesity epidemics, novel therapeutics are needed. Thioflavin T (ThT) is a benzothiazole used as an amyloid probe and has other properties such as anti-aging and antihyperglycemic effects. The current study aimed at investigating its effect on obesity. Materials and Methods: A mouse model of obesity was generated by feeding male NMRI mice with a high fat diet (HFD) for 8 weeks. After this period, mice diet was switched to normal rodent diet, and ThT was orally administered with a 12 mg/Kg dose. The treatment effect was assessed on biochemical parameters, adipokines (adiponectin and leptin), total antioxidant capacity and TNF-α. Histological investigation was made on samples taken from adipose tissue and liver. Results and Conclusion: After receiving HFD, mice exhibited significantly increased body weight compared with a control group as well as well as abnormality in biochemical parameters. A significantly effective result was obtained on body weight, blood glucose, cholesterol and ALT serum levels which decreased in the treated group. ThT caused also a significant decrease in leptin levels and TNF-α. Furthermore, the compound led to a reduction in the size of adipose tissue cells, as well as the number of lipid droplets in hepatic tissue. In conclusion, it is suggested that ThT possess an interesting potential for being used as an anti-obesity drug, especially when considering its previously reported effects as potential anti-diabetic and anti-ageing compound

Thin ply carbon/glass hybrid laminates to activate new damage mechanisms under indentation

Low 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

Building Reservoir Computing Hardware Using Low Energy-Barrier Magnetics

Biologically inspired recurrent neural networks, such as reservoir computers are of interest in designing spatio-temporal data processors from a hardware point of view due to the simple learning scheme and deep connections to Kalman filters. In this work we discuss using in-depth simulation studies a way to construct hardware reservoir computers using an analog stochastic neuron cell built from a low energy-barrier magnet based magnetic tunnel junction and a few transistors. This allows us to implement a physical embodiment of the mathematical model of reservoir computers. Compact implementation of reservoir computers using such devices may enable building compact, energy-efficient signal processors for standalone or in-situ machine cognition in edge devices.Comment: To be presented at International Conference on Neuromorphic Systems 202

New Approaches to quantifying tensile strength variability and size effects in unidirectional composites

Two methods were used to investigate the variability of tensile failure strain of unidirectional high strength carbon/epoxy. Scaled tests on glass/carbon hybrid specimens showed a significant size effect and reduction of failure strain with stressed volume consistent with a Weibull modulus of 25. Ply fragmentation tests were also carried out, producing multiple carbon fractures in a single specimen. Strains from these tests also fitted a Weibull distribution, and gave a similar Weibull modulus to the scaled tests

Hybrid effects in thin ply carbon/glass unidirectional laminates: Accurate experimental determination and prediction

Experimental results are presented which allow the hybrid effect to be evaluated accurately for thin ply carbon/epoxy-glass/epoxy interlayer hybrid composites. It is shown that there is an enhancement in strain at failure of up to 20% for very thin plies, but no significant effect for thicker plies. Hybrid specimens with thick carbon plies can therefore be used to measure the reference carbon/epoxy failure strain. The latter is significantly higher than the strain from all-carbon specimens in which there is an effect due to stress concentrations at the load introduction. Models are presented which illustrate the mechanisms responsible for the hybrid effect due to the constraint on failure at both the fibre and ply level. These results give a good understanding of how variability in the carbon fibre strengths can translate into hybrid effects in composite laminates