Porosity Effects on Interlaminar Fracture Behavior in Carbon Fiber-Reinforced Polymer Composites

Abstract

Fiber-reinforced polymer composite materials have become materials of choice for manufacturing application due to their high specific stiffness, strength and fatigue life, low density and thermal expansion coefficient. However, there are some types of defects such as porosity that form during the manufacturing processes of composites and alter their mechanical behavior and material properties. In his study, hand lay-up was conducted to fabricate samples of carbon fiber-reinforced polymer composites with three different vacuum levels in order to vary porosity content. Nondestructive evaluation, destructive techniques and mechanical testing were conducted. Nondestructive evaluation results showed the trend in percentages of porosity through-thickness. Serial sectioning images revealed significant details about the composite's internal structure such as the volume, morphology and distribution of porosity. Mechanical testing results showed that porosity led to a decrease in both Mode I static interlaminar fracture toughness and Mode I cyclic strain energy release rate fatigue life. The fractographic micrographs showed that porosity content increased as the vacuum decreased, and it drew a relationship between fracture mechanisms and mechanical properties of the composite under different modes of loading as a result of the porosity effects. Finally, in order to accurately quantify porosity percentages included in the samples of different vacuum levels, a comparison was made between the parameters and percentages resulted from the nondestructive evaluation and mechanical testing and the features resulted from fractography and serial sectioning.

Characteristic analysis of biaxially stretched PVDF thin films

“…In particular, with higher stretch ratio of R = 4 × 4 shown in Figure (e), the short fibrillar slit‐like porous structures grow with crack and porosity in both stretching directions. As known, more porosity in PVDF film would reduce material strength and resistance to crack propagation as well . Though the porosity and the crack do not have significant influence on the piezoelectric properties, these deficiencies will be a problem of quality reduction …”

Effect of Graphene Additive on Flexural and Interlaminar Shear Strength Properties of Carbon Fiber-Reinforced Polymer Composite

“…Nevertheless, Costa et al [35] emphasized in their review that the interlaminar shear strength can be significantly affected if the porosity content goes beyond 0.9%. In addition, Hakim et al [36] highlighted that higher porosity levels make the composite part sensitive to water penetration and environmental factors which detrimentally impact the static and fatigue strength. The minimum void percentage that we found can be attributed to the high vacuum pressure applied during the curing process.…”

“…The minimum void percentage that we found can be attributed to the high vacuum pressure applied during the curing process. Hakim et al [36] evaluated the impact of vacuum pressure on the porosity level. They examined three levels of vacuum pressure: poor (0 mmHg), medium (330 mmHg), and high (686 mmHg) and concluded that poor vacuum pressure induces 3.43% of porosity versus only 1.43% with high vacuum pressure.…”

A new approach to the structure–properties relationship evaluation for porous polymer composites

“…The effect of the porosity on the mechanical behavior of polymer composites is under the interest of many researchers. For example, Hakim et al [23] reported the influence of porosity on the interlaminar fracture behavior in carbon-fiber-reinforced polymer composites. Specifically, the increase of porosity led to the decrease in both interlaminar fracture toughness and thermal conductivity.…”