Transient thermal stresses at near surface elliptical holes

An experimental study is conducted to determine the influence of the near surface elliptical holes on the stress field when the surface experiences a rapid temperature change. The problem is formulated as a two-dimensional transient problem in a multiply connected semi-infinite region. It is assumed that the quasi-static formulation of thermoelasticity is valid. The experimental technique used was photothermoelasticity by means of heating. The transient thermal stress concentration factors around the elliptical boundary are obtained, and the variation of the stress concentration factor with the geometrical parameters (major and minor axes) and the angular orientation (measured as the angle between the major axis and straight boundary) of the ellipse are investigated;Four different ellipse sizes, with the ratio of the minor to major axis b/a = 0.50, 0.40, 0.33 and 0.30 and five different angular orientations, (theta) = 0 , 22.5(DEGREES), 45(DEGREES), 75(DEGREES) and 90(DEGREES), are used. The results are expressed in terms of non-dimensional variables and empirical equations for the maximum stress (stress concentration factor) for the different angular orientations are developed

Fracture toughness analysis of epoxy-recycled rubber-based composite reinforced with graphene nanoplatelets for structural applications in automotive and aeronautics

This study proposes a new design of lightweight and cost-efficient composite materials for the aeronautic industry utilizing recycled fresh scrap rubber, epoxy resin, and graphene nanoplatelets (GnPs). After manufacturing the composites, their bending strength and fracture characteristics were investigated by three-point bending (3PB) tests. Halpin-Tsai homogenization adapted to composites containing GnPs was used to estimate the moduli of the composites, and satisfactory agreement with the 3PB test results was observed. In addition, 3PB tests were simulated by finite element method incorporating the Halpin-Tsai homogenization, and the resulting stress-strain curves were compared with the experimental results. Mechanical test results showed that the reinforcement with GnPs generally increased the modulus of elasticity as well as the fracture toughness of these novel composites. Toughening mechanisms were evaluated by SEM fractography. The typical toughening mechanisms observed were crack deflection and cavity formation. Considering the advantageous effects of GnPs on these novel composites and cost efficiency gained by the use of recycled rubber, these composites have the potential to be used to manufacture various components in the automotive and aeronautic industries as well as smart building materials in civil engineering applications

Conductive 3D nano-biohybrid systems based on densified carbon nanotube forests and living cells

Conductive biohybrid cell-material systems have applications in bioelectronics and biorobotics. To date, conductive scaffolds are limited to those with low electrical conductivity or 2D sheets. Here, 3D biohybrid conductive systems are developed using fibroblasts or cardiomyocytes integrated with carbon nanotube (CNT) forests that are densified due to interactions with a gelatin coating. CNT forest scaffolds with a height range of 120–240 µm and an average electrical conductivity of 0.6 S/cm are developed and shown to be cytocompatible as evidenced from greater than 89% viability measured by live-dead assay on both cells on day 1. The cells spread on top and along the height of the CNT forest scaffolds. Finally, the scaffolds have no adverse effects on the expression of genes related to cardiomyocyte maturation and functionality, or fibroblast migration, adhesion, and spreading. The results show that the scaffold could be used in applications ranging from organ-on-a-chip systems to muscle actuators. Graphical abstract: [Figure not available: see fulltext.

Mechanical properties and characterization of epoxy composites containing highly entangled as-received and acid treated carbon nanotubes

Huntsman–Merrimack MIRALON® carbon nanotubes (CNTs) are a novel, highly entan-gled, commercially available, and scalable format of nanotubes. As-received and acid-treated CNTs were added to aerospace grade epoxy (CYCOM® 977-3), and the composites were characterized. The epoxy resin is expected to infiltrate the network of the CNTs and could improve mechanical properties. Epoxy composites were tested for flexural and viscoelastic properties and the as-re-ceived and acid treated CNTs were characterized using Field-Emission Scanning and Transmission Electron Microscopy, X-Ray Photoelectron Spectroscopy, and Thermogravimetric Analysis. Composites containing 0.4 wt% as-received CNTs showed an increase in flexural strength, from 136.9 MPa for neat epoxy to 147.5 MPa. In addition, the flexural modulus increased from 3.88 GPa for the neat epoxy to 4.24 GPa and 4.49 GPa for the 2.0 wt% and 3.0 wt% as-received CNT/epoxy compo-sites, respectively. FE-SEM micrographs indicated good dispersion of the CNTs in the as-received CNT/epoxy composites and the 10 M nitric acid 6 h treatment at 120 °C CNT/epoxy composites. CNTs treated with 10 M nitric acid for 6 h at 120 °C added oxygen containing functional groups (C– O, C=O, and O=C–O) and removed iron catalyst present on the as-received CNTs, but the flexural properties were not improved compared to the as-received CNT/epoxy composites

Modeling-Driven Damage Tolerant Design of Graphene Nanoplatelet/Carbon Fiber/Epoxy Hybrid Composite Panels for Full-Scale Aerospace Structures

The objective of this study is to design a new nano graphenecarbon fiberpolymer hybrid composite that can be used for the NASA SLS Composite Exploration Upper Stage (CEUS) forward skirt structure. The new material will improve the resistance to open-hole compression failure of the structure relative to traditional polymer fiber composites. The material is designed rapidly and with little cost using the Integrated Computational Materials Engineering (ICME) approach. Multiscale modeling and experiments are used to synergistically optimize the material design to yield improved properties and performance by controlling key processing parameters for manufacturing nano-enhanced materials. Specifically, the nanocomposite panel showed a 22 reduction in mass relative to the traditional composite panel, while both designs are equal in terms of ease of manufacture. This potential mass savings corresponds to an estimated 45 savings in materials and manufacturing costs. The multiscale ICME workflow developed for this project can be readily applied to the development of nano-enhanced composite materials and large aerospace structures. In addition, all key aspects of ICME were employed to complete this project including multiscale modeling, experimental characterization and visualization, data management, visualization, error and uncertainty quantification, and education. The results presented herein indicate a dramatic level of success, as well as the power and potential of ICME approach and multiscale modeling for composite materials

Transient thermal stresses at near surface elliptical holes

An experimental study is conducted to determine the influence of the near surface elliptical holes on the stress field when the surface experiences a rapid temperature change. The problem is formulated as a two-dimensional transient problem in a multiply connected semi-infinite region. It is assumed that the quasi-static formulation of thermoelasticity is valid. The experimental technique used was photothermoelasticity by means of heating. The transient thermal stress concentration factors around the elliptical boundary are obtained, and the variation of the stress concentration factor with the geometrical parameters (major and minor axes) and the angular orientation (measured as the angle between the major axis and straight boundary) of the ellipse are investigated;Four different ellipse sizes, with the ratio of the minor to major axis b/a = 0.50, 0.40, 0.33 and 0.30 and five different angular orientations, (theta) = 0 , 22.5(DEGREES), 45(DEGREES), 75(DEGREES) and 90(DEGREES), are used. The results are expressed in terms of non-dimensional variables and empirical equations for the maximum stress (stress concentration factor) for the different angular orientations are developed.</p

Multifunctional Energetic Structural Composites: Epoxy-Rubber Matrix With Nickel Aluminum Reinforcements

International audienc

Alternative composite design from recycled aluminum chips for mechanical pin-joint (knuckle) applications

In this work, an alternative aluminum matrix composite (AMCs) was designed from the recycled chips of the aluminium series of AA7075 (90 wt %) and AA1050 (10 wt %) given by French aeronautic company through combined method of powder metallurgy followed by Sintering + Forging. We aimed for the application for the connection link in a mechanism to transfer motion, for example; between the two railways wagons etc. and also some connecting link in aeronautical pieces as an alternative replacement for conventional alloys used in this area. First of all, A typical Al-Zn-Mg-Si-Ni matrix was developed and reinforced basically with B2O3 (5, 10%). Chip milling was performed using high energy milling in a planetary ball mill with an inert argon atmosphere to prevent oxidation of the powders. Two compositions were prepared with two different percentages of B2O3 and also one composition was kept without reinforcement for comparison with the reinforced ones. Mechanical properties, compression and dynamic drop weight tests of these composites designed here can be improved with the doping process and doping volume fractions. Micro-hardness results were compared according to the optimization conditions of the doping and the reinforcement. Static compression and impact-drop weight tests were carried out. The microstructure analyses have been carried out by Scanning Electron Microscope (SEM)

Toughening mechanism in epoxy resin modified recycled rubber based composites reinforced with gamma-alumina, graphene and CNT

In this research, low cost devulcanized recycled rubber based composites were designed with fine gamma alumina (d \u3c 5–10 μm) reinforcements containing minor reinforcements such as nano graphene platelets and Carbon Nano Tubes. After determination (in different wt% percentages) of the reinforcements with matrix, a special process was applied to complete successfully the manufacturing of the composites. After that, the relevant toughening mechanisms for the most suitable reinforcements were analyzed in detail for aeronautical engineering applications. For this purpose, certain mechanical and physical properties (ISO 13586:2000, KIc – Fracture toughness stress intensity factor and GIc- Critical energy release rate in mode I) have been determined by fracture toughness tests (static 3P bending test with single edge notch specimens, Charpy impact, etc.). Microstructural and fracture surfaces analysis have been carried out by means of Optical Microscopy (OM) and Scanning Electron Microscopy (SEM)

Toughening mechanisms on recycled rubber modified epoxy based composites reinforced with alumina fibers

Environmental and economic concerns has been a motivation for the material manufacturers to produce new, robust, lightweight and cost-effective materials. Therefore, aeronautic and automobile industries are investigating multifunctional composite materials that can meet their expectations. In this regard, polymer based composites can have high specific strength with the contribution of resistant fillers. As a polymer, epoxy is considered an appropriate matrix, which can be modified by different agents. First option is the addition of hard particles and second is that the inclusion of thermoplastics or the addition of elastomeric materials. Since, epoxy exhibits high brittleness due to its highly cross-linked nature, modifiers less rigid than the matrix can serve as unique tougheners enhancing the ductility. In this study, a good combination of both hard and soft modifiers is used. In addition to mechanical characteristics, using of fresh clean scrap EPDM rubbers adds an economic and environmental value to this study. Also, due to its favorable structural characteristics such as interlocking effects of fibers, addition of alumina fibers (AF) ensures desired mechanical properties in case of a homogeneous distribution. This paper primarily explains the mechanical behavior as well as damage mechanisms of epoxy-fresh scrap rubber composites. The mechanical and physical properties of these composite systems are studied in the present work. Dynamic Mechanical Analysis (DMA) analyses were carried out to determine thermal-mechanical properties. Three-point bending and fracture toughness tests were realized with single edge notched beam (SENB) and smooth specimens. Finally, scanning electron microscope (SEM) was used to observe fracture surfaces and the microstructure