Detection of Voids in Carbon/Epoxy Laminates and Their Influence on Mechanical Properties

Abstract

Defects, such as voids and delaminations, may significantly reduce the mechanical performance of components made of composite laminates. Distributed voids and porosity are generated during composite processing and are influenced by prepreg characteristics as well as by curing cycle parameters. On the basis of rheological and thermal analyses, as well as observations of laminates produced by different processing conditions, curing pressure appears the most influent factor affecting the void content. This work compares different methods for void analysis and quantitative evaluation (ultrasonic scan, micro-computed tomography, acid digestion, SEM image analysis) evidencing their applicative limitations. Carbon/epoxy laminates were produced in autoclave or oven by vacuum bag technique, using different processing conditions, so that void contents ranging from 0% to 7% volume were obtained. Effects of porosity over laminates mechanical performances are analysed. The results of tensile and compressive tests are discussed, considering the effect that different curing cycles have over void content as well as over fibre/resin fraction. Interlaminar strength, as measured by short beam shear tests, which is a matrix-dominated property, exhibits a reduction of failure strength up to 25% in laminates with the highest void content, compared to laminates with no porosity.

Voids in fiber-reinforced polymer composites: A review on their formation, characteristics, and effects on mechanical performance

“…They found the US technique incapable of identifying the voids in their case. For a woven carbon/epoxy composite, Di Landro et al 188 reported a general trend: Similar void contents were measured with micro-CT and density determination, but the values measured with SEM were smaller. They observed a higher discrepancy between the results of the three methods at void contents above 5-6%, attributed to the void orientation effects.…”

“…Using the k-means clustering algorithm, they could segment the voxel models into yarns, matrix, and voids, which can be used in creating realistic models of the composite. The voidage in tubular braided Kevlar/epoxy composites was evaluated using micro-CT by Melenka et al 188 They identified and quantified individual voids using MATLAB. A full analysis of void content, size (distribution), and location was performed, of which some results are presented in Void characteristics section.…”

Utilization of linseed cake as a postagricultural functional filler for poly(lactic acid) green composites

“…However, it is vital to remember that modifying the thermomechanical properties by the addition of LC is the result of the simultaneous impact of the following—the presence of rigid lignocellulosic structures; oil migration, which at the same time causes a nucleating effect; the creation of amorphous plasticizing domains in PLA; and a decrease in interfacial interactions between PLA and LC/LCA particles by the accumulation of migrating oil in the interfacial region. The decrease in tanδ is caused by the incorporation of organic rigid structures into the polymeric matrix and by the increase in PLA crystallinity . If we compare the changes of tanδ variations in the range of glass transition, we can observe that LC‐filled composites revealed better damping properties than materials modified with LCA filler, which may be attributed to the plasticizing effect caused by higher amounts of linseed oil in LC.…”

Effect of the Diameter Ratio on the Flexural Stress of Carbon Fibre Composite Rod

“…Analytical expressions were derived to obtain the normal and shear stress distributions in a three-point bending test [17]. Di Landro et al found that defects, such as voids and delaminations, significantly reduced the mechanical performance of components made of composite laminates [18]. The change in mechanical properties like tensile strength and hardness were investigated by changing the percentage composition of carbon by 30%, 35% and 45% in the carbon epoxy composite [19].…”