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In this paper, the effects of the stacking sequence on the mechanical behavior of composite laminates subjected to low velocity impacts is investigated, taking into account inter-laminar and intra-laminar damage onset and evolution. The response of the composite laminate configurations characterized by different stacking sequences subjected to low velocity impacts with different impact energies have been studied to estimate the influence on the load-time, displacement-time and energy-time histories. A Finite element (FE) model has been used to numerically simulate the behavior of the composite plates. ABAQUS/EXPLICT FE environment has been considered for the implementation and the analyses and cohesive elements have been adopted to model the inter-laminar damage formation and evolution in the analyzed composite plate. [ABSTRACT FROM AUTHOR]

In this paper, a numerical study on the skin–stringer debonding growth in composite panels under compressive load is presented. A novel numerical procedure, for the selection of proper material parameters governing the traction–separation law in Cohesive Zone Model (CZM) based elements, is introduced and demonstrated. Indeed, the proposed procedure uses Virtual Crack Closure Technique (VCCT) based FEM analyses on Double Cantilever Beam (DCB) and End Notched Flexure (ENF) specimen to characterize the traction–separation law, respectively, for fracture mode I and mode II. The established traction–separation laws are then applied to composite structures containing inter-laminar damages modeled by cohesive elements. To validate the proposed approach, a single stringer panel under compression with an artificial debonding between skin and stringer, has been considered. The numerical results, in terms of displacements and debonding size as a function of applied compressive load, have been compared to experimental data available in literature providing a good numerical–experimental correlation. [ABSTRACT FROM AUTHOR]

This paper presents two modelling strategies for the simulation of low velocity impact induced damage onset and evolution in composite plates. Both the strategies use a global–local technique to refine the mesh in the impact zone in order to increase the accuracy in predicting the impact phenomena without affecting the computational cost. Cohesive elements are used to simulate the inter-lamina damage behaviour (delaminations) and Hashin's failure criteria are adopted to predict the intra-lamina failure mechanisms. The two modelling strategies differ in terms of input parameters for the inter-lamina and intra-lamina damage evolution laws and in terms of modelling solutions in the impacted area. Comparisons between numerical and experimental results on composite plates subjected to different impact energies, according to the ASTM D7136 requirements, have been used to assess the peculiarities and the fields of application for the two proposed modelling strategies. Both the strategies have been tested by adopting the finite element code ABAQUS®. The different approaches to set the parameters of cohesive elements' constitutive laws and Hashin's criteria and the different choices made in quantifying the dependence of failure criteria on the finite elements' average size have been taken into account. [ABSTRACT FROM AUTHOR]

• The bond behaviour of multi-ply steel reinforced grout composites was investigated. • A minimum splice length of 100-200mm is recommended for SRG systems. • The full strength of low density steel textiles can be developed through short laps. • The performance of high density spliced textiles is limited to less than 40%. • The performance of multi-ply SRG is limited by the mortar/concrete bond strength. This paper presents an experimental investigation on Steel Reinforced Grout (SRG) systems comprising multiple layers of galvanized UHTSS textiles, with either 4 or 8 cords/in density, embedded within a geopolymer mortar. Lap-splice tests and single-lap bond tests were performed to develop an improved understanding of the textile-to-textile load transfer capacity and of the SRG-to-concrete substrate bond behaviour. The effects of number of textile plies, cord density and compressive strength of concrete on the bond behaviour are analysed. [ABSTRACT FROM AUTHOR]

Debonding of the fiber-reinforced polymer (FRP) from the substrate that occurs before its tensile strength is reached typically controls the effectiveness of the stress transfer mechanism between FRP composites and a quasi-brittle substrate, such as masonry. The FRP-substrate interface is usually modelled as a zero-thickness interface whose fracture Mode-II cohesive material law (CML) is defined in terms of shear stress and slip at the interface. In this paper, the effect of the shape of the CMLs of the FRP-brick and FRP-mortar interfaces on the stress transfer process will be presented and discussed. Several multi-linear CMLs, obtained from experimental data for both mortar and brick interfaces, will be adopted to obtain the load response of the FRP-masonry interface. It will be shown that the shape of the CMLs adopted does not strongly affect the load response if the fracture parameters are the same or similar among the CMLs. Finally, certain geometric relationships of brick and mortar joints imply more pronounced differences in terms of load response between the CMLs adopted. [ABSTRACT FROM AUTHOR]

A novel numerical methodology is used to investigate the behavior of an all-composite wing-box under a compressive load taking into account the presence of concurrent inter-laminar damages such as delaminations and skin-stringer debonds and their propagation. The proposed numerical methodology, based on linear structural analyses, is computationally inexpensive if compared to the VCCT and CZM based numerical techniques, hence, it appears to be particularly suitable for the preliminary design phase of complex structure. The presented linear approach is an evolution of a previous technique developed specifically for delaminations. Indeed, in this paper the linear approach has been enhanced to predict the propagation of inter-laminar damages with open crack surfaces such as skin-stringer debonds and it has been implemented in a commercial Finite Element platform. The effectiveness (in terms of computational cost and accuracy of results) of the suggested linear numerical methodology, in predicting the compressive behavior of complex composite structures with inter-laminar damages, has been confirmed by cross-comparisons with the standard non-linear VCCT technique. Finally, comparisons in terms of critical propagation load and Energy Release Rate distribution along the damage tip predictions, for several examined structural configurations with different damage extension and depth, have allowed to assess the field of applicability of the propose novel numerical methodology. [ABSTRACT FROM AUTHOR]

Abstract: The diagnosis and therapy of allergic disorders are usually performed with crude extracts which are a heterogeneous mixture of proteins with different allergenic potency. The knowledge of the allergenic composition is a key step for diagnostic and therapeutic options. Parietaria judaica pollen represents one of the main sources of allergens in the Mediterranean area and its major allergens have already been identified (Par j 1 and Par j 2). In addition, inhibition studies performed using a calcium-binding protein (CBP) from grass pollen (Phl p 7) showed the presence of a homologue of this cross-reactive allergen in the Parietaria extract. Screening of a cDNA library allowed us to isolate a 480bp cDNA containing the information for an 87 AA long protein with high level of homology to calcium-binding proteins from other allergenic sources. It was expressed as a recombinant allergen in Escherichia coli and purified by affinity chromatography. Its expression allowed us to study the prevalence of this allergen in a population of allergic patients in southern Europe. Immunoblotting and inhibition studies showed that this allergen shares a pattern of IgE epitopes in common with other 2-EF-hand calcium-binding proteins from botanically non-related species. The immunological properties of the Pj CBP were investigated by CD63 activation assay and CFDA-SE staining. In conclusion, DNA recombinant technology allowed the isolation, expression and immunological characterization of a cross-reactive calcium-binding protein allergen from Parietaria judaica pollen. [Copyright &y& Elsevier]