Improvement of Bending Strength of Carbon Fiber/Thermoplastic Epoxy Composites <br/>—Effects of Molecular Weight of Epoxy on Carbon Fiber/Matrix Interfacial Strength and Connection of Cracks in Matrix

The bending strength of carbon fiber/thermoplastic epoxy composites (CF/TP-EP Compo.) had bi-linear increase with increase of weight-average molecular weight (Mw) of matrix. The transition in the bending strength appeared at around 55k of Mw (“k” means 103). SEM observation of fractured surface of CF/TP-EP Compo. showed that the fracture mode changed from interfacial failure to fiber breakage dominated failure. The smooth surface of carbon fibers appeared at lower Mw than 55k while some resin remained on the fibers indicating good adhesion between carbon fiber and matrix at higher Mw than 55k. The interfacial shear strength between carbon fiber and matrix bi-linearly increased with an increase of Mw similarly to the bending strength of the composite, measured by the micro droplet test. The dynamic loss tanδ of the matrix measured at 2 Hz also showed a bi-linear relationship with respect to Mw having a knee point at Mw = 55k. The connection probability of two cracks introduced on each side of specimens also confirmed that the interfacial strength between carbon fiber and matrix is the key for the mechanical performance of CF/TP-EP Compo. in bending

Multi-instrument multi-scale experimental damage mechanics for fibre reinforced composites

© Published under licence by IOP Publishing Ltd. Reliable investigation of damage in fibre reinforced composites requires concurrent in- and ex-situ application of multiple instruments at different scale: digital image correlation, acoustic emission registration, optical/electron microscopy, C-scan, X-ray imaging and micro-computed tomography. The multi-instrument experimental mechanics allows detailed damage monitoring and inspection

Biaxial tensile properties of reinforcements in composites

The deformability of acomposite reinforcement depends onitsinternal structure and has a relevant influence on the quality of the composite part. Among the mechanical features of a composite reinforcement, the bi-axial behaviour plays an important role on its capability to drape a complex shape. In this chapter the methodologies employed to measure and to predict the bi-axial behaviour of composite reinforcements are discussed. The features of some experimental devices adopted to investigate the response to bi-axial loading of composite reinforcements are detailed. A prediction tool based on an analytical model of a plane weave reinforcement is briefly described and compared to experimental data. Finally, the characteristics of reliable numerical models, based on the finite element method, are highlighted in terms of information obtained at macro and meso-scale

Plane strain shakedown analysis of unidirectional fiber reinforced metal matrix composites

In this paper the determination of the shakedown domain in the space of macroscopic stresses of unidirectional fibre reinforced metal matrix composites is obtained solving a shakedown analysis problem defined over a Representative Volume. The analyses are based on the kinematic shakedown theorem and the assumption of plane strain state. The mathematical programming problem generated is solved by an iterative procedure

Biaxial tensile behaviour of composite reinforcements

The deformability of a composite reinforcement depends mainly on its internal structure and has a relevant influence on the quality of a composite component. Among the mechanical features of a composite reinforcement, the biaxial behavior plays an important role on its capability to drape a complex shape. This chapter details some of the methodologies employed to measure and to predict the tensile biaxial behavior of textile composite reinforcements. The features of some experimental biaxial loading devices are described, as well as some experimental results. A predictive analytical model for plain weave reinforcements is briefly described and compared to experimental data. Finally, the main characteristics of numerical models dedicated to meso-scale simulations, based on the finite element method, are highlighted

Mechanical modelling of monofilament technical textile components

A homogenization numerical approach for the prediction of the mechanical properties of technical textile structures is described in this paper. The numerical analyses deal with modelling at two scale levels. The first scale aims to predict the mechanical behaviour of the textile by the numerical analysis of a Representative Volume. The second scale modelling evaluates the mechanical response of the entire textile component employing the homogenized textile mechanical behaviour obtained in the first step. The numerical approach is used to predict the stress-strain state of a polyester monofilament textile component employed in a narrow industrial application, screen printing or serigraphy

Thermo-mechanical loading of GFRP reinforced thin concrete panels

The experimental investigation is focused on the thermo-mechanical behaviour of thin concrete panels reinforced with GFRP rebars. The considered thin panels (thickness of 4 cm) were exposed to increasing temperature and bending loading. These concrete elements are typical for low bearing function concrete layers in façade claddings. The influence of two aspects was studied: the concrete cover and the external surface of rebars. The heating condition was such that the temperature of the internal GFRP rebars reached about the transition temperature of the resins. This allowed to verify the variation of the deformability and the load carrying capacity of the panels with post-heating bending tests. As main outcome, the imposed temperature did not generate evident degradation of the GFRP reinforcement and of its adhesion to the concrete, while a reduction of the initial global stiffness was measured