Publications by John Botsis | EPFL Graph Search

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Hygro-thermal ageing of composite materials introduces a modification in the material properties of its constituents and the development of stresses that can lead to severe local damage like fracture of the reinforcing fibers and de-bonding of the latter from the matrix. The study of the complex stress field generated by this induced damage is helpful in designing more resistant materials. Modelling strain-stress filed in the vicinity of these discontinuities has led to the development of different analytic

Results on fracture, fatigue crack growth and debonding on compact tension specimens of a specially made composite material are reported. The specimens consisted of an epoxy matrix and layers of equally spaced long aligned glass fibers. The experimental data showed that for a range of fiber spacing lambda, the composite's strength sigma(A), scaled with the fiber spacing in the form of sigma(A) root lambda = constant. In all fatigue experiments, crack arrest was observed after a few fiber layers. Analysis of

Thin-ply composites represent a promising approach to further improve the performance of carbon fibre composite structures thanks to their ability to delay the onset of matrix cracking and delamination up to the point of fibre dominated failure. However, t ...

This study demonstrates the feasibility of using fibre Bragg grating (FBG) sensors to monitor the effects of hygrothermal ageing on the axial strains in a cylindrical epoxy specimen with a centrally located optical glass fibre. A 24 mm long FBG, inscribed ...

The Influence of SiO2 nanoparticles and rubber micro-fillers on the mechanical and thermal responses of an epoxy based composite is investigated using classical quantitative thermo-mechanical testing (tensile tests DMTA TMA) microstructural analysis (Micro ...

Friction welding is a joining technique for wood materials. The positive aspects of this technique are the speed of processing and the absence of chemical or mechanical agents, but the welded joints are not water resistant. To understand better the effect ...

Humanitarian actors involved in physical rehabilitation, such as the International Committee of the Red Cross (ICRC), usually provide their beneficiaries with lower-limb prostheses comprising Solid Ankle Cushion Heel (SACH) feet as these are considered app ...

In this study, a deep analysis of the reliability of lead-free (SnAgCu) solders in comparison with tin-lead solders have been done for a particular aerospace application. Creep properties of this solder composition have been investigated, and results have ...

Optical low coherence reflectometry and fiber Bragg gratings written in small diameter (50 micrometer) optical fibers were used for measurements of non-homogenous internal strain fields inside an epoxy specimen with sub-grating length resolution. The resul ...

A model for the homogenization of the elastoplastic properties of particle reinforced composites is proposed. The microstructure is described by means of a novel technique, consisting of generating particles in a pre-existent constrained Delaunay tetrahedralization of a cubic volume by means of a modified random adsorption algorithm. This technique allows generating models with different amounts of reinforcement by using the same finite element mesh. The obtained particle morphology is similar to that of ma

Identification of traction separation relations is at the forefront of damage and fracture mechanics of composite laminates. Such relations are of particular interest in fracture of laminates consisting of layers of different fiber orientations. In this st ...

Lightweight design demands and complexity requirements of modern high-end structures in aerospace, automotive, sports and bioengineering can be successfully covered by a combination of fiber reinforced polymers (FRPs) with metallic components. Conventional ...

Implanted rat bones play a key role in studies involving fracture healing, bone diseases or drugs delivery among other themes. In most of these studies the implants integration also depends on the animal daily activity and musculoskeletal loads, which affe ...

This article reports modeling techniques and results based on experimental Mode I characterization of a layered woven GFRP material with tufting reinforcement. Standard tuft and loop-less geometries are investigated on three different areal patterns to eva ...

A cohesive zone model (CZM) is proposed to assess the thickness scaling effect associated with fiber bridging during fracture. The CZM was developed through a multi-scale simulation approach and utilizes an embedded cell model of the Double Cantilever Beam ...

Fatigue delamination growth in composites is accompanied by large scale bridging (LSB) that yields important toughening effects. However, the extent of this mechanism depends on the laminate geometry rendering its modeling a challenging task. This work pre ...

Delamination is a very frequent damage mechanism that affects the integrity of laminated composites. In this study, the effect of ply orientation on crack growth resistance was analyzed for three different anti-symmetric interfaces (+/- 30 degrees, +/- 45 ...

As a second part of this series, the present study also addresses the water resistance of joints obtained by friction welding. Here, the mode II fracture is in focus, that is, 4-points end-notched flexure specimens (4-ENF) were investigated with various mo ...

Large scale bridging in mode-I delamination of layered composites is an important toughening mechanism. While its extent depends on constituent materials, it is also influenced by specimen geometry. Here, an analytical approach is adopted to express the th ...

The mode I delamination behavior of a unidirectional glass-fiber reinforced polymer with a prototype elasto-plastic polyurethane matrix (GF/PU) was investigated and compared with that of glass/epoxy (GF/EP) using double cantilever beam specimens. Fracture ...

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Analysis of hygrothermally induced fiber fracture in single fiber composite using fiber Bragg grating

Fracture and Interface Properties of a Composite with Long Aligned Fibers

Towards aerospace grade thin-ply composites: Effect of ply thickness, fibre, matrix and interlayer toughening on strength and damage tolerance

Monitoring of hygrothermal ageing effects in an epoxy resin using FBG sensor: A methodological study

Evaluation of residual strains in epoxy with different nano/micro-fillers using embedded fiber Bragg grating sensor

Influence of the moisture content on the fracture characteristics of welded wood joint. Part 1: Mode I fracture

A functional approach towards the design, development, and test of an affordable dynamic prosthetic foot

Reliability Analysis of Lead-free Solders

Distributed strain measurements using fiber Bragg gratings in small-diameter optical fiber and low-coherence reflectometry

An elastoplastic three-dimensional homogenization model for particle reinforced composites

Delamination in cross-ply laminates: Identification of traction-separation relations and cohesive zone modeling

Design optimization of a CFRP-aluminum joint for a bioengineering application

Influence of gait loads on implant integration in rat tibiae: Experimental and numerical analysis

The influence of through-thickness reinforcement geometry and pattern on delamination of fiber-reinforced composites: Part II - Modeling

A multi-scale based cohesive zone model for the analysis of thickness scaling effect in fiber bridging

Effects of large scale bridging in load controlled fatigue delamination of unidirectional carbon-epoxy specimens

Experiments and numerical modelling on angle-ply laminates under remote mode II loading

Influence of the moisture content on the fracture characteristics of welded wood joint. Part 2: Mode II fracture

An iterative analytical/experimental study of bridging in delamination of the double cantilever beam specimen

A comparative study of mode I delamination behavior of unidirectional glass fiber-reinforced polymers with epoxy and polyurethane matrices using two methods