Mechanical characterization of different epoxy resins enhanced with carbon nanofibers

Epoxy with carbon nanofibers (CNFs) are effective nano enhanced materials that can be prepared by easy and low-cost method. The present paper compares the improvements, in terms of flexural and viscoelastic properties, of two epoxy resins reinforced with different weight percentages (wt.%) of CNFs. These epoxy resins have different viscosities, and weight contents between 0% and 1% of CNFs were used to achieve the maximum mechanical properties. Subsequently, for the best configurations obtained, the sensitivity to the strain rate and the viscoelastic behaviour (stress relaxation and creep) were analysed based on international standards. It was possible to conclude that, for both resins, carbon CNFs promote significant improvements in all the studied mechanical properties, even for different contents by weight.   &nbsp

Fused filament fabrication-4D-printed shape memory polymers : a review

Additive manufacturing (AM) is the process through which components/structures are produced layer-by-layer. In this context, 4D printing combines 3D printing with time so that this combination results in additively manufactured components that respond to external stimuli and, consequently, change their shape/volume or modify their mechanical properties. Therefore, 4D printing uses shape-memory materials that react to external stimuli such as pH, humidity, and temperature. Among the possible materials with shape memory effect (SME), the most suitable for additive manufacturing are shape memory polymers (SMPs). However, due to their weaknesses, shape memory polymer compounds (SMPCs) prove to be an effective alternative. On the other hand, out of all the additive manufacturing techniques, the most widely used is fused filament fabrication (FFF). In this context, the present paper aims to critically review all studies related to the mechanical properties of 4D-FFF materials. The paper provides an update state of the art showing the potential of 4D-FFF printing for different engineering applications, maintaining the focus on the structural integrity of the final structure/component

Impact response of laminated cylindrical shells

Composite laminates subjected to low-velocity impact events on the through-thickness direction are conveniently studied and disseminated in the open literature. However, in terms of laminated cylindrical shells this subject is less common. Therefore, the main goal of the present work is to study the impact response of laminated composite cylindrical shells composed by different type of fibres. For this purpose, laminates with different configurations (6C, 2C+2K+2C and 2C+2G+2C), where the “number” represents the number of layers used and C=Carbon, K=Kevlar and G=Glass fibre layers, were analysed in terms of static and impact strength. It is possible to conclude that both static and impact performance are strongly influenced by the shells’ configuration. In terms of compressive static strength, the Kevlar hybrid shells present values 53.2% higher than the 6C shells, while the glass hybrid shells present values 17.3% lower. The impact analyses shows, regardless the similarity of the maximum loads for all configurations, that Kevlar hybrid shells achieved the highest elastic recuperation and the glass hybrid shells the maximum displacement

1st Virtual Conference on Structural Integrity - VCSI1 : Preface

n/

Static and fatigue behaviour of glass-fibre-reinforced polypropylene composites

This paper is concerned with fatigue of polypropylene/glass-fibre thermoplastic composites produced from a bi-directional woven cloth mixture of E glass fibres and polypropylene fibres. The latter becomes the matrix after the application of heat and pressure. This composite was manufactured with a fibre volume fraction Vf of 0.338. The effect of layer design on the static and fatigue performance was investigated. The S-N curves, the rise in the temperature of the specimens during the tests and the loss of stiffness, were obtained and discussed. The loss of stiffness was related to the rise of temperature and stress release observed in the material. The effect of load rate on the static properties was also studied and discussed accordingly.http://www.sciencedirect.com/science/article/B6V55-3VS2T96-7/1/dc7ea45782ce361f9703694595aebfa

Repair Delaminations in Carbon/epoxy Laminates

Delaminations are the most typical damage in composite laminates, and the industrial community is continually searching new techniques to combine efficiency with cost benefits. Therefore, this work intends to analyse the application of screws on repair of composite laminates containing delaminations. It was found that this technique is beneficial for delaminations with lengths higher than 15 mm. For example, considering delaminations with 20 mm, the compressive load increases around 46.4% relatively to the delaminated samples. However, for small lengths, this technique is not viable due to the stress concentration induced by the hole

Repair Delaminations in Carbon/epoxy Laminates

Delaminations are the most typical damage in composite laminates, and the industrial community is continually searching new techniques to combine efficiency with cost benefits. Therefore, this work intends to analyse the application of screws on repair of composite laminates containing delaminations. It was found that this technique is beneficial for delaminations with lengths higher than 15 mm. For example, considering delaminations with 20 mm, the compressive load increases around 46.4% relatively to the delaminated samples. However, for small lengths, this technique is not viable due to the stress concentration induced by the hole

Analysis of fatigue and damage in glass-fibre-reinforced polypropylene composite materials

This paper concerns fatigue studies of polypropylene/glass-fibre thermoplastic composites produced from a bi-directional woven cloth of co-mingled E-glass fibres and polypropylene fibres with a fibre volume fraction Vf of 0.338. The effect of lay-up design and load conditions on fatigue performance were investigated. The S-N curves, the rise in the temperature of the specimens, and the loss of stiffness during the tests, are discussed. Fatigue tests were performed in controlled displacement mode and in an imposed stress range. Similar results were obtained for both load conditions. The loss of stiffness was used as a damage parameter and related to the rise of temperature. The results show that the damage parameter E present a nearly linear relationship with the rise in temperature. A small deviation was probably caused by the stress release observed in the first period of fatigue life. ©http://www.sciencedirect.com/science/article/B6TWT-3X05J91-1/1/45fb7a3f3514542947ffe55bdef10f7