Gábor Romhány

Mode I fracture resistance of glass fiber mat-reinforced polypropylene composites at various degree of consolidation

Abstract The energy release rate at steady-state fracture of glass fiber mat-reinforced polypropylene (GMT-PP) composites of different degree of consolidation was determined by various methods considering the mechanical energy ( G ss ), acoustic emission energy ( G AE ) and heat ( G h ) release rates. All these energy release rates showed the same tendency, namely increase with increasing surface weight (consolidation degree) of the GMT-PP sheets. To determine the initiation fracture toughness ( K IC ) the resistance curve concept was adopted. K IC increased whereas the related strain energy release rate ( G IC ) did not change with the consolidation degree.

Essential Work of Fracture and Acoustic Emission Study on TPNR Composites Reinforced by Kenaf Fiber

Kenaf fiber (KF) based thermoplastic natural rubber (TPNR) composite was produced by melt blending with polypropylene (PP). Kenaf fiber (15% by volume) and TPNR were mixed in as Haake 600p internal mixer. The fracture behavior of the TPNR matrix and of TPNR—kenaf (with and without maleic anhydride grafted polypropylene, MAPP) composites was evaluated using the essential work of fracture (EWF) method and double edge notched tensile (DENT) specimens. Various ligament lengths were employed ranging from 4 to 12 mm. The strain rate was fixed at 2 mm/min. The specific work of fracture (we) and plastic work (βwp) showed the highest energy for TPNR that corresponds to its ductility and allows the application of the EWF approach. It was found that the presence of kenaf fibers and MAPP reduced the toughness of TPNR and changed the ductile fracture to brittle behavior. SEM observation revealed that energy absorption mechanisms include matrix deformation, fiber pullout, and fiber breakage. Acoustic emission (AE) was employed to analyze the failure processes further. The signals emitted by composites were substantially higher than that of the TPNR matrix, reflecting that also the failure mechanisms were affected by the fibers incorporated.

Failure Assessment and Evaluation of Damage Development and Crack Growth in Polymer Composites Via Localization of Acoustic Emission Events: A Review

ABSTRACT This review aims at showing how the location of acoustic emission (AE) in loaded polymer composites can be used to get a deeper insight into the onset and growth of damage, and associated failure events and sequences. Different location methods (experimental and theoretical) are briefly introduced along with AE characteristics in time and frequency domains. Linear (1D), planar (2D), and spatial (3D) locations of AE are examined through selected examples. The cited works demonstrate the versatile use of AE. Apart from damage and failure assessment, AE can be used to reconstruct crack growth, and thereby help determine the accurate fracture mechanical parameters. Unlike the detection of the development of damage, the identification of failure mechanisms by analyzing selected AE signal parameters, including their clustering, requires further research. Unraveling the failure mode is, however, a key topic with respect to structural integrity, residual strength, and lifespan expectation of composite parts. A recent major challenge is to establish a reliable, real-time structural health monitoring system making use of located AE events monitored by built-in sensors.

Investigation of oil palm and pineapple fiber reinforced phenol formaldehyde composites by acoustic emission technique

The fracture mechanics response of oil palm and pineapple fiber reinforced phenol formaldehyde composites was investigated. The fracture behaviour was influenced by the fiber content, the length of the fibers and the condition of the fiber-matrix interface. Single edge notched tensile specimens were cut from composite plates and examined. The fracture toughness was determined from force-elongation curves. Tensile tests and acoustic emission investigations were carried out simultaneously. It was found out that the failure mode for untreated and treated materials was quite different. Scanning electron microscopy micrographs were taken from the fracture surfaces.

Preparation of MWCNT/Carbon Fabric Reinforced Hybrid Nanocomposite and Examination of its Mechanical Properties

In our work we have prepared carbon fiber/epoxy composite and carbon fiber/carbon nanotube/epoxy hybrid nanocomposite laminates by hand laminating assisted by vacuumbag technology. During the production of the specimens we have encountered the viscosity increasing effect of nanotube filling, which we characterized by a viscosity test. The results of the test showed, that in the lowest shear rate range carbon nanotube filling can cause an increase of viscosity by three orders of magnitude, but also at higher shear rates the viscosity of the nanotube filled epoxy resin was ten times the viscosity of the unfilled resin. Mechanical properties of the composite and hybrid composite have been compared by tensile, bending and interlaminar shear tests. During the tensile tests AE signals have also been recorded. The fracture surfaces have been examined by SEM micrographs. The nanotube filling has decreased the tensile strength and the modulus of elasticity by 7-8 percent presumably indirectly, the bending properties didn’t change noticeably, but the interlaminar shear strength of the composite has increased by 15 percent thanks to nanotube filling of the matrix. The decrease of the delamination inclination of the hybrid composite has been affirmed both by the AE and SEM results.

The Effect of Electron Irradiation on the Mechanical Properties of MWCNT/Carbon Fiber Reinforced Hybrid Nanocomposites

In our work carbon fiber/epoxy composite and multiwalled carbon nanotube/carbon fiber/epoxy hybrid nanocomposite laminates have been prepared by resin transfer moulding (RTM) technology. The specimens have been irradiated using a high energy electron gun with multiple doses. The effect of the electron irradiation has been characterized using three point bending, interlaminar shear and instrumented falling weight impact tests.