Non-stationary oscillations of sandwich plates under local dynamic loading

The paper addresses the elastic response of composite sandwich panels to local\ud dynamic loading. The plane and axisymmetric formulations are considered; no\ud overall bending is assumed. The governing equations are derived using the static\ud Lamé equations for the core and the plate Kirchoff-Love dynamic theory for the\ud faces. The closed form solutions for the non-stationary excitation are obtained\ud using integral transformations technique. The solutions allow to predict the stressstrain state of the structure and are in good agreement with finite element analysis

Сравнительная клинико-гормональная характеристика состояния здоровья и качество жизни женщин с хирургической и естественной менопаузой

ГОРМОНЫДЕПРЕССИЯЖЕНЩИНЫКАЧЕСТВО ЖИЗНИМЕНОПАУЗАПОСТМЕНОПАУЗ

Sandwich Panel Cores for Blast Applications: Materials and Graded Density

Sandwich composites are of interest in marine applications due to their high strength-to-weight ratio and tailorable mechanical properties, but their resistance to air blast loading is not well understood. Full-scale 100 kg TNT equivalent air blast testing at a 15 m stand-off distance was performed on glass-fibre reinforced polymer (GFRP) sandwich panels with polyvinyl chloride (PVC); polymethacrylimid (PMI); and styrene acrylonitrile (SAN) foam cores, all possessing the same thickness and density. Further testing was performed to assess the blast resistance of a sandwich panel containing a stepwise graded density SAN foam core, increasing in density away from the blast facing side. Finally a sandwich panel containing compliant polypropylene (PP) fibres within the GFRP front face-sheet, was subjected to blast loading with the intention of preventing front face-sheet cracking during blast. Measurements of the sandwich panel responses were made using high-speed digital image correlation (DIC), and post-blast damage was assessed by sectioning the sandwich panels and mapping the damage observed. It was concluded that all cores are effective in improving blast tolerance and that the SAN core was the most blast tolerant out of the three foam polymer types, with the DIC results showing a lower deflection measured during blast, and post-blast visual inspections showing less damage suffered. By grading the density of the core it was found that through thickness crack propagation was mitigated, as well as damage in the higher density foam layers, thus resulting in a smoother back face-sheet deflection profile. By incorporating compliant PP fibres into the front face-sheet, cracking was prevented in the GFRP, despite damage being present in the core and the interfaces between the core and face-sheets

Compressive Failure of NCF Composites

The necessity to reduce environmental impact promotes transportation industry to reduce energy consumption of vehicles. One possible way to improve vehicles' structural efficiency is to utilize modern composite materials that offer excellent mechanical performance-to-weight ratio. Mass production of composite parts requires cost effective manufacturing methods. One potential rational method is to use dry textile preforms and liquid moulding methods, e.g vacuum infusion or resin transfer moulding. Among different types of textile preforms, non-crimp fabrics (NCFs) are most attractive for load bearing applications as they offer considerably higher in-plane mechanical properties compare to other textiles such as wovens or random mats. Composites manufactured with NCF fabrics are characterised by distinct fibre bundles separated by resin rich areas. These bundles are not perfectly straight but have a small yet significant waviness, both in-plane and out-of-plane. The waviness will influence the performance of NCF composites and especially the compressive properties. Design of structural parts made of NCF composites requires both a thorough understanding of the compressive failure process and effective failure prediction models. This is particularly relevant for the critical compressive loaded parts, such as bolted joints. The present work is concerned with the compressive failure of NCF composites and focuses on two major goals. First is to experimentally characterise the compressive failure process of various NCF composites and identify relevant damage modes and mechanisms. Secondly is to develop and propose suitable failure prediction models for reliable design of NCF composite parts with special emphasis on cost-effective methods relevant for industrial design processes. In the present work, a combination of experimental studies, modelling methods development and implementation of advanced state-of-the-art failure criteria have been performed. Optical methods were used to characterise the damage mechanisms in the material at different stress levels. This allowed both identification of the critical damage mechanisms and the whole damage progression sequence. Engineering models were developed to predict the compressive failure of NCF composites. In the models, the fibre bundles' waviness was dealt with in a cost-effective way. The models utilise a state-of-the-art failure criteria that predict both intra-laminar and inter-laminar damage. The proposed models demonstrated good accuracy in the predictions of both compressive and bearing failures. In addition, a cost-effective high-fidelity meso-scale modelling methodology was developed for bearing failure prediction of NCF composites. The methodology demonstrated a potential for cost-effective and highly detailed analysis of the bearing failure process and possible method for parameter studies of mechanical properties and their relation to the reinforcement architecture.QC 20191120</p

Compressive Failure of NCF Composites

The necessity to reduce environmental impact promotes transportation industry to reduce energy consumption of vehicles. One possible way to improve vehicles' structural efficiency is to utilize modern composite materials that offer excellent mechanical performance-to-weight ratio. Mass production of composite parts requires cost effective manufacturing methods. One potential rational method is to use dry textile preforms and liquid moulding methods, e.g vacuum infusion or resin transfer moulding. Among different types of textile preforms, non-crimp fabrics (NCFs) are most attractive for load bearing applications as they offer considerably higher in-plane mechanical properties compare to other textiles such as wovens or random mats. Composites manufactured with NCF fabrics are characterised by distinct fibre bundles separated by resin rich areas. These bundles are not perfectly straight but have a small yet significant waviness, both in-plane and out-of-plane. The waviness will influence the performance of NCF composites and especially the compressive properties. Design of structural parts made of NCF composites requires both a thorough understanding of the compressive failure process and effective failure prediction models. This is particularly relevant for the critical compressive loaded parts, such as bolted joints. The present work is concerned with the compressive failure of NCF composites and focuses on two major goals. First is to experimentally characterise the compressive failure process of various NCF composites and identify relevant damage modes and mechanisms. Secondly is to develop and propose suitable failure prediction models for reliable design of NCF composite parts with special emphasis on cost-effective methods relevant for industrial design processes. In the present work, a combination of experimental studies, modelling methods development and implementation of advanced state-of-the-art failure criteria have been performed. Optical methods were used to characterise the damage mechanisms in the material at different stress levels. This allowed both identification of the critical damage mechanisms and the whole damage progression sequence. Engineering models were developed to predict the compressive failure of NCF composites. In the models, the fibre bundles' waviness was dealt with in a cost-effective way. The models utilise a state-of-the-art failure criteria that predict both intra-laminar and inter-laminar damage. The proposed models demonstrated good accuracy in the predictions of both compressive and bearing failures. In addition, a cost-effective high-fidelity meso-scale modelling methodology was developed for bearing failure prediction of NCF composites. The methodology demonstrated a potential for cost-effective and highly detailed analysis of the bearing failure process and possible method for parameter studies of mechanical properties and their relation to the reinforcement architecture.QC 20191120</p

Failure of Sandwich Structures with Sub-Interface Damage

NR 2014080