A review of failure modes and fracture analysis of aircraft composite materials

This paper presents the results of an experimental investigation aiming at determining the mechanical properties of Glass Fiber Reinforced Polymer (GFRP) element produced by the Brazilian industry to classify it for structural applications.. The material samples used in this work were (i) prepared in accordance to ABNT-NBR15708:2011 recommendations, (ii) extracted from web and flange parts of different geometries of one standard H-shaped GFRP single profile, (iii) 2D fiber-reinforced fibrous and (iv) exhibited fibers' orientation on the longitudinal/pultrusion direction. A fairly extensive experimental program was carried out to cover both stiffness and strength structural characteristics of GFRP element, comprising the following mechanical failures modes: (i) direct tension and compression, (ii) two-point flexural bending, (iii) pin-bearing pushed-out and (iv) interlaminar shear deformation. Based on the obtained results, it was possible to conclude that the GFRP element analyzed displays structural classification compatible to E17 class mechanical requirement.

Mechanical Properties of Glass Fiber Reinforced Polymers Members for Structural Applications

Epoxy compatible P(St-co-GMA) copolymer based nanofibrous mats are introduced by electrospinning onto uni-directional (UD) and 0/90 twill weave carbon fiber/epoxy prepreg systems as interlayers. Anticipated in-plane strength improvement via higher matrix cracking resistance at the free edges, nanofibrous interlayered composites are verified by uni-axial tension tests on (0)6 and (0/90)6woven laminates. The ultimate tensile strength of the (0)6 laminates increased by 12%, whereas the tensile strength of the woven fabric composites increased by 18%. A localized interlayer reinforcing approach where the interlayers are incorporated at the vicinity of the hole is evaluated via open hole tension (OHT) tests of (0/90)6woven laminates. The OHT strength increased by 9%.

Global and local nanofibrous interlayer toughened composites for higher in-plane strength

Microscopic analysis of failure in woven carbon fabric laminates coupled with digital image correlation and acoustic emission

Glass fiber reinforced polymers (GFRP) have become a preferable material for reinforcing or strengthening reinforced concrete structures due to their corrosion resistance, high strength to weight ratio, and relatively low cost compared with carbon fiber reinforced polymers (CFRP). However, the limited fatigue life of GFRP hinders their use in infrastructure applications. For instance, the low fatigue life of GFRP caused design codes to impose stringent stress limits on GFRP that rendered their use non-economic under significant cyclic loads in bridges. In this paper, we demonstrate that the fatigue life of GFRP can be significantly improved by an order of magnitude by incorporating Multi-Wall Carbon Nanotubes (MWCNTs) during GFRP fabrication. GFRP coupons were fabricated and tested under static tension and cyclic tension with mean fatigue stress equal to 40% of the GFRP tensile strength. Microstructural investigations using scanning electron microscopy (SEM) and Fourier Transform Infrared (FTIR) spectroscopy were used for further investigation of the effect of MWCNTs on the GFRP composite. The experimental results show the 0.5 wt% and the 1.0 wt% MWCNTs were able to improve the fatigue life of GFRP by 1143% and 986%, respectively, compared with neat GFRP.

/pdf/improving-fatigue-performance-of-gfrp-composite-using-carbon-k69oyor0t3.pdf

Improving Fatigue Performance of GFRP Composite Using Carbon Nanotubes

This paper describes fractographic features observed in aerospace composites failed under tensile loads. Unidirectional Carbon Fibre Reinforced Plastic (UD CFRP) and Unidirectional Glass Fibre Reinforced Plastic (UD GFRP) composite specimens were fabricated and tested in tension. The morphology of fractured surfaces was studied at various locations to identify failure mechanism and characteristic fractographic features. CFRP composites displayed transverse crack propagation and the fracture surface showed three distinct regions, viz., crack origin, propagation and final failure. Significant variations in the fractographic features were noticed in crack propagation and final failure regions. Crack propagation region exhibited brittle fracture with chevron lines emanating from the crack origin. The entire crack propagation region exhibited radial marks on the individual fibre broken ends. On the other hand, the final fracture region revealed longitudinal matrix splitting and radial marks in majority of locations, and chop marks at some locations. The change in fracture mode in the final fracture was attributed to superimposition of bending loads. GFRP composites exhibited broom like fracture with extensive longitudinal splitting with radial marks present on individual fibre broken ends. Transverse fracture was observed at a few locations. These fracture features were analyzed and correlated with the loading conditions.

/pdf/fractographic-analysis-of-tensile-failures-of-aerospace-2zv7rlm9mg.pdf

Honnudike Venkateshwararao Ramachandra

Papers

Fractographic analysis of tensile failures of aerospace grade composites