Void Effects on the Interlaminar Shear Strength of Unidirectional Graphite-Fiber-Reinforced Composites

Abstract

A study was conducted to evaluate the effect of voids on the interlaminar shear strength (ILSS) of a polyimide matrix composite system. The graphite/PMR-15 composite was chosen for study because of the extensive amount of experience that has been amassed in the processing of this material. Composite densities and fiber contents of more than 30 different laminates were measured along with interlaminar shear strengths. Void contents were calculated and the void geometry and distribution were noted using microscope techniques such as those used in metallography. A good empirical correlation between ILSS and composite density was found. However, the most acceptable relationship between the ILSS and density was found to be a power equation that closely resembles theoretically derived expressions. As the void content increased, an increase in scatter in the strength data was observed. In laminates with low void content, the voids appeared to be more segregated in one area of the laminate. We found that void-free composites could be processed in matched metal die molds at pressures greater than 1.4 MPa and less than 6.9 MPa.

Optimization of curing cycle in carbon fiber-reinforced laminates: Void distribution and mechanical properties

“…It is well established that porosity leads to a marked reduction in the laminate mechanical properties [17,18], particularly those dominated by the matrix such as the interlaminar shear strength and the transverse tensile strength [19,20]. However, it was not always possible to distinguish the effect of porosity from other factors (such as ply clustering) because the porosity information was always limited.…”

Effect of curing cycle on void distribution and interlaminar shear strength in polymer-matrix composites

“…Their validity is not proven for long cylindrical voids in a viscous matrix surrounded by aligned fibers, the standard morphology observed in out-of-autoclave composites. In addition, although there are many papers in the open literature regarding the detrimental effect of voids on the mechanical performance of composites (Costa et al, 2001;Wisnom et al, 1996;Bowles and Frimpong, 1992), there is a lack of information regarding the influence of curing conditions on the actual volume fraction, shape and spatial distribution of voids within the laminate.…”

Influence of porosity on ultrasonic wave velocity, attenuation and interlaminar interface echoes in composite laminates: Finite element simulations and measurements

“…It is recognized that one of the detrimental defects in CFRP laminates is the porosity [1], i.e., distribution of minute pores within the laminate. Porosity levels of more than 2 % by volume fraction [2] can significantly degrade the mechanical properties of the composite laminates such as interlaminar shear strength [3][4][5][6][7], flexural strength [3,8], tensile strength [4,7], compression strength [9], etc.…”