Computational modelling and experimental characterisation of heterogeneous materials

Heterogeneous materials can exhibit behaviour under load that cannot be described by classical continuum elasticity. Beams in bending can show a relative stiffening as the beam depth tends to zero, a size effect. Size effects are recognised in higher order continuum elastic theories such as micropolar elasticity. The drawback of higher order theories is the requirement of addition constitutive relations and associated properties that are often difficult to establish experimentally. Furthermore the finite element method, of great benefit in classical elasticity, has shown limitations when applied to micropolar elasticity. The determination of additional constitutive properties and the computational modelling of micropolar elasticity will be discussed in the context of a model heterogeneous material loaded in simple 3 point bending. The model material was created by drilling holes in aluminium bar in a regular pattern, with the hole axis normal to the plane of bending. The bending tests show that a size effect is present. These results are compared against modelling the detailed beam geometries in the finite element package ANSYS, which again shows the size effect. These two bending test are used to extract the additional micropolar elastic material properties. A comparison is then made against analytical solutions,numerical solutions using a micropolar beam finite element and a micropolar plane stress control volume method.It will be shown that the need for extensive experimental testing to determine the additional constitutive properties may not be necessary with the appropriate use of numerical methods

Generation and characterization of T40/A5754 interfaces with lasersPatrice

Laser-induced reactive wetting and brazing of T40 titanium with A5754 aluminum alloy with 1.5 mm thickness was carried out in lap-joint configuration, with or without the use of Al5Si filler wire. A 2.4 mm diameter laser spot was positioned on the aluminum side to provoke spreading and wetting of the lower titanium sheet, with relatively low scanning speeds (0.1–0.6 m/min). Process conditions did not play a very significant role on mechanical strengths, which were shown to reach 250–300 N/mm on a large range of laser power and scanning speeds. In all cases considered, the fracture during tensile testing occurred next to the TiAl3 interface, but in the aluminum fusion zone. The interfacial resistance was then evaluated with the LASAT bond strength tester, based upon the generation and propagation of laser-induced shock waves. A 0.68 GPa uniaxial bond strength was estimated for the T40/A5754 interface under dynamic loading conditions

Fatigue characterization of T300/924 polymer composites with voids under tension‐tension and compression‐compression cyclic loading

Fibrous polymer composites exhibit excellent properties such as high specific stiffness/strength and good fatigue performance. However, as inherent defects of polymer composites, voids have been reported to have an impact on their load‐bearing properties including fatigue resistance. In the interest of safety, the effect of voids on fatigue behaviours of composites should be understood and quantified. In this article, the effect of voids on the fatigue of T300/924 composites was evaluated in terms of their fatigue life, stiffness degradation, and cracks propagation under tension‐tension and compression‐compression loadings. The failure probability was assessed by Weibull distribution. Furthermore, crack measurement and fractographic analysis reveal that the effect of voids on the failure mechanisms of the material under various loading configurations could be different. Lastly, an analytical residual stiffness model was proposed, and a good correlation was obtained between the experimental data and the prediction results.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142461/1/ffe12721_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142461/2/ffe12721.pd

Investigation of intrinsic de-bonding in bonded concrete overlays: Material characterisation and numerical study

© 2018 Growing Science Ltd. All rights reserved. This study investigates the evolution of intrinsic interfacial de-bonding of Roller Compacted Steel Fibre Reinforced Polymer Modified Concrete (RC-SFR-PMC) bonded on substrate Ordinary Portland Cement Concrete (OPCC), using both experimental and numerical techniques. The relative effects of evolving material inhomogeneity and composite dimensional stability during curing was studied as a function of overlay structural scale, using a 2D plane strain Interface Cohesive Zone Model (ICZM). The effects of creep coefficient on interface restraint capacity and ensuing cohesive zone length were clearly evaluated. The results showed that the applied curvature due to the measured shrinkage strain was inadequate to cause critical de-bonding. In the FEA results, while the rate of interface energy release generally varies as a function of the bi-material relative stiffness and overlay structural scale, it is also evident that the two variables lose effects as the overlay structural scale approaches 0.50. The overall indicative trend shows that the rate of energy release in compliant overlay when relative stiffness (α0. Therefore, a more compliant overlay typically exhibits less relative restraint to bending induced de-bonding

Strengthening Techniques & Failure Modes of RC Beam Strengthened Using Fibre Reinforced Polymer. A Review

strengthening of reinforced concrete (RC) beamusing Fibre Reinforced Polymer (FRP) revealed as the mostefficient material due to its various mechanical properties. Theprevious experimental studies conducted to discussstrengthening schemes for RC beam, based on the observed crackpattern and failure mechanism for strengthening RC beam. Thedevelopment of crack formation on RC beams under loadingidentifies the mode of failure and strengthening scheme required,such as to increase the flexural capacity of RC beam; FRP isapplied at the tension zone. Similarly, for shear and torsionstrengthening FRP wraps are being applied at the faces of thebeam. The studies have shown the high strength in shear andtorsion is achieved by applying U-shape wrap. Full warp giveshigh strength in torsion strengthening but practically theapplication of full wrap on RC beam is impossible and requiredmore in-depth study to propose practical solutions. However, thecombined effects of flexure, shear and torsion have not beendiscussed yet. Therefore, the strengthening schemes fromliterature are combined to propose new strengthening scheme forRC beam under combine the action of flexure, shear and torsion.However, experimental data are required to validate theproposed scheme

Investigation of the Mechanical Properties of a Carbon Fibre-Reinforced Nylon Filament for 3D Printing

Additive manufacturing (i.e., 3D printing) has rapidly developed in recent years. In the recent past, many researchers have highlighted the development of in-house filaments for fused filament fabrication (FFF), which can extend the corresponding field of application. Due to the limited mechanical properties and deficient functionality of printed polymer parts, there is a need to develop printable polymer composites that exhibit high performance. This study analyses the actual mechanical characteristics of parts fabricated with a low-cost printer from a carbon fibre-reinforced nylon filament. The results show that the obtained values differ considerably from the values presented in the datasheets of various filament suppliers. Moreover, the hardness and tensile strength are influenced by the building direction, the infill percentage, and the thermal stresses, whereas the resilience is affected only by the building direction. Furthermore, the relationship between the mechanical properties and the filling factor is not linear

Impact of nano sized SiC and Gr on mechanical properties of aerospace grade Al7075 composites

Aluminum composites exhibit high resistance to wear and corrosion, possess high strength, offer durability and more such properties. In this study, Al7075, reinforced with nano size SiC - Gr was produced by a stir casting technique and its microstructure and mechanical behavior were evaluated. Reinforcements were added in the range of 0 - 3 wt. %. The microstructure study, tensile and compression strength of the developed hybrid Metal Matrix Composites have been analyzed and examined. From the investigational study, it was found that the reinforcements are evenly dispersed in the base material. The porosity and density of the developed composites were found to be enhanced. The mechanical properties such as ultimate tensile and compressive strength of the developed MMCs could be improved by addition of SiC particulates compared to base material. Further, the strength of developed hybrid composites was found to be decreased by adding of solid lubricant such as graphite (Gr) particulates along with hard ceramic particulates. Finally, fractured surface of the tensile test specimens were analysed using a SEM analysis

GFRP - FAILURE CHARACTERISTICS ANALYSIS

The objective of this paper is to predict the ultimate failure load and also is to characterize the failure modes in GFRP composite coupons using Multi linear regression. IBM SSPS20 version is used to predict the ultimate failure load using Multi linear regression with failure loads as dependent variable and the load range of 10kg each and its corresponding hits as independent variable. The three point bending test was conducted on the GFRP composite coupons till failure of the GFRP composite coupons. Based on the effect of various failure modes the ultimate failures of the specimen were also predicted by means of multi linear regression method. Â

Nanofiller Fibre-Reinforced Polymer Nanocomposites

In this work, the technology of nano and micro-scale particle reinforcement concerning various polymeric fibre-reinforced systems including polyamides (PA), polyesters, polyurethanes, polypropylenes and high performance/temperature engineering polymers such as polyimide (PI), poly(ether ether ketone) (PEEK), polyarylacetylene (PAA) and poly p-phenylene benzobisoxazole (PBO) is reviewed. When the diameters of polymer fibre materials are shrunk from micrometers to submicrons or nanometers, there appear several unique characteristics such as very large surface area to volume ratio (this ratio for a nanofibre can be as large as 103 times of that of a microfibre), flexibility in surface functionalities and superior mechanical performance (such as stiffness and tensile strength) compared with any other known form of the material. However, nanoparticle reinforcement of fibre reinforced composites has been shown to be a possibility, but much work remains to be performed in order to understand how nanoreinforcement results in dramatic changes in material properties. The understanding of these phenomena will facilitate their extension to the reinforcement of more complicated anisotropic structures and advanced polymeric composite systems