A continuum damage model to simulate failure in composite plates under uniaxial compression

Experimental investigations and numerical simulations are performed in order to numerically predict the buckling behaviour of thin composite laminated specimens. Experiments are aimed at two objectives: the first is to completely characterize the carbon/epoxy material under simple loading configurations, the second is to test this material in buckling and post-buckling situations. The data collected with the first campaign of experiments are used to obtain the strength parameters required to define a damage model based on the failure theory by Tsai-Wu. This model is implemented in a Finite Element (FE) code and numerical simulations of buckling are executed for unidirectional and cross-ply laminates; results are in good agreement with experiments both in terms of determination of the critical loads and prediction of failure during post-buckling

On the Stress Intensity Factor of cracks emanating from circular and elliptical holes in orthotropic plates

Stress Intensity Factors (SIFs) for cracks emanating from circular holes in two-dimensional orthotropic bodies were numerically computed taking into account the effect of geometry and orthotropy. A semi-analytical expression for the correction factor was found fitting the numerical data. Finally, it was demonstrated how the same expression can be used to calculate the SIF for cracks emanating from elliptical holes once appropriate changes of variables are made

Study of RPC gas mixtures for the ARGO-YBJ experiment

The ARGO-YBJ experiment consists of a RPC carpet to be operated at the Yangbajing laboratory (Tibet, P.R. China), 4300 m a.s.l., and devoted to the detection of showers initiated by photon primaries in the energy range 100 GeV - 20 TeV. The measurement technique, namely the timing on the shower front with a few tens of particles, requires RPC operation with 1 ns time resolution, low strip multiplicity, high efficiency and low single counting rate. We have tested RPCs with many gas mixtures, at sea level, in order to optimize these parameters. The results of this study are reported.Comment: 6 pages, 3 figures. To be published in Nucl. Instr. Meth. A, talk given at the "5th International Workshop on RPCs and Related Detectors", Bari (Italy) 199

Estimating the mode I through-thickness intralaminar R-curve of unidirectional carbon fibre-reinforced polymers using a micromechanics framework combined with the size effect method

A three-dimensional micromechanics framework is developed to estimate the mode I through-thickness intralaminar crack resistance curve of unidirectional carbon fibre-reinforced polymers. Finite element models of geometrically-scaled single edge notch tension specimens were generated. These were modelled following a combined micro-/meso-scale approach, where the region at the vicinity of the crack tip describes the microstructure of the material, while the regions far from the crack tip represent the mesoscopic linear-elastic behaviour of the composite. This work presents a novel methodology to estimate fracture properties of composite materials by combining computational micromechanics with the size effect method. The size effect law of the material, and consequently the crack resistance curve, are estimated through the numerically calculated peak stresses. In-depth parametric analyses, which are hard to conduct empirically, are undertaken, allowing for quantitative and qualitative comparisons to be successfully made with experimental and numerical observations taken from literature

Resistance welding of carbon fibre reinforced PEKK by means of CNT webs

Single lap shear specimens were manufactured using resistance welding of carbon fibre reinforced substrates by means of CNT web-based heating elements. Heating elements were manufactured by embedding the CNT web layers between layers of PEKK/glass fibre and connecting them to copper electrodes. An experimental campaign explored their electrothermal behaviour influencing the welding process. Single lap shear specimens were then welded at a pressure of 0.05 MPa and different levels of power and duration. An optimum bond was obtained with a specific power of 80–90 kW/m2 and a time of 150 s, achieving a shear strength of 30 MPa. Post-mortem analysis revealed that fracture propagated within the substrates. This work represents a further step in the integration of CNT web-based heating elements in an industrial welding process

Tensile and impact properties of melt-blended nylon 6/ethylene-octene copolymer/graphene oxide nanocomposites.

The addition of stiff nanoparticles to a polymer matrix usually proves beneficial for the enhancement in stiffness and strength, however, the impact strength is usually lowered. Conversely, the use of elastomeric additives can enhance the toughness and impact strength but causes a reduction in overall stiffness and strength. To take advantage of the desirable effects of both additives, they may be simultaneously added to the host matrix. Graphene oxide (GO), along with a thermoplastic elastomer ethylene-octene copolymer (EOC), was chosen to be added to nylon 6 for the current investigation. Maleated EOC (EOC-g-MA) was used as a compatibilizer for this study. 3 wt% GO nanoparticles, 20 wt% ethylene-octene copolymer (EOC) and 3 wt% EOC-g-MA were added to nylon 6 to prepare the nylon 6/EOC/GO blend-based nanocomposites. A high shear rate screw running at 300 rpm was used for melt-blending with a twin-screw extruder. Increased stiffness and tensile strength were observed by the addition of GO nanoparticles while elongation at break, toughness and impact strength were lowered by the addition of GO. The addition of EOC and EOC-g-MA enhanced the elongation at break, toughness and impact strength. However, the stiffness and strength of nylon 6/EOC blend was lower than that of the neat nylon 6. The addition of GO nanoparticles and EOC to neat nylon 6 caused a reduction in its impact strength. However, simultaneous addition of EOC and EOC-g-MA to nylon 6 caused a significant increase in the impact strength compared to neat nylon 6 and yielded a nylon 6/EOC/EOC-g-MA bend with the highest impact strength. The addition of GO nanoparticles to this blend, however, again caused a significant reduction in the impact strength. Nylon 6/EOC/EOC-g-MA blend showed the highest toughness and impact strength. Simultaneous addition of EOC and GO helped achieve a balanced stiffness and toughness

The GAP-TPC

Several experiments have been conducted worldwide, with the goal of observing low-energy nuclear recoils induced by WIMPs scattering off target nuclei in ultra-sensitive, low-background detectors. In the last few decades noble liquid detectors designed to search for dark matter in the form of WIMPs have been extremely successful in improving their sensitivities and setting the best limits. One of the crucial problems to be faced for the development of large size (multi ton-scale) liquid argon experiments is the lack of reliable and low background cryogenic PMTs: their intrinsic radioactivity, cost, and borderline performance at 87 K rule them out as a possible candidate for photosensors. We propose a brand new concept of liquid argon-based detector for direct dark matter search: the Geiger-mode Avalanche Photodiode Time Projection Chamber (GAP-TPC) optimized in terms of residual radioactivity of the photosensors, energy and spatial resolution, light and charge collection efficiencyComment: 7 pages, 5 figures, Accepted for publication on JINS