Papers by Author: László Mihály Vas

Abstract: In this paper tensile and creep tests were performed on polypropylene (PP) and its glass fiber reinforced composites. The tensile tests were carried out on 6 different glass fiber content reinforced PP composites (0, 5, 10, 20, 30 and 40%) while the creep tests were performed on the unreinforced and 30% and 40% fiber reinforced ones of industrial importance. 50 N/s constant force rate was used until the specimen failed (tensile test) or the preset load level was reached (creep test). The applied load levels for the creep experiments were determined as given ratios of the average breaking force. The tensile breaking strain and tensile strength versus fiber content relationship were analyzed and described by empirical formulas based on the correction and averaging procedure developed.

Abstract: In this paper glass fibers, chopped roving pieces, and fiber mats were tested in case of emulsion bonded glass fiber mat samples. Relationships between the tensile strength properties of the different structural levels of the fiber mats were studied and fiber bundles as structural elements of fiber mats were modeled by idealized statistical fiber bundles developed by the Department of Polymer Engineering, BUTE. The geometrical and mechanical measurements were carried out by image processing methods and a computer aided tensile tester. The results proved that the modeling method gave a tool in understanding the failure behavior of the fiber mat samples and studying the effect of the structural parameters. The applicability of the modeling method is demonstrated by the good agreement with some measurements.

Abstract: The effect of span-to-thickness ratio (L/h) on the bending modulus was investigated in warp, 45°, 67.5° and weft directions in woven glass fiber reinforced polyester laminates. Using classical beam theory the results of the bending tests carried out for L/h = 5,..,50 were extended to the total range of definition (0≤L/h<∞) by applying rational fractional and exponential fractional functions. The extensions take the asymptotic behavior of the bending test for L/h = 0 and L/h = ∞ in account while providing the best fitting to the measured data. It has been shown that the exponential fractional estimations give better results regarding the form of functions that is independent from the directions.